decentralized two filter smoothing algorithms in discrete time systems we develop some decentralized fixed interval smoothing algorithms which are realized by the two filter form in linear discrete time systems where the decentralized estimation structure consists of a central processor and of two local processors two approaches based on local filtering and local smoothing are considered for solving the problems of decentralized smoothing smoothing update and real time smoothing it is then shown that the notion of decentralized kalman filtering plays a significant role in the derivation of the algorithms for the former approach and that the introduction of the hamiltonian system in discrete time immediately gives the solutions of the problems in the latter approach moreover some characteristics of the algorithms arising from each approach are also discussed

subdivision surfaces a new paradigm for thin shell finite element analysis we develop a new paradigm for thin shell finite element analysis based on the use of subdivision surfaces for i describing the geometry of the shell in its undeformed configuration and ii generating smooth interpolated displacement fields possessing bounded energy within the strict framework of the kirchhoff love theory of thin shells the particular subdivision strategy adopted here is loop s scheme with extensions such as required to account for creases and displacement boundary conditions the displacement fields obtained by subdivision are h2 and consequently have a finite kirchhoff love energy the resulting finite elements contain three nodes and element integrals are computed by a one point quadrature the displacement field of the shell is interpolated from nodal displacements only in particular no nodal rotations are used in the interpolation the interpolation scheme induced by subdivision is non local i e the displacement field over one element depend on the nodal displacements of the element nodes and all nodes of immediately neighbouring elements however the use of subdivision surfaces ensures that all the local displacement fields thus constructed combine conformingly to define one single limit surface numerical tests including the belytschko et al 10 obstacle course of benchmark problems demonstrate the high accuracy and optimal convergence of the method

otoacoustic emissions from normal hearing and hearing impaired subjects distortion product responses distortion product otoacoustic emissions dpoae were measured in normal hearing and hearing impaired human subjects analyses based on decision theory were used to evaluate dpoae test performance specifically relative operating characteristic roc curves were constructed and the areas under these curves were used to estimate the extent to which normal and impaired ears could be correctly identified by these measures dpoae amplitude and dpoae noise measurements were able to distinguish between normal and impaired subjects at 4000 8000 and to a lesser extent at 2000 hz the ability of these measures to distinguish between groups decreased however as frequency and audiometric criterion used to separate normal and hearing impaired ears decreased at 500 hz performance was no better than chance regardless of the audiometric criterion for normal hearing cumulative distributions of misses hearing impaired ears incorrectly identified as normal hearing and false alarms normal hearing ears identified as hearing impaired were constructed and used to evaluate test performance for a range of hit rates i e the percentage of correctly identified hearing impaired ears depending on the desired hit rate criterion values of 5 to 12 db spl for dpoae amplitudes and 8 to 15 db for dpoae noise accurately distinguished normal hearing ears from those with thresholds greater than 20 db hl for the two frequencies at which performance was best 4000 and 8000 hz it would appear that dpoae measurements can be used to accurately identify the presence of high frequency hearing loss but are not accurate predictors of hearing status at lower frequencies at least for the conditions of the present measurements

rotation free isogeometric thin shell analysis using pht splines this paper presents a novel approach for isogeometric analysis of thin shells using polynomial splines over hierarchical t meshes pht splines the method exploits the flexibility of t meshes for local refinement the main advantage of the pht splines in the context of thin shell theory is that it achieves c1 continuity so the kirchhoff love theory can be used in pristine form no rotational degrees of freedom are needed numerical results show the excellent performance of the present method

unified lagrangian formulation for solid and fluid mechanics and fsi problems abstract we present a lagrangian monolithic strategy for solving fluid structure interaction fsi problems the formulation is called unified because fluids and solids are solved using the same solution scheme and unknown variables the method is based on a mixed velocity pressure formulation each time step increment is solved via an iterative partitioned two step procedure the particle finite element method pfem is used for solving the fluid parts of the domain while for the solid ones the finite element method fem is employed both velocity and pressure fields are interpolated using linear shape functions for quasi incompressible materials the solution scheme is stabilized via the finite calculus fic method the stabilized elements for quasi incompressible hypoelastic solids and newtonian fluids are called vps s element and vps f element respectively other two non stabilized elements are derived for hypoelastic solids one is based on a velocity formulation v element and the other on a mixed velocity pressure scheme vp element the algorithms for coupling the solid elements with the vps f fluid element are explained in detail the unified formulation is validated by solving benchmark fsi problems and by comparing the numerical solution to the ones published in the literature

further assessment of forward pressure level for in situ calibration quantifying ear canal sound level in forward pressure has been suggested as a more accurate and practical alternative to sound pressure level spl calibrations used in clinical settings the mathematical isolation of forward and reverse pressure requires defining the thevenin equivalent impedance and pressure of the sound source and characteristic impedance of the load however the extent to which inaccuracies in characterizing the source and or load impact forward pressure level fpl calibrations has not been specifically evaluated this study examined how commercially available probe tips and estimates of characteristic impedance impact the calculation of forward and reverse pressure in a number of test cavities with dimensions chosen to reflect human ear canal dimensions results demonstrate that fpl calibration which has already been shown to be more accurate than in situ spl calibration can be improved particularly around standing wave null frequencies by refining estimates of characteristic i

isogeometric kirchhoff love shell formulations for general hyperelastic materials abstract we present formulations for compressible and incompressible hyperelastic thin shells which can use general 3d constitutive models the necessary plane stress condition is enforced analytically for incompressible materials and iteratively for compressible materials the thickness stretch is statically condensed and the shell kinematics are completely described by the first and second fundamental forms of the midsurface we use c 1 continuous isogeometric discretizations to build the numerical models numerical tests including structural dynamics simulations of a bioprosthetic heart valve show the good performance and applicability of the presented methods

square root rts smoothing algorithms two kinds of new square root algorithms for rauch tung striebel rts smoothing formulas are suggested stable square root algorithms and a fast square root or so called chandrasekhar type algori

