Level Rate Diagrams (LRDs) Flashcards
True or false
LRDs are the most important concept in HSD
True
Which provides more information between a CLD and a LRD?
A LRD.
What type of analysis do LRDs provide?
Has actual numbers allowing for quantitative analysis.
What are rates associated with?
Rates have flows associated with them.
Levels have accumulated over time and ___ conditions.
initial
What are LRDs an essential step in?
LRDs are an essential step in building a model for simulations.
What do LRDs shift focus away from?
Shifts focus away from an individual in the system to see larger accumulation.
What are the components of LRDs? (5)
- Level (stock)
- Rate (flow)
- Auxiliary variable
- Boundary
- Arrows
What is a Level (stock)?
Variable in a system that accumulates and represents the state of the system at a given time. (stuff of the model)
What is a Rate (flow)?
Variable in a system that represents the rate of change of a quantity over time and influences the level either positively (as an inflow) or negatively (as an
outflow).
What is an Auxiliary variable?
Additional variable that is neither a level nor a rate and often represents a coefficient, conversion factor or lookup table.
What does a boundary do?
Limits of a model.
What is the function of arrows in LRDs?
Links the components of a system drawing to illustrate dependencies.
What do state variables do?
Identifies the state of the system.
Levels (stocks) must be ______.
quantifiable
Accumulations all around us
- Levels with ____ rates can go up and levels with ____ rates can go down
inflows
outflows
Accumulation of the net flow rate over time
- Net flow rate = ______________________.
Net flow rate = inflow rate – outflow rate
How are levels (stocks) represented mathematically?
Mathematically represented by an integral.
How are rates always measured?
Always measured per unit time.
What is a rate?
Represented variables/events that cause levels to increase or decrease
Do rates have memory?
No memory.
How are rates mathematically represented?
Mathematically represented as derivatives dy/dx.
How do you get an increase and decrease in rate?
Increase: inflow
Decrease: outflow
What is the function of an auxiliary level? (3)
- Adds additional information to the model (not a level or rate)
- Adds model transparency and details (decreased abstractions or hidden information)
- Allows model to function properly
What could auxiliary variables contain? (3)
Could contain:
- Numerical value (constant)
- Equation or calculation
- Look up table
What do boundaries focus on?
Focuses on modelling and not real world phenomena.
What are boundaries?
Boundaries are an important part of modelling and define the part of the system we are interested in.
In terms of boundaries,
Start:
End:
Start: Source
End: Sink
What is the equation of an example level?
What is the equation for example rate?
What is the OTHER formula for example level?
What does the differentiation of a level result in?
What are the level rate pairs for the following? Distance (m) - Speed (m/s) - Energy (J) - Charge (C) -
Distance (m) - (m/s) Speed/Velocity
Speed (m/s) - (m/s^2) Acceleration
Energy (J) - (J/s) = W Power
Charge (C) - (C/s) = A Current
What is dimensional analysis?
Analysis of relationship between physical quantities.
What are the two parameters for dimensional analysis? (2)
- We analyse the units measured
- Treat units as algebraic
What are the base Si units? (5)
What are the Si prefixes?
