Resistance exercise has been widely reported to have positive rehabilitation effects for patients with neuromuscular and orthopaedic conditions. This paper presents an optimal design of magneto-rheological fluid dampers for variable resistance exercise devices. Adaptive controls for regulating the resistive force or torque of the device as well as the joint motion are presented. The device provides both isometric and isokinetic strength training for various human joints.
The transmission of sound and vibration across a sandwich structure has been studied in this paper. The main research issues are identified and the applied concept has been explained in detail. This concept has been validated in a previous study. It has been observed that successful manipulation of certain material parameters can minimize the sound and vibration transmission through the structure significantly. The results of this work could provide guidelines for material scientists to design new composite materials with better vibration and noise transmission properties.
Piezoelectric stack actuators have been used in structural acoustic controls, and active vibration isolation systems. In recent tests of heavy duty vibration isolation systems, it has been found that piezoelectric stack actuators under large loadings and high driving voltages can produce substantial heat to cause failure. This paper presents preliminary results of a research effort that was set out to investigate the heat production and thermal effects on the actuator performance In the paper, a general constitutive formulation of piezoelectric materials is presented starting from the first law of thermal dynamics. the constitutive equations involve thermoelastic, pyroelectric and, of course, piezoelectric effect. A variational principle based on Oden's approach is then developed. As a special case, the equations of motion for a circular multilayer stack piezoelectric actuator are derived from the variational principle. Numerical results of blocked force and free stroke of the actuator are presented in the paper. The effects of various parameters on these two common specifications of solid state actuators are studied.
Suppressing interior sound radiation in helicopters, fixed- wing aircraft and land vehicles is a very important problem. It has been studied quite extensively in the past few decades. There are two mainstream methods for this problem: active noise cancellation (ANC) using loudspeakers and sound radiation reduction via structural controls (often called active structural acoustic control or ASAC). An ANC system often requires an impractically high dimensionality to achieve the level of global noise reduction in a three dimensional volume that ASAC systems with a relatively low dimensionality are capable of, while actuators for structural control systems are power intensive and less reliable. This paper presents an acoustic boundary control method that may reserve the advantages of both ANC and ASAC. Numerical simulation results of interior noise control are presented to demonstrate the ability of the acoustic boundary control to cancel sound fields due to different primary sources. A discussion is also presented on the spatial characteristics of the acoustic boundary control as a function of frequency. An interesting phenomenon is discovered that may have significant implications to the actuator grouping studies.
There is a growing interest in the application of smart materials technology to the aircraft interior noise control problem. Some outstanding issues with the interior noise control problem include development of sensory systems that can lead to global sound level reduction in the cabin, and the safety concern of structural actuators used to reduce noise radiation. This paper presents two comparative studies: (1) comparison of several sensor configurations by using acoustic microphones, and (2) comparison of strain fields induced by discrete and distributed structural actuators. A uniform cylindrical shell is used as a simplified model of a section of fuselage. Extensive simulations have been conducted. Major findings of this paper are: (1) In order to control the interior noise in the shell where there is no acoustic source inside, one only needs to place acoustic sensors near the wall. Furthermore, if one uses the energy density as an error signal, one can reduce the number of error input channels substantially. In terms of the ability to lead to the global noise reduction, a 4-channel energy density sensor is found to be comparable to 32 microphones uniformly spaced on a ring. (2) Distributed piezoelectric actuators tend to introduce smoother strain fields on the shell than discrete actuators as measured by a strain index defined in the paper. This quantitative result agrees with one's intuition. Simulation results of adaptive control of multi-tone noise field using discrete and distributed structural actuators are also presented in the paper.
Conference Committee Involvement (6)
Active and Passive Smart Structures and Integrated Systems II
10 March 2008 | San Diego, California, United States
Active and Passive Smart Structures and Integrated Systems
19 March 2007 | San Diego, California, United States
Damping and Isolation
27 February 2006 | San Diego, California, United States
Damping and Isolation
7 March 2005 | San Diego, California, United States
Damping and Isolation
15 March 2004 | San Diego, CA, United States
Damping and Isolation
3 March 2003 | San Diego, California, United States
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