Showing papers in "Shock and Vibration in 1995"
TL;DR: In this article, the authors connect the mathematical theory of waves with the physical behavior of the free surface of water subjected to forces, together with concrete physical applications, and present a mathematical model of water waves.
Abstract: The purpose of this book, Water Waves as the author says, is to connect the mathematical theory of waves with the physical behavior of the free surface of water subjected to forces, together with concrete physical applications. The book is divided into four parts. In part one comprised of Chapters 1 and 2 the basic equations of hydrodynamics of an incompressible fluid in an irrotational flow are presented, and two approximate theories are discussed. One is the small amplitude waves and the other is shallow water theory. Part two is divided into three subdivisions and is concerned with the small amplitude wave theory. In Subdivision A, which consists of Chapters 3-5, simple harmonic wave motions are developed. The ideas of standing and traveling waves are presented and the uniqueness of the solution is discussed in Chapter 3. Chapter 4 treats some simple harmonic forced oscillations, in contrast with the free vibrations d,iscussed in Chapter 3. In Chapters 3 and 4 the water depth was assumed constant. Chapter 5 deals with simple harmonic waves for cases in which the water depth is not constant. Various methods for treating problems of propagation of progressing waves over a uniformly sloping beach are presented. Again, the uniqueness of the solution is discussed and a uniqueness theorem is derived. In Subdivision B, that comprised of Chapter 6, problems involving transient motions are treated. The Fourier transform technique is explained and used to obtain solutions for different cases. Subdivision C, which is the final subdivision in Part 2 consisting of Chapters 7-9, deals with
97 citations
TL;DR: In this paper, different methods of analysis from several fields of study, for example solid-state physics and civil, mechanical, and aerospace engineering, used to determine the effects of disorder in one-dimensional (1-D) and 2-D periodic structures.
Abstract: Extensive work has been done on the vibration characteristics of perfectly periodic structures. This article reviews the different methods of analysis from several fields of study, for example solid-state physics and civil, mechanical, and aerospace engineering, used to determine the effects of disorder in one-dimensional (1-D) and 2-D periodic structures. In the work examined, disorder has been found to lead to localization in 1-D periodic structures. It is important to understand localization because it causes energy to be concentrated near the disorder and may cause an overestimation of structural damping. The implications of localization for control are also examined.
55 citations
TL;DR: Theoretical and experimental performance characteristics of the new class of actively controlled constrained layer damping (ACLD) are presented in this paper, which consists of a viscoelastic damping layer sandwiched between two layers of piezoelectric sensor and actuator.
Abstract: Theoretical and experimental performance characteristics of the new class of actively controlled constrained layer damping (ACLD) are presented. The ACLD consists of a viscoelastic damping layer sandwiched between two layers of piezoelectric sensor and actuator. The composite ACLD when bonded to a vibrating structure acts as a “smart” treatment whose shear deformation can be controlled and tuned to the structural response in order to enhance the energy dissipation mechanism and improve the vibration damping characteristics. Particular emphasis is placed on studying the performance of ACLD treatments that are provided with sensing layers of different spatial distributions. The effect of the modal weighting characteristics of these sensing layers on the broad band attenuation of the vibration of beams fully treated with the ACLD is presented theoretically and experimentally. The effect of varying the gains of a proportional and derivative controller and the operating temperature on the ACLD performance is determined for uniform and linearly varying sensors. Comparisons with the performance of conventional passive constrained layer damping are presented also. The results obtained emphasize the importance of modally shaping the sensor and demonstrate the excellent capabilities of the ACLD.
49 citations
46 citations
TL;DR: In this article, a three-dimensional modeling procedure for cable-stayed bridges with rubber, steel, and lead energy dissipation devices is proposed to balance the significant reduction in earthquake-induced forces against tolerable displacements.
