Structural Dynamics Problems Research Articles

Anchored analysis of variance Petrov–Galerkin projection schemes for linear stochastic structural dynamics

In this paper, we propose anchored functional analysis of variance Petrov–Galerkin (AAPG) projection schemes, originally developed in the context of parabolic stochastic partial differential equations (Audouze C, Nair PB. 2014 Comput. Methods Appl. Mech. Eng. 276, 362–395. ( doi:10.1016/j.cma.2014.02.023 )) for solving a class of problems in linear stochastic structural dynamics. We consider the semi-discrete form of the governing equations in the time-domain and the proposed formulation involves approximating the dynamic response using a Hoeffding functional analysis of variance decomposition. Subsequently, we design a set of test functions for a stochastic Petrov–Galerkin projection scheme that enables the original high-dimensional problem to be decomposed into a sequence of decoupled low-dimensional subproblems that can be solved independently of each other. Numerical results are presented to demonstrate the efficiency and accuracy of AAPG projection schemes and comparisons are made to approximations obtained using Monte Carlo simulation, generalized polynomial chaos-based stochastic Galerkin projection schemes and the generalized spectral decomposition method. The results obtained suggest that the proposed approach holds significant potential for alleviating the curse of dimensionality encountered in tackling high-dimensional problems in stochastic structural dynamics with a large number of spatial and stochastic degrees of freedom.

Time‐domain Galerkin method for dynamic load identification

SummaryThis paper proposes a new method called time‐domain Galerkin method (TDGM) for investigating the structural dynamic load identification problems. Firstly, the shape functions are adopted to approximate three parameters, such as the dynamic load, kernel function response, and measured structural response Secondly, defining a residual function could be expressed as the difference of the measured response and the computational response. Thirdly, select an appropriate weighting function to multiply the defined residual function and make integral operation with respect to time to be zero. Finally, when the shape functions are chosen as the weighting function, it establishes the forward model called TDGM. Furthermore, the regularization method could have effectiveness in solving the ill‐posed matrix of load reconstruction and obtaining the accurate identified results of the dynamic load. Compared with the traditional Green kernel function method (GKFM), TDGM can effectively overcome the influences of noise and improve the accuracy of the dynamic load identification. Three numerical examples are provided to demonstrate the correctness and advantages of TDGM. Copyright © 2015 John Wiley & Sons, Ltd.

Random dynamic load identification based on error analysis and weighted total least squares method

In most cases, random dynamic load identification problems in structural dynamics are in general ill-posed. A common approach to treat these problems is to reformulate these problems into some well-posed problems by some numerical regularization methods. In a previous paper by the authors, a random dynamic load identification model was built, and a weighted regularization approach based on the proper orthogonal decomposition (POD) was proposed to identify the random dynamic loads. In this paper, the upper bound of relative load identification error in frequency domain is derived. The selection condition and the specific form of the weighting matrix is also proposed and validated analytically and experimentally, In order to improve the accuracy of random dynamic load identification, a weighted total least squares method is proposed to reduce the impact of these errors. To further validate the feasibility and effectiveness of the proposed method, the comparative study of the proposed method and other methods are conducted with the experiment. The experimental results demonstrated that the weighted total least squares method is more effective than other methods for random dynamic load identification.

Vibration Analysis of Flexible Rotating Rings Using a Spectral Element Formulation

In this work, the forced response of rotating rings exhibiting nonperiodic and periodic variations in material properties and geometry is assessed by means of the spectral element method (SEM). Based on the Euler–Bernoulli beam theory, a spectral element for a planar rotating ring is derived. This spectral element allows the investigation of the effects of structural damping, internal pressure and elastic foundations in the harmonic response of rotating rings. The dynamic response of rotating rings including periodic imperfections that lead to band gap effects is addressed. The spectral element formulation provides exact solutions within the range of validity of the applied theory using a reduced number of degrees-of-freedom. Thus, it contributes to reducing the computational time. It also provides a straightforward way to solve structural dynamics problems including arbitrary boundary conditions and discontinuities. The proposed formulation is validated by comparison with analytical solutions, which are available only for uniform homogenous rings.

