Modeling Splashing and Sloshing with SPH in LS-DYNA

Introduction

• Presenter: Erik Fanny, Dynamo Nordic
• Topic: Modeling splashing and sloshing using the Smooth Particle Hydrodynamics (SPH) module in LS-DYNA
• Purpose: Demonstrate SPH capabilities

Overview of the Webinar

1. Introduction and motivation
2. SPH theory essentials
3. Keywords and simulation setup
4. Examples
5. Summary

Theory of SPH

When is SPH Useful?

• Large material distortion
• Material decomposes into small fragments/droplets
• Fluid problems with moving boundaries and free surfaces

Characteristics of SPH

• Particle-based method
• Solved with explicit time integration
• Limitations:
  • Local mesh refinement issues
  • Some boundary conditions can be difficult

Historical Context

• Development in the late 1970s
• Theoretical improvements in the 1980s
• Applied in various fields: forging, extrusion, metal cutting, impact problems, fluid-structure interactions

Basic Principles

• Continuum approximated by distributed particles
• No convective term (independent material coordinates)
• Approximation involves kernel function W
• Particle approximation similar to quadrature formula
• Sparse scheme and gradient expression derived
• Neighbor search via bucket sort
• Conservation equations: mass, momentum, and energy

Important Keywords for SPH Simulations

Control Keywords

• Control MPP decomposition distributed SPH elements: Evenly distributes SPH elements to processors
• Control MPP i/o nodump: Suppresses dump files output

SPH Settings Keywords

• Control SPH:
  • NCBS: Number of time steps between particle sorting (default: 1)
  • Box ID: Deactivate particles leaving the box
  • IDIM: Space dimension (default: 3D, also for plane strain or axisymmetric problems)
  • Form: Particle approximation theory (15/16 recommended for fluids)
  • MarksV: Deactivate particles with velocity greater than max V
  • ITHK: Contact thickness (0 for zero thickness, 1 computed from volume)
• Section SPH: Default settings usually suffice, constants for smoothing lengths
• Element SPH: Mass settings (positive for element mass, negative value for volume of particle)

Material Properties

• MATERIAL (MATT NULL): Defines fluid material properties
  • RO: Mass density
  • PC: Pressure cutoff (negative in tension)
  • MU: Dynamic viscosity
  • EROD/EROS: Relative volume for erosion
• Equation of State: Pressure-density relations (e.g., US Murnaghan for incompressible flow)
  • Parameters for US Murnaghan: Gamma (often 7), KC0 (based on max fluid velocity), V0 (initial relative volume)
  • Option to reduce particle stiffness
  • Alternative: US (e.g., Green-Isochronous)

Contact Settings

• Contact automatic nodes to surface: SPH particles as slave parts

SPH Element Generation

Using LS-PrePost

• Generate SPH parts (e.g., box, sphere)
• Shell volume method: Requires watertight surface mesh
• Set density to -1 for volume computation
• Distance between particles setting

Examples

Example 1: Wheel Rolling Through Water

• Scenario: Wheel through 10mm water at 70 km/h
• Model: Explicit finite element, rigid components, 2.4M SPH particles
• Results: Splashing visualization

Example 2: Car Driving Through Water

• Scenario: Toyota Auris through 20mm water at 56 km/h
• Model: Explicit finite element, 1.5M elements
• Results: Water distribution and load analysis
• Simulation Time: ~16 hours on 32 cores

Example 3: Gearbox with Oil

• Scenario: Two gears partially filled with oil
• Model: Rigid gears, 300,000 SPH particles, prescribed motion
• Results: Oil distribution and splashing

Example 4: Fluid-Structure Interaction

• Scenario: Water wave impacting rigid column
• Model: Developed by LS-DYNA Technical Support Center
• Comparison: Simulation vs. experimental data

Summary

• SPH effectively models splashing and sloshing
• Easily coupled with finite element models
• Further learning: SPH course by Dynamo in Germany
• Contact: Erik Fanny (erik.fanny@dynamo.se)

Closing Remarks

• Thank you for attending
• Q&A and further contact details