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lifecycle ones, based on our previous method.
Improved point is to integrate lifecycle assessment
in order to consider its results as one of valuation
characteristics of the integrated optimization.
Figure 1 shows the overview of the proposed
integrated optimization method. As shown in this
figure, this method consists of functional / layout
optimization plus LCA. Functional optimization is
the main part of the proposed method and executed
just one time. Functional optimization is based on
the hierarchical genetic algorithm (HGA)
(Yoshimura and Izui, 2002) in order to consider
hierarchical nature of a functional structure. In the
proposed method, performance, cost, total area and
total carbon emission are considered as valuation
characteristics of the functional optimization. Any of
them can be configured as an objective function and
the rest of them are configured as constraint
conditions. The proposed method assumes that
performance and cost can be calculated by simply
summing up the values associated with each part,
whereas total area and total carbon emission can not
be calculated by simple summation. Therefore,
layout optimization and LCA are repeatedly invoked
from the functional optimization to obtain the layout
with minimum area and total carbon emissions
respectively for every design proposal and for every
generation of the functional optimization. Layout
optimization is based on the traditional genetic
algorithm and the sequence-pair representation
(Murata, Fujiyoshi, Nakatake, and Kajitani, 1996).
Generation of solutions
Evaluation of solutions
Layout optimization
using GA
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•Performance
•Carbon emission
•Cost
•Area
(Selection, crossover, mutation)
Functional optimization using HGA
Optimal solution
Functional structure including alternatives
•Optimal functional structure
•Optimal layout
Lifecycle assessment
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Figure 1: Overview of the integrated optimization.
Due to space limitation, the following section
only describes the part of LCA. See the reference
(Kobayashi, Suzuki and Higashi, 2009) for the
details of functional / layout optimization and their
integration.
2.2 Lifecycle Assessment
In the practical LCA, there are various valuation
characteristics such as emissions of CO2, SOx and
NOx throughout entire product’s lifecycle, usage
rate of renewable material and reuse / recycle rate.
This paper adopts carbon emission as a valuation
characteristic of the propsoed method, because CO
2
reduction is one of most interested problems in order
to fight global warming in recent years. Total carbon
emission of each design proposal obtained during
functional optimization processes is calculated by
the following concepts.
(a) Value of carbon emissions is evaluated and
configurated for each part by executing LCA.
(b) All parts can be classified into two types. One
has the fixed value of carbon emissions and the other
has the value of carbon emissions per unit area.
Most parts belong to the former type, whereas an
electronic substrate, for example, belongs to the
latter type. Actual value of carbon emissions of the
latter type is calculated by multiplying unit carbon
emissions by the area calculated by layout
optimization.
(c) Total carbon emission of a design proposal
GHG
total
is defined by the below equation.
n
j
jj
m
i
itotal
uGHGAreaGHGGHG
11
(1)
Where GHG
i
is the fixed value of carbon emissions
of part i, whereas, uGHG
j
is the value of carbon
emissions per unit area of part j. Area
j
is the value of
area of part j.
3 CASE STUDY
3.1 Problem Description
In the case study, internal devices of a personal
computer are designed using the proposed method .
“Internal devices” means that input devices, a
display and an enclosure are not included.
A computer consists of the following 5
components: motherboard, HDD, cooling system,
power supply and auxiliary storage. Motherboard,
cooling system and power supply can be
decomposed into more than one part, whereas HDD
and auxiliary storage can not be decomposed any
more. Table 1 shows an example of their alternatives.
Prices and sizes are configured by surveying their
retail price and measuring their size. Performances
INTEGRATED OPTIMIZATION OF FUNCTIONAL AND LAYOUT DESIGNS BASED ON GENETIC ALGORITHM -
Consideration of Carbon Emission troughout Product's Lifecycle
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