high order finite elements for shells in this article the p version finite element method is applied to thin walled structures two different hierarchic element formulations are compared a shell approach as well as a shell like solid formulation both approaches are compared for linear elastic and elastoplastic problems special emphasis is placed on the efficiency as well as on determining the area of application for both formulations

a class of path valued markov processes and its applications to superprocesses let s be a continuous markov process satisfying certain regularity assumptions we introduce a path valued strong markov process associated with s which is closely related to the so called superprocess with spatial motion s in particular a subseth of the state space of s intersects the range of the superprocess if and only if the set of paths that hith is not polar for the path valued process the latter property can be investigated using the tools of the potential theory of symmetric markov processes a set is not polar if and only if it supports a measure of finite energy the same approach can be applied to study sets that are polar for the graph of the superprocess in the special case when s is a diffusion process we recover certain results recently obtained by dynkin

complementary retrieval for distorted images in today s computer networks the amount of digital images increases rapidly and enormously however images may be distorted through different types of processing such as histogram equalization quantization smoothing compression noise corruption geometric transformation and changing of illumination it is imperative to develop an effective method to retrieve the original images from very large image databases because only the original images are stored for economy in this study a new image normalization method is first proposed to solve the problem with illumination varying a complementary retrieval method is then proposed to resist various types of processing according to the type of distortion all processing are classified into three distortion categories low frequency high frequency and geometric transformation in addition different features are resistant to different distortion categories however the distortion by which a query image is corrupted is usually unknown hence a complementary analysis is proposed to determine the distortion category for each query image and the feature resistant to the estimated category is used to retrieve the desired original image as a result an effective retrieval method is achieved the feasibility and effectiveness of our method are demonstrated by experimental results

a mortar segment to segment contact method for large deformation solid mechanics abstract contact modeling is still one of the most difficult aspects of non linear implicit structural analysis most 3d contact algorithms employed today use node on segment approaches for contacting dissimilar meshes two pass node on segment contact approaches have the well known deficiency of locking due to over constraint in this work we develop and demonstrate a segment to segment contact approach based on the mortar method by eliminating the over constraint this method appears to be much more robust than the node on segment approach furthermore node on segment approaches suffer when individual nodes slide out of contact at contact surface boundaries or when contacting nodes slide from facet to facet this causes jumps in the contact forces due to the discrete nature of the constraint enforcement and difficulties in convergence for implicit solution techniques these jumps in forces are avoided in the segment to segment approach since penetration is measured by the occluded weighted volume which varies smoothly with perturbations until now all mortar schemes have been developed for small deformation sliding and have mainly been applied on flat surfaces here we will present the integration scheme and the linearization approach used for handling the contact surface integrals in the event of large sliding the schemes are designed to conserve linear momentum and can be applied to arbitrarily curved 3d surfaces although expensive our numerical examples demonstrate that the approach is far more robust than even smoothed node on segment contact techniques that is problems previously not solvable with node on segment can now be solved with our segment to segment contact

finite deformation post buckling analysis involving inelasticity and contact constraints this paper is concerned with the numerical solution of large deflection structural problems involving finite strains subject to contact constraints and unilateral boundary conditions and exhibiting inelastic constitutive response first a three dimensional finite strain beam model is summarized and its numerical implementation in the two dimensional case is discussed next a penalty formulation for the solution of contact problems is presented and the correct expression for consistent tangent matrix is developed finally basic strategies for tracing limit points are reviewed and a modification of the arc length method is proposed the good performance of the procedures discussed is illustrated by means of numerical examples

on the solvability of closest point projection procedures in contact analysis analysis and solution strategy for surfaces of arbitrary geometry abstract the uniqueness and existence of the closest point projection procedure widely used in contact mechanics are analyzed in the current article first a projection domain for c 2 continuous surfaces is created based on the geometrical properties of surfaces then any point from the projection domain has a unique projection onto the given surface it is shown that in order to construct a continuous projection domain for arbitrary globally c 1 or c 0 continuous surfaces a projection routine should be generalized and also include a projection onto a curved edge and onto corner points criteria of uniqueness and existence of the corresponding projection routine are given and discussed from the geometrical point of view some examples showing the construction of the projection domain as well as the necessity of a generalized projection routine are given

mortar based frictional contact formulation for higher order interpolations using the moving friction cone abstract finite element discretizations including contact usually apply the standard nts node to segment element thus a coupling with higher order solid elements leads to inconsistencies in the transmission of contact stresses one can circumvent this using the mortar method which includes a weak projection of the contact constraints in this paper we present a penalty formulation based on the mortar concept for two dimensional large deformation frictional contact the discretization of the contact surfaces contains quadratic approximations which can be used within a quadratic approximation of the solid elements to obtain a simple and efficient matrix formulation the moving friction cone algorithm is applied

