the finite deformation theory for beam plate and shell part v the shell element with drilling degree of freedom based on biot strain due to the facts that the spatial moment force is non conservative and the three components of the finite rotation pseudo vector are not independent the ordinary variational principle based on a functional achieving its stationary value is not suitable for the problem subject to non conservative loading the finite element method proposed in this paper is based on the virtual work principle rigid normal assumption polar decomposition and total lagrangian formulation

physically based adaptive preconditioning for early vision several problems in early vision have been formulated in the past in a regularization framework these problems when discretized lead to large sparse linear systems in this paper we present a novel physically based adaptive preconditioning technique which can be used in conjunction with a conjugate gradient algorithm to dramatically improve the speed of convergence for solving the aforementioned linear systems a preconditioner based on the membrane spline or the thin plate spline or a convex combination of the two is termed a physically based preconditioner for obvious reasons the adaptation of the preconditioner to an early vision problem is achieved via the explicit use of the spectral characteristics of the regularization filter in conjunction with the data this spectral function is used to modulate the frequency characteristics of a chosen wavelet basis and these modulated values are then used in the construction of our preconditioner we present the preconditioner construction for three different early vision problems namely the surface reconstruction the shape from shading and the optical flow computation problems performance of the preconditioning scheme is demonstrated via experiments on synthetic and real data sets

on the physical significance of higher order kinematic and static variables in a three dimensional shell formulation abstract in recent years considerable attention has been given to the development of higher order plate and shell models these models are able to approximately represent three dimensional effects while pertaining the efficiency of a two dimensional formulation due to pre integration of the structural stiffness matrix across the thickness especially the possibility to use unmodified complete three dimensional material laws within shell analysis has been a major motivation for the development of such models while the theoretical and numerical formulation of so called 7 parameter shell models including a thickness stretch of the shell has been discussed in numerous papers no thorough investigation of the physical significance of the additional kinematic and static variables coming along with the extension into three dimensions is known to the authors however realization of the mechanical meaning of these quantities is decisive for both a proper modeling of shell structures e g concerning loading and kinematic boundary conditions and a correct interpretation of the results in the present paper the significance of kinematic and static variables appearing in a 7 parameter model proposed by buchter and ramm 1992a are discussed it is shown how these quantities refine the model behavior and how they can be related to the classical variables such as curvatures and stress resultants furthermore the special role of the material law within such a formulation is addressed it is pointed out that certain requirements must hold for the variation of kinematic and static variables across the thickness to ensure correct results in this context it is found that the considered 7 parameter model can be regarded as optimal with respect to the number of degrees of freedom involved

geometric multigrid for high order regularizations of early vision problems abstract the surface estimation problem is used as a model to demonstrate a framework for solving early vision problems by high order regularization with natural boundary conditions because the application of algebraic multigrid is usually constrained by an m matrix condition which does not hold for discretizations of high order problems a geometric multigrid framework is developed for the efficient solution of the associated optimality systems it is shown that the convergence criteria of hackbusch w hackbusch iterative solution of large sparse systems of equations springer 1993 are met and in particular the general elliptic regularity required is proved further the galerkin formalism is used together with a multicolored ordering of unknowns to permit vectorization of a symmetric gauss seidel relaxation in image processing systems the implementation is analyzed computationally and inaccuracies are corrected by lumping and by proper floating point representations direct one dimensional calculations are used to estimate the effect of regularization order regularization strength relaxation and data support on the multigrid reduction factor a finite difference formulation is ruled out in favor of a finite element formulation a representative problem from magnetic resonance coil sensitivity estimation is solved using increasingly higher orders of regularization and the results are compared in terms of accuracy and multigrid convergence

eigenderivative analysis of asymmetric non conservative systems in general the damping matrix of a dynamic system or structure is such that it can not be simultaneously diagonalized with the mass and stiffness matrices by any linear transformation for this reason the eigenvalues and eigenvectors and consequently their derivatives become complex expressions for the first and second order derivatives of the eigenvalues and eigenvectors of these linear non conservative systems are given traditional restrictions of symmetry and positive definiteness have not been imposed on the mass damping and stiffness matrices the results are derived in terms of the eigenvalues and left and right eigenvectors of the second order system so that the undesirable use of the first order representation of the equations of motion can be avoided the usefulness of the derived expressions is demonstrated by considering a non proportionally damped two degree of freedom symmetric system and a damped rigid rotor on flexible supports copyright 2001 john wiley sons ltd

