Pressue BC in SPH method
Samin Haeri
l...@schwer.net
I would try a “rigid” plate, comprised of shells/solids that is in contact with the SPH particles, and apply the force=area*pressure to that plate.
The contact works best if the “rigid” body has the same elastic properties as the SPH particles. --len
--
You received this message because you are subscribed to the Google Groups "LS-DYNA2" group.
To unsubscribe from this group and stop receiving emails from it, send an email to ls-dyna2+u...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/ls-dyna2/b890864a-ba9a-41f3-a731-40961e7dd71fn%40googlegroups.com.
James Kennedy
Dear Samin,
See if the following are of some help:
The purpose of this research was to investigate the prospect of continuous flow modelling in LSDYNA using SPH-FEM coupling. The both methods (SPH and FEM) are based on the continuum mechanics, however, SPH implementation uses Lagrangian material framework, while FEM uses an Eulerian formulation for the fluid analysis, and Lagrangian formulation for the solid analysis. The Lagrangian framework of the SPH means that we need to generate particles at one end, and to destroy them on the other, in order to generate a continuous fluid flow. The simplest way to do this is by using activation and deactivation planes, which is a solution implemented in the commercial LS- DYNA solver. Modelling of continuous fluid flow is practical in mechanical (naval) engineering for hydrofoil analysis and in bioengineering for blood vessel simulations. Results show that velocity fields obtained by SPH-FEM coupling are similar to velocity fields obtained by FEM. FEM only solution has a clear advantage in regards to execution time, however, SPH-FEM coupling offers greater insight into fluid structure interaction, that justifies the extra computational cost.
Topalovic, M., Nikolic, A., Vulovic, S., and Milovannovic, V., “FSI Analysis with Continuous Fluid Flow Using FEM and SPH Methods in LS-DYNA”, Journal of the Serbian Society for Computation al Mechanics. Vol. 15, No, 2, pp 93-100, 2021.
3. SPH fluid flow in LS-DYNA
Commercial LS- DYNA solver package (Hallquist 2006) is primarily used for crash simulations and dynamic analysis, while continuous fluid flow in SPH is not the main focus of research and development. For Incompressible Computational Fluid Dynamics (ICFD) LS- DYNA has a specific ICFD solver used for aerodynamics, hemodynamics, free-surface problems, ship hydrodynamics, etc. This solver uses an Eulerian formulation where incompressibility constraint may be applied. However, in this paper, we will focus on SPH solver of the LS- DYNA package and its potential for continuous fluid flow analysis. There are no examples, or published papers using this feature, however, in the manual (Hallquist 2006) there is a description of keywords BOUNDARY_SPH_FLOW and CONTROL_SPH (BOXID) that are used for activation and deactivation of SPH particles (Hallquist 2006), which can be used to create the continuous fluid flow. In this paper, we will test this feature on two sets of examples: one is hydrofoil, a structure similar to an airplane wing, which generates lift and raises the vessel hull over water, thus reducing the drag, and the other test case is simulation of blood flow in bioengineering. In all examples coupling between SPH and FEM methods is used, in the first case hydrofoil is modelled with shell FEM elements, and in the second case shell elements are used to model blood vessels. Schematics of these models are shown in Fig. 1
http://www.sscm.kg.ac.rs/jsscm/downloads/Vol15No2/Vol15No2_09.pdf
The capabilities of the Smooth Particle Hydrodynamic (SPH) method to accurately capture the main features of a hydraulic jump has been investigated. Two conceptually different modeling approaches were tested, the Tank and Inflow approach. The Tank approach incorporated the
modeling of a large reservoir tank which in the other case was replaced with an inlet condition. Successful outcomes were achieved for the Tank case but not for the more efficient and less computationally costly Inflow case due to poorly implemented boundary conditions in the software:
Jonsson, P., "Smoothed Particle Hydrodynamic Modeling of Hydraulic Jumps", Master's Thesis, Department of Applied Physics and Mechanical Engineering, Lulea University of Technology, Lulea, Sweden, April, 2011.
3.1.1 Inlet Boundary Condition
The inlet boundary condition is implemented and is applied by using the BOUNDARY_SPH_FLOW k-word. Initially, the user defines all particles representing the inflow and has the ability to choose whether the particles move according to a prescribed velocity, displacement or acceleration (LSTC, 2010). At time , all particles are deactivated in a similar fashion as particles outside the computational box but move according to the prescribed motion defined. The boundary of activation where 21 the SPH-particles are activated and the particle approximation is computed is defined by a predefined node and a vector. The ability of the BOUNDARY_SPH_FLOW k-word is promising but it is unfortunately not working properly as two distinct problems arose during the simulations. Firstly, deactivated particles were affected by gravity outside the boundary of activation and the computational box which resulted in unwanted vertical motion. Secondly, random particles outside the boundary of activation which were supposed to move according to the prescribed motion remained stationary in initial positions which resulted in a discontinuous inflow of particles. The first problem where resolved by the support office at the Nordic official distributor of LS-DYNA, Engineering Research AB (ERAB). The update was implemented in the development version of LSDYNA which the author was able to try but the second problem still remained.
http://pure.ltu.se/portal/files/32732164/LTU-EX-2011-32691127.pdf
This study focus on Smoothed Particle Hydrodynamics (SPH) modeling of two dimensional hydraulic jumps in horizontal open channel flows. Insights to the complex dynamics of hydraulic jumps in a generalized test case serves as a knowledgebase for real world applications such as spillway channel flows in hydropower systems. In spillways, the strong energy dissipative mechanism associated with hydraulic jumps is a utilized feature to reduce negative effects of erosion to spillway channel banks and in the old river bed
2.3 Numerical setup
The geometrical setup of the problem can be seen in Figure 2 where the fluid enters the domain using the BOUNDARY_SPH_FLOW inlet condition with an prescribed inlet velocity of and depth The horizontal plane situated between the inlet and the weir measures and is prefilled to a depth equal to weir height. Both the prefill of the horizontal plane and the weir assembly was introduced to trigger the hydraulic jump faster. Furthermore, at downstream of the inlet the outlet is situated.
Sincerely,
James M. Kennedy
KBS2 Inc.
August 30, 2024
From: ls-d...@googlegroups.com [mailto:ls-d...@googlegroups.com]
On Behalf Of Samin Haeri
Sent: Friday, August 30, 2024 9:36 AM
To: LS-DYNA2 <ls-d...@googlegroups.com>
Subject: [LS-DYNA2] Pressue BC in SPH method
Hello everyone,
How can I apply pressure boundary condition at the inlet or outlet of a fluid modeling by SPH method?
Thanks a lot
--