Showing papers in "Shock and Vibration in 2005"
TL;DR: In this paper, a method for modeling arbitrary growth of dynamic cracks without remeshing is presented, which is based on a local partition of unity and combined with level sets, so that the discontinuities can be represented entirely in terms of nodal data.
Abstract: A method for modelling arbitrary growth of dynamic cracks without remeshing is presented. The method is based on a local partition of unity. It is combined with level sets, so that the discontinuities can be represented entirely in terms of nodal data. This leads to a simple method with clean data structures that can easily be incorporated in general purpose software. Results for a mixed-mode dynamic fracture problem are given to demonstrate the method.
59 citations
TL;DR: In this article, an integrated approach for identifying structural damage is presented, which utilizes piezoelectric (PZT) materials to actuate/sense the dynamic response of the structures.
Abstract: This paper illustrates an integrated approach for identifying structural damage. The method presented utilizes piezoelectric (PZT) materials to actuate/sense the dynamic response of the structures. Two damage identification techniques are integrated in this study, including impedance methods and Lamb wave propagations. The impedance method monitors the variations in structural mechanical impedance, which is coupled with the electrical impedance of the PZT patch. In Lamb wave propagations, one PZT patch acting as an actuator launches an elastic wave through the structure, and responses are measured by an array of PZT sensors. The changes in both wave attenuation and reflection are used to detect and locate the damage. Both the Lamb wave and impedance methods operate in high frequency ranges at which there are measurable changes in structural responses even for incipient damage such as small cracks, debonding, or loose connections. The combination of the local impedance method with the wave propagation based approach allows a better characterization of the system’s structural integrity. The paper concludes with experimental results to demonstrate the feasibility of this integrated active sensing technology.
55 citations
TL;DR: In this article, an anti-swing controller is designed based on two techniques: a time-delayed feedback of the load swing angle and an anti swing fuzzy logic controller (FLC).
Abstract: We designed a feedback controller to automate crane operations by controlling the load position and its swing. First, a PD tracking controller is designed to follow a prescribed trajectory. Then, another controller is added to the control loop to damp the load swing. The anti-swing controller is designed based on two techniques: a time-delayed feedback of the load swing angle and an anti-swing fuzzy logic controller (FLC). The rules of the FLC are generated by mapping the performance of the time-delayed feedback controller. The same mapping method used for generating the rules can be applied to mimic the performance of an expert operator. The control algorithms were designed for gantry cranes and then extended to tower cranes by considering the coupling between the translational and rotational motions. Experimental results show that the controller is effective in reducing load oscillations and transferring the load in a reasonable time. To experimentally validate the theory, we had to compensate for friction. To this end, we estimated the friction and then applied a control action to cancel it. The friction force was estimated by assuming a mathematical model and then estimating the model coefficients using an off-line identification technique, the method of least squares (LS).
48 citations
TL;DR: In this article, the benefits of angular sampling when measuring various signals in rotating machines are presented and discussed and the results are extracted from studies on transmission error measurements with optical encoders in the field of power transmissions and can be broadened to include phase difference measurements, such as torsional vibrations.
Abstract: The benefits of angular sampling when measuring various signals in rotating machines are presented and discussed herein The results are extracted from studies on transmission error measurements with optical encoders in the field of power transmissions and can be broadened to include phase difference measurements, such as torsional vibrations, and applied to control, monitoring and measurement in rotating machines with discrete geometry The main conclusions are primarily that the use of angular sampling enables the exact location of harmonics and, consequently, the obtaining of spectral amplitude components with precision This is always true even if the resolution of encoders is not directly related to the studied discrete geometry It then becomes possible to compare these harmonics under different operating conditions, especially when speed varies, without changing any parameters in spectral analysis (window length, spectral resolution, etc) Moreover, classical techniques of improving signal to noise ratio by averaging become fully efficient in the detection of defective elements This study has been made possible thanks to the technique of transmission error measurement with optical encoders that allows the comparison of sampling procedures, based on the same raw data
37 citations
TL;DR: In this article, the authors focused on the application of two different diagnostic techniques aimed to identify the most important faults in rotating machinery as well as on the simulation and prediction of the frequency response of rotating machines.
