This class provides hydrodynamic behaviour for underwater vehicles It is shamelessly based off Brian Bingham's plugin for VRX. which in turn is based of Fossen's equations described in "Guidance and Control of Ocean Vehicles" [1]. The class should be used together with the buoyancy plugin to help simulate behaviour of maritime vehicles. Hydrodynamics refers to the behaviour of bodies in water. It includes forces like linear and quadratic drag, buoyancy (not provided by this plugin), etc. More...
#include <Hydrodynamics.hh>
Public Member Functions | |
| Hydrodynamics () | |
| Constructor. More... | |
| ~Hydrodynamics () override | |
| Destructor. More... | |
| void | Configure (const Entity &_entity, const std::shared_ptr< const sdf::Element > &_sdf, EntityComponentManager &_ecm, EventManager &) override |
| Documentation inherited. More... | |
| void | PostUpdate (const UpdateInfo &_info, const EntityComponentManager &_ecm) override |
| Documentation inherited. More... | |
| void | PreUpdate (const UpdateInfo &_info, EntityComponentManager &_ecm) override |
| Documentation inherited. More... | |
 Public Member Functions inherited from System | |
| System ()=default | |
| Constructor. More... | |
| virtual | ~System ()=default |
| Destructor. More... | |
Detailed Description
This class provides hydrodynamic behaviour for underwater vehicles It is shamelessly based off Brian Bingham's plugin for VRX. which in turn is based of Fossen's equations described in "Guidance and Control of Ocean Vehicles" [1]. The class should be used together with the buoyancy plugin to help simulate behaviour of maritime vehicles. Hydrodynamics refers to the behaviour of bodies in water. It includes forces like linear and quadratic drag, buoyancy (not provided by this plugin), etc.
System Parameters
The exact description of these parameters can be found on p. 37 and p. 43 of Fossen's book. They are used to calculate added mass, linear and quadratic drag and coriolis force.
Diagonal terms:
- <xDotU> - Added mass in x direction [kg]
- <yDotV> - Added mass in y direction [kg]
- <zDotW> - Added mass in z direction [kg]
- <kDotP> - Added mass in roll direction [kgm^2]
- <mDotQ> - Added mass in pitch direction [kgm^2]
- <nDotR> - Added mass in yaw direction [kgm^2]
- <xUabsU> - Quadratic damping, 2nd order, x component [kg/m]
- <xU> - Linear damping, 1st order, x component [kg]
- <yVabsV> - Quadratic damping, 2nd order, y component [kg/m]
- <yV> - Linear damping, 1st order, y component [kg]
- <zWabsW> - Quadratic damping, 2nd order, z component [kg/m]
- <zW> - Linear damping, 1st order, z component [kg]
- <kPabsP> - Quadratic damping, 2nd order, roll component [kg/m^2]
- <kP> - Linear damping, 1st order, roll component [kg/m]
- <mQabsQ> - Quadratic damping, 2nd order, pitch component [kg/m^2]
- <mQ> - Linear damping, 1st order, pitch component [kg/m]
- <nRabsR> - Quadratic damping, 2nd order, yaw component [kg/m^2]
- <nR> - Linear damping, 1st order, yaw component [kg/m]
Cross terms
In general we support cross terms as well. These are terms which act on non-diagonal sides. We use the SNAMe convention of naming search terms. (x, y, z) correspond to the respective axis. (k, m, n) correspond to roll, pitch and yaw. Similarly U, V, W represent velocity vectors in X, Y and Z axis while P, Q, R representangular velocity in roll, pitch and yaw axis respectively.
- Added Mass: <{x|y|z|k|m|n}Dot{U|V|W|P|Q|R}> e.g. <xDotR> Units are either kg or kgm^2 depending on the choice of terms.
- Quadratic Damping With abs term (this is probably what you want): <{x|y|z|k|m|n}{U|V|W|P|Q|R}abs{U|V|W|P|Q|R}> e.g. <xRabsQ> Units are either kg/m or kg/m^2.
- Quadratic Damping (could lead to unwanted oscillations): <{x|y|z|k|m|n}{U|V|W|P|Q|R}{U|V|W|P|Q|R}> e.g. <xRQ> Units are either kg/m or kg/m^2.
- Linear Damping: <{x|y|z|k|m|n}{U|V|W|P|Q|R}>. e.g. <xR> Units are either kg or kg or kg/m. Additionally the system also supports the following parameters:
- <water_density> - The density of the fluid its moving in. Defaults to 998kgm^-3. [kgm^-3]
- <link_name> - The link of the model that is being subject to hydrodynamic forces. [Required]
- <namespace> - This allows the robot to have an individual namespace for current. This is useful when you have multiple vehicles in different locations and you wish to set the currents of each vehicle separately. If no namespace is given then the plugin listens on the
/ocean_currenttopic for aVector3dmessage. Otherwise it listens on/model/{namespace name}/ocean_current.[String, Optional] - <default_current> - A generic current. [vector3d m/s, optional, default = [0,0,0]m/s]
- <disable_coriolis> - Disable Coriolis force [Boolean, Default: false]
- <disable_added_mass> - Disable Added Mass [Boolean, Default: false]. To be deprecated in Garden.
Loading external currents
One can use the EnvironmentPreload system to preload currents into the plugin using data files. To use the data you may give CSV column names by using lookup_current_* tags listed below:
- <lookup_current_x> - X axis to use for lookup current
- <lookup_current_y> - Y axis to use for lookup current
- <lookup_current_z> - Z axis to use for lookup current If any one of the fields is present, it is assumed current is to be loaded by a data file and the topic will be ignored. If one or two fields are present, the missing fields are assumed to default to zero.
Example
An example configuration is provided in the examples folder. The example uses the LiftDrag plugin to apply steering controls. It also uses the thruster plugin to propel the craft and the buoyancy plugin for buoyant force. To run the example run.
To control the rudder of the craft run the following
To apply a thrust you may run the following command
The vehicle should move in a circle.
Ocean Currents
When underwater, vehicles are often subject to ocean currents. The hydrodynamics plugin allows simulation of such currents. We can add a current simply by publishing the following:
You should observe your vehicle slowly drift to the side.
Citations
[1] Fossen, Thor I. Guidance and Control of Ocean Vehicles. United Kingdom: Wiley, 1994.
Constructor & Destructor Documentation
◆ Hydrodynamics()
| Hydrodynamics | ( | ) |
Constructor.
◆ ~Hydrodynamics()
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override |
Destructor.
Member Function Documentation
◆ Configure()
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overridevirtual |
Documentation inherited.
Implements ISystemConfigure.
◆ PostUpdate()
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overridevirtual |
Documentation inherited.
Implements ISystemPostUpdate.
◆ PreUpdate()
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overridevirtual |
Documentation inherited.
Implements ISystemPreUpdate.
The documentation for this class was generated from the following file: