Inventory System Simulation Pemodelan Sistem
Kapan saat yang tepat untuk meng- order? Berapa banyak yang perlu di-order? Inventory Systems
Inventory Costs Ordering Cost – Harga awal order, K – Harga per unit, c – Banyaknya unit yang di-order, Q i Holding (Storage) Cost – Harga per periode per unit yang disimpan, h – Level penyimpanan, X i Shortage (Unsatisfied Demand) Cost – Per periode per unit yang disimpan, p
Ketika posisi penyimpanan (level penyimpanan + banyaknya order) berada di atau di bawah level s, lakukan order untuk membawa posisi penyimpanan hingga S. (s,S) Ordering Policy
Demand in period i, D i Constant lead time, L Cost Information (K, c, h, p) Inventory control policy parameters (s, S) – decision variables Before ordering – Inventory level at period i, X i : (On hand) – (Backorders) – Inventory position at period i, Y i : (Inventory level) + (On order) Order quantity at period i, Q i Inputs and State Variables
Problem Formulation
Contoh Daily demand for refrigerators at Hotpoint City has a probability distribution Lead time is not fixed but has a probability distribution Customers who arrive and find Hotpoint out of stock will shop elsewhere and Hotpoint will lose the sale Kondisi ini tidak memenuhi kriteria model inventori yang dijelaskan sebelumnya Kondisi ini tidak memenuhi kriteria model inventori yang dijelaskan sebelumnya
Simulation Approach Simulasi dapat membandingkan aturan peng- order-an Akan dibandingkan dua aturan berikut: – Order 10 ketika simpanan hanya 6 atau kurang – Order 12 ketika simpanan hanya 3 atau kurang
Hotpoint Input Data Current inventory = 10 Holding costs: $2/refrigerator/day Order costs: $50 per order Shortage costs: $30 per occurrence (sale is lost) Demand/dayLead Time Demand/day Prob Lead Time Prob days day days days
RANDOM NUMBER MAPPINGS DAILY DEMAND PROB RN LEAD TIME (DAYS) PROB RN
SIMULATION OF Q*= 10; r* = 6 COSTS DAY BI RN DEM EI LOST ORDER RN LT ORD HOLD SHORT YES YES YES Based on this one 10-day simulation average daily cost = $26.20.
SIMULATION OF Q*= 12; r* = 3 COSTS DAY BI RN DEM EI LOST ORDER RN LT ORD HOLD SHORT YES YES Based on this one 10-day simulation average daily cost = $ THE OTHER POLICY APPEARS BETTER!