1.2.5
EVALUATING ALTERNATIVES
What
is it?
The
purpose of evaluating alternatives is to help the Planning Committee make sound
decisions about which design strategies they will advocate in the design plan.
Alternatives are evaluated to determine their effectiveness in addressing the
concerns, taking advantage of
opportunities, and meeting objectives in the planning area.
When
do we do it?
It
is the fifth step in the basic steps of design process.
After
alternatives or strategies have been identified, the Design Planning Committee
and Technical Advisory Committee evaluate the acceptability of the
alternatives. A facilitator is used during this step, and technical advisors
are available to provide information and answer questions.
Evaluate
alternatives by examining the benefits and drawbacks of each alternative.
During the evaluation of alternatives, careful consideration is given to
social, economic, and ecological factors that influence the predicted outcome.
Encourage discussion and use visual aids to help explain alternatives.
Technical advisors can prepare technical specifications and a short concise
narrative for each alternative. For each alternative include costs, and positive
and negative benefits.
The
Planning Committee considers the “effects” and the “impacts” of each
alternative. The alternatives are compared to benchmark conditions to evaluate
their ability to solve problems, meet quality criteria and meet the Planning
Committee’s objectives. Technical advisors can help the committee evaluate the
effects of each alternative and describe the impacts. The effects are outcomes
or results of the management strategy. Impacts are the differences between
initial conditions and the effects of the alternatives.
Public
review or comment may be needed during the evaluation of alternatives. This
will help inform the Planning Committee about the various effects and
acceptability of the alternatives.
After
alternatives have been evaluated, the next step is to make decisions as to
which alternatives are the most acceptable to the Design Planning Committee.
1.2.6 Communication:
Communication in
the design process involves the sharing and communicating the design requirements,
design specifications and the designed data for the relevant purpose. The
communication resembles the important space in the design process, as it is one
of the major step in the design and synthesis in the design process.
Communication is accomplished by the
various means such as drawings, graphs, charts etc. The drawing includes either
hand drawing or CAD drawing. Drawings are mostly used in design process, as it
possesses all most all information about the component to be designed or
designed. The other drawing software also used to communicate the design
processes. Communication also involves the plotting and sharing of graphs,
charts in the form of information. These materials also are the major modes of
communication as a single graph can describe much data and information required
for the further process. Drawings are mostly used in design process, as it
possesses all most all information about the component to be designed or
designed.
1.2.7 Feedback from Manufacturer and User
In
design process, the feedback from the manufacturer and the user about the final
design is very important. The manufacturer comments on the feasibility of the
design, availability of the components of the design, availability of the raw
materials, cost of production, possibility of mass production. Based on the
comments of the manufacturer the design might have to be altered. A perfect or
ideal design is most often modified to meet the manufacturer’s needs. For
example, to reduce the cost of production by use of cheaper material the life
of the product may be compromised. However, if the higher cost of production
outcomes better performance as in efficiency of a vehicle, there is nothing to
comment in the design.
The
feedback from the users is also an important aspect in the design process. The
users may not comment on the details of the design but their complaints on
durability, ease of maintenance, ease of operation are of good help in making
the product user friendly. Most often the feedback from the users is gathered
through prototype of the design manufactured in a small quantity. Based on
their feedback, modifications in the design are made and the new product is
launched that meets the demand of the users. Also the feedback is being
gathered from time to time. If bigger issues regarding the product arise, the
design is further altered.
1.3
COMMUNICATING THE DESIGN:
1.3.1
DRAWING AND CAD:
Almost
everything around us has been created by or is influenced by engineers.
Buildings, vehicles, roads, railways, food growing and processing, books,
medical care, recreation, so on. Hence, drawing and CAD plays important role in
design process. A designer needs to have the skills to generate and work with
this model in order to communicate ideas and develop a design. Computer-aided
design (CAD) is the use of computer systems to assist in the creation,
modification, analysis, or optimization of a design.CAD software is used to
increase the productivity of the designer, improve the quality of design,
improve communications through documentation, and to create a database for
manufacturing.CAD output is often in the form of electronic files for print,
machining, or other manufacturing operations.Its use in electronic design is
known as Electronic Design Automation, or EDA. In mechanical design, it is also
known as computer-aided drafting (CAD) or computer-aided design and drafting.
1.3.2
Charts and Graphs
This
is a measure of actual performance and the theoretical performance. An outline
is specified and workers are guided to work as per this outline.
Gantt
chart is an example of this. It is a scheduling technique that helps is
immediate comparison between planned work and the actual process of work. This
helps management to take corrective measures if improving the company’s
performance.
Similarly,
graph may me another way of representing the ongoing progress of work. This may
be used to show a two dimensional study of data and facts. Comparison of an
entity with another or comparison between various entities may be done by the
help of graphs.
2.
Material selection:
Material
selection
is a step in the process of designing any physical object. In the context of
product design the main goal of material selection is to minimize cost while
meeting product performance goals. Systematic selection of the best material
for a given application begins with properties and costs of candidate
materials. For example, a thermal blanket must have poor thermal conductivity
in order to minimize heat transfer for a given temperature difference.
Systematic
selection for applications requiring multiple criteria is more complex. For
example, a rod which should be stiff and light requires a material with high
Young's modulus and low density. If the rod will be pulled in tension, the
specific modulus, or modulus divided by density
, will determine the best material. But because a plate's
bending stiffness scales as its thickness cubed, the best material for a stiff
and light plate is determined by the cube root of stiffness divided by density
. For a stiff beam in bending the material index is
An Ashby plot, named for Michael ashbeyof
Cambridge , is a scatter plot which displays two or more properties of
many materials or classes of materials. An Ashby plot useful for the example of
the stiff, light part discussed above would have Young's modulus on one axis
and density on the other axis, with one data point on the graph for each
candidate material. On such a plot, it is easy to find not only the material
with the highest stiffness, or that with the lowest density, but that with the
best ratio
. Using a log scale on both axes facilitates selection of the
material with the best plate stiffness
.
The first Ashby plot on the right
shows density and Young's modulus, without a log scale. Metals are represented
by blue squares, ceramics by green, and polymers by red. It was generated by
the Material Grapher.
Plot using Ashby's own CES Selector
software.
The second plot shows the same
materials attributes for a database of approx 100 materials. Materials families
(polymers, foams, metals, etc.) are identified by the larger colored bubbles.
The image is created using Prof Mike Ashby's own CES Selector software and data
from Granta Design.
2.1
Information on material properties
Material
selection is a part of design process which seems most important. Preference
may be given to strength but what property of material is most essential is to
be prioritized. Selecting a material requires information about its strength,
stiffness, hardness, impact load bearing capacity, temperature effects, fatigue
strength and cost of the material.
Among
all properties, some of them are most important and they are given more
priority. Information about single material does not suggest the selection,
different materials are to be studied taking full information and compare the
properties. The information will help listing all available materials and rank
them in order beginning with the best material.
Strength
is not the only property that will fulfill all requirements. A durable design
may be done with the balanced properties of material suitable for the design.
Next part of selection is related to economy. Information about the cost of
material plays vital role. An economic design is preferred over costly
durability.
Properties
requirement varies with design. Handbooks are available with specifications of
material properties. Alloys, Cold drawn, hot rolled, forged and other
mechanically deformed materials and other verities of material with their
properties make confusion. This is the reason for requirement of detailed
information over material properties. For completeness of available materials
this might require a large source of material data. As mentioned earlier, once
the list is formed, select a manageable amount of materials from top of list
and find out the best material with economic and balanced properties as per the
design requirements.
Compiled by:
Name : Pradip
Pantha
No comments:
Post a Comment