co rotational beam elements with warping effects in instability problems the present paper investigates the formulation of 3d co rotational beam elements for the buckling and post buckling analysis of frame structures following pacoste and eriksson comput methods app

modal analysis and shape optimization of rotating cantilever beams when a cantilever beam rotates about an axis perpendicular to its neutral axis its modal characteristics often vary significantly if the geometric shape and the material property of the beam are given the modal characteristic variations can be accurately estimated following a well established analysis procedure employing assumed mode method or finite element method in many practical design situations however some modal characteristics are usually specified as design requirements and the geometric shape that satisfies the requirements needs to be found in the present study certain modal characteristic requirements such as maximum or minimum slope natural frequency loci are specified and the geometric shapes that satisfy the requirements are obtained through an optimization procedure

locking free isogeometric collocation methods for spatial timoshenko rods in this work we present the application of isogeometric collocation techniques to the solution of spatial timoshenko rods the strong form equations of the problem are presented in both displacement based and mixed formulations and are discretized via nurbs based isogeometric collocation several numerical experiments are reported to test the accuracy and efficiency of the considered methods as well as their applicability to problems of practical interest in particular it is shown that mixed collocation schemes are locking free independently of the choice of the polynomial degrees for the unknown fields such an important property is also analytically proven

on the solution of almansi michell s problem abstract this paper develops a hamiltonian formalism for the solution of almansi michell s problem that generalizes the corresponding solution of saint venant s problem saint venant s and almansi michell s problems can be represented as homogenous and non homogenous hamiltonian systems respectively the solution of almansi michell s problem is determined by the coefficients of the hamiltonian matrix but also by the distribution pattern of the applied loading the solution proceeds in two steps first for the homogenous problem a projective transformation is constructed based on a symplectic matrix and second the effects of the external loading are taken into account by augmenting this projection with the help of this projection the three dimensional governing equations of almansi michell s problem are reduced to a set of one dimensional beam like equations leading to a recursive solution process furthermore the three dimensional displacement strain and stress fields can be recovered from the one dimensional solution numerical examples show that the predictions of the proposed approach are in excellent agreement with exact solutions of two dimensional elasticity and three dimensional fem analysis

parallel algorithms for circle detection in images abstract the detection of circles in images is an important task in many computer vision applications when the three parameters center coordinates and radius of a circle are quantized into o n values each a sequential algorithm using the hough transform runs with a time complexity of o n 4 where n n is the size of the image when information about the gradient direction is also used the complexity of the sequential algorithm reduces to o n 3 this paper proposes three parallel algorithms for circle detection on an n n mesh of processing elements operating in the simd mode the first two algorithms use the hough transform and the third is based on a tracing algorithm the first algorithm uses only the gradient magnitude and takes o n 3 time the second uses both the gradient magnitude and gradient direction and runs in o n 2 time the third method uses a midpoint circle scan conversion algorithm and runs with a complexity of o n 2 this algorithm is the most efficient of the three it does not use the gradient direction and offers an improvement of o n 2 over its sequential counterpart that runs in o n 4 time when implemented with a table look up operation this algorithm has a low proportionality constant and offers a significant improvement in computational speed

a robust real time ellipse detector abstract in this paper we present an improved ellipse detector that may be used in real time face detection in this algorithm we first extract edges from the image using a robust edge detector which is then followed by a rule based method finally we decompose the parameter space of the hough transform to achieve computational efficiency our extensive experimental results show indeed that the proposed detector is capable of detecting ellipse features with an excellent accuracy under various image conditions at a high speed 10 frames per second on a pentium iii 500 mhz pc

on board selection of relevant images an application to linear feature recognition we propose an on board selection scheme for aerial and space images based on linear feature detection in a feature hyperspace the detection task is performed by means of the radon transform rt and the wavelet transform a fast algorithm for the rt computation is described and counteractions against the discretization errors are proposed a new wavelet based algorithm is introduced which performs a fine analysis of the waveforms of the rt peaks yielding a possibly error free detection in images corrupted by a high level of noise a technique based on the feature hyperspace is proposed able to significantly exploit all the available pieces of information on these peaks results of the tests on synthetic and real images are reported which show that this method achieves satisfactory results making the detection task highly reliable in the presence of both noise and clutter

an isogeometric implicit g1 mixed finite element for kirchhoff space rods abstract in the paper we present a multi patch isogeometric mixed element with implicit geometric continuity at the ends for the analysis of non polar kirchhoff space rods rotations are introduced at the ends of the element analogously to the hermitian interpolation performing a change of basis for the configuration space a mixed method in which the internal forces are interpolated by means of an l 2 projection leading to a b formulation is used to cope with the membrane flexural locking that affects the solution the efficiency of the method in avoiding locking and instabilities is investigated the formulation adopted has the advantage with respect to other formulations that a non full global stiffness matrix is obtained this approach appears very appealing for efficient analyses of general assemblies of 3d non polar elements

