Department: Mechanical Engineering ![[clear]](close-x.png "Remove this limiter")
508 matches in the database.
These are records: 1 - 30.
[1] [2] [3] [4] [5] … [17]
1.
Agarwal, Neeraj R.
Modeling, Validation and Analysis of an Advanced Thermal Management System for Conventional Automotive Powertrains.
Degree: MS, Mechanical Engineering, 2012, Ohio State University
► Reducing vehicle fuel consumption while maintaining same or better performance characteristics has…
(more)
▼ Reducing vehicle fuel consumption while maintaining same or better performance characteristics has been one of the main focuses of auto car manufacturers. In this sense, OEMs are introducing thermal management system (TMS) in modern vehicles that help attain rapid fluid warm-up during cold-start conditions. This leads to lower fluid viscosities early on in a drive cycle and hence reduced losses in the engine and powertrain components, resulting in lower fuel consumption. Rapid fluid warm-up also helps improve passenger comfort by providing necessary heating or cooling on demand. Through this work, a model characterizing the low frequency energy and power transfer in the engine and powertrain components is formulated. An advanced TMS consisting of components for waste heat energy recovery is proposed and its model is formulated. The combined set of these models is called the Vehicle Energy Simulator (VES). The model is thoroughly calibrated and validated using experimental data from steady state and transient testing; results are included in detail. The validated VES is then used to investigate control strategies for valves that are part of the TMS, used to control fluid flow to the various heat exchangers in order to attain rapid warm-up of coolant, engine oil and transmission fluid. It is seen that, the use of advanced TMS, over a conventional thermal management system, results in 3.4% reduction in fuel consumption. The investigation leads to recommendation of a reasonable first generation for a genetic algorithm optimization to be used to find the “optimal trajectory” for thermal-system-valve actuation during a drive cycle for reducing fuel consumption.
Advisors/Committee Members: Canova, Marcello.
Subjects: Automotive Engineering; Engineering
Keywords: Engine Thermal Management, Engine Modeling, Heat Exchanger Modeling, Thermal Management System, Control-Oriented Model
More Like This
2.
Agrawal, Rajiv.
A Constraint Management Approach for Optimal Design of Mechanical Systems.
Degree: PhD, Mechanical Engineering, 1991, Ohio State University
► Design of mechanical systems is a complex process. Often the design can…
(more)
▼ Design of mechanical systems is a complex process. Often the design can be modelled as a network of equality and inequality constraints. Though the solution strategy to handle these constraints varies from one design scenario to another, the underlying concepts of constraint management are applicable to most designs. This thesis uses these concepts to develop a generic framework for the interactive design of mechanical systems. The goal of the research is to provide a constraint management shell where the mathematical model for the design can be expressed in a declarative manner. A nonlinear occurrence matrix is used to represent the governing equality and inequality constraints. Constraint management algorithms for design decomposition, forward and backward dependency are presented by using the nonlinear occurrence matrix. Further, the occurrence matrix approach is also used to handle the initial basis selection and basis interchange issues in the Generalized Reduced Gradient (GRG) method for constraint optimization. The optimization phase also considers discrete variables. Discrete variables represent design variables that are either integer-valued, or have to adhere to standard dimensions. A Branch and Bound algorithm is used with the GRG method to handle the discrete variables. Robust numerical tools are developed to handle the solution of simultaneous nonlinear equations, an essential part of the both the GRG method for optimization and general constraint satisfaction. As an illustration of the design framework, a design method for spur and helical gears based on the American Gear Manufacturers Association (AGMA) standards is presented.Keywords: Constraint Management, Nonlinear Constrained Discrete Optimization, Branch and Bound Algorithm, Generalized Reduced Gradient Method, Simultaneous Nonlinear Equations, Gear Design.
Advisors/Committee Members: Kinzel, Dr. G. L.
More Like This
3.
Ahmadkhanlou, Farzad.
Design, Modeling And Control Of Magnetorheological Fluid-Based Force Feedback Dampers For Telerobotic Systems.
Degree: PhD, Mechanical Engineering, 2008, Ohio State University
► The overall goal of the research done in this dissertation is to…
(more)
▼ The overall goal of the research done in this dissertation is to develop next generation force feedback systems by combining novel Magnetorheological (MR) fluid based electromechanical systems with microstructural analysis and advanced control system design. Four MR fluid based systems are designed, prototyped and tested with medical applications: A two degree of freedom (2-DOF) force feedback joystick and a 5-DOF force feedback manipulator for telerobotic surgery application, a passive and a semiactive orthopedic knee brace for rehabilitation application. Furthermore, a force feedback steering wheel is modified using MR damper with application to steer-by-wire automobiles. The test results show the appropriate performance of MR fluid based systems used in haptic and force feedback applications.
Advisors/Committee Members: Washington, Gregory.
Subjects: Mechanical engineering
Keywords: Magnetorheological fluid; force feedback; haptic; telerobotic; microstructural analysis; constitutive equation; joystick; orthopedic knee brace; MR damper; telesurgery
More Like This
4.
Ahuett-Garza, Horacio.
Characterization of loads in die casting and prediction of die deflections.
Degree: PhD, Mechanical Engineering, 1996, Ohio State University
► Die casting dies deflect during a casting operation. These deflections affect the…
(more)
▼ Die casting dies deflect during a casting operation. These deflections affect the quality of the casting operation and the part. The goal of this work is to model and predict die casting die deflections. The theoretical problem is that of determining the thermoelastic deflections of a body under periodic thermo mechanical boundary conditions. This problem is complicated by the existence of several different time and dimension scales. From the perspective of the loads, there are two different time scales: Cavity pressures due to the processes of filling and intensification are applied in fractions of a second Clamping forces are applied throughout the duration of the casting cycle The thermal response of the die is characterized also by at least two time scales: Time for solidification (seconds) Time to reach quasi-steady state conditions (hours). For results to be of practical use, deflections must be computed with a resolution of fractions of a millimeter in models whose size is in the order of a meter. Because of the wide range of conditions, a very important task in this work is that of sorting out the interaction between the different loads, and clarifying what loads are relevant. A modeling approach was developed using ABAQUS, a commercial FEM system. The die behavior predicted by this approach is consistent with what is observed in the field. The procedure is also tested on a limited basis against field data. As a result, values of certain parameters and boundary conditions are defined. Based on the results of the simulations, the behavior of the die has been characterized and deflection data has been prepared in a form that can be used for design purposes. A global perspective of the characteristics of loads in die casting has been prepared. This characterization has allowed a correlation of the behavior of the die with certain die design parameters and process conditions.
Advisors/Committee Members: Miller, Allen.
More Like This
6.
Ai, Shiwen.
SENSING AND CONTROL OF TIP-SAMPLE INTERACTION FORCE OF A THREE-AXIS COMPLIANT MICRO-MANIPULATOR.