transient three dimensional domain decomposition problems frame indifferent mortar constraints and conserving integration the present work deals with transient large deformation domain decomposition problems the tying of dissimilar meshed grids is performed by applying the mortar method in this connection a reformulation of the original linear mortar constraints is proposed which retains frame indifference for arbitrary discretizations of the interface furthermore a specific coordinate augmentation technique is proposed to make possible the design of an energy momentum scheme numerical examples demonstrate the robustness and enhanced numerical stability of the newly developed energy momentum scheme for three dimensional problems copyright 2009 john wiley sons ltd

on the role of frame invariance in structural mechanics models at finite rotations in this work we re examine so called geometrically exact models for structures such as beams shells or solids with independent rotation field with respect to invariance under superposed rigid body motion a special attention is given to clarifying the issues pertaining to the finite element implementation which guarantees that the invariance of the continuum problem is preserved by its discrete approximation several numerical simulations dealing with finite rotations of structural models are presented in order to further illustrate and confirm the given theoretical considerations

a hausdorff measure classification of g polar sets for the superdiffusions we establish relations betweeng polar sets of superdiffusions and the restricted hausdorff dimension as an application we give new proofs of dynkin s criteria for thes polarity andh polarity established earlier by dawson iscoe perkins and le gall under more restrictive assumptions

a modified node to segment algorithm passing the contact patch test summary several investigations have shown that the classical one pass node to segment nts algorithms for the enforcement of contact constraints fail the contact patch test this implies that the algorithms may introduce solution errors at the contacting surfaces and these errors do not necessarily decrease with mesh refinement the previous research has mainly focused on the lagrange multiplier method to exactly enforce the contact geometry conditions the situation is even worse with the penalty method due to its inherent approximation that yields a solution affected by a non zero penetration the aim of this study is to analyze and improve the contact patch test behavior of the one pass nts algorithm used in conjunction with the penalty method for 2d frictionless contact the paper deals with the case of linear elements for this purpose several sequential modifications of the basic formulation have been considered which yield incremental improvements in results of the contact patch test the final proposed formulation is a modified one pass nts algorithm which is able to pass the contact patch test also if used in conjunction with the penalty method in other words this algorithm is able to correctly reproduce the transfer of a constant contact pressure with a constant proportional penetration copyright q 2009 john wiley sons ltd

consistent development of a beam to beam contact algorithm via the curve to solid beam contact analysis for the nonfrictional case summary beam to beam contact can be dually described depending on the scale as contact between curves or contact between surfaces the surface to surface algorithm requires a computationally expensive continuum description of the beams the curve to curve ctc contact algorithm is generated from the corresponding closest point projection cpp procedure determining a minimal distance between curves and involves less expensive beam finite elements the existence and uniqueness criterion of the cpp procedure formulated already in earlier publications is analyzed in detail especially in the case of multiple solutions for parallel curves it is shown that the ctc contact algorithm cannot be applied for general parallel curves which can be generated in an arbitrary range of angles between the tangent lines a new curve to solid beam contact algorithm is here developed this algorithm requires a special solid beam finite element and is combining the advantages of surface contact together with the flexibility of the application to beam to beam contact further a special case with parallel tangent vectors is considered from the classical hertzian contact problem it is found numerically that the corresponding length of a contact zone is well correlated with the hertz theory a possible application of the developed strategy for wire ropes is analyzed numerically this article is protected by copyright all rights reserved

super brownian motion path properties and hitting probabilities sample path properties of super brownian motion including a one sided modulus of continuity and exact hausdorff measure function of the range and closed support are obtained analytic estimates for the probability of hitting balls lead to upper bounds on the hausdorff measure of the set of k multiple points and a sufficient condition for a set to be polar

color based object recognition abstract the purpose is to arrive at recognition of multicolored objects invariant to a substantial change in viewpoint object geometry and illumination assuming dichromatic reflectance and white illumination it is shown that normalized color rgb saturation s and hue h and the newly proposed color models c 1 c 2 c 3 and l 1 l 2 l 3 are all invariant to a change in viewing direction object geometry and illumination further it is shown that hue h and l1l2l3 are also invariant to highlights finally a change in spectral power distribution of the illumination is considered to propose a new color constant color model m1m2m3 to evaluate the recognition accuracy differentiated for the various color models experiments have been carried out on a database consisting of 500 images taken from 3 d multicolored man made objects the experimental results show that highest object recognition accuracy is achieved by l1l2l3 and hue h followed by c1c2c3 normalized color rgb and m1m2m3 under the constraint of white illumination also it is demonstrated that recognition accuracy degrades substantially for all color features other than m1m2m3 with a change in illumination color the recognition scheme and images are available within the pictoseek and pic2seek systems on line at http www wins uva nl research isis zomax

