efficient arnoldi type algorithms for rational eigenvalue problems arising in fluid solid systems we develop and analyze efficient methods for computing damped vibration modes of an acoustic fluid confined in a cavity with absorbing walls capable of dissipating acoustic energy the discretization in terms of pressure nodal finite elements gives rise to a rational eigenvalue problem numerical evidence shows that there are no spurious eigenmodes for such discretization and also confirms that the discretization based on nodal pressures is much more efficient than that based on raviart thomas finite elements for the displacement field the trimmed linearization method is used to linearize the associated rational eigenvalue problem into a generalized eigenvalue problem gep of the form ax lbx for solving the gep we apply arnoldi algorithm to two different types of single matrices b 1a and ab 1 numerical accuracy shows that the application of arnoldi on ab 1 is better than that on b 1a

semidiscrete finite element approximations of a linear fluid structure interaction problem semidiscrete finite element approximations of a linear fluid structure interaction problem are studied first results concerning a divergence free weak formulation of the interaction problem are reviewed next semidiscrete finite element approximations are defined and the existence of finite element solutions is proved with the help of an auxiliary discretely divergence free formulation a discrete inf sup condition is verified and the existence of a finite element pressure is established strong a priori estimates for the finite element solutions are also derived then by passing to the limit in the finite element approximations the existence of a strong solution is demonstrated and semidiscrete error estimates are obtained

a hexahedral face element for elastoacoustic vibration problems a finite element method to compute elastoacoustic vibration modes in 3d problems is analyzed it is based on displacement formulations for solid and fluid the discretization consists of classical isoparametric hexahedral elements for the former and hexahedral raviart thomas elements for the latter to avoid spurious modes the meshes on fluid and solid domains do not need to coincide on the common interface since the kinematic constraint is weakly imposed the generalized eigenvalue problem is written in a matrix form which allows using a standard matlab eigensolver numerical results showing the good performance of the method and the convenience of using incompatible meshes are reported

rayleigh quotients for coupled free vibrations abstract based upon the general thin shell theory and basic equations in fluid mechanics three kinds of rayleigh s quotients for coupled fluid structure free vibrations are developed for arbitrary tanks fully or partially filled with i inviscid irrotational and incompressible fluid with the effects of free surface waves neglected ii inviscid irrotational and incompressible fluid with the effects of free surface waves considered and iii inviscid irrotational and compressible fluid respectively theorems concerning stationary values of the respective rayleigh quotients are proved by utilizing the generalized orthogonality relationships for the wet modes of these three kinds of liquid containing tank models thus the mathematical foundations for calculating approximately the eigenvalues and eigenvectors in fluid structure interaction systems are presented an example of applying the rayleigh quotient to predicting a natural frequency of a cylindrical tank partially filled with fluid is provided and the result is compared with that available

a variational principle for the formulation of partitioned structural systems a continuum based variational principle is presented for the formulation of the discrete governing equations of partitioned structural systems this application includes coupled substructures as well as subdomains obtained by mesh decomposition the present variational principle is derived by a series of modifications of a hybrid functional originally proposed by atluri for finite element development the interface is treated by a displacement frame and a localized version of the method of lagrange multipliers interior displacements are decomposed into rigid body and deformational components to handle floating subdomains both static and dynamic versions are considered an important application of the present principle is the treatment of nonmatching meshes that arise from various sources such as separate discretization of substructures independent mesh refinement and global local analysis the present principle is compared with that of a globalized version of the multiplier method copyright 2000 john wiley sons ltd

adjustments to zatsiorsky seluyanov s segment inertia parameters zatsiorsky et al in contemporary problems in biomechanics pp 272 291 crc press massachusetts 1990a obtained by means of a gamma ray scanning technique the relative body segment masses center of mass cm positions and radii of gyration for samples of college aged caucasian males and females although these data are the only available and comprehensive set of inertial parameters regarding young adult caucasians they have been rarely utilized for biomechanical analyses of subjects belonging to the same or a similar population the main reason is probably that zatsiorsky et al used bony landmarks as reference points for locating segment cms and defining segment lengths some of these landmarks were markedly distant from the joint centers currently used by most researchers as reference points the purpose of this study was to adjust the mean relative cm positions and radii of gyration reported by zatsiorsky et al in order to reference them to the joint centers or other commonly used landmarks rather than the original landmarks the adjustments were based on a number of carefully selected sources of anthropometric data

mls based variable node elements compatible with quadratic interpolation part i formulation and application for non matching meshes two dimensional variable node elements compatible with quadratic interpolation are developed using the moving least square mls approximation the mapping from the parental domain to the physical element domain is implicitly obtained from mls approximation with the shape functions and their derivatives calculated and saved only at the numerical integration points it is shown that the present mls based variable node elements meet the patch test if a sufficiently large number of integration points are employed for numerical integration the cantilever problem with non matching meshes is chosen to check the feasibility of the present mls based variable node elements and the result is compared with that from the lower order case compatible with linear interpolation copyright 2005 john wiley sons ltd

doubly asymptotic approximations for vibration analysis of submerged structures doubly asymptotic approximations daa s are differential equations for boundary element analysis of the dynamic interaction between a complex structure and a surrounding infinite medium t l geers j acoust soc am 64 1500 1508 1978 p g underwood and t l geers int j solids struct 17 687 697 1981 in this paper the use of first and second order daa s for vibration analysis of submerged structures is examined first the governing discrete element equations for the general problem are set down and discussed then the accuracy of three daa forms is studied through the generation of numerical results for a submerged spherical shell although the first order daa is found to be inadequate the two second order forms show considerable promise work supported by the david w taylor naval ship r d center

effect of arm swing direction on forward and backward jump performance this study quantified and compared how the directional differences in arm swing affected mechanical and physiological parameters during forward and backward jumping seven subjects maximally performed three types of forward and backward squat jumps no arm swing fj bj forward arm swing fjf bjf and backward arm swing fjb bjb from a force platform all performances were captured with a 3 d motion capture system electromyograms emgs of the lower extremity muscles were obtained variables were calculated by combining kinematic and kinetic data the jump displacement and center of mass velocity at take off were significantly larger in fjf than in fj or fjb and larger in bjb than in bj or bjf suggesting that the best performance was obtained by employing the same arm swing direction as a given jump direction the total work by three lower and two upper extremity joints was significantly larger in fjf than in fj or fjb and larger in bjb than in bj or bjf for the lower extremity joints hip work was the greatest in fjf and bjb the integrated emg of the biceps femoris when the hip power was produced was significantly larger in fjf and bjb than under other conditions these results suggest that if the arm swing direction is the same as a given jump direction the activation level of the hip extensor is greater to counter large loads which make the hip joint flex during the push off phase which result in increased hip extension torque power and work