ParaVoxel: A Domain Decomposition Based Fixed Grid Preprocessor

In this paper, a parallel cartesian fixed grid mesh generator for structural and fluid dynamics problems is presented. The method uses the boundary representation of a body and produces a set of equal sized cells which are classified in three different types according to its location with respect to the body. Cells are inside, outside or intersecting the boundary of the body. This classification is made by knowing the number of nodes of a cell that are inside body. That process is accomplished very efficiently as the nodes can be classified in batch. Once boundary cells are identified, its geometry is approximated by the convex hull of the nodes inside the body and the intersection points of the boundary against the cell edges. This paper presents the basics of the Fixed Grid Meshing algorithm, followed by some domain decomposition modifications and the data structures required for its parallel implementation. A set of examples and a brief discussion on the possibility of applying this algorithm together with other approaches is presented.

A perturbation approach for the identification of uncertain structures

This paper deals with the identification of linear structural systems with random parameters. The stiffness matrix of a four-storey shear frame structure is assumed to be linearly dependent on a random parameter ruling the damage evolution of the columns. The evaluation of natural frequencies and the mode-shapes is in the context of random eigenvalue problems in structural dynamics. Using a Taylor expansion of the mass and stiffness matrices, a perturbation technique is first applied to derive the asymptotic solution up to the second order. Then, the evaluation of the statistic of the frequencies and mode-shapes is derived up to the second order. Finally a stochastic identification technique is proposed to characterize the statistics of the random parameter.

An unconditionally stable implicit time integration algorithm: Modified quartic B-spline method

In Ref. [1] an effective conditionally stable explicit time integration scheme using quartic B-spline function was proposed for solving the problems in structural dynamics. The current paper presents a scheme where this method is developed to an implicit unconditionally stable time integration method. Using quartic B-spline basis function, this method gained second order of acceleration at each time-step. In this research, in order to applying the stabilization process, first, a series of implicit standard formulas were derived from previous formulation. Then after inserting two controlling parameters γ and β in the standard formulas, unconditional stability is guaranteed.

Adaptive Reduced Basis Methods Applied to Structural Dynamic Analysis

The reduced basis methods (RBM) have been demonstrated as a promising numerical technique for statics problems and are extended to structural dynamic problems in this paper. Direct step-by-step integration and mode superposition are the most widely used methods in the field of the finite element analysis of structural dynamic response and solid mechanics. Herein these two methods are both transformed into reduced forms according to the proposed reduced basis methods. To generate a reduced surrogate model with small size, a greedy algorithm is suggested to construct sample set and reduced basis space adaptively in a prescribed training parameter space. For mode superposition method, the reduced basis space comprises the truncated eigenvectors from generalized eigenvalue problem associated with selected sample parameters. The reduced generalized eigenvalue problem is obtained by the projection of original generalized eigenvalue problem onto the reduced basis space. In the situation of direct integration, the solutions of the original increment formulation corresponding to the sample set are extracted to construct the reduced basis space. The reduced increment formulation is formed by the same method as mode superposition method. Numerical example is given in Section 5 to validate the efficiency of the presented reduced basis methods for structural dynamic problems.

A Robust and Efficient Composite Time Integration Algorithm for Nonlinear Structural Dynamic Analysis

This paper presents a new robust and efficient time integration algorithm suitable for various complex nonlinear structural dynamic finite element problems. Based on the idea of composition, the three-point backward difference formula and a generalized central difference formula are combined to constitute the implicit algorithm. Theoretical analysis indicates that the composite algorithm is a single-solver algorithm with satisfactory accuracy, unconditional stability, and second-order convergence rate. Moreover, without any additional parameters, the composite algorithm maintains a symmetric effective stiffness matrix and the computational cost is the same as that of the trapezoidal rule. And more merits of the proposed algorithm are revealed through several representative finite element examples by comparing with analytical solutions or solutions provided by other numerical techniques. Results show that not only the linear stiff problem but also the nonlinear problems involving nonlinearities of geometry, contact, and material can be solved efficiently and successfully by this composite algorithm. Thus the prospect of its implementation in existing finite element codes can be foreseen.

