DESIGN PROCESS Ship Design and Construction S.N.A.M.E., Jersey City 2003 Engineering design is an interactive and iterative process combining creativity and analysis which serves a lim
Trang 1DESIGN PROCESS
Ship Design and Construction
S.N.A.M.E., Jersey City 2003
Engineering design is an interactive and iterative process combining creativity and analysis
which serves a limited objective; the achievement of a technically and operationally successful
cost-effective technology
Naval architecture requires the discipline of a well-defined objective if a client’s requirements
are to be met and the design procedure itself requires a disciplined and structured approach A
vessel, irrespective of type or size, is a synergy of integrated systems and parts and indeed naval
architecture at its widest scope may be considered as systems engineering In order to achieve
that synergy in an economical and practical time-frame a design project demands a rational,
structured procedure underpinned by careful planning and management
Two key features of the process of marine design are that in the first instance it is an interactive
process; i.e., variation in any one parameter impacts upon any number of others, and in the
second instance it is an iterative procedure, mostly as a consequence of being interactive but also
because of the progressive resolution of detail The design process is also an obviously
evolutionary, where form, features and detail are continuously developed, beginning with a
concept image and finishing with a highly detailed design It is a convergent process of
developing complete compatibility between all aspects of the design and with the client’s
requirements
The design of a marine vessel combines the requirements and ideas of many functions from the
vessel operator, owner, designer and constructor Without proper integration and collaboration
the end product may prove unsatisfactory Additionally, design is a decision-making process
There are 2 factors that complicate design decision-making, namely the uncertainty involved in
both the inputs and outcomes and knowing what information must be considered in developing
the outcomes from the selected options Computer models are used to reduce the uncertainty in
design decision-making Some models provide only a single deterministic value for the
outcome Today this is usually not acceptable What is required is a set of outcomes and their
probability The old design spiral has given way to the design option space and set-based
design
Ship design is a multi-disciplinary activity and requires the use of systems engineering Because
of the extent of the required knowledge traditional design is accomplished by dividing the
overall product into manageable parts, each of which has a disciplinary focus Systems
involving people working together
to support of form a basis argument
doing sth again and again to improve it
an idea or a principle
that is connected to sth
sth that become very familiar
sth that happen only in certain way
Shape combine several academic disciplines in an approach to a problem
Trang 2engineering focuses on the relationship of the different systems and disciplines involved in their
design and integration of them all in order to provide the best outcome Systems engineering
provides a framework which offers the ability to develop design options and to enable
decision-making to make a rational selection of one of the options To develop a design option space
requires 2 distinctly different activities; design synthesis and parametric selection
The design option space may contain too many options for an individual or even a team of
designers to consider every option even with the extensive use of computer modelling Often
only a small number of options may be selected for further analysis and even if the best of these
is finally selected it remains possible that the overall best possible design or global optimum was
not considered This means that the selected design was sub-optimal Mathematical methods to
find the single optimum solution within the option space are often limited and may also miss the
best option It is therefore better to have a method to show the outcomes of sets of options rather
than have just a single solution Then the decision-making tools can be applied to all the options
and the best one selected
The design spiral has been used to describe the preferred ship design process for many years It
is focussed on a series of activities which converge as efficiently as possible on a single solution
to the design requirements of a specific project This approach often involves making decisions
based on incomplete information and/or compromise Thus it either requires significant rework
(iterations) to reach an acceptable design or acceptance of a design which is not the best
FINAL DETAIL DESIGN
MISSION REQUIREMENTS (REVIEW)
CAPACITIES (VOLUMETRIC ANALYSIS)
MANOEUVRABILITY ANALYSIS
WEIGHT ESTIMATION
GENERAL ARRANGEMENT
STABILITY & TRIM (INTACT & DAMAGED)
STRUCTURAL DESIGN
& ANALYSIS
HULL FORM (PARAMETERS & LINES)
PROPULSION FORMAT
& SYSTEMS
ECONOMIC & COST ANALYSES
SEAKEEPING ANALYSIS
RESISTANCE &
POWER ANALYSIS
Figure 1.1 The basic design spiral
the act of combining separate idea
the best possible
Trang 3The rational formation of a vessel’s design within the design spiral approach has been considered
an appropriate analogy for the process due to the obvious convergence inherent in a spiral and where each circuit is representative of the iterative nature of the design process The spiral is superimposed over sectors indicating the sequential design elements undertaken during the process
The design spiral is illustrated in Figure 1.1 The sectors indicated are broad descriptions of the primary elements of marine design which themselves contain numerous design analyses The
spiral is only illustrative of the process and is not a time line as the man-hours (or duration)
required by each element increases as the project progresses It should also be noted that spiral complexity will increase with increased complexity of vessel and operational requirements; for example, intermediate elements (e.g., vibration analyses, signature assessments) may be essential components of the spiral for particular vessel types
This single iterative design approach was named as point-to-point design and is often believed to
result in an optimum design, whereas experience has shown that this is not the case Most design synthesis programs follow this same approach and attempt to converge on an acceptable design
The design bounding approach is an alternative design process that uses the option space It considers a number of vessels within a range of values for all dimensions and coefficients which bracket or bound the domain space that contains all the solutions While it involves performing the design calculations for every combination, it avoids the need for iteration and many calculations may be made very quickly via computers