finite element approximation of a displacement formulation for time domain elastoacoustic vibrations this paper deals with the numerical solution of a system of second order in time partial differential equations modeling the vibrations of a coupling between an elastic solid and an inviscid compressible fluid both media are described in terms of their respective displacement fields the problem is solved in the time domain by combining a newmark s scheme for time discretization with a finite element method for space discretization the latter combines standard lagrangian elements in the solid with lowest order raviart thomas elements in the fluid stability is proved and numerical results showing the good behavior of the method are reported

space time finite element techniques for computation of fluid structure interactions we describe the space time finite element techniques we developed for computation of fluid structure interaction fsi problems among these techniques are the deforming spatial domain stabilized space time dsd sst formulation and its special version and the mesh update methods including the solid extension mesh moving technique semmt also among these techniques are the block iterative quasi direct and direct coupling methods for the solution of the fully discretized coupled fluid and structural mechanics equations we present some test computations for the mesh moving techniques described we also present numerical examples where the fluid is governed by the navier stokes equations of incompressible flows and the structure is governed by the membrane and cable equations overall we demonstrate that the techniques we have developed have increased the scope and accuracy of the methods used in computation of fsi problems 2005 elsevier b v all rights reserved

whole body inverse dynamics over a complete gait cycle based only on measured kinematics this paper presents a three dimensional 3d whole body multi segment model for inverse dynamics analysis over a complete gait cycle based only on measured kinematic data the sequence of inverse dynamics calculations differs significantly from the conventional application of inverse dynamics using force plate data a new validated smooth transition assumption was used to solve the indeterminacy problem in the double support phase kinematic data is required for all major body segments and hence a whole body gait measurement protocol is presented finally sensitivity analyses were conducted to evaluate the effects of digital filtering and body segment parameters on the accuracy of the prediction results the model gave reasonably good estimates of sagittal plane ground forces and moment however the estimates in the other planes were less good which we believe is largely due to their small magnitudes in comparison to the sagittal forces and moment the errors observed are most likely caused by errors in the kinematic data resulting from skin movement artefact and by errors in the estimated body segment parameters a digital filtering cut off frequency of 4 5 hz was found to produce the best results it was also shown that errors in the mass properties of body segments can play a crucial role with changes in properties sometimes having a disproportionate effect on the calculated ground reactions the implication of these results is that even when force plate data is available the estimated joint forces are likely to suffer from similar errors

free vibration analysis of cylindrical tanks partially filled with liquid abstract a simple but effective modal solution based on the underlying ideas of the hierarchical finite element method is presented for evaluating the free vibration characteristics of vertical thin circular cylindrical shells partially or completely filled with liquid and subjected to any variationally consistent set of boundary conditions on the lower and upper boundaries effects of static liquid pressure in plane inertias and liquid free surface motions are taken into account the solution of the shell problem is obtained through a procedure in which sander s shell equations are transformed into a new system of first order ordinary differential equations which are solved by the galerkin error minimization procedure the system variables are those quantities which appear in the boundary conditions on a rotationally symmetric edge of a cylindrical shell the liquid is taken as non viscous and incompressible and the coupling between the deformable shell and this medium is taken into account the solution for the liquid velocity potential is assumed as a sum of two sets of linear combinations of suitable harmonic functions which satisfy laplace equation and the relevant boundary conditions this procedure leads to a determinantal equation for the determination of the shell and liquid natural frequencies and the associated mode shapes application of the method to a few selected cases and comparisons of the numerical results with those obtained by other theories and from experiments are found to be good and demonstrate the effectiveness and accuracy of the present methodology

the xfem for high gradient solutions in convection dominated problems convection dominated problems typically involve solutions with high gradients near the domain boundaries boundary layers or inside the domain shocks the approximation of such solutions by means of the standard finite element method requires stabilization in order to avoid spurious oscillations however accurate results may still require a mesh refinement near the high gradients herein we investigate the extended finite element method xfem with a new enrichment scheme that enables highly accurate results without stabilization or mesh refinement a set of regularized heaviside functions is used for the enrichment in the vicinity of the high gradients different linear and non linear problems in one and two dimensions are considered and show the ability of the proposed enrichment to capture arbitrary high gradients in the solutions copyright c 2009 john wiley sons ltd

a monolithic approach for interaction of incompressible viscous fluid and an elastic body based on fluid pressure poisson equation this paper describes a new monolithic approach based on the fluid pressure poisson equation ppe to solve an interaction problem of incompressible viscous fluid and an elastic body the ppe is derived so as to be consistent with the coupled equation system for the fluid structure interaction fsi based on this approach we develop two kinds of efficient monolithic methods in both methods the fluid pressure is derived implicitly so as to satisfy the incompressibility constraint and all other unknown variables are derived fully explicitly or partially explicitly the coefficient matrix of the ppe for the fsi becomes symmetric and positive definite and its condition is insensitive to inhomogeneity of material properties the arbitrary lagrangian eulerian ale method is employed for the fluid part in order to take into account the deformable fluid structure interface to demonstrate fundamental performances of the proposed approach the developed two monolithic methods are applied to evaluate the added mass and the added damping of a circular cylinder as well as to simulate the vibration of a rectangular cylinder induced by vortex shedding copyright 2005 john wiley sons ltd

a new coupling strategy for fluid solid interaction problems by using the interface element method this paper presents a new approach to simulate fluid solid interaction fsi problems involving non matching meshes the coupling between the fluid and solid domains with dissimilar finite element meshes consisting of 4 node quadrilateral elements is achieved by using the interface element method continuity and compatibility conditions across the interface between fluid and solid meshes are satisfied exactly by introducing the interface elements defined on an interfacing region importantly a consistent transfer of loads through the interface elements guarantees the present method to be an efficient approach of the solution strategy to fsi problems an arbitrary lagrangian eulerian description is adopted for the fluid domain while for the solid domain an updated lagrangian formulation is considered to accommodate finite deformations of an elastic structure the fluid equations for velocity and pressure and the solid equations for velocity are strongly coupled in a single computational domain by means of the interface elements numerical results are presented for fsi problems involving non matching meshes to demonstrate the effectiveness of the methodology copyright 2009 john wiley sons ltd

a symmetric weak form of biot s equations based on redundant variables representing the fluid using a helmholtz decomposition of the fluid displacement vector field a novel symmetric weak formulation of biot s equations for linear acoustic wave propagation in layered poroelastic media is presented the primary variables used are the frame displacement the acoustic pore pressure the scalar potential and the vector potential obtained from a helmholtz decomposition of the fluid displacement also a symmetric weak form based on the frame displacement the pore pressure and the fluid displacement is obtained as an intermediate result hp finite element simulations of a double leaf partition based on this new weak formulation is verified against simulation results from the classical frame displacement fluid displacement formulation and a frame displacement pore pressure formulation all three formulations simulated displays the same rate of convergence with respect to finite element bases polynomial degree the novel formulation also extends a previously published frame displacement pore pressure scalar fluid displacement potential formulation with an implicit irrotational fluid displacement assumption to a full representation of biot s equations copyright 2010 john wiley sons ltd

