Mastering Quasi-Static Analysis with LS-Dyna: A Comprehensive Guide

Quasi-static analysis has become an essential tool in modern engineering simulation. By modeling how loads are applied gradually, it minimizes inertial effects and replicates conditions close to static equilibrium. This allows engineers to study slow-evolving physical phenomena with precision and confidence.

While implicit solvers are often the go-to method, explicit methods offer unique advantages, particularly in handling highly nonlinear or complex simulations. In this guide, we’ll explore how Ansys LS-Dyna, a multiphysics solver renowned for its versatility, empowers engineers to master quasi-static analysis.

What is LS-Dyna?

Originally developed for explicit dynamic analysis, LS-Dyna has grown into a robust multiphysics simulation package. Today, it enables engineers to integrate structural, fluid, thermal, and electromagnetic domains into a single workflow.

Key features of LS-Dyna include:

• Dual Solver Capabilities: supports both explicit and implicit methods for dynamic and static simulations.
• Multiphysics Integration: includes CFD solvers, thermal analysis, electromagnetics, NVH/acoustics, particle methods, and even isogeometric modeling.
• Crash-Test Validation: prevalidated barrier and occupant models built to industry standards.
• Auxiliary Tools: LS-PrePost for post-processing, LS-Opt for optimization, and LS-TSC for topology optimization.

This seamless coupling makes LS-Dyna indispensable in industries such as automotive, aerospace, civil engineering, and biomechanics.

Explicit vs Implicit Methods

The choice of time integration scheme is central to any simulation:

• Implicit Methods
  • Solve equations iteratively (for example, using Newton-Raphson).
  • Unconditionally stable, allowing larger time steps.
  • Ideal for long-duration, less nonlinear problems.
• Explicit Methods
  • Solve equations step-by-step, directly.
  • Conditionally stable, with time steps limited by mesh size and wave speed.
  • Perfect for highly nonlinear problems, for example buckling, cracking, or sudden stress changes.

Quasi-Static Analysis: The Essentials

Quasi-static analysis bridges the gap between static and dynamic simulation. It models slow load applications where acceleration and velocity remain minimal, ensuring inertial effects are negligible.

To achieve accurate quasi-static results using explicit methods, engineers must carefully manage inertial suppression:

• Slow Load Application: Ramp up loads gradually to reduce dynamic energy.
• Prescribed Motions: Provide better kinetic energy control than force-based methods.
• Energy Balancing: Monitor energy ratios; internal energy should dominate kinetic energy.
• Mass Scaling: Artificially increase mass to permit larger time steps.

Preloading Techniques: Building Realism

Real-world systems often carry initial stresses before main loads are applied. LS-Dyna supports various preloading strategies:

• Direct Preloading: Apply loads during the explicit phase (risk of stress waves if abrupt).
• Dynamic Relaxation: A refined approach where preloads are applied smoothly until equilibrium.
  • Explicit Relaxation: uses damping to suppress transients.
  • Implicit Relaxation: applies loads with implicit solvers for stability.

Dynamic relaxation is particularly useful for minimizing noise and creating a clean transition into the main analysis.

Restart Analysis: Modular Workflows

One of LS-Dyna’s standout features is its restart analysis capability, enabling simulations to be paused, modified, and resumed without starting from scratch.

Types of restart include:

• Simple Restart: extends simulation time.
• Small Restart: modifies boundary conditions, contacts, or deletes entities.
• Full Restart: introduces entirely new models or parts.

Establishing Quasi-Static Conditions

Verification is crucial. Engineers should confirm quasi-static conditions by monitoring:

• Loading and Reaction Forces: alignment indicates equilibrium.
• Energy Monitoring: internal energy should far exceed kinetic energy.
• Debugging Runs: shorter trial simulations help optimize time steps and setups.

Applications and Benefits

Quasi-static analysis with LS-Dyna offers engineers:

• Versatility: Handles buckling, cracking, and nonlinear challenges.
• Efficiency: Restart workflows save computation by avoiding full resets.
• Accuracy: Preloading and energy management replicate real-world conditions.

Applications span industries, from crash safety (ROPS) and civil infrastructure to biomechanics and advanced material testing.

Key Takeaways

• Use explicit methods for highly nonlinear problems.
• Slow load applications are central to suppressing inertial effects.
• Combine preloading and restart analysis for realistic, efficient workflows.
• Apply mass scaling carefully to expand time-step limits without distorting results.

In Conclusion

Quasi-static analysis redefines how engineers approach slow-moving scenarios, bridging the static and dynamic realms. With its advanced solver options, multiphysics integration, and restart workflows, Ansys LS-Dyna stands as a powerful platform for tackling today’s most complex engineering challenges.

Whether simulating rollover protection, civil infrastructure collapse, or biomechanical load histories, and much more, mastering these principles empowers engineers to unlock new levels of precision.

Find out more about Ansys LS-Dyna

Watch our webinar, ‘Coffee with an Expert: Quasi static simulations using Ansys LS-Dyna’, on-demand