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1.
In this paper, a new lattice Boltzmann model based on the rebuilding-divergency method for the Poisson equation is proposed.
In order to translate the Poisson equation into a conservation law equation, the source term and diffusion term are changed
into divergence forms. By using the Chapman-Enskog expansion and the multi-scale time expansion, a series of partial differential
equations in different time scales and several higher-order moments of equilibrium distribution functions are obtained. Thus,
by rebuilding the divergence of the source and diffusion terms, the Laplace equation and the Poisson equation with the second
accuracy of the truncation errors are recovered. In the numerical examples, we compare the numerical results of this scheme
with those obtained by other classical method for the Green-Taylor vortex flow, numerical results agree well with the classical
ones. 相似文献
2.
In this paper we continue the study, which was initiated in (Ben-Artzi et al. in Math. Model. Numer. Anal. 35(2):313–303,
2001; Fishelov et al. in Lecture Notes in Computer Science, vol. 2667, pp. 809–817, 2003; Ben-Artzi et al. in J. Comput. Phys. 205(2):640–664, 2005 and SIAM J. Numer. Anal. 44(5):1997–2024, 2006) of the numerical resolution of the pure streamfunction formulation of the time-dependent two-dimensional Navier-Stokes equation.
Here we focus on enhancing our second-order scheme, introduced in the last three afore-mentioned articles, to fourth order
accuracy. We construct fourth order approximations for the Laplacian, the biharmonic and the nonlinear convective operators.
The scheme is compact (nine-point stencil) for the Laplacian and the biharmonic operators, which are both treated implicitly
in the time-stepping scheme. The approximation of the convective term is compact in the no-leak boundary conditions case and
is nearly compact (thirteen points stencil) in the case of general boundary conditions. However, we stress that in any case
no unphysical boundary condition was applied to our scheme. Numerical results demonstrate that the fourth order accuracy is
actually obtained for several test-cases. 相似文献
3.
Given a data set in a metric space, we study the problem of hierarchical clustering to minimize the maximum cluster diameter,
and the hierarchical k-supplier problem with customers arriving online.
We prove that two previously known algorithms for hierarchical clustering, one (offline) due to Dasgupta and Long and the
other (online) due to Charikar, Chekuri, Feder and Motwani, output essentially the same result when points are considered
in the same order. We show that the analyses of both algorithms are tight and exhibit a new lower bound for hierarchical clustering.
Finally we present the first constant factor approximation algorithm for the online hierarchical k-supplier problem. 相似文献
4.
In this paper we solve a conjecture on the zeros of R-Bonacci polynomials in the case when r=3 (Tribonacci polynomials) and determine the zero attractor of the Tribonacci polynomials. Universality of the zero attractor
is also established.
相似文献
5.
In practice, the clearances of joints in a great number of mechanical systems are well under control. In these cases, some
of the existing methods become unpractical because of the little differences in the order of magnitude between relative movements
and computational errors. Assuming that the effects of impacts are negligible, we proved that both locations and forces of
contacts in joints can be fully determined by parts of joint reaction forces. Based on this fact, a method particularly suited
for multibody systems possessing frictional joints with tiny clearances is presented. In order to improve the efficiency of
computation, recursive formulations are proposed based on the interactions between bodies. The proposed recursive formulations
can improve the computation of joint reaction forces. With the methodology presented in this paper, not only the motion of
bodies in a multibody system but also the details about the contacts in joints, such as forces of contacts and locations of
contact points, can be obtained. Even with the assumption of impact free, the instants of possible impacts can be detected
without relying upon any ambiguous parameters, as indicated by numerical examples in this paper. 相似文献
6.