on continuum immersed strategies for fluid structure interaction abstract continuum immersed strategies are widely used these days for the computational simulation of fluid structure interaction problems the principal characteristic of such immersed techniques is the representation of the immersed solid via a momentum forcing source in the navier stokes equations in this paper the immersed finite element method ifem introduced by zhang et al 2004 41 for the analysis of deformable solids immersed in an incompressible newtonian viscous fluid is further enhanced by means of three new improvements a first update deals with the modification of the conservation of mass equation in the background fluid in order to account for non isochoric deformations within the solid phase a second update deals with the incompressibility constraint for the solid phase in the case of isochoric deformations where an enhanced evaluation of the deformation gradient tensor is introduced in a multifield hu washizu variational sense in order to overcome locking effects the third update is focussed on the improvement of the robustness of the overall scheme by introducing an implicit one step time integration scheme with enhanced stability properties in conjunction with a consistent newton raphson linearisation strategy for optimal quadratic convergence the resulting monolithic methodology is thoroughly studied for a range of lagrangian and nurbs based shape finite element functions for a series of numerical examples with the purpose of studying the effect of the spatial semi discretisation in the solution comparisons are also established with the newly developed immersed structural potential method ispm by gil et al 2010 7 for benchmarking and assessment of the quality of the new formulation

an isogeometric continuum shell element for non linear analysis an isogeometric continuum shell formulation is proposed in which nurbs basis functions are used to construct the reference surface of the shell through the thickness behavior is interpolated using a higher order b spline which is in contrast to the standard continuum shell solid like shell formulation where a linear lagrange shape function is typically used in the thickness direction the present formulation yields a complete isogeometric representation of the continuum shell the shell element is implemented in a standard finite element code using bezier extraction which facilitates numerical integration on the reference surface of the shell through the thickness integration is done using a connectivity array which determines the support of a b spline basis function over an element the formulation has been verified using different linear and geometrically non linear examples the ability of the formulation in modelling buckling of static delaminations in composite materials is also demonstrated

space time finite element techniques for computation of fluid structure interactions we describe the space time finite element techniques we developed for computation of fluid structure interaction fsi problems among these techniques are the deforming spatial domain stabilized space time dsd sst formulation and its special version and the mesh update methods including the solid extension mesh moving technique semmt also among these techniques are the block iterative quasi direct and direct coupling methods for the solution of the fully discretized coupled fluid and structural mechanics equations we present some test computations for the mesh moving techniques described we also present numerical examples where the fluid is governed by the navier stokes equations of incompressible flows and the structure is governed by the membrane and cable equations overall we demonstrate that the techniques we have developed have increased the scope and accuracy of the methods used in computation of fsi problems 2005 elsevier b v all rights reserved

relation of distortion product otoacoustic emission input output functions to loudness the aim of this study is to further explore the relationship between distortion product otoacoustic emission dpoae measurements and categorical loudness scaling cls measurements using multiple linear regression mlr analysis recently thorson et al j acoust soc am 131 1282 1295 2012 obtained predictions of cls loudness ratings from dpoae input output i o functions using mlr analysis the present study extends that work by 1 considering two different and potentially improved mlr models one for predicting loudness rating at specified input level and the other for predicting the input level for each loudness category and 2 validating the new models predictions using an independent set of data strong correlations were obtained between predicted and measured data during the validation process with overall root mean square errors in the range 10 43 16 78 db for the prediction of cls input level supporting the view that dpoae i o measurements can predict cls loudness ratings and input levels and thus may be useful for fitting hearing aids

a 3d isogeometric be fe analysis with dynamic remeshing for the simulation of a deformable particle in shear flows abstract a three dimensional isogeometric coupled boundary element and finite element approach based on analysis suitable t splines is developed for the simulation of deformable capsules suspended in shear flows boundary element analysis is used to solve the fluid stokes equation whereas the hydrodynamic membrane load is computed via isogeometric analysis under the assumption that the membrane is a hyper elastic thin shell with negligible bending resistance the smoothness of the t spline basis functions accommodate large deformations of the capsule without the need for additional smoothing techniques and can be used to accurately compute the membrane load a balanced distribution of membrane elements can be constructed using an unstructured locally refined mesh these properties are coupled with an adaptive temporal implicit integration scheme several benchmark examples are solved to illustrate the accuracy and potential of the method the approach is then applied to simulate the dynamics of a capsule in a real geometry of a brain capillary

new square root smoothing algorithms this paper presents new square root smoothing algorithms for the three best known smoothing formulas 1 rauch tung striebel rts formulas 2 desai weinert yusypchuk dwy formulas called backward rts formulas and 3 mayne fraser mf formulas called two filter formulas the main feature of the new algorithms is that they use unitary rotations to replace all matrix inversion and backsubstitution steps common in earlier algorithms with unitary operations this feature enables more efficient systolic array and parallel implementations and leads to algorithms with better numerical stability and conditioning properties

reliability of distortion product otoacoustic emissions and their relation to loudness the reliability of distortion product otoacoustic emission dpoae measurements and their relation to loudness measurements was examined in 16 normal hearing subjects and 58 subjects with hearing loss the level of the distortion product l d was compared across two sessions and resulted in correlations that exceeded 0 90 the reliability of dpoaes was less when parameters from nonlinear fits to the input output i o functions were compared across visits next the relationship between dpoae i o parameters and the slope of the low level portion of the categorical loudness scaling cls function soft slope was assessed correlations of 0 65 0 74 and 0 81 at 1 2 and 4 khz were observed between cls soft slope and combined dpoae parameters behavioral threshold had correlations of 0 82 0 83 and 0 88 at 1 2 and 4 khz with cls soft slope combining dpoaes and behavioral threshold provided little additional information lastly a multivariate approach utilizing the entire dpoae i o function was used to predict the cls rating for each input level db spl standard error of the estimate when using this method ranged from 2 4 to 3 0 categorical units cu suggesting that dpoae i o functions can predict cls measures within the cu step size used in this study 5

