bluuebunny/crossref_metadata_2025_split huggingface dataset:
Computation of waves generated by submarine landslides
Authors: Verriere M. , Lenoir M. 
Published: August 2005

AbstractWaves generated by submarine landslides are treated as three‐dimensional flows of a perfect incompressible fluid. For the solution of the Cauchy‐Poisson problem a time‐discretization is applied which leads at each time step to a non‐homogeneous free surface condition; the solution is then divided into two parts. The first part, subject to the true free surface condition, is computed in a simplified domain with constant depth. The second part involves a homogeneous free surface condition, a corrected bottom condition and the true bathymetry. In the case of constant depth, unconditional stability of the time discretization is derived. In the case of variable depth, mass and energy conservation is derived. Numerical results are presented. Comparison is made with other methods for the generation of axisymmetric waves. The transient propagation along a rectilinear coast is studied, including a comparison between two different bathymetries; trapping of energy is observed.
Finite volume computation of the turbulent flow over a hill employing 2D or 3D non‐orthogonal collocated grid systems
Authors: Coelho P. J. , Pereira J. C. F. 
Published: August 2005

AbstractA general numerical method for the solution of the complete Reynolds‐averaged Navier‐Stokes equations for 2D or 3D flows is described. The method uses non‐orthogonal co‐ordinates, Cartesian velocity components and a pressure‐velocity‐coupling algorithm adequate for non‐staggered grid systems. The capability of the method and the overall performance of the κ–ϵ eddy viscosity model are demonstrated by calculations of 2D and 3D flow over a hill. Solution error estimations based on fine grids, e.g. 320 × 192 control volumes, together with comparisons with standard turbulence model modifications, low‐Reynoldsnumber or streamline curvature effects, have allowed the investigation of model drawbacks in predicting turbulent flows over surface‐mounted hills.
Periodic solution of turbulent oscillating channel flows
Authors: Zhong Qin , Olson M. D. 
Published: August 2005

AbstractThe time‐dependent turbulent Navier–Stokes equations are solved numerically by a finite element method with an algebraic eddy viscosity model (Baldwin–Lomax formulation) for oscillating turbulent channel flows. The method of averaging is used to analyse the resulting periodic motion of the fluid. Numerical results are obtained for various Strouhal numbers and relative amplitudes. A comparison is made between the numerical and published experimental results. It appears that for low relative amplitudes in a certain range of frequencies the agreement is satisfactory.
Numerical simulation of twin‐jet impingement on a flat plate coupled with cross‐flow
Authors: Chuang Shu‐Hao , Chen Ming‐Hua , Lii Shen‐Wu , Tai Fang‐Mei 
Published: August 2005

AbstractTheoretical research to simulate twin‐jet impingement with cross‐flow has been undertaken. An impinging twin jet coupled with cross‐flow in closed ground effect has been studied by using the compressible Navier‐Stokes equation with a Jones–Launder κ–ϵ two‐equation turbulence model. The velocity results without cross‐flow were compared with the data of Saripalli et al. and found to show good agreement. The calculated results show that several recirculating zones are distributed around the flow field. Their size and location are closely related to the jet exit height above the ground, the nozzle space and the strength of cross‐flow. In addition, a fountain upwash flow occurs between the nozzles, and two low‐pressure recirculating zones are induced by the interaction between the nozzle mainstream and the fountain upwash flow. This induce a loss of lift force of the aircraft. The effects of the cross‐flow induce the sudden decrease in the lift force of the aircraft; the stronger the cross‐flow, the lower is the lift force of the flow field.
Cell vertex finite volume discretizations in three dimensions
Authors: Crumpton P. I. , Shaw G. J. 
Published: August 2005

AbstractThe cell vertex method is generalized to three dimensions. It is proved that there exists a one‐parameter family of eight‐point three‐dimensional methods with second‐order truncation error on parallelepipeds. Using different triangulations of control volume faces, various finite volume methods are derived. Some of these are identified as members of the aforementioned one‐parameter family and may be regarded as second‐order upwind schemes. A Fourier analysis is used to investigate the spectral properties of these discretizations.Numerical experiments illustrate that second‐order global accuracy is achieved on parallelepiped grids, as suggested by the theory. Randomly perturbed, stretched, sheared meshes are used to test these methods to destruction. It is found that upwinding improves both the accuracy on distorted meshes and the spectrum of the discretization.
The numerical solution of the thin film flow surrounding a horizontal cylinder resulting from a vertical cylindrical jet
Authors: Hunt Roland 
Published: August 2005

