A three‐dimensional explicit element‐free galerkin methodBelytschko, T; Krysl, P; Krongauz, Y
doi: 10.1002/(SICI)1097-0363(199706)24:12<1253::AID-FLD558>3.0.CO;2-Zpmid: N/A
The formulation and implementation of a three‐dimensional meshless method, the element‐free Galerkin (EFG) method, are described. The formulation is intended for dynamic problems with geometric and material non‐linearities solved with explicit time integration, but some of the developments are applicable to other solution methods. The mechanical formulation is posed in the reference configuration so that the shape functions and their derivatives need to be computed only once. A method for speeding up the calculation of shape functions and their derivatives is presented. Results are presented for sloshing problems and Taylor bar impact problems, including an impact problem in which the bar impacts with an angle of obliquity. © 1997 John Wiley & Sons, Ltd.
Finite element simulation of vacuum arc remeltingGartling, D. K.; Sackinger, P. A.
doi: 10.1002/(SICI)1097-0363(199706)24:12<1271::AID-FLD559>3.0.CO;2-#pmid: N/A
Vacuum arc remelting is a process for producing homogeneous ingots of reactive and macrosegregation‐sensitive alloys. A mathematical model of the transport phenomena in the ingot melt is presented together with a discussion of the various simplifying assumptions and approximations that make the problem tractable, with particular attention on transport in the interdendritic mushy zone and on the magnetohydrodynamics. The finite element method is used to discretize the equations for the non‐isothermal flow problem and the quasi‐static electromagnetic problem. Coupling of the finite element solutions for the two field problems is accomplished using the Parallel Virtual Machine software. An analysis of the fluid flow and heat transport in the melt pool of the solidifying ingot shows some of the factors that influence ingot quality during quasi‐steady growth conditions. © 1997 John Wiley & Sons, Ltd.
Finite element analysis of air flow around permeable sand fencesHatanaka, Katsumori; Hotta, Shintaro
doi: 10.1002/(SICI)1097-0363(199706)24:12<1291::AID-FLD560>3.0.CO;2-Npmid: N/A
A numerical study of the turbulent air flow in a trench trap and the turbulent flow around a permeable sand fence is reported in this paper. The two‐dimensional modified k–ε turbulence model proposed by Kato and Launder is used to predict the turbulent characteristics of the air flow. The discretization method for the governing equations is the three‐step Taylor/Galerkin finite element method proposed by the authors. For the flow in a trench trap the numerical results are compared with experimental data obtained under realistic conditions using a large wind tunnel. For the air flow around a permeable sand fence a pressure loss model is used to represent the effect of the porosity of the fence on the flow field. © 1997 John Wiley & Sons, Ltd.
Predicting the wind noise from the pantograph cover of a trainHolmes, Bayard S.; Dias, João B.; Jaroux, Belgacem A.; Sassa, Takamitsu; Ban, Yasuhiro
doi: 10.1002/(SICI)1097-0363(199706)24:12<1307::AID-FLD561>3.0.CO;2-8pmid: N/A
Finite element and boundary element calculations are combined to predict the flow noise radiated from a 1/10th‐scale model of an aerodynamic cover used around the pantograph on a train at 250 km h−1. The solutions of the unsteady air flow over the cover and the resulting sound propagation are divided into two parts in order to keep the problem tractable. First the unsteady fluid flow is solved using large‐eddy simulation (LES). The pressure histories on the cover are then used to predict the radiated sound, using a boundary element method to solve the Helmholtz equation. The result thus leans heavily on assumptions about the coupling of the two solutions, the propagation of sound in a disturbed medium and the efficacy of LES. The predicted sound pressure levels are compared with experimental measurements made in an anechoic wind tunnel. © 1997 John Wiley & Sons, Ltd.
Parallel overlapping scheme for viscous incompressible flowsKaiho, M.; Ikegawa, M.; Kato, C.
doi: 10.1002/(SICI)1097-0363(199706)24:12<1341::AID-FLD563>3.0.CO;2-Gpmid: N/A
A 3D parallel overlapping scheme for viscous incompressible flow problems is presented that combines the finite element method, which is best suited for analysing flow in any arbitrarily shaped flow geometry, with the finite difference method, which is advantageous in terms of both computing time and computer storage. A modified ABMAC method is used as the solution algorithm, to which a sophisticated time integration scheme proposed by the present authors has been applied. Parallelization is based on the domain decomposition method. The RGB (recursive graph bisection) algorithm is used for the decomposition of the FEM mesh and simple slice decomposition is used for the FDM mesh. Some estimates of the parallel performance of FEM, FDM and overlapping computations are presented. © 1997 John Wiley & Sons, Ltd.
Parallel finite element simulation of large ram‐air parachutesKalro, V.; Aliabadi, S.; Garrard, W.; Tezduyar, T.; Mittal, S.; Stein, K.
doi: 10.1002/(SICI)1097-0363(199706)24:12<1353::AID-FLD564>3.0.CO;2-6pmid: N/A
In the near future, large ram‐air parachutes are expected to provide the capability of delivering 21 ton payloads from altitudes as high as 25,000 ft. In development and test and evaluation of these parachutes the size of the parachute needed and the deployment stages involved make high‐performance computing (HPC) simulations a desirable alternative to costly airdrop tests. Although computational simulations based on realistic, 3D, time‐dependent models will continue to be a major computational challenge, advanced finite element simulation techniques recently developed for this purpose and the execution of these techniques on HPC platforms are significant steps in the direction to meet this challenge. In this paper, two approaches for analysis of the inflation and gliding of ram‐air parachutes are presented. In one of the approaches the point mass flight mechanics equations are solved with the time‐varying drag and lift areas obtained from empirical data. This approach is limited to parachutes with similar configurations to those for which data are available. The other approach is 3D finite element computations based on the Navier–Stokes equations governing the airflow around the parachute canopy and Newton’s law of motion governing the 3D dynamics of the canopy, with the forces acting on the canopy calculated from the simulated flow field. At the earlier stages of canopy inflation the parachute is modelled as an expanding box, whereas at the later stages, as it expands, the box transforms to a parafoil and glides. These finite element computations are carried out on the massively parallel supercomputers CRAY T3D and Thinking Machines CM‐5, typically with millions of coupled, non‐linear finite element equations solved simultaneously at every time step or pseudo‐time step of the simulation. © 1997 John Wiley & Sons, Ltd.
Parallel finite element computation of missile aerodynamicsSturek, W. B.; Ray, S.; Aliabadi, S.; Waters, C.; Tezduyar, T. E.
doi: 10.1002/(SICI)1097-0363(199706)24:12<1417::AID-FLD567>3.0.CO;2-Npmid: N/A
A flow simulation tool, developed by the authors at the Army HPC Research Center, for compressible flows governed by the Navier–Stokes equations is used to study missile aerodynamics at supersonic speeds, high angles of attack and for large Reynolds numbers. The goal of this study is the evaluation of this Navier–Stokes computational technique for the prediction of separated flow fields around high‐length‐to‐diameter (L/D) bodies. In particular, this paper addresses two issues: (i) turbulence modelling with a finite element computational technique and (ii) efficient performance of the computational technique on two different multiprocessor mainframes, the Thinking Machines CM‐5 and CRAY T3D. The paper first provides a discussion of the Navier–Stokes computational technique and the algorithm issues for achieving efficient performance on the CM‐5 and T3D. Next, comparisons are shown between the computation and experiment for supersonic ramp flow to evaluate the suitability of the turbulence model. Following that, results of the computations for missile flow fields are shown for laminar and turbulent viscous effects. © 1997 John Wiley & Sons, Ltd.