Abstract: This paper is focused on the application of two different diagnostic techniques aimed to identify the most important faults in rotating machinery as well as on the simulation and prediction of the frequency response of rotating machines. The application of the two diagnostics techniques, the orbit shape analysis and the model based identification in the frequency domain, is described by means of an experimental case study that concerns a gas turbine-generator unit of a small power plant whose rotor-train was affected by an angular misalignment in a flexible coupling, caused by a wrong machine assembling. The fault type is identified by means of the orbit shape analysis, then the equivalent bending moments, which enable the shaft experimental vibrations to be simulated, have been identified using a model based identification method. These excitations have been used to predict the machine vibrations in a large rotating speed range inside which no monitoring data were available. To the best of the authors' knowledge, this is the first case of identification of coupling misalignment and prediction of the consequent machine behaviour in an actual size rotating machinery. The successful results obtained emphasise the usefulness of integrating common condition monitoring techniques with diagnostic strategies.
34 citations
TL;DR: In this paper, a physics-based model using classical plate theory is developed to provide a basic understanding of the actual physical process of asymmetric Lamb mode wave generation and propagation in a plate.
Abstract: Two approaches used for monitoring the health of thin aerospace structures are active interrogation and passive monitoring. The active interrogation approach generates and receives diagnostic Lamb waves to detect damage, while the passive monitoring technique listens for acoustic waves caused by damage growth. For the application of both methods, it is necessary to understand how Lamb waves propagate through a structure. In this paper, a Physics-Based Model (PBM) using classical plate theory is developed to provide a basic understanding of the actual physical process of asymmetric Lamb mode wave generation and propagation in a plate. The closed-form model uses modal superposition to simulate waves generated by piezoceramic patches and by simulated acoustic emissions. The generation, propagation, reflection, interference, and the sensing of the waves are represented in the model, but damage is not explicitly modeled. The developed model is expected to be a useful tool for the Structural Health Monitoring (SHM) community, particularly for studying high frequency acoustic wave generation and propagation in lieu of Finite Element models and other numerical models that require significant computational resources. The PBM is capable of simulating many possible scenarios including a variety of test cases, whereas experimental measurements of all of the cases can be costly and time consuming. The model also incorporates the sensor measurement effect, which is an important aspect in damage detection. Continuous and array sensors are modeled, which are efficient for measuring waves because of their distributed nature.
23 citations
TL;DR: In this paper, a polynomial response surface model is developed, relating system parameters to measurable output features, and the response surface is used in an inverse sense to identify system parameters from measured output features.
Abstract: Metamodels have been used with success in many areas of engineering for decades but only recently in the field of structural dynamics. A metamodel is a fast running surrogate that is typically used to aid an analyst or test engineer in the fast and efficient exploration of the design space. Response surface metamodels are used in this work to perform parameter identification of a simple five degree of freedom system, motivated by their low training requirements and ease of use. In structural dynamics applications, response surface metamodels have been utilized in a forward sense, for activities such as sensitivity analysis or uncertainty quantification. In this study a polynomial response surface model is developed, relating system parameters to measurable output features. Once this relationship is established, the response surface is used in an inverse sense to identify system parameters from measured output features. A design of experiments is utilized to choose points, representing a fraction of the full design space of interest, for fitting the response surface metamodel. Two parameters commonly used to characterize damage in a structural system, stiffness and damping, are identified. First changes are identified and located with success in a linear 5DOF system. Then parameter identification is attempted with a nonlinear 5DOF system and limited success is achieved. This work will demonstrate that use of response surface metamodels in an inverse sense shows promise for use in system parameter identification for both linear and weakly nonlinear systems and that the method has potential for use in damage identification applications.
