adaptive fractionally spaced blind cma equalization excess mse the performance of the constant modulus algorithm cma a reference algorithm for adaptive blind equalization is studied in terms of the excess mean square error emse due to the nonvanishing step size of the gradient descent algorithm an analytical approximation of emse is provided emphasizing the effect of the constellation size and resulting in design guidelines

a new approach to multipath correction of constant modulus signals an adaptive digital filtering algorithm that can compensate for both frequency selective multipath and interference on constant envelope modulated signals is presented the method exploits the fact that multipath reception and various interference sources generate incidental amplitude modulation on the received signal a class of so called constant modulus performance functions is developed which sense this am term but are insensitive to the angle modulation simple adaptive algorithms for finite impulse response fir digital filters are developed which employ a gradient search of the performance function one of the resulting algorithms is simulated for the example of an fm signal degraded by specular multipath propagation substantial improvements in noise power ratio npr are observed e g 25 db with moderately rapid convergence time these results are then extended to include tonal interference on a fm signal and intersymbol interference on a qpsk data signal

blind equalization of constant modulus signals using an adaptive observer approach the paper addresses the problem of blind equalization of constant modulus signals which are degraded by frequency selective multipath propagation and additive white noise an adaptive observer is used to update the weights of an fir equalizer in order to restore the signal s constant modulus property the observer gain is selected using fake algebraic riccati methods in order to guarantee local stability the performance of this method is compared to the constant modulus algorithm for simulated fm fdm signals and exhibits significantly better convergence properties particularly for heavy tailed noise

asymptotic properties of the algebraic constant modulus algorithm the algebraic constant modulus algorithm acma is a noniterative blind source separation algorithm it computes jointly beamforming vectors for all constant modulus sources as the solution of a joint diagonalization problem we analyze its asymptotic properties and show that unlike cma it converges to the wiener beamformer when the number of samples or the signal to noise ratio snr goes to infinity we also sketch its connection to the related jade algorithm and derive a version of acma that converges to a zero forcing beamformer this gives improved performance in applications that use the estimated mixing matrix such as in direction finding

extended immersed boundary method using fem and rkpm abstract the proposed extended immersed boundary method eibm has several distinct features in comparison with the immersed boundary ib method in the ib method the interaction between the immersed elastic boundary and the surrounding viscous fluid is replaced with an equivalent body force distribution within the fluid domain the key ingredient of the ib method is the enforcement of the energy input from the equivalent body force into the fluid domain to be the same at all time as that of the elastic forces within the ib in eibm instead of the volumeless immersed elastic boundary we consider the submerged elastic solid which occupies a finite volume within the fluid domain in particular we replace the kinematic and dynamic matching of the fluid solid interface and the effect of the submerged solid with a judiciously chosen collection of equivalent nodal forces calculated in the context of finite element formulations the employment of the finite element representation enables a realistic stress analysis for the submerged solid subject to large deformations finally in eibm we also replace the discretized delta function commonly used in the ib method with the kernel functions in meshless reproducing kernel particle method rkpm with this improvement using the same finite support domain we could improve the discretized delta function from c 1 to c n continuity where n is chosen according to the required smoothness and resolution of such functions and more importantly enables the use of non uniform meshing in the fluid domain these extensions may eventually open doors to the modelling of complex biological fluid involving molecular cellular and flexible vessel flow interactions

a sharp interface immersed boundary method for compressible viscous flows an immersed boundary method for computing viscous subsonic compressible flows with complex shaped stationary immersed boundaries is presented the method employs a ghost cell technique for imposing the boundary conditions on the immersed boundaries the current approach leads to a sharp representation of the immersed boundaries a property that is especially useful for flow simulations at high reynolds numbers another unique feature of the method is that it can be applied on cartesian as well as generalized body non conformal curvilinear meshes a mixed second order central difference quick scheme is used which allows a high degree of control over the numerical damping a bilinear interpolation scheme used in conjunction with the ghost cell approach results in second order global as well as local spatial accuracy the solver is parallelized for distributed memory platforms using domain decomposition and message passing interface mpi and salient features of the parallel algorithm are presented the accuracy fidelity and efficiency of the solver are examined by simulating flow past circular cylinders and airfoils and comparing against experimental data and other established results finally we present results from a simulation of wing tip flow at a relatively high reynolds number in order to demonstrate the ability of the solver to model complex non canonical three dimensional flows

a finite element based level set method for fluid elastic solid interaction with surface tension summary a numerical method for simulating fluid elastic solid interaction with surface tension is presented a level set method is used to capture the interface between the solid bodies and the incompressible surrounding fluid within an eulerian approach the mixed velocity pressure variational formulation is established for the global coupled mechanical problem and discretized using a continuous linear approximation in both velocity and pressure three ways are investigated to reduce the spurious oscillations of the pressure that appear at the fluid solid interface first two stabilized finite element methods are used the mini element and the algebraic subgrid method second the surface integral corresponding to the surface tension term is treated either by the continuum surface force technique or by a surface local reconstruction algorithm finally besides the direct evaluation method proposed by bruchon et al an alternative method is proposed to avoid the explicit computation of the surface curvature which may be a source of difficulty these different issues are addressed through various numerical examples such as the two incompressible fluid flow the elastic inclusion embedded into a newtonian fluid or the study of a granular packing copyright 2012 john wiley sons ltd

stochastic blind equalization based on pdf fitting using parzen estimator this work presents a new blind equalization approach that aims to force the probability density function pdf at the equalizer output to match the known constellation pdf quadratic distance between pdf s is used as the cost function to be minimized the proposed method relies on the parzen window method to estimate the data pdf and is implemented by a stochastic gradient descent algorithm the kernel size of the parzen estimator allows a dual mode switch or a soft switch between blind and decision directed equalization the proposed method converges faster than the constant modulus algorithm cma working at the symbol rate with a similar computational burden and reduces the residual error of the cma in multilevel modulations at the same time a comparison with the most common blind techniques is presented

numerical modelling of electromechanical coupling using fictitious domain and level set methods we present a finite element formulation for simulation of electromechanical coupling using a combination of fictitious domain and level set methods the electric field is treated with a fixed eulerian like mesh whereas the structure taken as a perfect conductor is modelled with a conventional lagrangian approach the compatibility between the potential of the conductor and of the electric domain is obtained by introducing a lagrange multiplier function defined on the boundary of the conductor the electromechanical forces are obtained using a variational formulation for the coupled electromechanical domain we use a heaviside function on the level set to remove the electric energy in the conductor domain results are presented for an radio frequency switch and an element of a comb drive

