perfect ideal and balanced matrices abstract in this paper we survey results and open problems on perfect ideal and balanced matrices these matrices arise in connection with the set packing and set covering problems two integer programming models with a wide range of applications we concentrate on some of the beautiful polyhedral results that have been obtained in this area in the last 30 years this survey first appeared in ricerca operativa

aeroelastic dynamic analysis of a full f 16 configuration for various flight conditions an overview is given of recent advances in a three field methodology for modeling and solving nonlinear fluid structure interaction problems and its application to the prediction of the aeroelastic frequencies and damping coefficients of a full f 16 configuration in various subsonic transonic and supersonic airstreams is reported in this three field methodology the flow is described by the arbitrary lagrangian eulerian form of the euler equations the structure is represented by a detailed finite element model and the fluid mesh is unstructured dynamic and updated by a robust torsional spring analogy method simulation results are presented for stabilized accelerated low g and high g flight conditions and correlated with flight test data consequently the practical feasibility and potential of the described computational fluid dynamics based computational method for the flutter analysis of high performance aircraft particularly in the transonic regime are discussed

extrapolation effects on coupled computational fluid dynamics computational structural dynamics simulations between them passing loads from the e ow code to the structural code and displacements back theother way forunsteady problems the sequencing is done within the pseudotime loop used for the e ow solver and removes sequencing errors the mesh movement for the aerodynamic solver is done using transe nite interpolation of displacements 7 we restrict ourselves in this note to the case of a wing modeled structurally by a plate this case is interesting as a building block to more complex structural descriptions transformation of data between the two grids is broken into two components in and out of the plane of the structural model the outplane treatment follows the considerations of ref 5 the in plane treatment turns out to have a much stronger ine uence on the test case considered next the two approaches used are the ine nite plate spline ips 8 and linear interpolation for ips a solution of the thin plate equation is forced to pass through the known structural points and is then evaluated at the projected aerodynamic points for the required displacements for linear interpolation each projected e uid point is associated with a triangle on the structural mesh and the deformation is calculated using a linear approximation within the triangle in both cases the relationship between displacements on the e uid and structural grids is linear and the principle of virtual work is then applied for transferring forces iii test cases

interfacing of fluid and structural models via innovative structural boundary element method an innovative structural boundary element method bem solver is developed for interfacing the computational fluid dynamics cfd and computational structural dynamics csd grids formulated as a solid mechanics problem with a minimum strain energy requirement the bem solver generates a truly three dimensional universal spline matrix the universal spline matrix is a vector operator that includes the coupling of displacements and forces along all axes based on a similar formulation an exterior bem solver is also developed to account for the flowfield grid deformation thus the bem solver allows a unified treatment of the displacement and force transformation for cfd csd interfacing as well as the computation of the flowfield grid deformation the solution procedure is fully automated and no additional model generation is required therefore is ideally suitable for computational aeroelasticity and multidisciplinary optimization applications

a linear expected time algorithm for deriving all logical conclusions implied by a set of boolean inequalities consider a setr ofm binary relations on a set ofn boolean variables r may imply a contradiction the fixation of some variables at 0 or at 1 and or the identification of some pairs of variables in direct or complemented form an o n expected time algorithm is given for the derivation of all such logical conclusions computational experiments with problems involving up to 2000 variables are reported on the proposed algorithm is more than 100 times faster than previous methods whenn 100

solving variational inequalities by a modified projection method with an effective step size in this paper we propose a new projection method for the solution of variational inequality problems the method is simple which uses only function evaluations and projections onto the feasible set we adopt a new step size rule and a new search direction in the new method under the mild conditions we prove the proposed method is globally convergent preliminary numerical results are reported

an extension of the ko nig egerva ry property to node weighted bidirected graphs given a bidirected graphg and a vectorb of positive integral node weights an integer linear program ip is defined on g b ip generalizes the node packing problem on a node weighted undirected graph in the sense that it reduces to the latter wheng is undirected a polynomial time algorithm is given that recognizes whether cp the linear program obtained by relaxing the integrality constraints of ip has an integral optimal solution also an efficient method for solving the linear programming dual of cp is described