the adaptive hough transform we introduce the adaptive hough transform aht as an efficient way of implementing the hough transform ht method for the detection of 2 d shapes the aht uses a small accumulator array and the idea of a flexible iterative coarse to fine accumulation and search strategy to identify significant peaks in the hough parameter spaces the method is substantially superior to the standard ht implementation in both storage and computational requirements in this correspondence we illustrate the ideas of the aht by tackling the problem of identifying linear and circular segments in images by searching for clusters of evidence in 2 d parameter spaces we show that the method is robust to the addition of extraneous noise and can be used to analyze complex images containing more than one shape

nonlinear isogeometric spatial bernoulli beam abstract a new element formulation of a geometrically nonlinear spatial curved beam assuming bernoulli theory including torsion without warping is proposed the element formulation is derived directly from the 3d continuum by means of nonlinear kinematics thus accounting for large displacements the geometric description of the proposed element is adapted from the spatial rod of greco and cuomo 2013 and extended to a nonlinear element formulation the proposed formulation can handle arbitrary orientations of the cross section along the beam in this publication nurbs are used as basis functions for discretization since they can easily provide the required c 1 continuity between elements the presented element formulation has four degrees of freedom three for displacements and one for the rotation around the center line in order to prove the accuracy of the developed spatial bernoulli beam several numerical examples are presented and compared to analytic solutions and other element formulations

finite element theory for curved and twisted beams based on exact solutions for three dimensional solids part 2 anisotropic and advanced beam models consistent finite element formulations for beams made of anisotropic materials and taking into account non classic inhomogeneous torsion have been developed the formulations are based on a kinematical hypothesis that includes exact solutions for three dimensional solids under terminal loading they describe warping of the cross sections in and out of their planes as well as their rigid displacements and rotations their large deformation and geometrically exact description by finite rotations are considered for the cases of monoclinic orthotropic and transversely isotropic materials exact solutions for the solid made from a monoclinic material have been deduced c 1998 elsevier science s a all rights reserved

a fast ellipse circle detector using geometric symmetry through the use of a global geometric symmetry a fast ellipse circle detector is proposed in this paper based on the geometric symmetry the proposed method first locates candidates of ellipse and circle centers in the meantime according to these candidate centers all feature points in an input image are grouped into several subimages then for each subimage by using geometric symmetry again all ellipses and circles are obtained the method significantly reduces the time required to evaluate all possible parameters without using edge direction information experimental results are given to show the correctness and effectiveness of the proposed method

a spatially curved beam element with warping and wagner effects this paper presents a new spatially curved beam element with warping and wagner effects that can be used for the non linear large displacement analysis of members that are curved in space the non linear behaviour of members curved in space shows that the wagner effects are substantial in the large twist rotation analysis most existing finite beam element models such as abaqus and ansys cannot predict the non linear large displacement response of members curved in space correctly because the wagner effects viz the wagner moment and the corresponding finite strain terms have not been considered in these finite beam elements as a consequence these finite beam elements do not provide correct predictions for the out of plane buckling and postbuckling behaviour of arches as well in this paper the symmetric tangent stiffness matrix has been derived based on the finite rotations parameterized by the conventional displacements the warping and wagner effects both the wagner moment and the corresponding finite strain terms and their constitutive relationship are included in the spatially curved beam element two components of the initial curvature the initial twist and their interactions with the displacements are also considered in the spatially curved beam element this ensures that the large twist rotation analysis for the members curved in space is accurate comparisons with existing experimental analytical and numerical results show that the spatially curved beam element is accurate and efficient for the non linear elastic analysis of curved members buckling and postbuckling analysis of arches and in its ability to predict large deflections and twist rotations in more arbitrarily curved members copyright 2005 john wiley sons ltd

a geometrical nonlinear eccentric 3d beam element with arbitrary cross sections abstract in this paper a finite element formulation of eccentric space curved beams with arbitrary cross sections is derived based on a timoshenko beam kinematic the strain measures are derived by exploitation of the green lagrangean strain tensor thus the formulation is conformed with existing nonlinear shell theories finite rotations are described by orthogonal transformations of the basis systems from the initial to the current configuration since for arbitrary cross sections the centroid and shear center do not coincide torsion bending coupling occurs in the linear as well as in the finite deformation case the linearization of the boundary value formulation leads to a symmetric bilinear form for conservative loads the resulting finite element model is characterized by 6 degrees of freedom at the nodes and therefore is fully compatible with existing shell elements since the reference curve lies arbitrarily to the line of centroids the element can be used to model eccentric stiffener of shells with arbitrary cross sections