an embedded dirichlet formulation for 3d continua this paper presents a new approach for imposing dirichlet conditions weakly on non fitting finite element meshes such conditions also called embedded dirichlet conditions are typically but not exclusively encountered when prescribing dirichlet conditions in the context of the extended finite element method xfem the methods key idea is the use of an additional stress field as the constraining lagrange multiplier function the resulting mixed hybrid formulation is applicable to 1d 2d and 3d problems the method does not require stabilization for the lagrange multiplier unknowns and allows the complete condensation of these unknowns on the element level furthermore only non zero diagonal terms are present in the tangent stiffness which allows the straight forward application of state of the art iterative solvers like algebraic multigrid amg techniques within this paper the method is applied to the linear momentum equation of an elastic continuum and to the transient incompressible navier stokes equations steady and unsteady benchmark computations show excellent agreement with reference values the general formulation presented in this paper can also be applied to other continuous field problems

a feedback approach to the steady state performance of fractionally spaced blind adaptive equalizers this paper proposes a new approach to the analysis of the steady state performance of constant modulus algorithms cma which are among the most popular adaptive schemes for blind equalization a major feature of the proposed feedback approach is that it bypasses the need for working directly with the weight error covariance matrix in so doing approximate expressions for the steady state mean square error of several cm algorithms are derived including cma2 2 cma1 2 normalized cma and a new normalized cma variant with less bias a comparison among the various algorithms is also performed along with several simulation results the conclusions confirm the superior performance of cma2 2

multiple emitter location and signal parameter estimation processing the signals received on an array of sensors for the location of the emitter is of great enough interest to have been treated under many special case assumptions the general problem considers sensors with arbitrary locations and arbitrary directional characteristics gain phase polarization in a noise interference environment of arbitrary covariance matrix this report is concerned first with the multiple emitter aspect of this problem and second with the generality of solution a description is given of the multiple signal classification music algorithm which provides asymptotically unbiased estimates of 1 number of incident wavefronts present 2 directions of arrival doa or emitter locations 3 strengths and cross correlations among the incident waveforms 4 noise interference strength examples and comparisons with methods based on maximum likelihood ml and maximum entropy me as well as conventional beamforming are included an example of its use as a multiple frequency estimator operating on time series is included

blind identification of fir systems driven by markov like input signals we propose a new algorithm for the blind identification and equalization of finite impulse response fir systems using the second order statistics of the received signal the new algorithm is set in the same context as the algorithms of tong et al 1994 and moulines et al 1995 however unlike those earlier approaches it is designed to allow correlated input signals specifically the algorithm accommodates finite memory sources and sources whose autocorrelation function decays exponentially numerical simulations compare the equalization performance of the new algorithm to those of tong and moulines it is shown that our algorithm yields consistently lower bit error rates at a wide variety of signal to noise ratios and at various equalizer lengths moreover the algorithm maintains this advantage even if it has no a priori information of source correlation or if source symbols are uncorrelated

using a signed distance function for the simulation of metal forming processes formulation of the contact condition and mesh adaptation from a lagrangian approach to an eulerian approach this paper proposes to use the metric properties of the distance function between two bodies in contact or gap function in simulations involving contact problems first the normal vectors which are involved in the formulation of the contact condition are defined through the gradient of this distance function this definition avoids to deal with the numerical penetration parameter which is generally introduced otherwise furthermore it allows the contact problem to be extended in a simple way to an eulerian formulation second this paper investigates two mesh adaptation strategies based on the properties of the distance function the first strategy consists in building a size map according to the values of this function in order to refine locally the mesh and consequently to improve the description of the contact surface the second strategy consists in adapting locally the mesh to the geometry of the contact surface this anisotropic adaptation is performed by constructing a metric map that allows the mesh size to be imposed in the direction of the distance function gradient a lot of elements are saved when compared with the isotropic case throughout this paper many numerical simulations are presented in the context of the forging process the deformable material is pressed between two rigid tools furthermore the algorithm used to calculate the signed distance to a surface mesh is detailed in appendix of this paper

steady state analysis of the multistage constant modulus array the multistage constant modulus cm array is a cascade adaptive beamforming system that can recover several narrowband cochannel signals without training we examine its steady state properties at convergence using a stochastic analysis and computer simulations based on a wiener model of convergence for the gradient adaptive algorithms closed form expressions are derived for the cm array and canceller weight vectors as well as the effective source direction vectors at all stages along the cascade system the signal capture and direction finding capabilities of the system are also discussed computer simulations for stationary and fading sources are presented to confirm the theoretical results and to illustrate the rapid convergence behavior of the adaptive algorithms

the enriched space time finite element method est for simultaneous solution of fluid structure interaction the paper introduces a weighted residual based approach for the numerical investigation of the interaction of fluid flow and thin flexible structures the presented method enables one to treat strongly coupled systems involving large structural motion and deformation of multiple flow immersed solid objects the fluid flow is described by the incompressible navier stokes equations the current configuration of the thin structure of linear elastic material with non linear kinematics is mapped to the flow using the zero iso contour of an updated level set function the formulation of fluid structure and coupling conditions uniformly uses velocities as unknowns the integration of the weak form is performed on a space time finite element discretization of the domain interfacial constraints of the multi field problem are ensured by distributed lagrange multipliers the proposed formulation and discretization techniques lead to a monolithic algebraic system well suited for strongly coupled fluid structure systems embedding a thin structure into a flow results in non smooth fields for the fluid based on the concept of the extended finite element method the space time approximations of fluid pressure and velocity are properly enriched to capture weakly and strongly discontinuous solutions this leads to the present enriched space time est method numerical examples of fluid structure interaction show the eligibility of the developed numerical approach in order to describe the behavior of such coupled systems the test cases demonstrate the application of the proposed technique to problems where mesh moving strategies often fail copyright 2007 john wiley sons ltd

on line blind multichannel equalization based on mutually referenced filters this paper presents a novel approach to the blind linear equalization of possibly nonminimum phase and time varying communication channels in the context of channel diversity we introduce the concept of mutually referenced equalizers mres in which several filters are considered the outputs of which act as training signals for each other a corresponding constrained multidimensional mean square error mse cost function is derived the minimization of which is shown to be a necessary and sufficient condition for equalization the links with a standard linear prediction problem are demonstrated the proposed technique exhibits properties of important practical concern 1 the proposed algorithm is globally convergent 2 simple closed form solutions exist for the mres but the mres also lend themselves readily to adaptive implementation in particular the recursive least squares rls algorithm can be used to offer optimal convergence rate 3 the mre method provides a solution for all equalization delays which results in robustness properties with respect to snr and ill defined channel lengths

an unfitted nitsche method for incompressible fluid structure interaction using overlapping meshes we consider the extension of the nitsche method to the case of fluid structure interaction problems on unfitted meshes we give a stability analysis for the space semi discretized problem and show how this estimate may be used to derive optimal error estimates for smooth solutions irrespectively of the mesh interface intersection we also discuss different strategies for the time discretization using either fully implicit or explicit coupling loosely coupled schemes some numerical examples illustrate the theoretical discussion