22 citations
TL;DR: In this paper, a mathematical model is proposed for the rope force as a function of the displacement and velocity of the weight, where the effects of the type of rope, drop height, drop weight, whether the rope has been subjected to static precycling, and the number of previous dynamic tests are examined.
Abstract: Large tensile forces, known as snap loads, can occur when a slack rope becomes taut. Such forces may damage the rope or masses connected to it. Experiments are described in which one end of a rope is attached to the top of a drop tower and the bottom end is attached to a weight. The weight is raised to a certain height and then released. The force at the top of the rope and the acceleration of the weight are recorded during the first snap load that occurs. Repeated drop tests are performed on each rope. The effects of the type of rope, drop height, drop weight, whether the rope has been subjected to static precycling, and the number of previous dynamic tests are examined. A mathematical model is proposed for the rope force as a function of the displacement and velocity of the weight.
22 citations
TL;DR: In this article, a line of minima is defined to define a relationship between the absolute acceleration and relative displacement transmissibility of a sprung mass using a hydraulic mount as a means of suspension.
Abstract: Based on RMS averaging of the frequency response functions of the absolute acceleration and relative displacement transmissibility, optimal parameters describing the hydraulic engine mount are determined to explain the internal mount geometry. More specifically, it is shown that a line of minima exists to define a relationship between the absolute acceleration and relative displacement transmissibility of a sprung mass using a hydraulic mount as a means of suspension. This line of minima is used to determine several optimal systems developed on the basis of different clearance requirements, hence different relative displacement requirements, and compare them by means of their respective acceleration and displacement transmissibility functions. In addition, the transient response of the mount to a step input is also investigated to show the effects of the optimization upon the time domain response of the hydraulic mount.
21 citations
TL;DR: In this paper, a new updating method based on measured frequency response functions is presented, where the objective function of the minimization procedure is formed by the difference between the measured and the analytical frequency responses.
Abstract: This study presents a new updating method based on measured frequency response functions. The objective function of the minimization procedure is formed by the difference between the measured and the analytical frequency responses. The updating parameters are the correction coefficients related to each the elementary mass and stiffness matrices. While making use of a number of incomplete measurements for some frequencies, one builds a non-linear system of equations. The linearisation of the numerical system leads to an iterative procedure. An intrinsic frequency parametrization is proposed in order to accelerate the convergence of the iterative system. The obtained results are comparable with those of the known least squares methods.
20 citations
TL;DR: In this article, a novel and promising approach for the prediction of the dynamic stiffness of hydrobushings is presented, combining Finite Element and CFD methods, combining the rubber structure of the mount and the flow of fluid through the inertia track.
Abstract: A novel and promising approach for the prediction of the dynamic stiffness of hydrobushings is presented, combining Finite Element and CFD methods. The rubber structure of the mount is modelled in ABAQUS and the flow of fluid through the inertia track is calculated in FLUENT. The obtained results from the latter simulation are incorporated in the finite element code for the final stiffness prediction. The calculation is very sensitive to both rubber and fluid properties. The dynamic behaviour of rubber material has accurately been characterised with a new simple shear specimen in a forced non-resonant test. Satisfactory results are obtained when comparing numerical simulations to experimental tests in a practical application. Discrepancies between simulations and tests are mainly due to the simplifications assumed when creating the model. Nevertheless, stiffness of the mount is well predicted and so is the damping, although the frequency at which its maximum value is achieved is underestimated by 4-6 Hz, result that could be improved if non-stationary boundary conditions were considered when solving the fluid flow and incorporating it to the finite element code.
TL;DR: In this article, a steel frame walkway has been the subject of studies on the effects of multiple pedestrians with respect to loading and response mitigation, including direct measurement of damping forces and absorbed energy using a force plate.
