Fluid-Structure Interaction

The model washer we use for the sake of simulation, is very similar to industrial top-loaders. The drum has a diameter and height of 40 and 42 centimeters, respectively. The impeller has a diameter of 30 centimeters and follows a sinusoidal rotation with a maximum velocity which reaches 1470 rotations per minute. In the beginning of the simulation, a 20 centimeter square piece of cloth is positioned above the impeller. The washing machine drum is completely filled with water, and as the impeller starts rotating, the cloth is deformed and drawn towards the moving rotor as it interacts with water and the solid parts of the washer. The following videos illustrate the motion of the surfaces (rigid and deformable) that participate in this simulation, as well as the velocity and the vorticity fields in planes that pass from the axis of symmetry of the washing machine.


Top-loading washer: Motion of the rigid impeller and interaction with the cloth deformable material
Top-loading washer: Slice of the velocity field
Top-loading washer: Slice of the vorticity field


Elements of the Structural Module


The basic ingredients of the structural solver for the deformable surfaces of the fluid-structure interaction module of our software can be summarized as follows. In the heart of the method exists a structural model for the deformation of the solid surfaces. The deformable solids that need to be simulated, are more like clothes than like elastic materials. The structural model must reflect this fact and must be able to deliver results close to fabric-like materials that tend to deform a lot. Self-collisions are very important in this setting, because clothes can react under bending, but nevertheless can exhibit large bending deformations. The result of these bending deformations is that the solid structure folds intensively, and parts of it approach other parts of itself. Naturally, an algorithm for detecting and treating collisions is in effect. Collision treatment is of utmost importance, since the deformable surfaces collide with each other and also with non-deformable solid objects with predefined movement. Other important components of the algorithm are the immersion of the deformable surfaces in the fluid, the modeling of friction between all solid surfaces, and, finally, the appropriate coupling of all models with an efficient temporal integrator for the dynamical system that defines the motion of the deformable solids.


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