الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 180 |  |  |
| | | from | 180 | | |
Abstract
Thesis Summary
A supply chain network is a set of organizations, responsible for
fulfilling the downstream requests. Coordinating decisions across the
supply chain network represents an important issue in supply chain
operations. In an ever changing, constrained, and competitive
environment, any form of flexibility or a way for industrial
organizations to reconfigure their resources is a turning point for better
adaptation to changes. In this thesis, two problems were investigated:
first, the lot sizing coordinated decisions in constrained supply chains
and second, order quantity allocation of alternative materials.
The goal of lot sizing problems in supply chains is to establish a
policy that would maximize profit or minimize relevant costs when
implemented. The optimal policy depends on the assumptions made
about the way costs are incurred, how demand is satisfied, and how
constraints and limitations are faced during supply chain operations. In
real industrial problems, there might be constraints on the size and
number of shipments, size and number of production lots, space and
monetary limitations, etc. In the present work, the first proposed model
considers constrained situations seeking feasible and practical lot
sizing decisions in a multi-echelon supply chain. The demand occurs
continuously at constant known rate. Integer non-linear programming
was used to optimize the problem.
The results show that, constraints have major role in
determining the lot or shipment size at each echelon. The effect of
problem parameters on the optimal decisions was studied. The
parameters under consideration are holding costs, shipment/set-up
costs, demand, production rate, and material percent defective. It was
found that, in general, increasing demand rate increases the total
number of shipments per period and based on which the material and
product shipment quantities are determined. However, it does not
always guarantee an increase in the number of production runs per
VIII
period. Moreover, an increase in the integer number of shipments per
production run results in a decrease of number of production runs per
period. It was also found that the manufacturer is a key decision maker
in deciding the lot size at different supply chain members when
maximizing the total profit of the system.
The second proposed model, in this thesis, addresses one of the
mitigation strategies that can help in overcoming system constraints.
The developed model is based on the following assumptions: 1)
alternative materials can be separately manufactured and turned into
same products with same quality; 2) these materials yield different
scrap percentages when manufactured, 3) they are manufactured using
different manufacturing times, and 4) they have different purchase
prices related to their quality. The problem is modeled in mathematical
integer linear programming to determine the optimal quantity mix
from alternative materials to maximize profit for certain operating
conditions.
Analysis of a single-period model for three-echelon supply
chain and two-material setting states that cost and quality are not the
only drivers for orders allocation, as capacity restriction increases.
Improved supply chain performance, represented by higher profit
and/or higher fill rates with required quality, may be achieved by
considering alternative materials. In general, capacity limitations
oblige the decision maker to go for the extra production that can result
from using an expensive alternative material for higher profit, unless
the materials produce similar defective percentages or require similar
operational conditions. Robust optimization (seeking conservative
solutions) against quality variation gave same trends at lower profits.
Further analysis of a multi-period model for three-echelon supply
chain considering inventory at the manufacturers was conducted. It
shows that, against system constraints, inventory improves the fill rate
while using alternative materials improves the profit.
IX
Keywords: supply chains; lot sizing; integer replenishment policy;
finite production; integer non-linear programming; order quantity
allocation; alternative materials; imperfect quality.