explicit time domain transmitting boundary for dam reservoir interaction analysis an explicit time domain transmitting boundary for the analysis of dam reservoir interactions is presented this transmitting boundary is a semi analytical solution of the governing wave equation of the far field of the reservoir by using this transmitting boundary the radiation condition and water compressibility can readily be incorporated in the time domain analysis of dam reservoir systems therefore the finite element method can be used to accurately analyse a dam reservoir system including the semi infinite reservoir while maintaining its efficiency in time domain analysis numerical results have excellent agreement with the available analytical solution results also show that the proposed explicit transmitting boundary is more efficient computationally than the implicit transmitting boundary presented by tsai and lee

adaptive kernel search a heuristic for solving mixed integer linear programs abstract we introduce adaptive kernel search aks a heuristic framework for the solution of general mixed integer linear programs mips aks extends and enhances kernel search a heuristic framework that has been shown to produce high quality solutions for a number of specific combinatorial optimization problems in a short amount of time aks solves a sequence of carefully constructed restricted mips using a commercial mip solver the computational effort required to solve the first restricted mip guides the construction of the subsequent mips the restricted mips are constructed around a kernel which contains the variables that are presumably non zero in an optimal solution computational results for a set of 137 instances show that aks significantly outperforms other state of the art heuristics for solving mips aks also compares favorably to cplex and offers more flexibility to trade off solution quality and computing time

a new class of functions for measuring solution integrality in the feasibility pump approach mixed integer optimization is a powerful tool for modeling many optimization problems arising from real world applications finding a first feasible solution represents the first step for several mixed integer programming mip solvers the feasibility pump is a heuristic for finding feasible solutions to mixed integer linear programming milp problems which is effective even when dealing with hard mip instances in this work we start by interpreting the feasibility pump as a frank wolfe method applied to a nonsmooth concave merit function then we define a general class of functions that can be included in the feasibility pump scheme for measuring solution integrality and we identify some merit functions belonging to this class we further extend our approach by dynamically combining two different merit functions finally we define a new version of the feasibility pump algorithm which includes the original version of the feasibility pump as a special case and we present computational results on bi

the cohomology rings of moduli spaces of bundles over riemann surfaces the cohomology of the moduli space ji n d of semistable bundles of coprime rank n and degree d over a fixed riemann surface m of genus g 2 has been much studied over the last two decades and a great deal is known about it it is known that the cohomology has no torsion 2 the betti numbers have been computed using various different methods 2 5 11 and a set of generators for the cohomology ring is known 2 the purpose of this article is to provide a method of deciding when an expression in these generators is a relation and in particular when the rank n is two to prove two conjectures about the relations between the generators due to mumford and to newstead and ramanan newstead and ramanan conjectured that certain relations hold among the generators whereas mumford conjectured that a certain set of relations is a complete set in fact the conjecture of newstead and ramanan has two parts the first of which was proved by gieseker in 1982 4 the second part of their conjecture which is the part examined in this article was given an independent proof recently by thaddeus 19 who has a very different method of obtaining information about the relations in the cohomology ring the computation of the betti numbers of the moduli spaces i n d in 2 stimulated a general method of computing betti numbers of quotients in the sense of mumford s geometric invariant theory 14 of nonsingular complex projective varieties by complex reductive group actions see 8 9 10 similarly the ideas applied in this article to finding generators and relations for the cohomology rings of the moduli spaces i n d also lead to an analogous method of obtaining generators and relations for the rational cohomology rings of geometric invariant theoretic quotients the first section provides background material on the cohomology of the moduli spaces i n d in the second section mumford s conjecture is proved when the rank n is two the method could in principle be used to decide whether the conjecture is true for rank n 2 but appears to become significantly more complicated in the general case the third section gives a method for deciding when an expression in the generators is a relation and the fourth

on quantum gauge theories in two dimensions two dimensional quantum yang mills theory is studied from three points of view i by standard physical methods ii by relating it to the largek limit of three dimensional chern simons theory and two dimensional conformal field theory iii by relating its weak coupling limit to the theory of reidemeister ray singer torsion the results obtained from the three points of view agree and give formulas for the volumes of the moduli spaces of representations of fundamental groups of two dimensional surfaces