an analytical constant modulus algorithm iterative constant modulus algorithms such as godard 1980 and cma have been used to blindly separate a superposition of cochannel constant modulus cm signals impinging on an antenna array these algorithms have certain deficiencies in the context of convergence to local minima and the retrieval of all individual cm signals that are present in the channel we show that the underlying constant modulus factorization problem is in fact a generalized eigenvalue problem and may be solved via a simultaneous diagonalization of a set of matrices with this new analytical approach it is possible to detect the number of cm signals present in the channel and to retrieve all of them exactly rejecting other non cm signals only a modest amount of samples is required the algorithm is robust in the presence of noise and is tested on measured data collected from an experimental set up

misadjustment and tracking analysis of the constant modulus array the constant modulus cm array is a blind adaptive beamformer that can separate cochannel signals a follow on adaptive signal canceler may be used to perform direction finding of the source captured by the array in this paper we analyze the convergence and tracking properties of the cm array using a least mean square approximation expressions are derived for the misadjustment of the adaptive algorithms and a tracking model is developed that accurately predicts the behavior of the system during fades it is demonstrated that the adaptive canceler contributes more to the overall misadjustment than does the adaptive cm beamformer computer simulations are presented to illustrate the transient properties of the system and to verify the analytical results

topology optimization for turbulent flow with spalart allmaras model abstract in this research a new finite element fe based topology optimization to for turbulent flow was developed using the spalart allmaras s a equation which is one of the reynolds averaged navier stokes rans equations despite many innovative works on the subject of fluidic to it is rare to consider the influence of turbulent flow in to to consider the effect of complex turbulent fluid motion this research considered the s a model developed mainly for aerodynamic flows for a successful to one primary issue is modification of the s a turbulent model to account for topological evolution during the optimization process to address this issue we proposed the addition of penalization terms to the original governing equations to show the validity of the present approach and the effect of turbulent flow on optimal layouts some two dimensional benchmark designs studied for laminar flow were reconsidered by considering the effect of turbulent flow the eddy viscosity values were increased at some local regions due to the boussinesq hypothesis and naturally optimal layouts affected by the spatially varying viscosity were obtained in turbulent flow it was also found that the balance between the inertia force and the viscosity force plays an important role in topological designs

numerical simulation of premixed combustion using an enriched finite element method in this paper we present a novel discretization technique for the simulation of premixed combustion based on a locally enriched finite element method fem use is made of the g function approach to premixed combustion in which the domain is divided into two parts one part containing the burned and another containing the unburned gases a level set or g function is used to define the flame interface separating burned from unburned gases the extended finite element method x fem is employed which allows for velocity and pressure fields that are discontinuous across the flame interface lagrange multipliers are used to enforce the correct essential interface conditions in the form of jump conditions across the embedded flame interface a persisting problem with the use of lagrange multipliers in x fem has been the discretization of the lagrange multipliers in this paper the distributed lagrange multiplier technique is adopted we will provide results from a spatial convergence analysis showing good convergence however a small modification of the interface is required to ensure a unique solution finally results are presented from the application of the method to the problems of moving flame fronts the darrieus landau instability and a piloted bunsen burner flame

direction of arrival estimation for constant modulus signals in many cases where direction finding is of interest the signals impinging on an antenna array are known to be phase modulated and hence to have a constant modulus cm this is a strong property by itself it is already sufficient for source separation and can be used to construct improved direction finding algorithms we first derive the relevant cramer rao bounds crbs for arbitrary array configurations and specialize to uniform linear arrays we then propose a simple suboptimal direction estimation algorithm in which the signals are separated using the cm property followed by direction finding on the decoupled signals compared with the esprit algorithm and the crb for arbitrary signals the algorithm shows good results

immersed electrokinetic finite element method a new method is proposed for modelling the electrokinetic induced mechanical motion of particles in a fluid domain under an applied electric field in this method independent solid meshes move in a fixed background field mesh that models the fluid and the electric field this simple strategy removes the need for expensive mesh updates furthermore the reproducing kernel particle functions enable efficient coupling of various immersed deformable solids with the surrounding viscous fluid in the presence of an applied electric field the electric force on a particle is calculated by the maxwell stress tensor method for the first time three dimensional assembly of nano biomaterials of various geometries and electrical properties have been comprehensively studied using the new method simulation of the dynamic process of electro manipulation of individual and multiple cells agrees well with experimental data preliminary results for selective deposition of viruses and stretching of a dna molecule are also presented copyright 2006 john wiley sons ltd

the extended generalized finite element method an overview of the method and its applications an overview of the extended generalized finite element method gefm xfem with emphasis on methodological issues is presented this method enables the accurate approximation of solutions that involve jumps kinks singularities and other locally non smooth features within elements this is achieved by enriching the polynomial approximation space of the classical finite element method the gefm xfem has shown its potential in a variety of applications that involve non smooth solutions near interfaces among them are the simulation of cracks shear bands dislocations solidification and multi field problems copyright 2010 john wiley sons ltd

fluid structure interaction with large structural displacements the calculation of viscous flows inside deformable structures faces major difficulties when enforcing the kinematic compatibility at the fluid structure interface and updating the geometry of the domain this paper proposes to overcome these problems by considering the fluid and the structure as a unique continuous medium to be studied in a fixed reference configuration the resulting problem is then split into a fluid and a structural part through an additive decomposition of the space of kinematically admissible test functions this approach treats the structure in a fully lagrangian way and uses an associated arbitrary lagrangian eulerian ale formulation for the fluid such a strategy has three advantages which are detailed in the present paper it can be discretised in time by implicit stable energy conserving time integration schemes and solved by simple iterative uncoupled algorithms the fluid and the structural problems can be approximated by independent finite element spaces the most recent geometrically exact nonlinear shell models can be used for the structures the full strategy has been implemented into an industrial cfd code results obtained in the simulation of industrial hydraulic shock absorbers are presented at the end of the paper

cumulant based inverse filter criteria for mimo blind deconvolution properties algorithms and application to ds cdma systems in multipath tugnait 1995 and chi and chen proposed multi input multi output inverse filter criteria mimo ifc using higher order statistics for blind deconvolution of mimo linear time invariant systems this paper proposes three properties on the performance of the mimo linear equalizer associated with mimo ifc for any signal to noise ratio including p1 perfect phase equalization property p2 a relation to mimo minimum mean square error mimo mmse equalizer and p3 a connection with the one obtained by mimo super exponential algorithm mimo sea that usually converges fast but does not guarantee convergence for finite data based on p2 a fast algorithm for computing the theoretically optimum mimo equalizer is proposed moreover based on p3 a fast mimo ifc based algorithm with performance similar to that of the mimo sea and with guaranteed convergence is proposed as well as its application to suppression of multiple access interference and intersymbol interference isi for multiuser asynchronous ds cdma systems in multipath finally some simulation results are presented to support the analytic results and the proposed algorithms

