[CenterRime]

Good day.

For solve problem of catamaran course stability we need moving and floating catamaran hull case.
On forum I was not able to found open examples and solution.
Floating Body Forces

At present we have accomplished this steps
1. Have OpenFoam installed and compilled interFoam tutorials
2. Read OpenFoam manuals and user guide about meshes and meshes dynamic chapters.
3. Make model for computation a drag force of catamaran hull and turning(yaw) moment for various drift angles
4. Developed post-process Python script for the computation data of pressure on hull with normal to surface and cell area normalization.
Script for calculation of drag force and yaw moment of the hull
5. Build case for rigidBodyMotion study.
6. Start study problem of wave solver for rigid body motion. gfmFoam solver. GFM - ghost fluid method
https://www.sciencedirect.com/scienc...29801820309537
https://az659834.vo.msecnd.net/event...9ed9233c153490
7. A calibration calculation of the coefficient of hydrodynamic resistance of bodies of a simple shape has been performed and a comparison with generally accepted experimental values has been carried out.
8. The calculation of the resistance to rectilinear motion, the drift force and the turning moment for the hulls of a catamaran of different shapes of the same displacement is carried out.

We will really appreciate any advice and help.
All results and case we will publish on github.

[CenterRime]

Quote from OpenFoam source

Class
floatingBody
Description
Floating body is a representation of the mesh and 6-DOF forces with the
following characteristics:
1) Mesh representation is given as a list of patches representing the hull.
Patches can be used to capture individual components (eg. keel,
bulb, rudder, hull etc.)
2) Mesh is structured in the following way
Hull is created with symmetry around the y-z plane
Incoming velocity is in -x direction
Mesh can be of one of following types
2.1) Single zone mesh, with or without prismatic layers
2.2) Two-component GGI mesh with a spherical interface
2) Flow force calculation is based on turbulent single-phase or
free surface flow for all patches. Only the force on wetted surfaces
(gamma = 1) is considered
3) External propulsion force is given as direction and height above
centre of gravity. Force magnitude equals to total drag force
in opposing direction
4) 6-DOF solver
Holds inertial parameters of the boat
Force balance includes hydrodynamic forces and external propulsion force
Motion can be constrained in each of the following:
Forward motion (x)
Sideways motion (y)
Vertical motion (z)
Roll angle (x-rot)
Pitch angle (y-rot)
Yaw angle (z-rot)

https://github.com/Unofficial-Extend...floatingBody.H

Question is what solver it is need to accomplish this float body movement along x direction.
Look like this manual is helpful.
https://www.tfd.chalmers.se/~hani/ku...usUrquhart.pdf

[CenterRime]

After some efforts we have working case in CfdOf (OpenFoam GUI under FreeCad)
Hull3.zip
And results in DualSPHysics project
All velocity around moving catamaran hull
velocity_of_stream_around_catamaran_hull.jpg
and velocity around moving catamaran hull by Y axis
velocity_of_stream_around_catamaran_hull_Y.jpg
DSPH project here
WaterHullSTL_DSPH.zip

[CenterRime]

Gradually mastering the calculations in OpenFoam.

We have obtained the result of calculations of the flow around asymmetric knife-shaped catamaran hulls. Flow 3m/s

alpha_water.png
- wave formation of the flow (alpha.water)

- flow acceleration distribution along the Y axis
y_velocity_hull.png

- flow acceleration distribution along the X axis
x_velocity_hull.png

- pressure distribution in the flow
pressure_around_hull.png


Project in CfdOF for freeCad
Hull_catamaran_flow.zip

[CenterRime]

The essence of the problem that has not yet been solved and a brief description of what has been done in a month.

CFD part.
1. OpenFoam is so far the only open source CDF package available that can calculate models with the movement of floating bodies with two phases - air and water. Other packages are either commercial or do not have such calculation capabilities.