Degree: MS, Mechanical Engineering, 2011, Ohio State University
► The atomic force microscope is able to measure sample topography and manipulate…
(more)
▼ The atomic force microscope is able to measure sample topography and manipulate nano objects by maintaining a certain tip-sample interaction force that is sensed through laser deflection measurement. This work propose a systematic way to solve the drift issue due to ambient temperature change, which is detrimental to AFM metrology and force spectroscopy. A magnetic actuator is introduced to integrate with traditional AFM control system to precisely control the force of tip-sample interaction with magnetic actuator force model continuously updated using real-time calibration during the tip-sample interaction process. Conventionally AFM experiments need to wait about one hour after turning the measurement laser after the thermal drift caused by laser heating reaches thermal steady state. We show with the proposed techniques how the AFM can maintain its tip-sample interaction force and be immune to thermal drift. Therefore, there is no need to wait until the thermal balance of cantilever before AFM experiments can be performed. This idea is also extended to a multi-axis probe developed in our group. The combined techniques together permit precise tip-sample interaction force control in two-axis and drift-free scanning on samples with unknown geometry and steep features such as sidewall and reentrant.
Advisors/Committee Members: Menq, Chia-Hsiang.
Subjects: Mechanical Engineering
Keywords: micro-manipulator; tip-sample force
More Like This
7.
AL-AZMI, BADER SHABEEB.
ANALYSIS OF TRANSPORT MODELS AND COMPUTATION ALGORITHMS FOR FLOW THROUGH POROUS MEDIA.
Degree: PhD, Mechanical Engineering, 2003, Ohio State University
► Computational investigation of variant models and boundary conditions in the area of…
(more)
▼ Computational investigation of variant models and boundary conditions in the area of fluid flow and heat transfer in porous media is presented in this dissertation. This study is divided into four major parts. In the first part, a summary of variant models of fluid flow and heat transfer through porous media found in the literature is presented. These variances can be categorized into four primary sections, constant porosity, variable porosity, thermal dispersion and local thermal non-equilibrium. Models for constant porosity and variable porosity are presented in terms of Darcy, Brinkman and Forchheimer terms. The second part focuses on the interfacial conditions between a porous layer and a fluid layer. It is found that these interface conditions can be classified as a slip or a no slip. The no slip conditions assume a continuity of the property, velocity and/or temperature, while a discontinuity at the interface is assumed for the slip interface conditions. It is shown that in general, the variances have a more pronounced effect on the velocity field and a substantially smaller effect on the temperature field and even a smaller effect on the Nusselt number distributions. When constant heat flux boundary conditions are present, it is found that researchers use inconsistent wall temperature and heat flux boundary conditions at the solid walls of the porous medium. Therefore, the third topic of this dissertation explores the problem of constant heat flux boundary conditions in porous media under local thermal non-equilibrium conditions. For the second and the third parts, correlations that relate various models to each other are presented. The fourth and last part deals with the additional effects of variable porosity, thermal dispersion and local thermal non-equilibrium to the problem of free surface flows in porous media. Results show that the involvement of these effects can be significant for some cases. The finite difference method is used in generating all numerical results in this study. Throughout this study pertinent parameters such as porosity, Darcy number, Reynolds number, inertia parameter, particle diameter and solid-to-fluid conductivity ratio are used to demonstrate the results of the analyses.
Advisors/Committee Members: Vafai, Kambiz.
Subjects: Engineering, Mechanical
Keywords: Porous Media; Varaible Porosity; Thermal Dispersion; Local Thermal Non-Equilibrium; Interfacial Boundary Conditions; Constant Heat Flux Boundary Conditions
More Like This
8.
Ali, Ahmad A.
Analysis of heat and mass transfer between air and falling film desiccant for different flow configurations in the presense of ultrafine particles.
Degree: PhD, Mechanical Engineering, 2003, Ohio State University
► This work focuses on the enhancement of heat and mass transfer between…
(more)
▼ This work focuses on the enhancement of heat and mass transfer between air and falling desiccant film for different flow channel configurations. Cu-Ultrafine particles are added to the desiccant film to investigate the enhancement in heat and mass transfer between air and desiccant film for dehumidification and cooling processes of the air and regeneration of desiccant film. A detailed comparative study between parallel and counter flow channels is performed using a parametric study to investigate the enhancements in dehumidification, cooling, and regeneration processes in terms of the pertinent parameters. The results reveal that the parallel flow arrangement provides better dehumidification and cooling for the air than the counter flow channel for a wide range of parameters. Next, the inclined parallel and counter flow configurations are investigated using an Alternating Direction Implicit (ADI) and successive over-relaxation methods to discretize the vorticity and stream-function equations, respectively. A parametric study is employed to investigate the inclination angle effects in enhancing the heat and mass transfer in terms of the controlling parameters. It is shown that inclination angle plays a significant role in enhancing the dehumidification, cooling, and regeneration processes. Finally, the enhancements in heat and mass transfer in cross flow channel between air and desiccant film is examined based on a parametric study to investigate the dehumidification and cooling processes of the air in terms of the pertinent controlling parameters. These parameters are air and desiccant Reynolds numbers, dimensions of the channel, volume fraction of Cu-ultrafine particles, and thermal dispersion effects. It is found that an increase in the Cu-volume fraction enhances dehumidification and cooling capabilities and produces more stable Cu-desiccant film.
Advisors/Committee Members: VAFAI, KAMBIZ.
Keywords: FILM DESICCANT; flow channel
More Like This
9.
Alleman, Coleman.
Molecular Dynamics Investigations of Polystyrene-Based Binary Thin Film Systems: Interfacial Properties and Mechanical Behavior.
Degree: MS, Mechanical Engineering, 2011, Ohio State University
► Implementation and development of novel nanoscale biomedical devices and procedures depends critically…
(more)
▼ Implementation and development of novel nanoscale biomedical devices and procedures depends critically upon the ability to manufacture affordable nanoscale polymer structures. This, in turn, depends upon understanding of the properties of the polymer materials at these scales, where material properties are often divergent from those observed at larger scales. In this thesis, a molecular dynamics (MD) based approach is developed to analyze these properties at an atomic resolution. Under the hypothesis that the emergence of new properties in nanoscale polymers is due to the increased importance of interface effects, the primary focus of this work is the differentiation of material behavior at various interfaces. The first study presented here analyzes a polystyrene (PS) - carbon dioxide (CO2) interface. The main result of this study is a quantification of the impact of CO2 on the glass transition behavior of PS. It is shown that introduction of CO2 depresses the glass transition temperature Tg significantly and that this depression increases with increasing CO2 pressure. For the highest CO2 pressure studied (7 MPa), observed Tg for the polymer is more than 50 K below the value for bulk PS. In the study of this binary system, a number of techniques are developed for the measurement and analysis of properties like free volume and mobility. These techniques are applied to quantify the dependence of various important properties of PS on spatial location, temperature, and CO2 pressure. The results of the first study suggest that the bonding of PS should be facilitated by the introduction of CO2, possibly enabling bonding at near room temperature. The second study presented here examines this possibility, using a MD model of PS thin films to study the impact of CO2 on the structure of a symmetric PS-PS interface during bonding at 300 K. The properties of the interface are used to analyze the results of simulations which show that the strongest interface is produced for a CO2 pressure of ~2 MPa. It is determined that this strength is largely determined by the development of chain segments that bridge the interface. The number of bridges that develop is shown to be dependent on atomic mobility near the interface, which is a maximum for PS in the presence of CO2 at ~2 MPa. The final study presented in this work examines free surface and silica substrate interface effects on the glass transition behavior of PS thin films. The change in Tg for freestanding and silica-supported PS thin films is estimated using MD. It is shown that a freestanding PS thin film roughly 20 nm in thickness exhibits a depression in Tg of 33 K below the bulk value. It is also shown that a silica-supported PS thin film exhibits a depressed Tg, but that the competition between polymer-substrate and polymer free surface effects limits this depression to 19 K for a film of identical composition. It is concluded that the deviation in the thin film Tg values is driven by changes in atomic mobility due to interface and free surface effects.