improved methods for the blind system identification using higher order statistics it is demonstrated by a detailed analysis of blind system identification that under specific system configurations a recently published least squares algorithm shows a poor convergence behavior especially if the system order is overdetermined to overcome these problems a supplementary condition is introduced that guarantees proper convergence in most cases an alternative approach for the blind identification of mixed phase systems the so called cumulant zero matching method is presented in this approach the solution of a set of nonlinear equations which is necessary in the least squares method is replaced by the calculation of zeros of polynomials the main advantage over the least squares solution is that overdetermination of the system order is rather harmless since it only results in additional zeros in the origin of the z plane the different methods for system identification presented are illustrated by simulation results

blind source separation the location of local minima in the case of finitely many samples cost functions used in blind source separation are often defined in terms of expectations i e an infinite number of samples is assumed an open question is whether the local minima of finite sample approximations to such cost functions are close to the minima in the infinite sample case to answer this question we develop a new methodology of analyzing the finite sample behavior of general blind source separation cost functions in particular we derive a new probabilistic analysis of the rate of convergence as a function of the number of samples and the conditioning of the mixing matrix the method gives a connection between the number of available samples and the probability of obtaining a local minimum of the finite sample approximation within a given sphere around the local minimum of the infinite sample cost function this shows the convergence in probability of the nearest local minima of the finite sample approximation to the local minima of the infinite sample cost function we also answer a long standing problem of the mean squared error mse behavior of the finite sample least squares constant modulus algorithm ls cma namely whether there exist ls cma receivers with good mse performance we demonstrate how the proposed techniques can be used to determine the required number of samples for ls cma to exceed a specified performance the paper concludes with simulations that validate the results

a monolithic smoothing gap algorithm for contact impact based on the signed distance function a new algorithm has been developed for smoothing the surfaces in finite element formulations of contact impact a key feature of this method is that the smoothing is done implicitly by constructing smooth signed distance functions for the bodies these functions are then employed for the computation of the gap and other variables needed for implementation of contact impact the smoothed signed distance functions are constructed by a moving least squares approximation with a polynomial basis results show that when nodes are placed on a surface the surface can be reproduced with an error of about one per cent or less with either a quadratic or a linear basis with a quadratic basis the method exactly reproduces a circle or a sphere even for coarse meshes results are presented for contact problems involving the contact of circular bodies copyright c 2002 john wiley sons ltd

fixed grid fluid structure interaction in two dimensions based on a partitioned lattice boltzmann and p fem approach over the last decade the lattice boltzmann method which was derived from the kinetic gas theory has matured as an efficient approach for solving navier stokes equations the p fem approach has proved to be highly efficient for a variety of problems in the field of structural mechanics our goal is to investigate the validity and efficiency of coupling the two approaches to simulate transient bidirectional fluid structure interaction problems with geometrically non linear structural deflections a benchmark configuration of self induced large oscillations for a flag attached to a cylinder can be accurately and efficiently reproduced within this setting we describe in detail the force evaluation techniques displacement transfers and the algorithm used to couple these completely different solvers as well as the results and compare them with a benchmark reference solution computed by a monolithic finite element approach copyright 2009 john wiley sons ltd

a fully eulerian formulation for fluid structure interaction problems in this work we present a fully eulerian framework for fluid structure interaction fsi problems coupling the incompressible navier stokes equations with a hyperelastic solid the fully eulerian framework is a monolithic implicit variational formulation for the coupled problem in contrast to the well established arbitrary lagrangian eulerian ale coordinates the fully eulerian framework formulates both subproblems fluid and solid in eulerian coordinates this concept circumvents various difficulties connected to ale coordinates since no artificial domain mapping is used the formulation is an interface capturing method and uses an extension of the solid s deformation the initial point set to detect the interface location by construction very large deformation as well as topology changes like contact of the solid to the domain boundary or other solid parts are possible

fully eulerian fluid structure interaction for time dependent problems abstract a fully eulerian framework formulation for solving time dependent fluid structure interaction problems is proposed in this work although some preliminary work on this approach exists for stationary configurations it remains to validate nonstationary processes the formulation is stated in an implicit monolithic frame of reference a finite difference scheme is used for temporal discretization whereas the spatial discretization is based on a galerkin finite element scheme the nonlinear problem is solved with a newton method and with analytical evaluation of the jacobian matrix in contrast to interface tracking methods for example the arbitrary lagrangian eulerian approach the interface must be captured which is similar to the level set method consequently the interface is allowed to intersect mesh cells which is a crucial difficulty of this method where appropriate treatment must be suggested the proposed formulation is substantiated by three numerical tests in which the performance of fully eulerian fluid structure interaction is demonstrated

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

an enriched finite element method and level sets for axisymmetric two phase flow with surface tension a finite element method for axisymmetric two phase flow problems is presented the method uses an enriched finite element formulation in which the interface can move arbitrarily through the mesh without remeshing the enrichment is implemented by the extended finite element method x fem which models the discontinuity in the velocity gradient at the interface by a local partition of unity it provides an accurate representation of the velocity field at interfaces on an eulerian grid that is not conformal to the weak discontinuity the interface is represented by a level set which is also used in the construction of the element enrichment surface tension effects are considered and the interface curvature is computed from the level set field the method is demonstrated by several examples copyright 2003 john wiley sons ltd

uniformly more powerful tests in a one sided multivariate problem abstract we consider a testing problem in which a normal mean vector is at the origin under the null hypothesis and in a cone under the alternative and the covariance matrix is unknown perlman studied the likelihood ratio lr test and found that it is biased and hence does not compare favorably with hotelling s t2 we point out that certain tests of perlman are uniformly more powerful as well as simpler than the lr test these are the corresponding lr tests when the alternative is replaced with a half space that contains the cone we prove that these tests are unbiased by developing some basic results on stochastic ordering critical values for these tests are given simulation results suggest that the new tests are also uniformly more powerful than hotelling s t2 for the special case when the cone is the positive orthant we discuss an issue about invariant test finally we discuss the assumption of unknown covariance matrix and conclude that the new tests are more useful for small samples than for

a fictitious domain approach to the direct numerical simulation of incompressible viscous flow past moving rigid bodies application to particulate flow abstract in this article we discuss a methodology that allows the direct numerical simulation of incompressible viscous fluid flow past moving rigid bodies the simulation methods rest essentially on the combination of a lagrange multiplier based fictitious domain methods which allow the fluid flow computations to be done in a fixed flow region b finite element approximations of the navier stokes equations occurring in the global model c time discretizations by operator splitting schemes in order to treat optimally the various operators present in the model the above methodology is particularly well suited to the direct numerical simulation of particulate flow such as the flow of mixtures of rigid solid particles and incompressible viscous fluids possibly non newtonian we conclude this article with the presentation of the results of various numerical experiments including the simulation of store separation for rigid airfoils and of sedimentation and fluidization phenomena in two and three dimensions

