POM 2 Flashcards
The average time (in days) it takes a unit to flow through the system
Days-of-Supply=T
The number of times the average inventory flows through a process in a period of time (usually one year).
Inventory Turns (Turnover)=R/I=1/T
The ratio of the cost to hold an item in inventory during a designated time period (typically a year) relative to the cost to purchase the item
Inventory holding cost percentage
The actual holding cost incurred for each unit of item in inventory =πππ£πππ‘πππ¦ βππππππ πππ π‘ πππππππ‘πππ βπππ π‘ πππ π’πππ‘ βπππππ‘β ππ π‘πππ π‘βπ ππ‘ππ π π‘ππ¦πππ ππ πππ£πππ‘πππ¦
Inventory holding cost per unit
The probability that all demand is served within an interval of time
In-stock probability
The probability that demand for an item exceeds its inventory during a period of time
Stockout probability = 1- in-stock probability
The fraction of demand satisfied
Fill rate
Reasons for Bullwhip Effect
Overreactive Ordering,Order Batching, Price Promotions
Overreactive Ordering
Share information along the supply chain so everyone is aware
Avoid the overreactive temptation
Order Batching
Reduce minimum batch quantities for orders
Price Promotions
Eliminate price promotions
Variability Due to Supply Chain Partner Performance
Failure in Quantity
Failure in Quality
Failure in Finances
Failure in Operating Practice
Variability Due to Disruptions
Natural Disruptions
Political/Economic Disruptions
To ensure a stable process, we need:
Arrival rate (demand) < Capacity rate (supply)
queue will grow without limit
or this can only be temporary
if process is stable
Queue growth rate
Demand β Capacity
Length of queue at time t
t * (Demand β Capacity)
Time to serve the Qth person in queue
Q/Capacity
Time to serve the person arriving at time t
t*(Demand - Capacity)/Capacity
Average time to serve a unit
Β½T(Demand βCapacity)/Capacity
The queue length depends on:
Demand- On average how often do customers arrive?; Supply- On average how long does it take to serve a customer?; Variability- How to measure variability?
Demand
π = average interarrival time
Supply
π = average processing time
Variability
Coefficient of variation = standard deviation / mean
CVa and CVp for arrival and service processes
Utilization
flow rate / capacity = (1/π)/(1/π) = π/π
Average time in queue:
π_π=πΓ(ππ‘ππππ§ππ‘πππ/(1βππ‘ππππ§ππ‘πππ))Γ((πΆπ_π^2+πΆπ_π^2)/2)
Average time in the system
π=ππ+π
Average number of customers waiting in line:
πΌ_π=π Γπ_π=(π_π/π)
Average number of customers in service:
πΌ_π=π Γπ=π/π
Average total number of customers in the system
πΌ=πΌ_π+πΌ
Multiple Servers- ππ‘ππππ§ππ‘πππ
(ππππ€ πππ‘π)/πππππππ‘π¦=(1/π)/(π/π)=π/(πΓπ)
Minimum number of servers
ππππππ’π ππ’ππππ ππ π πππ£πππ >π/π
Are pooling systems quicker or slower than separated queue systems
quicker
Are pooling systems quicker or slower than separated queue systems
quicker
The process of creating statements about outcomes of variables that presently are uncertain and will only be realized in the future
Forecasting
Daily to monthly
Used for staffing, scheduling, and short-term pricing
Short-term forecast
center line
is the average
