23-Ind-A6 Systems Simulation · December 2013

Question 2 of 14: Question 2 (Part A, Q2 — Process Flow Diagram)

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

National Exams — December 2013 — 98-Ind-A6 Systems Simulation. Three-hour, closed-book exam; one of two permitted calculators (Sharp or Casio), one 8.5″×11.0″ aid sheet (both sides). Format: 14 sub-questions across four parts — Part A (do 1 of 2, 25 marks), Part B (do 3 of 5, 15 marks), Part C (do 1 of 3, 10 marks), Part D (do 2 of 4, 20 marks); 7 questions, 70 marks constitute a complete paper. All fourteen sub-questions are solved below for completeness (the source restarts its own numbering at 1 within each Part). Statistical tables (Normal, t, chi-square, F) were supplied with the exam; the values below are the same table values obtained by direct computation.

Reference texts: Banks, Carson, Nelson & Nicol, Discrete-Event System Simulation (5th ed., Pearson) — simulation study design, random-number generation, input/output data analysis, variance reduction, verification & validation, queueing simulation; Montgomery, Design and Analysis of Experiments (9th ed., Wiley) — factorial designs and ANOVA.

Question 2 (Part A, Q2 — Process Flow Diagram) (25 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Given. The same supply-chain description as Question 1: a Nanticoke steel source, a seasonal ship/year-round truck transport choice, a capacity-limited Halifax yard, and four consumers of yard steel — BSL's own hull line and the three subcontractors — whose outputs (hull sections, sub-assemblies) converge on final vessel assembly.

Find. A block-and-arrow process flow diagram whose blocks map directly onto the entities/events a discrete-event simulation would code.

Process flow diagram: steel enters at Nanticoke, is transported (mode chosen per month — ship if April–December and a ship-capacity check passes, else truck) into the yard's steel inventory, then drawn down by four parallel consumers whose sub-assemblies/hull sections converge at final assembly.

Correlation to model code. Each block is a queue/resource the code would instantiate and each arrow an entity flow the code would move on an event: an Order/Ship event creates a steel-plate entity at Nanticoke and schedules its arrival (transit-time distribution keyed to the mode chosen — a decision block, not drawn as a box, that tests calendar month against the Seaway's April–December window); an Arrival event attempts to add the plate to the Yard's steel-inventory level, blocking/queueing if the 2000 m³ cap would be exceeded; a Draw event at BSL Hull or at each subcontractor removes UNIF(1,3) sheets per sub-assembly from yard inventory (rejected/delayed if insufficient) and, after a subcontractor's own production-time distribution, returns a sub-assembly entity that re-enters the yard's WIP inventory (occupying UNIF(30,50) m³) before final assembly. The diagram is therefore already close to an entity-flow / event-graph sketch: boxes are the resources the code checks capacity against, arrows are the entity-movement statements between them.

Concept & Theory

Topic. Process flow / conceptual model diagramming as a bridge from problem statement to code.

Key relations. None numeric — the diagram encodes entities (steel plates, sub-assemblies), resources (yard capacity, subcontractor capacity), and the events that move entities between them.

Why this works. A conceptual flow diagram that names the same nouns the code will name (a "Yard" resource with a capacity attribute, a "Draw" event per consumer) shortens the gap between design and implementation and gives reviewers something concrete to validate against the real process before any code is written.

Common pitfall. Drawing a diagram that reads left-to-right as prose (a flowchart of the narrative) rather than as entities queueing for shared resources — the useful version explicitly shows the SHARED, capacity-limited resource (the yard) that every consumer competes for, since that is exactly what the simulation must resolve.

Source. Banks, Carson, Nelson & Nicol, Discrete-Event System Simulation, ch. 3 (conceptual modeling / entities, attributes, events).

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