super exponential methods for blind deconvolution a class of iterative methods for solving the blind deconvolution problem i e for recovering the input of an unknown possibly nonminimum phase linear system by observation of its output is presented these methods are universal do not require prior knowledge of the input distribution are computationally efficient and statistically stable and converge to the desired solution regardless of initialization at a very fast rate the effects of finite length of the data finite length of the equalizer and additive noise in the system on the attainable performance intersymbol interference are analyzed it is shown that in many cases of practical interest the performance of the proposed methods is far superior to linear prediction methods even for minimum phase systems recursive and sequential algorithms are also developed which allow real time implementation and adaptive equalization of time varying systems

the tone capture properties of cma based interference suppressors an earlier paper introduced the constant modulus algorithm cma an adaptive filtering technique for correcting multipath and interference induced degradations in constant envelope waveforms such as fm and qpsk signals this algorithm exploits the fact that both multipath propagation and additive interference disrupt the constant envelope property of the received signal by sensing the received envelope variations the adaptive algorithm can reset the coefficients of an fir digital filter so as to remove the variations and in the process suppress the various interference components from the desired signal this paper examines a problem that arises when using cma to suppress narrow band interference if both the interferer and the signal have constant envelope and are spectrally nonoverlapping then it is possible to find two different filter solutions one which suppresses the interferer and another which captures the interferer and suppresses the desired signal this paper examines how capture can occur and how it may be prevented this problem is studied by characterizing the algorithm s behavior to an input consisting of only two sinusoids assuming slow adaptation the n dimensional adaptive weight recursion is shown to compress into a two by two recursion in the tone output amplitudes this simplified recursion is then analyzed to determine what combinations of input amplitudes signal to interference ratios and filter initial conditions lead to lock and which lead to the capture of the interferer the results are then broadened to include multiple input tones and signals with nonzero bandwidth

the analysis of multiple endpoints in clinical trials treatment comparisons in randomized clinical trials usually involve several endpoints such that conventional significance testing can seriously inflate the overall type i error rate one option is to select a single primary endpoint for formal statistical inference but this is not always feasible another approach is to apply bonferroni correction i e multiply each p value by the total number of endpoints its conservatism for correlated endpoints is examined for multivariate normal data a third approach is to derive an appropriate global test statistic and this paper explores one such test applicable to any set of asymptotically normal test statistics quantitative binary and survival endpoints are all considered within this general framework two examples are presented and the relative merits of the proposed strategies are discussed

a nitsche cut finite element method for the oseen problem with general navier boundary conditions abstract in this work a nitsche based imposition of generalized navier conditions on cut meshes for the oseen problem is presented other methods from literature dealing with the generalized navier condition impose this condition by means of substituting the tangential robin condition in a classical galerkin way these methods work fine for a large slip length coefficient but lead to conditioning and stability issues when it approaches zero we introduce a novel method for the weak imposition of the generalized navier condition which remains well posed and stable for arbitrary choice of slip length including zero the method proposed here builds on the formulation done by juntunen and stenberg 2009 they impose a robin condition for the poisson problem by means of nitsche s method for an arbitrary combination of the dirichlet and neumann parts of the condition the analysis conducted for the proposed method is done in a similar fashion as in massing et al 2018 but is done here for a more general type of boundary condition the analysis proves stability for all flow regimes and all choices of slip lengths also an l 2 optimal estimate for the velocity error is shown which was not conducted in the previously mentioned work a numerical example is carried out for varying slip lengths to verify the robustness and stability of the method with respect to the choice of slip length even though proofs and formulations are presented for the more general case of an unfitted grid method they can easily be reduced to the simpler case of a boundary fitted grid with the removal of the ghost penalty stabilization terms

on blind beamforming for multiple non gaussian signals and the constant modulus algorithm a new method for blindly separating multiple cochannel non gaussian signals received by a sensor array is presented the method is based on a cumulant based least squares criterion that for identically distributed negative kurtosis signals is proven to be identical to the 2 2 constant modulus cm cost function commonly used by cm algorithms a computationally simple algorithm is proposed to minimize the criterion the algorithm performs well even when the number of samples is small thus allowing its application in dynamic environments e g moving emitters for the special case of two signals only the minimization is obtained analytically simulation results are included

ode analysis and redesign in blind adaptation in blind adaptation the dynamics of an unknown channel system is recovered together with the transmitted symbol sequence input signal this paper generalizes the author s previous algorithm 1994 1997 that is not derived by criterion minimization to include adaptive regressor filtering the resulting scheme which adapts a finite dimensional iir channel model is designed to converge only to a well defined set of parameters when binary symbols are transmitted over the channel this provides a partial solution to the recently discussed ill convergence problem in blind adaptation some connections to adaptive control theory are noted

waveform preserving blind estimation of multiple independent sources the problem of blind estimation of source signals is to estimate the source signals without knowing the characteristics of the transmission channel it is shown that the minimum variance unbiased estimates can be obtained if and only if the transmission channel can be identified blindly it is shown that the channel can be blindly identified if and only if there is not more than one gaussian source this condition suggests that waveform preserving blind estimation can be achieved over a wide range of signal processing applications including those cases in which the source signals have identical nongaussian distributions the constructive proof of the necessary and sufficient condition serves as a foundation for the development of waveform preserving blind signal estimation algorithms examples are presented to demonstrate the applications of the theoretical results

isogeometric enriched field approximations boundaries with specified behavior phase boundaries crack surfaces or singular points are geometrically speaking lower dimensional features relative to two or three dimensional geometrical domains often the distinguishing characteristics of the behavior at these features are known a priori and may be exploited to enrich isogeometric models explicit geometrical representations possess parametrically computable tangents normals and curvature while in implicit strategies the geometric exactness of enriching lower dimensional features is not exploited or retrieved only in the limit of mesh refinement in the present work cad inspired hierarchical partition of unity field compositions are extended to modeling explicitly defined enrichments within the isogeometric framework the base approximations are enriched isogeometrically on parametrically defined lower dimensional geometrical features of the base entity and by constructing distance fields from them the efficiency and robustness of distance computations is significantly improved by composing monotonic distance measures defined piecewise on the enriching geometric entity using r functions the procedure allows both the behavioral approximation as well as the material description to be enriched enabling the modeling of material damage or alternatively local stiffening further the enrichments may ensure known function value or its derivative function value enrichments are demonstrated to model dirichlet boundary conditions and propagating cracks the derivative enrichments are used to model neumann boundary conditions as well as strain jumps across material interfaces the material enrichments are demonstrated through the use of a cohesive damage law to model arbitrary crack initiation and propagation within the domain

adaptive multistage beamforming using cyclic higher order statistics chos a new blind beamforming algorithm for signals that exhibit higher order cyclostationarity is presented exploiting some previous theoretical developments we show how cyclic cumulants of the received signals can be used to obtain the weights of the beamformer that perform blind extraction the method is based on a spatial interpretation of a deconvolution procedure known as the super exponential algorithm the basic block processing algorithm is made fully adaptive using an adaptive urv scheme and applied to a typical mobile communications scenario where several cochannel interferers corrupt the signals of interest