Alireza Pourshahid Daniel Amyot Liam Peyton Sepideh Ghanavati Pengfei Chen Michael Weiss Alan J. Forster 《Electronic Commerce Research》2009,9(4):269-316
A number of recent initiatives in both academia and industry have sought to achieve improvements in e-businesses through the
utilization of Business Process Management (BPM) methodologies and tools. However there are still some inadequacies that need
to be addressed when it comes to achieving alignment between business goals and business processes. The User Requirements
Notation (URN), recently standardized by ITU-T, has some unique features and capabilities beyond what is available in other
notations that can help address alignment issues. In this paper, a URN-based framework and its supporting toolset are introduced
which provide business process monitoring and performance management capabilities integrated across the BPM lifecycle. The
framework extends the URN notation with Key Performance Indicators (KPIs) and other concepts to measure and align processes
and goals. An example process for controlling access to a healthcare data warehouse is used to illustrate and evaluate the
framework. Early results indicate the feasibility of the approach. 相似文献
7.
An efficient and accurate numerical scheme is proposed, analyzed and implemented for the Kawahara and modified Kawahara equations
which model many physical phenomena such as gravity-capillary waves and magneto-sound propagation in plasmas. The scheme consists
of dual-Petrov-Galerkin method in space and Crank-Nicholson-leap-frog in time such that at each time step only a sparse banded
linear system needs to be solved. Theoretical analysis and numerical results are presented to show that the proposed numerical
is extremely accurate and efficient for Kawahara type equations and other fifth-order nonlinear equations.
This work is partially supported by the National Science Council of the Republic of China under the grant NSC 94-2115-M-126-004
and 95-2115-M-126-003.
This work is partially supported by NSF grant DMS-0610646. 相似文献
8.
The paper considers the Baer-Nunziato model for two-phase flow in porous media, with discontinuous porosity. Computing solutions of the Riemann problem rests on capturing the jump in the solution across the porosity jump. A recent study (Lowe in J. Comput. Phys. 204:598–632, 2005) showed that numerical discretizations may fail to correctly capture the jump conditions across the so-called compaction wave, and yield incorrect solutions. We have formulated the Baer-Nunziato system using the Riemann invariants across the porosity jump, and propose a hybrid algorithm that uses the Riemann invariants formulation across the compaction wave, and the conservative formulation away from the compaction wave. The paper motivates and describes the hybrid scheme and present numerical results. 相似文献
9.
Computing the duplication history of a tandem repeated region is an important problem in computational biology (Fitch in Genetics
86:623–644, 1977; Jaitly et al. in J. Comput. Syst. Sci. 65:494–507, 2002; Tang et al. in J. Comput. Biol. 9:429–446, 2002). In this paper, we design a polynomial-time approximation scheme (PTAS) for the case where the size of the duplication block
is 1. Our PTAS is faster than the previously best PTAS in Jaitly et al. (J. Comput. Syst. Sci. 65:494–507, 2002). For example, to achieve a ratio of 1.5, our PTAS takes O(n
5) time while the PTAS in Jaitly et al. (J. Comput. Syst. Sci. 65:494–507, 2002) takes O(n
11) time. We also design a ratio-6 polynomial-time approximation algorithm for the case where the size of each duplication block
is at most 2. This is the first polynomial-time approximation algorithm with a guaranteed ratio for this case.
Part of work was done during a Z.-Z. Chen visit at City University of Hong Kong. 相似文献
10.
The local discontinuous Galerkin (LDG) viscous flux formulation was originally developed by Cockburn and Shu for the discontinuous
Galerkin setting and later extended to the spectral volume setting by Wang and his collaborators. Unlike the penalty formulations
like the interior penalty and the BR2 schemes, the LDG formulation requires no length based penalizing terms and is compact.
However, computational results using LDG are dependant of the orientation of the faces especially for unstructured and non
uniform grids. This results in lower solution accuracy and stiffer stability constraints as shown by Kannan and Wang. In this
paper, we develop a variant of the LDG, which not only retains its attractive features, but also vastly reduces its unsymmetrical
nature. This variant (aptly named LDG2), displayed higher accuracy than the LDG approach and has a milder stability constraint
than the original LDG formulation. In general, the 1D and the 2D numerical results are very promising and indicate that the
approach has a great potential for 3D flow problems. 相似文献
11.
12.
