SPHaptics: A Real-Time Bidirectional Haptic Interaction Framework for Coupled Rigid-Soft Body and Lagrangian Fluid Simulation in Virtual Environments

TL;DR

The paper tackles the challenge of delivering stable, real-time, bidirectional haptic feedback in multiphysics simulations that couple rigid/soft bodies with Lagrangian fluids for VR. It introduces a unified SPH-based framework with two-way fluid–solid coupling and a smoothed haptic loop, implemented inside Unity and accelerated on the GPU. Key contributions include a stable coupling scheme, a haptic feedback integration within a multiphysics loop, and a prototype VR system with real-time tactile interactions demonstrated through fluid stirring, soft-tissue manipulation, and rigid-body tasks. The results show real-time performance at about 60 Hz for scenes with tens of thousands of particles, indicating practical potential for immersive educational applications and tactile-rich VR experiences.

Abstract

Haptic feedback enhances immersion in virtual environments by allowing users to physically interact with simulated objects. Supporting accurate force responses in multiphysics systems is challenging because physically based simulation of fluid, rigid, and deformable materials is computationally demanding, especially when interaction must occur in real time. We present a unified framework for real-time, bidirectional haptic interaction with rigid bodies, deformable objects, and Lagrangian fluids in virtual reality (VR). Our approach integrates Smoothed Particle Hydrodynamics (SPH) with two-way force coupling and feedback smoothing to maintain stability and produce physically meaningful tactile responses. This enables users to manipulate objects immersed in fluid and feel reaction forces consistent with fluid-structure behavior. We demonstrate the capabilities of our framework through interactive VR scenarios involving fluid stirring, soft tissue manipulation, and rigid-body interaction. The proposed system advances haptic-enabled multiphysics simulation by unifying fluid, soft-body, and rigid-body dynamics into a single platform suitable for immersive educational applications.

Figures (8)

• Figure 1: A rigid sphere and soft cloth plane represented as particles within the unified SPH simulation. SPH fluid particles are colored by pressure.
• Figure 2: The real-time isosurface generated using the marching cubes algorithm in parallel on the GPU.
• Figure 3: A single ray traced frame of the recorded OBJ fluid sequence from Unity. Rendered in Blender with Cycles utilizing a principled BSDF shader.
• Figure 4: Three balls of different densities are shown interacting with water and a cloth plane and are manipulated using the haptic device. The wood, plastic, and metal balls have densities of $0.1$, $0.3$, and $1.0$, and the water has a density of $1.0$.
• Figure 5: The user interacting with a surgical scene, holding a scalpel and performing an incision on a soft body that represents skin with fluid blood underneath. Force from cutting the skin as well as from the blood can be felt.