finite element vibration analysis of fluid solid systems without spurious modes this paper deals with the finite element approximation of the vibration modes of a problem with fluid structure interaction displacement variables are used for both the fluid and the solid to avoid the typical spurious modes of this formulation we introduce a nonconforming discretization error estimates for the approximation of eigenvalues and eigenvectors are given

hydroelastic vibration of a circular plate submerged in a bounded compressible fluid abstract an analytical method for the linear free vibration of a circular plate submerged in a fluid was developed by the rayleigh ritz method based on the fourier bessel series expansion it is assumed that the plate is clamped at an offcenter location of a rigid cylindrical container and the fluid bisected by the plate in the container is non viscous and compressible since a combination of the dry modal functions of the circular plate can approximate the wet vibration modes the functions were used to form a set of linearly independent functions of the rayleigh ritz method it was found that the theoretical results could predict well the fluid coupled natural frequencies with excellent accuracy compared with the finite element analysis results the effects of the fluid compressibility and the offcenter distance on the natural frequencies were also observed

a survey of formal methods for determining the centre of rotation of ball joints abstract the determination of an accurate centre of rotation cor from segment marker positions is of interest across a wide range of applications but particularly for clinical gait analysis and for estimating the hip joint centre during surgical intervention of the knee for limb alignment purposes for the first time in this survey of formal methods we classify analyse and compare different methods geometric algebraic bias compensated algebraic and pratt sphere fit methods as well as the centre transformation technique the holzreiter approach the helical pivot technique the schwartz transformation techniques the minimal amplitude point method and the stoddart approach for the determination of spherical joint centres from marker position data in addition we propose a new method the symmetrical cor estimation or score in which the coordinates of the joint centre must only remain constant relative to each segment thus not requiring the assumption that one segment should remain at rest for each method 1000 cor estimations were analysed with the application of isotropic independent and identically distributed gaussian noise standard deviation 0 1 cm to each of the marker positions to all markers on the segment simultaneously and the two in combination for the test conditions used here most techniques were capable of determining the cor to within 0 3 cm as long as the spherical range of motion rom of the joint was 45 or more under the most stringent conditions tested however the score was capable of best determining the cor to within approximately 1 2 mm with a rom of 20 the correct selection and application of these methodologies should help improve the accuracy of surgical navigation and clinical kinematic measurement

treatment of acoustic fluid structure interaction by localized lagrange multipliers formulation a new concept is presented for modeling the dynamic interaction between an acoustic fluid and an elastic structure the coupling of this multiphysics system is done by inserting a kinematic interface frame between the fluid and the structure and using node collocated lagrange multipliers to connect the frame to each subsystem the time domain response analysis is performed by a partitioned analysis procedure the main advantages of this localized lagrange multiplier llm primal dual coupling method are complete localization of the structure and fluid subsystems elimination of the conventional predictor in the partitioned time integration method and the ability to accommodate non matching meshes the standard newmark time integrator is used on both the fluid and structure models it is shown that if the integrator is a stable and second order accurate for a monolithic treatment it retains those properties for both mortar and llm partitioned solution procedures infinite and finite piston problems are used to explain and verify the methodology a sequel paper under preparation presents and discusses a set of benchmark and application examples that involve the response of existing dams to seismic excitation

non linear coupled slosh dynamics of liquid filled laminated composite containers a two dimensional finite element approach abstract this paper brings into focus some of the interesting effects arising from the non linear motion of the liquid free surface due to sloshing in a partially filled laminated composite container along with the associated coupling due to fluid structure interaction effects the finite element method based on two dimensional fluid and structural elements is used for the numerical simulation of the problem a numerical scheme is developed on the basis of a mixed eulerian lagrangian approach with velocity potential as the unknown nodal variable in the fluid domain and displacements as the unknowns in the structure domain the fe formulation based on galerkin weighted residual method along with an iterative solution procedure are explained in detail followed by a few numerical examples numerical results obtained by the present investigation for the rigid containers are first compared with the existing solutions to validate the code for non linear sloshing without fluid structure coupling thereafter the computational procedures are advanced to obtain the coupled interaction effect of non linear sloshing in laminated composite containers

reduced models for modal analysis of fluid structure systems taking into account compressibility and gravity effects abstract it is proposed to investigate and discuss from theoretical point of view various reduced order variational formulations for modal analysis of linear vibrations of bounded fluid structure systems with free surface taking into account possible gravity compressibility interactions in a non homogeneous fluid situation those formulations are based on substructural synthesis techniques and various modal reduction schemes are then obtained in a previous paper various original formulations have been exhibited associated to numerical validation the present paper starts from those formulations in order to construct theoretically various reduced order models

eigenvalue problems for vibrating structures coupled with quiescent fluids with free surface abstract vibrations of plates shells and plate shell systems coupled with sloshing quiescent and inviscid fluid have been advantageously studied by inserting the sloshing condition into the eigenvalue problem here a formulation of this particular eigenvalue problem for symmetric matrices is obtained in fact in the previous studies this technique has given eigenvalue problems for non symmetric matrices for which the problem of the existence of complex eigenvalues arises the present analysis deals with compressible and incompressible fluids and the discretization of the system is obtained by using the rayleigh ritz method the rayleigh quotient of the system is manipulated to obtain expressions suitable for symmetric formulations of the eigenvalue problem in particular the rayleigh quotient is transformed into a simpler expression where the potential energies of the compressible fluid and free surface waves do not appear the method is applied to a vertical simply supported circular cylindrical shell partially filled by an incompressible sloshing liquid a case with large interaction between sloshing and bulging modes is considered and interesting phenomena are observed

a posteriori error estimates in finite element acoustic analysis we present an a posteriori error estimator for the approximations of the acoustic vibration modes obtained by a finite element method which does not present spurious or circulation modes for non zero frequencies we prove that the proposed estimator is equivalent to the error in the approximation of the eigenvectors up to higher order terms with constants independent of the eigenvalues numerical results for some test examples are presented which show the good behavior of the estimator when it is used as local error indicator for adaptive refinement

