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Simulation configuration

The OSP system structure configuration format is based on the OSP Inteface Specification OSP-IS and is used to configure the simulation system structure, including connections between FMUs and setting of initial values for input and parameter variables. The configuration format is XML according to schema OspSystemStructure.xsd. Description of the OspSystemStructure elements and their attributes are shown below. Code implementation examples follow.

<OspSystemStructure>

<OspSystemStructure> is the root element that contains xml elements as specified below.

<OspSystemStructure> Description
<StartTime> Simulation starting time, unit in seconds.
<BaseStepSize> Base step size of co-simulation, aka, macro time step size, unit in seconds.
<Algorithm> Co-simulation master algorithm, currently a fixedStep algorithm is supported.
<Simulators> Contains all sub-simulators in the system specified as <simulator> elements.
<Functions> Contains all functions, currently supported functions include LinearTransformation, Sum, VectorSum.
<Connections> Contains all scalar and variableGroup connections between simulators, or between simulators and functions. Sub-elements may include: <VariableConnection>, <SignalConnection>, <VariableGroupConnection> and <SignalGroupConnection>.
<?xml version="1.0" encoding="utf-8" ?>
<OspSystemStructure
        xmlns="http://opensimulationplatform.com/MSMI/OSPSystemStructure"
        version="0.1">
    <StartTime>0.0</StartTime>
    <BaseStepSize>0.01</BaseStepSize>
    <Algorithm>fixedStep</Algorithm>
    <Simulators> ... <Simulators>
    <Functions> ... </Functions>
    <Connections> ... </Connections>
</OspSystemStructure>

<Simulator>

Each running simulator must be assigned to a model(fmu). One FMU can be used by several simulators given different names. <Simulator> may contain sub-element <InitialValues>. <InitialValues> is optional when initial values of one or multiple variables in the simulator needs to be defined.

attribute Description
name Define an unique name for each simulator.
source Source of the simulator, example below shows three different options to specify the path to a simulator.
stepSize Simulation step size for this individual simulator, aka. micro time step size.
sub-element attribute Description
<InitialValues> variable Contains sub-element <InitialValue> defying all initial values of variables in need. Attribute variable is a string that refers to a variable in the simulator.
<InitialValue> value Contains sub-element specifying the variable type which can be <Real>, <Integer>, <Boolean>, or <String>. Attribute value gives the initial value of the variable.
    <Simulators>
        <Simulator name="model1" source="../fmu1.fmu" stepSize="0.001">
            <InitialValues>
                <InitialValue variable="variable1">
                    <Real value="0.1"/>
                </InitialValue>
                <InitialValue variable="variabl2">
                    <Boolean value="true"/>
                </InitialValue>
            </InitialValues>
        </Simulator>
        <Simulator name="model2" source="fmu2.fmu" stepSize="0.001"/>
        <Simulator name="model3" source="fmu-proxy://localhost:9090?file=fmu3.fmu" stepSize="0.001"/>
        ...
    </Simulators>

<Function>

Functions are provided to handle manipulations of variables outside individual FMUs, for example, arithmetical operation. This is especially important when different models are provided by different vendors.

Function attribute Description
LinearTransformation offset The linear transformation function is the operation that preserves the operations of addition and scalar multiplication, with attribute offset being the additional part.
  factor factor is the multiplication factor of the linear transformation function.
Sum inputCount Total count of the inputs, must match with total number in connections for this function.
VectorSum inputCount Total count of the inputs, must match with total number in connections for this function.
  numericType Numeric type can be either real or integer.
  dimension Dimension of the vector.
   <Functions>
        <LinearTransformation name="function1" factor="0.1" offset="1"/>
        <Sum name="function2" inputCount="3"/>
        <VectorSum name="function2" inputCount="2" numericType="real" dimension="3"/>
    </Functions>

<Connection>

As defined in OSP-IS, connections are configured through variables and variableGroups. It is highly recommended to follow the specification for its interfaces when exporting a model for connections.

sub-element attribute Description
<VariableConnection> simulator; name Contains sub-elements <Variable> with attributes specifying the simulator of which the variable belongs to and name of the variable.
<SignalConnection> simulator; name Contains sub-elements <Variable> with attributes specifying the simulator of which the variable belongs to and name of the variable.
  function; name Contains sub-elements <Signal> with attributes specifying the function of which the signal belongs to and name of the signal.
<VariableGroupConnection> simulator; name Contains sub-elements <VariableGroup> with attributes specifying the simulator of which the variable group belongs to, and the name of the variable group.
<SignalGroupConnection> simulator; name Contains sub-elements <VariableGroup> with attributes specifying the simulator of which the variable group belongs to, and the name of the variable group.
  function; name Contains sub-elements <SignalGroup> with attributes specifying the function of which the signal group belongs to, and the name of the signal group.
    <Connections>
        <VariableConnection>
            <Variable simulator="simulator1" name="variable1"/>
            <Variable simulator="simulator2" name="variable1"/>
        </VariableConnection>

        <SignalConnection>
            <Variable simulator="simulator1" name="variable1"/>
            <Signal function="function1" name="signal1"/>
        </SignalConnection>
     
        <VariableGroupConnection>
            <VariableGroup simulator="simulator1" name="variableGroup1"/>
            <VariableGroup simulator="simulator2" name="variableGroup1"/>
        </VariableGroupConnection>

        <SignalGroupConnection>
            <VariableGroup simulator="simulator1" name="variableGroup1"/>
            <SignalGroup function="function1" name="signalGroup1"/>
        </SignalGroupConnection>
    </Connections>

Alternatively, co-simulation configuration using the SSP standard is also supported. The SSP standard is one of the standardization projects of the FMI standard. The normative XML Schema 1.0 schema for the MAP SSP can be found here. OspSystemStructure.xml is recommended and prioritized when both the .xml and .ssd files are available.


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