fast surface interpolation using hierarchical basis functions an alternative to multigrid relaxation that is much easier to implement and more generally applicable is presented conjugate gradient descent is used in conjunction with a hierarchical multiresolution set of basis functions the resultant algorithm uses a pyramid to smooth the residual vector before the direction is computed simulation results showing the speed of convergence and its dependence on the choice of interpolator the number of smoothing levels and other factors are presented the relationship of this approach to other multiresolution relaxation and representation schemes is also discussed

a variational approach to magnetic resonance coil sensitivity estimation a variational method for estimating a magnetic resonance coil sensitivity from its corresponding non uniform illumination of magnetic resonance images is proposed and analyzed the estimated sensitivity can then be used to correct non uniformities and indeed to facilitate high speed parallel image acquisition the data available for estimation include two images of the same field of view but obtained with and without a uniform coil sensitivity the non uniformly illuminated image is ideally the product of the uniformly illuminated image with the coil sensitivity thus the desired sensitivity is estimated roughly from a quotient of the two given images over the effective data support however the measurements are corrupted by noise the data are discontinuous at tissue boundaries and yet the coil sensitivity is very smooth in the selected estimation procedure the sum of a residual and a high order penalty is minimized in this form the problem is related to the surface estimation problem of early vision in the present context higher coil sensitivity decay rates are captured non parametrically by higher order penalties together with natural boundary conditions the role of alternative penalties and boundary conditions is investigated both analytically and numerically although high order operators are often approximated numerically with a product of low order factors such factorizations are shown here to lead to conspicuously spurious boundary conditions for surface estimation with sparse data support furthermore while finite elements present a natural numerical approach for solving the optimality system it is demonstrated here that lumping is required to avoid aberrant consequences in the limit of vanishing regularization corresponding to an ever improving signal to noise ratio finally with a proper analytical and numerical formulation the estimation procedure is demonstrated for a magnetic resonance imaging application involving parallel image acquisition

calculating derivatives of repeated and nonrepeated eigenvalues without explicit use of eigenvectors the analysis of inverse problems in parametric model updating often require the sensitivities of eigenvalues the calculation of these sensitivities is mathematically related to the derivatives of the eigenvalues with respect to the model parameters a common method to calculate these derivatives is the nelson method which requires the eigenvectors the method introduced in this paper is derived from the characteristic equation of the underlying general eigenvalue problem and allows the derivatives of eigenvalues with respect to the model parameters to be calculated without explicit use of the eigenvectors the method is extended for the case of repeated eigenvalues which leads to restrictions on the parameterization for repeated eigenvalues of multiplicity two these restrictions are formulated expicitly applications and limitations of the method are demonstrated by examples

finite deformation higher order shell models and rigid body motions this paper focuses on the developments of higher order shell models by employing the new concept of interpolation surfaces i surfaces inside the shell body we introduce n n p 3 i surfaces and choose the values of displacements with correspondence to these surfaces as fundamental shell unknowns such choice allows first to develop various higher order shell models in a very compact form and second to derive non linear strain displacement relationships which are completely free for arbitrarily large rigid body motions the general 3n parameter shell model is proposed in the framework of the lagrangian description the special 9 12 and 15 parameters cases corresponding to n 3 4 and 5 have been dealt in detail the proposed shell models account for thickness stretching and the complete 3d constitutive equations are utilized the displacement vectors of equally located i surfaces for each model are represented in a convected curvilinear coordinate system allowing one to develop directly finite deformation geometrically exact shell finite elements which could be discussed in future works 2008 elsevier ltd all rights reserved

