# Homework Help: Water resistance as a spring constant

1. Jul 4, 2014

### Dell

i am working on a project for a dynamic sculpture
we want the sculpture to be able to sway and our idea includes placing the sculpture on a floating base(almost like a catamaran) , with wind forces the sculpture will sway.

i would like to know how i may model the water resistance/buoyancy on the floating base using finite element software, the software i use has spring capabilities and i need to know how to evaluate the spring stiffness so it will react like water, to calculate the deformations

2. Jul 4, 2014

### Staff: Mentor

Water can flow (change the equilibrium positions), springs cannot. Springs can store potential energy in their length, water cannot (it is incompressible to a really good approximation). I doubt you can model water with springs.

3. Jul 5, 2014

### CWatters

Springs typically produce a force that is proportional to their linear displacement. The force required to push a boat hull into the water depends on the volume of water displaced rather than the linear displacement.

So it depends on the cross section of your hull. If your hulls had a uniform cross section (say cubes of polystyrene?) then the volume displaced would proportional to the vertical displacement and it might be easy to model each hull as a vertical spring.

However water also has a considerable damping effect which might be significant if the things moving.

4. Jul 20, 2014

### henneh

Just model the resistance as a pressure, it will have a favourable effect against the applied wind forces. Water should not be treated as a support, it has no shear strength unlike soils say which are typically modelled as springs