collinear segment detection using ht neighborhoods in this paper geometrical analysis is used to extract novel straight line segment features from the wings around the peaks of the hough transform ht based on these features a practical segment detection method is proposed which has the ability to determine complete straight line segment parameters including the location of the center length slope and the euclidean distance to the origin the proposed method does not rely on edge point verification in the image space i e the complete set of segment features are determined only using the information embodied in the ht data the proposed method can distinguish between highly collinear straight line segments segment detection is robust to disturbing edge points especially ones collinear with the object a predefined collinear segment resolution that provides a theoretical criterion to determine straight line contiguity is derived image processing and analysis experiments show consistent robust performance

the multiple window parameter transform the multiwindow transform an extension of parameter transform techniques that increase performance and scope by exploiting the long range correlated information contained in multiple portions of an image is presented multiple window transforms allow the extraction of high dimensional features with improvement in accuracy over conventional techniques while keeping linear to low order polynomial computational and space requirements with respect to image size and dimensionality of the features using correlated information provides a direct link between extracted features and supporting regions in the image this coupled with evidence integration techniques is used to suppress noisy or nonexistent feature hypotheses parameter spaces are implemented as constraint satisfaction networks where feature hypotheses with overlapping support in the image compete after an iterative relaxation phase surviving hypotheses have disjoint support forming a segmentation of the image examples show the performance and provide insight about the behavior

edge curvature and convexity based ellipse detection method in this paper we propose a novel ellipse detection method for real images the proposed method uses the information of edge curvature and their convexity in relation to other edge contours as clues for identifying edge contours that can be grouped together a search region is computed for every edge contour that contains other edge contours eligible for grouping with the current edge contour a two dimensional hough transform is performed in an intermediate step in which we use a new relationship score for ranking the edge contours in a group instead of the conventional histogram count the score is found to be more selective and thus more efficient in addition we use three novel saliency criteria that are non heuristic and consider various aspects for quantifying the goodness of the detected elliptic hypotheses and finally selecting good elliptic hypotheses the thresholds for selection of elliptic hypotheses are determined by the detected hypotheses themselves such that the selection is free from human intervention the method requires a few seconds in most cases so it is suitable for practical applications the performance of the proposed ellipse detection method has been tested on a dataset containing 1200 synthetic images and the caltech 256 dataset containing real images in both cases the results show that the proposed ellipse detection method performs far better than existing methods and is close to the ideal results with precision recall and f measure all very close to 1 further the method is robust to the increase in the complexity of the images such as overlapping ellipses occluded ellipses while the performance of the contemporary methods deteriorates significantly

lower order circle and ellipse hough transform in this work we present two new algorithms for the detection of circles and ellipses which use the fht algorithm as a basis fast circle hough transform fcht and fast ellipse hough transform feht the first stage of these two algorithms devoted to obtaining the centers of the figures is computationally the most costly with the objective of improving the execution times of this stage it has been implemented using a new focusing algorithm instead of the typical polling process in a parameter space this new algorithm uses a new strategy that manages to reduce the execution times especially in the case where multiple figures appear in the image or when they are of very different sizes we also perform a labeling of the image points that permits discriminating which of these belong to each figure saving computations in subsequent stages

arc based evaluation and detection of ellipses we propose the use of elliptic arcs as a reliable criterion for ellipse evaluation and reconstruction a technique based on pixel connectivity is developed for detecting the endpoints and subtended angles of elliptic arcs model based distance and angular connectivity are introduced for quick and meaningful estimation of elliptic arcs an iterative algorithm for multiple ellipse fitting based on arc detection is presented experimental results confirm the robustness and accuracy of the algorithm for the fitting of multiple overlapping ellipses

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

finite rotations in dynamics of beams and implicit time stepping schemes we examine theoretical and computational aspects of three dimensional finite rotations pertinent to the dynamics of beams the model problem chosen for consideration is the reissner beam theory capable of modelling finite strains and finite rotations in geometrically exact manner special emphasis is placed on clarifying the geometry aspects finite rotation updates and the associated linearization procedure pertaining to different choices of rotation parameters the latter is shown to play an important role in constructing the optimal implementation of a time stepping scheme 1998 john wiley sons ltd

a fast discrete approximation algorithm for the radon transform this paper addresses fast parallel methods for the computation of the radon or hough transform the radon transform of an image is a set of projections of the image taken at different angles its computation is important in image processing and computer vision for problems such as pattern recognition and reconstruction of medical images a unique new method for combining partial results is presented from which an algorithm is constructed that computes a provably good approximation to the discrete radon transform the approximate discrete radon transform adrt algorithm computes 4 n 4 projections through an n times n image in time o n 2 mathrm lg n the majority of previous algorithms are o n 3 the method is quite simple and easy to parallelize a parallel version of the adrt requires only o mathrm lg n parallel steps on o n 2 processors ignoring communication time an additional property of the algorithm is that it can be applied directly to compute the backprojection step of the inverse rt