a finite element boundary element method for large displacement fluid structure interaction with potential flow this work concerns the interaction of light membrane structures enclosing incompressible fluids large displacements and collapsed boundaries initially slender subdomains are characteristic of this class of problems a finite element boundary element fe be coupled discretization is presented as an enabling technology addressing these challenges by avoiding volumetric meshing as required by arbitrary lagrangian eulerian or immersed boundary type methods the presented formulation includes a compatibility condition to which a physical interpretation is given and a regularizing bending stiffness observed to be necessary from both the theoretical well posedness and numerical stability point of view a cheap contact load is designed to deal with possibly complex geometries reusing already computed discrete boundary element kernels numerical experiments show the capabilities of the proposed scheme

reduced basis isogeometric methods rb iga for the real time simulation of potential flows about parametrized naca airfoils abstract we present a reduced basis rb method based on isogeometric analysis iga for the rapid and reliable evaluation of pde systems characterized by complex geometrical features at the current state of the art this is the first case of coupling between rb and iga methods the construction of the rb method relies on an isogeometric boundary element method iga bem as the high fidelity technique allowing a direct interface with computer aided design cad tools a suitable empirical interpolation method eim ensures an efficient offline online decomposition between the construction and the evaluation of the rb method we consider the real time simulation of potential flows past airfoils parametrized with respect to the angle of attack and the naca number identifying their shape and we provide a validation of our methodology with respect to experimental data and reference numerical codes showing in both cases a very good agreement

a hierarchic family of isogeometric shell finite elements a hierarchic family of isogeometric shell finite elements based on nurbs shape functions is presented in contrast to classical shell finite element formulations inter element continuity of at least c1 enables a unique and continuous representation of the surface normal within one nurbs patch this does not only facilitate formulation of kirchhoff love type shell models for which the standard galerkin weak form has a variational index of 2 but it also offers significant advantages for shear deformable reissner mindlin type shells and higher order shell models for a 5 parameter shell formulation with reissner mindlin kinematics a hierarchic difference vector which accounts for shear deformations is superimposed onto the rotated kirchhoff love type director of the deformed configuration this split into bending and shear deformations in the shell kinematics results in an element formulation which is free from transverse shear locking without the need to apply further remedies like reduced integration assumed natural strains or mixed finite element formulations the third member of the hierarchy is a 7 parameter model including thickness change and allowing for application of unmodified three dimensional constitutive laws the phenomenon of curvature thickness locking coming along with this kinematic extension again is automatically avoided by the hierarchic difference vector concept without any further treatment membrane locking and in plane shear locking are removed by two different approaches firstly elimination via the discrete strain gap dsg method and secondly removal of parasitic membrane strains using a hybrid mixed method based on the hellinger reissner variational principle the hierarchic kinematic structure of the three different shell formulations allows a straightforward combination of these elements within one mesh and is thus the ideal basis for a model adaptive approach

extended isogeometric boundary element method xibem for three dimensional medium wave acoustic scattering problems a boundary element method bem based on non uniform rational b splines nurbs is used to find solutions to three dimensional wave scattering problems governed by the helmholtz equation the method is extended in a partition of unity sense multiplying the nurbs functions by families of plane waves this method is called the extended isogeometric boundary element method xibem in this paper the collocation xibem formulation is described and numerical results are given the numerical results are compared against closed form or converged solutions comparisons are made against the conventional boundary element method and the non enriched isogeometric bem igabem when compared to non enriched boundary element simulations using xibem significantly reduces the number of degrees of freedom required to obtain a solution of a given error thus with a fixed computational resource problems of a shorter wavelength can be solved

treatment of reissner mindlin shells with kinks without the need for drilling rotation stabilization in an isogeometric framework this work presents a framework for the computation of complex geometries containing intersections of multiple patches with reissner mindlin shell elements the main objective is to provide an isogeometric finite element implementation which neither requires drilling rotation stabilization nor user interaction to quantify the number of rotational degrees of freedom for every node for this purpose the following set of methods is presented control points with corresponding physical location are assigned to one common node for the finite element solution a nodal basis system in every control point is defined which ensures an exact interpolation of the director vector throughout the whole domain a distinction criterion for the automatic quantification of rotational degrees of freedom for every node is presented an isogeometric reissner mindlin shell formulation is enhanced to handle geometries with kinks and allowing for arbitrary intersections of patches the parametrization of adjacent patches along the interface has to be conforming the shell formulation is derived from the continuum theory and uses a rotational update scheme for the current director vector the nonlinear kinematic allows the computation of large deformations and large rotations two concepts for the description of rotations are presented the first one uses an interpolation which is commonly used in standard lagrange based shell element formulations the second scheme uses a more elaborate concept proposed by the authors in prior work which increases the accuracy for arbitrary curved geometries numerical examples show the high accuracy and robustness of both concepts the applicability of the proposed framework is demonstrated

variational implementation of immersed finite element methods dirac distributions are often crucial components of the solid fluid coupling operators in immersed solution methods for fluid structure interaction fsi problems this is certainly so for methods like the immersed boundary method ibm or the immersed finite element method ifem where dirac distributions are approximated via smooth functions by contrast a truly variational formulation of immersed methods does not require the use of dirac distributions either formally or practically this has been shown in the finite element immersed boundary method feibm where the variational structure of the problem is exploited to avoid dirac distributions at both the continuous and the discrete level in this paper we generalize the feibm to the case where an incompressible newtonian fluid interacts with a general hyperelastic solid specifically we allow i the mass density to be different in the solid and the fluid ii the solid to be either viscoelastic of differential type or purely elastic and iii the solid to be either compressible or incompressible at the continuous level our variational formulation combines the natural stability estimates of the fluid and elasticity problems in immersed methods such stability estimates do not transfer to the discrete level automatically due to the non matching nature of the finite dimensional spaces involved in the discretization after presenting our general mathematical framework for the solution of fsi problems we focus in detail on the construction of natural interpolation operators between the fluid and the solid discrete spaces which guarantee semi discrete stability estimates and strong consistency of our spatial discretization