We study the problem of solving simple stochastic games, and give both an interesting new algorithm and a hardness result. We show a reduction from fine approximation of simple stochastic games to coarse approximation of a polynomial sized game, which can be viewed as an evidence showing the hardness to approximate the value of simple stochastic games. We also present a randomized algorithm that runs in \(\tilde{O}(\sqrt{|V_{\mathrm{R}}|!})\) time, where |V R| is the number of RANDOM vertices and \(\tilde{O}\) ignores polynomial terms. This algorithm is the fastest known algorithm when |V R|=ω(log?n) and \(|V_{\mathrm{R}}|=o(\sqrt{\min{|V_{\min}|,|V_{\max}|}})\) and it works for general (non-stopping) simple stochastic games. 相似文献
13.
Changing basic conditions in the field of logistics requires intuitive planning methods as well as new ways of supporting
and educating the operative staff. VR and AR show a great promise for that.
相似文献
Rupert ReifEmail: URL: http://www.fml.mw.tum.de |
14.
Christophe Vandekerckhove Ioannis Kevrekidis Dirk Roose 《Journal of scientific computing》2009,39(2):167-188
The long-term dynamic behavior of many dynamical systems evolves on a low-dimensional, attracting, invariant slow manifold,
which can be parameterized by only a few variables (“observables”). The explicit derivation of such a slow manifold (and thus,
the reduction of the long-term system dynamics) is often extremely difficult or practically impossible. For this class of
problems, the equation-free framework has been developed to enable performing coarse-grained computations, based on short
full model simulations. Each full model simulation should be initialized so that the full model state is consistent with the
values of the observables and close to the slow manifold. To compute such an initial full model state, a class of constrained
runs functional iterations was proposed (Gear and Kevrekidis, J. Sci. Comput. 25(1), 17–28, 2005; Gear et al., SIAM J. Appl. Dyn. Syst. 4(3), 711–732, 2005). The schemes in this class only use the full model simulator and converge, under certain conditions, to an approximation
of the desired state on the slow manifold. In this article, we develop an implementation of the constrained runs scheme that
is based on a (preconditioned) Newton-Krylov method rather than on a simple functional iteration. The functional iteration
and the Newton-Krylov method are compared in detail using a lattice Boltzmann model for one-dimensional reaction-diffusion
as the full model simulator. Depending on the parameters of the lattice Boltzmann model, the functional iteration may converge
slowly or even diverge. We show that both issues are largely resolved by using the Newton-Krylov method, especially when a
coarse grid correction preconditioner is incorporated. 相似文献
15.
The convergence to steady state solutions of the Euler equations for high order weighted essentially non-oscillatory (WENO)
finite difference schemes with the Lax-Friedrichs flux splitting (Jiang and Shu, in J. Comput. Phys. 126:202–228, 1996) is investigated. Numerical evidence in Zhang and Shu (J. Sci. Comput. 31:273–305, 2007) indicates that there exist slight post-shock oscillations when we use high order WENO schemes to solve problems containing
shock waves. Even though these oscillations are small in their magnitude and do not affect the “essentially non-oscillatory”
property of the WENO schemes, they are indeed responsible for the numerical residue to hang at the truncation error level
of the scheme instead of settling down to machine zero. Differently from the strategy adopted in Zhang and Shu (J. Sci. Comput.
31:273–305, 2007), in which a new smoothness indicator was introduced to facilitate convergence to steady states, in this paper we study the
effect of the local characteristic decomposition on steady state convergence. Numerical tests indicate that the slight post-shock
oscillation has a close relationship with the local characteristic decomposition process. When this process is based on an
average Jacobian at the cell interface using the Roe average, as is the standard procedure for WENO schemes, such post-shock
oscillation appears. If we instead use upwind-biased interpolation to approximate the physical variables including the velocity
and enthalpy on the cell interface to compute the left and right eigenvectors of the Jacobian for the local characteristic
decomposition, the slight post-shock oscillation can be removed or reduced significantly and the numerical residue settles
down to lower values than other WENO schemes and can reach machine zero for many test cases. This new procedure is also effective
for higher order WENO schemes and for WENO schemes with different smoothness indicators. 相似文献
16.