geometric quantization and multiplicities of group representations the heisenberg uncertainty principle says that it is impossible to determine simultaneously the position and momentum of a quantum mechanical particle this can be rephrased as follows the smallest subsets of classical phase space in which the presence of a quantum mechanical particle can be detected are its lagrangian submanifolds for this reason it makes sense to regard the lagrangian submanifolds of phase space as being its true points see weinstein 17 now let g be a compact lie group and g x x x a hamiltonian action of g on x see w for definitions it is well known that the fixed points of this action form a symplectic submanifold of x see for instance guillemin and sternberg 5 however what can one say about the fixed points of g we will show that they are also the points of a symplectic manifold xc this manifold is the marsden weinstein reduction of x with respect to the zero orbit in g and will be described in sect 2 it was introduced in a completely different context fl om ours by marsden and weinstein 12 problems in classical mechanics can often be reduced to the study of hamiltonian systems on symplectic manifolds and problems in quantum mechanics to the study of linear operators on hilbert space this fact has inspired a number of efforts to quantize symplectic geometry by devising schemes for associating hilbert space to symplectic manifolds the no go theorems of groenwald and van hove impose some embarrassing limitations on all such schemes however it seems to be a useful idea heuristically to think of every symplectic manifold x a ic 1 as being symbiotically associated with a hilbert space xq a t in such a way that the classical observables on the first space correspond to quantum observables on the second space the heuristics further suggests that if g is a group of symmetries of x la i j it should also be a group of symmetries of xq a tum in this heuristic spirit we will state the main conjecture of this paper

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

octane a new heuristic for pure 0 1 programs we propose a new heuristic for pure 0 1 programs which finds feasible integer points by enumerating extended facets of the octahedron the outer polar of the unit hypercube we give efficient algorithms to carry out the enumeration and we explain how our heuristic can be embedded in a branch and cut framework finally we present computational results on a set of pure 0 1 programs taken from miplib and other sources

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

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

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

solving zero one mixed integer programming problems using tabu search we describe a tabu search ts approach for solving general zero one mixed integer programming mip problems that exploits the extreme point property of zero one solutions specialized choice rules and aspiration criteria are identified for the problems expressed as functions of integer infeasibility measures and objective function values the first level ts mechanisms are then extended with advanced level strategies and learning we also look at probabilistic measures in this framework and examine how the learning tool target analysis ta can be applied to identify better control structures and decision rules computational results are reported on a portfolio of multiconstraint knapsack problems our approach is designed to solve thoroughly general 0 1 mip problems and thus contains no problem domain specific knowledge yet it obtains solutions for the multiconstraint knapsack problem whose quality rivals and in some cases surpasses the best solutions obtained by special purpose methods that have been created to exploit the special structure of these problems

boundary element acoustics fundamentals and computer codes fundamentals of linear acoustics the helmholtz integral equation two dimensional problems three dimensional problems the normal derivative integral equation indirect variational boundary element method in acoustics acoustic eigenvalue analysis by boundary element methods time domain three dimensional analysis extended kirchhoff integral formulations

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

on a method for vibration analysis of viscous compressible fluid structure systems a fluid structure interaction formulation for viscous compressible fluid is under consideration the formulation involves finite element approximation of linearized navier stokes equations and response determination made by means of modal superposition analysis standard and simplified schemes of the viscous compressible fluid structure interaction problem solution are developed the schemes are based on the frequency condensation method of a complex eigenvalue problem solving free and forced oscillations of several fluid structure systems are studied by the standard and simplified schemes the analysis of the results obtained shows that the simplified scheme provides a saving of 90 of the computational time required to define oscillation of the structure with viscous compressible fluid in the lowest frequency range a certain influence of the fluid viscosity on the transient response of the fluid structure system is also demonstrated copyright 2004 john wiley sons ltd

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

intersection theory on the moduli space of curves and the matrix airy function we show that two natural approaches to quantum gravity coincide this identity is nontrivial and relies on the equivalence of each approach to kdv equations we also investigate related mathematical problems

transient sound fields from impacted plates comparison between numerical simulations and experiments a comparison between measured and simulated transient acoustic fields generated by a thin rectangular impacted steel plate is reported the plate vibration is modelled in the time domain using a finite difference scheme of second order in time and fourth order in space 2 4 scheme and the radiated acoustic pressure is obtained by solving numerically the rayleigh integral equation by using a simple boundary element method trapezoidal rule the simulated results are evaluated in the form of the spatial pressure distribution at times short after the impact excitation the measurements are performed using an optical method pulsed two reference beam holographic interferometry results in the form of 2 d projections of the acoustic pressure field are obtained and compared with the simulations a high degree of similarity is found between the measured and simulated sound fields