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 stabilized nitsche cut finite element method for the oseen problem abstract we provide the numerical analysis for a nitsche based cut finite element formulation for the oseen problem which has been originally presented for the incompressible navier stokes equations by schott and wall 2014 and allows the boundary of the domain to cut through the elements of an easy to generate background mesh the formulation is based on the continuous interior penalty cip method of burman et al 2006 which penalizes jumps of velocity and pressure gradients over inter element faces to counteract instabilities arising for high local reynolds numbers and the use of equal order interpolation spaces for the velocity and pressure since the mesh does not fit the boundary dirichlet boundary conditions are imposed weakly by a stabilized nitsche type approach the addition of cip like ghost penalties in the boundary zone allows to prove that our method is inf supstable and to derive optimal order a priori error estimates in an energy type norm irrespective of how the boundary cuts the underlying mesh all applied stabilization techniques are developed with particular emphasis on low and high reynolds numbers two and three dimensional numerical examples corroborate the theoretical findings finally the proposed method is applied to solve the transient incompressible navier stokes equations on a complex geometry

an algebraic multigrid approach to solve extended finite element method based fracture problems summary this article proposes an algebraic multigrid amg approach to solve linear systems arising from applications where strong discontinuities are modeled by the extended finite element method the application of amg methods promises optimal scalability for solving large linear systems however the straightforward or black box use of existing amg techniques for extended finite element method problems is often problematic in this paper we highlight the reasons for this behavior and propose a relatively simple adaptation that allows one to leverage existing amg software mostly unchanged numerical tests demonstrate that optimal iterative convergence rates can be attained that are comparable with amg convergence rates associated with linear systems for standard finite element approximations without discontinuities published 2012 this article is a us government work and is in the public domain in the usa

recursive least squares constant modulus algorithm for blind adaptive array we consider the problem of blind adaptive signal separation with an antenna array based on the constant modulus cm criterion an approximation to the cm cost function is proposed which allows the use of the recursive least squares rls optimization technique a novel rls constant modulus algorithm rls cma is derived where the modulus power of the array output can take on arbitrary positive real values i e fractional values allowed simulations are performed to compare the performance of the proposed rls cma to other well known algorithms for blind adaptive beamforming results indicate that the rls cma has a significantly faster convergence rate and better tracking ability

performance predictions for parameter estimators that minimize cost functions using wirtinger calculus with application to cm blind equalization we present calculations of the first order bias and first order variance of parameters which are estimated batch wise from the global minimum of a cost function of complex valued signals embedded in zero mean gaussian noise the derivation involves the calculation of the multidimensional taylor series of the non analytic cost function up to third order using the elegant wirtinger calculus whereas closed form expressions for the variance can be obtained straightforwardly from a second order taylor series and have been presented in various other contexts an exact expression for the bias cannot be derived in general in this paper we propose approximate expressions for the first order bias and confirm them in a comparison of results from extensive analytical calculations with results from monte carlo mc simulations for the statistical efficiency of a batch processing blind equalizer using the constant modulus cm criterion we study the equalization of independent and identically distributed i i d random symbols and obtain asymptotic for large batch size expressions for the averages of the bias and variance over zero mean random real valued signals of binary phase shift keying bpsk and complex valued signals of m ary psk modulation m 2 finally we compare the statistical efficiency of the cm estimator with the one of the maximum likelihood ml blind estimation of the path parameters and equalized symbols with cm constraint

nitsche xfem for the coupling of an incompressible fluid with immersed thin walled structures abstract in this paper we introduce a nitsche xfem method for fluid structure interaction problems involving a thin walled elastic structure lagrangian formalism immersed in an incompressible viscous fluid eulerian formalism the fluid domain is discretized with an unstructured mesh not fitted to the solid mid surface mesh weak and strong discontinuities across the interface are allowed for the velocity and pressure respectively the fluid solid coupling is enforced consistently using a variant of nitsche s method with cut elements robustness with respect to arbitrary interface intersections is guaranteed through suitable stabilization several coupling schemes with different degrees of fluid solid time splitting implicit semi implicit and explicit are investigated a series of numerical test in 2d involving static and moving interfaces illustrates the performance of the different methods proposed

an embedded mesh method in a multiple material ale abstract a new approach for treating the mechanical interactions of overlapping finite element meshes is presented referred to as embedded mesh methods here these overlapping mesh methods typically include a foreground solid mesh and a background euler fluid grid or solid mesh a number of different approaches have been used in previous work to characterize the interactions of the background and foreground meshes at the interface lagrange multipliers are well suited to enforce the continuity constraints but care must be taken such that the resulting formulation is stable several lagrange multiplier techniques are examined in this work and applied to coupling solid meshes and fluid structure interaction type problems in addition details regarding implementation in a two step multi material arbitrary lagrangian eulerian ale code are presented example problems demonstrate convergence and applicability to a range of problems in particular the fluid structure interaction examples focus on blast applications

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

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

step up multiple testing of parameters with unequally correlated estimates we consider the problem of simultaneously testing k or to 2 hypotheses on parameters theta 1 theta k using test statistics t 1 t k such that a specified familywise error rate alpha is achieved dunnett and tamhane 1992a proposed a step up multiple test procedure in which testing starts with the hypothesis corresponding to the least significant test statistic and proceeds towards the most significant stopping the first time a significant test result is obtained and rejecting the hypotheses corresponding to that and any remaining test statistics the parameter estimates used in the t statistics were assumed to be normally distributed with a common variance which was a known multiple of an unknown sigma 2 and known correlations which were equal in the present article we show how the procedure can be extended to include unequally correlated parameter estimates unequal correlations occur for example in experiments involving comparisons among treatment groups with unequal sample sizes we also compare the step up and step down multiple testing approaches and discuss applications to some biopharmaceutical testing problems

super exponential blind adaptive beamforming the objective of the beamforming with the exploitation of a sensor array is to enhance the signals of the sources from desired directions suppress the noises and the interfering signals from other directions and or simultaneously provide the localization of the associated sources in this paper we present a higher order cumulant based beamforming algorithm namely the super exponential blind adaptive beamforming algorithm which is extended from the super exponential algorithm sea and the inverse filter criteria ifc while both sea and ifc assume noise free conditions this requirement is no longer needed and all the noise components are taken into account in the proposed algorithm two special conditions are derived under which the proposed blind beamforming algorithm achieves the performance of the corresponding optimal nonblind beamformer in the sense of minimum mean square error mmse simulation results show that the proposed algorithm is effective and robust to diverse initial weight vectors its performance with the use of the fourth order cumulants is close to that of the nonblind optimal mmse beamformer