Abstract: A three-dimensional modeling procedure is proposed for cable-stayed bridges with rubber, steel, and lead energy dissipation devices. The passive control technique is investigated by considering the response of bridge models with and without energy dissipation devices. The impact of various design parameters on the seismic response of current and future bridge designs is studied. Appropriate locations and properties of the passive devices can achieve better performance for cable-stayed bridges by balancing the significant reduction in earthquake-induced forces against tolerable displacements. Proper design of passive systems can help provide solutions for retro-fitting some existing bridges.
42 citations
TL;DR: A successful defense conversion has occurred recently with the application of high capacity fluid damping devices from the defense community for use as seismic energy dissipation elements in commercial buildings, bridges, and related structures as mentioned in this paper.
Abstract: Today's economic climate demands that conversion of military technology for commerical applications be a part of an aerospace and defense company's strategic planning. Toward this goal, a successful defense conversion has occurred recently with the application of high capacity fluid damping devices from the defense community for use as seismic energy dissipation elements in commercial buildings, bridges, and related structures. These products have been used by the military for many years for attenuation of weapons grade shock, typically applied to shipboard equipment or land based strategic weapons. Commercial energy dissipation devices historically have involved heavy yielding sections or hysteretic joints.
29 citations
TL;DR: In this article, the authors considered laminates having two opposite edges simply supported by trigonometric functions describing the mode shapes between the simply supported edges, and the governing plate equations were reduced to ordinary differential equations.
Abstract: In the present work, laminates having two opposite edges simply supported are considered. The boundary conditions at the other two opposite edges may be general, and between these two edges, the thickness of the plate may be nonuniform. The theory used for the vibration analysis of such laminates includes shear deformation and rotatory inertia. The solution approach of the problem is semianalytical. By using the trigonometric functions describing the mode shapes between the simply supported edges, the governing plate equations are reduced to ordinary differential equations. The solution of the reduced equations is then sought by the differential quadrature method. The results reported in this article serve two objectives of the present investigations. One, it is demonstrated that the proposed semianalytical quadrature method offers a numerically accurate and computationally efficient technique for the title problem. Two, the relative effects of shear deformation and rotatory inertia are analyzed in a quantitative manner.
24 citations
TL;DR: In this paper, the optimal damping of beams constrained by viscoelastic layers when only one or several portions of the beam are covered is studied. But the problem is solved using a genetic algorithm, and numerical results for minimum and maximum damping are compared to experimental results.
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. © 1995 John Wiley & Sons. Inc.
24 citations
TL;DR: In this paper, the rotordynamic coefficients of fixed-pad thrust bearing are calculated by using the out-domain method, and a general analysis method is developed to investigate the coupled dynamics of a rotor equipped with journal and thrust bearings simultaneously.
Abstract: The rotordynamic coefficients of fixed-pad thrust bearing are introduced and calculated by using the out-domain method, and a general analysis method is developed to investigate the coupled dynamics of a rotor equipped with journal and thrust bearings simultaneously. Considerations include the effects of static tilt parameters of the rotor on rotordynamic coefficients of thrust bearing and the action of thrust bearing on system dynamics. It is shown that thrust bearing changes the load distribution of journal bearings and the static deflection of the rotor and delays the instability of the system considerably in lateral shaft vibration.
18 citations
TL;DR: In this paper, two approaches using an approximate problem formulation strategy are proposed to design restraint systems for automotive crashworthiness using the traditional lumped parameter analysis methods, one approach uses a first-order approximation based on finite difference derivatives with a nonlocal step size and the second and more effective approach uses second-order curve fitting strategy.
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.
17 citations
TL;DR: In this paper, a hybrid control system for reducing building vibration under a spectrum of earthquake load amplitudes is presented, which is accomplished by an energy dissipation device called the active slip brace device (ASBD).