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

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

intersection numbers of polygon spaces we study the intersection ring of the space m 1 m of polygons in r 3 we find homology cycles dual to generators of this ring and prove a recursion relation in m the number of edges for their intersection numbers this result is an analog of the recursion relation appearing in the work of witten and kontsevich on moduli spaces of punctured curves and in the work of weitsman on moduli spaces of flat connections on two manifolds of genus g with m marked points based on this recursion formula we obtain an explicit expression for the computation of the intersection numbers of polygon spaces and use it in several examples among others we study the special case of equilateral polygon spaces where all i s are the same and compare our results with the expressions for these particular spaces that have been determined by kamiyama and tezuka finally we relate our explicit formula for the intersection numbers with the generating function for intersection pairings of the moduli space of flat connections of yoshida as well as with equivalent expressions for polygon spaces obtained by takakura and konno through different techniques

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

a heuristic for bilp problems the single source capacitated facility location problem abstract in the single source capacitated facility location problem sscflp each customer has to be assigned to one facility that supplies its whole demand the total demand of customers assigned to each facility cannot exceed its capacity an opening cost is associated with each facility and is paid if at least one customer is assigned to it the objective is to minimize the total cost of opening the facilities and supply all the customers in this paper we extend the kernel search heuristic framework to general binary integer linear programming bilp problems and apply it to the sscflp the heuristic is based on the solution to optimality of a sequence of subproblems where each subproblem is restricted to a subset of the decision variables the subsets of decision variables are constructed starting from the optimal values of the linear relaxation variants based on variable fixing are proposed to improve the efficiency of the kernel search framework the algorithms are tested on benchmark instances and new very large scale test problems computational results demonstrate the effectiveness of the approach the kernel search algorithm outperforms the best heuristics for the sscflp available in the literature it found the optimal solution for 165 out of the 170 instances with a proven optimum the error achieved in the remaining instances is negligible moreover it achieved on 100 new very large scale instances an average gap equal to 0 64 computed with respect to a lower bound or the optimum when available the variants based on variable fixing improved the efficiency of the algorithm with minor deteriorations of the solution quality

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

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

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

on the variation in the cohomology of the symplectic form of the reduced phase space is called the momentum mapping of the hamiltonian t action given 1 1 the condition 1 2 just means that t acts along the fibers of j for the basic definitions and properties of non commutative hamiltonian group actions see am the results of this paper can easily be extended to hamiltonian actions of arbitrary compact connected lie groups by applying our results to the action of its maximal toms and using the equivariance of the momentum mapping for some more details see the remarks at the end of sect 2 we will assume throughout this paper that the momentum map is proper that is j i u is compact for each compact subset u of t now let r be a regular value of j that is t j tmm t is surjective for all meye j 1 4 then ye is a smooth submanifold of m compact because

exploring relaxation induced neighborhoods to improve mip solutions given a feasible solution to a mixed integer programming mip model a natural question is whether that solution can be improved using local search techniques local search has been applied very successfully in a variety of other combinatorial optimization domains unfortunately local search relies extensively on the notion of a solution neighborhood and this neighborhood is almost always tailored to the structure of the particular problem being solved a mip model typically conveys little information about the underlying problem structure this paper considers two new approaches to exploring interesting domain independent neighborhoods in mip the more effective of the two which we call relaxation induced neighborhood search rins constructs a promising neighborhood using information contained in the continuous relaxation of the mip model neighborhood exploration is then formulated as a mip model itself and solved recursively the second which we call guided dives is a simple modification of the mip tree traversal order loosely speaking it guides the search towards nodes that are close neighbors of the best known feasible solution extensive computational experiments on very difficult mip models show that both approaches outperform default cplex mip and a previously described approach for exploring mip neighborhoods local branching with respect to several different metrics the metrics we consider are quality of the best integer solution produced within a time limit ability to improve a given integer solution of both good and poor quality and time required to diversify the search in order to find a new solution