Advisors/Committee Members: Ghosh, Somnath.
Subjects: Mechanical Engineering; Polymers
Keywords: polystyrene; carbon dioxide; silica; glass transition temperature; bonding; interface; thin film; molecular dynamics
More Like This
10.
Al-Zkeri, Ibrahim Abdullah.
Finite element modeling of hard turning.
Degree: PhD, Mechanical Engineering, 2007, Ohio State University
► During hard turning, the cutting tool is exposed to a very severe…
(more)
▼ During hard turning, the cutting tool is exposed to a very severe environment due to the hardness of the machined steels and the small contact area between the tool and the workpiece. Moreover, the residual stress patterns that are generated near the machined surface are influenced by many factors such as process variables, tool wear, and cutting edge preparation. For a tool to perform successfully under these severe conditions and for an enhanced surface integrity, factors such as the cutting tool edge geometry, feed rate, and cutting speed have to be carefully selected. In this study, the two-dimensional finite element method (FEM) is used as a tool for understanding the fundamentals of hard turning process and for predicting the effect of CBN tool edge preparation (edge hone radius, chamfer angle) and cutting conditions (cutting speed, feed rate) on the hard turning variables (cutting forces, chip morphology, tool stresses and temperature, and residual stresses). In addition, a methodology for obtaining flow stress data for machining simulations from machining and compression tests has been developed. The flow stress data that are obtained using this methodology provided better predictions of hard turning variables than other flow stress data obtained from a single test for the same cutting conditions. Practical hard turning is a 3D process. Hence, using the new enhancement to computers and software, two numerical methods are used to study the 3D hard turning process: 1) simplification of the 3D hard turning process using an analytical model and 2D FEM and 2) 3D FEM. While the methodology used to represent the 3D cutting process of AISI 4340 in a 2D process gives results close to the values predicted using 3D cutting simulation, it provides predictions of cutting forces that are lower than the measured forces. On the other hand, the modeling of hard turning of AISI 52100 using 3D FEM gives close predictions of cutting force but not of the depth and feed force. However, the simulations ran smoothly and the use of more reliable flow stress data and finer mesh for the workpiece are expected to improve the predictions.
Advisors/Committee Members: Altan, Taylan.
Subjects: Engineering, Mechanical
Keywords: Finite Element Method, Machining, Hard Turning, Residual Stress, Edge Preparation
More Like This
11.
Ambike, Satyajit S.
Characteristics of Spatial Human Arm Motion and the Kinematic Trajectory Tracking of Similar Serial Chains.
Degree: PhD, Mechanical Engineering, 2011, Ohio State University
► This work studies spatial reaching motion in healthy humans. Research suggests that…
(more)
▼ This work studies spatial reaching motion in healthy humans. Research suggests that for individual instances of movement, the central nervous system (CNS) composes an explicit wrist path, which is transformed into joint motions in a time-invariant fashion. This is the time invariance hypothesis (TIH), and its validation for spatial motion is the first goal of this study. The human arm is typically modeled as a multi-link, serial chain. When one joint of a serial chain is actuated, it simultaneously causes movement at other joints because of interaction effects. Based on horizontal-plane reaching studies, the leading joint hypothesis (LJH) proposes that the interaction effects at (mostly) the proximal joint in the multi-link serial-chain model of the arm are low. Therefore, the CNS ignores this interaction effect to simplify the computation of joint torques and control of the joint trajectory. The second objective of this dissertation is to validate the LJH for spatial motion. In a spatial reaching experiment, healthy subjects performed point-to-point reaching movements at three distinct speeds. Data analysis revealed time-invariant wrist paths only for some subjects in some reaching tasks, suggesting that the TIH is not a truly general organizing principle for spatial reaching motion. Therefore, this hypothesis needs refinement and further investigation. On the other hand, the interaction effects at the shoulder joint were small for a majority of the movements in this experiment so, the LJH was successfully extended to spatial motion. The TIH identifies the inputs and outputs of the first stage in the process of composing the muscle activations for a given motor task. A computational algorithm that can potentially be used to execute this transformation was developed next. The algorithm, called speed-ratio control, also has beneficial applications in commercial robot control. It is demonstrated that the application of this algorithm to robotic serial chains provides greater navigational accuracy in the vicinity of certain kinds of singularities. Speed ratio control applies to non-redundant serial chains. The simplest model of the human arm consists of three-degree-of-freedom spherical joints at the shoulder and the wrist and a revolute joint at the elbow. This yields seven degrees of freedom for the arm. For positioning and orienting the hand relative to the thorax, only six degrees of freedom are necessary. The human arm is, therefore, a redundant serial chain. The formal process of extending the algorithm to redundant serial chains is undertaken. Initial work in which three- and four-degree-of-freedom planar chains track point paths is presented. Speed ratio control allows the resolution of the redundancy in the mechanism by maximizing the output-space tracking accuracy. Examples show superior local tracking performance with this approach compared to path tracking using unweighted pseudoinverse solutions.
Advisors/Committee Members: Schmiedeler, James P.
Subjects: Kinesiology; Mechanical Engineering; Robotics
Keywords: Human Motor Control; Spatial Arm Motion; Time Invariance Hypothesis; Leading Joint Hypothesis; Serial Robots; Spatial Trajectory Tracking; Speed Ratio Control; Singularity Tracking; Redundant Serial Chains
More Like This
13.
Anantharaman, Satish.
RESIDUAL STRESS MEASUREMENT IN PLASTIC WELDED JOINS AND ITS APPLICATION TO THE DESIGN AND MANUFACTURE OF HYBRID ELECTRIC VEHICLE BATTERIES.
Degree: MS, Mechanical Engineering, 2009, Ohio State University
► Hybrid electric vehicle (HEV) battery modules are designed for extended life (8-10…
(more)
▼ Hybrid electric vehicle (HEV) battery modules are designed for extended life (8-10 years) under real world environmental and driving conditions. The complex design and assembly of these battery modules coupled with aggressive chemicals in the electrolyte necessitate the use of plastics as enclosure material. Residual stresses resulting from plastic welding processes is a major cause for failure of a battery system. In order to minimize the effects of these residual stresses, it is important to undertake a systematic study to quantify and reduce them. Photoelasticity and solvent testing methods were used to experimentally determine residual stresses in hot plate and through transmission laser welded (TTLW) polycarbonate. The peak residual stresses measured by the two methods were in good agreement. Solvent testing technique was also used to successfully quantify the peak residual stress in vibration welded plastic assemblies used in HEV batteries. It was found that processes with shorter heating times and faster cooling rates, like vibration welding and TTLW, resulted in higher residual stresses. Annealing after welding could also be used to reduce the residual stress levels by as much as 40%. Hot plate welding has slower heating and cooling rates resulting in the lowest level of residual stresses and often eliminating the need for annealing. Minimization of the effects of residual stresses on battery performance and life through material and process selection and design modifications were also investigated.
Advisors/Committee Members: Benatar, Avraham.