non linear exact geometry 12 node solid shell element with three translational degrees of freedom per node this paper presents the finite rotation exact geometry eg 12 node solid shell element with 36 displacement degrees of freedom the term eg reflects the fact that coefficients of the first and second fundamental forms of the reference surface and christoffel symbols are taken exactly at each element node the finite element formulation developed is based on the 9 parameter shell model by employing a new concept of sampling surfaces s surfaces inside the shell body we introduce three s surfaces namely bottom middle and top and choose nine displacements of these surfaces as fundamental shell unknowns such choice allows one to represent the finite rotation higher order eg solid shell element formulation in a very compact form and to derive the strain displacement relationships which are objective that is invariant under arbitrarily large rigid body shell motions in convected curvilinear coordinates the tangent stiffness matrix is evaluated by using 3d analytical integration and the explicit presentation of this matrix is given the latter is unusual for the non linear eg shell element formulation copyright 2011 john wiley sons ltd

the computation of visible surface representations a computational theory of visible surface representations is developed the visible surface reconstruction process that computes these quantitative representations unifies formal solutions to the key problems of 1 integrating multiscale constraints on surface depth and orientation from multiple visual sources 2 interpolating dense piecewise smooth surfaces from these constraints 3 detecting surface depth and orientation discontinuities to apply boundary conditions on interpolation and 4 structuring large scale distributed surface representations to achieve computational efficiency visible surface reconstruction is an inverse problem a well posed variational formulation results from the use of a controlled continuity surface model discontinuity detection amounts to the identification of this generic model s distributed parameters from the data finite element shape primitives yield a local discretization of the variational principle the result is an efficient algorithm for visible surface reconstruction

characteristics of sensitivity analysis of repeated frequencies 5huang x z and zan s wing and fin buffet on the standard dynamic model rto rto tr 26 ac 323 avt tp 19 neuilly sur seine france oct 2000 6goura g s l time marching analysis of flutter using computational fluid dynamics ph d dissertation dept of aerospace engineering univ of glasgow glasgow scotland u k sept 2001 7goura g s l badcock k j woodgate m a and richards b e a data exchange method for fluid stucture interaction problems aeronautical journal vol 105 no 1046 2001 pp 215 221 8goura g s l badcock k j woodgate m a and richards b e implicit method for the time marching analysis of flutter aeronautical journal vol 105 no 1046 2001 pp 199 214 9melville r nonlinear simulation of aeroelastic instability aiaa paper 2001 0570 jan 2001 e livne associate editor

snakes active contour models a snake is an energy minimizing spline guided by external constraint forces and influenced by image forces that pull it toward features such as lines and edges snakes are active contour models they lock onto nearby edges localizing them accurately scale space continuation can be used to enlarge the capture region surrounding a feature snakes provide a unified account of a number of visual problems including detection of edges lines and subjective contours motion tracking and stereo matching we have used snakes successfully for interactive interpretation in which user imposed constraint forces guide the snake near features of interest

direct analytical methods for solving poisson equations in computer vision problems direct analytical methods are discussed for solving poisson equations of the general form delta u f on a rectangular domain some embedding techniques that may be useful when boundary conditions obtained from stereo and occluding boundary are defined on arbitrary contours are described the suggested algorithms are computationally efficient owing to the use of fast orthogonal transforms applications to shape from shading lightness and optical flow problems are also discussed a proof for the existence and convergence of the flow estimates is given experiments using synthetic images indicate that results comparable to those using multigrid can be obtained in a very small number of iterations

statistical model based damage detection and localization subspace based residuals and damage to noise sensitivity ratios the vibration based structural health monitoring problem is addressed as the double task of detecting damages modeled as changes in the eigenstructure of a linear dynamic system and localizing the detected damages within a fem of the monitored structure the proposed damage detection algorithm is based on a residual generated from a stochastic subspace based covariance driven identification method and on the statistical local approach to the design of detection algorithms this algorithm basically computes a global test which performs a sensitivity analysis of the residuals to the damages relative to uncertainties and noises how this residual relates to some residuals for damage localization and model updating is discussed damage localization is stated as a detection problem this problem is addressed by plugging aggregated sensitivities of the modes and mode shapes w r t fem structural parameters in the above setting this results in directional tests which perform the same type of damage to noise sensitivity analysis of the residual as for damage detection how the sensitivity aggregation mechanism relates to sub structuring is outlined numerical results obtained on one example are reported

