Boat hydrodynamic forces estimation

CFD_fan · December 3, 2019, 06:08

Dear all,

I'm new to OpenFOAM, and currently learning v1906 (Windows bash Ubuntu 18.04 LTS). My goal is to evaluate the hydrodynamic forces, such as lift and drag from both water and air, acting on a small boat (length 10m), when the boat starts from its top speed (20 m/s), WITHOUT propulsion, slows down to zero speed. The motion of the boat is purely longitudinal, including forward, heave and pitch.

According to literature, to perform such dynamic simulation, a technique called 'overset' may be helpful. There are other dynamic mesh techniques too. However, it seems the 'overset' technique is quite powerful to deal with large magnitude body motion. I tried an example in OpenFOAM \multiphase\overInterDyMFoam\floatingBody, in which a solid body is simulated to float on the water. I succeed in running the simulation, and here are the questions:

1. Is this tutorial example a good template to start my own simulation? If so, where can I find more detailed tutorials on overset simulations? Especially for the procedures in setup the problem and the involved math. I wish I can understand this in a systematic way.

2. Is a very large background mesh of water and air necessary? In real life, from top speed to zero speed, the boat travels a certain distance. It makes sense that during the simulation, the boat always stays within the background mesh. However, to achieve this, the background mesh may have to be very large. Is it a good idea to scale down the boat (e.g., from 10 m to 1 m, like from a real boat to a boat model)?

3. Should the background mesh of water and air fixed with respect to the earth (inertial system)? In simulation, I assume that the un-disturbed velocity of both water and air are zero with respect to earth. Since I'm most interested in body forces coming from water and air rather than water free surface, is it possible to move the background mesh with a constant forward speed with respect to earth? So that the size of the background mesh can be smaller than a fixed one, to allow the boat always stays within the mesh. If so, what would be the procedures to set up such a simulation?

Than you very much, your advice is highly appreciated.

mAlletto · December 4, 2019, 19:12

There are a few tutorials here you may find useful https://wiki.openfoam.com/Collection_by_authors

December 3, 2019, 06:08	Boat hydrodynamic forces estimation	#1
CFD_fan New Member Jim Join Date: Dec 2019 Posts: 2 Rep Power: 0	Dear all, I'm new to OpenFOAM, and currently learning v1906 (Windows bash Ubuntu 18.04 LTS). My goal is to evaluate the hydrodynamic forces, such as lift and drag from both water and air, acting on a small boat (length 10m), when the boat starts from its top speed (20 m/s), WITHOUT propulsion, slows down to zero speed. The motion of the boat is purely longitudinal, including forward, heave and pitch. According to literature, to perform such dynamic simulation, a technique called 'overset' may be helpful. There are other dynamic mesh techniques too. However, it seems the 'overset' technique is quite powerful to deal with large magnitude body motion. I tried an example in OpenFOAM \multiphase\overInterDyMFoam\floatingBody, in which a solid body is simulated to float on the water. I succeed in running the simulation, and here are the questions: 1. Is this tutorial example a good template to start my own simulation? If so, where can I find more detailed tutorials on overset simulations? Especially for the procedures in setup the problem and the involved math. I wish I can understand this in a systematic way. 2. Is a very large background mesh of water and air necessary? In real life, from top speed to zero speed, the boat travels a certain distance. It makes sense that during the simulation, the boat always stays within the background mesh. However, to achieve this, the background mesh may have to be very large. Is it a good idea to scale down the boat (e.g., from 10 m to 1 m, like from a real boat to a boat model)? 3. Should the background mesh of water and air fixed with respect to the earth (inertial system)? In simulation, I assume that the un-disturbed velocity of both water and air are zero with respect to earth. Since I'm most interested in body forces coming from water and air rather than water free surface, is it possible to move the background mesh with a constant forward speed with respect to earth? So that the size of the background mesh can be smaller than a fixed one, to allow the boat always stays within the mesh. If so, what would be the procedures to set up such a simulation? Than you very much, your advice is highly appreciated.

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December 4, 2019, 19:12		#2
mAlletto Senior Member Michael Alletto Join Date: Jun 2018 Location: Bremen Posts: 616 Rep Power: 16	There are a few tutorials here you may find useful https://wiki.openfoam.com/Collection_by_authors