7 FCM Properties in MADE

Causal Strength

The causal strength parameter is assigned at the connection between input and output properties within an item's Functions editor (or between pair and component flow properties). This value defines the level of influence (or weighting) the input flow property exerts on the output flow property. Within MADE, a user can set the causal strength of a connection within the range of 1.0 to 10.0. This is then scaled down to a 0.10 to 1.00 range suitable for input into the FCM analysis.

Figure 8 shows the Causal Strength slider in the Properties viewer for a "Flow rate -> Flow rate" connection on the "Refine" function of "Primary Fuel Filter": Source = Refine Liquid Flow rate (Primary Fuel Filter), Target = Refine Liquid Flow rate (Primary Fuel Filter), Function = Refine, Polarity = Positive (selected) / Negative, Response Filter = No Filter, Acausal unchecked, Causal Strength slider = 10.00.

Polarity

Each connection also has a polarity parameter. This is assigned to represent whether the relationship between the input and output flow properties has a positive or negative causality i.e. a positive polarity maintains the direction of the flow response, whereas a negative polarity will change the direction of a flow response.

For example, a connection with a positive polarity indicates that an increase in the input flow property will cause an increase in the output flow property. Similarly, a connection with a negative polarity indicates that an increase to the input flow property will cause a decrease in the output flow property.

(Figure 9 illustrates the same "Flow rate -> Flow rate" Properties viewer as Figure 8, highlighting the Polarity radio-button control.)

Initial Value

The initial value parameter is assigned at the flow properties. This value represents the state of the flow parameter prior to beginning any response analysis. Similarly to causal strength, the initial value is set as a value between -10.0 and 10.0. Prior to simulation, it is scaled down to a value between -1.0 and 1.0.

Figure 10 shows the Properties viewer for the output flow property "Flow rate" on Primary Fuel Filter's "Refine" function: Name = Flow rate, Flow Property = Flow rate, Function = Refine - Liquid (OUT), Unit = gal/s, Initial Value slider = 0.0 (range -10 to 10), Internal Damping slider = 0.0 (range 0 to 10).

Perturbation

Flow properties in the system can be perturbed for the purposes of simulating a failure in the system (seen as either an increase or a decrease of the flow property from its nominal state). Within MADE, flow properties are perturbed from the right-click menu of an item. The user may have the option to perturb a flow property up or down using the arrow symbols; this will result in a perturbation of that flow property of magnitude 1.0 in either the up or down direction. The user may also select to "Perturb by Value", in which case they may select a value in the range of -3.0 to 3.0 with which to perturb the flow property.

Figure 11 shows perturbing a Liquid Flow rate down on the "Lift Pump" item in a MADE system model (Diesel Engine subsystem), via the right-click context menu: System Model, Failure Diagram, Functions, Maintenance Actions, Cut/Copy/Paste/Delete, Zoom In/Out, End Effect Item, Fault Tree, Response Paths (submenus), Propagate All..., Override Failure Diagram, Failure Injection → Liquid Flow rate → Up / Down (Down selected) / Perturb by Value, Response Simulation, Clear Perturbation.

Figure 12 ("Perturb a Flow by Value") shows the "Perturb by Value - Increase Liquid Flow rate (Lift Pump)" dialog: a Perturbation slider ranging from -4 to 4, currently set to 0.00, with instructions "Use the slider below to define the direction and strength of perturbation."

Internal Damping

The weight coefficient in MADE is used to define the level of "internal feedback" a flow property has, or more simply, the impact of the flow property's previous value on the newly calculated value. As this coefficient is effectively a causal connection between the flow property and itself, these values are represented in the weighting matrix along the principal diagonal.

Using the earlier example weighting matrix:

     [ AA  AB   AC  ]
W =  [ BA  BB   BC  ]
     [ CA  CB   CC  ]

The internal damping variable for concept (or FFP) A will appear in the top-left corner of the matrix, in the AA position.

The weight coefficient is edited in MADE at the flow property with a value between 0.0 and 10.0, which is scaled to a 0.0 to -1.00 range (unlike causal strength, the weight coefficient includes the polarity parameter within the value itself).

For example, setting an internal damping value of 5.0 will yield a scaled value of -0.5 (scaling down by a factor of 10 and applying a negative polarity).

Figure 13 shows the Properties viewer for the "Flow rate" output flow property on the "Lift Pump" item's "Increase" function: IN FLOWS Mechanical-rotational (Angular velocity selected) and Liquid (unchecked properties) feeding OUT FLOWS Liquid (Flow rate checked). Name = Flow rate, Flow Property = Flow rate, Function = Increase - Liquid (OUT), Initial Value slider = 0.0, Internal Damping slider = 0.0 (range 0 to 10).