computational aspects of vector like parametrization of three dimensional finite rotations theoretical and computational aspects of vector like parametrization of three dimensional finite rotations which uses only three rotation parameters are examined in detail in this work the relationship of the proposed parametrization with the intrinsic representation of finite rotations via an orthogonal matrix is clearly identified careful considerations of the consistent linearization procedure pertinent to the proposed parametrization of finite rotations are presented for the chosen model problem of reissner s non linear beam theory pertaining details of numerical implementation are discussed for the simplest choice of the finite element interpolations for a 2 node three dimensional beam element a number of numerical simulations in three dimensional finite rotation analysis are presented in order to illustrate the proposed approach

dynamics of flexible beams undergoing overall motions abstract a modelling method for straight beams undergoing large overall motions as well as small elastic deformations is presented in this paper different from the classical linear cartesian modelling method which employs three cartesian deformation variables the present modelling method uses a non cartesian variable along with two cartesian variables to describe the elastic deformation a quadratic form of the strain energy expressed with the hybrid set of deformation variables is used to obtain the generalized active forces and a geometric constraint equation relating the non cartesian variable and cartesian variables is used to obtain the generalized inertia forces in the equations of motion the present modelling method not only provides accurate simulation results but also clarifies the limit of validity of the classical linear cartesian modelling method

geometrically exact 3d beam theory implementation of a strain invariant finite element for statics and dynamics geometrically exact 3d beam theory has been used as a basis for development of a variety of finite element formulations it has recently become apparent that the important requirement of objectivity of adopted strain measures although provided by the theory itself does not automatically extend to a finite element formulation in this paper we present a new finite element formulation of the geometrically exact 3d beam theory specifically designed to preserve the objectivity of the adopted strain measures in order to do so the current local rotations are interpolated in a manner similar to that adopted in co rotational approaches however no approximations typical for co rotational approaches are introduced into the procedure so in contrast to co rotational formulations the present formulation fully preserves the geometric exactness of the theory a range of numerical examples serves to illustrate the problem and to assess the formulation

a fast hough transform for segment detection the authors describe a new algorithm for the fast hough transform fht that satisfactorily solves the problems other fast algorithms propose in the literature erroneous solutions point redundance scaling and detection of straight lines of different sizes and needs less storage space by using the information generated by the algorithm for the detection of straight lines they manage to detect the segments of the image without appreciable computational overhead they also discuss the performance and the parallelization of the algorithm and show its efficiency with some examples

multiresolution hough transform an efficient method of detecting patterns in images a new multiresolution coarse to fine search algorithm for efficient computation of the hough transform is proposed the algorithm uses multiresolution images and parameter arrays logarithmic range reduction is proposed to achieve faster convergence discretization errors are taken into consideration when accumulating the parameter array this permits the use of a very simple peak detection algorithm comparative results using three peak detection methods are presented tests on synthetic and real world images show that the parameters converge rapidly toward the true value the errors in rho and theta as well as the computation time are much lower than those obtained by other methods since the multiresolution hough transform mht uses a simple peak detection algorithm the computation time will be significantly lower than other algorithms if the time for peak detection is also taken into account the algorithm can be generalized for patterns with any number of parameters

nonlinear analysis of members curved in space with warping and wagner effects abstract the centroidal axis of a member that is curved in space is generally a space curve the curvature of the space curve is not necessarily in the direction of either of the principal axes of the cross section but can be resolved into components in the directions of both of these principal axes hence a member curved in space is primarily subjected to combined compressive biaxial bending and torsional actions under vertical or gravity loading in addition warping actions in particular may occur in curved members with an open thin walled cross section and as the deformations increase significant interactions of the compressive biaxial bending and torsional actions occur and profoundly nonlinear deformations are developed in the nonlinear range of structural response this makes the nonlinear behaviour of a member curved in space very complicated making it difficult to obtain a consistent differential equation of equilibrium for the nonlinear analysis of members curved in space in addition because torsion is one of the primary actions in these members when the torsional deformations become large the wagner effects including both wagner moment and the conjugate wagner strain terms are increasingly significant and need to be included in the nonlinear analysis this paper takes advantage of the merits of so called geometrically exact beam theory and the weak form formulation of the differential equations of equilibrium in beam theory and it develops consistent differential equations of equilibrium for the nonlinear elastic analysis of members curved in space with warping and wagner effects the application of the nonlinear differential equations of equilibrium to various problems is illustrated

objectivity of strain measures in the geometrically exact three dimensional beam theory and its finite element implementation the paper discusses the issue of discretization of the strainconfiguration relationships in the geometrically exact theory of threedimensional 3d beams which has been at the heart of most recent