Abstract: As part of a continuing study on effects of humans on loading and dynamic response of footbridges, a steel frame walkway has been the subject of studies on the effects of multiple pedestrians with respect to loading and response mitigation. Following finite element modeling and experimental modal analysis to identify the low frequency vibration modes likely to be excited by normal walking, the variation of response with pedestrian density and of system damping and natural frequency with occupancy by stationary pedestrians were both studied. The potentially mitigating effect of stationary occupants is still not well understood and the study included direct measurement of damping forces and absorbed energy using a force plate. The various tests showed that energy dissipation measured directly was consistent with the observed change in damping, that vertical and lateral response both varied approximately with square root of number of pedestrians, and that the simple model of a human as a single mass-spring-damper system may need to be refined to fit observed changes in modal parameters with a crowd of humans present. Modal parameter changes with moving pedestrians were small compared to those with stationary pedestrians indicating that within limits, modal parameters for the empty structure could be used in analysis.
TL;DR: In this paper, the SMA-TVA employs SMA wires, which exhibit variable stiffness, as the spring element of the TVA to adapt to the changes in the primary system's natural frequency.
Abstract: A conventional passive tuned vibration absorber (TVA) is effective when it is precisely tuned to the frequency of a vibration mode; otherwise, it may amplify the vibrations of the primary system. In many applications, the frequency often changes over time. For example, adding or subtracting external mass on the existing primary system results in changes in the system’s natural frequency. The frequency changes of the primary system can significantly degrade the performance of TVA. To cope with this problem, many alternative TVAs (such as semiactive, adaptive, and active TVAs) have been studied. As another alternative, this paper investigates the use of Shape Memory Alloys (SMAs) in passive TVAs in order to improve the robustness of the TVAs subject to mass change in the primary system. The proposed SMA-TVA employs SMA wires, which exhibit variable stiffness, as the spring element of the TVA. This allows us to tune effective stiffness of the TVA to adapt to the changes in the primary system's natural frequency. The simulation model, presented in this paper, contains the dynamics of the TVA along with the SMA wire model that includes phase transformation, heat transfer, and the constitutive relations. Additionally, a PID controller is included for regulating the applied voltage to the SMA wires in order to maintain the desired stiffness. The robustness analysis is then performed on both the SMA-TVA and the equivalent passive TVA. For our robustness analysis, the mass of the primary system is varied by ± 30% of its nominal mass. The simulation results show that the SMA-TVA is more robust than the equivalent passive TVA in reducing peak vibrations in the primary system subject to change of its mass.
TL;DR: In this article, a spherical model for the bubble created by an underwater explosion is enhanced to account, in approximate fashion, for the effect of bubble distortion on translation and dilation, which consists of introducing artificial drag in the form C|ν| P, where ν is translation velocity, and C, P produce an optimum fit to empirical formulas for the second dilation maximum and first two translation jumps.
Abstract: A spherical model for the bubble created by an underwater explosion is enhanced to account, in approximate fashion, for the effect of bubble distortion on translation and dilation. The enhancement consists of introducing artificial drag in the form C|ν| P , where ν is translation velocity, and C, P produce an optimum fit to empirical formulas for the second dilation maximum and first two translation jumps. The recommended values are C =0 .4 and P =1 for charge weights between 100 lb-1000 lb and and depths exceeding 200 ft.
TL;DR: The history of the development of Cap constitutive models is reviewed in this paper, where the basic behavior of the early models is briefly discussed and compared, and the reasons for the introduction of Cap Models are outlined.
Abstract: The history of the development of Cap constitutive models is reviewed. The Cap family of models provides a powerful, yet adaptable way of representing many aspects of the dynamic stress-strain behavior of geological materials. These models have been extensively used for more than three decades to characterize the highly nonlinear behavior of soils, rocks and concrete, and are particularly well suited to the dynamic analysis arising in ground shock and seismic applications. The modern series of Cap Models is based on the adaptation of several earlier models, and was introduced in the early 1970’s as a result of university and corporate R&D technology development sponsored by the United States government. Dr. Eugene Sevin played a role in these activities during his tenure at the Defense Nuclear Agency. In this paper, the basic behavior of the early models is briefly discussed and compared, and the reasons for the introduction of Cap Models are outlined. Many adaptations of the Cap Model have been developed since the first model was introduced, and the salient features of some of these model extensions are also reviewed.