paper a new computationally efficient fixed interval discrete time smoother the rauch tung streibel smoother recursion is used to derive a new smoother algorithm based upon a decomposition of the linear model dynamical equation and maximizing use of rank 1 matrix modification this new algorithm it turns out parallels bierman s forward recursive square root information filter backward recursive u d factorized covariance algorithm the new result features computational efficiency reliance on numerically stable matrix modification algorithms and reduced computer storage

on the relationship between the lagrange multiplier method and the two filter smoother some relationships between the lagrange multiplier method and a two filter smoother are explored using orthogonal projection lemmas for linear discrele time systems the obtained expectation results are applied to algebraically derive a forward pass fixed interval smoothing algorithm that utilizes backward pass information filter outputs furthermore a convenient form for numerically efficient and stable algorithms is developed and the derived equation can also be used to quantitatively evaluate the effect of initial statistics on the smoothed estimate numerical results pertaining to a linearized version for the in track motion of a satellite travelling in a circular orbit are included to illustrate the use of the given algorithms

a nurbs based immersed methodology for fluid structure interaction abstract we introduce an isogeometric immersed and fully implicit formulation for fluid structure interaction fsi the method focuses on viscous incompressible flows and nonlinear hyperelastic incompressible solids which are a common case in various fields such as for example biomechanics in our fsi method we utilize an eulerian mesh on the whole domain and a lagrangian mesh on the solid domain the lagrangian mesh is arbitrarily located on top of the eulerian mesh in a non conforming fashion due to the formulation of our problem based on the immersed finite element method ifem we do not need mesh update or remeshing algorithms the fluid structure interface is the boundary of the lagrangian mesh but cuts arbitrarily the eulerian mesh the generalized method is used for time discretization and nurbs based isogeometric analysis is employed for the spatial discretization on both fluid and solid domains the information transfer between the two meshes is carried out using the nurbs functions which avoids the use of the so called discretized delta functions the higher order and especially the higher continuity of nurbs functions allow us to deal with severe mesh distortion in the lagrangian mesh in comparison with classical c 0 linear piecewise functions as we prove numerically our numerical solutions attain good agreement with theoretical data for free falling objects in two and three dimensions which confirms the feasibility of our methodology

combining and updating of local estimates and regional maps along sets of one dimensional tracks in this paper we consider the problem of combining and updating estimates that may have been generated in a distributed fashion or may represent estimates generated at different times of the same process sample path the first of these cases has applications in decentralized estimation while the second has applications in updating maps of spatially distributed random quantities given measurements along several tracks the method of solution for the second problem uses the result of the first and the similarity in the formulation and solution of these problems emphasizes the conceptual similarity between many problems in decentralized control and in the analysis of random fields

convergence estimates for a plane elasticity problem solved by the galerkin boundary integral formulation with nurbs abstract a classical mixed boundary value problem of linear elasticity in two dimensions in the galerkin boundary integral formulation is considered we prove a priori error estimates of the solution to this problem by the isogeometric adaptive method using nurbs the estimates include approximation of the boundary of the domain

nitsche s method combined with space time finite elements for ale fluid structure interaction problems we propose a weak method for handling the fluid structure interface in finite element fluid structure interaction based on nitsche s method abh math univ hamburg 36 1971 9 we assume transient incompressible newtonian flow and for the structure undamped linear elasticity for the time discretization we use the time continuous energy conserving galerkin method for the structure and for the fluid we employ the time discontinuous galerkin method this means that the velocity becomes piecewise constant on each timestep for the fluid matching the time derivative of the displacements in the solid which is also piecewise constant over a time step we formulate the method and report some numerical examples using space time oriented elements for the fluid in order to mimic lagrangian or ale type simulations

blended isogeometric shells abstract we propose a new isogeometric shell formulation that blends kirchhoff love theory with reissner mindlin theory this enables us to reduce the size of equation systems by eliminating rotational degrees of freedom while simultaneously providing a general and effective treatment of kinematic constraints engendered by shell intersections folds boundary conditions the merging of nurbs patches etc we illustrate the blended theory s performance on a series of test problems

optimal convergence for adaptive iga boundary element methods for weakly singular integral equations in a recent work feischl et al in eng anal bound elem 62 141 153 2016 we analyzed a weighted residual error estimator for isogeometric boundary element methods in 2d and proposed an adaptive algorithm which steers the local mesh refinement of the underlying partition as well as the multiplicity of the knots in the present work we give a mathematical proof that this algorithm leads to convergence even with optimal algebraic rates technical contributions include a novel mesh size function which also monitors the knot multiplicity as well as inverse estimates for nurbs in fractional order sobolev norms

latency of tone burst evoked auditory brain stem responses and otoacoustic emissions level frequency and rise time effects simultaneous measurement of auditory brain stem response abr and otoacoustic emission oae delays may provide insights into effects of level frequency and stimulus rise time on cochlear delay tone burst evoked abrs and oaes tboaes were measured simultaneously in normal hearing human subjects stimuli included a wide range of frequencies 0 5 8 khz levels 20 90 db spl and tone burst rise times abr latencies have orderly dependence on these three parameters similar to previously reported data by gorga et al j speech hear res 31 87 97 1988 level dependence of abr and tboae latencies was similar across a wide range of stimulus conditions at mid frequencies frequency dependence of abr and tboae latencies were similar the dependence of abr latency on both rise time and level was significant however the interaction was not significant suggesting independent effects comparison between abr and tboae latencies reveals that the ratio of tboae latency to abr forward latency the level dependent component of abr total latency is close to one below 1 5 khz but greater than two above 1 5 khz despite the fact that the current experiment was designed to test compatibility with models of reverse wave propagation existing models do not completely explain the current data