perfect and ideal 0 1 matrices a 0 1 matrix a is said to be perfect resp ideal if the corresponding generalized packing resp covering polytope is integral given a 0 1 matrix a we construct a 0 1 matrix that is perfect if and only if a is perfect a similar result is obtained for the generalized covering problem we also extend some known results on perfect 0 1 matrices to the 0 1 case

improved radial basis function fluid structure coupling via efficient localized implementation previous work by the authors has developed a universal interpolation scheme using radial basis functions rbfs which results in a unified formulation for robust fluid structure interpolation and high quality mesh motion the method has several significant advantages primarily all volume mesh structural mesh and flow solver type dependence is removed entirely as all operations are performed on totally arbitrary point clouds of any form hence all connectivity requirements are removed from both the coupling and mesh motion problems furthermore only matrix vector multiplications are required during unsteady simulation because dependence relations are computed once prior to any simulation and then remain constant this property means that the method is both perfectly parallel and totally independent from the flow solver however the full method is expensive since the dependence matrix between two sets of points is n points1 n points2 the fluid structure coupling behaviour can also be influenced by parameters used in the interpolation to alleviate these difficulties a more efficient form of the rbf fluid structure coupling is presented which also greatly reduces the interpolation parameter influence a pointwise form of the partition of unity approach is developed that localizes the interpolation with results presented for static aeroelastic simulations of the brite euram multi disciplinary optimization wing using a very fine mesh containing 58000 surface points it is shown that a 58 reduction in data size is achieved and equally importantly the interpolation has a much smaller influence on final aeroelastic results

perfect 0 pl matrices and perfect bidirected graphs abstract perfect 0 1 matrices and perfect bidirected graphs are independently defined but are closely related in this paper we discuss these relations and give several characterizations of perfectness the generalized stable set problem associated with bidirected graphs is a generalization of the maximum weighted stable set problem we also give a brief proof that if a given bidirected graph is perfect then the problem can be solved in polynomial time

tight bounds and 2 approximation algorithms for integer programs with two variables per inequality the problem of integer programming in bounded variables over constraints with no more than two variables in each constraint is np complete even when all variables are binary this paper deals with integer linear minimization problems inn variables subject tom linear constraints with at most two variables per inequality and with all variables bounded between 0 andu for such systems a 2 approximation algorithm is presented that runs in time o mnu2 log un2m so it is polynomial in the input size if the upper boundu is polynomially bounded the algorithm works by finding first a super optimal feasible solution that consists of integer multiples of 1 2 that solution gives a tight bound on the value of the minimum it furthermore has an identifiable subset of integer components that retain their value in an integer optimal solution of the problem these properties are a generalization of the properties of the vertex cover problem the algorithm described is in particular a 2 approximation algorithm for the problem of minimizing the total weight of true variables among all truth assignments to the 2 satisfiability problem

a new projection method for variational inequality problems we propose a new projection algorithm for solving the variational inequality problem where the underlying function is continuous and satisfies a certain generalized monotonicity assumption e g it can be pseudomonotone the method is simple and admits a nice geometric interpretation it consists of two steps first we construct an appropriate hyperplane which strictly separates the current iterate from the solutions of the problem this procedure requires a single projection onto the feasible set and employs an armijo type linesearch along a feasible direction then the next iterate is obtained as the projection of the current iterate onto the intersection of the feasible set with the halfspace containing the solution set thus in contrast with most other projection type methods only two projection operations per iteration are needed the method is shown to be globally convergent to a solution of the variational inequality problem under minimal assumptions preliminary computational experience is also reported

two new self adaptive projection methods for variational inequality problems abstract in this paper we propose two new projection methods for solving variational inequality problems vi the method is simple it uses only function evaluation and projection onto the feasible set under the conditions that the underlying function is continuous and satisfies some generalized monotonicity assumption the methods are proven to converge to a solution of variational inequality globally some preliminary computational results are reported to illustrate the efficiency of the methods