review of coupling methods for non matching meshes abstract domain decomposition is nowadays a common way to speed up complex computations however the discrete meshes used in the different domains do not have to match at their common interface especially when different physical fields are involved such as in fluid structure interaction computations exchange of information over this interface is therefore no longer trivial in this paper six methods that can deal with the information transfer between non matching meshes in fluid structure interaction computations are compared for different criteria this is done for analytical test cases as well as a quasi 1d fluid structure interaction problem two methods based on radial basis functions one with compact support and one using thin plate splines are favoured over the other methods because of their high accuracy and efficiency

a parametric study on fluid structure interaction problems abstract this paper deals with finite element analysis of the fluid structure systems considering the coupled effect of elastic structure and fluid the equations of motion of the fluid considered inviscid and compressible are expressed in terms of the pressure variable alone the elastic structure and the fluid domain are treated as two separate systems and discretized with finite elements the solution of the coupled system is accomplished by solving the two systems separately with the interaction effects at the fluid solid interface enforced by a developed iterative scheme non divergent pressure and displacement are obtained simultaneously through a few numbers of iterations studies show the accuracy of the proposed algorithm while comparing with the existing ones available in the literature the parametric study of the coupled system shows the importance of fluid height and material property of the structure

nitsche s method combined with space time finite elements for ale fluid structure interaction problems we propose a weak method for handling the fluid structure interface in finite element fluid structure interaction based on nitsche s method abh math univ hamburg 36 1971 9 we assume transient incompressible newtonian flow and for the structure undamped linear elasticity for the time discretization we use the time continuous energy conserving galerkin method for the structure and for the fluid we employ the time discontinuous galerkin method this means that the velocity becomes piecewise constant on each timestep for the fluid matching the time derivative of the displacements in the solid which is also piecewise constant over a time step we formulate the method and report some numerical examples using space time oriented elements for the fluid in order to mimic lagrangian or ale type simulations

coupled vibrations of cantilever cylindrical shells partially submerged in fluids with continuous simply connected and non convex domain abstract the approach developed in the present paper is applied for the coupled vibration analysis of a cantilever cylindrical shell partially submerged in a fluid with a continuous simply connected and non convex domain the shell is partially and concentrically submerged in a rigid cylindrical container partially filled by a fluid which is assumed to be incompressible and inviscid the velocity potential for fluid motion is formulated in terms of eigenfunction expansions using the collocation method the interaction between the fluid and the structure takes into account by using the compatibility requirement along the wet surface of the shell and the rayleigh ritz method is used to calculate natural frequencies and modes of the coupled system the validity of the developed theoretical method is verified by comparing the results with those obtained from the finite element analysis furthermore the effects of submergence depth radial distance between shell and container and circumferential wavenumbers on the natural frequencies and modes of the coupled system are investigated

finite element solution of new displacement pressure poroelastic models in acoustics abstract this paper deals with acoustical behavior of porous materials having an elastic solid frame firstly an overview to poroelastic models is presented and then we focus our attention on non dissipative poroelastic materials with open pores assuming periodic structure we compute the coefficients in the model by using homogenization techniques which require solving boundary value problems in the elementary cell next we propose a finite element method in order to compute the response to a harmonic excitation of a three dimensional enclosure containing a free fluid and a poroelastic material the finite element used for the fluid is the lowest order face element introduced by raviart and thomas that eliminates the spurious modes whereas for displacements in porous medium the mini element is used in order to achieve stability of the method

finite element analysis of the vibration problem of a plate coupled with a fluid we consider the approximation of the vibration modes of an elastic plate in contact with a compressible fluid the plate is modelled by reissner mindlin equations while the fluid is described in terms of displacement variables this formulation leads to a symmetric eigenvalue problem reissner mindlin equations are discretized by a mixed method the equations for the fluid with raviart thomas elements and a non conforming coupling is used on the interface in order to prove that the method is locking free we consider a family of problems one for each thickness t 0 and introduce appropriate scalings for the physical parameters so that these problems attain a limit when t to 0 we prove that spurious eigenvalues do not arise with this discretization and we obtain optimal order error estimates for the eigenvalues and eigenvectors valid uniformly on the thickness parameter t finally we present numerical results confirming the good performance of the method

a new strategy for solving fluid structure problems a scheme for treating unsymmetrical coupled systems is outlined such systems occur naturally in connection with fluid structure interaction where an acoustic fluid is contained in an elastic structure the discretization is performed by means of the finite element method using displacement formulation in the structure and either pressure or displacement potential in the fluid based on the eigenvalues of each subdomain some simple steps give a standard eigenvalue problem it might also be concluded that the unsymmetrical matrices have real eigenvalues

accurate pressure post process of a finite element method for elastoacoustics this paper deals with a post process to obtain a more accurate approximation of the fluid pressure from a finite element computation of the vibration modes of a fluid structure coupled system the underlying finite element method based on a displacement formulation for both media consists of using raviart thomas elements for the fluid combined with standard continuous elements for the solid an easy to compute post process of the pressure is derived the relation between this post process and an alternative finite element approximation of the problem based on discretizing the fluid pressure by enriched crouzeix raviart elements is studied higher order estimates for the l2 norm of the post processed pressure are proved by exploiting this relation as a by product higher order l2 estimates for the solid displacements obtained with the original method are also proved

partitioned formulation of internal fluid structure interaction problems by localized lagrange multipliers abstract a partitioned formulation of compressible internal fluid structure interaction problems is presented by employing a displacement model for both the fluid and structure partitioning is effected by a localized version of the method of lagrange multipliers which assigns two independent sets of lagrange multipliers to the structural and fluid interfaces two major features of the present formulation include an interface compliance normalization that helps capture the predominant physics of interaction phenomena when the interfaces are characterized by two radically different rigidities and a novel transformation of the displacement model into a fluid pressure model that is suitable for both transient and vibration analyses the present formulation first solves for the interface lagrange multipliers which are subsequently used to solve for the structural displacements and the fluid displacement or pressure by employing two independent analysis modules

orthogonality of wet modes in coupled vibrations of cylindrical shells containing liquids abstract on the basis of flugge s thin shell equations and a linear potential flow theory general orthogonality relations of wet modes for cylindrical storage vessels containing liquids are established some applications of these relations to dynamic response analysis under arbitrary excitation are also discussed

law of error in tsallis statistics in order to theoretically explain the ubiquitous existence of power law behavior such as chaos and fractals in nature tsallis entropy has been successfully applied to the generalization of the traditional boltzmann gibbs statistics the fundamental information measure of which is shannon entropy tsallis entropy s sub q is a one parameter generalization of shannon entropy s sub 1 in the sense that lim sub q spl rarr 1 s sub q s sub 1 the generalized statistics using tsallis entropy are referred to as tsallis statistics in order to present the law of error in tsallis statistics as a generalization of gauss law of error and prove it mathematically we apply the new multiplication operation determined by q logarithm and q exponential the fundamental functions in tsallis statistics to the definition of the likelihood function in gauss law of error the present maximum likelihood principle mlp leads us to determine the so called q gaussian distribution which coincides with one of the tsallis distributions derived from the maximum entropy principle for tsallis entropy under the second moment constraint