cohesive zone models higher order continuum theories and reliability methods for computational failure analysis a concise overview is given of various numerical methods that can be used to analyse localization and failure in engineering materials the importance of the cohesive zone approach is emphasized and various ways to incorporate the cohesive zone methodology in discretization methods are discussed numerical representations of cohesive zone models suffer from a certain mesh bias for discrete representations this is caused by the initial mesh design while for smeared representations it is rooted in the ill posedness of the rate boundary value problem that arises upon the introduction of decohesion a proper representation of the discrete character of cohesive zone formulations which avoids any mesh bias can be obtained elegantly when exploiting the partition of unity property of finite element shape functions the effectiveness of the approach is demonstrated for some examples at different scales moreover examples are shown how this concept can be used to obtain a proper transition from a plastifying or damaging continuum to a shear band with gross sliding or to a fully open crack true discontinuum when adhering to a continuum description of failure higher order continuum models must be used meshless methods are ideally suited to assess the importance of the higher order gradient terms as will be shown finally regularized strain softening models are used in finite element reliability analyses to quantify the probability of the emergence of various possible failure modes

image analysis using multigrid relaxation methods image analysis problems posed mathematically as variational principles or as partial differential equations are amenable to numerical solution by relaxation algorithms that are local iterative and often parallel although they are well suited structurally for implementation on massively parallel locally interconnected computational architectures such distributed algorithms are seriously handi capped by an inherent inefficiency at propagating constraints between widely separated processing elements hence they converge extremely slowly when confronted by the large representations of early vision application of multigrid methods can overcome this drawback as we showed in previous work on 3 d surface reconstruction in this paper we develop multiresolution iterative algorithms for computing lightness shape from shading and optical flow and we examine the efficiency of these algorithms using synthetic image inputs the multigrid methodology that we describe is broadly applicable in early vision notably it is an appealing strategy to use in conjunction with regularization analysis for the efficient solution of a wide range of ill posed image analysis problems

numerical analysis of rotationally symmetric shells by the modal superposition method the system of differential equations governing the analysis of rotationally symmetric shells under time dependent or static surface loadings is formulated with the transverse meridional and circumferential displacements as the dependent variables the thickness of the shell may vary and four homogeneous boundary conditions may be prescribed at each boundary edge of the shell the governing differential equations for each fourier harmonic are obtained by use of fourier series in the circumferential direction of the shell influence coefficients at each of the node points along the shell meridian are obtained for each fourier component by employing ordinary finite difference representations for the meridional co ordinate derivatives with these influence coefficients a set of homogeneous flexibility equations governing the free vibration characteristics of the shell is obtained and solved for the frequencies and mode shapes for each fourier component the solutions under time dependent or static surface loadings and due to initial displacements and velocities are then obtained by expanding the solutions in terms of the modes of free vibration of the shell for each fourier component the solution for the total shell response is obtained by fourier series summation solutions for typical shells have been found to be in excellent agreement with solutions by the method of temporal and spatial finite differences solutions for a parabolic shell are presented as an example the solution is also presented for a published cylindrical shell example and is seen to be in excellent agreement with the published finite element method results

regularization of inverse visual problems involving discontinuities inverse problems such as the reconstruction problems that arise in early vision tend to be mathematically ill posed through regularization they may be reformulated as well posed variational principles whose solutions are computable standard regularization theory employs quadratic stabilizing functionals that impose global smoothness constraints on possible solutions discontinuities present serious difficulties to standard regularization however since their reconstruction requires a precise spatial control over the smoothing properties of stabilizers this paper proposes a general class of controlled continuity stabilizers which provide the necessary control over smoothness these nonquadratic stabilizing functionals comprise multiple generalized spline kernels combined with noncontinuous continuity control functions in the context of computational vision they may be thought of as controlled continuity constraints these generic constraints are applicable to visual reconstruction problems that involve both continuous regions and discontinuities for which global smoothness constraints fail