bussgang zero crossing equalization an integrated hos sos approach an integrated higher order statistics hos and second order statistics sos based equalization technique is presented as an extension of the bussgang equalization algorithm this extension allows one to simultaneously take account of the statistical knowledge about the data source as done in the conventional hos approaches and in particular by bussgang like equalization algorithms such as super exponential constant modulus etc and the spectral redundancy usually present in pulse amplitude modulation pam and quadrature amplitude modulation qam modulated signals exploited by sos based approaches the technique presented employs a new form of sos equalization that naturally integrates into the bussgang scheme it is based on a zero crossing zc property of the received signal when it is passed through a suitable filter the novel equalization scheme is presented in a bayesian estimation framework after illustration of the general bussgang paradigm and of the principles of the zc approach from simulated experiments results show that the extended bussgang zc equalizer not only outperforms conventional bussgang equalizers but is also robust to situations where hos and sos approaches individually fail

shrinkage linear and widely linear complex valued least mean squares algorithms for adaptive beamforming in this paper shrinkage linear complex valued least mean squares sl clms and shrinkage widely linear complex valued least mean squares swl clms algorithms are devised for adaptive beamforming by exploiting the relationship between the noise free a posteriori and a priori error signals the sl clms method is able to provide a variable step size to update the weight vector for the adaptive beamformer significantly enhancing the convergence speed and decreasing the steady state misadjustment on the other hand besides adopting a variable step size determined by minimizing the square of the augmented noise free a posteriori errors the swl clms approach exploits the noncircular properties of the signal of interest which considerably improves the steady state performance simulation results are presented to illustrate their superiority over the clms complex valued normalized lms variable step size recursive least squares rls algorithms and their corresponding widely linear based schemes additionally our proposed algorithms are more computationally efficient than the rls solutions though they may have a slightly slower convergence rate

testing hypotheses about an identified treatment when there are multiple endpoints abstract the problem of comparing an identified treatment with k other treatments is considered in a multivariate setting many formulations of composite alternative hypotheses are possible for example one might wish to examine whether the identified treatment is superior to the other treatments on all components of the response vector i e is uniformly best or whether the identified treatment is better than each treatment on at least one component i e is admissible for testing whether the identified treatment is uniformly best the known optimality of the min test in the univariate case is extended to the multivariate case if the distribution is multivariate normal then the min test is shown to be a likelihood ratio test for testing whether the identified treatment is admissible a min test based on the bonferroni inequality is suggested for the multivariate normal with unknown covariance matrix the likelihood ratio test is also a min test but it has less stable power characteristics than

on the construction of blending elements for local partition of unity enriched finite elements for computational efficiency partition of unity enrichments are preferably localized to the sub domains where they are needed it is shown that an appropriate construction of the elements in the blending area the regionwhere the enriched elements blend to unenriched elements is often crucial for good performance of local partition of unity enrichments an enhanced strain formulation is developed which leads to good performance the optimal rate of convergence is achieved for polynomial enrichments it is shown that a proper choice of the finite element shape functions and partition of unity shape functions also improves the accuracy and convergence the methods are illustrated by several examples the examples deal primarily with the signed distance function enrichment for treating discontinuous derivatives inside an element but other enrichments are also considered results show that both methods provide optimal rates of convergence

on the nonvanishing stability of undesirable equilibria for fir godard blind equalizers the existence of undesirable equilibria of godard 1980 or constant modulus algorithms cma is demonstrated for all finite dimensional fir equalizers sufficient stability conditions are presented for these equilibria it is shown that for the godard 2 algorithm these undesirable equilibria are locally stable as long as the equalizer length remains finite results indicate that merely increasing the equalizer length does not necessarily nullify the potential for local convergence by godard algorithms

the immersed fictitious element method for fluid structure interaction volumetric consistency compressibility and thin members a weak form and an implementation are given for fluid structure interaction by the immersed fictitious element method for compressible fluids the weak form is applicable to models where the fluid is described by eulerian coordinates while the solid is described by lagrangian coordinates which suits their intrinsic characteristics a unique feature of the method is the treatment of the fictitious fluid by a lagrangian description which simplifies the interface conditions methods for enforcing volumetric consistency between the fluid and solid and treating thin members are given although a compressible viscous fluid is considered here the new developments can be applied to incompressible fluids

blind equalization for correlated input symbols a bussgang approach this paper addresses the problem of blind equalization in the case of correlated input symbols and it shows how the knowledge of the symbol sequence probability distribution can be directly incorporated in a bussgang blind equalization scheme numerical results pertaining to both linear and nonlinear modulation schemes show that a significant improvement in equalization performance is obtained by exploiting the symbol sequence probability distribution using the approach herein described

testing whether an identified treatment is best summary we consider the problem of testing whether an identified treatment is better than each of k treatments suppose there are univariate test statistics si that contrast the identified treatment with treatment i for i 1 2 k the min test is defined to be the a level procedure that rejects the null hypothesis that the identified treatment is not best when for all i si rejects the one sided hypothesis at the a level that the identified treatment is not better than the ith treatment in the normal case where si are t statistics the min test is the likelihood ratio test for distributions satisfying mild regularity conditions if attention is restricted to test statistics that are monotone nondecreasing functions of si then regardless of their covariance structure the min test is an optimal a level test tables of the sample size needed to achieve power 5 8 90 and 95 are given for the min test when the si are student s t and wilcoxon

procedures for comparing samples with multiple endpoints summary five procedures are considered for the comparison of two or more multivariate samples these procedures include a newly proposed nonparametric rank sum test and a generalized least squares test also considered are the following tests ordinary least squares hotelling s p and a bonferroni per experiment error rate approach applications are envisaged in which each variable represents a qualitatively different measure of response to treatment the null hypothesis of no treatment difference is tested with power directed towards alternatives in which at least one treatment is uniformly better than the others in all simulations the nonparametric procedure provided relatively good power and accurate control over the size of the test and is recommended for general use alternatively the generalized least squares procedure may also be useful with normally distributed data in moderate or large samples a convenient expression for this procedure is obtained and its asymptotic relative efficiency with respect to the ordinary least squares test is evaluated clinical trials are often conducted for the purpose of evaluating the relative efficacy of two or more modes of therapy when the therapies are administered to independent groups and efficacy is measured on the basis of a single response variable appropriate parametric and nonparametric one way analysis of variance anova procedures and their properties are well known often however efficacy is measured by more than one variable although univariate methods for assessing each characteristic individually are useful in this setting there is often the additional need for a single overall objective probability statement that addresses the question of whether or not the experimental therapy is efficacious this need is particularly acute when the medical question is controversial and the sample size is small although a large literature exists on the comparison of multivariate samples the procedures tend to be infrequently used in practice as pointed out by meier 1975 p 523 the standard analysis for the comparison of two multivariate samples which is based on hotelling s t2 statistic addresses somewhat the wrong question and consequently has very poor power for the alternatives of primary interest specifically the t2 procedure addresses the question are one or more of the treatments different making no distinction between variables that change favorably and variables that change unfavorably a second approach would be to assign per experiment error rates to each of the univariate tests by using bonferroni s inequality i e by multiplying each univariate p value by the number of variables studied the desired overall probability statement is then given by the minimum of the per experiment univariate p values although this approach may be useful in some settings it may lack power for alternatives in which most or all measures of efficacy are improved this will be of particular concern when the number k of endpoints studied is large relative to sample size in fact statistical significance will not be possible in some instances this problem will be exacerbated when the measures of efficacy are highly