TL;DR: In this paper, a two-fluid, computational fluid dynamics study of the phenomena of bubble collapse under a submersed flat plate has been performed, in order to handle the rapidly changing bubble-water interface accurately, second order upwind differencing is used in calculating the advection term.
Abstract: A two-fluid, computational fluid dynamics study of the phenomena of bubble collapse under a submersed flat plate has been performed. In order to handle the rapidly changing bubble-water interface accurately, second order upwind differencing is used in calculating the advection term. Good agreement with experimental data is obtained for the pressure distribution on the plate. The computational results provide insight into the phenomenology of the jet impact, the formation of a radial hydraulic jump, and the complex interaction of that hydraulic jump with the collapsing toroidal bubble.
TL;DR: In this paper, a pre-acting isolator based on a passive elastic element (a spring) separating the object to be protected from the base is proposed, and the limiting performance of the isolator is investigated for a single-degree-of-freedom system subject to an instantaneous impact.
Abstract: Pre-acting control in shock/impact isolation systems is studied. With pre-acting control, the isolation system begins to respond to an impact before this impact has been applied to the base. The limiting performance of the isolator with pre-acting control is investigated for a single-degree-of-freedom system subject to an instantaneous impact. The isolation performance index is defined as the maximum of the absolute value of the displacement of the object to be isolated relative to the base, provided that the magnitude of the control force transmitted to the object does not exceed a prescribed value. It is shown that there is a substantial advantage in the use of pre-acting isolators over isolators without pre-action. Particular attention is given to a pre-acting isolator based on a passive elastic element (a spring) separating the object to be protected from the base. An example illustrates the calculation of the design parameters of such an isolator.
TL;DR: In this paper, the damping coefficients of a longitudinally vibrating elastic rod with locally and non-locally reacting damping were analyzed and it was shown that at any mode of locally or non-local damped elastic rod, the variation of damping ratio with damper location is linearly proportional to absolute value of the mode shape of undamped system.
Abstract: Eigencharacteristics of a longitudinally vibrating elastic rod with locally and non-locally reacting damping are analyzed. The rod is considered as a continuous system and complex eigenfrequencies are determined as solution of a characteristic equation. The variation of the damping ratios with respect to damper locations and damping coefficients for the first four eigenfrequencies are obtained. It is shown that at any mode of locally or non-locally damped elastic rod, the variation of damping ratio with damper location is linearly proportional to absolute value of the mode shape of undamped system. It is seen that the increasing damping coefficient does not always increase the damping ratio and there are optimal values for the damping ratio. Optimal values for external damping coefficients of viscous dampers and locations of the dampers are presented.
TL;DR: In this article, a design methodology for the vibration confinement of axial vibrations in nonhomogenous rods is proposed, which is achieved by a proper selection of a set of spatially dependent functions characterizing the rod material and geometric properties.
Abstract: A design methodology for the vibration confinement of axial vibrations in nonhomogenous rods is proposed. This is achieved by a proper selection of a set of spatially dependent functions characterizing the rod material and geometric properties. Conditions for selecting such properties are established by constructing positive Lyapunov functions whose derivative with respect to the space variable is negative. It is shown that varying the shape of the rod alone is sufficient to confine the vibratory motion. In such a case, the vibration confinement requires that the eigenfunctions be exponentially decaying functions of space, where the notion of spatial domain stability is introduced as a concept dual to that of the time domain stability. It is also shown that vibration confinement can be produced if the rod density and/or stiffness are varied with respect to the space variable while the cross-section area is kept constant. Several case studies, supporting the developed conditions imposed on the spatially dependent functions for vibration confinement in vibrating rods, are discussed. Because variation in the geometric and material properties might decrease the critical buckling loads, we also discuss the buckling problem.
TL;DR: In this article, a simple and accurate method is proposed for the vibration analysis of rectangular plates with one or more guided edges, in which bicubic B-spline interpolation in combination with a new type of basis cubic Bspline functions is used to approximate the plate deflection.