nonsingular isogeometric boundary element method for stokes flows in 3d abstract isogeometric analysis iga is emerging as a technology bridging computer aided geometric design cagd most commonly based on non uniform rational b splines nurbs surfaces and engineering analysis in finite element and boundary element isogeometric methods fe iga and iga bem the nurbs basis functions that describe the geometry define also the approximation spaces in the fe iga approach the surfaces generated by the cagd tools need to be extended to volumetric descriptions a major open problem in 3d this additional passage can be avoided in principle when the partial differential equations to be solved admit a formulation in terms of boundary integral equations leading to boundary element isogeometric analysis iga bem the main advantages of such an approach are given by the dimensionality reduction of the problem from volumetric based to surface based by the fact that the interface with cagd tools is direct and by the possibility to treat exterior problems where the computational domain is infinite by contrast these methods produce system matrices which are full and require the integration of singular kernels in this paper we address the second point and propose a nonsingular formulation of iga bem for 3d stokes flows whose convergence is carefully tested numerically standard gaussian quadrature rules suffice to integrate the boundary integral equations and carefully chosen known exact solutions of the interior stokes problem are used to correct the resulting matrices extending the work by klaseboer et al 2012 27 to iga bem

immersed finite element method abstract in this paper the immersed finite element method ifem is proposed for the solution of complex fluid and deformable structure interaction problems encountered in many physical models in ifem a lagrangian solid mesh moves on top of a background eulerian fluid mesh which spans over the entire computational domain hence the mesh generation is greatly simplified moreover both fluid and solid domains are modeled with the finite element methods and the continuity between the fluid and solid sub domains are enforced via the interpolation of the velocities and the distribution of the forces with the reproducing kernel particle method rkpm delta function in comparison with the immersed boundary ib method the higher ordered rkpm delta function enables the fluid domain to have nonuniform spatial meshes with arbitrary geometries and boundary conditions the use of such kernel functions may eventually open doors to multi scale and multi resolution modelings of complex fluid structure interaction problems rigid and deformable spheres dropping in channels are simulated to demonstrate the unique capabilities of the proposed method the results compare well with the experimental data to the authors knowledge these are the first solutions that deal with particulate flows with very flexible solids

a natural framework for isogeometric fluid structure interaction based on bem shell coupling abstract the interaction between thin structures and incompressible newtonian fluids is ubiquitous both in nature and in industrial applications in this paper we present an isogeometric formulation of such problems which exploits a boundary integral formulation of stokes equations to model the surrounding flow and a non linear kirchhoff love shell theory to model the elastic behavior of the structure we propose three different coupling strategies a monolithic fully implicit coupling a staggered elasticity driven coupling and a novel semi implicit coupling where the effect of the surrounding flow is incorporated in the non linear terms of the solid solver through its damping characteristics the novel semi implicit approach is then used to demonstrate the power and robustness of our method which fits ideally in the isogeometric paradigm by exploiting only the boundary representation b rep of the thin structure middle surface

construction and applications of discrete time smoothing error models we present a unified perspective on techniques for constructing both forward and backward markovian realizations of the error process associated with discrete time fixed interval smoothing several alternative approaches are presented each of which provides additional insight and connections with other results in linear estimation theory in addition two applications of such models are described the first is a problem in the validation of an error model for a measurement system while the second concerns the problems of updating and combining smoothed estimates we also present an example of the use of our updating solution for the mapping of random fields based on several sets of data tracks

quadrature formulas based on spline quasi interpolation for hypersingular integrals arising in iga sgbem abstract in this paper we study the construction of quadrature rules for the approximation of hypersingular integrals that occur when 2d neumann or mixed laplace problems are numerically solved using boundary element methods in particular the galerkin discretization is considered within the isogeometric analysis setting and spline quasi interpolation is applied to approximate integrand factors then integrals are evaluated via recurrence relations convergence results of the proposed quadrature rules are given with respect to both smooth and non smooth integrands numerical tests confirm the behavior predicted by the analysis finally several numerical experiments related to the application of the quadrature rules to both exterior and interior differential problems are presented

estimation of the area function of human ear canals by sound pressure measurements a method to determine the area function of a duct i e the variation of the cross section along the middle axis of the duct is described it is shown that it is sufficient to measure the sound pressure at three locations in the duct to get knowledge of the area function the calculated approximation fits the true area function the better the broader the bandwidth of the sound pressure signals is chosen the bandwidth is bounded by the condition that no higher modes of sound propagation must be excited in principle the area function can be determined by solving a linear system of equations and executing a simple iterative algorithm some more work however is necessary to stabilize the computation against unavoidable small measuring errors the calculated area function reproduces the acoustical transformation characteristics with good precision in spite of this the calculated area function may disagree with the real area function in some regions especially at the edges such errors occur if the deviations of the area function from constant cross section correspond to frequencies outside the range of measurement the method was applied to determine the area function of human ear canals and the results are presented

a nitsche type formulation and comparison of the most common domain decomposition methods in isogeometric analysis this paper provides a detailed elaboration and assessment of the most common domain decomposition methods for their application in isogeometric analysis the methods comprise a penalty approach lagrange multiplier methods and a nitsche type method for the nitsche method a new stabilized formulation is developed in the context of isogeometric analysis to guarantee coercivity all these methods are investigated on problems of linear elasticity and eigenfrequency analysis in 2d in particular focus is put on non uniform rational b spline patches which join nonconformingly along their common interface thus the application of isogeometric analysis is extended to multi patches which can have an arbitrary parametrization on the adjacent edges moreover it has been shown that the unique properties provided by isogeometric analysis that is high order functions and smoothness across the element boundaries carry over for the analysis of multiple domains copyright 2013 john wiley sons ltd

distortion product otoacoustic emission measured with continuously varying stimulus level distortion product otoacoustic emissions dpoae are measured by stimulating the ear with two simultaneous tones a novel method for measuring dpoaes has been developed in which the tone levels vary continuously instead of in discrete steps varying the tone levels continuously may offer advantages for characterizing dpoae level as a function of stimulus level for equivalent primary levels dpoae levels measured with the continuous level method were the same as levels obtained with the discrete level method thus validating the new method continuous level measurements were used to determine the optimal l1 for each l2 in individual subjects n 20 at f2 1 2 4 and 8 khz by using a lissajous path that covered a wide range of stimulus levels the optimal l1 defined as the l1 that resulted in the largest dpoae for each l2 varied across subjects and across frequency the optimal difference between l1 and l2 decreased with increasing l2 at all frequencies and increased with frequency when l2 was low whe