on three dimensional surface reconstruction methods a survey is presented of some of the surface reconstruction methods that can be found in the literature the focus is on a small recent and important subset of the published reconstruction techniques the techniques are classified based on the surface representation used implicit versus explicit functions a study is made of the important aspects of the surface reconstruction techniques one aspect is the viewpoint invariance of the methods this is an important property if object recognition is the ultimate objective the robustness of the various methods is examined it is determined whether the parameter estimates are biased and the sensitivity to obscuration is addressed the latter two aspects are particularly important for fitting functions in the implicit form a detailed description is given of a parametric reconstruction method for three dimensional object surfaces that involves numeric grid generation techniques and variational principle formulations this technique is invariant to rigid motion in dimensional space

wavelet methods for fast resolution of elliptic problems this paper shows that the use of wavelets to discretize an elliptic problem with dirichlet or neumann boundary conditions has two advantages an explicit diagonal preconditioning makes the condition number of the corresponding matrix become bounded by a constant and the order of approximation is locally of spectral type in contrast with classical methods using a conjugate gradient method one thus obtains fast numerical algorithms of resolution a comparison is also drawn between wavelet and classical methods

a reduced integration solid shell finite element based on the eas and the ans concept geometrically linear problems in this paper a new reduced integration eight node solid shell finite element is presented the enhanced assumed strain eas concept based on the hu washizu variational principle requires only one eas degree of freedom to cure volumetric and poisson thickness locking one key point of the derivation is the taylor expansion of the inverse jacobian with respect to the element center which closely approximates the element shape and allows us to implement the assumed natural strain ans concept to eliminate the curvature thickness and the transverse shear locking the second crucial point is a combined taylor expansion of the compatible strain with respect to the center of the element and the normal through the element center leading to an efficient and locking free hourglass stabilization without rank deficiency hence the element requires only a single integration point in the shell plane and at least two integration points in thickness direction the formulation fulfills both the membrane and the bending patch test exactly which has to the authors knowledge not yet been achieved for reduced integration eight node solid shell elements in the literature owing to the three dimensional modeling of the structure fully three dimensional matenal models can be implemented without additional assumptions

partial derivatives of repeated eigenvalues and their eigenvectors the analysis of inverse problems in linear modeling often require the sensitivities of the eigenvalues and eigenvectors the calculation of these sensitivities is mathematically related to the corresponding partial derivatives which do not exist for any parameterization inasmuch as eigenvalues and eigenvectors are coupled by the constitutional equation of the general eigenvalue problem their derivatives are coupled too conditions on the parameterization are derived and formulated as theorems which ensure the existence of the partial derivatives of the eigenvalues and eigenvectors with respect to these parameters the application of the theorems is demonstrated by examples

interpolation using wavelet bases efficient solutions to regularization problems can be obtained using orthogonal wavelet bases for preconditioning good approximate solutions can be obtained in only two or three iterations with each iteration requiring only o n operations and o n storage locations two and three dimensional examples are shown using both synthetic and real range data

a continuum based shell theory for non linear applications the paper introduces a non linear shell theory which provides a complete three dimensional state of stress since the theory is derived from simple three dimensional continuum mechanics it is very easy to understand as an example the theory is applied to quadrilateral shell elements which provide only displacement degrees of freedom located at nodes on the outer surfaces and one degree of freedom at the middle surface it is proposed to eliminate this degree of freedom on element level so that the elements have the same layout as the equivalent brick elements but have a better behaviour in bending have stress resultants and are cheaper with respect to computational effort the advantages with respect to implementation in a finite element program as well as in special applications are obvious however well known conditioning problems in thin shell applications must be expected therefore emphasis is put on this issue in the example problems it is shown that the elements can give acceptable answers in engineering applications and offer a potential for material non linear applications which will be considered in a forthcoming paper