an adaptive remeshing strategy for flows with moving boundaries and fluid structure interaction the primary objective of this work is to extend the capability of the arbitrary lagrangian eulerian ale based strategy for solving fluid structure interaction problems this is driven by the fact that the ale mesh movement techniques will not be able to treat problems in which fluid structure interface experiences large motion in addition for certain problems the need arises to capture accurately flow features such as a region with high gradients of the solution variables this can be achieved by incorporating an adaptive remeshing procedure into the solution strategy as in our previous works comput methods appl mech eng 2006 195 1633 1666 comput methods appl mech eng 2006 195 5754 5779 here the fluid flow is governed by the incompressible navier stokes equations and modelled by using stabilized low order velocity pressure finite elements the motion of the fluid domain is accounted for by an arbitrary lagrangian eulerian ale strategy the flexible structure is represented by means of appropriate standard finite element formulations while the motion of the rigid body is described by rigid body dynamics for temporal discretization of both fluid and solid bodies the discrete implicit generalized method is employed the resulting strongly coupled set of non linear equations is then solved by means of a novel partitioned solution procedure which is based on the newton raphson methodology and incorporates full linearization of the overall incremental problem within the adaptive solution strategy the quality of fluid mesh and the solution quality indicator are evaluated regularly and compared against the appropriate remeshing criteria to decide whether a remeshing step is required the adaptive remeshing procedure follows closely the standard computational procedure in which the adaptive remeshing process produces a mesh that can capture salient features of the flow field for the problems under consideration in this work the motion of the fluid boundary very often results in boundaries with very high curvatures and a fluid domain that contain areas with small cross sections to be able to generate meshes that give result with acceptable accuracy these local geometrical features need to be included in determining the element density distribution the numerical examples demonstrate the robustness and efficiency of the methodology copyright 2007 john wiley sons ltd

exploration of the validity of the two dimensional sagittal plane assumption in modeling the standing long jump most previous standing long jump studies have been based on the assumption of two dimensional sagittal plane motion with bilateral symmetry the purpose of this study was to investigate the validity of this assumption standing long jump trials were collected using six adult male participants each participant stood with a foot on each of two force plates and performed eight standing long jumps for maximal distance inverse dynamics analyses were performed for two dimensional 2d and three dimensional 3d models and joint moments powers and work values were compared the differences between these models with respect to the validity of the common planar jumping assumption were analyzed good agreement was observed between 2d and 3d methods for the lower body with minimal differences in sagittal plane moments power and work for the ankle knee and lower back there were significant but relatively small differences in the sagittal plane kinematics and kinetics at the hip for the upper body the results contradicted the sagittal plane assumption in that significant moments and power were generated about the abduction adduction axis of the shoulder and a similar amount of work was performed about both abduction adduction and flexion extension axes of the shoulder the elbow also showed significant differences in power and work these results indicate that an assumption of planar motion should be sufficient for many studies of the standing long jump that only examine lower body movement however for studies that include upper body motion diagnosing injury risk or investigating gender differences a 3d model may be more appropriate

possible generalization of boltzmann gibbs statistics with the use of a quantity normally scaled in multifractals a generalized form is postulated for entropy namelys q k 1 i 1 w p i q q 1 whereq characterizes the generalization andp i are the probabilities associated withw microscopic configurations w the main properties associated with this entropy are established particularly those corresponding to the microcanonical and canonical ensembles the boltzmann gibbs statistics is recovered as theq 1 limit

generalized log likelihood functions and bregman divergences based on a two parameter generalization of gauss law of error a generalized log likelihood is related to a bregman divergence this relation is a two parameter generalization of the well known relation between log likelihood and kullback leibler divergence

role of arm motion in the standing long jump the role of arm motion on the performance of the standing long jump was investigated three males performed a series of jumps with free jfa and with restricted jra arm motion to determine if arm swing improves jumping distance the subjects jumped off a force platform and the motion of the body segments were recorded with a four camera passive motion capture system jumping performance was defined as the horizontal displacement of the toe between the initial and landing td positions the subjects jumped 21 2 further on an average with arm movement 2 09 0 03 m than without 1 72 0 03 m seventy one percent of the increase in performance in jfa was attributable to a 12 7 increase in the take off to velocity of the center of gravity cg increases in the horizontal displacement of the cg before to and in the horizontal position of the toe with respect to the cg at td accounted for the remaining 29 of the improvement in jumping distance the added balance and control provided by the arms throughout the jumping motion contributed to performance improvement in jfa the subjects were able to remedy excessive forward rotation about the cg by swinging the arms backwards during the flight phase without the freedom to swing the arms during flight the subjects had to eliminate any excessive forward rotation while still in contact with the ground this tendency in jra was manifest in the premature decline in the vertical ground reaction force vgrf and the development of a counterproductive backward rotating moment about the cg just before to

reduced symmetric models for modal analysis of internal structural acoustic and hydroelastic sloshing systems abstract it is proposed to investigate several variational formulations for modal analysis of bounded fluid structure systems taking into account in particular compressibility effects in the fluid for internal vibroacoustic problems either gravity effects in the context of an incompressible fluid for hydroelastic sloshing interaction problems appropriate reduced symmetric matrix models are constructed using zero frequency static solutions of the fluid in this respect attention is paid to the behaviour of the fluid structure equations with regard to their validity for zero frequency static limit

a reduction method for structure acoustic and poroelastic acoustic problems using interface dependent lanczos vectors a reduction method is proposed for analysing structure acoustic and poroelastic acoustic problems within a finite element framework this includes systems consisting of an acoustic fluid domain coupled to a flexible structural domain and or a porous sound absorbing material domain the studied problem is reduced by dividing the system into a number of physical subdomains a set of basis vectors is derived for each of these subdomains including both normal modes and interface dependent vectors that take account of the influence of connecting subdomains the method is verified in two numerical examples using the proposed method for both solving the structure acoustic eigenvalue problem and performing a frequency response analysis in an acoustic cavity with one wall covered by porous material c 2005 elsevier b v all rights reserved less

an improved interface element with variable nodes for non matching finite element meshes extensive improvements of the interface element method iem are proposed for the efficient treatment of non matching finite element meshes our approach enables us to establish the master element via the moving least square mls approximation and so to remove the cumbersome process of constructing interface elements the values of shape functions and their derivatives are therefore mapped from the master element as in the conventional finite element method for the assurance of convergence and compatibility condition a patch test is demonstrated through several examples of 2d linear elasticity the convergence rate is compared between the present interface element and the previous version