a scaled boundary isogeometric formulation for the elasto plastic analysis of solids in boundary representation abstract this contribution deals with the nonlinear analysis of boundary represented solids with elasto plastic material behavior based on the so called scaled boundary isogeometric formulation sb iga the proposed approach combines the features of the scaled boundary finite element method and isogeometric analysis based on the original boundary representation of the cad model a formulation is provided where the geometrical description of the boundary is sufficient to define the entire surface the domain is parameterized by a radial scaling parameter emanating from a scaling center and a parameter in circumferential direction along the boundary non star shaped domains are tackled by standard sub structuring here conforming discretizations are considered for the two dimensional case according to the isogeometric paradigm nurbs basis functions are employed for the approximation of the solution the displacement response is derived based on a multiplicative decomposition of the approximation in circumferential and radial scaling direction the boundary value problem is solved with the galerkin method the newton raphson iterative scheme is employed to obtain the nonlinear response several benchmark tests demonstrate the accuracy and computational efficiency of the formulation

brief square root information filtering and fixed interval smoothing with singularities the square root information filter algorithm and the related covariance smoother algorithm have been generalized to handle singular state transition matrices and perfect measurements this allows the use of srif techniques for problems with delays and state constraints the generalized algorithms use complete qr factorization to isolate deterministically known parts of the state and nonsingular parts of the state transition and disturbance influence matrices these factorizations and the corresponding changes of coordinates are used to solve the recursive least squares problems that are basic to the srif technique numerical stability computation time and storage requirements are comparable to the traditional srif algorithms

multi patch nonsingular isogeometric boundary element analysis in 3d abstract a multi patch nonsingular isogeometric boundary element method igabem for 3d problems is presented that provides accurate solutions for multi patch igabem in order to conveniently implement this method based on the greville abscissae a new collocation method moves the first and the last collocation points of each parametric direction inside of their patches and a simple method for merging equations handles the extra equations the numerical results verify the accuracy and efficiency of the present method by comparing it to the conventional igabem

distribution of standing wave errors in real ear sound level measurements standing waves can cause measurement errors when sound pressure level spl measurements are performed in a closed ear canal e g during probe microphone system calibration for distortion product otoacoustic emission dpoae testing alternative calibration methods such as forward pressure level fpl minimize the influence of standing waves by calculating the forward going sound waves separate from the reflections that cause errors previous research compared test performance burke et al 2010 and threshold prediction rogers et al 2010 using spl and multiple fpl calibration conditions and surprisingly found no significant improvements when using fpl relative to spl except at 8 khz the present study examined the calibration data collected by burke et al and rogers et al from 155 human subjects in order to describe the frequency location and magnitude of standing wave pressure minima to see if these errors might explain trends in test performance results indicate that while individual resu

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

isogeometric fluid structure interaction analysis with emphasis on non matching discretizations and with application to wind turbines abstract in this paper we develop a framework for fluid structure interaction fsi modeling and simulation with emphasis on isogeometric analysis iga and non matching fluid structure interface discretizations we take the augmented lagrangian approach to fsi as a point of departure here the lagrange multiplier field is defined on the fluid structure interface and is responsible for coupling of the two subsystems thus the fsi formulation does not rely on the continuity of the underlying function spaces across the fluid structure interface in order to produce the correct coupling conditions between the fluid and structural subdomains however in deriving the final fsi formulation the interface lagrange multiplier is formally eliminated and the formulation is written purely in terms of primal variables avoiding the use of lagrange multipliers adds efficiency to the proposed formulation as an added benefit the ability to employ non matching grids for multi physics simulations leads to significantly relaxed requirements that are placed on the geometry modeling and meshing tools for iga we show an application of the proposed fsi formulation to the simulation of the nrel 5 mw offshore wind turbine rotor where the aerodynamics domain is modeled using volumetric quadratic nurbs while the rotor structure is modeled using a cubic t spline based discretization of a rotation free kirchhoff love shell we conclude the article by showing fsi coupling of a t spline shell with a low order finite element method fem discretization of the aerodynamics equations this combined use of iga and fem is felt to be a good balance between speed robustness and accuracy of fsi simulations for this class of problems

on the hyper elastic formulation of the immersed boundary method abstract the immersed boundary ib method is both a mathematical formulation and a numerical method for fluid structure interaction problems in which immersed incompressible visco elastic bodies or boundaries interact with an incompressible fluid previous formulations of the ib method were not able to treat appropriately immersed materials of finite nonzero thickness modeled by general hyper elastic constitutive laws because of the lack of appropriate transmission conditions between the immersed body and the surrounding fluid in the case of a nonzero jump in normal stress at the solid fluid interface such a jump does not arise when the solid is comprised of fibers that run parallel to the interface but typically does arise in other cases e g when the solid contains elastic fibers that terminate at the solid fluid interface we present a derivation of the ib method that takes into account in an appropriate way the missing term the derivation presented in this paper starts from a separation of the stress that appears in the principle of virtual work the stress is divided into its fluid like and solid like components and each of these two terms is treated in its natural framework i e the eulerian framework for the fluid like stress and the lagrangian framework for the solid like stress we describe how the ib method can be used in conjunction with standard formulations of continuum mechanics models for immersed incompressible elastic materials and present some illustrative numerical experiments

