Transient Structural Response Research Articles

An Investigation of Single Event Transient Response in 45-nm and 32-nm SOI RF-CMOS Devices and Circuits

This paper uses charge deposition by two-photon absorption to present the first investigation of the physical mechanisms underlying the single event transient (SET) response of cascode structures in a 45-nm RF-CMOS/SOI technology, provides the first experimental comparison of SET between 45-nm and 32-nm RF-CMOS/SOI devices, and presents implications for circuit design in both technologies. This work leverages a number of different device types and is supported by calibrated TCAD simulations.

A Novel Time-Domain Reflection Coefficient Function: TM Case

In determining electromagnetic transient response of structure placed above the half space, the half space properties can be taken into account via the reflection coefficient (RC) approximation. The choice of an RC function used in RC approximation is often important with regards to accuracy and computational efficiency of the overall method. In this paper, a new time-domain RC function for the case of TM polarization is presented. The function is derived using Gaver-Stehfest algorithm for numerical inverse Laplace transform and does not require the use of Bessel functions. The resulting formulation is rather simple, and, as the results indicate, accurate and computationally efficient.

A time-reversal process for beam trusses subjected to impulse loads

Spatial structures are often subjected to impulse loads which give rise to high-frequency (HF) waves. The objectives of the research outlined in this paper are twofold: (i) develop a reliable direct model of the transient dynamic response of built-up structures subjected to such impulse loads and (ii) use this model in a time-reversal inverse process in order to possibly detect the location of the shocks. The present study is more particularly focused on beam assemblies, as typically encountered in aerospace applications. At first, a transport model describing the evolution of the HF vibrational energy density in a three-dimensional beam truss is outlined, with an emphasis on the consideration of the reflection/transmission phenomena at the beam junctions. The latter contribute to spread HF waves within the entire structure, yielding a diffuse (noisy) vibrational energy field amenable to be efficiently time-reversed for the purpose of locating the source which has generated it. The time-reversal process itself is presented in a subsequent part. Its originality lies in the consideration of quadratic observables (energy densities) as the processed data. The approach is illustrated by a numerical simulation performed on a three-dimensional beam truss.

Optimal apparent damping as a function of the bandwidth of an array of vibration absorbers

The transient response of a resonant structure can be altered by the attachment of one or more substantially smaller resonators. Considered here is a coupled array of damped harmonic oscillators whose resonant frequencies are distributed across a frequency band that encompasses the natural frequency of the primary structure. Vibration energy introduced to the primary structure, which has little to no intrinsic damping, is transferred into and trapped by the attached array. It is shown that, when the properties of the array are optimized to reduce the settling time of the primary structure's transient response, the apparent damping is approximately proportional to the bandwidth of the array (the span of resonant frequencies of the attached oscillators). Numerical simulations were conducted using an unconstrained nonlinear minimization algorithm to find system parameters that result in the fastest settling time. This minimization was conducted for a range of system characteristics including the overall bandwidth of the array, the ratio of the total array mass to that of the primary structure, and the distributions of mass, stiffness, and damping among the array elements. This paper reports optimal values of these parameters and demonstrates that the resulting minimum settling time decreases with increasing bandwidth.

Transient response of structures with uncertain properties to nonlinear shock loading

A method is presented to predict the transient response of a structure at the driving point following an impact or a shock loading. The displacement and the contact force are calculated solving the discrete convolution between the impulse response and the contact force itself, expressed in terms of a nonlinear Hertzian contact stiffness. Application of random point process theory allows the calculation of the impulse response function from knowledge of the modal density and the geometric characteristics of the structure only. The theory is applied to a wide range of structures and results are experimentally verified for the case of a rigid object hitting a beam, a plate, a thin and a thick cylinder and for the impact between two cylinders. The modal density of the flexural modes for a thick slender cylinder is derived analytically. Good agreement is found between experimental, simulated and published results, showing the reliability of the method for a wide range of situations including impacts and pyroshock applications.

Transient marine electromagnetic responses of 3D resistive structures: Implications for navigation

The marine controlled-source electromagnetic method has become a popular technique for mapping the electrical resistivity structure of the seafloor. Electromagnetic fields, produced by an electric dipole transmitter, diffuse through the earth and are recorded on the seabed by nodal or cable based electric dipole receivers. Accurate information on transmitter and receiver geometry is extremely important for proper interpretation; errors in the position and orientation of the transmitter and/or the receivers propagate into errors in the predicted seafloor resistivity. We consider the special situation where a receiver cable is towed in the vicinity of a transmitter which is located on the seafloor with a known position and orientation. We theoretically and numerically examine the response of this system for a selection of 1D, 2D, and 3D models, and show that although the electromagnetic field recorded at early times contains information about the subsurface resistivity, the late time decay of the transient response is only a function of the seawater conductivity and receiver position for all the models we consider. In fact, the shape of the late time decay is almost exactly the same as that of a dipole in a wholespace having the same resistivity as seawater. This shows that late time transient information can be used to determine the position of the receiver cable, whereas early time information can be used to determine the resistivity structure of the seafloor.