AbstractThe numerical solution of the thin film flow surrounding a horizontal cylinder resulting from a single vertical cylindrical jet is obtained. This is effected by transforming the domain of the flow, which contains a free surface, onto a rectangular parallelepiped and using a marching strategy to solve the ensuing parabolic equations. The flow terminates at a finite distance along the cylinder, its position depending on the velocity and mass flux of the jet. A comparison with the usual two‐dimensional model in which the jet is replaced by a vertical sheet shows that such a representation is valid provided the overall width of the flow is not too large. In particular, the differences in heat transfer characteristics amount to a few per cent, thus validating the use of the two‐dimensional model when applied to heat exchanger tubes. A comparison with the more usual multicolumn case is also considered.
Multivariant finite elements for three‐dimensional simulation of viscous incompressible flows
Authors: Gupta Mahesh , Kwon Tai H. , Jaluria Yogesh 
Published: August 2005

AbstractWithin multivariant elements, which have restricted degrees of freedom at some nodes, different velocity components have different variations. Shape functions for the multivariant elements Q Po and R Po are developed. With such shape functions the value of a velocity component within a multivariant element is shown to depend upon all the independent components of velocity at the nodes of the element.The use of the Q1 P0 element to simulate flows with discontinuous boundary conditions generated disturbance throughout the flow domain, giving erroneous pressure and velocity distributions. The Q Po element restricted the disturbance due to such discontinuities to a small region near the singular points, whereas the P Po element completely eliminated the fluctuations. Flows with discontinuous boundary conditions were simulated with reasonable accuracy by partially relaxing the no‐slip condition on the Q1 Po elements near the singular points.
A new outflow boundary condition
Authors: Papanastasiou T. C. , Malamataris N. , Ellwood K. 
Published: August 2005

AbstractBoundary conditions come from Nature. Therefore these conditions exist at natural boundaries. Often, owing to limitations in computing power and means, large domains are truncated and confined between artificial synthetic boundaries. Then the required boundary conditions there cannot be provided naturally and there is a need to fabricate them by intuition, experience, asymptotic behaviour and numerical experimentation. In this work several kinds of outflow boundary conditions, including essential, natural and free boundar conditions, are evaluated for two flow and heat transfer model problems. A new outflow boundary condition, called hereafter the free boundary condition, is introduced and tested. This free boundary condition is equivalent to extending the validity of the weak form of the governing equations to the synthetic outflow instead of replacing them there with unknown essential or natural boundary conditions. In the limit of zero Reynolds number the free boundary condition minimizes the energy functional among all possible choices of outflow boundary conditions. A review of results from applications of the same boundary conditions to several other flow situations is also presented and discussed.
Flux difference splitting for 1D open channel flow equations
Authors: Alcrudo Francisco , Garcia‐Navarro Pilar , Saviron Jose‐Maria 
Published: August 2005

AbstractAn upwind finite difference scheme based on flux difference splitting is presented for the solution of the equations governing unsteady open channel hydraulics. An approximate Jacobian needed for splitting the flux differences is defined that satisfies the conditions required to construct a first‐order upwind conservative discretization of the equations. Added limited second‐order corrections make the resulting scheme robust and accurate for the computation of all regimes of open channel flow. Some numerical results and comparisons with other classical schemes under exacting conditions are presented.
Calculation of two‐dimensional shear‐driven cavity flows at high reynolds numbers
Authors: Huser A. , Biringen S. 
Published: August 2005

AbstractThe time‐dependent Navier–Stokes equations are numerically integrated for two‐dimensional incompressible viscous flow in a shear‐driven square cavity. Using a time‐splitting method and finite differences on a staggered mesh, the momentum and pressure equations are directly solved by a tensor product method where one finite difference direction is diagonalized by eigenvalue decomposition. The effects of increasing Reynolds number are studied and the developing boundary layer is captured by using a finely clustered mesh. At Re = 30000 the flow is in a continuously developing unsteady regime. Power spectrum plots indicate that the unsteady flow oscillates with one fundamental frequency and exhibits some characteristics of transition between laminar and turbulent states.
Application of a vortex method to free surface flows
Authors: Chen Liyong , Vorus William S. 
Published: August 2005

AbstractVortex methods have found wide applications in various practical problems. The use of vortex methods in free surface flow problems, however, is still very limited. This paper demonstrates a vortex method for practical computation of non‐linear free surface flows produced by moving bodies. The method is a potential flow formulation which uses the exact non‐linear free surface boundary condition at the exact location of the instantaneous free surface. The position of the free surface, on which vortices are distributed, is updated using a Lagrangian scheme following the fluid particles on the free surface. The vortex densities are updated by the non‐linear dynamic boundary condition, derived from the Euler equations, with an iterative Lagrangian numerical scheme.The formulation is tested numerically for a submerged circular cylinder in unsteady translation. The iteration is shown to converge for all cases. The results of the unsteady simulations agree well with classical linearized solutions. The stability of the method is also discussed.
A boundary element formulation using the simple method
Authors: Grigor'Ev M. M. 
Published: August 2005