Subjects: Mechanical engineering
Keywords: residual stress, plastic, welding
More Like This
15.
Asmus, Amy Renee.
The effects of manual pruning tool design parameters on muscle activity, wrist posture, and perceived efffort.
Degree: MS, Mechanical Engineering, 2005, Ohio State University
► This study examined effects of pruning tool design and subject age on…
(more)
▼ This study examined effects of pruning tool design and subject age on muscle activity, wrist posture, and perceived effort. Twelve right handed female subjects each used four different pruners, labeled A, B, C, and D, of different mechanical designs and various handle sizes, shapes, and features. The women, selected in age categories of under 30 years of age and over 50 years of age, performed a series of cuts on dowel rods of uniform size. One pruner had an angled handle and a rotating power gear to assist the hand (A), another did not have an angled handle and was considered the control (B). Two others, also with angled handles (C and D), were identical to each other except for their size. The smaller pruner (D) has been marketed to users with smaller hands.The study observed fourteen dependent measures. Electromyographic data for four muscles involved in gripping were recorded: flexor digitorum superficialis (FDS), flexor carpi ulnaris (FCU), flexor digitorum radialis (FCR), and muscles of the thenar eminence. The 50th and 90th percentile normalized activity levels were examined. Wrist goniometers were used to record wrist position data for radial/ulnar deviation (R/U) and flexion/extension (F/E). A discomfort and effort survey obtained subjective data about each pruner. Anthropometric data, specifically hand anthropometry, was also recorded for the subjects. Combined EMG, subjective, and wrist data results indicate a benefit to primer A. All subjects were sensitive to the design features of the pruners, but additional significant differences between pruners were seen among the older group. These differences were seen in the normalized peak activity of the two wrist flexor muscles.Of the small and the large pruners, the large pruner (C) required less muscular effort than the small pruner (D). This was true even for users with smaller hands. This is most likely because the larger pruners provide a mechanical advantage with more leverage than the smaller pruners. Studies such as this one may assist pruning tool users, whether professional gardeners or beginners, to make informed product decisions based on a quantitative evaluation of design features, as well as consideration of subjective assessments.
Advisors/Committee Members: Sommerich, Carolyn M.
More Like This
16.
Ay, Haluk.
Linear and Nonlinear Models of Human Hand-Arm Dynamics and Torque Tool Interaction.
Degree: PhD, Mechanical Engineering, 2011, Ohio State University
► The use of powered torque tools in manufacturing industries increases the productivity…
(more)
▼ The use of powered torque tools in manufacturing industries increases the productivity and accuracy of fastener tightening processes. However, prolonged exposure to the impulsive forces in torque tool operation likely poses risks of upper extremity injuries and musculoskeletal disorders. The human hand-arm response to such impulsive forces should be understood to reduce the risks associated with torque tools. This dissertation presents contributions to hand-arm modeling and parameter extraction methods for interaction with impulsive forces in torque tool operation. First, an improved parameter identification protocol is developed for an existing linear hand-arm model. The protocol is validated with human subjects’ testing for physical capacity assessment. The mean time-to-peak displacement and relative peak force errors based on the identified model parameters are 2.8 ms and 1.6%, respectively. Second, the validated protocol is used to determine the linear model parameters for in situ torque tool operation. A second step of human testing is conducted with commercially available direct current torque tools. The extracted model parameters provide 10.5 ms mean time-to-peak displacement and 6.8% mean relative peak force errors. Third, a novel device is developed that mechanically simulates the linear human hand-arm dynamics. The extracted in situ linear model parameters are utilized. The device is used to test commercially available right-angle tools for ergonomics-relevant evaluation. The peak force and displacement R2 between the device and human operator data are 0.98 and 0.85, respectively. Fourth, a mechanical system is developed that simulates the human hand-arm dynamics with conceptually similar nonlinearities. Experiments are carried out on the testing apparatus with the mechanical system attached. The range of peak displacement error for the tested torque amplitudes and durations are 0.8% to 1.9%. Similarly, peak force and time-to-peak displacement errors range from 2.3% to 10.5% and from 3.3 ms to 4.8 ms, respectively. The testing protocol is verified in terms of repeatability and nonlinear model parameter identification accuracy. Finally, a nonlinear model is developed to represent human hand-arm dynamics in torque tool operation. The model implements stiffness modulation and delay assumptions. A third step of human subjects’ testing is conducted. Various combinations of torque amplitude, duration, tool orientation, working posture and hand-arm resistance levels are tested. The nonlinear and linear model accuracy is compared to each other. The nonlinear model peak displacement and force errors range from -0.82% to 0.50% and from -0.22% to 2.38%, respectively. On the other hand, the linear model peak displacement and force errors range from 2.01% to 7.33% and from -7.44% to 19.92%, respectively. The ranges of time-to-peak displacement error for the nonlinear and linear model are from 0.49 ms to 1.26 ms and from -10.82 ms to 15.66 ms, respectively. The nonlinear model provides more accurate displacement and force estimation results than the linear model for all test conditions.
Advisors/Committee Members: Luscher, Anthony F.
Subjects: Biomechanics; Mechanical Engineering; Occupational Health; Occupational Safety
Keywords: human hand arm dynamics modeling , torque tool ergonomics
More Like This
17.
Bahk, Cheon-Jae.
Analytical Study on Nonlinear Dynamics of Planetary Gears.
Degree: PhD, Mechanical Engineering, 2012, Ohio State University
► This work aims to advance the understanding of nonlinear dynamics of planetary…
(more)
▼ This work aims to advance the understanding of nonlinear dynamics of planetary gears and the influence of the key system parameters on dynamic response. Analytical solutions of nonlinear dynamic model are mainly used to conduct investigations on interesting nonlinear dynamic behaviors. An analytical lumped-parameter model, which is parametrically excited by time-varying mesh stiffness and includes tooth separation, shows nonlinear dynamic response. The accuracy of the model is correlated against a benchmark finite element analysis over broad mesh frequency ranges. The nonlinear dynamic model is analytically solved by perturbation analysis. Concise, closed-form expressions of planetary gear dynamic response are obtained for various resonances. The analytical solution is validated by numerical integration and the harmonic balance method. The rapid calculation of dynamic response with acceptable accuracy demonstrates that the analytical solutions are effective for performing parametric studies. The explicit inclusion of key system parameters in the analytical solution shows the impact of the system parameters on planetary gear nonlinear vibration. Mesh stiffness discontinuity from tooth contact loss is considered for the analytical solution that gives nonlinear vibrations. Correlation between the external torque and vibration amplitude proves that tooth contact loss can occur even under large torque. Resonances at multiple harmonics of the mesh frequency are distinguished by different excitation sources. Nonlinear subharmonic resonance characterized by response jump phenomena on both sides of the mesh frequency range where resonance occurs is examined. The impact of system parameters on planetary gear vibrations is investigated by using a generalized planetary gear model including bearing stiffness and relative mesh phase. Use of the well-defined modal properties and closed-form expressions of resonant response confirm the existing mesh phasing rules to suppress selected vibration modes of primary resonance. Extended suppression rules for super- and subharmonic resonances are proposed. In addition to the suppression conditions, the analytical solution discovers the dependence of dynamic response on the system parameters and vibration modes, which provides practical guidance for finding optimal design parameters for vibration reduction. A nonlinear analytical tooth profile modification model for planetary gear dynamic response is developed. Perturbation analysis gives a closed-form expression for the frequency response relation including the fundamental tooth profile modification parameters of the modification amount and length. Different effects of tooth profile modification on static transmission error and dynamic response are compared in terms of the modification amount. Strong influence of system parameters on the dynamic effect of tooth profile modification is discovered.
