INTERCONNECTIONS section

Table of Contents

• Syntax
• Rules
• Connecting to constants
• Variable substitution and arithmetic
• Example
• See also

The <INTERCONNECTIONS> section defines how SimObjects are connected. Connections link input ports to output ports or to constant values.

Syntax

Connections are specified as attributes of <Connection> tags:

<INTERCONNECTIONS>
    <Connection
        someObject.SomeInport="anotherObject.SomeOutport"
        anotherObject.AnotherInport="yetAnotherObject.SomeOutport"
    />
</INTERCONNECTIONS>

Each attribute has the form:

<inputObject>.<inputPort> = "<outputObject>.<outputPort>"

or, to connect to a constant value:

<inputObject>.<inputPort> = "<constant value>"

Rules

• All input ports must be connected. Every input port of every SimObject must appear on the left-hand side of a connection. Unconnected input ports cause a runtime error.
• Output ports may be left unconnected. Not all outputs need to be consumed.
• Multiple <Connection> tags are allowed. You can group connections into separate tags for readability:

<INTERCONNECTIONS>
    <!-- Environment connections -->
    <Connection
        vessel.CurrentVelocity="environment.CurrentVelocity"
        vessel.WaveElevation="environment.WaveElevation"
    />
 
    <!-- Mechanical connections -->
    <Connection
        cable.PosA="mass1.Pos"
        cable.PosB="0,0,0"
    />
</INTERCONNECTIONS>

Connecting to constants

When an input port is set to a literal value rather than an output port, the value is parsed as a comma-separated list of numbers. The list must contain exactly as many numbers as the input port declares, or the run stops with *"Constant value for input port <object,port> is incorrectly defined"*:

<!-- mass.Force is a downward force, in whatever force unit this library uses. -->
<Connection
    cable.PosB="0,0,0"
    mass.Force="0,0,-9810"
/>

Warning

The magnitude 9810 cannot be interpreted without knowing the unit system of the library that provides mass: FhSim defines no units and converts nothing. - on the third component means "downward" only by the Z-up visualisation convention, which the integrator itself does not know about. See Units and coordinate conventions.

Variable substitution and arithmetic

Connection values can use $Variable references defined in the VARIABLES section, and are then passed through the arithmetic evaluator, so cable.PosB="0,0,-$Depth/2" is valid. See Arithmetic in attribute values for exactly when a value is treated as an expression:

<VARIABLES>
    <Var Name="AnchorPos" Value="10,0,-50"/>
</VARIABLES>
 
<INTERCONNECTIONS>
    <Connection cable.PosB="$AnchorPos"/>
</INTERCONNECTIONS>

Example

<INTERCONNECTIONS>
    <Connection
        cable.PosA="mass1.Pos"
        cable.PosB="mass2.Pos"
    />
 
    <Connection
        mass1.Force="cable.ForceA"
        mass2.Force="cable.ForceB"
    />
</INTERCONNECTIONS>

The first connection links the cable endpoints to the positions of two mass objects. The second connects the cable reaction forces back to the masses.

See also

• OBJECTS section — SimObject names are defined here.
• Basic modelling concepts — how ports are defined in SimObjects.
• Units and coordinate conventions — what the numbers in a connection mean.