on finite element implementation of geometrically nonlinear reissner s beam theory three dimensional curved beam elements abstract finite element implementation of the three dimensional finite strain beam theory of reissner is considered in this work in contrast with some earlier works on the subject discussed here are the beam elements whose reference axes are arbitrary space curved lines we have shown that an improved representation of curved reference geometry significantly increases the accuracy of the results however it also makes the choice of non locking finite element interpolations somewhat more delicate a hierarchical displacement interpolation proposed here is proved to be capable of eliminating both shear and membrane locking phenomena a very satisfying non locking performance is demonstrated for a set of problems in nonlinear elasto statics

superdiffusions and parabolic nonlinear differential equations we establish connections between superdiffusion processes and one class of nonlinear parabolic differential equations analytic results due to brezis and friedman baras and pierre and others are used to investigate the graphs of superdiffusions a survey of the literature and general comments are presented in section 4

deformed trademark retrieval based on 2d pseudo hidden markov model abstract a new deformed trademark retrieval method based on two dimensional pseudo hidden markov model 2d phmm is proposed in this paper most trademark retrieval systems focus on color features shape silhouettes or the combination of color and shape however these approaches adopted individual silhouettes as shape features leading to the following two crucial problems first most trademarks have various numbers of decomposed components while the silhouette based approaches cannot handle the variety correctly second the infringement cases in which trademarks are changed by non rigid deformation in particular nonlinear deformation may escape detection thus our method focuses on the overall appearance of trademarks and incorporates color and shape features into 2d phmm to tackle the above two problems the reason to involve 2d phmm is that it has high tolerance to noise and distortion moreover contextual information can be incorporated into it in a natural and elegant way however 2d phmm is computation intensive and sensitive to rotation scale and translation variations thus it is the main originality of this paper to include the advantages of 2d phmm but to exclude its disadvantages as a result similar trademarks can be retrieved effectively even those with different numbers of components or non rigid deformation various experiments have been conducted on a trademark database to prove the effectiveness and practicability of the proposed method

on some aspects for contact with rigid surfaces surface to rigid surface and curves to rigid surface algorithms abstract special algorithms allowing a simplified description of contact between deformable body and rigid surfaces are developed based on the geometrically exact covariant description of contact a special attention is given to various geometric combinations where the contact can be represented as a contact between surfaces and b contact between a curve and a surface for contact between surfaces leading to the segment to analytical surface stas approach two algorithms can be distinguished based on the selection of a coordinate system for the closest point projection cpp procedure a rigid surface is a slave surface and b rigid surface is a master surface a special combination of both contact kinematics for the surface to surface and for the curve to curve approaches is employed for the contact between a curve and a surface leading to the curve to rigid surface ctrs approach the last algorithm is verified with the well known euler formula for the rope cylinder interaction as well as with a new derived generalization into a 3d spiral rope on a cylinder the developed algorithms can be straightforwardly implemented within an iso geometric approach as well as within the conventional finite elements where rigid surfaces are given by cad patches any type of elements can be employed for the contacting deformable surface curve because the algorithms are formulated in a covariant form

a probabilistic approach to one class of nonlinear differential equations we establish connections between positive solutions of one class of nonlinear partial differential equations and hitting probabilities and additive functionals of superdiffusion processes as an application we improve results on superprocesses by using the recent progress in the theory of removable singularities for differential equations

three dimensional mortar based frictional contact treatment in isogeometric analysis with nurbs a three dimensional mortar based frictional contact treatment in isogeometric analysis with nurbs is presented in the finite deformation regime within a setting where the nurbs discretization of the contact surface is inherited directly from the nurbs discretization of the volume the contact integrals are evaluated through a mortar approach where the geometrical and frictional contact constraints are treated through a projection to control point quantities the formulation delivers a non negative pressure distribution and minimally oscillatory local contact interactions with respect to alternative lagrange discretizations independent of the discretization order these enable the achievement of improved smoothness in global contact forces and moments through higher order geometrical descriptions it is concluded that the presented mortar based approach serves as a common basis for treating isogeometric contact problems with varying orders of discretization throughout the contact surface and the volume

illumination invariant image retrieval and video segmentation abstract images or videos may be imaged under different illuminants than models in an image or video proxy database changing illumination color in particular may confound recognition algorithms based on color histograms or video segmentation routines based on these here we show that a very simple method of discounting illumination changes is adequate for both image retrieval and video segmentation tasks we develop a feature vector of only 36 values that can also be used for both these objectives as well as for retrieval of video proxy images from a database the new image metric is based on a color channel normalization step followed by reduction of dimensionality by going to a chromaticity space treating chromaticity histograms as images we perform an effective low pass filtering of the histogram by first reducing its resolution via a wavelet based compression and then by a dct transformation followed by zonal coding we show that the color constancy step color band normalization can be carried out in the compressed domain for images that are stored in compressed form and that only a small amount of image information need be decompressed in order to calculate the new metric the new method performs better than previous methods tested for image or texture recognition and operates entirely in the compressed domain on feature vectors apart from achieving illumination invariance for video segmentation so that e g an actor stepping out of a shadow does not trigger the declaration of a false cut the metric reduces all videos to a uniform scale thus thresholds can be developed for a training set of videos and applied to any new video including streaming video for segmentation as a one pass operation