shape optimization of 2d structures using simulated annealing the goal of this study is to obtain globally optimum shapes for two dimensional structures subject to quasi static loads and restraints for this purpose a technique is proposed using which the volume or weight of a structure can be minimized the emphasis is on how one can define the shape precisely and find a shape that accurately reflects the globally optimum shape as design constraints stresses developed in the structure should not exceed the maximum allowable stress and connectivity of the structure should not be lost during shape changes optimization is achieved by a stochastic search algorithm called direct simulated annealing dsa which seeks the global minimum through randomly generated configurations in order to obtain random configurations a boundary variation technique is used in this technique a set of key points is chosen and connected by cubic splines to describe the boundary of the structure whenever the positions of the key points are changed in random directions a new shape is obtained thus coordinates of the key points serve as design variables in order to apply the optimization procedure a general computer code was developed using ansys parametric design language a number of cases were examined to test its effectiveness the results show that this technique can be applied to two dimensional shape optimization problems with high reliability even for cases where the entire free boundary is allowed to vary 2007 elsevier b v all rights reserved

extended hough transform for linear feature detection improving the accuracy of line segment detection reduces the complexity of subsequent high level processing common in cartographic feature detection we developed a new extension to the hough transform and reported on its application to building extraction we expanded the hough space by a third parameter the horizontal or vertical coordinate of the image space to provide incremental information as to the length of the lineal feature being sought using this extended ht transform allowed us to more accurately detect the true length of a line segment in addition we used a bayesian probabilistic approach to process our extended hough space that further increased the accuracy of our extended hough transform

geodesic finite elements for cosserat rods we introduce geodesic finite elements as a new way to discretize the non linear configuration space of a geometrically exact cosserat rod these geodesic finite elements naturally generalize standard one dimensional finite elements to spaces of functions with values in a riemannian manifold for the special orthogonal group our approach reproduces the interpolation formulas of crisfield and jelenic geodesic finite elements are conforming and lead to objective and path independent problem formulations we introduce geodesic finite elements for general riemannian manifolds discuss the relationship between geodesic finite elements and coefficient vectors and estimate the interpolation error then we use them to find static equilibria of hyperelastic cosserat rods using the riemannian trust region algorithm of absil et al we show numerically that the discretization error depends optimally on the mesh size copyright 2009 john wiley sons ltd

isogeometric configuration design sensitivity analysis of finite deformation curved beam structures using jaumann strain formulation abstract using an isogeometric approach a continuum based configuration design sensitivity analysis dsa method is developed for curved kirchhoff beams with multi patch junctions under the total lagrangian formulation large deformations considering the initial curvature of curved beams are described by geometrically exact beam theory gebt and jaumann strain formulation in the isogeometric approach the higher order continuity and the exact description of initial geometry are naturally embedded using nurbs basis functions in multi patch models c 0 continuity of physical displacement or c 1 continuity of displacement component at junction is weakly imposed using the lagrange multiplier method the superior accuracy of isogeometric analysis iga is verified through the comparison with the results of finite element analysis fea using cubic hermite interpolation in the dsa a material derivative is utilized and the kinematical description of gebt is consistently employed to express orientation design variations contrary to the iga based dsa the hermite basis function explicitly depends on design in the fea based dsa due to its element length parameter moreover since the design velocity field is approximated using the nodal velocity imposed at nodal tangential vector the amount of design perturbations should be very small to obtain precise design sensitivity

the hough transform has o n complexity on n n mesh connected computers this paper presents algorithms for implementing an important image processing operation the hough transform on a mesh connected computer mcc the mcc consists of an n times n array of processors each of which holds a single pixel of the image the mcc operates in a single instruction stream multiple data stream simd mode which is in agreement with the hardware constraints found in existing meshes five algorithms for computing the hough transform are presented these algorithms use a number of different techniques and they have varying time complexities and architectural requirements the most notable algorithm presented computes any p angles of the hough transform in o n p time and uses only a constant amount of memory per processor because the hough transform is a particular case of the discrete radon transform all of the algorithms will be presented for computing the radon transform of gray level images

block decomposition and segmentation for fast hough transform evaluation the decomposition of binary images using rectangular blocks of foreground pixels as primitives is considered based on this type of decomposition a fast method for evaluating the hough transform is introduced a complexity analysis of the proposed block hough transform algorithm sets constraints on the complexity of algorithms used for block decomposition so that the total decomposition and hough transform application time is much less than the time consumed by the usual point hough transform using this analysis we propose two algorithms for the decomposition and segmentation of binary images into rectangular blocks a combination of these methods leads to significant acceleration in the identification of linear features which is demonstrated in various image processing experiments 1999 pattern recognition society published by elsevier science ltd all rights reserved

robust ellipse detection with gaussian mixture models the euclidian distance between gaussian mixtures has been shown to be robust to perform point set registration jian and vemuri 2011 we propose to extend this idea for robustly matching a family of shapes ellipses optimisation is performed with an annealing strategy and the search for occurrences is repeated several times to detect multiple instances of the shape of interest we compare experimentally our approach to other state of the art techniques on a benchmark database for ellipses and demonstrate the good performance of our approach highlightswe extend the framework based on l2 to estimate a parametric family of curves we propose a non isotropic and multidimensional modeling for the density functions we propose a method for detecting multiple instances of an ellipse