Advisors/Committee Members: Parker, Robert G.
Subjects: Mechanical Engineering
Keywords: Planetary gear; Nonlinear dynamics; Vibration; Perturbation analysis; Tooth separation; Mesh phase; Tooth profile modification
More Like This
18.
Bai, Jie.
A Homogenization based Continuum Plasticity-Damage Model for Ductile Frature of Materials Containing Heterogeneities.
Degree: PhD, Mechanical Engineering, 2008, Ohio State University
► This paper develops an adaptive concurrent multi-level computational model for multi-scale analysis…
(more)
▼ This paper develops an adaptive concurrent multi-level computational model for multi-scale analysis of composite structures undergoing damage initiation and growth due to microstructural damage induced by debonding at the fiber-matrix interface. The model combines macroscopic computations using a continuum damage model with explicit micromechanical computations of stresses and strain, including explicit debonding at the fiber-matrix interface. The macroscopic computations are done by conventional FEM models while the Voronoi cell FEM is used for micromechanical analysis. Three hierarchical levels of different resolution adaptively evolve in this to improve the accuracy of solutions by reducing modeling and discretization errors. There levels include: (a) level-0 of pure macroscopic analysis using a continuum damage mechanics (CDM) model; (b) level-1 of asymptotic homogenization based macroscopic-microscopic RVE modeling to monitor the breakdown of continuum laws and signal the need for microscopic analyses; and (c) level-2 regions of pure micromechanical modeling with explicit depiction of the local microstructure. Numerical examples are solved to demonstrate the effectiveness and accuracy of the multi-scale model.To use the framework of this multi-scale computational model for ductile fracture analysis, This paper develops an accurate and computationally efficient homogenization based continuum plasticity-damage or HCPD model for macroscopic analysis of ductile failure in multi-phase porous ductile materials, such as cast aluminum alloys. The overall framework of the HCPD model follows the structure of an anisotropic Gurson-Tvergaard-Needleman (GTN) type elasto-plasticity model for porous ductile materials. To account for orientation dependence, the anisotropic HCPD model is expressed in the evolving material principal coordinate system and is assumed to remain orthotropic in it throughout the deformation history. Parameters in this model are calibrated from results of homogenization of microstructural variables obtained by LE-VCFEM analysis of the microstructural RVE containing inclusions, matrix and voids. Anisotropy parameters are found to evolve with plastic deformation in the microstructure. The model also incorporates a novel void nucleation criterion obtained by homogenizing micromechanical damage evolution by inclusion and matrix cracking. The overall model also incorporates realistic estimates of RVE length scales in the microstructure, as well as non-local characteristic length scales in the macrostructure. Comparison of the anisotropic HCPD model results with homogenized micromechanics results shows excellent agreement. On the other hand, the HCPD model has a huge efficiency advantage over the micromechanics models and is hence a very effective tool in making macroscopic damage predictions in structures with explicit reference to the microstructural composition.
Advisors/Committee Members: Ghosh, Somnath.
Subjects: Mechanical engineering
Keywords: Ductile fracture, Plasticity-Damage Model
More Like This
19.
Banerjee, Anindo.
A Model to Predict Sun Gear Radial Orbit of a Planetary Gear Set having Manufacturing Errors.
Degree: MS, Mechanical Engineering, 2012, Ohio State University
► In this study, a two-dimensional analytical model is proposed to predict radial…
(more)
▼ In this study, a two-dimensional analytical model is proposed to predict radial motions of the floating sun gear of an n-planet gear set due to gear run-out errors, carrier eccentricity and planet pin hole position errors. This analytical model is based on an earlier model proposed by Hidaka for a three-planet gear set having only gear run-out errors. The proposed model extends Hidaka’s formulations to include four- and five-planet gear sets as well as pin hole position errors on the carrier. The model is used to perform parametric studies on the relation between errors (types, amplitudes and relative orientation angles) and the resultant sun gear radial motions. A frequency-domain representation of sun gear motions is introduced to provide means to use any measured sun orbit as a diagnostics tool such that the error content of the gear set can be directly identified. At the end, the proposed analytical model results are compared to sun orbit measurements of Boguski et al. and predictions of a finite element based computational model to demonstrate its accuracy.
Advisors/Committee Members: Kahraman, Ahmet.
Subjects: Mechanical Engineering
Keywords: sun orbit; sun gear radial orbit; manufacturing errors
More Like This
20.
Bao, Ainan.
Ignition of hydrocarbon fuels by a repetitively pulsed nanosecond pulse duration plasma.
Degree: PhD, Mechanical Engineering, 2008, Ohio State University
► The dissertation presents experimental and kinetic modeling studies of ignition of hydrocarbon-air…
(more)
▼ The dissertation presents experimental and kinetic modeling studies of ignition of hydrocarbon-air flows by a high voltage, repetitively pulsed, nanosecond pulse duration plasma. A high reduced electric field during the pulse results in efficient electronic excitation and molecular dissociation, and extremely low duty cycle of the repetitively pulsed nanosecond discharge improves the plasma stability and helps sustain a diffuse and uniform nonequilibrium plasma. Gaseous fuel ignition experiments using a pulser (16-18 kV peak voltage, 20-30 nsec pulse duration, up to 50 kHz pulse repetition rate) generating a plasma in premixed ethylene-air and methane-air flows demonstrated flow ignition occurring at low air plasma temperatures, 200-300 0C. The experiments showed that adding fuel to the air flow increased the flow temperature in the plasma, up to 500-600 0C. At these conditions, the reacted fuel fraction was up to 80%, and significant amounts of combustion products were detected. Replacing air with nitrogen at the same flow and plasma conditions resulted in much less plasma temperature rise. This suggests that low-temperature plasma chemical reactions can oxidize significant amounts of hydrocarbons and increase the temperature of the air-fuel mixture, prior to ignition. Ignition occurs when the flow temperature becomes close to autoignition temperature. The present results also showed that plasma assisted ignition occurred at a low discharge power, ~1% of heat of combustion. Ignition was achieved for liquid methanol- and ethanol-air mixtures, and significant plasma temperature rise and fuel oxidation were detected. A kinetic model was developed to simulate plasma assisted ignition of hydrocarbon-air mixtures by the repetitively pulsed nanosecond plasma. The model was validated by comparing with O atom concentration measurements in single-pulse air and air-fuel discharges. Kinetic modeling at the present experimental conditions did not predict significant fuel oxidation or ignition. The model predicts that ignition would occur if the discharge power is 2.5 times higher than measured in the experiments. The difference between two hydrocarbon oxidation mechanisms predictions suggests that neither of them might be applicable at the low-temperature conditions. This demonstrates the need for development and validation of a low-temperature hydrocarbon oxidation in non-equilibrium plasmas.
Advisors/Committee Members: Adamovich, Igor V.
Subjects: Engineering, Mechanical
Keywords: Nonequilibrium plasma; Nanosecond pulse; Ignition
More Like This
21.
Barszcz, Benjamin Daniel.