a mortar finite element method using dual spaces for the lagrange multiplier the mortar finite element method allows the coupling of different discretization schemes and triangulations across subregion boundaries in the original mortar approach the matching at the interface is realized by enforcing an orthogonality relation between the jump and a modified trace space which serves as a space of lagrange multipliers in this paper this lagrange multiplier space is replaced by a dual space without losing the optimality of the method the advantage of this new approach is that the matching condition is much easier to realize in particular all the basis functions of the new method are supported in a few elements the mortar map can be represented by a diagonal matrix in the standard mortar method a linear system of equations must be solved the problem is considered in a positive definite nonconforming variational as well as an equivalent saddle point formulation

consistent mesh tying methods for topologically distinct discretized surfaces in non linear solid mechanics this work presents a new technique for joining dissimilar meshes in non linear finite element analysis with the novel result that the adjoining surfaces do not need to be spatially coincident for patch tests to be passed the work builds in some sense on results previously presented by dohrmann et al international journal for numerical methods in engineering 1991 40 1205 but considerably generalizes upon the results presented there most importantly it is shown that consistency of the tied finite element formulation may be achieved such that implementation of element formulations is not affected through the use of a three field variational principle applied over the contacting region a key conclusion of the work is that although the approach advocated bears some resemblance to mortar element schemes for contact analysis see for example mcdevitt and laursen international journal for numerical methods in engineering 2000 48 1525 a straightforward application of a mortaring scheme is not sufficient to guarantee patch test passage when dissimilar meshing of curved surfaces leads to local open volumes or overlaps between tied surfaces in their reference configurations the proposed algorithm is demonstrated through a number of numerical examples performed within a matrix free non linear equation solving framework published in 2003 by john wiley sons ltd

geometrically exact theory for contact interactions of 1d manifolds algorithmic implementation with various finite element models abstract the intuitive understanding of contact between bodies is based on the geometry of adjoining bodies a more sophisticated approach of an advanced analysis including the application of various numerical methods is to take advantage of the geometry of an analyzed object and describe the problem in the best coordinate system the best coordinate system to describe contact interaction in all its geometrical details is a coordinate system attached to the geometrical features of contacting bodies this leads to a systematical analysis of geometrical situations leading to contact pairs surface to surface line to surface point to surface line to line point to line each contact pair is inherited with a special coordinate system based on its geometrical properties the current contribution is concentrating on contact between 1d manifolds in 3d space this is the majority of edge to edge beam to beam cable to edge etc contact cases the geometrically exact curve to curve contact approach is then systematically combined together with various finite element approaches classical finite elements isogeometric beam finite elements and also with a new developed solid beam approach examples illustrating the diversity of various finite element combinations e g within knot mechanics are shown

on illumination invariance in color object recognition abstract several color object recognition methods that are based on image retrieval algorithms attempt to discount changes of illumination in order to increase performance when test image illumination conditions differ from those that are obtained when the image database was created here we investigate under what general conditions illumination change can be described using a simple linear transform among rgb channels for a multi colored object and adduce a different underlying principle than that usually suggested the resulting new method the linear color algorithm is more accurately illuminant invariant than previous methods an implementation of the method uses a combination of wavelet compression and dct transform to fully exploit the technique of low pass filtering for efficiency results are very encouraging with substantially better performance than other methods tested the method is also fast in that the indexing process is entirely carried out in the compressed domain and uses a feature vector of only 63 integers

a mixed formulation of mortar based frictionless contact abstract a class of mortar based frictionless contact formulations is derived based on a classical three field mixed variational framework within a penalty regularization complemented by uzawa augmentations discrete mortar constraints are naturally induced by the variational setting major aspects of earlier mortar approaches are obtained through constrained lumped or unconstrained recovery procedures for the mixed kinematic and kinetic mortar quantities from their projected counterparts two and three dimensional examples at the infinitesimal and finite deformation regimes highlight the local and global quality of the contact interactions

on the choice of finite rotation parameters in this work we discuss some aspects of the three dimensional finite rotations pertinent to the formulation and computational treatment of the geometrically exact structural theories among various possibilities to parameterize the finite rotations special attention is dedicated to a choice featuring an incremental rotation vector some computational aspects pertinent to the implementation of the newton iterative scheme and the newmark time stepping algorithm applied to solving these problems are examined representative numerical simulations are presented in order to illustrate the performance of the proposed formulation