a geometrically exact rod model incorporating shear and torsion warping deformation abstract a fully nonlinear three dimensional rod model is developed that incorporates transverse shear and torsion warping deformation the geometric setting is that of a constrained body model with configuration space modeled on r3 so 3 r a differentiable manifold the proposed model incorporates the classical notion of bi moment and bi shear in a fully nonlinear geometrically exact context explicit properly invariant constitutive equations that generalize those of the linearized theory are developed the underlying variational formulation of the model is discussed and computational procedures employing a galerkin projection are addressed numerical examples are presented that illustrate the performance of the formulation

a split and merge based ellipse detector with self correcting capability a novel ellipse detector based upon edge following is proposed in this paper the detector models edge connectivity by line segments and exploits these line segments to construct a set of elliptical arcs disconnected elliptical arcs which describe the same ellipse are identified and grouped together by incrementally finding optimal pairings of elliptical arcs we extract hypothetical ellipses of an image by fitting an ellipse to the elliptical arcs of each group finally a feedback loop is developed to sieve out low confidence hypothetical ellipses and to regenerate a better set of hypothetical ellipses in this aspect the proposed algorithm performs self correction and homes in on difficult ellipses detailed evaluation on synthetic images shows that the algorithm outperforms existing methods substantially in terms of recall and precision scores under the scenarios of image cluttering salt and pepper noise and partial occlusion additionally we apply the detector on a set of challenging real world images successful detection of ellipses present in these images is demonstrated we are not aware of any other work that can detect ellipses from such difficult images therefore this work presents a significant contribution towards ellipse detection

vibration reduction of rotating frame structure based on quadratic performance index abstract an efficient method based on quadratic performance index and lyapunov s second method is developed for the vibration reduction optimization of frame structure rotating at a constant angular velocity four optimization formulations and algorithms are studied for both low and high angular velocity these formulations consider both linear vs nonlinear dynamic models as well as direct integration and lypunov method to evaluate performance index three numerical examples are presented to compare the effectiveness of the four algorithms numerical results show that all the four optimization methods can reduce vibration at low rotating speed and find very similar optimal designs however at high rotating speed dynamic model of rotating structure must consider nonlinear axial strain in order to obtain correct dynamic response since the lyapunov s second method is not applicable for the nonlinear model and the nfti nonlinear dynamic model with nonlinear axial strain and time integration method is very inefficient the present study develops a perturbation method linearizes the nonlinear dynamic model and establishes the lnfla linearized dynamic model with nonlinear axial strain the lyapunov s second method numerical examples show the optimization method lnfla provides an efficient numerical method for vibration reduction of rotating frame structure with both low and high rotating speed

theory and numerics of three dimensional beams with elastoplastic material behaviour a theory of space curved beams with arbitrary cross sections and an associated finite element formulation is presented within the present beam theory the reference point the centroid the centre of shear and the loading point are arbitrary points of the cross section the beam strains are based on a kinematic assumption where torsion warping deformation is included each node of the derived finite element possesses seven degrees of freedom the update of the rotational parameters at the finite element nodes is achieved in an additive way applying the isoparametric concept the kinematic quantities are approximated using lagrangian interpolation functions since the reference curve lies arbitrarily with respect to the centroid the developed element can be used to discretize eccentric stiffener of shells due to the implemented constitutive equations for elastoplastic material behaviour the element can be used to evaluate the load carrying capacity of beam structures copyright 2000 john wiley sons ltd

an ellipse detection method from the polar and pole definition of conics abstract a new multistage hough transform approach to the problem of ellipse detection in images is presented the proposed approach is based on the polar and pole definition of conics and its advantage lies in avoiding the propagation of parameter estimation error over the successive stages of the hough transform the proposed method is capable of detecting partially visible ellipses overlapping ellipses and groups of concentric ellipses a set of experimental results is presented to demonstrate these capabilities of the suggested approach

isogeometric collocation for three dimensional geometrically exact shear deformable beams abstract we extend the isogeometric collocation method to the geometrically nonlinear beams an exact kinematic formulation able to represent three dimensional displacements and rotations without any restriction in magnitude is presented without the introduction of the moving frame concept a displacement based formulation is adopted full linearization of the strong form of the governing equations is derived consistently with the underlying geometric structure of the configuration manifold incremental rotations are parametrized through eulerian rotation vectors and configuration updates are performed by means of the exponential map numerical tests demonstrate that the proposed combination of isogeometric collocation method with the chosen rotations parametrization results in an efficient computational scheme able to model complex problems with high accuracy

linear band detection based on the euclidean distance transform and a new line segment extraction method abstract a linear band which is a straight line segment with some width i e thickness is a more structured higher level feature compared to edge or line features in spite of the usefulness of linear bands as features papers dealing with their detection problem are rare in this paper we propose a new method for detecting linear bands in gray scale images we first talk about our opinion on what types of linear bands a desirable detector should be able to detect and then give a description on how we designed our detector to achieve the goal our method consists largely of two parts 1 extracting the candidate center line pixels of the linear bands contained in an input gray scale image sub parts edge detection euclidean distance transform ridge detection in a distance map and noisy ridge pixel removal 2 extracting line segments from the result of 1 using our new line segment detection method sub parts modified hough transform base line segment grouping redundant line segment removal and postprocessing experimental results show that our method is practical and robust