Dynamic Tuning of Hydraulic Engine Mount Using Multiple Inertia Tracks.
Degree: MS, Mechanical Engineering, 2010, Ohio State University
► Passive hydraulic engine mounts are commonly employed for motion control and vibration…
(more)
▼ Passive hydraulic engine mounts are commonly employed for motion control and vibration isolation in vehicle powertrain systems. Such devices are often tuned in terms of their low frequency resonance and damping ratio (say corresponding to the engine bounce mode) to control noise and vibration and improve the ride comfort, quality, and safety of the vehicle. Mount tuning concepts with one inertia track and one decoupler using the track length or diameter are well understood, but the dynamic response with multiple tracks, orifices, or decouplers is not. To overcome this void in the literature, dynamic tuning concepts of hydraulic engine mounts, with emphasis on multiple (n-) inertia tracks, fixed decoupler-type designs, are analytically and experimentally examined in this thesis. Since a wide variety of n-inertia track configurations is possible, dynamic stiffness models are developed to explain a family of such configurations, based on linear time-invariant lumped fluid system theory. Furthermore, a new n-track prototype mount concept is designed, built, and tested in a controlled manner, with the capability of varying the type (capillary tube, orifice) and number (n) of inertia tracks, in addition to length and diameter of each. This prototype is used to examine several designs with alternate n-track configurations for improving performance compared to the n = 1 track case. Three narrowband devices are designed and tested to refine existing theory for predicting peak frequency of loss angle, in addition to examining and validating an n = 3 track mount for the first time. Two broadband devices are designed and tested successfully by tuning damping ratios of the mount with orifice-type tracks for the first time. Several n-track mount designs with orifice-type tracks are also proposed, which successfully describe a special broad-tuned design utilizing a controlled ‘leakage’ path flow area for the first time. Lastly, a quasi-linear dynamic stiffness model is developed to study excitation amplitude- and frequency-dependent behavior of equivalent inertia track resistance, which should lead to nonlinear models of n-track devices and improved adaptive or active mounts in future studies. Chief contributions of this work include experimentally validated extensions of prior lumped parameter, linear time-invariant dynamic stiffness models, which are now applicable to predictions for narrow-tuned and/or broad-tuned mounting devices with n greater than or equal to 2.
Advisors/Committee Members: Singh, Dr. Rajendra.
Subjects: Acoustics; Design; Engineering; Mechanical engineering
Keywords: hydraulic engine mount; multiple inertia tracks; noise vibration and harshness; vehicle dynamics; vibration isolation; motion control
More Like This
22.
Bayar, Kerem.
Development of a Vehicle Stability Control Strategy for a Hybrid Electric Vehicle Equipped With Axle Motors.
Degree: PhD, Mechanical Engineering, 2011, Ohio State University
► Hybrid-electric vehicles have been available to consumers for over a decade, and…
(more)
▼ Hybrid-electric vehicles have been available to consumers for over a decade, and plug-in hybrid and pure electric vehicles are rapidly becoming mainstream products with the introduction of vehicles such as the Chevrolet Volt and the Nissan Leaf in 2011. These vehicles have in common an electric powertrain, comprised of one or more electric motors and of a battery pack which in the case of hybrid vehicles supplements and internal combustion engine. It is well understood that hybrid and electric vehicles have the benefit of significant reduction in CO2 emissions and in the use of petroleum as a fuel. However, one additional benefit of hybrid and electric vehicles remains so far under-utliized: the use of the electric traction system to enhance vehicle stability control. This potentially or low cost feature could provide additional motivation for customers to choose hybrid or electric vehicles over conventional ones. This dissertation documents the conception and development of a novel control strategy to allocate braking and tractive forces in a hybrid electric vehicle equipped with axle motors, for the purpose of enhancing the vehicle stability control system. The work described in this dissertation documents the development of a hierarchical control strategy, its design and stability proofs, and its evaluation using software and model in-the-loop methods. The work includes the development of a dynamic HEV simulator that is capable of evaluating vehicle dynamics responses during emergency maneuvers, to demonstrate its stability. For this purpose, a hybrid powertrain simulation model including batteries, motors, differential, shaft, wheel, and electro-hydraulic brake system models are developed. Furthermore, a simple yet reliable vehicle dynamics model is integrated with the powertrain model to capture longitudinal, lateral, yaw and roll degrees of freedoms of the vehicle. The development of the simulator is a minor, but an original contribution of this dissertation. The principal contribution of this work is a novel and systematic vehicle stability control (VSC) strategy that distributes the corrective longitudinal force and yaw moment action to generate individual wheel slip ratios by blending regenerative axle motor braking and/or traction with individual wheel braking; so as to track the desired vehicle speed and yaw rate without causing excessive vehicle sideslip angles. This dissertation shows that including the axle electric motors within the proposed VSC frame, improves the performance of vehicle stability control in comparison to production vehicle VSC strategies. The potential benefit of electric motors, namely their ability to provide rapid braking/tractive torque actuation, is utilized in addition to the friction brakes within the proposed VSC scheme. The resulting strategy is the first published result that shows that yaw tracking and vehicle stabilization can be performed without interfering in the driver’s longitudinal speed demand. Furthermore, the strategy limits the yaw rate in order to keep the vehicle sideslip angle in the safe range, by increasing the understeer coefficient whenever a sideslip angle safety threshold is exceeded. A secondary benefit of the proposed VSC scheme is its energy saving feature, thanks to the use of highly efficient electric motors and their regenerative braking capability in comparison to a standard vehicle stability control schemes that use only the brake and engine intervention. Finally, the proposed VSC strategy is tested in real time, by using a model-in-the-loop simulation set-up, using state-of-the-art hardware-in-the-loop computer systems. Model-in-the-loop simulation results for different road conditions and steering maneuvers showed that the proposed VSC performs satisfactorily in real time as well, suggesting that is amenable to in-vehicle implementation.
Advisors/Committee Members: Rizzoni, Giorgio.
Subjects: Automotive Engineering
Keywords: vehicle stability control, hybrid electric vehicle, yaw rate, sideslip angle
More Like This
23.
Behera, Santosh K.
Molecular Dynamics Simulation of Crack Propagation in Nickel.
Degree: MS, Mechanical Engineering, 2010, Ohio State University
► Crack propagation in ductile materials involves emission of dislocations, twin boundaries and…
(more)
▼ Crack propagation in ductile materials involves emission of dislocations, twin boundaries and creation of stacking faults that contribute to the overall plastic deformation. In this thesis a systematic method of identifying and quantifying these processes is developed and implemented for the case of crack propagation in a single crystal of nickel. A method to identify the crack surface and construct an equivalent ellipse is also discussed. With a focus towards development of a crack propagation law using atomic level detail, two methods for quantication of elastic, plastic and surface energies have been developed. First method uses the local structure analysis to compute the plastic energy and surface energy and using the total energy of the system elastic energy is computed. The second method uses the stiness of the system to estimate the elastic energy at each timestep and from the remaining energy surface energy and plastic energy are further isolated.
Advisors/Committee Members: Ghosh, Somnath.
Subjects: Engineering; Materials science; Mechanical engineering; Mechanics
More Like This
24.
Belisle, Kathryn J.
Experimental and Finite Element Analysis of a Simplified Aircraft Wheel Bolted Joint Model.