О ВАРИАЦИОННЫХ УРАВНЕНИЯХ РАСШИРЕННОЙ ТЕОРИИ N-ГО ПОРЯДКА УПРУГИХ ОБОЛОЧЕК И ИХ ПРИЛОЖЕНИИ К НЕКОТОРЫМ ЗАДАЧАМ ДИНАМИКИ

One of topical problems of thick shells theory consists in an accurate modelling of high-frequency shell vibrations and wave propagation, as well as in the application of developed mathematical models to engineering problems of structural dynamics. Many observed processes of both periodic and non-steady shell dynamics cannot be adequately simulated on the groundwork of most traditional hypothesis-based shell theories. Therefore the engineering practice requires new shell models considering higher degrees of freedom besides the displacement and rotation vectors and taking into account the interference of tangential and transversal motions. Here a variant of the N’th order shell model of I.N. Vekua type is analyzed. The proposed model improves the A. Amosov’s shell theory; it is based on the Lagrange’s formalism of analytical mechanics extended to continuum systems, on the dimensional reduction approach, and on the biorthogonal expansion technique. The shell is finally represented by a material surface framed by a set of generalized coordinates (or field variables) and a scalar generator function – the surficial density of the Lagrangian. The dynamic equations for the shell are formulated as generalized Lagrange equations of the second kind. A propagation of normal waves in a plane elastic layer is considered, the corresponding homogeneous problem of N’th order plate theory is formulated, and its solution analysis is extended. In particular, the investigation of the second longitudinal propagating mode and its modelling by approximated plate theories are expanded. The main feature of the second mode is the “inverse wave” effect, i.e. the opposite signs of the phase and group velocities at small wavenumbers. It was shown earlier that the accurate dispersion curves for both phase frequency and group velocity can be obtained on the basis of the fourth- and fifth-order theories. Using the known solution of the spectral problem of N’th order plate theory the eigenfunctions are obtained. The second propagating mode evaluation at the smallest wavenumbers is modelled, the forms of the second propagating wave are investigated, and the approximation of the waveforms at some wavenumbers by plate theories of various orders is estimated. The accuracy of the approximation of the “inverse wave” by some applied theories of various orders based on the orthogonal expansions of displacement vector is discussed. © PNRPU

Stochastic Dynamic Analysis of Structures with Spatially Uncertain Material Parameters

This paper investigates the uncertainty quantification in structural dynamic problems with spatially random variation in material and damping parameters. Uncertain and locally varying material parameters are represented as stochastic field by means of the Karhunen–Loève (KL) expansion. The stiffness and damping properties of the structure are considered uncertain. Stochastic finite element of structural modal analysis is performed in which modal responses are represented using the generalized polynomial chaos (gPC) expansion. Knowing the KL expansions of the random parameters, the nonintrusive technique is employed on a set of random collocation points where the structure deterministic finite element model is executed to estimate the unknown coefficients of the polynomial chaos expansions. A numerical case study is presented for a cantilever beam with random Young's modulus involving spatial variation. The proportional damping constants are estimated from the experimental modal analysis. The expected value, standard deviation, and probability distribution of the random eigenfrequencies and the damping ratios are evaluated. The results show high accuracy compared to the Monte-Carlo (MC) simulations with 3000 realizations. It is also demonstrated that the eigenfrequencies and the damping ratios are equally affected from material uncertainties.

Dissipative, noniterative integration algorithms with unconditional stability for mildly nonlinear structural dynamic problems

A new family method is proposed to efficiently perform a nonlinear dynamic analysis with comparable accuracy. In fact, it integrates unconditional stability, explicit formulation and desired numerical damping together. Consequently, it is very promising for solving an inertia-type problem. The unconditional stability implies no limitation on step size, and an explicit formulation implies no iteration procedures. In addition, the desired numerical damping is continuously controlled, and it is possible to have zero damping. This damping can suppress the spurious high-frequency responses, while the low-frequency modes are almost unaffected and can be accurately integrated.