finite element analysis of unbounded and incompressible fluid domains a finite element technique of analysing the hydrodynamic pressure resulting from the vibration of a structure submerged in an unbounded fluid domain is presented a suitable boundary condition is proposed for the surface where the unbounded fluid domain is truncated pressure is assumed to be the nodal unknown and the fluid is treated as being incompressible and inviscid the proposed method is computationally very efficient and its implementation in a finite element program is quite straightforward the efficiency of the method is demonstrated by analysing some two dimensional problems

the feasibility pump in this paper we consider the np hard problem of finding a feasible solution if any exists for a generic mip problem of the form min ctx ax b xj integer j trivially a feasible solution can be defined as a point x p x ax b that is equal to its rounding where the rounded point is defined by x j if j and x j otherwise and represents scalar rounding to the nearest integer replacing equal with as close as possible relative to a suitable distance function x suggests the following feasibility pump fp heuristic for finding a feasible solution of a given mip we start from any x p and define its rounding at each fp iteration we look for a point x p that is as close as possible to the current by solving the problem min x x p assuming x is chosen appropriately this is an easily solvable lp problem if x 0 then x is a feasible mip solution and we are done otherwise we replace by the rounding of x and repeat we report computational results on a set of 83 difficult 0 1 mips using the commercial software ilog cplex 8 1 as a benchmark the outcome is that fp in spite of its simple foundation proves competitive with ilog cplex both in terms of speed and quality of the first solution delivered interestingly ilog cplex could not find any feasible solution at the root node for 19 problems in our test bed whereas fp was unsuccessful in just 3 cases

time harmonic solution for acousto elastic interaction with controllability and spectral elements the classical way of solving the time harmonic linear acousto elastic wave problem is to discretize the equations with finite elements or finite differences this approach leads to large scale indefinite complex valued linear systems for these kinds of systems it is difficult to construct efficient iterative solution methods that is why we use an alternative approach and solve the time harmonic problem by controlling the solution of the corresponding time dependent wave equation in this paper we use an unsymmetric formulation where fluid structure interaction is modeled as a coupling between pressure and displacement the coupled problem is discretized in space domain with spectral elements and in time domain with central finite differences after discretization exact controllability problem is reformulated as a least squares problem which is solved by the conjugate gradient method

numerical study and comparison of alternative time discretization schemes for an ultrasonic guided wave propagation problem coupled with fluid structure interaction abstract discretization is a crucial step in the numerical treatment of coupled multiphysics problems in the present paper we focus on the numerical solution of ultrasonic guided waves ugws propagation problem coupled with fluid structure interaction we track ugws propagation through fluid solid and their interface where the structure is in motion discretization is done via a finite element method for this we follow the rothe method in which discretization in time is followed by space discretization solving the resulting problem according to the monolithic approach further we provide a systematic analysis of alternative discretization schemes time steps and mesh refinements specifically we contrast one first order time discretization scheme cf backward euler and three second order schemes cf crank nicolson shifted crank nicolson and fractional step first we establish the robustness of the convergence result second we estimate the experimental order of convergence for alternative schemes and space time discretization combinations

hyperpolygon spaces and moduli spaces of parabolic higgs bundles abstract given an n tuple of positive real numbers we consider the hyperpolygon space x the hyperkahler quotient analogue to the kahler moduli space of polygons in r 3 we prove the existence of an isomorphism between hyperpolygon spaces and moduli spaces of stable rank 2 holomorphically trivial parabolic higgs bundles over c p 1 with fixed determinant and trace free higgs field this isomorphism allows us to prove that hyperpolygon spaces x undergo an elementary transformation in the sense of mukai as crosses a wall in the space of its admissible values we describe the changes in the core of x as a result of this transformation as well as the changes in the nilpotent cone of the corresponding moduli spaces of parabolic higgs bundles moreover we study the intersection rings of the core components of x in particular we find generators of these rings prove a recursion relation in n for their intersection numbers and use it to obtain explicit formulas for the computation of these numbers using our isomorphism we obtain similar formulas for each connected component of the nilpotent cone of the corresponding moduli spaces of parabolic higgs bundles thus determining their intersection rings as a final application of our isomorphism we describe the cohomology ring structure of these moduli spaces of parabolic higgs bundles and of the components of their nilpotent cone