Abstract: A simple and accurate method is proposed for the vibration analysis of rectangular plates with one or more guided edges, in which bicubic B-spline interpolation in combination with a new type of basis cubic B-spline functions is used to approximate the plate deflection. This type of basis cubic B-spline functions can satisfy simply supported, clamped, free, and guided edge conditions with easy numerical manipulation. The frequency characteristic equation is formulated based on classical thin plate theory by performing Hamilton's principle. The present solutions are verified with the analytical ones. Fast convergence, high accuracy and computational efficiency have been demonstrated from the comparisons. Frequency parameters for 13 cases of rectangular plates with at least one guided edge, which are possible by approximate or numerical methods only, are presented. These results are new in literature.
TL;DR: In this article, a modal perturbation method is introduced to approximately determine the dynamic characteristics of a Timoshenko beam, which can be transformed into a set of nonlinear algebraic equations.
Abstract: Timoshenko beams have been widely used in structural and mechanical systems. Under dynamic loading, the analytical solution of a Timoshenko beam is often difficult to obtain due to the complexity involved in the equation of motion. In this paper, a modal perturbation method is introduced to approximately determine the dynamic characteristics of a Timoshenko beam. In this approach, the differential equation of motion describing the dynamic behavior of the Timoshenko beam can be transformed into a set of nonlinear algebraic equations. Therefore, the solution process can be simplified significantly for the Timoshenko beam with arbitrary boundaries. Several examples are given to illustrate the application of the proposed method. Numerical results have shown that the modal perturbation method is effective in determining the modal characteristics of Timoshenko beams with high accuracy. The effects of shear distortion and moment of inertia on the natural frequencies of Timoshenko beams are discussed in detail.
TL;DR: In this article, the authors present a review of the optimum vibration control problems based on the idea of limiting performance, and discuss recent development of vibration control devices, as well as their applications.
Abstract: As vibration control requirements become increasingly stringent, designers and users of vibration control equipment turn to devices and systems combining various physical mechanisms. Subsystems based on different physical effects can be combined to achieve the optimal performance for the application. Building an optimal product line that would cover a wide field of applications by combining several products, as opposed to creating one optimal device for a particular application, presents an optimum vibration control problem. This paper reviews optimum vibration control problems based on the idea of limiting performance, and discusses recent development of vibration control devices.
TL;DR: In this paper, a state space method for modal identification of a mechanical system from its time domain impulse or initial condition responses is presented, where the key step is the identification of the characteristic polynomial coefficients of an adjoint system.
Abstract: A new state space method is presented for modal identification of a mechanical system from its time domain impulse or initial condition responses. A key step in this method is the identification of the characteristic polynomial coefficients of an adjoint system. Once these coefficients are determined, a canonical state space realization of the adjoint system and the system's modal parameters are formulated straightforwardly. This method is conceptually and mathematically simple and is easy to be implemented. Detailed mathematical treatments are demonstrated and numerical examples are provided to illustrate the use and effectiveness of the method.
TL;DR: In this paper, a nonlinear Model Predictive Control (MPC) strategy is introduced to deal with the time delay in the secondary path and the nonlinearity in the primary path of the active noise control system.
Abstract: In this paper, an improved nonlinear Active Noise Control (ANC) system is achieved by introducing an appropriate secondary source. For ANC system to be successfully implemented, the nonlinearity of the primary path and time delay of the secondary path must be overcome. A nonlinear Model Predictive Control (MPC) strategy is introduced to deal with the time delay in the secondary path and the nonlinearity in the primary path of the ANC system. An overall online modeling technique is utilized for online secondary path and primary path estimation. The secondary path is estimated using an adaptive FIR filter, and the primary path is estimated using a Neural Network (NN). The two models are connected in parallel with the two paths. In this system, the mutual disturbances between the operation of the nonlinear ANC controller and modeling of the secondary can be greatly reduced. The coefficients of the adaptive FIR filter and weight vector of NN are adjusted online. Computer simulations are carried out to compare the proposed nonlinear MPC method with the nonlinear Filter-x Least Mean Square (FXLMS) algorithm. The results showed that the convergence speed of the proposed nonlinear MPC algorithm is faster than that of nonlinear FXLMS algorithm. For testing the robust performance of the proposed nonlinear ANC system, the sudden changes in the secondary path and primary path of the ANC system are considered. Results indicated that the proposed nonlinear ANC system can rapidly track the sudden changes in the acoustic paths of the nonlinear ANC system, and ensure the adaptive algorithm stable when the nonlinear ANC system is time variable.