Abstract: A hybrid control system for reducing building vibration under a spectrum of earthquake load amplitudes is presented The hybrid control is accomplished by an energy dissipation device called the active slip brace device (ASBD) The hybrid control system uses the ASBD to regulate the energy dissipation characteristics of the building during its response to earthquakes by utilizing active control principles The ASBD consists of a Coulomb friction interface with a clamping mechanism on the interface The clamping force on the friction interface is altered at short time intervals during building vibration Computer simulations of building response with and without ASBD are compared
TL;DR: A broad overview of the dynamic response of shell structures can be found in this paper, where the authors provide an understanding of the basic themes behind the detailed codes and stimulate, not restrict, positive innovation.
Abstract: Shell structures are indispensable in virtually every industry. However, in the design, analysis, fabrication, and maintenance of such structures, there are many pitfalls leading to various forms of disaster. The experience gained by engineers over some 200 years of disasters and brushes with disaster is expressed in the extensive archival literature, national codes, and procedural documentation found in larger companies. However, the advantage of the richness in the behavior of shells is that the way is always open for innovation. In this survey, we present a broad overview of the dynamic response of shell structures. The intention is to provide an understanding of the basic themes behind the detailed codes and stimulate, not restrict, positive innovation. Such understanding is also crucial for the correct computation of shell structures by any computer code. The physics dictates that the thin shell structure offers a challenge for analysis and computation. Shell response can be generally categorized by states of extension, inextensional bending, edge bending, and edge transverse shear. Simple estimates for the magnitudes of stress, deformation, and resonance in the extensional and inextensional states are provided by ring response. Several shell examples demonstrate the different states and combinations. For excitation frequency above the extensional resonance, such as in impact and acoustic excitation, a fine mesh is needed over the entire shell surface. For this range, modal and implicit methods are of limited value. The example of a sphere impacting a rigid surface shows that plastic unloading occurs continuously. Thus, there are no short cuts; the complete material behavior must be included.
TL;DR: In this article, Wily et al. provided an explicit formula for the normalization of nonlinear differential equations and showed that the undamped Duffing equation can be represented by an exact polynomial differential amplitude equation in a finite number of terms.
Abstract: Normal form theory is important for studying the qualitative behavior of nonlinear oscillators. In some cases, higher order normal forms are required to understand the dynamic behavior near an equilibrium or a periodic orbit. However, the computation of high-order normal forms is usually quite complicated. This article provides an explicit formula for the normalization of nonlinear differential equations. The higher order normal form is given explicitly. Illustrative examples include a cubic system, a quadratic system and a Duffing-Van der Pol system. We use exact arithmetic andfind that the undamped Duffing equation can be represented by an exact polynomial differential amplitude equation in a finite number of terms. © 1995 John Wily & Sons, Inc.
TL;DR: In this paper, suspension instabilities in an electrodynamic maglev system with three and five-degrees-of-freedom vehicles traveling on a double L-shaped set of guideway conductors were investigated with various experimentally measured magnetic force data incorporated into theoretical models.
Abstract: Suspension instabilities in an electrodynamic maglev system with three- and five-degrees-of-freedom DOF vehicles traveling on a double L-shaped set of guideway conductors were investigated with various experimentally measured magnetic force data incorporated into theoretical models. Divergence and flutter were obtained from both analytical and numerical solutions for coupled vibration of the three-DOF maglev vehicle model. Instabilities of five direction motion (heave, slip, roll, pitch, and yaw) were observed for the five-DOF vehicle model. The results demonstrate that system parameters such as system damping, vehicle geometry, and coupling effects among five different motions play very important roles in the occurrence of dynamic instabilities of maglev vehicles.
TL;DR: In this article, the physical significance of transmission zeros in the dynamic transfer function between sensor location and actuator location 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.
Abstract: Feedback control offtexible 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. © 1995 John Wiley & Sons, Inc.
TL;DR: In this paper, a finite difference technique in a coupled Eulerian-Lagrangian scheme is used to 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.
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
TL;DR: In this paper, the authors discuss the time frequency analysis of machinery diagnostic vibration signals and compare the Choi-Williams distribution with the short time Fourier transform, the Wigner transform, and the Choi distribution.
