4 Item Functions

Functions in MADE act to show a relationship between the various outputs and inputs of different subsystems, components or pairs. The relationship defined in model items affect the response propagation in a system. To fully complete these functions, input and output flows need to be created, then connected via internal causal linkages and finally connected throughout the system.

4.1 Assigning Functions and Flows

In MADE, functions are defined in terms of the operation of the item (a function verb) and the required inputs and outputs for that item. Both functions and flows are selected from a set taxonomy developed specifically for MADE modelling purposes. The functions editor consists of two main sections: a functions/flows section, and a Function Definition area (grey area to the right).

To open the Functions Editor:

• Select (Right-click) an item from the system model and select Functions
• Alternatively, select an item, then select Modeling → Functions from the main menu

The user selects the functions tab and flows tab in the following order:

1. Select and drag the required item Function(s)
2. Select the Flows tab
3. Select and drag the appropriate input Flow(s)
4. Select and drag the appropriate output Flow(s)

The list of functions can be viewed by expanding categories (e.g. Branch, Channel, Connect, Control, Convert, Provide, Signal, Stop, Support) or by typing into the search field. A tooltip appears displaying the definition of a function during a mouse-over action — e.g. hovering over "Store" (under category Provide) shows: "Store: To accumulate material or energy. Example: A DC electrical battery stores electrical energy. Synonyms: Accumulate, bunch, bundle, cache, capture, collect, contain, group, keep, pack, stock."

Once a suitable function has been found, left click and drag it to the Function Definition area on the right. The function will appear as a brown rectangle with In Flows and Out Flows.

5 Item Flows

Flows can be considered as the energy, material or signal that is received, consumed, processed or emitted by a system or item. In MADE modelling, items have input and output flows – these flows are connected internally by means of causality. For example, the input pressure flow entering a valve will determine flow rate output of liquid flow exiting the valve. Externally, input and output flows are used to connect one model item to another. For example, the output flow rate from a valve is connected to the input flow of a pump component.

Selecting Input & Output Flows:

• Click on the Flows tab (right of the Functions tab) in the Functions editor.
• Select an appropriate flow from either Energy, Material or Signal.
• Select (left click) the term and drag it into In Flows and Out Flows boxes inside a function.

The Flows taxonomy tree includes categories: Energy; Material (Gas, Liquid, Mixture Gas-Gas, Mixture Gas-Liquid, Mixture Liquid-Liquid, Solid, Mixture Solid, Mixture Liquid-Solid, Mixture Gas-Solid, Solid-Solid, Generic); Signal. For a "Liquid" flow, the IN FLOWS/OUT FLOWS panels list checkbox properties: Bulk modulus, Contamination, Density, Dynamic pressure, Dynamic viscosity, Flow direction, Flow rate, Flow velocity, Kinematic viscosity, Reynolds number, Static pressure, Temperature, Timing, Volume.

6 Item Flow Properties

Flow properties are the defining categories for every flow. These properties represent the functional requirements of the component and are used to define its function and functional failure modes. Flow properties can be commonly shared between similar categories of flows (e.g. Liquid, Gas & Solid flows under the Material category) or have unique flows (e.g. Heat Flow and Temperature flow properties are unique to Thermal flow). Energy flows use radio buttons which limit the user to one flow property per flow while Material and Signal flow use checkboxes to allow multiple selection. Input flow properties should also be linked to output flow properties using a causal connection to ensure that an injected failure during a failure simulation analysis can propagate through each item (see Causal Connections).

Note on selecting flow properties: The number of flow properties selected will dictate the complexity of the system. For example, a downstream item will require the same properties selected as upstream model items. Multiple selected flow properties also increase the complexity of failure diagrams and simulations. It is recommended that the user select the minimum amount of flow properties or consider the dominating flow properties of the system beforehand.

6.1 Selection of Flow Properties

Flows inserted into a function will display a list of flow properties. Each Material and Signal flow property is selected using a checkbox, whereas Energy flows are selected with radio buttons. Radio buttons prevent the user from selecting multiple flow properties – this is a requirement for Bond Graph analysis. If multiple flow properties need to be defined, the user can insert multiple energy flows from the flow taxonomy.