AbstractA new boundary element method is described for calculation of the steady incompressible laminar flows. The method is based on the well‐known SIMPLE algorithm. The new boundary element method allows one to find the fields of the pressure and velocity corrections without inner iterations, thus reducing the computational time drastically. This makes it different from the method developed by Patankar and Spalding.32However, the new method demands a much larger computer strorage. The boundary integral equations are discretized with the help of constant boundary elements and constant cells. The values of the integrals along the boundary elements and the cells for the two‐dimensional domain are found analytically. To preserve the stability in the iteration process, under‐relaxation for the convection terms is used. This paper gives the results of calculations of the flows between two plane parallel plates atRe= 20 andRe= 200, the flows in a square cavity with a moving upper lid atRe= 1 andRe= 100 and the flow in a plane channel with sudden symmetric expansion atRe=46·6.
Finite element modelling of sheared flow effects on the radiation characteristics of acoustic sources in a circular duct
Authors: Steck James E. , Eversman Walter 
Published: August 2005

AbstractThe recent interest in propeller noise generation, stimulated by development of new propeller types for commerical propjets, has generated a need for the ability of measure the noise characteristics of propellers. However, wind tunnel noise measurements are affected by reflections from the wind tunnel walls. Computer codes predicting the free‐field noise of a propeller and its noise field in a circular wind tunnel allow validating the use of wind tunnel measurements to predict free‐field noise characteristics. A wind tunnel contains flow which is uniform in the duct axial direction, but can vary in the radial direction. It can be shown that a third‐order differential equation governs the acoustic pressure field for such a duct containing radially sheared subsonic flow. This third‐order problem is then posed as a coupled pair of equations which are second‐order in terms of acoustic density and first‐order in terms of an artificial variable which represents the effects of the flow being sheared. It is shown that this form of the problem allows a natural extension of the existing numerical solution techniques for non‐sheared flow. The sheared flow problem is presented, and a finite element method is developed to yield a solution for propeller‐type acoustic forces. The finite element code and method are refined with numerical experiments, and results are presented for a specific propeller and duct geometry. Good agreement is shown between this method and an alternate approach to the sheared flow problem using a piecewise constant representation of the velocity in the boundary layer. This validates both the numerical methods.
Flux difference splitting for open‐channel flows
Authors: Glaister P. 
Published: August 2005

AbstractA finite difference scheme based on flux difference splitting is presented for the solution of the one‐dimensional shallow‐water equations in open channels, together with an extension to two‐dimensional flows. A linearized problem, analogous to that of Riemann for gas dynamics, is defined and a scheme, based on numerical characteristic decomposition, is presented for obtaining approximate solutions to the linearized problem. The method of upwind differencing is used for the resulting scalar problems, together with a flux limiter for obtaining a second‐order scheme which avoids non‐physical, spurious oscillations. The scheme is applied to a one‐dimensional dam‐break problem, and to a problem of flow in a river whose geometry induces a region of supercritical flow. The scheme is also applied to a two‐dimensional dam‐break problem. The numerical results are compared with the exact solution, or other numerical results, where available.
The analysis of unsteady incompressible flows by a three‐step finite element method
Authors: Jiang Chun Bo , Kawahara Mutsuto 
Published: August 2005

AbstractThis paper describes a three‐step finite element method and its applications to unsteady incompressible fluid flows. Stability analysis of the one‐dimensional pure convection equation shows that this method has third‐order accuracy and an extended numerical stability domain in comparison with the Lax‐‐Wendroff finite element method. The method is cost‐effective for incompressible flows because it permits less frequent updates of the pressure field with good accuracy. In contrast with the Taylor‐Galerkin method, the present method does not contain any new higher‐order derivatives, which makes it suitable for solving non‐linear multidimensional problems and flows with complicated boundary conditions. The three‐step finite element method has been used to simulate unsteady incompressible flows. The numerical results obtained are in good agreement with those in the literature.
A second‐order upwind finite‐volume method for the Euler solution on unstructured triangular meshes
Authors: Pan Dartzi , Cheng Jen‐Chieh 
Published: August 2005

AbstractA scheme for the numerical solution of the two‐dimensional (2D) Euler equations on unstructured triangular meshes has been developed. The basic first‐order scheme is a cell‐centred upwind finite‐volume scheme utilizing Roe's approximate Riemann solver. To obtain second‐order accuracy, a new gradient based on the weighted average of Barth and Jespersen's three‐point support gradient model is used to reconstruct the cell interface values. Characteristic variables in the direction of local pressure gradient are used in the limiter to minimize the numerical oscillation around solution discontinuities. An Approximate LU (ALU) factorization scheme originally developed for structured grid methods is adopted for implicit time integration and shows good convergence characterisitics in the test. To eliminate the data dependency which prohibits vectorization in the inversion process, a black‐gray‐white colouring and numbering technique on unstructured triangular meshes is developed for the ALU factorization scheme. This results in a high degree of vectorization of the final code. Numerical experiments on transonic Ringleb flow, transonic channel flow with circular bump, supersonic shock reflection flow and subsonic flow over multielement aerofoils are calculated to validate the methodology.
Linear and non‐linear iterative methods for the incompressible Navier‐Stokes equations
Authors: Clift Simon S. , Forsyth Peter A. 
Published: August 2005