An online coupled state/input/parameter estimation approach for structural dynamics

In many practical structural applications, unknown states, inputs and parameters are present. However, most methods require one or more of these variables to be known in order to estimate the other(s). In this research an estimation technique which employs physical models is proposed to perform coupled state/input/parameter estimation. In order to obtain a modeling technique which allows the estimation of a wide range of parameters in a generic fashion at a minimal computational cost (even real-time), the use of a parametric model reduction technique is proposed. The reduced model is coupled to an extended Kalman filter (EKF) with augmented states for the unknown inputs and parameters. This leads to a very efficient framework for estimation in structural dynamics problems. Special attention is also given to the measurement requirements in order to obtain an adequate observability of all unknown quantities and the necessity for at least one displacement level measurement is shown. The proposed methodology is validated numerically and experimentally. The approach is shown to be easy to tune and provides good results with different measurement methods.

Meshfree modeling of dynamic response of mechanical structures

Transient nature of the loading conditions applied to the structural components makes dynamic analysis one of the important components in the design-analysis cycle. Time-varying forces and accelerations can substantially change stress distributions and cause a premature failure of the mechanical structures. In addition, it is also important to determine dynamic response of the structural elements to the frequency of the applied loads. In this paper we describe the first application of the meshfree Solution Structure Method (SSM) to the structural dynamics problems. SSM is a meshfree method which enables construction of the solutions to the engineering problems that satisfy exactly all prescribed boundary conditions. This method is capable of using spatial meshes that do not conform to the shape of a geometric model. Instead of using the grid nodes to enforce boundary conditions, it employs distance fields to the geometric boundaries and combines them with the basis functions and prescribed boundary conditions at run time. This defines unprecedented geometric flexibility of the SSM as well as the complete automation of the solution procedure. In the proposed approach we will use SSM to enforce initial and boundary conditions, while transient behavior is enforced by time marching schemes used to solve systems of ordinary differential equations. In the paper we will explain the key points of the SSM as well as investigate the accuracy and convergence of the proposed approach by comparing our results with the ones obtained using traditional finite element analysis. Despite in this paper we are dealing with 2D in-plane vibrations, the proposed approach has a straightforward application to model vibrations of 3D structures.

Efficient solution of the fuzzy eigenvalue problem in structural dynamics

Purpose – Many analysis and design problems in engineering and science involve uncertainty to varying degrees. This paper is concerned with the structural vibration problem involving uncertain material or geometric parameters, specified as fuzzy parameters. The requirement is to propagate the parameter uncertainty to the eigenvalues of the structure, specified as fuzzy eigenvalues. However, the usual approach is to transform the fuzzy problem into several interval eigenvalue problems by using the α-cuts method. Solving the interval problem as a generalized interval eigenvalue problem in interval mathematics will produce conservative bounds on the eigenvalues. The purpose of this paper is to investigate strategies to efficiently solve the fuzzy eigenvalue problem. Design/methodology/approach – Based on the fundamental perturbation principle and vertex theory, an efficient perturbation method is proposed, that gives the exact extrema of the first-order deviation of the structural eigenvalue. The fuzzy eigenvalue approach has also been improved by reusing the interval analysis results from previous α-cuts. Findings – The proposed method was demonstrated on a simple cantilever beam with a pinned support, and produced very accurate fuzzy eigenvalues. The approach was also demonstrated on the model of a highway bridge with a large number of degrees of freedom. Originality/value – This proposed Vertex-Perturbation method is more efficient than the standard perturbation method, and more general than interval arithmetic methods requiring the non-negative decomposition of the mass and stiffness matrices. The new increment method produces highly accurate solutions, even when the membership function for the fuzzy eigenvalues is complex.