fast surface interpolation using multiresolution wavelet transform discrete formulation of the surface interpolation problem usually leads to a large sparse linear equation system due to the poor convergence condition of the equation system the convergence rate of solving this problem with iterative method is very slow to improve this condition a multiresolution basis transfer scheme based on the wavelet transform is proposed by applying the wavelet transform the original interpolation basis is transformed into two sets of bases with larger supports while the admissible solution space remains unchanged with this basis transfer a new set of nodal variables results and an equivalent equation system with better convergence condition can be solved the basis transfer can be easily implemented by using an qmf matrix pair associated with the chosen interpolation basis the consequence of the basis transfer scheme can be regarded as a preconditioner to the subsequent iterative computation method the effect of the transfer is that the interpolated surface is decomposed into its low frequency and high frequency portions in the frequency domain it has been indicated that the convergence rate of the interpolated surface is dominated by the low frequency portion with this frequency domain decomposition the low frequency portion of the interpolated surface can be emphasized as compared with other acceleration methods this basis transfer scheme provides a more systematical approach for fast surface interpolation the easy implementation and high flexibility of the proposed algorithm also make it applicable to various regularization problems

an investigation of a finite rotation four node assumed strain shell element the paper presents a shell formulation based on the degenerated solid approach the theory employs covariant strains and performs explicit integration through the shell thickness the rigid body motion is exactly represented the consistent tangent stiffness matrix is evaluated for the four node quadrilateral it is shown in the final part that this type of element which distinguishes itself by a very simple and easily understandable theory gives good answers for linear as well as non linear applications

one point quadrature shell element with through thickness stretch a general purpose one point quadrature shell element accounting for through thickness deformation is developed in the shell a complete 3 d constitutive law is introduced leading to a 7 parameter theory which explicitly accounts for thickness change and also for a linear variation of thickness stretch an interpolation scheme for the shell director is developed to avoid thickness locking the developed shell element covers flexible warping behavior by using a local nodal coordinate system at each node which is updated with second order accuracy a physical stabilization scheme for zero energy modes is employed based on the decomposition of the strain field into constant and linear terms with respect to the natural coordinates the rigid body projection is applied to treat rigid body rotations effectively linear and nonlinear patch tests including elasto plasticity and contact are performed and the results are compared with analytical or previously reported results the results are also compared with those of 5 parameter shell elements in order to show that there is no significant deterioration in accuracy especially for thin shell applications

fast wavelet transforms and numerical algorithms i a class of algorithms is introduced for the rapid numerical application of a class of linear operators to arbitrary vectors previously published schemes of this type utilize detailed analytical information about the operators being applied and are specific to extremely narrow classes of matrices in contrast the methods presented here are based on the recently developed theory of wavelets and are applicable to all calderon zygmund and pseudo differential operators the algorithms of this paper require order o n or o n log n operations to apply an n n matrix to a vector depending on the particular operator and the version of the algorithm being used and our numerical experiments indicate that many previously intractable problems become manageable with the techniques presented here

height and gradient from shading the method described here for recovering the shape of a surface from a shaded image can deal with complex wrinkled surfaces integrability can be enforced easily because both surface height and gradient are represented the robustness of the method stems in part from linearization of the reflectance map about the current estimate of the surface orientation at each picture cell the new scheme can find an exact solution of a given shape from shading problem even though a regularizing term is included this is a reflection of the fact that shape from shading problems are it not ill posed when boundary conditions are available or when the image contains singular points

sensitivity of repeated eigenvalues to perturbations two methods for calculating the derivatives of a repeated eigenvalue of viscously damped vibrating systems with respect to a parameter are given the first method implements the subspace spanned by the eigenvectors corresponding to the repeated eigenvalue the second method is based on an explicit formula that uses the characteristic equation directly without explicitly employing the eigenvector data examples demonstrate the various results

large deformation analysis of contact in degenerate shell elements a new formulation is presented for the analysis of contact in degenerate shell elements this formulation accounts for the transverse stress and strain through the shell thickness and can accommodate double sided shell contact the kinematic contact conditions are expressed accurately in terms of the physical shell contacting surfaces and the problem is formulated in terms of variational inequalities vi large deformations and rotations are accounted for by invoking the appropriate stress and strain measures the solution of the variational inequality is obtained using lagrange multipliers this guarantees that the kinematic contact constraints are accurately satisfied and that the solution is free from user defined parameters two examples involving three beams in contact and ring compression are simulated to establish the validity of the developed formulations and the solution technique 1998 john wiley sons ltd