Degree: MS, Mechanical Engineering, 2009, Ohio State University
► The goal of this thesis is to establish a correlation between experimental…
(more)
▼ The goal of this thesis is to establish a correlation between experimental and finite element strains in key areas of an aircraft wheel bolted joint. The critical location in fatigue is the rounded interface between the bolt-hole and mating face of the joint, called the mating face radius. A previous study considered this area of a bolted joint but only under the influence of bolt preload. The study presented here considered both preload and an external bending moment. This study used a more complete single bolted joint model incorporating the wheel rim flange and the two main loads seen at the bolted joints; bolt preload and the external load created by tire pressure on the wheel rim. A 2x3 full factorial DOE was used to establish the joint’s response to various potential load combinations assuming two levels of preload and three levels of external load. The model was analyzed both experimentally and in finite element form. The strain results around the mating face radius were compared between the two analyses. Several parameters were identified that could affect the correlation between the results. The finite element model was modified to incorporate each of these factors and the new results were compared against the original finite element results and the experimental data. The best correlation was found when the finite element model preload was adjusted such that the mating face radius strains under only preload matched those of the experimental results.
Advisors/Committee Members: Luscher, Anthony.
Subjects: Mechanical engineering
Keywords: bolted joint; assembled joint; finite element analysis; aircraft wheel
More Like This
25.
Belknap, Eric.
Mechanical characterization of SAW-based sensors for wireless high temperature strain measurements.
Degree: MS, Mechanical Engineering, 2011, Ohio State University
► The measurement of strain typically involves the installation of resistive strain gages…
(more)
▼ The measurement of strain typically involves the installation of resistive strain gages that are connected by lead-wires that are routed to the appropriate instrumentation. In addition to the obvious drawbacks that lead-wires present, most strain gages cannot be used in high temperature environments. Strain gages that are made for high temperature environments have complicated procedures for installation and operation. In recent years it has been shown that Surface Acoustic Wave (SAW) devices can be used to measure strain wirelessly. Additionally, SAW device based wireless strain sensors do not require any external power and, depending on the SAW device material, can be used up to 600 °C. Before SAW devices can be used for wireless strain measurements, much still needs to be learned about the mechanical behavior of the device materials, package components, and adhesives used to assemble and attach the devices. This work will start with measurement and analysis of basic mechanical properties for the following two SAW device materials: Lithium Niobate and Langasite. Lithium Niobate can be used at temperatures up to 300 °C, and Langasite is capable up to 600 °C. The elastic modulus of both materials has been measured in the wafer orientations corresponding to optimal SAW device operation. Since these SAW materials will eventually be used at high temperatures, thermal expansion properties have also been explored. The selection of the best performing adhesive to bond the sensor was determined by a series of experiments. Complete sensor packages were modeled in order to evaluate sensor stiffening effects on the strain measurement. The sensor adhesive layer was also evaluated for its effectiveness at strain transfer from the substrate material to the SAW device.
Advisors/Committee Members: Walter, Mark.
Subjects: Mechanical Engineering
Keywords: SAW device; high temperature strain; strain gage; wireless strain gage
More Like This
26.
Bellman, Karen L.
Identification of Low Potential Onset of Concentration Polarization and Concentration Polarization Mitigation in Water Desalination Membranes.
Degree: MS, Mechanical Engineering, 2012, Ohio State University
► Identification of concentration polarization regimes in nanocapillary array membranes for electrokinetically driven…
(more)
▼ Identification of concentration polarization regimes in nanocapillary array membranes for electrokinetically driven flow was investigated in a parametric study varying both nominal pore diameter (10, 50, 100 nm) and potassium phosphate buffer solution concentration (0.2, 1, 10 mM) used as the background electrolyte. The applied voltage for the electrokinetic flow was kept below 1 V (tested range from 10-750 mV) and was chosen to conduct experiments in a regime where minimal Faradaic or charge transfer reactions occur for transport across nanopores. Methylene blue at a concentration of 0.14 mM was used as a tracking dye to indicate the transport of charged carriers in the presence of these relatively low applied potentials. An electrical circuit model of the nanopore and the surrounding solution was developed. For an electrokinetic radius of 3.56 or less, the concentration time gradient of dye indicates onset of concentration polarization regimes. Mitigation of polarization was performed with commercial forward osmosis (FO) membranes in permeation cells using a new electrical mitigation method that has been developed as part of this work. Initial proof-of-concept experiments show that for the membranes tested, a flux enhancement of over 40% was achieved.
Advisors/Committee Members: Prakash, Shaurya.
Subjects: Energy; Engineering; Environmental Engineering; Mechanical Engineering
Keywords: concentration polarization mitigation, membrane flux enhancement, water purification, electrokinetic flow, nanocapillary array membrane
More Like This
27.
Bezaire, Beth Ann.
Modeling and Control of an Electrically-Heated Catalyst.
Degree: MS, Mechanical Engineering, 2011, Ohio State University
► Current model-based design research on automotive catalytic converters mainly fall into three…
(more)
▼ Current model-based design research on automotive catalytic converters mainly fall into three basic categories: either modeling the catalyst as a continuous system based on physics, discretizing the system to reduce modeling complexity, or developing a highly-simplified, mean-value model for control. Continuous models are computationally intensive and therefore not well-suited for implementation into a vehicle model for Hardware in the Loop or control design. Highly-simplified models are calibrated for a particular system without incorporating the governing physical laws into the model, and mean-value models are only able to predict the response for a single lumped element. Although a simplified, mean-value model can be developed to accurately predict system response, it does not lend itself to being extended to broader applications without significant re-calibration efforts. Therefore, a model is needed that can account for the physics of the system so it can be extended to further applications while decreasing computation time to allow the model to be implemented for Hardware in the Loop and vehicle control design. This research investigates the development of such a model to predict automotive catalytic converter thermal response during warm-up. A one-dimensional, lumped-parameter model of a three-way catalyst was developed in Matlab/Simulink. The catalyst length was divided into discrete elements. Each discrete element contained states for the temperatures of the gas, substrate, and can wall. Heat transfer mechanisms were modeled from physics-based equations. For each discrete element, these equations modeled the enthalpy of the gas flow axially through the catalyst, convective heat transfer between the gas and substrate, conduction between discrete elements axially along the catalyst for the substrate and for the can, conduction between the substrate and can wall, and convection from the can wall to ambient. Model predictions were validated against experimental results for thermal transients. The application of this model was analysis for a plug-in electric vehicle application with electrically-heated catalyst (EHC). The model was used to compare the catalyst thermal response with and without the EHC. These results facilitated the development of a control strategy for the EHC, as well as recommendations for improving the overall vehicle control strategy. For further development, this model can also be extended to a two- or three-dimensional application. A two-dimensional catalyst model would be of interest to account for temperature gradients in the radial direction through the catalyst.
Advisors/Committee Members: Midlam-Mohler, Shawn.
Subjects: Automotive Engineering; Mechanical Engineering
Keywords: emissions; hybrid vehicle; electrically-heated catalyst; EHC; PHEV
More Like This
28.
Bharadwaj, Shravan.
Active Friction Control via Piezoelectrically Generated Ultrasonic Vibrations.