Vibration of an initially stressed rectangular plate due to an accelerated traveling mass

This paper presents a combined application of the Ritz method, the Differential Quadrature (DQ) method, and the Integral Quadrature (IQ) method to vibration problem of rectangular plates subjected to accelerated traveling masses. In this study, the Ritz method with beam eigenfunctions is first used to discretize the spatial partial derivatives with respect to a co-ordinate direction of the plate. The DQ and IQ methods are then employed to analogize the resultant system of partial differential equations. The resulting system of ordinary differential equations is then solved by using the Newmark time integration scheme. The mixed scheme combines the simplicity of the Ritz method and high accuracy and efficiency of the DQ method. The accuracy of the proposed method is demonstrated by comparing the calculated results with those of the existing literature. It is shown that highly accurate results can be obtained using a small number of Ritz terms and DQM sampling points. Finally, the effects of following parameters having something to do with the title problem are investigated: moving load speed and acceleration, and transverse inertia of the moving load. Numerical results show that all the above-mentioned parameters have significant effects on the transient response of such structures under traveling dynamic loads.

Transient Dynamic Response and Failure of Sandwich Composite Structures under Impact Loading with Fluid Structure Interaction

The objective of this study is to examine the Fluid Structure Interaction (FSI) effect on transient dynamic response and failure of sandwich composite structures under impact loading. The primary sandwich composite used in this study consisted of a 6.35 mm balsa core and a multi-ply symmetrical plain weave 6 oz E-glass skin. Both clamped sandwich composite plates and beams were studied using a uniquely designed vertical drop-weight testing machine. There were three impact conditions on which these experiments focused. The first of these conditions was completely dry (or air surrounded) testing. The second condition was completely water submerged. The final condition was also a water submerged test with air support at the backside of the plates. The tests were conducted sequentially, progressing from a low to high drop height to determine the onset and spread of damage to the sandwich composite when impacted with the test machine. The study showed the FSI effect on sandwich composite structures is very critical such that impact force, strain response, and damage size are generally much greater with FSI under the same impact condition. As a result, damage initiates at much lower impact energy conditions with the effect of FSI. Neglecting to account for FSI effects on sandwich composite structures results in very non-conservative analysis and design. Additionally, it was observed that the damage location changed for sandwich composite beams with the effect of FSI.

Dynamic analysis of large-scale SSI systems for layered unbounded media via a parallelized coupled finite-element/boundary-element/scaled boundary finite-element model

An algorithm for a parallelized coupled model based on finite element method (FEM), boundary element method (BEM), and scaled boundary FEM (SBFEM) for harmonic and transient dynamic response of large-scale 2D structures embedded in or on layered soil media is presented. The BEM and SBFEM are used for modelling the dynamic response of the unbounded media. The standard FEM is used for modelling the finite region and the embedded structure. The objective of the development of this parallelized coupled model is to use the power of high performance computing, and to take into account the advantages and evade the disadvantages of the above mentioned numerical methods for modelling of the unbounded media in soil-structure interaction (SSI) systems. The development of the parallel algorithm for this model is essential for solving arbitrarily shaped large-scale SSI problems, which cannot be solved within reasonable elapsed times by a serial algorithm. The efficiency of the proposed parallel algorithm and the validity of the coupled model are shown by means of three numerical examples, indicating the excellent accuracy and applicability of the parallel algorithm with considerable time-savings in large-scale problems.

Numerical and experimental study of hydrodynamic impact and elastic response of one free-drop wedge with stiffened panels

This paper deals with the study of the slamming load and response of one complex 3D steel wedge with deadrise angle 22°. The stiffened panels on both sides of the wedge are made up of 9 longitudinal stiffeners and 5 transverse frames. In order to study the effect of flexibility on the elastic responses, the cross sections of the stiffeners and frames on each side were designed with different sizes. It is one segment of an idealized ship structure with V-shaped wedge bottom that was used in a series of free-drop experiments impacting still water. The acceleration, slamming pressures, and stress responses were measured. In this paper, one uncoupled method combining Wagner theory and the finite element method is presented to analyze this slamming problem for the 3D structure. The matched asymptotic theory is expanded to predict both the motion and the slamming pressure on the free-drop rigid body. Then slamming pressures are added on the finite element model to predict the transient structural responses. The numerical and experimental results of this slamming problem for a 3D structure are compared. Good agreement is achieved and the hydroelastic effects are discussed.