reliable and efficient computation of optical flow in this paper we present two very efficient and accurate algorithms for computing optical flow the first is a modified gradient based regularization method and the other is an ssd based regularization method for the gradient based method to amend the errors in the discrete image flow equation caused by numerical differentiation as well as temporal and spatial aliasing in the brightness function we propose to selectively combine the image flow constraint and a contour based flow constraint into the data constraint by using a reliability measure each data constraint is appropriately normalized to obtain an approximate minimum distance of the data point to the linear flow equation constraint instead of the conventional linear flow constraint these modifications lead to robust and accurate optical flow estimation we propose an incomplete cholesky preconditioned conjugate gradient algorithm to solve the resulting large and sparse linear system efficiently our ssd based regularization method uses a normalized ssd measure based on a similar reasoning as in the gradient based scheme as the data constraint in a regularization framework the nonlinear conjugate gradient algorithm in conjunction with an incomplete cholesky preconditioning is developed to solve the resulting nonlinear minimization problem experimental results on synthetic and real image sequences for these two algorithms are given to demonstrate their performance in comparison with competing methods reported in literature

generalized energy momentum method for non linear adaptive shell dynamics in the present study a generalization of the energy momentum method denoted by generalized energy momentum method applied to the non linear dynamics of shells will be developed within the framework of the generalized a method this algorithmic environment contains the unconditionally stable energy momentum method and its numerically damped version as well as the classical newmark and a methods as special cases in order to control the size of the time steps of the integration scheme with respect to accuracy and eaciency an adaptive time stepping procedure based on local a posteriori error estimation will be improved for non linear dynamical systems and applied to the proposed class of algorithms the spatial discretization is realized by an eight noded finite shell element of reissner mindlin type including an extensible shell director field permitting the application of three dimensional material laws the original formulation of this finite element will be developed for non linear dynamic analysis and adapted for the employment within the introduced energy conserving decaying time integration scheme 1999 elsevier science s a all rights reserved

design sensitivity analysis for repeated eigenvalues in structural design eigenvalue sensitivity can be analytically computed using fox and kapoor s formula however if the eigenvalues are not distinct the calculation of eigenvalue sensitivities for the repeated eigenvalues using fox s formula sometimes does not yield correct answers unless the eigenvectors associated with the repeated eigenvalues are properly defined it has been found in this paper that for two types of frequently designed structures although the repeated eigenvalues exist their sensitivities with respect to specific design variables can be found without forming an auxiliary eigenequation as proposed by earlier researchers

finite element concepts for finite elastoplastic strains and isotropic stress response in shells theoretical and computational analysis this paper presents appropriate finite element concepts accounting for finite elastoplastic strains and isotropic stress response in arbitrary shells three parameterization strategies for the calculation of thin and thick smooth shells as well as shell intersections are discussed in detail in this context the importance of the deformation gradient for an efficient implementation is especially emphasized according to the parameterizations the computational plasticity algorithms are derived in general three dimensional 3 d form for thick shell structures and a restricted 2 d form satisfying the plane stress state underlying thin shells in order to describe arbitrary shell geometries the isoparametric concept is applied to all proposed finite element formulations these are based on quadrilateral 4 node mixed finite shell elements the variational approaches of the enhanced assumed strain method the assumed natural strain concept and the reduced integration technique are accurately considered by means of representative numerical examples the performance of the three different finite element concepts is demonstrated furthermore their individual properties are addressed with respect to efficiency and numerical accuracy thus crucial consequences for an optimal modelling of finite plastic strains in shells can be outlined

optimal solid shells for non linear analyses of multilayer composites ii dynamics abstract we are presenting a simple low order solid shell element formulation having only displacement degrees of freedom dofs i e without rotational dofs that has an optimal number of parameters to pass the patch tests and thus allows for efficient and accurate analyses of large deformable multilayer shell structures using elements at extremely high aspect ratio with the dynamics referred to a fixed inertial frame the elements can be used to analyze multilayer shell structures undergoing large overall motion the formulation of this element is based on the mixed hu washizu variational principle leading to a novel enhancing strain tensor enhanced assumed strain eas method that renders the computation particularly efficient with improved in plane and out of plane bending behavior poisson thickness locking especially in refined analyses of composite structures involving a large number of high aspect ratio layers the energy momentum conserving algorithm in the context of current solid shell element is presented we discuss the eas formulation based on the displacement gradient and its complexity compared to formulation on the green lagrange strain shear locking and curvature thickness locking are treated using the assumed natural strain ans method the element has an optimal combination of the ans method and the minimal number of eas parameters required to pass the plate bending patch test numerical examples involving dynamic analyses with conservation of energy and momentum of multilayer shell structures having a large range of element aspect ratios are presented several implicit direct integration methods with without numerical dissipation are used and compared in terms of the accuracy stability and cost in multilayer shell structure finally we note that the topic in this paper is a fitting dedication to professor ekkehard ramm who has made important pioneering contributions in this research direction