influence of primary level and primary frequency ratios on human distortion product otoacoustic emissions the combined influence of primary level differences l1 l2 and primary frequency ratio f2 f1 on distortion product otoacoustic emission dpoae level was investigated in 20 normal hearing subjects dpoaes were recorded with continuously varying stimulus levels neely et al j acoust soc am 117 1248 1259 2005 for the following stimulus conditions f2 1 2 4 and 8 khz and f2 f1 1 05 to 1 4 various l1 l2 including one individually optimized to produce the largest dpoae for broadly spaced primary frequencies at low l2 levels the largest dpoaes were recorded when l1 was much higher than l2 with l1 remaining relatively constant as l2 increased as f2 fl decreased the largest dpoaes were observed when l1 was closer to l2 and increased as l2 increased optimal values for l1 l2 and f2 f1 were derived from these data in general average dpoae levels for the new l1 l2 and f2 f1 were equivalent to or larger than those observed for other stimulus combinations including the l1 l2 described by kummer et al j acoust soc am 103 3431 3444 1998 and those defined by neely et al in which l1 l2 was evaluated but f2 f1 was fixed at 1 2

isogeometric reissner mindlin shell analysis with exactly calculated director vectors abstract an isogeometric reissner mindlin shell derived from the continuum theory is presented the geometry is described by nurbs surfaces the kinematic description of the employed shell theory requires the interpolation of the director vector and of a local basis system hence the definition of nodal basis systems at the control points is necessary for the proposed formulation the control points are in general not located on the shell reference surface and thus several choices for the nodal values are possible the proposed new method uses the higher continuity of the geometrical description to calculate nodal basis system and director vectors which lead to geometrical exact interpolated values thereof thus the initial director vector coincides with the normal vector even for the coarsest mesh in addition to that a more accurate interpolation of the current director and its variation is proposed instead of the interpolation of nodal director vectors the new approach interpolates nodal rotations account is taken for the discrepancy between interpolated basis systems and the individual nodal basis systems with an additional transformation the exact evaluation of the initial director vector along with the interpolation of the nodal rotations lead to a shell formulation which yields precise results even for coarse meshes the convergence behavior is shown to be correct for k refinement allowing the use of coarse meshes with high orders of nurbs basis functions this is potentially advantageous for applications with high numerical effort per integration point the geometrically nonlinear formulation accounts for large rotations the consistent tangent matrix is derived various standard benchmark examples show the superior accuracy of the presented shell formulation a new benchmark designed to test the convergence behavior for free form surfaces is presented despite the higher numerical effort per integration point the improved accuracy yields considerable savings in computation cost for a predefined error bound

a monolithic approach to fluid structure interaction using space time finite elements abstract the paper presents a simultaneous solution procedure for fluid structure interaction problems the structural motion is described by geometrically nonlinear elastodynamics the fluid is modeled by the incompressible navier stokes equations the space time finite element method is applied to both continua leading to an almost uniform discretization in which velocity variables are used for fluid and structure in order to enforce momentum conservation and geometric continuity at the interface a weighted residual formulation of coupling conditions is introduced the discretized model equations for fluid structure and coupling conditions are formulated in a single equation system the nonlinear system and the fluid mesh movement are solved in a single iteration loop two dimensional examples of membrane flutter and vortex excited plate vibrations demonstrate the efficiency of the methodology

fast isogeometric boundary element method based on independent field approximation abstract an isogeometric boundary element method for problems in elasticity is presented which is based on an independent approximation for the geometry traction and displacement field this enables a flexible choice of refinement strategies permits an efficient evaluation of geometry related information a mixed collocation scheme which deals with discontinuous tractions along non smooth boundaries and a significant reduction of the right hand side of the system of equations for common boundary conditions all these benefits are achieved without any loss of accuracy compared to conventional isogeometric formulations the system matrices are approximated by means of hierarchical matrices to reduce the computational complexity for large scale analysis for the required geometrical bisection of the domain a strategy for the evaluation of bounding boxes containing the supports of nurbs basis functions is presented the versatility and accuracy of the proposed methodology are demonstrated by convergence studies showing optimal rates and real world examples in two and three dimensions

an extended isogeometric thin shell analysis based on kirchhoff love theory abstract an extended isogeometric element formulation xiga for analysis of through the thickness cracks in thin shell structures is developed the discretization is based on non uniform rational b splines nurbs the proposed xiga formulation can reproduce the singular field near the crack tip and the discontinuities across the crack it is based on the kirchhoff love theory where c 1 continuity of the displacement field is required this condition is satisfied by the nurbs basis functions hence the formulation eliminates the need of rotational degrees of freedom or the discretization of the director field facilitating the enrichment strategy the performance and validity of the formulation is tested by several benchmark examples

t spline finite element method for the analysis of shell structures a t spline surface is a nonuniform rational b spline nurbs surface with t junctions and is defined by a control grid called t mesh the t mesh is similar to a nurbs control mesh except that in a t mesh a row or column of control points is allowed to terminate in the inner parametric space this property of t splines makes local refinement possible in the present study shell formulation based on the t spline finite element method fem is presented shell formulation based on nurbs or t splines has fundamental limitations because rotational dofs which are necessary in the shell formulation cannot be defined on control points in this study the simple mapping scheme in which every control point is mapped into one geometric point on the surface is employed to eliminate the limitations using this mapping scheme t spline fem can be easily extended to the analysis of shells the proposed shell formulation is verified through various benchmarking problems this study is a part of the efforts by the authors for the integration of cad cae processes

non body fitted fluid structure interaction divergence conforming b splines fully implicit dynamics and variational formulation abstract immersed boundary ib methods deal with incompressible visco elastic solids interacting with incompressible viscous fluids a long standing issue of ib methods is the challenge of accurately imposing the incompressibility constraint at the discrete level we present the divergence conforming immersed boundary dcib method to tackle this issue the dcib method leads to completely negligible incompressibility errors at the eulerian level and various orders of magnitude of increased accuracy at the lagrangian level compared to other ib methods furthermore second order convergence of the incompressibility error at the lagrangian level is obtained as the discretization is refined in the dcib method the eulerian velocity pressure pair is discretized using divergence conforming b splines leading to inf sup stable and pointwise divergence free eulerian solutions the lagrangian displacement is discretized using non uniform rational b splines which enables to robustly handle large mesh distortions the data transfer needed between the eulerian and lagrangian descriptions is performed at the quadrature level using the same spline basis functions that define the computational meshes this conduces to a fully variational formulation sharp treatment of the fluid solid interface and a 0 5 increase in the convergence rate of the eulerian velocity and the lagrangian displacement measured in l 2 norm in comparison with using discretized dirac delta functions for the data transfer by combining the generalized method and a block iterative solution strategy the dcib method results in a fully implicit discretization which enables to take larger time steps various two and three dimensional problems are solved to show all the aforementioned properties of the dcib method along with mesh independence studies verification of the numerical method by comparison with the literature and measurement of convergence rates