topology optimization for stationary fluid structure interaction problems using a new monolithic formulation this paper outlines a new procedure for topology optimization in the steady state fluid structure interaction fsi problem a review of current topology optimization methods highlights the difficulties in alternating between the two distinct sets of governing equations for fluid and structure dynamics hereafter the fluid and structural equations respectively and in imposing coupling boundary conditions between the separated fluid and solid domains to overcome these difficulties we propose an alternative monolithic procedure employing a unified domain rather than separated domains which is not computationally efficient in the proposed analysis procedure the spatial differential operator of the fluid and structural equations for a deformed configuration is transformed into that for an undeformed configuration with the help of the deformation gradient tensor for the coupling boundary conditions the divergence of the pressure and the darcy damping force are inserted into the solid and fluid equations respectively the proposed method is validated in several benchmark analysis problems topology optimization in the fsi problem is then made possible by interpolating young s modulus the fluid pressure of the modified solid equation and the inverse permeability from the damping force with respect to the design variables

a symmetric finite element formulation for acoustic fluid structure interaction analysis a symmetric finite element formulation for coupled acoustic vibration between a fluid and a structure is proposed the fluid is described by the pressure and a displacement potential the derivation of the finite element formulation is based on the weak solution of conservation of mass and linear momentum and on the galerkin method numerical results and analytical results show good agreement

a simple explicit implicit finite element tearing and interconnecting transient analysis algorithm summary a simple explicit implicit finite element tearing and interconnecting feti algorithm afeti ei algorithm is presented for partitioned transient analysis of linear structural systems the present algorithm employs two decompositions first the total system is partitioned via spatial or domain decomposition to obtain the governing equations of motions for each partitioned domain second for each partitioned subsystem the governing equations are modally decomposed into the rigid body and deformational equations the resulting rigid body equations are integrated by an explicit integrator for its stability is not affected by step size restriction on account of zero frequency contents 0 the modally decomposed partitioned deformation equations of motion are integrated by an unconditionally stable implicit integration algorithm it is shown that the present afeti ei algorithm exhibits unconditional stability and that the resulting interface problem possesses the same solution matrix profile as the basic feti static problems the present simple dynamic algorithm as expected falls short of the performance of the feti dp but offers a similar performance of implicit two level feti d algorithm with a much cheaper coarse solver hence its simplicity may offer relatively easy means for conducting parallel analysis of both static and dynamic problems by employing the same basic scalable feti solver especially for research mode numerical experiments copyright 2011 john wiley sons ltd

free vibration of a partially liquid filled and submerged horizontal cylindrical shell abstract the dynamic characteristics i e natural frequencies and mode shapes of a partially filled and or submerged horizontal cylindrical shell are examined in this investigation it is assumed that the fluid is ideal and fluid forces are associated with inertial effects only namely the fluid pressure on the wetted surface of the structure is in phase with the structural acceleration the in vacuo dynamic characteristics of the cylindrical shell are obtained using standard finite element software in the wet part of the analysis it is assumed that the shell structure preserves its in vacuo mode shapes when in contact with the contained and or surrounding fluid and that each mode shape gives rise to a corresponding surface pressure distribution of the shell the fluid structure interaction effects are calculated in terms of generalized added masses using a boundary integral equation method together with the method of images in order to impose an appropriate boundary condition on the free surface to assess the influence of the contained and or surrounding fluid on the dynamic behaviour of the shell structure the wet natural frequencies and associated mode shapes were calculated and compared with available experimental measurements

a virtual element method for the acoustic vibration problem we analyze in this paper a virtual element approximation for the acoustic vibration problem we consider a variational formulation relying only on the fluid displacement and propose a discretization by means of mathrm h mathrm div h div virtual elements with vanishing rotor under standard assumptions on the meshes we show that the resulting scheme provides a correct approximation of the spectrum and prove optimal order error estimates with this end we prove approximation properties of the proposed virtual elements we also report some numerical tests supporting our theoretical results

vibration analysis of fluid solid systems using a finite element displacement formulation this report presents a finite element solution for the vibration interaction between an inviscid fluid and a solid the equation of motion governing the inviscid fluid is expressed in terms of the displacements reduced integration is used when computing the element stiffness matrix contributed by the fluid in addition a projection is used on the element mass matrix in order to remove the spurious modes which result from the use of reduced integration

non linear sloshing in partially liquid filled containers with baffles a finite element method is used for computing the non linear sloshing response of liquid in a two dimensional rigid rectangular tank with rigid baffles the potential formulation is considered for the liquid domain and a mixed eulerian langrangian scheme is adopted the solution is obtained by the galerkin method the fourth order runge kutta method is employed to advance the solution in the time domain a regridding technique is applied to the free surface of the liquid which effectively eliminates the numerical instabilities without the use of artificial smoothing through the comparison with the available results for the rectangular tank without baffle the validity of the present formulation is checked and then extended to the solution of tanks with rigid baffles the effects of baffle parameters such as position dimension and numbers on the non linear sloshing response are examined the present numerical solution procedure is also applied to the non linear sloshing problems in a circular cylindrical container with annular baffle copyright 2006 john wiley sons ltd

mathematical analysis of a finite element method without spurious solutions for computation of dielectric waveguides in this paper we propose a finite element method to compute dielectric waveguides which does not present spurious solutions in addition to a theoretical analysis showing the good stability properties of this method we give numerical results for some classical test problems

linearized formulation for fluid structure interaction application to the linear dynamic response of a pressurized elastic structure containing a fluid with a free surface abstract to control the linear vibrations of structures partially filled with liquids is of prime importance in various industries such as aerospace naval civil and nuclear engineering it is proposed here to investigate a linearized formulation adapted to a rational computation of the vibrations of such coupled systems its particularity is to be fully lagrangian since it considers the fluid displacement field with respect to a static equilibrium configuration as the natural variable describing the fluid motion as classically done in structural dynamics as the coupled system considered here is weakly damped in the low frequency domain low modal density the analysis of the vibrations of the associated undamped conservative system constitutes the main objective of this paper one originality of the present formulation is to take into account the effect of the pressurization of the tank on the dynamics of the system particularly in the case of a compressible liquid we propose here a new way of deriving the linearized equations of the coupled problem involving a deformable structure and an inner inviscid liquid with a free surface a review of the classical case considering a heavy incompressible liquid is followed by an application to the new case involving a light compressible liquid a solution procedure in the frequency domain is proposed and a numerical discretization using the finite element method is discussed in order to reduce the computational costs an appropriate reduced order matrix model using modal synthesis approach is also presented