To select a flow property:

• Select (Left-click) the checkbox/radio-button of input and output flow properties
• To collapse the list of flow properties, select the collapse icon

6.2 Changing a Display Name (Functions, Flows, Flow Properties)

MADE uses a comprehensive, fixed taxonomy to define functions, flows and flow properties. MADE also provides the user with customization features in the form of a display name which overwrites the MADE taxonomy if required to better represent a functional flow.

To change the display name of the flow for easier identification:

• Click on a function, flow or flow property name
• Select or ensure the Properties viewer is displayed
• From the General tab, select the text field for Display Name
• Select the item to update the changed display from the Properties viewer

For example, the display name Fuel may be used to further specify the fluid (Liquid) flow.

6.3 Create Internal Causal Connections

Internal causal connections define the relationship between the input flows and output flows within a model item. Causal connections allow the user to assign polarity, filters and other causal properties which can affect the results of a system failure or response simulation.

To create a causal connection:

• Select (left click) an input flow property.
• While holding the button drag the cursor to the checkbox of an output flow property.
• After releasing the button, the user will see a black arrow between the input and output flow with a plus symbol within circle at the midpoint of the causal connection.

6.4 Setting Causal Connection Properties

The connection that is established represents the causal relationship between disturbances to the input and the response of the output. The causal relationship is defined by the polarity, response filter, causality and causal strength of the connection. Causal strength is defined as the degree to which the target functional output flow will be perturbed up or down by the input flow. Causal strength is determined by the user and is covered in more detail in the RAM Module User Manual.

Table 2: Flow polarities based on filtering and causal connection polarity

Flow Input	Response Filter	Causal Connection Polarity	Flow Output
Positive	No Filter	Positive	Positive
Positive	No Filter	Negative	Negative
Positive	Block Positive	Positive	No output
Positive	Block Positive	Negative	No output
Positive	Block Negative	Positive	Positive
Positive	Block Negative	Negative	Negative
Negative	No Filter	Positive	Negative
Negative	No Filter	Negative	Positive
Negative	Block Positive	Positive	Negative
Negative	Block Positive	Negative	Positive
Negative	Block Negative	Positive	No output
Negative	Block Negative	Negative	No output

To select causal connection properties:

• Select (left click) a causal connection.
• Select or ensure the Properties viewer is displayed.
• From the General tab select a polarity radio button (only one polarity per connection).
• Select a Response Filter from the drop-down menu.
• Select the Acausal checkbox to limit the causal connection to the initial flow and prevent its application to subsequent feedback loops.
• Set Causal strength from its default 10.00 value.

Note on Subsystems: Causal connections between input and output flows in a subsystem are automatically generated by MADE when the functional connections between its child components are completed.

The Properties view for a causal connection ("Flow rate -> Static pressure") shows: Source = "Store Liquid Flow rate (Fuel Tank)"; Target = "Store Fuel Static pressure (Fuel Tank)"; Function = "Store"; Polarity = Positive/Negative (radio buttons); Response Filter = "No Filter" (dropdown); Acausal (checkbox); Causal Strength slider from 1 to 10, default value 10.00 shown at far right of the slider.

6.5 Connecting Item Functional Flows (External)

Functional connections between components, subsystems and the system are used to represent the functional interdependence between them. These interdependencies can be identified and analyzed using failure simulations or failure injections.

To connect items in the system model:

• Create two items (e.g. components) in the system model
• Ensure that the items to be connected have functions, input flows and output flows
• Select (Left-click) the output flow of the originating item in the system model – this is represented by the colored horizontal line on the right boundary of the item
• Drag the cursor to connect the flow to the incoming flow port of the receiving item – this is represented by the colored, arrow-shaped port on the left boundary of the item

Example: the output flow of fuel from the Fuel Tank is connected to the input flow of fuel into the Diesel Engine.

Note to connecting items: MADE prevents the user from connecting dissimilar flows, or identical flows with different activated flow properties, as this would imply that an operation has occurred outside of the functional items of the system. An attempted connection between fuel (from the Fuel Tank) and electrical energy (to the Diesel Engine) is blocked and shown with a "no entry" cursor indicator.

6.6 Using Connectors in the System Model

Connectors are triangle-shaped objects located in the middle of a functional connection. They are used to redirect and manage connections between items which may otherwise overlap with other items or connections in the system model.

To create a connector:

• Select (Right-click) a connection line
• Select New Connector from the right-click menu
• Select Connector or a specific orientation i.e. North, East, South or West
• Move the Connector to the desired location on the system model