Shock and Vibration - Volume 2, issue 6

Authors: Maslen, Eric H.

Article Type: Research Article

Abstract: Feedback control of flexible structures naturally involves actuators and sensors that often cannot be placed at the same point in the structure. It has been widely recognized that this noncollocation can lead to difficult control problems and, in particular, difficulty in achieving high robustness to variation in the dynamic properties of the structure. This problem has previously been traced to transmission zeros in the dynamic transfer function between sensor location and actuator location, especially those lying on the positive real axis in the complex plane. In this artie/e, the physical significance of these zeros is explored and the dynamic properties …of beams that give rise to real positive zeros are contrasted to those of torsional and compressive systems that do not. Show more

DOI: 10.3233/SAV-1995-2601

Citation: Shock and Vibration, vol. 2, no. 6, pp. 429-435, 1995

Authors: Gaberson, Howard A.

Article Type: Research Article

Abstract: This article discusses time frequency analysis of machinery diagnostic vibration signals. The short time Fourier transform, the Wigner, and the Choi–Williams distributions are explained and illustrated with test cases. Examples of Choi–Williams analyses of machinery vibration signals are presented. The analyses detect discontinuities in the signals and their timing, amplitude and frequency modulation, and the presence of different components in a vibration signal.

DOI: 10.3233/SAV-1995-2602

Citation: Shock and Vibration, vol. 2, no. 6, pp. 437-444, 1995

Authors: Marcelin, J.-L. | Shakhesi, S. | Pourroy, F.

Article Type: Research Article

Abstract: This article deals with the optimal damping of beams constrained by viscoelastic layers when only one or several portions of the beam are covered. The design variables are the dimensions and locations of the viscoelastic layers and the objective function is the maximum damping factor. The discrete design variable optimization problem is solved using a genetic algorithm. Numerical results for minimum and maximum damping are compared to experimental results. This is done for a various number of materials and beams.

DOI: 10.3233/SAV-1995-2603

Citation: Shock and Vibration, vol. 2, no. 6, pp. 445-450, 1995

Authors: Huang, H. | Kiddy, K.C.

Article Type: Research Article

Abstract: The nonlinear interaction problem is analyzed by simultaneously solving the mass, momentum, and energy conservation equations together .with appropriate material constitutive equations governing the fluid dynamics of the explosion gaseous product and the water and the structural dynamics of the compliant shell. A finite difference technique in a coupled Eulerian–Lagrangian scheme is used. The computer program PISCES 2DELK is employed to carry out the numerical computations. The results demonstrate that to rigorously analyze the response of a submerged structure to a nearby explosion, the interactions among the explosion shock wave, the structure, its surrounding media, and the explosion bubble need …to be considered. Show more

DOI: 10.3233/SAV-1995-2604

Citation: Shock and Vibration, vol. 2, no. 6, pp. 451-460, 1995

Authors: Fitz-Coy, Norman

Article Type: Research Article

Abstract: A mathematical procedure that quantitatively addresses issues critical to the design and operation of multiaxis vibration simulators is presented. Both kinematic and dynamic issues are considered. The analysis is applied to both 3 and 6 degrees of freedom configurations. The existence of singular configurations is mentioned and appropriate corrective measures are recommended. A methodology for determining the required actuator commands is also presented.

DOI: 10.3233/SAV-1995-2605

Citation: Shock and Vibration, vol. 2, no. 6, pp. 461-470, 1995

Authors: Bennett, J.A. | Park, G.J.

Article Type: Research Article

Abstract: One of the more difficult optimal design tasks occurs when the data describing the system to be optimized is either highly nonlinear or noisy or both. This situation arises when trying to design restraint systems for automotive crashworthiness using the traditional lumped parameter analysis methods. The nonlinearities in the response can come from either abrupt changes in the occupants interaction with the interior or from relatively minor fluctuation in the response due to the interactions of two restraint systems such as belts and airbags. In addition the calculated response measures are usually highly nonlinear functions of the accelerations. Two approaches …using an approximate problem formulation strategy are proposed. One approach uses a first-order approximation based on finite difference derivatives with a nonlocal step size. The second and more effective approach uses a second-order curve fitting strategy. Successful example problems of up to 16 design variables are demonstrated. A conservative design strategy using a derivative-based constraint padding is also discussed. The approach proves effective because analytical expressions are available for the second-order terms. Show more

DOI: 10.3233/SAV-1995-2606

Citation: Shock and Vibration, vol. 2, no. 6, pp. 471-479, 1995

Authors: Mao, S.G. | Leung, A.Y.T.