2. Data for the OpenFoam core needs to be prepared. There are several commercial and non-commercial programs for such training.
Data can be divided into two categories - 3D models (mesh) and calculation conditions.
Meshes were obtained based on the plugin for Blender and the plugin for FreeCad
Calculation conditions must be prepared manually. These are about 100 basic and about 200 more detailed parameters.

3. Commercial packages have written typical calculation scenarios and detailed explanations of calculation methods. The non-commercial packages only have the most basic scenarios.

For example, in the calculations that we have so far been carried out, only the most basic model of fluid behavior is used. This model can be much closer to the experimental data.

The solution may be to write scripts of typical Python scripts and provide open access to scripts and documentation.
The CfdOF package is closest to solving this problem.
However, the CfdOF package does not open ready-made calculation models. Manual calculation scenarios have not yet been created.

Another option is to create scripts in a trial version of a commercial program (for example, SimFoam) and perform the calculation in the OpenFoam core. Obviously commercial packages will discourage this practice. Wasting time arguing with commercial software is boring.
The OpenFoam and CfdOF forums are silent for now.

Model tests.
In short, model tests do not allow accurate measurement of integral and differential parameters.
Therefore, such model tests are usually used to refine the calculation parameters and train the calculation neural network.
Also, to answer design questions, it is necessary to make about fifty models symmetrical along two axes of symmetry. Even if made from gypsum with sawdust, it is time-consuming. We don't have a CNC yet.

We try further.

[CenterRime]

To calculate the turning moment on the body, a model of a uniform incompressible flow is sufficient.

For such a model, it is possible to set the size of the entrained layer, turbulence, body fluid friction resistance, and other characteristics.

The proposed method for calculating the turning moment of the hulls of catamarans and trimarans of equal displacement at low speeds: At a speed not exceeding 5 m/s, wave formation and wave interference between the bodies can be neglected.

For such a calculation, OpenFoam offers the output of data on the projection and the pressure on each section of the body along the X, Y, Z axes in the form of a table for each moment of time.

The condition of equal displacement of hull models can be fulfilled in the simulation program by measuring the volume of the model below the waterline. For models that are not symmetrical along the X axis, the center of buoyancy (center of magnitude) can be calculated in the FreeShip program.



The following calculation method can be proposed:

1. We place the body model with the axis of rotation in the CPU in the center of coordinates.

2. We direct the flow at a constant speed at a measured drift angle.

3. We display the pressure values on the sections of the body in the form of a table.

4. We write a script that analyzes tabular pressure data on the right and left hull, if necessary, on the right and left side of the hull.

5. The script displays a beautiful report on the total value and graphs of the values of resistance to rectilinear motion and turning moment along the longitudinal axis of hulls of a given shape and equal displacement.



We try further.

[CenterRime]

General explanation of mesh movement
https://openfoam.org/release/2-3-0/mesh-motion/


For rigid body motion need setup correct center of mass and moment of inertia
Inertia in rigidBodyMotion
Planing boat simulation with InterDyMFoam and force ramp for make it stable


rotor motion
http://www.diva-portal.org/smash/get...FULLTEXT01.pdf




Look like all this is good examples of floating body.


But how we may move a hull forward?
Usually most models of hull in flow it is floating body with restrains on X axis movement and parameters of flow velocity.
Look like this is suitable for most hull movements computation tasks.

We need combine at last two or more solvers for this model.
Here is really good work for catamaran modelling in OpenFoam.
https://www.mdpi.com/2073-4441/14/17/2623




Simulate the movement of boats

[linuxguy123]

Originally Posted by CenterRime

But how we may move a hull forward?
Usually most models of hull in flow it is floating body with restrains on X axis movement and parameters of flow velocity.

Look like this is suitable for most hull movements computation tasks.

I am quite interested in this project.

My guess is that you don't move the hull. You move the waves past the hull and the hull stays stationary.

We need combine at last two or more solvers for this model.
Here is really good work for catamaran modelling in OpenFoam.
https://www.mdpi.com/2073-4441/14/17/2623


Simulate the movement of boats

I'll have a look at these.