No abstract

The purpose of this two-part work is to apply active mode localization to distributed parameter systems where the number of control sensors and actuators is a limiting factor. In this part, the theoretical development portion of the study, two approaches are presented that shape system eigenvectors using feedback control, generating localization to produce areas of isolation with relatively low vibration amplitudes compared to other parts of the structure. The first approach uniformly shapes all eigenvectors of a vibrating system, but can require many actuators to do so. The second more general approach uses singular value decomposition (SVD) to shape selected eigenvectors of a system, localizing the response of these modes to any disturbance, and requiring few actuators. [S0739-3717(00)70202-9]

The effects of healing time and anterior cruciate ligament reconstruction on healing of the medial collateral ligament and stability of the knee joint were evaluated in a rabbit model of an O'Donoghue triad injury (rupture of the medial collateral ligament with removal of the anterior cruciate ligament and part of the medial meniscus). At time 0 and at 6 and 12 weeks postoperatively, the anterior-posterior translation and varus-valgus rotation of the knee, the structural properties of the femur-medial collateral ligament-tibia complex, and the mechanical properties of the substance of the medial collateral ligament were evaluated. Although anterior-posterior translation increased significantly with time, we could not demonstrate a significant temporal effect on varus-valgus rotation. The ultimate load, elongation at failure, and energy absorbed to failure improved with time. In addition, with time, failure of the complex occurred more often in the ligament substance than at the osseous insertion. Because healing time did not affect the cross-sectional area or modulus of the medial collateral ligament, the improved structural properties of the complex resulted not from improvements in the mechanical properties of the tissue but rather from healing of the tibial insertion site. By 12 weeks, the reconstructed knees had only minor signs of osteoarthrosis on the tibiofemoral surfaces; this is in contrast to the findings in anterior cruciate ligament-deficient knees in our earlier study. Additionally, at 12 weeks, the stiffness of the complexes from the reconstructed group was 1.3 times that of the anterior cruciate ligament-deficient group (p < 0.05), and te ultimate load had increased by a factor of 1.6 (p < 0.05). Our findings demonstrate that reconstruction of the anterior cruciate ligament in the rabbit helps to stabilize the joint, improves healing of the medial collateral ligament, and may decrease the incidence of early-onset osteoarthrosis after an O'Donoghue triad injury.

The purpose of this two-part work is to apply active mode localization techniques to distributed parameter systems where control actuator and sensor placement is a limiting factor. In this paper, Part 2 of the study, the SVD eigenvector shaping technique examined in Part 1 is utilized to numerically and experimentally localize the response of a simply supported beam. This is done for two reasons. First, it demonstrates the application of this modified mode localization technique to a distributed parameter system. Second, it shows that it is possible to use this method to produce vibration isolation, reducing the absolute displacements in designated portions of the system while simultaneously curtailing the number of necessary control sensors and actuators. [S0739-3717(00)70302-3]

No abstract

The purpose of this study is to apply feedback control to a physical system in order to localize structural vibration. This is accomplished using an eigenstructure placement technique called eigenvector scaling. Active eigenvector scaling mimics one of the properties of passive mode localization, namely the confinement of vibrational energy, by re-forming or scaling portions of all the system mode shapes. This produces areas of localization, with relatively large amplitudes and high vibrational energy levels, and areas of isolation, with relatively small amplitudes and little vibrational energy. Because all mode shapes are scaled in the same fashion, the system response reflects this vibration confinement regardless of the type of disturbance input. In this paper, the above statements are supported using control law development and analysis as well as experimental application and numerical simulations. [S0739-3717(00)70402-8]

No abstract

A test device has been developed and validated to simulate physiologic loading of the hip during stair climbing. Forces about the hip joint were measured in static simulations of stair climbing using simulated extensor, abductor and adductor muscle groups to support the joint. Femoral flexion angle (to model step length and height) and applied hip flexion moment (to model trunk lean) were varied to examine the effects of different loading conditions on the hip. In stair climbing the maximum total joint force was six times body weight at 34 degrees of femoral flexion and 60 N m of hip flexion moment. Joint forces increased with hip flexion moment and varied little with femoral flexion angle, except for the posteriorly directed force. This component, which twists implants about the femoral shaft, increased with femoral flexion angle but changed little with hip flexion moment.