unified fluid structure interpolation and mesh motion using radial basis functions a multivariate interpolation scheme using radial basis functions is presented which results in a completely unified formulation for the fluid structure interpolation and mesh motion problems the method has several significant advantages primarily all volume mesh structural mesh and flow solver type dependence is removed and all operations are performed on totally arbitrary point clouds of any form hence all connectivity and user input requirements are removed from the computational fluid dynamics computational structural dynamics cfd csd coupling problem as only point clouds are required to determine the coupling also it may equally well be applied to structured and unstructured grids or structural and aerodynamic grids that intersect again because no connectivity information is required furthermore no expensive computations are required during an unsteady simulation just matrix vector multiplications since the required dependence relations are computed only once prior to any simulation and then remain constant this property means that the method is both perfectly parallel since only the data relevant to each structured block or unstructured partition are required to move those points and totally independent from the flow solver hence a completely generic black box tool can be developed which is ideal for use in an optimization approach aeroelastic behaviour of the brite euram mdo wing is analysed in terms of both static deflection and dynamic responses and it is demonstrated that responses are strongly dependent on the exact cfd csd interpolation used mesh quality is also examined during the motion resulting from a large surface deformation global grid quality is shown to be preserved well with local grid orthogonality also being maintained well particularly at and near the moving surface where the original orthogonality is retained copyright 2007 john wiley sons ltd

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

modified self adaptive projection method for solving pseudomonotone variational inequalities abstract in this paper a self adaptive projection method with a new search direction for solving pseudomonotone variational inequality vi problems is proposed which can be viewed as an extension of the methods in b s he x m yuan j z zhang comparison of two kinds of prediction correction methods for monotone variational inequalities computational optimization and applications 27 2004 247 267 and x h yan d r han w y sun a self adaptive projection method with improved step size for solving variational inequalities computers mathematics with applications 55 2008 819 832 the descent property of the new search direction is proved which is useful to guarantee the convergence under the relatively relaxed condition that f is continuous and pseudomonotone the global convergence of the proposed method is proved numerical experiments are provided to illustrate the efficiency of the proposed method

conservative load projection and tracking for fluid structure problems the loose coupling of computational fluid dynamics and computational structural dynamics solvers introduces some problems related to the information transfer between the codes some techniques developed to solve the problems of the load transfer and interface surface tracking are presented the main criterion is to achieve conservation of total loads and total energy the load projection scheme is based on gaussian integration and fast interpolation algorithms for unstructured grids the surface tracking algorithm also based on interpolation is important for many applications including aeroelastic deformation of wings due to aerodynamic loads the methodologies not only improve present fluid structure interaction simulations but also increase the range of their applicability these techniques are of general character and can be used in other multidisciplinary applications as well

a modified projection method with a new direction for solving variational inequalities in this paper we propose a new projection method for solving variational inequality problems which can be viewed as an improvement of the method of li et al m li l z liao x m yuan a modified projection method for co coercive variational inequality european journal of operational research 189 2008 310 323 by adopting a new direction under the same assumptions as those in li et al 2008 we establish the global convergence of the proposed algorithm some preliminary computational results are reported which illustrated that the new method is more efficient than the method of li et al 2008

higher order time integration through smooth mesh deformation for 3d fluid structure interaction simulations in this paper we present a higher order accurate in time partitioned integration scheme imex for fluid structure interaction the scheme is based on a combination of an implicit l stable multi stage runge kutta scheme and an explicit runge kutta scheme fluid and structure dynamics are integrated using the implicit scheme and only the pressure loads acting on the structure are integrated explicitly for an academic problem we show that mesh optimization functions which are often necessary in standard mesh deformation algorithms can have a detrimental effect on the temporal order and accuracy we use a radial basis function rbf interpolation with a thin plate spline to create a smooth displacement field for the whole fluid domain which does not affect the order of the imex time integration scheme for reasonable accuracies the imex schemes outperform a second order staggered scheme by a factor of 2 3 as an example for a three dimensional real world problem a simulation of a transonic wing flutter case the agard 445 6 wing is performed for this test case a clear third order time accuracy is observed for imex3

binary integer programs with two variables per inequality several recent papers have shown that some properties of the maximum weight stable set problem hold true in the more general setting of binary integer programs with two variables per inequality in this paper we show that in fact the two problems are equivalent by using the transitive closure of the binary integer program and possibly reducing the number of variables by fixing complementing or identifying them we use this equivalence to prove two conjectures made by johnson and padberg regarding the perfection of bidirected graphs