AbstractIn this study, the discretized finite volume form of the two‐dimensional, incompressible Navier‐Stokes equations is solved using both a frozen coefficient and a full Newton non‐linear iteration. The optimal method is a combination of these two techniques. The linearized equations are solved using a conjugate‐gradient‐like method (CGSTAB). Various types of preconditioning are developed. Completely general sparse matrix methods are used. Investigations are carried out to determine the effect of finite volume cell anisotropy on the preconditioner. Numerical results are given for several test problems.
A conservative and shape‐preserving semi‐Lagrangian method for the solution of the shallow water equations
Authors: Garcia‐Navarro P. , Priestley A. 
Published: August 2005

AbstractSemi‐Lagrangian methods are now perhaps the most widely researched algorithms in connection with atmospheric flow simulation codes. In order to investigate their applicability to hydraulic problems, cubic Hermite polynomials are used as the interpolant technique. The main advantage of such an approach is the use of information from only two points. The derivatives are calculated and limited so as to produce a shape‐preserving solution. The lack of conservation of semi‐Lagrangian methods, however, is widely regarded as a serious disadvantage for hydraulic studies, where non‐linear problems in which shocks may develop are often encountered. In this work we describe how to make the scheme conservative using an FCT approach. The method proposed does not guarantee an unconditional shock‐capturing ability but is able to correctly reproduce the discontinuous flows common in open channel simulation without any shock‐fitting algorithm. It is a cheap way to improve existing 1D semi‐Lagrangian codes and allows stable calculations beyond the usual CFL limits. A basic semi‐Lagrangian method is presented that provides excellent results for a linear problem: the new techniques allow us to tackle non‐linear cases without unduly degrading the accuracy for the simpler problems. Two one‐dimensional hydraulic problems are used as test cases, water hammer and dam break. In the latter case, because of the non‐linearity, special care is needed with the low‐order solution and we show the advantages of using Leveque's large‐time step version of Roe's scheme for this purpose.
Numerical simulation of free shear flows and far‐field sound pressure directivity
Authors: Soh W. Y. 
Published: August 2005

AbstractAn implicit spatial differencing technique with fourth‐order accuracy has been developed based on the Pade compact scheme. A dispersion‐relation‐preserving concept has been incorporated into the numerical scheme. Two‐dimensional Euler computation of a spatially developing free shear flow with and without external excitation has been performed to demonstrate the capability of the numerical scheme developed. Results are in good agreement with theory and experimental observation regarding the growth rate of the fluctuating velocity, the convective velocity and the vortex‐pairing process. The far‐field sound pressure generated by the computed shear flow solution using Lighthill's acoustic analogy shows a strong directivity with a zone of silence at the flow angle.
A comparison of second‐order and fourth‐order pressure gradient algorithms in a σ‐co‐ordinate ocean model
Authors: McCalpin John D. 
Published: August 2005

AbstractIn stratified three‐dimensional models the use of a boundary‐fitted vertical co‐ordinate is known to produce errors in the horizontal pressure gradient calculation near steep topography. The error is due to the splitting of the horizontal pressure gradient term in each of the momentum equations into two parts and the subsequent incomplete cancellation of the truncation errors of those parts. In order to minimize these pressure gradient errors, a fourth‐order‐accurate pressure gradient calculation has been implemented and installed in SPEM, a three‐dimensional primitive equation ocean model. The stability and accuracy of the new scheme are compared with those of the original second‐order‐accurate model in a series of calculations of unforced flow in the vicinity of an isolated seamount. The new scheme is shown to have much smaller pressure gradient errors over a wide range of parameter space as well as a greater parametric domain of numerical stability.
Solution of the axisymmetric inverse problem by higher‐order line doublets
Authors: Zedan M. F. 
Published: August 2005

AbstractThe axial singularity inverse method for designing bodies of revolution has been improved by using higher‐order doublet elements. The performance of the method for various element orders and other solution parameters is presented in detail. The results indicate that the method is generally more robust, less sensitive to insets and has a better‐conditioned coefficient matrix compared with the source method of the same order. The condition number of the matrix is shown to increase with the thickness of the body, the order of the method, the number of elements and the degree of stretching of the node distribution. In general, good performance is attained for most bodies even with ƒr as low as 2 by using 10–12 second‐order doublet elements with insets greater than 0.02L from rounded ends. Increasing the insets to 0.06L appears to improve the accuracy of the method for most bodies but slows its convergence.