a computational framework for fluid structure interaction finite element formulation and applications abstract this work is concerned with the modelling of the interaction of fluid flow with flexibly supported rigid bodies the fluid flow considered is governed by the incompressible navier stokes equations and modelled by employing stabilised low order velocity pressure finite elements the motion of the fluid domain is accounted for by an arbitrary lagrangian eulerian ale strategy the rigid body motion excited by the fluid flow is restricted by the elastic and damping properties of the supports for the temporal discretisation the discrete implicit generalised method is employed the resulting strongly coupled set of nonlinear equations is solved by means of a novel partitioned solution procedure which is based on the newton raphson methodology and incorporates full linearisation of the overall incremental problem the strong coupling is resolved and optimal convergence of the residuals is achieved several numerical examples are presented to demonstrate the robustness and efficiency of the methodology the examples clearly capture the phenomena of vortex induced oscillations and galloping

square root bryson frazier smoothing algorithms some new square root algorithms for bryson frazier smoothing formulas are suggested square root algorithms and a fast square root or so called chandrasekhar type algorithm the new square root algorithms use square root arrays composed of smoothed estimates and their error covariances these algorithms provide many advantages over the conventional algorithms with respect to systolic array and parallel implementations as well as numerical stability and conditioning for the case of constant parameter systems a fast square root algorithm is suggested which requires less computation than others

covariance factorization algorithms for fixed interval smoothing of linear discrete dynamic systems efficient factorized covariance smoothers designed to work with factorized covariance filters are derived for linear discrete dynamic systems the approach to factorized covariance smoothers either u d or square root uses outputs from factorized covariance filters and is closely derived from the g j bierman s earlier algorithm 1974 the dyer mcreynolds covariance smoother these algorithms are more efficient than the bierman s newer smoother 1983 based upon rank 1 process noise updates the efficiency of the new algorithms increases significantly as the order of process noise increases for full process noise they can be implemented in a way that avoids the inverse of the transition matrix

a finite element boundary element method for three dimensional large displacement fluid structure interaction abstract this paper presents a hybrid finite element boundary element method for fluid structure interaction simulations of inflatable structures the flow model consists of the steady stokes equation which admits a boundary integral formulation the structure is represented by a kirchhoff love shell the boundary element approximation of the stokes equation reduces the flow problem to an integral equation on the actual structure configuration thus obviating the need for volumetric meshing of the strongly deforming fluid domain the stokes model moreover exhibits a lubrication effect that acts as an intrinsic mechanism to treat the ubiquitous self contact that occurs in inflation problems the aggregated fluid structure interaction problem composed of the boundary integral equation and the kirchhoff love shell connected by dynamic and kinematic interface conditions is approximated by means of isogeometric discretizations to accommodate the smoothness requirements on the approximation spaces imposed by the flexural rigidity in the kirchhoff love shell and to provide an accurate and smooth representation of the boundary for the boundary element method auxiliary results presented in this paper are 1 a parametrization free kirchhoff love formulation 2 establishment of a cubic relationship between distance and tractions due to the lubrication effect and 3 the interpretation of the lagrange multiplier pertaining to fluid incompressibility as the total excess pressure

efficient isogeometric nurbs based solid shell elements mixed formulation and b method abstract in this work solid shell nurbs elements are developed in order to address static problems of slender structures under small perturbations a single layer of elements is considered through the thickness of the shell and the degree of approximation in that direction is chosen to be equal to two a full 3d constitutive relation is assumed the objective is to obtain highly accurate low degree elements to be used in coarse meshes in order to do that we propose a mixed method from which we derive a b projection to deal with locking the main idea is to modify the interpolation of the average stresses and strains through the thickness more precisely we develop two finite elements the first element which is based on the mixed method or equivalently on the b projection is extremely accurate but leads to a fully populated global stiffness matrix to improve the efficiency the second element uses a local least squares type procedure to define a new b projection leading to a sparse global stiffness matrix the quality and efficiency of the methods are assessed through several usual test cases and by comparison with other published techniques

a new forward pass fixed interval smoother using the u d information matrix factorization abstract a new u d factorized smoothing algorithm that is numerically stable and reliable is developed by using a forward pass fixed interval smoother recursion introducing a gain for a backward pass information filter and the notion of an input to the smoother and decomposing the system noises into each element it is shown that three famous u d algorithms can be naturally applied to construct such a smoother the new result does not necessitate two burdensome matrix inversions or any algebraic computations equivalent to them for the transition matrix and the predicted error covariance which are at present necessary for the bierman s u d smoother consequently compared with the result of bierman the present algorithm can deal with a broader system which may cover a time delay system and provide an improvement in computation speed and computer storage

three dimensional extension of non linear shell formulation based on the enhanced assumed strain concept conventional shell formulations such as 3 or 5 parameter theories or even 6 parameter theories including the thickness change as extra parameter require a condensation of the constitutive law in order to avoid a significant error due to the assumption of a linear displacement field across the thickness this means that the normal stress in thickness direction has to either vanish or be constant in general these extra constraints cannot be satisfied explicitly or they lead to elaborate strain expressions the main objective of the present study is to introduce directly a complete 3 d constitutive law without modification therefore a 7 parameter theory is utilized which includes a linear varying thickness stretch as extra variable allowing also large strain effects