locking free isogeometric collocation formulation for three dimensional geometrically exact shear deformable beams with arbitrary initial curvature abstract this paper presents a displacement based and a mixed isogeometric collocation formulations for three dimensional geometrically exact shear deformable beams with arbitrarily curved initial geometry strong forms of both formulations are consistently linearized with respect to the underlying configuration manifold high efficiency is achieved by using a geometrically consistent kinematic model in which incremental rotations are parametrized through the spatial rotation vector several numerical tests demonstrate that the proposed mixed formulation is totally locking free for any choice of approximation degree mixed formulation also exhibits higher robustness in the incremental iterative algorithm elimination of shear locking and low computational cost assured by the combination of isogeometric collocation with a consistent kinematic model result in a very efficient accurate and geometrically powerful method able to handle geometrically complex beam problems

geometrically exact thin walled beam including warping formulated on the special euclidean group se 3 abstract based on a formulation on the special euclidean group s e 3 a geometrically exact thin walled beam with an arbitrary open cross section is proposed to deal with the finite deformation and rotation issues the beam strains are based on a kinematic assumption where warping deformation and wagner effects are included such that the nonlinear behavior of a thin walled beam is predicted accurately particular under large torsion to reduce the nonlinearity of rigid motion static and dynamic equations are derived in the s e 3 framework based on the local frame approach as the value of the iteration matrix including the jacobian matrix of inertial and internal forces is invariable under arbitrary rigid motion the number of updates required during the computation process decreases sharply which drastically improves the computational efficiency furthermore the isogeometric analysis iga based on the non uniform rational b splines nurbs basis functions which promotes the integration of computer aided design cad and computer aided engineering cae is adopted to interpolate the displacement rotation and warping fields separately the interpolated strain measures satisfy the objectivity by removing the rigid motion of the reference point to obtain the symmetric jacobian matrix of internal forces the linearization operation is conducted based on the previously converged configuration a lie group s e 3 extension of the generalized time integration method is utilized to solve the equations of motion for thin walled beams finally the proposed formulation is successfully tested and validated in several static and dynamic numerical examples

avoiding shear locking for the timoshenko beam problem via isogeometric collocation methods in this work we study isogeometric collocation methods for the timoshenko beam problem considering both mixed and displacement based formulations in particular we show that locking free solutions are obtained for mixed methods independently on the approximation degrees selected for the unknown fields moreover several numerical tests are provided in order to support our theoretical results and to show the good behavior and the flexibility of isogeometric collocation methods in this context

ellipse fitting using the finite rate of innovation sampling principle standard approaches for ellipse fitting are based on the minimization of algebraic or geometric distance between the given data and a template ellipse when the data are noisy and come from a partial ellipse the state of the art methods tend to produce biased ellipses we rely on the sampling structure of the underlying signal and show that the x and y coordinate functions of an ellipse are finite rate of innovation fri signals and that their parameters are estimable from partial data we consider both uniform and nonuniform sampling scenarios in the presence of noise and show that the data can be modeled as a sum of random amplitude modulated complex exponentials a low pass filter is used to suppress noise and approximate the data as a sum of weighted complex exponentials the annihilating filter used in fri approaches is applied to estimate the sampling interval in the closed form we perform experiments on simulated and real data and assess both objective and subjective performances in comparison with the state of the art ellipse fitting methods the proposed method produces ellipses with lesser bias furthermore the mean squared error is lesser by about 2 to 10 db we show the applications of ellipse fitting in iris images starting from partial edge contours and to free hand ellipses drawn on a touch screen tablet

und unite and divide method in fourier and radon domains for line segment detection in this paper we extend our previously proposed line detection method to line segmentation using a so called unite and divide und approach the methodology includes two phases namely the union of spectra in the frequency domain and the division of the sinogram in radon space in the union phase given an image its sinogram is obtained by parallel 2d multilayer fourier transforms cartesian to polar mapping and 1d inverse fourier transform in the division phase the edges of butterfly wings in the neighborhood of every sinogram peak are firstly specified with each neighborhood area corresponding to a window in image space by applying the separated sinogram of each such windowed image we can extract the line segments the division phase identifies the edges of butterfly wings in the neighborhood of every sinogram peak such that each neighborhood area corresponds to a window in image space line segments are extracted by applying the separated sinogram of each windowed image our experiments are conducted on benchmark images and the results reveal that the und method yields higher accuracy has lower computational cost and is more robust to noise compared to existing state of the art methods