LNG 화물창 단열구조의 슬로싱 충격응답 간이해석법에 관한 연구

To ensure structural integrity of membrane type LNG tank, the rational assessment of the sloshing impact responses of tank structures should be preceded. The sloshing impact pressures acting on the insulation system of LNG tank are typical irregular loads and the resulting structural responses show very complex behaviors accompanied with fluid structure interaction. So it is not easy to estimate them accurately and immense time consuming calculation process would be necessary. In this research, a simplified method to analyse the dynamic structural responses of LNG tank insulation system under pressure time histories obtained by sloshing model test or numerical analysis was studied. The proposed technique based on the concept of linear combination of the triangular response functions which are the transient responses of structures under the unit triangular impact pressure acting on structures. The validity of suggested method was verified through the example calculations and applied to the dynamic structural response analysis of a real Mark III membrane type insulation system using the sloshing impact pressure time histories obtained by model test.

Stabilized SPH-based simulations of impact dynamics using acceleration-corrected artificial viscosity

Artificial viscosity in SPH-based computations of impact dynamics is a numerical artifice that helps stabilize spurious oscillations near the shock fronts and requires certain user-defined parameters. Improper choice of these parameters may lead to spurious entropy generation within the discretized system and make it over-dissipative. This is of particular concern in impact mechanics problems wherein the transient structural response may depend sensitively on the transfer of momentum and kinetic energy due to impact. In order to address this difficulty, an acceleration correction algorithm was proposed in Shaw and Reid (“Heuristic acceleration correction algorithm for use in SPH computations in impact mechanics”, Comput. Methods Appl. Mech. Engrg., 198, 3962–3974) and further rationalized in Shaw et al. (An Optimally Corrected Form of Acceleration Correction Algorithm within SPH-based Simulations of Solid Mechanics, submitted to Comput. Methods Appl. Mech. Engrg). It was shown that the acceleration correction algorithm removes spurious high frequency oscillations in the computed response whilst retaining the stabilizing characteristics of the artificial viscosity in the presence of shocks and layers with sharp gradients. In this paper, we aim at gathering further insights into the acceleration correction algorithm by further exploring its application to problems related to impact dynamics. The numerical evidence in this work thus establishes that, together with the acceleration correction algorithm, SPH can be used as an accurate and efficient tool in dynamic, inelastic structural mechanics.

Systematic design of slow-light photonic waveguides

A pulse-delaying optimization scheme based on topology optimization for transient response of photonic crystal structures (PhCs) is formulated to obtain slow-light devices. The optimization process is started from a qualified W1 PhC waveguide design with group index ng≈40 obtained from a simple Edisonian parameter search. Based on this, the proposed pulse delaying and subsequent pulse restoring strategies yield a design that increases the group index by 75% to ng≈70±10% for an operational full-width at half-maximum (FWHM) bandwidth BFWHM=6 nm, and simultaneously minimizes interface penalty losses between the access ridge and the W1 PhC waveguide. To retain periodicity and symmetry, the active design set is limited to the in-/outlet region and a distributed supercell, and manufacturability is further enhanced by density filtering techniques combined with material phase projections.

Transient vibrational power flows in slender random structures: Theoretical modeling and numerical simulations

This paper deals with some recent developments for the modeling and numerical simulation of high-frequency (HF) vibrations of randomly heterogeneous slender structures. A time-domain approach is proposed to take account of the multiple reflection and scattering of vibrational waves in this frequency range. The mathematical model is derived from the semiclassical analysis of strongly oscillating (HF) solutions of quantum or classical wave systems, including acoustic, electromagnetic, or in the present case, elastic waves. This theory shows that the phase space energy density associated to these waves satisfies a radiative transfer equation in a random medium at length scales comparable to the small wavelength. The proposed model also considers energetic boundary and interface conditions consistent with the boundary and interface conditions imposed on the solutions of the underlying wave system. They are given in the form of power flow reflection/transmission operators for the energy rays impinging on a boundary or an interface. Nodal/spectral discontinuous “Galerkin” finite element methods and Monte-Carlo methods are implemented to integrate the radiative transfer equations supplemented with boundary and interface conditions. Some numerical simulations are presented to illustrate the theory: the first one deals with an assembly of random thick beams, and the second one with an assembly of random thick shells. This research applies to the prediction of the linear transient responses of engineering structures to impact loads or shocks, as encountered in the aerospace industry for example.

A novel method to calculate transient response of thin-wire structure above the layered lossy half-space

A novel hybrid method combining time domain integral equation(TDIE) with finite difference time domain(FDTD) is proposed to calculate transient response of thin wire structure above a layered lossy half-space. The time domain reflections of electromagnetic waves from layered half-space are obtained by one-dimensional FDTD method. Then, transient response of thin-wire induced by two excitation sources (incident wave and reflected wave) is achieved by employing the TDIE. The computed results illustrate the feasibility and high efficiency of the presented scheme.