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.
TL;DR: In this article, the nonlinear response of two-degree-of-freedom systems with repeated natural frequencies and cubic nonlinearity to a principal parametric excitation was studied.
Abstract: The method of normal forms is used to study the nonlinear response of two-degree-of-freedom systems with repeated natural frequencies and cubic nonlinearity to a principal parametric excitation. The linear part of the system has a nonsemisimple one-to-one resonance. The character of the stability and various types of bifurcation including the formation of a homoclinic orbit are analyzed. The results are applied to the flutter of a simply supported panel in a supersonic airstream.
TL;DR: In this paper, a semianalytical algorithm is proposed for the solutions and their stability of a piecewise nonlinear system and the conventional harmonic balance method is modified by the introduction of Toeplitz Jacobian matrices (TJM) and by the alternative applications of fast Fourier transformation (FFT) and its inverse.
Abstract: A semianalytical algorithm is proposed for the solutions and their stability of a piecewise nonlinear system. The conventional harmonic balance method is modified by the introduction of Toeplitz Jacobian matrices (TJM) and by the alternative applications of fast Fourier transformation (FFT) and its inverse. The TJM/FFT method substantially reduces the amount of computation and circumvents the necessary numerical differentiation for the Jacobian. An arc-length algorithm and a branch switching procedure are incorporated so that the secondary branches can be independently traced. Oscillators with piecewise nonlinear characteristics are taken as illustrative examples. Flip, fold, and Hopf bifurcations are of interest.
TL;DR: In this article, an experimental program to determine the response of thin-walled steel projectiles to the impact with concrete targets was conducted, where the projectiles were fired against 41-MPa concrete targets at an impact velocity of 290 m/s.
Abstract: An experimental program to determine the response of thin-walled steel projectiles to the impact with concrete targets was recently conducted. The projectiles were fired against 41-MPa concrete targets at an impact velocity of 290 m/s. This article contains an outline of the experimental program, an examination of the results of a typical test, and predictions of projectile deformation by classical shell theory and computational simulation. Classical shell analysis of the projectile indicated that the predicted impact loads would result in circumferential buckling. A computational simulation of a test was conducted with an impact/penetration model created by linking a rigid-body penetration trajectory code with a general-purpose finite element code. Scientific visualization of the resulting data revealed that circumferential buckling was induced by the impact conditions considered.
TL;DR: In this paper, the self-compensating dynamic balancer (SCDB) is composed of a circular disk with a groove containing ball and a low viscosity damping fluid, and the equations of motion of the rotating system with SCDB were derived by the Lagrangian method.
Abstract: The self-compensating dynamic balancer (SCDB) is composed of a circular disk with a groove containing ball and a low viscosity damping fluid. The equations of motion of the rotating system with SCDB were derived by the Lagrangian method. To consider dynamic stability of the motion, perturbation equations were investigated. Based on the results of stability investigation, ball positions that result in a balanced system are stable above the critical speed with small damping (β′>3.8 case). At critical speed the perturbed motion is said to be stable for large damping (β′>2.3 case). However, below critical speed the balls cannot stabilize the system in any case.
TL;DR: A general finite element formulation using cubic Hermitian interpolation for dynamic analysis of pipes conveying fluid is presented in this paper, where both the effects of shearing deformations and rotary inertia are considered.
Abstract: A general finite element formulation using cubic Hermitian interpolation for dynamic analysis of pipes conveying fluid is presented. Both the effects of shearing deformations and rotary inertia are considered. The development retains the use of the classical four degrees-of-freedom for a two-node element. The effect of moving fluid is treated as external distributed forces on the support pipe and the fluid finite element matrices are derived from the virtual work done due to the fluid inertia forces. Finite element matrices for both the support pipe and moving fluid are derived and given explicitly. A numerical example is given to demonstrate the validity of the model.
