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Finite pointset method

The finite pointset method (FPM) in continuum mechanics numerically solves problems like fluid flow simulations by representing the medium with discrete points holding local properties such as density, velocity, and pressure. Points may move with the medium (Lagrangian approach) or remain fixed as the medium flows through them (Eulerian approach), with hybrid methods also used. Known as a particle method in computer graphics, FPM is a meshfree method that easily adapts to complex and evolving geometries like the blowing of a glass bottle. It effectively handles nonlinear problems involving viscous fluids, heat, mass transfer, and elastic or plastic deformations.

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Description

In the simplest implementations, the finite point set is stored as an unstructured list of points in the medium. In the Lagrangian approach the points move with the medium, and points may be added or deleted in order to maintain a prescribed sampling density. The point density is usually prescribed by a smoothing length defined locally. In the Eulerian approach the points are fixed in space, but new points may be added where there is need for increased accuracy. So, in both approaches the nearest neighbors of a point are not fixed, and are determined again at each time step.

Advantages

This method has various advantages over grid-based techniques; for example, it can handle fluid domains, which change naturally, whereas grid based techniques require additional computational effort. The finite points have to completely cover the whole flow domain, i.e. the point cloud has to fulfill certain quality criteria (finite points are not allowed to form “holes” which means finite points have to find sufficiently numerous neighbours; also, finite points are not allowed to cluster; etc.).

The finite point cloud is a geometrical basis, which allows for a numerical formulation making FPM a general finite difference idea applied to continuum mechanics. That especially means, if the point reduced to a regular cubic point grid, then FPM would reduce to a classical finite difference method. The idea of general finite differences also means that FPM is not based on a weak formulation like Galerkin's approach. Rather, FPM is a strong formulation which models differential equations by direct approximation of the occurring differential operators. The method used is a moving least squares idea which was especially developed for FPM.

History

In order to overcome the disadvantages of the classical methods many approaches have been developed to simulate such flows.234567 A classical grid free Lagrangian method is Smoothed Particle Hydrodynamics (SPH), which was originally introduced to solve problems in astrophysics.89

It has since been extended to simulate the compressible Euler equations in fluid dynamics and applied to a wide range of problems.101112 The method has also been extended to simulate inviscid incompressible free surface flows.13. The implementation of the boundary conditions is the main problem of the SPH method.

Another approach for solving fluid dynamic equations in a grid free framework is the moving least squares or least squares method.141516171819 With this approach boundary conditions can be implemented in a natural way just by placing the finite points on boundaries and prescribing boundary conditions on them.20 The robustness of this method is shown by the simulation results in the field of airbag deployment in car industry. Here, the membrane (or boundary) of the airbag changes very rapidly in time and takes a quite complicated shape (Kuhnert et al. 2000).

Tiwari et al. (2003) performed simulations of incompressible flows as the limit of the compressible Navier–Stokes equations with some stiff equation of state.21 This approach was first used in Monaghan (1992) to simulate incompressible free surface flows by SPH. The incompressible limit is obtained by choosing a very large speed of sound in the equation of state such that the Mach number becomes small. However, the large value of the speed of sound restricts the time step to be very small due to the CFL-condition.22

The projection method of Chorin is a widely used approach to solve problems governed by the incompressible Navier–Stokes equation in a grid based structure.23 In Tiwari et al. (2001), this method has been applied to a grid free framework with the help of the weighted least squares method. The scheme gives accurate results for the incompressible Navier–Stokes equations. The occurring Poisson equation for the pressure field is solved by a grid free method. It has been shown that the Poisson equation can be solved accurately by this approach for any boundary conditions. The Poisson solver can be adapted to the weighted least squares approximation procedure with the condition that the Poisson equation and the boundary condition must be satisfied on each finite point. This is a local iteration procedure.24

Software

References

  1. T., Belytschko; Y., Krongauz; M., Flemming; D., Organ; S., Liu W. K. (1996), "Smoothing and accelerated computations in the element-free Galerkin method", Journal of Computational and Applied Mathematics, 74 (1–2): 111–126, doi:10.1016/0377-0427(96)00020-9 /wiki/Journal_of_Computational_and_Applied_Mathematics ↩

  2. P., Hansbo (1992), "The characteristic streamline diffusion method for the time-dependent incompressible Navier-Stokes equations", Computer Methods in Applied Mechanics and Engineering, 99 (2–3): 171–186, Bibcode:1992CMAME..99..171H, doi:10.1016/0045-7825(92)90039-M /wiki/Bibcode_(identifier) ↩

  3. Harlow, Francis H.; E., Welch J. (1965), "Numerical study of large amplitude free surface motions", Physics of Fluids, 8 (5): 842–851, doi:10.1063/1.1761784 /wiki/Francis_H._Harlow ↩

  4. J., Kelecy F.; H., Pletcher R. (1997), "The development of free surface capturing approach for multi dimensional free surface flows in closed containers", Journal of Computational Physics, 138 (2): 939–980, Bibcode:1997JCoPh.138..939K, doi:10.1006/jcph.1997.5847 /wiki/Journal_of_Computational_Physics ↩

  5. B., Kothe D.; C., Mjolsness R. (1992), "RIPPLE: A new model for incompressible flows with free surfaces", AIAA Journal, 30 (11): 2694–2700, Bibcode:1992AIAAJ..30.2694K, doi:10.2514/3.11286 https://digital.library.unt.edu/ark:/67531/metadc1068468/ ↩