constraint networks in vision applications in machine vision of constraint networks based on an augmented lagrangian formulation are discussed only those applications that have a fundamental significance are addressed the first of these provides a generalization of the harris coupled depth slope analog model of visual reconstruction because of the generality of the approach one can derive many more alternative structures and the mathematical setting places this approach within the bounds of mixed finite element theory this offers many advantages in terms of the associated mathematical theory and implementation on digital machines the second use is in data fusion which is a crucial task for systems using multiple sensors or methods of analysis of data

computing eigenvalues eigenvectors and frequency responses of structures with non proportional damping abstract this paper presents algorithms to compute eigenvalues eigenvectors and frequency response matrix of a linear structure with non proportional damping the method is based on derivatives of repeated or unrepeated complex eigenvalues and complex eigenvectors since eigenvectors are not unique for a repeated eigenvalue a special algorithm is developed to select the correct eigenvector for a given non proportional damping the advantage of the proposed method is that it only requires the knowledge of natural frequencies and mode shapes of the undamped structure the validity of this method is established by comparing numerical results from this algorithm to exact answers

on poisson solvers and semi direct methods for computing area based optical flow simchony chellappa and shao 1990 proposed a semi direct method for computing area based optical flow their method is based on the iterative application of a direct poisson solver this method is restricted to dirichlet boundary conditions i e it is applicable only when velocity vectors at the boundary of the domain are known a priori the authors show both experimentally and through analysis that the semi direct method converges only for very large smoothness at such levels of smoothness the solution is obtained merely by filling in the known boundary values the data from the image is almost totally ignored next the authors consider the concus and golub method 1973 another semi direct method for computing optical flow this method always converges but the convergence is too slow to be of any practical value the authors conclude that semi direct methods are not suited for the computation of area based optical flow

kinematics of finite rotation shells with in plane twist parameter abstract the paper concerns shell equations derived from a 3d mixed formulation with explicit rotations the constitutive equation is postulated in terms of the relaxed biot stress and right stretch strain the shell kinematics is based on the reissner hypothesis and on a constant linear approximation of the rotation tensor with respect to the thickness coordinate the rotation around the shell director is parametrized by the drill and in plane twist parameters with the latter one associated with the linear approximation the in plane twist parameter is new and hence consequences of its presence for the shell rotation constrains and strain measures are examined and compared to the formulation with the drill rotation only in the presented formulation the drill rotation is retained explicitly and can be recovered from the drill rotation constraint while the in plane twist parameter is an internal parameter of the theory in this way the enhanced shell kinematics does not increase the number of degrees of freedom of a discrete model

a theory for multiresolution signal decomposition the wavelet representation multiresolution representations are effective for analyzing the information content of images the properties of the operator which approximates a signal at a given resolution were studied it is shown that the difference of information between the approximation of a signal at the resolutions 2 sup j 1 and 2 sup j where j is an integer can be extracted by decomposing this signal on a wavelet orthonormal basis of l sup 2 r sup n the vector space of measurable square integrable n dimensional functions in l sup 2 r a wavelet orthonormal basis is a family of functions which is built by dilating and translating a unique function psi x this decomposition defines an orthogonal multiresolution representation called a wavelet representation it is computed with a pyramidal algorithm based on convolutions with quadrature mirror filters wavelet representation lies between the spatial and fourier domains for images the wavelet representation differentiates several spatial orientations the application of this representation to data compression in image coding texture discrimination and fractal analysis is discussed