TL;DR: The implementation and application of h-adaptivity in an explicit finite element program for nonlinear structural dynamics is described, with particular emphasis on developing procedures for general purpose structural dynamics programs and efficiently handling adaptivity in shell elements.
Abstract: The implementation and application of h-adaptivity in an explicit finite element program for nonlinear structural dynamics is described. Particular emphasis is placed on developing procedures for general purpose structural dynamics programs and efficiently handling adaptivity in shell elements. New projection techniques for error estimation and projecting variables on new meshes after fission or fusion are described. Several problems of severe impact are described.
TL;DR: In this paper, the transmission of sinusoidal vibrations through beds of cohesive particulate solids was measured and results were interpreted in terms of a critical state model to predict the elastic swelling constant k, and the cohesive stress C.
Abstract: The transmission of sinusoidal vibrations through beds of cohesive particulate solids was measured. Results were interpreted in terms of a critical state model to predict the elastic swelling constant k, and the cohesive stress C. Factorial experimental design was used to identify significant parameters. Factors that affect k include percent moisture, bulk density, sample size, sample shape, the presence of a supporting membrane, and loading order. Factors that affect C include percent moisture and particle size distribution. Factors affecting k were interpreted in terms of their effects upon bed structure and factors affecting C in terms of an equivalent pore water pressure due to capillary and liquid bridge effects. The critical state model was modified to incorporate general relationships between axial and radial strains. © 1995 John Wiley & Sons, Inc.
TL;DR: In this article, an accurate beam finite element is used to solve nonlinear vibration of arched beams and framed structures, and nonlinear governing equations of a skeletal structure are integrated numerically using symplectic integration schemes so that the Poincare integral invariant of a Hamiltonian flow are preserved during the evolution.
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 Poincare 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
TL;DR: In this article, the basic formulation of two well-established finite element model (FEM) updating techniques for improved dynamic analysis, namely the response function method (RFM) and the inverse eigensensitivity method (IESM), is summarized.
Abstract: This article summarizes the basic formulation of two well-established finite element model (FEM) updating techniques for improved dynamic analysis, namely the response function method (RFM) and the inverse eigensensitivity method (IESM). Emphasis is placed on the similarities in their mathematical formulation, numerical treatment, and on the uniqueness of the resulting updated models. Three case studies that include welded L-plate specimens, a car exhaust system, and a highway bridge were examined in some detail and measured vibration data were used throughout the investigation. It was experimentally observed that significant dynamic behavior discrepancies existed between some of the nominally identical structures, a feature that makes the task of model updating even more difficult because no unequivocal reference data exist in this particular case. Although significant improvements were obtained in all cases where the updating of the FE model was possible, it was found that the success of the updated models depended very heavily on the parameters used, such as the selection and number of the frequency points for RFM, and the selection of modes and the balancing of the sensitivity matrix for IESM. Finally, the performance of the two methods was compared from general applicability, numerical stability, and computational effort standpoints.
TL;DR: In this article, an adaptive piezoelectric laminated cylindrical shell composite with continuous curvature changes is studied, and its natural frequencies and controlled damping ratios are evaluated.
Abstract: Adaptive structures with controllable geometries and shapes are rather useful in many engineering applications, such as adaptive wings, variable focus mirrors, adaptive machines, micro-electromechanical systems, etc. Dynamics and feedback control effectiveness of adaptive shells whose curvatures are actively controlled and continu ously changed are evaluated. An adaptive piezoelectric laminated cylindrical shell composite with continuous curvature changes is studied, and its natural frequencies and controlled damping ratios are evaluated. The curvature change of the adaptive shell starts from an open shallow shell (300) and ends with a deep cylindrical shell (360°). Dynamic characteristics and control effectiveness (via the proportional veloc ity feedback) of this series of shells are investigated and compared at every 30° curvature change. Analytical solutions suggest that the lower modes are sensitive to curvature changes and the higher modes are relatively insensitive. © 1995 John Wiley & Sons, Inc.