Marta Mesquita Margarida Moz Ana Paias José Paixão Margarida Pato Ana Respício 《Journal of Scheduling》2011,14(4):319-334
Operational planning within public transit companies has been extensively tackled but still remains a challenging area for
operations research models and techniques. This phase of the planning process comprises vehicle-scheduling, crew-scheduling
and rostering problems. In this paper, a new integer mathematical formulation to describe the integrated vehicle-crew-rostering
problem is presented. The method proposed to obtain feasible solutions for this binary non-linear multi-objective optimization
problem is a sequential algorithm considered within a preemptive goal programming framework that gives a higher priority to
the integrated vehicle-crew-scheduling goal and a lower priority to the driver rostering goals. A heuristic approach is developed
where the decision maker can choose from different vehicle-crew schedules and rosters, while respecting as much as possible
management’s interests and drivers’ preferences. An application to real data of a Portuguese bus company shows the influence
of vehicle-crew-scheduling optimization on rostering solutions. 相似文献
17.
This article considers the global robust output regulation problem via output feedback for a class of cascaded nonlinear systems with input-to-state stable inverse dynamics. The system uncertainties depend not only on the measured output but also all the unmeasurable states. By introducing an internal model, the output regulation problem is converted into a stabilisation problem for an appropriately augmented system. The designed dynamic controller could achieve the global asymptotic tracking control for a class of time-varying reference signals for the system output while keeping all other closed-loop signals bounded. It is of interest to note that the developed control approach can be applied to the speed tracking control of the fan speed control system. The simulation results demonstrate its effectiveness. 相似文献
18.
Mario E. Caire Francisco J. Lopez David H. Williams 《The Journal of supercomputing》2009,48(2):163-182
A distributed approach is described for solving lineality (or linearity) space (LS) problems with large cardinalities and a large number of dimensions. The LS solution has applications in engineering, science, and business, and includes a subset of solutions of the more general extended linear complementarity problem (ELCP). A parallel MATLAB framework is employed and results are computed on an 8-node Rocks based cluster computer using
Remote Procedure Calls (RPCs) and the MPICH2 Message Passing Interface (MPI). Results show that both approaches perform comparably
when solving distributed LS problems. This indicates that when deciding which parallel approach to use, the implementation details particular to the
method are the decisive factors, which in this investigation give MPICH2 MPI the advantage.
相似文献
Mario E. CaireEmail: |
19.
A p-type spectral-element method using prolate spheroidal wave functions (PSWFs) as basis functions, termed as the prolate-element
method, is developed for solving partial differential equations (PDEs) on the sphere. The gridding on the sphere is based
on a projection of the prolate-Gauss-Lobatto points by using the cube-sphere transform, which is free of singularity and leads
to quasi-uniform grids. Various numerical results demonstrate that the proposed prolate-element method enjoys some remarkable
advantages over the polynomial-based element method: (i) it can significantly relax the time step size constraint of an explicit
time-marching scheme, and (ii) it can increase the accuracy and enhance the resolution. 相似文献
20.
Traditional set associative caches are seriously prone to conflict misses. We propose an adapted new skewed associative architecture
as an attempt to alleviate this problem. It has already been shown that skewed associative caches can reduce the rate of conflict
misses by using different hash functions to index different banks. Building on this observation, we propose yet another approach
to further reduce the rate of conflict misses, nicknamed YAARC (Yet Another Approach to Reducing Conflicts) that uses different hash functions to index into a single bank. Mathematical modeling and simulation results are exploited
to evaluate the impact of YAARC on the rate of conflict misses. Mathematical analysis show the superiority of YAARC caches
over set and skewed associative caches from the conflict miss point of view. Simulations, using some benchmarks from SPEC
CPU2000 benchmark suit that former researchers have reported them as the best candidates for cache performance evaluation,
also show nearly 43% conflict miss rate improvement for the skewed associative cache over the set associative cache, and nearly
31% improvement for the YAARC cache over the skewed associative cache. This implies that YAARC caches considerably outperform
set and skewed associative caches from the conflict miss point of view. Since production of YAARC caches require a dispensable
amount of hardware overhead, they can be considered as a cost effective approach to minimize the rate of conflict misses.
相似文献
Behrouz ZolfaghariEmail: |