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Marine systems simulation
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Marine systems simulation
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Net cage structure with wake effect.
Collaboration diagram for Net cage with wake:Net cage structure with wake effect. The net structure is defined as a collection of triangular or square net elements and cable elements that are placed within a common node structure. Net elements are used to simulate the net structure while cable elements are used to simulate support ropes integrated into the net structure. The theoretical background for the net structure objects is based on Priour (1997, 1999, 2001, 2003, 2005), Kristiansen and Faltinsen (2012) and Morison's equation. This simObject also includes a very simplified model of the effects of dead fish in the cage.
Wake effects are implemented to affect incoming current speed within each net element (between twines defined in the element) and between separate net elements. Net elements affected by wake effects from other elements are identified based on the initial orientation of cage with regards to current direction. Initialisation of this class will take some time as polynomial approximations representing the wake effects associated with each element in the structure are computed before simulation startup to save computational loads during simulation.
| Parameter | Default | Comment |
| AddedDragPerMPS | 0 | Adds additional linear drag to the net. This extra drag is calculated as <AddedDragPerMPS> multiplied by the net speed. If kept at "0", the drag formulation is unaffected by this effect. |
| WakeEffectBetweenElementsOn | false | Switch to turn on or off wake effects working between elements in the net structure. |
| WakeEffectBetweenTwinesInElementsOn | false | Switch to turn on or off wake effects working between the twines within the net elements. |
| UseReynoldsDependentDragCoefficient | true | Switch to turn on or off whether a Reynolds dependent drag formulation (Kristiansen and Faltinsen, 2012) should be used. If false, modified cross-flow is applied |
| CageShape | - | If set to "Circular", the net cage model is able to identify the elements that should experience wake effects from upstream net elements. Otherwise, wake effect between elements will not work. |
| CageCentreAxis | - | x-y coordinates of initial centre axis of cage. Used to identify elements that should experience wake effects from upstream net elements. |
| DeadFishWeightInWater | 0 | Submerged weight (due to gravity) of simulated dead fish in the cage bottom. |
| DeadFishInertia | 0,0,0 | Intertia of simulated dead fish in the cage bottom. |
| MembraneIsInSystem | - | Refers to obsolete experimental functionality. Should always be kept at "0". |
| File | - | Name (including path) of file that contains the description of the net/cable elements comprising the net structure. |
| TerminateOnSteadyState | true | Switch to set whether the simulation should terminate when it reaches steady state or not. When simulating without waves, this function can allow shorter simulations, but it should be set to "false" when waves are applied. |
| NodesInputForce | - | Vector providing the tag-names of the nodes that should have an input port that takes in external forces. The tag-names are mapped to node numbers in the element description file provided in the "File" parameter. |
| NodesOutputPosAndVel | - | Vector providing the tag-names of the nodes that should have output ports that write the current node position and velocity. The tag-names are mapped to node numbers in the element description file provided in the "File" parameter. |
| NodesInputPosAndVel | - | Vector providing the tag-names of the nodes that should have input ports that take in the external values for node position and velocity. The tag-names are mapped to node numbers in the element description file provided in the "File" parameter. |
| NodesOutputForce | - | Vector providing the tag-names of the nodes that should have an output port that writes the forces acting on the node. The tag-names are mapped to node numbers in the element description file provided in the "File" parameter. |
| Tag | Size | Comment |
| <node_tag_name>Pos | 3 | Sets the position of the node referred to by <node_tag_name>. This value can be constant or obtained from the outputs of another simObject. |
| <node_tag_name>Vel | 3 | Sets the velocity of the node referred to by <node_tag_name>. This value can be constant or obtained from the outputs of another simObject. |
| <node_tag_name>Force | 3 | External forces affecting the node referred to by <node_tag_name>. This value can be constant or obtained from the outputs of another simObject. |
| MembraneDepth | 1 | Port for obsolete and experimental functionality. Should be kept at "-1.0" at all times. |
| Tag | Size | Comment |
| <node_tag_name>Pos | 3 | Position of the node referred to by <node_tag_name>. |
| <node_tag_name>Vel | 3 | Velocity of the node referred to by <node_tag_name>. |
| <node_tag_name>InternalForce | 3 | Internal net forces acting on the node referred to by <node_tag_name>. This value contains the force components computed by the net structure (e.g. hydrodynamic forces, tension forces) |
| NodeSumForce | 3 | Sum of forces in all nodes in the net structure. |
| NodeSumHydDynForce | 3 | Sum of hydrodynamic forces in all nodes in the net structure. |
| NodeSumDragForceAbs | 1 | Absolute value of the total drag force acting on all nodes in the net structure. |
| NodeSumDragForceDirection | 1 | Direction in rad of the total drag force acting on all nodes in the net structure. |
| NodeSumLiftForce | 1 | Absolute value of the total lift force acting on all nodes in the net structure. |
| Tag | Size | Comment |
| Pos_<i> | 3 | Position of node with index <i>. |
| Vel_<i> | 3 | Velocity of node with index <i>. |
1.9.4