a parallel hp fem infrastructure for three dimensional structural acoustics this paper describes a parallel three dimensional numerical infrastructure for the solution of a wide range of time harmonic problems in structural acoustics and vibration high accuracy and rate of error convergence in the mid frequency regime is achieved by the use of hp finite and infinite element approximations the infrastructure supports parallel computation in both single and multi frequency settings multi frequency solves utilize concurrent factoring of the frequency dependent linear algebraic systems and are naturally scalable scalability of large scale single frequency problems is realized by using feti dp an iterative domain decomposition scheme numerical examples are presented to cover applications in vibratory response of fluid filled elastic structures as well as radiation and scattering from elastic structures submerged in an infinite acoustic medium we demonstrate both the numerical accuracy as well as parallel scalability of the infrastructure in terms of problem parameters that include wavenumber and number of frequencies polynomial degree of finite infinite element approximations as well as the number of processors scalability and accuracy is evaluated for both single and multiple frequency sweeps on four high performance parallel computing platforms sgi altix sgi origin ibm p690 sp and linux cluster results show good performance on shared as well as distributed memory architecture copyright 2006 john wiley sons ltd

finite element analysis of pressure formulation of the elastoacoustic problem in this paper we analyze the non symmetric pressure displacement formulation of the elastoacoustic vibration problem and show its equivalence with the symmetric stiffness coupling formulation we introduce discretizations for these problems based on lagrangian finite elements we show that both formulations are also equivalent at discrete level and prove optimal error estimates for eigenfunctions and eigenvalues both formulations are rewritten such as to be solved with a standard matlab eigensolver we report numerical results comparing the efficiency of the methods over some test examples

partitioned formulation of internal and gravity waves interacting with flexible structures abstract this paper presents a partitioned modeling of internal and gravity fluid waves that interact with flexible structures the governing interaction model consists of three completely partitioned entities fluid model structural model and interface model that acts as an internal constraint on the fluid structure interface boundary thus the proposed partitioned multi physics modeling can employ two completely modular fluid and structure software modules plus an interface solver hence amenable to partitioned solution algorithms the interface discretization can exploit the nonmatching interface algorithm previously developed via the method of localized lagrange multipliers also noted is that the present fluid model can make use of widely available finite element software for standard poisson type problems

the order of convergence of eigenfrequencies in finite element approximations of fluid structure interaction problems in this paper we prove a double order for the convergence of eigenfrequencies in fluid structure vibration problems we improve estimates given recently for compressible and incompressible fluids to do this we extend classical results on finite element spectral approximation to nonconforming methods for noncompact operators

orthogonality of wet modes in coupled vibration abstract the orthogonality property of wet modes for arbitrary storage vessels filled or partially filled with compressible fluid is investigated by means of love s thin shell equations and a linear potential flow theory the proof shows that the wet modes do possess the orthogonality property for all kinds of fluid filled tanks with zero boundary energy conditions when incompressible fluid is considered and the effect of free surface waves is neglected it is pointed out that there is another kind of orthogonality relationship among wet modes when a compressible fluid is contained or and the effect of the free surface waves is considered

an extended finite element method lagrange multiplier based approach for fluid structure interaction abstract this paper presents a new fixed grid fluid structure interaction scheme that can be applied to the interaction of most general structures with incompressible flow it is based on an extended finite element method xfem based strategy the extended eulerian fluid field and the lagrangian structural field are partitioned and iteratively coupled using lagrange multiplier techniques for non matching grids the approach allows the simulation of the interaction of thin and bulky structures exhibiting large deformations finally qualitative examples and a benchmark computation demonstrate key features and accuracy of the method

interactions of an elastic solid with a viscous fluid eigenmode analysis abstract in this paper we study the interaction of a viscous fluid with an elastic solid of particular interest are the eigenmodes of the coupled system starting from the navier stokes equations for the fluid and the linear elasticity equations for the solid we derive the linear equations governing the motion of the system it is shown how a variational formulation of the problem may be obtained by re scaling the displacement unknowns the finite element technique is then used to discretize the equations the resulting quadratic eigenvalue problem is solved by means of an inverse iteration procedure

a new approach to the development of automatic quadrilateral mesh generation a methodology for the automatic mesh generation of quadrilateral elements is proposed the methodology is based on the facts that i a region can always be subdivided entirely into quadrilaterals if the polygon which forms the boundary of the region has an even number of sides ii a quadrilateral can be formed by two triangles which share a common side by taking advantage of the techniques developed in an existing automatic triangular mesh generator quadrilateral meshes can be generated according to the distribution of user specified element size over the domain of interest in particular an automatic quadrilateral mesh generator based on the advancing front technique for triangular mesh generation1 is described techniques to improve the quality of the generated quadrilateral meshes are introduced the robustness and versatility of the mesh generator are demonstrated by a variety of examples

explicit synchronous partitioned algorithms for interface problems based on lagrange multipliers abstract traditional explicit partitioned schemes exchange boundary conditions between subdomains and can be related to iterative solution methods for the coupled problem as a result these schemes may require multiple subdomain solves acceleration techniques or optimized transmission conditions to achieve sufficient accuracy and or stability we present a new synchronous partitioned method derived from a well posed mixed finite element formulation of the coupled problem we transform the resulting differential algebraic equation dae to a hessenberg index 1 form in which the algebraic equation defines the lagrange multiplier as an implicit function of the states using this fact we eliminate the multiplier and reduce the dae to a system of explicit odes for the states explicit time integration both discretizes this system in time and decouples its equations as a result the temporal accuracy and stability of our formulation are governed solely by the accuracy and stability of the explicit scheme employed and are not subject to additional stability considerations as in traditional partitioned schemes we establish sufficient conditions for the formulation to be well posed and prove that classical mortar finite elements on the interface are a stable choice for the lagrange multiplier we show that in this case the condition number of the schur complement involved in the elimination of the multiplier is bounded by a constant the paper concludes with numerical examples illustrating the approach for two different interface problems

a nonconforming finite element method for a two dimensional curl curl and grad div problem a numerical method for a two dimensional curl curl and grad div problem is studied in this paper it is based on a discretization using weakly continuous p 1 vector fields and includes two consistency terms involving the jumps of the vector fields across element boundaries optimal convergence rates up to an arbitrary positive epsilon in both the energy norm and the l 2 norm are established on graded meshes the theoretical results are confirmed by numerical experiments

a variational approach for coupling kinematically incompatible structural models abstract in this work an extended variational framework aimed at properly addressing the coupling of kinematically incompatible structural models is presented the main goal is to variationally state the theoretical bases to deal with the coupling of structural models with different dimensionality in this approach the coupling conditions are naturally derived from the governing variational principle formulated at the continuous level furthermore by means of a real parameter we manage to build different continuous mechanical models that have different mechanical and mathematical features in particular the coupling of 3d solid models and 2d shell models under naghdi hypothesis is treated by introducing the corresponding kinematical assumptions into the proposed extended variational principle also the coupling between 3d solid and 1d beam models under bernoulli hypothesis is presented moreover for the continuous 3d 2d coupled problem a numerical approximation is addressed via the finite element method and some numerical results are given comparing the responses of the system when the discrete model varies by changing the value of the parameter finally a discussion comprising the main conclusions of the work is given

