23-Ind-A6 Systems Simulation · December 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
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 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. BSL has a 30-year warship-building contract and must plan a Nanticoke→Halifax steel supply chain (ship, seasonal April–December, or truck, year-round) feeding both BSL's own hull production and three subcontractors (Alpha Angle Iron, Bravo Builders, Charlie Construction) of differing capacity and location, all through a 2000 m³ Halifax yard. Demand ramps from 20 to 40 sheets/month over 25 years then tapers to 0; peak sub-assembly demand is 50–70/month, each sub-assembly needs UNIF(1,3) sheets, and each sub-assembly occupies UNIF(30,50) m³ in the yard.
Find. A management-facing memo that pitches a discrete-event simulation study of this supply chain: why it is needed, what data it needs, how long it will take, how it will be checked, and what BSL gains from it.
MEMORANDUM
To: Ms. Leslie Feist, Program Manager – Warship Program
From: Angus L. MacDonald, Industrial Engineer
Re: Proposal – Discrete-Event Simulation of the Nanticoke–Halifax Steel Supply Chain
Background. Bridge Shipyards' 30-year warship contract requires a sustained, multi-decade steel supply chain that has no direct precedent at BSL: material sourced from Nanticoke, ON must reach Halifax by a mode (ship or truck) that is itself seasonally constrained, be staged in a space-limited yard, and be split among BSL's own hull line and three sub-contractors of very different capacity. Because the ramp-up, peak, and wind-down phases span 30 years and the system mixes queueing (yard space), seasonality (the Welland Canal/St. Lawrence Seaway close December–March), and variability (UNIF sub-assembly steel content and footprint), the interactions are too complex to size by hand with confidence — a discrete-event simulation is the appropriate tool.
Objectives. (1) Determine the yard holding-area size needed, across all 30 years of the demand profile, to avoid stock-outs at BSL and at every subcontractor with a specified service level (e.g. ≥95% of months with no shortage); (2) recommend a steel-ordering/delivery policy (mode split between ship and truck, order timing and quantity) that respects the 2000 m³ yard cap; (3) quantify how sensitive the required yard size is to subcontractor mix and to the winter stockpile requirement.
Data needed and how to collect it. Historical Nanticoke–Halifax transit-time distributions for both ship and truck (from freight carriers — the same pilot data-collection exercise already begun for the shipping-firm comparison); confirmed subcontractor monthly capacity ranges and their own steel-to-sub-assembly conversion rates (interviews/contracts with Alpha, Bravo, Charlie); the demand ramp profile by month for the full 30-year horizon (from BSL's own program schedule); and the UNIF parameters given for sub-assembly steel content and footprint (validate these against a small sample of completed sub-assemblies once production starts, rather than assuming the initial estimate is exact).
Timeline (educated estimate). Data collection and conceptual model design: 4 weeks; model construction and verification: 6 weeks; input distribution fitting and validation against available historical/pilot data: 3 weeks; experimentation (yard-size and policy sensitivity runs) and final validation/sign-off: 3 weeks. Total: approximately 16 weeks (4 months) to a management-ready recommendation.
Verification and validation plan. Verification: structured code walkthroughs and unit tests on each sub-model (arrival process, mode choice, yard capacity check, subcontractor allocation) with traced, hand-computable test cases; a warm-up/steady-state check before trusting output statistics. Validation: since the full system does not yet exist, validate what CAN be validated now — the transit-time input distributions against the pilot carrier data, the queueing/capacity logic against known analytical bounds (e.g. an M/M/c approximation of the yard as a sanity check), and face validity of the whole model with BSL's own production planners before any policy is acted on; re-validate against real operating data once shipments begin.
Benefits. A validated simulation lets BSL test yard-size and mode-split decisions on paper, years before they are needed, at a fraction of the cost of learning by real shortage or overbuild; it makes the 30-year ramp-up/wind-down explicit rather than relying on a single steady-state estimate; and it gives the program a defensible, quantitative basis (service level vs. yard-area cost trade-off) for a capital decision that would otherwise be a guess.