Novel Partitioned Integration Method Based on Newmark's Scheme for Structural Dynamic Problems

Systems of ODEs arising from transient structural dynamics generally exhibit high-frequency/low-frequency and linear/nonlinear behaviours of subsets of state variables. This paper resorts to the use of different time integrators with different time steps for subsystems, to tailor each method and its time step to the solution behaviour of the corresponding subsystem. Anovel partitioned integration method with the acceleration continuity is proposed whose velocity continuity is also ensured by means of the mass projection strategy. Both its stability and accuracy properties are examined through numerical analysis on Single-DoF split mass system.

A Cross Weighted-Residual Time Integration Scheme for Structural Dynamics

In this article, we develop a novel stable time integration scheme for the transient analysis of structural dynamics problems. A second-order (in time) differential operator equation (e.g. obtained after finite element discretization in space) is written as a pair of first-order equations in terms of displacements and velocities. Then the solution is sought by minimizing the inner product of the residuals in the two equations (an unconventional approach) over typical time interval to obtain a symmetric set of algebraic equations involving displacements and velocities at two subsequent intervals. The new time integration scheme is termed the cross weighted-residual (CWR) time integration scheme because each of the two residuals takes the other one as a weight function in the minimization. The CWR time integration scheme is developed by using a uniform linear time approximation of the displacement and velocity fields to yield only a single step time integration scheme, which is comparable to the Newmark family of time integration scheme. A reduced integration technique is used to prevent velocity locking, which is caused by linear approximation of both the displacement and velocity fields. For the verification of the consistency and the stability, the CWR time integration scheme is tested with single-degree as well as multi-degree of freedom problems. The scheme performs extremely well compared with those of the well-known Newmark family of time integration schemes.

Two dynamic explicit methods based on double time steps

The primary purpose of this paper is to develop novel fast dynamic methods for large-scale problems of structural dynamics at the least computational efforts. The explicit method of double time steps (EMDTS) is proposed through integration with the assumption of linear acceleration in two time steps. The corrected explicit method of double time steps (CEMDTS) is obtained after correcting the EMDTS. The analyses of stability, accuracy, numerical dissipation and dispersion are performed on the proposed methods. Finally, both linear and nonlinear numerical examples are utilised for the comparison of the two new methods and the established methods. The results show that the EMDTS is unstable in undamped linear systems; however, the CEMDTS has a nondissipative property and the same stability condition as the explicit central difference method (ECDM). The amplitude error of the EMDTS is greater than that of the CEMDTS and the ECDM when the time step is large. The CEMDTS possesses excellent comprehensive properties with less damping ratio error and periodic error than the ECDM in the case of small time steps at almost the same computational efforts. Three numerical examples manifest that the CEMDTS is better than the EMDTS, and endowed with good accuracy and stable properties.

Event-driven integration of linear structural dynamics models under unilateral elastic constraints

This paper proposes an algorithm for the numerical simulation of linear structural dynamics problems under unilateral elastic constraints, i.e., constraints with a linear force/displacement characteristic whenever active. The presented procedure relies on an event-driven strategy for the handling of the contact constraints, in combination with one-step schemes dedicated to the time integration of the second-order equations of motion. Efficiency of the procedure follows from the use of cubic Hermite interpolation to continuously extend the normal gap functions that reflect the openings of the contact interfaces. Robustness follows from the proper handling of complex numerical situations, e.g., numerical grazing or discontinuity sticking, through appropriate algorithm structure and numerical implementation. And, integration stability is guaranteed by the very nature of the algorithm and that of the one-step integration scheme. Following a detailed coverage of the integration procedure and the countermeasures to the expected numerical difficulties, three application examples are treated for illustration purposes. A MATLAB implementation of the procedure is provided online; download and usage information are given in Appendix A.

Integrated modelling of the structural and functional reconfiguration of complex objects

Particularly urgent formulation and solution of various classes of scheduling problems of structural dynamics of complex objects (CO). This article is based on a generalized settheoretic formulation of the problem of planning the structural-functional reconfiguration of the CO is considered a complex model of planning and management of the processing and transfer of material and / or information resources to restructure, and a model of parametric synthesis image of the CO, providing the robustness of its reconfiguration plans under the optimistic and pessimistic scenarios for the structural dynamics of the CO.