Article Type: Research Article

Abstract: An accurate beam finite element is used to solve nonlinear vibration of arched beams and framed structures. The nonlinear governing equations of a skeletal structure are integrated numerically using symplectic integration schemes so that the Poincaré integral invariant of a Hamiltonian flow are preserved during the evolution. The element stiffness matrices are not required to be assembled into global form, because the integration is completed on an element level so that many elements can be handled in core by a small computer. Testing examples include arched beams and frames with and without damping in free and forced vibration. The dynamic …symmetry breaking phenomena are noted at the dynamic buckling point. Show more

DOI: 10.3233/SAV-1995-2607

Citation: Shock and Vibration, vol. 2, no. 6, pp. 481-492, 1995

Authors: Lin, Y.J. | Lu, Y. | Lee, T. | Choi, B.

Article Type: Research Article

Abstract: This article presents the application of the fuzzy logic (FL) concept to the active control of a multiple degree of freedom reaction compensating platform system that is designed and used for isolating vibratory disturbances of space-based devices. The physical model used is a scaled down two-plate platform system. In this work, simulation is performed and presented. According to the desired performance specifications, a full range of investigation regarding the development of an FL stabilization controller for the system is conducted. Specifically, the study includes four stages: comprehensive dynamic modeling of the reaction compensating system; analysis of the dynamic responses of …the platform system when it is subjected to various disturbances; design of an FL controller capable of filtering the vibratory disturbances transmitted to the bottom plate of the platform system; performance evaluation of the developed FL controller through computer simulations. To simplify the simulation work, the system model is linearized and the system component parameter variations are not considered. The performance of the FL controller is tested by exciting the system with an impulsive force applied at an arbitrarily chosen point on the top plate. It is shown that the proposed FL controller is robust in that the resultant active system is well stabilized when subjected to a random external disturbance. The comparative study of the performances of the FL controlled active reaction and passive reaction compensating systems also reveals that the FL controlled system achieves significant improvements in reducing vibratory accelerations over passive systems. Show more

DOI: 10.3233/SAV-1995-2608

Citation: Shock and Vibration, vol. 2, no. 6, pp. 493-506, 1995

Authors: Vold, Håvard | Leuridan, Jan

Article Type: Research Article

Abstract: The analysis of the periodic components in noise and vibration signals measured on rotating equipment such as car power trains, must be done more and more under rapid changes of an axle, or reference RPM. Normal tracking filters (analog or digital implementations) have limited resolution in such situations; wavelet methods, even when applied after resampling the data to be proportional to an axle RPM, must compromise between time and frequency resolution. The authors propose the application of nonstationary Kalman filters for the tracking of periodic components in such noise and vibration signals. These filters are designed to accurately track signals …with a known structure among noise and signal components of different, “unknown,” structure. The tracking characteristics of these filters, i.e., the predicted signal amplitude versus time values versus exact signal amplitude versus time values, can be tailored to accurate tracking of harmonics buried in other signal components and noise, even at high rates of change of the reference RPM. A key to the successful construction is the precise knowledge of the structure of the signal to be tracked. For signals that vary with an axle RPM, an accurate estimate of the instantaneous RPM is essential, and procedures to this end will also be presented. Show more

DOI: 10.3233/SAV-1995-2609

Citation: Shock and Vibration, vol. 2, no. 6, pp. 507-515, 1995

Article Type: Book Review

DOI: 10.3233/SAV-1995-2610

Citation: Shock and Vibration, vol. 2, no. 6, pp. 517-518, 1995

Article Type: Other

DOI: 10.3233/SAV-1995-2611

Citation: Shock and Vibration, vol. 2, no. 6, pp. 521-522, 1995

Article Type: Other

DOI: 10.3233/SAV-1995-2612

Citation: Shock and Vibration, vol. 2, no. 6, pp. 523-523, 1995

Article Type: Other

DOI: 10.3233/SAV-1995-2613

Citation: Shock and Vibration, vol. 2, no. 6, pp. 525-528, 1995