Master of Science (M.S.), University of Dayton, 2014, Mechanical Engineering

Many industrial machines incorporate a multitude of moving and rotating parts necessary for the machinery to perform its intended functions. Rotating machinery, like turbines and compressors, include multiple parts that rotate under heavy loads and high speeds. Shafts are a common medium to transmit these loads and speeds. Quite often, these shafts are required to be stepped to create multiple distinct diameters for carry and located other components. The addition of these steps must be design with care such that a proper radius is selected between two diameters. Parts operating in this field will run for long periods of time and must maintain under multiple start/stop cases and can eventually cause failures. Rotor and torsional dynamic analyses are completed on most if not all rotors in the turbomachinery field. The 45 degree rule is a method of simplification for modeling abrupt changes in diameter. This rule of thumb states a line from the lesser of two steps on a shaft can be drawn at a 45 degree angle to the outside diameter of the greater step. The material outside this line can be modeled with zero modulus and actual density. This region of material does not significantly impact the torsional stiffness of the area. The purpose of this research is to find the effect this modeling approach has on the computed strength, stiffness, and overall rotordynamic properties of a rotating shaft. This will also demonstrate the “Best case” shoulder combination with various fillet radii and/or other angle orientation as well as illustrate additional areas this theory may be applicable. Additional considerations will be made for defective or non-homogeneous material (e.g., inclusions, cracks, and scratches) that may be contained within the region under consideration and their effect on the overall region's computed strength and stiffness. The purpose of this research is split into three claims. The first claim states that after the removal of the material outside the 4 (open full item for complete abstract)

Committee: Thomas Whitney Dr. (Advisor); Dave Myszka Dr. (Committee Member); Steven Donaldson Dr. (Committee Member); Raed Hasan Dr. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2009, EMC - Mechanical Engineering

In this research, the fault detection and diagnosis using a model-based technique for the cracked rotor vibration system is developed and implemented. More specifically, the observer based or filter bank approach is employed in the fault detection and diagnosis process in order to detect the occurrence of a crack and diagnose the position and the depth of the crack in rotating machinery. The fault detection and diagnosis process is consisted of two parts. The first part is the filter bank or the residual generation which generates the residual vectors corresponding to each observer. The second part is a voting algorithm which searches the observer that corresponds to the behavior of the real system. The type of filter contained in the filter bank is the discrete time-variant Kalman filter. The filter is specifically designed to track the cracked rotor vibration system. Since the filter is time-variant, the state matrix at the current time step of the filter is updated by the state estimated value from the previous time step. Constructing the filter bank with the presented filter allows the fault detection and diagnosis process to perform very well under the environment of the process and measurement noises which is unavoidable in real systems. The voting algorithm evaluates every observer to find the observer behaving the closest to the real system based on the score achieved by each observer. The score is calculated by the information of the residual mean, the residual autocorrelation of each observer, the correlation coefficient between the real system measurements, and the observer outputs. In order to evaluate the fault detection and diagnosis process performance, the fault detection and diagnosis process is tested with the simulated real system containing various sets of system parameters. The results and discussions are presented.

Committee: Kenneth A. Loparo PhD (Committee Chair); Dario Gasparini PhD (Committee Member); Robert L. Mullen PhD (Committee Member); Maurice L. Adams PhD (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2008, EMC - Mechanical Engineering

Crack failure is among the most dreaded failures experienced in rotating machinery. It is therefore important to be able to detect a crack before failure occurs and cost effective to know the location and severity of a crack making it possible to predict the behavior and life of the machinery. This dissertation outlines a method of crack detection using the elastic wave created by the snapping shut of a radial crack to determine these characteristics. To determine the feasibility of such a method, preliminary research is performed by examining the behavior of a crack in 4-point-bending. A theoretical solution for the elastic wave behavior is determined by modeling the behavior as the collinear impact between two shafts. A theoretical impact velocity is found using finite element modeling to examine crack geometry. A pendulum experiment is performed in order to examine the validity of the assumed theoretical acceleration at the shaft end. The experimental acceleration response is smaller than the theory because the volume of air caught between the shaft face and the wall has to be expelled. This is explained by Reynolds lubrication equation which proves this hypothesis. An experiment to test the 4-point-bending theory is presented. More work is needed to determine the feasibility of such a crack detection method, such as running a 4-point-bending experiment as the design for which is presented.

Committee: Maurice Adams PhD (Advisor); Kenneth Loparo PhD (Committee Member); Iwan Alexander PhD (Committee Member); Joseph Prahl PhD (Committee Member) Subjects: Engineering; Mechanical Engineering