geometrically exact beam finite element formulated on the special euclidean group se 3 abstract this paper describes a dynamic formulation of a straight beam finite element in the setting of the special euclidean group se 3 first the static and dynamic equilibrium equations are derived in this framework from variational principles then a non linear interpolation formula using the exponential map is introduced it is shown that this framework leads to a natural coupling in the interpolation of the position and rotation variables next the discretized internal and inertia forces are developed the semi discrete equations of motion take the form of a second order ordinary differential equation on a lie group which is solved using a lie group time integration scheme it is remarkable that no parameterization of the nodal variables needs to be introduced and that the proposed lie group framework leads to a compact and easy to implement formulation some important numerical and theoretical aspects leading to a computationally efficient strategy are highlighted and discussed for instance the formulation leads to invariant tangent stiffness and mass matrices under rigid body motions and a locking free element the proposed formulation is successfully tested in several numerical static and dynamic examples

on rigid components and joint constraints in nonlinear dynamics of flexible multibody systems employing 3d geometrically exact beam model abstract in this work we discuss the finite element implementation of the internal constraints in a three dimensional 3d geometrically exact beam model which can be formulated as holonomic constraint relationships model problems chosen for a more detailed consideration include a general joint constraint between beams and the beam connected to a rigid component appropriate modifications of the standard form of the geometrically exact beam element arrays are carried out in order to impose explicitly these kinds of constraints into time integration schemes for nonlinear dynamics consequently only the minimum number of unknowns is retained for the global set of nonlinear equations to be solved thus avoiding the use of the extra variables the lagrange multipliers and the pertinent difficulties in integrating the system of differential algebraic equations a number of numerical simulations considering dynamic analysis of multibody systems with rigid flexible components and joint constraints are presented in order to illustrate versatility of the proposed procedure

multiple ellipses detection in noisy environments a hierarchical approach detection of multiple ellipses in noisy environments is a basic yet challenging task in many vision related problems the key area of difficulty is on distinguishing the pixels pertaining to each target in the presence of noise to tackle with the issue we propose a hierarchical approach which is motivated by the fact that any segment of an ellipse can identify itself in ellipse reconstruction first we find all the neat edges without any branches followed by an ellipse fitting on each of them second some target candidates are estimated based on the neat edges by a proposed grouping strategy finally the targets are detected based on the candidates by a proposed selective competitive algorithm to distinguish the true pixels of each target a real application of the proposed method is illustrated in addition to some other demonstrative experiments

integration of elastic multibody systems by invariant conserving dissipating algorithms i formulation abstract this work presents a novel methodology for the dynamic analysis of general non linear flexible multibody systems in part i we develop the 6 d compact representation of motion for those body models which motion may be described by a displacement field plus an independent rotation field this approach explores the fundamental properties of rigid body motion and in particular the coupled nature of linear and angular quantities in both kinematics and dynamics inspiring a novel parameterization technique based on the exponential map using the proposed approach we derive the governing equations for the case of multibody systems composed by rigid bodies and geometrically non linear beams connected by holonomic constraints these equations provide the starting point for the derivation of a class of numerical algorithms characterized by non conventional conservation properties in part ii of this work we develop the algorithms and illustrate their properties with the aid of some numerical applications

an inertia capacitance beam substructure formulation based on the bond graph method with application to rotating beams in this paper a novel inertia capacitance ic beam substructure formulation based on the ic field presentation from the bond graph method is developed the ic beam provides a modular systematic and graphical approach to beam modeling these features allow the modeler to focus more on the modeling and less on the mathematics as such the ic beam is proposed as an alternative to the many existing types of beam models available in the literature the ic beam is formulated in the center of mass body fixed coordinate system allowing for easy interfacing in a multibody system setting this floating frame approach is also computationally cheap elastic deformations in the ic beam are assumed to be small and described by modal superposition the formulation couples rigid body and elastic deformations in a nonlinear fashion the formulation is also compact and efficient detailed derivations for a two dimensional planar ic beam with bending modes are presented a modal acceleration method based on the decoupling of bending modes is proposed for use in the ic beam the rotating beam spin up maneuver problem is solved the karnopp margolis method is applied to ensure complete integral causality for an efficient numerical system geometric substructuring technique is applied to model large deflections the ic beam is shown to be capable of solving the rotating beam problem accurately and efficiently

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

lane departure warning for mobile devices based on a fuzzy representation of images the use of driver assistance systems is a current trend in the car industry however most driver assistance systems require the use of multiple sensors increasing the cost of their implementation in cars and making them inaccessible to many users in this paper we present an efficient lane departure warning system for mobile devices which is real time accurate and accessible to most users on the one hand the accuracy of the system relies on line detection based on hough transforms a combination that has proven to be reliable for this goal in many approaches on the other hand the reduction of the computational time to achieve real time processing is due mainly to a proposed fuzzy representation of images finally we also present various tests that show that the system proposed runs at up to 20 fps on a mobile device with a dual core cpu at 1 0 ghz with a resolution of 320240px