long term simulation of large deformation mechano chemical fluid structure interactions in ale and fully eulerian coordinates in this work we develop numerical schemes for mechano chemical fluid structure interactions with long term effects we investigate a model of a growing solid interacting with an incompressible fluid a typical example for such a situation is the formation and growth of plaque in blood vessels this application includes two particular difficulties first growth may lead to very large deformations up to full clogging of the fluid domain we derive a simplified set of equations including a fluid structure interaction system coupled to an ode model for plaque growth in arbitrary lagrangian eulerian ale coordinates and in eulerian coordinates the latter novel technique is capable of handling very large deformations up to contact the second difficulty stems from the different time scales while the dynamics of the fluid demand to resolve a scale of seconds growth typically takes place in a range of months we propose a temporal two scale approach using local small scale problems to compute an effective wall stress that will enter a long scale problem our proposed techniques are substantiated with several numerical tests that include comparisons of the eulerian and ale approaches as well as convergence studies

a local space time discontinuous finite element method we present a locally enriched space time finite element method for solving hyperbolic problems with discontinuities the space time formulation is coupled to a standard semidiscrete finite element method the discontinuities are captured by a space time version of the extended finite element method which treats arbitrary moving discontinuities since the discontinuities are local the enriched space time method is only needed around the discontinuities which provides significant computational savings the coupling is implemented through a weak enforcement of the continuity of the flux between the space time and semidiscrete domains in a manner similar to discontinuous galerkin methods the method is illustrated through one dimensional problems it displays remarkable accuracy in capturing moving discontinuities both in their amplitude and speed

derivative recovery and a posteriori error estimate for extended finite elements this paper is the first attempt at error estimation for extended finite elements the goal of this work is to devise a simple and effective local a posteriori error estimate for partition of unity enriched finite element methods such as the extended finite element method xfem in each element the local estimator is the l2 norm of the difference between the raw xfem strain field and an enhanced strain field computed by extended moving least squares xmls derivative recovery obtained from the raw nodal xfem displacements the xmls construction is tailored to the nature of the solution the technique is applied to linear elastic fracture mechanics in which near tip asymptotic functions are added to the mls basis the xmls shape functions are constructed from weight functions following the diffraction criterion to represent the discontinuity the result is a very smooth enhanced strain solution including the singularity at the crack tip results are shown for two and three dimensional linear elastic fracture mechanics problems in mode i and mixed mode the effectivity index of the estimator is close to 1 and improves upon mesh refinement for the studied near tip problem it is also shown that for the linear elastic fracture mechanics problems treated the proposed estimator outperforms one of the superconvergent patch recovery technique of zienkiewicz and zhu which is only c0 parametric studies of the general performance of the estimator are also carried out

the extended finite element method xfem for solidification problems an enriched finite element method for the multi dimensional stefan problems is presented in this method the standard finite element basis is enriched with a discontinuity in the derivative of the temperature normal to the interface the approximation can then represent the phase interface and the associated discontinuity in the temperature gradient within an element the phase interface can be evolved without re meshing or the use of artificial heat capacity techniques the interface is described by a level set function that is updated by a stabilized finite element scheme several examples are solved by the proposed method to demonstrate the accuracy and robustness of the method copyright 2001 john wiley sons ltd

fluid structure interaction by the discontinuous galerkin method for large deformations a discontinuous galerkin method for large deformation fluid structure interaction problems is developed the fluid structure interface can be arbitrarily aligned relative to the fluid grid an eulerian description is used for the fluid with a lagrangian description of the solid results are presented for several examples that show excellent agreement with immersed fictitious element methods copyright 2008 john wiley sons ltd

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

the fixed mesh ale approach applied to solid mechanics and fluid structure interaction problems in this paper we propose a method to solve solid mechanics and fluid structure interaction problems using always a fixed background mesh for the spatial discretization the main feature of the method is that it properly accounts for the advection of information as the domain boundary evolves to achieve this we use an arbitrary lagrangian eulerian ale framework the distinctive characteristic being that at each time step results are projected onto a fixed background mesh for solid mechanics problems subject to large strains the fixed mesh fm ale method avoids the element stretching found in fully lagrangian approaches for fsi problems fm ale allows for the use of a single background mesh to solve both the fluid and the structure copyright 2009 john wiley sons ltd

a simple algorithm for localized construction of non matching structural interfaces a simple and effective algorithm for the modular construction of non matched interfaces is presented for the partitioned solution of large scale structural problems the formulation is based on a recently developed four field variational principle which introduces a connection frame between the interfaced partitions a key result of the present study is a frame nodal placement criterion that uniquely determines the frame discretization into piecewise linear elements so that the interface patch test condition is satisfied a priori the method is demonstrated with several 2d and 3d example problems

algebraic distance estimations for enriched isogeometric analysis abstract in problems with evolving boundaries interfaces or cracks blending functions are used to enrich the underlying domain with the known behavior on the enriching entity the blending functions are typically dependent on the distance from the propagating boundaries for boundaries defined by free form curves or surfaces the distance fields have to be constructed numerically this may require either a polytope approximation to the boundary and or an iterative solution to determine the exact distance to the boundary in this paper a purely algebraic and computationally efficient technique is described for constructing distance measures from non uniform rational b splines nurbs boundaries that retain the geometric exactness of the boundaries while eliminating the need for iterative and non robust distance calculation the constructed distance measures are level sets of the implicitized constituent bezier patches of the nurbs surfaces that are obtained purely algebraically since in general the implicitized functions extend beyond the parametric range of the generating bezier patch algorithmic procedures are developed to trim these global implicit functions to the boundaries of the bezier patch boolean compositions are then carried out between adjoining bezier patches to construct a composite distance field over the domain the compositions rely on r functions that are also algebraic in nature the developed technique is demonstrated by constructing algebraic distance field for complex geometries and by solving a variety of examples culminating in the analysis of steady state heat conduction in a solid with arbitrary shaped three dimensional cracks