GPU-SPHysics:

All the SPHysics examples can be done with GPU-SPHysics, with a faster execution thanks to the usage of the GPU. GPU-SPHysics has been used with the Nvidia GT 8600 (32 streaming processors), GT 8800 (112 streaming processors), the GTX 280 (240 streaming processors) , and the Tesla 1060 (240 streaming processors).
GPU-SPHysics is programmed in C++ and CUDA, the Nvidia extension to C, which provides the calls to the video card. CUDA is available for free from the Nvidia site: CUDA Zone.

GPU-SPHysics has two versions: 2D and 3D. The models include three different options for interpolation kernels: quadratic, cubic spline, and the Wendland kernel. Kernel correction for gradients is available if desired based on Chen et al. (1999), and Müller et al. (2003). XSPH (Monaghan, 1989) and Shepard and MLS filtering are also available.

Speedup

The speedup is calculated against the performance of the GPU code when run on a single CPU, an Intel Core2 Duo at 2.5GHz. (Note that this code is not optimal for CPU execution; it does not consider the symmetry in particle interactions, evaluating them twice (once per particle instead of once per particle pair). Although the independent, repeated evaluation is almost a necessity on the GPU, it is an unnecessary burden on the CPU; optimizing it away would improve the CPU speed by a factor of two, halving the speed-ups.)

The table below presents the speed-ups for the three major parts of the SPH algorithm : neighbor list construction, forces calculation and integration for the 3D dam break with 677000 particles.

Considering that neighbor list construction, forces calculation and integration take respectively 56%, 42% and 2% of the calculation time we achieve a global speedup of 92 on a GTX 280.

3D Examples

Dam Break (or Bore in a Box)

Gómez-Gesteira and Dalrymple (2004) examined the "bore in a box" case, which was a dam break into a wet region with a structure, representing a tsunami attack on a building--shown in red below. The whole domain is surround by a wall. The GPU version of this case with over 100 times more particles (nearly five million) is more fully resolved showing the run-up jets in front of the obstacle and at the back wall corners.

The colors in the figure are associated with the magnitude of the velocity. The dam was located at the left of the figure (wall now removed). Note the bow wave around the square building in the middle of the box and the wake behind it. The dam break bore has reached the back wall and is beginning to fall back into the domain.

Waves in the Surf Zone

Breaking water waves are a particularly difficult problem, due to the nonlinearity of the waves, the splash-up and engendered turbulence. Dalrymple and Rogers (2008) used SPHysics to model waves in the surf zone. GPU-SPHysics has been applied to this problem using a Tesla card. This simulation, with over four million particles, provides a realistic looking surf zone, with three-dimensional coherent turbulent structures despite the two-dimensional wavemaker.

By increasing the width of the wavetank, we get to study features that occur on the open coast. For example, here is a tank as wide as it is long. Features such as wave setup on the shoreline is observed as well as some three-dimensionality in the waves (snapshot taken after about a dozen waves).

Levee Failure

The nature of the failure of a section of a levee, such as those on the Industrial Canal in New Orleans, govern the associated damage due to the impact of the flood waters. The short movie shows the slow failure of a wall section and the impact on flooding. Catastrophic wall failure (rapid falling of the wall) leads to much stronger impact forces as the water flows straight out from the levee rather than along the jetty as in this case. Download movie: WallFail6.m4v

The levee section is failing (note velocity magnitude is color coded); there is a splash off the lip of the falling wall, and water is flowing along the levee due to the slow nature of the breach.

Falling levee section is now overtopped and flood waters are flowing between the houses. Note the run-up in front of the houses due to the flow impact.

2D Examples

Falling Jets

Objects and bodies of fluid can be prescribed with initial velocities. On the left, below, is a snapshot of a 1.5 m long vertical "jet" with an imposed vertical velocity of -1.5 m/s taken 0.26 s after impact. Pinch-off (the closing of the penetration cavity by gravity) has not yet occurred.