deformed logarithms and entropies by solving a differential functional equation inposed by the maxent principle we obtain a class of two parameter deformed logarithms and construct the corresponding two parameter generalized trace form entropies generalized distributions follow from these generalized entropies in the same fashion as the gaussian distribution follows from the shannon entropy which is a special limiting case of the family we determine the region of parameters where the deformed logarithm conserves the most important properties of the logarithm and show that important existing generalizations of the entropy are included as special cases in this two parameter class

non linear kinetics underlying generalized statistics abstract the purpose of the present effort is threefold firstly it is shown that there exists a principle that we call kinetical interaction principle kip underlying the non linear kinetics in particle systems independently on the picture kramers boltzmann used to describe their time evolution secondly the kip imposes the form of the generalized entropy associated to the system and permits to obtain the particle statistical distribution both as stationary solution of the non linear evolution equation and as the state which maximizes the generalized entropy thirdly the kip allows on one hand to treat all the classical or quantum statistical distributions already known in the literature in a unifying scheme and on the other hand suggests how we can introduce naturally new distributions finally as a working example of the approach to the non linear kinetics here presented a new non extensive statistics is constructed and studied starting from a one parameter deformation of the exponential function holding the relation f x f x 1

analysis of a finite element method for pressure potential formulation of elastoacoustic spectral problems a finite element method to approximate the vibration modes of a structure enclosing an acoustic fluid is analyzed the fluid is described by using simultaneously pressure and displacement potential variables whereas displacement variables are used for the solid a mathematical analysis of the continuous spectral problem is given the problem is discretized on a simplicial mesh by using piecewise constant elements for the pressure and continuous piecewise linear finite elements for the other fields error estimates are settled for approximate eigenvalues and eigenfrequencies finally implementation issues are discussed

dynamics of structures coupled with elastic media a review of numerical models and methods abstract this paper reviews issues and developments in the field of structure environment interaction problems in which the environment is an elastic body possibly unbounded it covers in particular the fields of soil structure interaction ground borne noise and vibration emitted by transportation systems and wave diffraction by obstacles in an elastic medium the general setting for a linear bounded structure coupled to an unbounded linear environment through a bounded interface is first recalled and the domain decomposition technique classically used for its description is put up extensions for the cases of nonlinear structure and uncertain environment are then discussed finally the ongoing research in the fields of unbounded interface moving interface and multiple interfaces are reviewed and summarized

an eulerian lagrangian method for fluid structure interaction based on level sets abstract we describe a method for fluid structure interaction with the interface and free surfaces defined by level sets the fluid is treated by an eulerian mesh whereas the solid or structure by a lagrangian mesh the level set method provides a compact framework for writing the weak form and for developing and computing the discretized equations lagrange multiplier methods and penalty methods are used to couple the fluid and structure results are presented for a few compressible fluid problems representative of high pressure waves

finite element analysis for a pressure stress formulation of a fluid structure interaction spectral problem the aim of this paper is to analyze an elastoacoustic vibration problem employing a dual mixed formulation in the solid domain the cauchy stress tensor and the rotation are the primary variables in the elastic structure while the standard pressure formulation is considered in the acoustic fluid the resulting mixed eigenvalue problem is approximated by a conforming galerkin scheme based on the lowest order lagrange and arnold falk winther finite element subspaces in the fluid and solid domains respectively we show that the scheme provides a correct approximation of the spectrum and prove quasi optimal error estimates finally we report some numerical experiments

finite element computation of the vibration modes of a fluid solid system abstract in this paper we solve the interior elastoacoustic problem by a finite element method which does not present spurious or circulation modes for nonzero frequencies it consists of classical triangular lagrangian elements for the solid and lowest order triangular raviart thomas elements for the fluid transmission conditions at the fluid solid interface are taken into account in a weak sense numerical results for some test examples are presented which show the good performance of the proposed methodology

the d alembert lagrange principal equations and applications to floating flexible systems this paper addresses the dynamics and quasi statics of floating flexible structures as well as extensions to unconstrained substructures and partitions of coupled mechanical systems the principal solution is defined as the state of self equilibrated forces obtained as the particular solution of the rigid motion and interface equilibrium equations this solution is independent of the stress strain constitutive properties as well as of the compatibility equations for statically determinate systems the principal solution is the final force solution for statically indeterminate systems the correction due to flexibility and compatibility is orthogonal to the principal solution the formulation is done in the context of d alembert s principle which supplies the d alembert lagrange principal equations for floating bodies these are obtained by summation of virtually working forces and moments acting on the floating systems applications of this approach are demonstrated on a set of dynamic and quasi static example problems of increasing generality linkage to variational principles with an interface potential is eventually discussed as providing the theoretical foundation for handling interacting semi discrete subsystems linked by node collocated lagrange multipliers copyright 2008 john wiley sons ltd

a technique for the systematic choice of admissible functions in the rayleigh ritz method abstract a simple and systematic choice of admissible functions which are the eigenfunctions of the closest simple problem extracted from the one considered is proposed the extracted problem must be less constrained than the original one in other words it must be a problem where some constraints or other complications e g added masses are eliminated elastic constraints replace the eliminated rigid ones the convergence is also analyzed this approach has practical applications when it is possible to extract a problem with eigenfunctions expressed in closed form it also allows a very simple calculation of the potential energy of the system solutions for several cases involving beams are given in order to show the power of the method application of the method to circular plates and shells is also addressed

sloshing in partially filled liquid containers numerical and experimental study for 2 d problems abstract this paper deals with the numerical and experimental studies of sloshing of liquid in partially filled prismatic containers subjected to external excitation meshless local petrov galerkin mlpg method is used for computing the nonlinear sloshing response of liquid in a two dimensional rigid prismatic tank at every instant of time velocity potential is computed at each node and the nodal positions are updated a local symmetric weak form lswf for nonlinear sloshing of liquid is developed and a truly meshless method based on lswf and moving least squares mls approximation is presented for the solution of laplace equation with the requisite boundary conditions an experimental set up is also designed to study the behavior of liquid sloshing in partially filled prismatic tank the resulting slosh heights for various excitation frequencies and amplitudes are compared with the data obtained from the numerical studies the numerical results are close to that obtained experimentally and little variations in the data are due to ineptness of the experimental set up and the input parameters