TL;DR: In this article, the performance of adaptive Finite Impulse Response (FIR) filters on the identification of vibrating structures is evaluated on real experiments using an aluminum cantilever beam containing piezoelectric sensors and actuators and a steel pinned-pinned beam instrumented with accelerometers and an electromechanical shaker.
Abstract: The present work is aimed at assessing the performance of adaptive Finite Impulse Response (FIR) filters on the identification of vibrating structures. Four adaptive algorithms were used: Least Mean Squares (LMS), Normalized Least Mean Squares (NLMS), Transform-Domain Least Mean Squares (TDLMS) and Set-Membership Binormalized Data-Reusing LMS Algorithm (SMBNDRLMS). The capability of these filters to perform the identification of vibrating structures is shown on real experiments. The first experiment consists of an aluminum cantilever beam containing piezoelectric sensors and actuators and the second one is a steel pinned-pinned beam instrumented with accelerometers and an electromechanical shaker.
TL;DR: In this paper, a weak formulation of mixed state equations including boundary conditions of laminated cylindrical shells is presented, giving up any assumptions about displacement models and stress distribution, and analytical solutions are obtained for the thermoelastic dynamic response of a thick closed laminated shell subjected to temperature variation.
Abstract: Giving up any assumptions about displacement models and stress distribution, weak formulation of mixed state equations including boundary conditions of laminated cylindrical shell are presented. Thermal stresses mixed Hamilton equation of closed cylindrical shell is established. The analytical solutions are obtained for the thermoelastic dynamic response of a thick closed laminated shell subjected to temperature variation. Every equation of elasticity can be satisfied, and all elastic constants can be taken into account. Arbitrary precision of a desired order can be obtained.
TL;DR: Savin's contributions span from basic research into experimental and theoretical mechanics, through to application of complex concepts which spill over into the arena of all types of threats, including the current arena of terror threats as discussed by the authors.
Abstract: The papers provided in this special issue of the Shock and Vibration Journal reflect well on the remarkable range of contributions of the person to whom it is dedicated: Dr. Eugene Sevin. Over these many decades, Gene Sevin has functioned productively as a researcher in experimental and theoretical mechanics, an educator and professor, a director in planning of complex program elements, and indeed a leader in the field of shock mechanics. The spectrum of his contributions span from basic research into experimental and theoretical mechanics, through to application of complex concepts which spill over into the arena of all types of threats, including the current arena of terror threats. His association with many universities and institutions, such as the Illinois Institute of Technology, Beersheva University in Israel, and the Office of the Secretary of Defense in the Pentagon demonstrate his versatility and accomplishments. Indeed, his service on many National Academy of Engineering and other panels also illustrates his participation and productivity in giving guidance at a very high level to key government programs. The Shock and Vibration community is indeed fortunate to have Dr. Eugene Sevin as a significant participant, as he has assisted this community in a constructive and positive direction.
TL;DR: In this article, an approach to transform asymmetric systems into symmetric systems by equivalence transformation is presented, and conditions of symmetrizability obtained are more "liberal" and numerical calculations of this transformation are more straightforward.
Abstract: This paper presents an approach to transform asymmetric systems into symmetric systems by equivalence transformation and discusses what forms of restrictions should be imposed on the system matrices so that they can be simultaneously transformed into symmetric matrices. Conditions of symmetrizability obtained here are more "liberal" and numerical calculations of this transformation are more straightforward. Several examples are provided to illustrate the new approach.