An edge‐based smoothed finite element method (ES‐FEM) using 3‐node triangular elements for 3D non‐linear analysis of spatial membrane structures

AbstractAn edge‐based smoothed finite element method using 3‐node triangular membrane elements (ES‐FEM‐T3) is proposed to analyze three‐dimensional (3D) spatial membrane structures under large deflection, rotation, and strain. In our 3D formulation, co‐rotational local coordinate systems associated with the edge‐based smoothing domains are constructed. Edge‐based gradient smoothing for the spatial membrane structure is performed in global Cartesian coordinate system and transformed into the co‐rotational local coordinate system. The smoothed strain and stress can then be properly evaluated in the co‐rotational local coordinate system after the elimination of the rigid body motions simply by coordinates transformation. Explicit time integration scheme is used to compute the transient response of the 3D spatial membrane structure to time‐domain excitations, and the dynamic relaxation method is employed to obtain steady‐state solutions. The numerical results demonstrate that the proposed method produces much better solution accuracy and computational efficiency than the standard FEM using T3 membrane element. Copyright © 2010 John Wiley & Sons, Ltd.

Experimental Study of Impact on Composite Plates with Fluid-Structure Interaction

The transient dynamic response of composite structures under water is affected by Fluid Structure Interaction (FSI), which results in an added mass effect as well as damping. Because the density of composites is comparable to that of water, the added mass effect becomes even more critical to the transient dynamic response of composites in water. In this study, an experimental testing set-up was designed and fabricated, and testing was conducted to investigate FSI effects on composite laminate plates immersed in fluid and subjected to impact loading. Square composite laminates made of carbon fiber weave and vinyl ester resin were subjected to impact loading using a specially developed vertical drop-weight testing machine. The composite samples were fitted with gages to provide time-history on strains and impact forces generated during impact. Impact tests were performed on four-side clamped laminate plates in airbacked wet, water-backed wet, and dry environments. The results showed non-uniform effects on transient responses of wet composites with FSI. Generally, wet impacts on composite plates increased both transient impact forces and strains significantly compared to dry impacts under the same impact mass and velocity condition. The findings of this study will provide a better understanding for use of composite materials in underwater structural applications where impact loading is expected.

Topology optimization for transient response of photonic crystal structures

An optimization scheme based on topology optimization for transient response of photonic crystal structures is developed. The system response is obtained by a finite-element time-domain analysis employing perfectly matched layers as an absorbing boundary condition. As an example a waveguide-side-coupled microcavity is designed. The gradient-based optimization technique is applied to redistribute the material inside the microcavity such that the Q factors of a monopole and a dipole mode are improved by 375% and 285%, respectively, while maintaining strong coupling. This is obtained by maximizing the stored energy inside the microcavity in the decaying regime of the transient response. Manufacturable designs are achieved by filtering techniques capable of controlling minimum length scales of the design features.

Effect of hysteretic smoothness on inelastic response spectra with constant‐ductility

AbstractThis paper presents an efficient methodology for computing constant‐ductility inelastic response spectra. The computation of constant‐ductility spectra involves numerical root‐finding algorithms to find the strongest structure providing a desired ductility response. Smooth inelastic structural behavior is modeled using a first‐order nonlinear differential equation and the transient structural response is solved using an implicit algorithm requiring Newton iterations at each time step. For structural models with smooth hysteretic behavior (not piece‐wise linear), a simple root‐finding method involving a combination of hyperbolic fits, linear interpolation, and Newton's method converges upon the highest strength (conservative) solution with a small number of iterations. The effect of the hysteretic smoothness on the occurrence of multiple roots is examined for two near‐fault and two far‐fault earthquake records, and for two measures of ductility and for normalized hysteretic energy. The results indicate how the smoothness of the hysteretic behavior affects ductility demand and constant‐ductility response spectra. Copyright © 2010 John Wiley & Sons, Ltd.

Adjoint sensitivities of time-periodic nonlinear structural dynamics via model reduction

This work details a comparative analysis of six methods for computing the transient system response and adjoint design derivatives of a nonlinear structure under a periodic external actuation. Time marching via implicit integration, a time-periodic spectral element method, and a time-periodic finite difference method are all considered, each with or without POD-based model reduction of the system of equations. Details of each method, and the concomitant adjoint sensitivities, are provided in terms of accuracy, stability, and Jacobian sparsity patterns. Each method is used for a gradient-based optimization of a nonlinear planar beam, periodically actuated at its root, subject to a large number of structural design parameters. The method with the lowest computational design cost is found to be a strong function of the harmonic content and the nonlinearity of the transient response.