Measurement of roadway roughness and automobile ride acceleration spectra

See this work in the Center for Transportation Research Library catalog: https://library.ctr.utexas.edu/Presto/catalogid=31632The present study is designed to support an overall program for the evaluation and establishment of ride quality criteria in transportation systems. This report, which is restricted to the automobile, outlines the procedures and equipment employed to measure, record, and analyze automotive vibrations and highway or roadway roughness. Detailed automobile vibration responses and corresponding roadway roughness have been measured and recorded here for 20 different roadway sections which are typical of those found in the Austin - Travis County, Texas, area. Our highway roughness models are also compared to some of the roughness models found in the literature.Department of Transportation Office of University Research (Washington D.C.)Center for Transportation ResearchSee this work in the Center for Transportation Research Library catalog

Recent Applications of Higher-Order Spectral Analysis to Nonlinear Aeroelastic Phenomena

Recent applications of higher-order spectral (HOS) methods to nonlinear aeroelastic phenomena are presented. Applications include the analysis of data from a simulated nonlinear pitch and plunge apparatus and from F-18 flight flutter tests. A MATLAB model of the Texas A&MUniversity s Nonlinear Aeroelastic Testbed Apparatus (NATA) is used to generate aeroelastic transients at various conditions including limit cycle oscillations (LCO). The Gaussian or non-Gaussian nature of the transients is investigated, related to HOS methods, and used to identify levels of increasing nonlinear aeroelastic response. Royal Australian Air Force (RAAF) F/A-18 flight flutter test data is presented and analyzed. The data includes high-quality measurements of forced responses and LCO phenomena. Standard power spectral density (PSD) techniques and HOS methods are applied to the data and presented. The goal of this research is to develop methods that can identify the onset of nonlinear aeroelastic phenomena, such as LCO, during flutter testing

Part I. The Stability of a Membrane in a Subsonic Flow. Part II. The Stability of a Grid of Panels in a Supersonic Flow

Part I. An experimental investigation has been made on the stability of small aspect ratio rectangular membranes in a subsonic flow. The leading and trailing edges of the membrane were attached to rigid streamlined supports while the two streamwise edges were free. Both surfaces of the membrane were exposed to the airstream, and the membrane tension was applied through the trailing edge. The results of the test show that two types of flutter (instability) occur. The first to appear as the wind speed was increased from zero, with a fixed tension level in the membrane, was a small amplitude flutter which has a shallow wave like motion traveling in the streamwise direction. At higher wind speeds this motion was damped out. A narrow equilibrium zone or boundary existed which separated the first type of flutter from a second type of motion having a traveling wave of larger amplitude and greater speed. This second type of flutter had no tendency to damp out, but became more violent as the wind speed was increased. The span of the slender membrane is the physical parameter that uniquely determines and controls the first flutter boundary; its mass plays no part here, but does affect the equilibrium zones. Appendix A contains an obvious formulation of the slender membrane flutter problem. Part II. A theoretical investigation has been made on the stability of a grid of panels in a supersonic flow. The problem is formulated by considering this structure as a limiting case of a more general configuration composed of a ring of panels (i.e. an axially stiffened cylindrical shell) whose outer surface is exposed to a supersonic flow parallel to its axis. It is shown that the stability analysis of this more general configuration can be reduced to the analysis of an "equivalent" single panel using the circulant matrix idea. The reduction procedure, applicable to most cyclic configurations, allows for all types of inter-element (panel) coupling and is subject to the sole restriction that the dynamic phenomenon be satisfactorily described by linear theory. It is shown that at least five different multi-panel configurations can be obtained from this general problem by taking the appropriate limiting process. The stability (flutter) analysis of one of these limiting cases is discussed for high Mach number flows where only an elastic coupling exists between neighboring panels.</p

Dynamic Modelling for Automobile Acceleration Response and Ride Quality Over Rough Roadways

See this work in the Center for Transportation Research Library catalog: https://library.ctr.utexas.edu/Presto/catalogid=5739Current interest in dynamics and vibration of ground transportation vehicles arises from the fact that excessive levels can lead to unsafe operation and give an uncomfortable ride to passengers. Current work by the U.S. Department of Transportation in high-speed tracked air-cushion and magnetically levitated vehicles centers around suspension design (both active and passive) for isolating guideway roughness effects from the main body of the vehicle. The work described herein arose from a need to evaluate vibration acceptance criteria for use in both vehicle systems design and guideway specification. This report deals with the first part of a study of automobile riding quality. Three different models of an intermediate sedan together with two different models for roadway roughness are compared. Roadway models compared are, first, a random input single track model with statistics governed by a power spectral density proportional to the square of the wavelength and, second, a model using a data sequence with a zero order hold where the data sequence is obtained from measured evaluation profiles of actual roadway sections. Frequency weighted rms acceleration responses are compared with serviceability indices of roadway test sections. It is concluded that the commonly used roadway model is inadequate and that more complete roadway information regarding statistics of right and left wheel tracks, together with a vehicle model including body roll motions, is necessary to predict ride quality. Use of the ISO Standard on Whole Body Vibration Tolerances as a basis of frequency weighting provides a good correlation with subjective response measured in terms of the roadway servicability index.Department of Transportation Office of University Research (Washington D.C.)Center for Transportation ResearchSee this work in the Center for Transportation Research Library catalog

General Hybrid Meshes and Its Application to Flow/Structure Interactions

I would like to express my profound gratitude to my advisor, Professor Yannis Kallinderis, for his advices, comments, and encouragement during my dissertation research. I am also grateful to him for asking questions that helped me consolidating my ideas and giving me considerable freedom to follow my own paths in research. His good sense of humor also has been invaluable to me while I was struggling with research. I would like to express my sincere appreciation to the members of my dissertation committee. I am extremely indebted to Professor Clinton Dawson, my co-advisor, for his comments and advices about my work as well as hosting me at the Institute of Computational Engineering and Sciences (ICES) and providing the excellent parallel computing resources of the Center for Subsurface Modeling (CSM) at ICES. My heartfelt gratitude must be expressed to Professor Graham Carey for his advices both in academics and life. Prof. Carey brought me a perspective view of my dissertation, and helped me to identify important parts and less important parts. I wish to thank Professor Spyridon Kinnas for giving me a chance to present m