Browsing by Subject "Vibration isolation"
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Item Evaluation of systems containing negative stiffness elements for vibration and shock isolation(2012-05) Fulcher, Benjamin Arledge; Haberman, Michael R.; Seepersad, Carolyn C.; Wilson, Preston S.The research presented in this thesis focuses on the modeling, design, and experimentation of systems containing negative stiffness mechanisms for both vibration and shock isolation. The negative stiffness element studied in this research is an axially compressed beam. If a beam is axially compressed past a critical value, it becomes bistable with a region of negative stiffness in the transverse direction. By constraining a buckled beam in its metastable position through attaching a stiff linear spring in mechanical parallel, the resulting system can reach a low level of dynamic stiffness and therefore provide vibration isolation at low frequencies, while also maintaining a high load-carrying capacity. In previous research, a system containing an axially compressed beam was modeled and tested for vibration isolation [7]. In the current research, variations of this model were studied and tested for both vibration and shock isolation. Furthermore, the mathematical model used to represent the compressed beam in [7] was improved and expanded in current research. Specifically, the behavior exhibited by buckled beams of transitioning into higher-mode shapes when placed under transverse displacement was incorporated into the model of the beam. The piecewise, nonlinear transverse behavior exhibited by a first-mode buckled beam with a higher-mode transition provides the ability of a system to mimic an ideal constant-force shock isolator. Prototypes manufactured through Selective Laser Sintering were dynamically tested using a shaker table. Vibration testing confirmed the ability of a system containing a constrained negative stiffness element to provide enhanced vibration isolation results with increasing axial compression on a beam. However, the results were limited by the high sensitivity of buckled beam behavior to geometrical and boundary condition imperfections. Shock testing confirmed the ability of a system containing a buckled beam with a higher-mode transition to mimic the theoretically ideal constant-force shock isolator.Item Vibration Isolation of a Locomotive Mounted Energy Storage Flywheel(2011-02-22) Zhang, XiaohuaUtilizing flywheels to store and reuse energy from regenerative braking on locomotives is a new technology being developed in the Vibration Control and Electromechanics Lab at Texas A&M. This thesis focuses on the motion analysis of a locomotive mounted energy storage flywheel system for a variety of support motion inputs. Two input cases, sinusoidal floor input and ramp input, are analyzed in different sections. Simulation results and methods of ensuring the operating success of the flywheel system are provided at the end of each section. Section 1 introduces the problem and method being used to study the vibration under different circumstances. Section 2 analyzes the response of the flywheel system to sinusoidal floor input given by Ahmadian and Venezia 2000. Natural frequency and transmissibility of the system are utilized to explain the simulation results carried out in the frequency domain. It is found that the motion differences between flywheels(rotors) and magnetic bearings(stators) are guaranteed to be small. Section 3 emulates the locomotive traversing a bump with 1:150 slope. Simulation shows that catcher(backup) bearings are needed to limit the vibration of rotors through a bump. It is also found that gyroscopic effect causes problems in vibration isolation. Section 4 explores de-levitation method and installation of gimbals as possible remedies to this problem. Finally, a summary of simulation results from different input cases is made.