arch dam fluid interactions by fem bem and substructure concept arch dams can be conveniently analysed by the finite element method for dam fluid interaction problems the fluid domain may be more conveniently handled by the boundary element method as a substructure first before connecting to the dam substructure the added mass matrix calculated from the fluid domain is symmetrized and lumped first so that the banded and symmetrical characteristics of the finite element method are retained in the boundary element formulation a mirror image method and quadratic elements are used for computational efficiency and accuracy the strong singular terms are handled by using a solution which satisfies the governing equation and the free surface boundary condition infinite boundary conditions at the upstream of the reservoir can be reasonably approximated from the fundamental solution with accurate results if the interior pressure distribution in the fluid domain is neglected numerical solutions on hydrodynamic pressure distribution and the natural frequencies of the dam reservoir system with various water levels are obtained and compared with available analytical and experiment results

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

kernel search an application to the index tracking problem abstract in this paper we study the problem of replicating the performances of a stock market index i e the so called index tracking problem and the problem of out performing a market index i e the so called enhanced index tracking problem we introduce mixed integer linear programming milp formulations for these two problems furthermore we present a heuristic framework called kernel search we analyze and evaluate the behavior of several implementations of the kernel search framework to the solution of the index tracking problem we show the effectiveness and efficiency of the framework comparing the performances of these heuristics with those of a general purpose solver the computational experiments are carried out using benchmark and newly created instances

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

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

an optimization based approach for solving a time harmonic multiphysical wave problem with higher order schemes this study considers developing numerical solution techniques for the computer simulations of time harmonic fluid structure interaction between acoustic and elastic waves the focus is on the efficiency of an iterative solution method based on a controllability approach and spectral elements we concentrate on the model in which the acoustic waves in the fluid domain are modeled by using the velocity potential and the elastic waves in the structure domain are modeled by using displacement traditionally the complex valued time harmonic equations are used for solving the time harmonic problems instead of that we focus on finding periodic solutions without solving the time harmonic problems directly the time dependent equations can be simulated with respect to time until a time harmonic solution is reached but the approach suffers from poor convergence to overcome this challenge we follow the approach first suggested and developed for the acoustic wave equations by bristeau glowinski and periaux thus we accelerate the convergence rate by employing a controllability method the problem is formulated as a least squares optimization problem which is solved with the conjugate gradient cg algorithm computation of the gradient of the functional is done directly for the discretized problem a graph based multigrid method is used for preconditioning the cg algorithm

symmetrization procedure for structure fluid cavity system involving pseudostatic correction this paper deals with a pressure displacement formulation based on the finite element method of an elastoacoustic coupling problem since directly solving the resulting system iscpu intensive for large models the solution is usually based on only a few uncoupled structural modes in vacuum and rigid cavity modes however this classical pressuredisplacement formulation leads to nonsymmetric eigenvalue problems furthermore if this method is accurate for weak coupling models significant errors occur when the truncated modes are coupled to the ones used in the analysis the present paper suggests a method combining the pseudostatic correction of the truncated modes in modal analysis with a symmetrization technique of the eigenvalue problems it allows the calculation of the real coupled modes and frequencies as well as the computation of an accurate elastoacoustic response even for the strong coupling of a structure with a heavy fluid liquid it is less cpu expensive than the classical method because it leads to a diagonalized system

a numerical method for vibro acoustic problems with incompatible finite element meshes using b spline functions this paper describes a new method for computing fluid structure coupling with incompatible finite element meshes using uniform cubic b spline functions ucbfs a modal approach is used which has the advantage of computing the individual structural and fluid mode shapes using independent meshes in order to compute the fluid structure coupling for the incompatible meshes it is necessary to interpolate the structure and fluid mode shapes over a common geometric mesh this mesh is defined by the shell itself which is also interpolated by ucbf using a minimum number of geometric control nodes new structural and fluid meshes are first derived from the geometric mesh by defining two different element multiplicities an extrapolation algorithm is then developed to deduce the values of fluid and structure functions displacement and pressure over the two new meshes the ucbfs are finally used to interpolate mode shapes of fluid and structure from the two previous meshes into a common mesh having the two new functions on the same common mesh provides the fluid structure coupling for incompatible meshes the method is illustrated for 2 d and 3 d coupled problems corresponding to shells of revolution plates and 3 d shells