  6. V., Maronnier; M., Picasso; J., Rappaz (1999), "Numerical simulation of free surface flows", Journal of Computational Physics, 155 (2): 439–455, Bibcode:1999JCoPh.155..439M, doi:10.1006/jcph.1999.6346 /wiki/Journal_of_Computational_Physics ↩

  7. S., Tiwari; S., Manservisi (2000), Modeling incompressible Navier-Stokes flows by LSQ-SPH, Berichte des Fraunhofer ITWM, Kaiserslautern, Germany ↩

  8. B., Lucy L. (1977), "A numerical approach to the testing of the fission hypothesis", Astronomical Journal, 82: 1013–1024, Bibcode:1977AJ.....82.1013L, doi:10.1086/112164 /wiki/Bibcode_(identifier) ↩

  9. A., Gingold R.; J., Monaghan J. (1977), "Smoothed particle hydrodynamics: theory and application to non-spherical stars", Monthly Notices of the Royal Astronomical Society, 181 (3): 375–389, doi:10.1093/mnras/181.3.375 /wiki/Monthly_Notices_of_the_Royal_Astronomical_Society ↩

  10. J., Monaghan J. (1992), "Smoothed particle hydrodynamics", Annual Review of Astronomy and Astrophysics, 30: 543–574, Bibcode:1992ARA&A..30..543M, doi:10.1146/annurev.aa.30.090192.002551 /wiki/Annual_Review_of_Astronomy_and_Astrophysics ↩

  11. J., Monaghan J.; A., Gingold R. (1983), "Shock Simulation by particle method SPH", Journal of Computational Physics, 52 (2): 374–389, Bibcode:1983JCoPh..52..374M, doi:10.1016/0021-9991(83)90036-0 /wiki/Journal_of_Computational_Physics ↩

  12. P., Morris J.; J., Fox P.; Y., Zhu (1997), "Modeling Low Reynolds Number Incompressible Flows Using SPH", Journal of Computational Physics, 136 (1): 214–226, Bibcode:1997JCoPh.136..214M, doi:10.1006/jcph.1997.5776 /wiki/Journal_of_Computational_Physics ↩

  13. J., Monaghan J. (1994), "Simulating free surface flows with SPH", Journal of Computational Physics, 110 (2): 399–406, Bibcode:1994JCoPh.110..399M, doi:10.1006/jcph.1994.1034 /wiki/Journal_of_Computational_Physics ↩

  14. T., Belytschko; Y., Krongauz; M., Flemming; D., Organ; S., Liu W. K. (1996), "Smoothing and accelerated computations in the element-free Galerkin method", Journal of Computational and Applied Mathematics, 74 (1–2): 111–126, doi:10.1016/0377-0427(96)00020-9 /wiki/Journal_of_Computational_and_Applied_Mathematics ↩

  15. A., Dilts G. (1996), Moving least squares particle hydrodynamics. I: consistency and stability, Hydrodynamics methods group report, Los Alamos National Laboratory, doi:10.1002/(SICI)1097-0207(19990320)44:8<1115::AID-NME547>3.0.CO;2-L /wiki/Doi_(identifier) ↩

  16. J., Kuhnert (1999), General smoothed particle hydrodynamics, Ph.D. thesis, Kaiserslautern University, Germany ↩

  17. J., Kuhnert (2000), An upwind finite pointset method for compressible Euler and Navier-Stokes equations, preprint, ITWM, Kaiserslautern, Germany ↩

  18. S., Tiwari S.; J., Kuhnert J. (2001), Grid free method for solving Poisson equation, Berichte des Fraunhofer ITWM, Kaiserslautern, Germany, ISSN 1434-9973 https://d-nb.info/1027386806/34 ↩

  19. S., Tiwari; S., Manservisi (2000), Modeling incompressible Navier-Stokes flows by LSQ-SPH, Berichte des Fraunhofer ITWM, Kaiserslautern, Germany ↩

  20. J., Kuhnert (1999), General smoothed particle hydrodynamics, Ph.D. thesis, Kaiserslautern University, Germany ↩

  21. S., Tiwari; J., Kuhnert (2003), "Particle method for simulations of free surface flows", in Hou, Thomas Y.; Tadmor, Eitan (eds.), Hyperbolic Problems: Theory, Numerics, Applications: Proceedings of the Ninth International Conference on Hyperbolic Problems held in CalTech, Pasadena, March 25–29, 2002, doi:10.1007/978-3-642-55711-8, ISBN 978-3-642-55711-8 978-3-642-55711-8 ↩

  22. J., Monaghan J. (1992), "Smoothed particle hydrodynamics", Annual Review of Astronomy and Astrophysics, 30: 543–574, Bibcode:1992ARA&A..30..543M, doi:10.1146/annurev.aa.30.090192.002551 /wiki/Annual_Review_of_Astronomy_and_Astrophysics ↩

  23. A., Chorin A. (1968), "Numerical solution of the Navier-Stokes equations", Journal of Mathematics of Computation, 22 (104): 745–762, doi:10.2307/2004575, JSTOR 2004575 /wiki/Doi_(identifier) ↩

  24. S., Tiwari S.; J., Kuhnert J. (2001), Grid free method for solving Poisson equation, Berichte des Fraunhofer ITWM, Kaiserslautern, Germany, ISSN 1434-9973 https://d-nb.info/1027386806/34 ↩