Home HomeF. Venancio-Filho, Federal University of Rio de Janeiro (Brazil)
This paper introduces initially a general formulations for frequency-domain dynamic and vibration analysis using discrete Fourier transforms through the Implicit Fourier transform concept. The issues of treatment of initial conditions in the frequency-domain and convergence are analysed. An efficient iterative method for the frequency domain dynamic analysis of MDOF systems and a method for analysis of nonlinear systems are introduced.
sv970542.pdf (Scanned)
TOPKam W. Ng, Office of Naval Research (U.S.A.)
Vibration of finite cylindrical shell was controlled using active constrained layer damping technique. In active constrained layerdamping, a visco-elastic damping layer is sandwiched between two piezo-electric layers to provide built-in sensing and control capabilities that actively tune the shear of the visco-elastic layer, in response to the structural vibrations. The sensing, as indicated by the sensor voltage Vs, is provided by the piezoelectric layer which is directly bonded to the structure. The actuation is generated by the other piezo-electric layer which acts as an active constrained layer that is activated by the control voltage Vc. Specifically, two damping patch configurations at various locations were tested and evaluated. Results showed that the rectangular damping patches bonded on the end cap are more effective than the triangular patches bonded to the free end of the cylinder. Performance of the combination of two and more patches is similar to the single patch. Overall results showed that the active constrained layer is viable and has greater vibration suppression than the passive constrained layer damping. To improve the active constrained layer technique, there is a need for high force and high displacement actuators, and more robust controllers.
sv970157.pdf (Scanned) TOP
Hyun Chul Park, Pohang University of Science and Technology (Korea)
Young Kyu Kang, Pohang University of Science and Technology (Korea)
Interaction between the structure and the control is investigated numerically and verified experimentally for the active vibration control of carbon/epoxy laminated composite beams with collocated piezoceramic sensors and actuators. Finite element method is used for the analysis of dynamic characteristics of the laminated composite beams with and without the piezoceramic sensors/actuators. Damping and stiffness of the adhesive layer and the piezoceramics are taken into account in the finite element modeling. Tailoring that varies the stiffness and the damping properties of the laminated composite beam is used with stacking sequence of [\Theta_4/O_2/90_2]_s, where \Theta = 0, 15, 30, 45, 60, 75 and 90 degree. Optimal control theory is applied for the analysis of control characteristics of the beam. Experiments on the active vibration control of the laminated composite beams has been carried out by making use of direct negative velocity feedback with constant gain. Active and passive damping ratios and modal damping of the first bending of the beams are measured experimentally. They are in good agreement with those of the finite element analysis. When the feedback gain is small, the active control follows trends of the passive control but adds additional effects due to the active control. But for large feedback gains, the active control is dominant over the passive control. The active control is more effective to the structure with higher stiffness than to the structure with lower stiffness, when the feedback gain is large.
sv970261.pdf (Scanned) TOP
Isao Yokomichi, Kitakyushu College of Technology (Japan)
Masaharu Aisaka, ISUZU Motors Limited (Japan)
Yoshiaki Araki, Kyushu Institute of Technology (Japan)
A shot impact damper consists of a bed of granular materials moving in a container mounted on a multibody vibrating system. This paper deals with the damping characteristic of a multi-degree-of-freedom (MDOF) system that is provided with the impact damper when the damper may be applied to any point of the system. In the theoretical analysis, the particle bed is assumed to be a mass which moves unidirectionally in a container, and collides plastically with its ends. Equations of motion are developed for an equivalent single-degree-of-freedom (SDOF) system and attached damper mass with use made of the normal mode approach. The modal mass is estimated such that it represents the equivalent mass on the point of maximum displacement in each of the vibrating modes. The mass ratio is modified with the modal vector to in-clude the effect of impact interactions. Results of the analysis are applied to the special case of a three-degree-of freedom (3DOF) system, and the effects of the damper parameters including mode shapes and damper location are determined. Numerical and experimental studies are made of the damping performance of plural dampers located at selected positions throughout a multibody system. The impact vibration model, including the motion forms comprising riding or separation of damper masses on individual vibrating bodies is developed, and the resulting formulation is analyzed by using the modal synthesis method. For n degree-of-freedom system, the existence of as many as 2\^n combinations of motion forms are identified through digital simulation. Results of numerical studies were compared to, and were found to be in good agreement, with experimental results. It is found that the shot impact damper with properly selected mass ratio and with container clearance effectively suppresses the resonance peaks over a frequency range.
sv970249.pdf (Scanned) TOP