Degree: MS, Mechanical Engineering, 2009, Ohio State University
► The ability to control the effective friction coefficient between sliding surfaces is…
(more)
▼ The ability to control the effective friction coefficient between sliding surfaces is a problem of significant interest in automotive applications. For reducing friction, lubricants or different material combinations are typically used. In this research, the role of ultrasonic vibrations on the friction coefficient between sliding surfaces is investigated, with the goal of being able to control the friction coefficient in an automotive seat belt system by modulating the vibrations at the interface between the D-ring and seat belt webbing. These ultrasonic vibrations are generated using piezoelectric materials that respond mechanically to an electrical input. To that end, a systematic approach is developed, with the help of experiments and models, to predict and characterize the frictional force between sliding surfaces in the presence of ultrasonic vibrations under various controlling parameters.The applied ultrasonic vibrations may be tangential, perpendicular or out-of-plane to the direction of sliding velocity. For rigid surfaces in contact, maximum friction reduction has been reported in the case of tangential vibrations. It has been shown that the extent of friction reduction depends on the ratio of the velocity of the ultrasonic vibrations to the sliding velocity. A series of experiments over a wide range of loads and speeds are designed to characterize the friction reduction effect between solid-solid contacts and Hertzian contacts in the case of seat belts. Using Coulomb and Dahl friction models, the mechanism of friction reduction in the presence of ultrasonic vibrations is studied. System level analytical modeling is presented which consists of a single degree-of-freedom model with LuGre friction at the sliding interface. By controlling parameters such as load, system stiffness, contact stiffness and the control force generated by the piezoelectric stack, characterization plots are obtained which can help optimize design parameters of ultrasonic lubrication systems. In summary, this research investigates the potential of ultrasonic vibrations in actively controlling friction in automotive seat belt systems and other systems in which the use of lubricants is undesirable. For a given ultrasonic power, the extent of reduction decreases at higher speeds and loads. Active control of friction would help improve the performance, efficiency and lifetime of general sliding mechanisms.
Advisors/Committee Members: Dapino, Marcelo.
Subjects: Mechanical engineering
Keywords: Active control, piezoelectric, friction, sliding, ultrasonic vibrations
More Like This
29.
Bhatnagar, Himanshu.
Computational Modeling of Failure in Thermal Barrier Coatings under Cyclic Thermal Loads.
Degree: PhD, Mechanical Engineering, 2009, Ohio State University
► In this dissertation, finite element models are used to investigate catastrophic failure…
(more)
▼ In this dissertation, finite element models are used to investigate catastrophic failure of thermal barrier coatings (TBCs) due to delaminations along susceptible interfaces of thermally grown oxide (TGO) with the ceramic top coat and the inter-metallic bond coat. The materials and geometries in the studies are chosen to be representative of TBC materials in real applications. The characteristics of the failure modes along the TGO and bond coat interface (e.g. buckling instability and strain energy driven delamination propagation) are investigated using thermo-elastic finite element models. The solution of a linear elastic eigen-value problem determines the onset of the buckling instability with a pre-existing delamination between bond coat and the TGO. The virtual crack extension method is employed to study strain energy release rate driven interfacial delamination at wavy interfaces. The materials and geometries in the study are chosen to be representative of TBC materials in real applications. Extensive sensitivity analyses are conducted to identify the critical design parameters affecting the onset of buckling and extension of interfacial delamination, as well as to develop parametric relations that enhance the understanding of these mechanisms. Finally, a numerical exercise demonstrates that the buckling instability is the leading failure mechanism at flat interfaces or at the locations of minimum cross-section in a wavy interface. However, in the vicinity of waviness, crack extension becomes a dominant mode of failure. The top coat crack initiation and propagation is investigated using a thermo-elastic finite element model with bond coat creep. Cracks are assumed to initiate when the maximum principal stress exceeds rupture stress of the top coat. A sensitivity analysis estimates the contribution of geometric and material parameters and forms a basis to develop parametric relation to estimate maximum principal stress. Subsequently, crack propagation simulations using a hysteretic cohesive zone model are performed for parametric combinations which initiate cracks away from the interface. These analyses conclude that parametric combinations initiating top coat cracks also assist in propagation and eventual delamination of TGO and top coat interface. A homogenization based continuum damage mechanics (HCDM) modeling framework is proposed for TBC failure effects of top coat microstructural defects. An extended Voronoi cell finite element (X-VCFEM)is employed to perform the micro-mechanical analysis of RVE and the results show that HCDM model has limited validity due to loss of material stability with significant damage. A sensitivity analysis reveals that the range of HCDM validity is dependent on top coat cohesive energy.
Advisors/Committee Members: Ghosh, Somnath.
Subjects: Mechanical engineering
Keywords: Thermal barrier coating; top coat; bond coat; TGO; interface debonding; buckling; instability; delamination; energy release rate; competing failure mechanisms; cracking; cyclic thermal loads; damage initiation; damage propagation; parametric studies
More Like This
30.
Bigelow, Kimberly Edginton.
Identification of Key Traditional and Fractal Postural Sway Parameters to Develop a Clinical Protocol for Fall Risk Assessment in Older Adults.
Degree: PhD, Mechanical Engineering, 2008, Ohio State University
► Falls are a major problem for older adults. Balance impairment is one…
(more)
▼ Falls are a major problem for older adults. Balance impairment is one of several major fall risk factors. One of the best ways to measure balance is posturography; however, lack of standardization in testing and reporting first need to be overcome to make the tool clinically useful. This study comprehensively examined four testing conditions, traditional time-domain postural sway parameters, and newer, promising fractal measures to develop a clinical protocol to differentiate fallers and non-fallers. One hundred-fifty individuals aged 65 through 97 participated in this study. Sixty second quiet-standing trials were taken in four testing conditions: eyes open, comfortable stance; eyes closed, comfortable stance; eyes open, narrow stance; and eyes closed, narrow stance. Eight traditional postural-sway parameters and six fractal dimensions were calculated. Stepwise logistic binary regression was performed to identify the group of the postural sway parameters and physical characteristics that best differentiated fallers from non-fallers for each condition. This analysis was performed twice with fallers defined using two different definitions: at least one fall in the past year and multiple falls in the past year. Results found that individuals who had fallen at least once were not well differentiated from non-fallers. A single fall, or lack of, does not indicate the presence, or absence, of postural instability and should not be used clinically to identify fall risk. Multiple fallers were differentiated from individuals who had not fallen or had only fallen once. Medial-Lateral Sway Velocity was the most important postural sway parameter in differentiating the two groups in all conditions. Logistic regression promoted the use of the eyes closed, comfortable stance condition to best differentiate individuals based on fall history. The associated model included, in order or importance: Medial-Lateral Velocity, Anterior-Posterior Short-Term Fractal Dimension, Medial-Lateral Short-Term Fractal Dimension, Body Mass Index, and Age. This model demonstrated very good ability in identifying non-fallers as low-risk, and moderate accuracy in correctly identifying fallers as high-risk. Fractal analysis was an important inclusion and revealed novel findings of two distinct scaling regions. Future prospective work is necessary to extend findings to prediction of future falls.
Advisors/Committee Members: Berme, Necip.
Subjects: Biomedical research; Biostatistics; Engineering; Gerontology; Mechanical engineering
Keywords: falls; postural instability; balance; posturography; fractals; fall-risk; balance measurement; postural sway; older adults
More Like This
[1] [2] [3] [4] [5] … [17]