In more recent years the set-based design approach has been offered as the best approach Set-based design is an alternative approach to the common single design approach where a design is iterated and improved until an acceptable solution is developed Set-based design deliberately considers a set of designs that will meet the requirements until all unknowns are determined and then the best alternative is selected It is basically a ‘weeding-out’ process Set-based design has been shown to provide better design in shorter time
It is because of the iterative nature of many design approaches that the principle of least
commitment should be followed That is, progressing from step to step in the design process, no
irreversible decision should be taken until it is necessary This principle of least commitment provides maximum flexibility in each step and the assurance that more alternatives remain available as long as possible thus permitting the eventual selection of the best alternative
The principle of least commitment has been shown to result in more efficient design primarily due to the reduced requirement for iteration since better decisions are being made at each step of the process This is the goal behind the set-based approach
based on reason rather than emotion
a basic/permenant of sth
certain or likely to happen
consider to be similar or
connected in someway
done in a planned way
smallest in size, quantity and degree
cannot be changed back
Trang 43 The Design Process
The mission statement is a centralised compendium of information necessary to design the vessel and criteria to test its economic feasibility The objectives of the design team or the owner and key elements of the strategic plan should also be embodied in the mission statement A second purpose of the mission statement is to prevent the unintentional or accidental deviation from the original objectives The mission statement becomes a control document that aids management and the vessel acquisition team This is the first response to the design brief
Design in this context means to prepare calculations, technical model and documentation (drawings), specifications and to support these with experimental testing where required The design phase lends substance to the mission statement by establishing a configuration, shape, dimensions, layout and other characteristics which can be represented visually on paper or computer It is the point at which the centre of effort shifts from management science to design, particularly naval architecture and marine engineering
This design and engineering phase of the vessel acquisition process progresses through distinct and increasingly more definitive stages These are:
It should be noted that the fourth stage (detailed design) wherein the working drawings are prepared is usually executed after the building contract is signed The shipbuilder usually prepares the working and shop drawings There are rare occasions when an owner may cause the detailed design to be undertaken prior to contracting with a shipyard This is more likely to be done for smaller vessels, service craft or specialised vessels or where the vessel owner may purchase a set of working drawings from a designer or a shipyard
The written (i.e., text) component of a design may take the form of specifications, reference to industry standards, classification rules, government regulations, manufacturer’s specifications or shipbuilders detailed standards These then also become an integral part of the design
The step in the design process that follows data collation and development of the mission
statement is the concept design stage It is the point where the project starts to develop form and
dimension and involves the transformation of a qualitative set of requirements into an early design configuration with some of the principal characteristics defined The concept design effort usually results in a drawing, partially or fully dimensioned and may also include developing a written description of the concept It will normally include one or more design alternatives
collection of facts, drawings on particular subject
the act of moving away
the act of getting sth
the most important or main part
Trang 5The concept design stage requires a small team who should be creative and innovative It has been suggested that the concept design phase often takes between 4 and 80 man-days While it
is difficult to put such bounds on the amount of time required for conceptual design it requires one to several orders of magnitude less effort than preliminary or contract design
The concept design phase may often be referred to as the cost and feasibility phase The
principal objective of this phase is to clarify the owner’s requirements, i.e., the vessel’s mission and principal required performance attributes which reflect the desired balance between capability and affordability
Typically several cycles of synthesis and analysis are performed punctuated by consultations with the owner, during which the range of options studied is progressively narrowed Through this process a consistent set of performance requirements is established which can be satisfied by
a practical design solution and is within the client’s budget
The role of the design team is to perform parametric studies that sketch out the design alternatives in sufficient detail and the cost (capital and operating), performance and risks (cost, technical and schedule) of each can be assessed and compared The alternatives are often referred to as feasibility studies because the feasibility of each proposed combination of the major design requirements must be established Because performance, cost and risk are being
compared among the alternatives, relative accuracy and consistency among the alternatives is stressed rather than the absolute accuracy
At the conclusion of the process the mission of the new vessel will have been defined along with the principal performance requirements (i.e., capabilities) In addition a feasibility study will have been created which represents an initial solution to the stated requirements Near the end of the phase this feasibility study is developed in greater detail to become a concept design
Products of the design team during the concept design phase would rarely exceed the following:
the possibility that can be made, done or achieved
a smaller or less important part of sth larger
Trang 65 Preliminary Design
The second design stage in the evolution of a vessel is the preliminary design The preliminary
design is an engineering effort which builds on and provides much greater detail than does the concept design It is a second iteration in the design process For those who think in terms of the design spiral it is the second circuit of the spiral which is meant to converge on a more accurate and improved set of vessel characteristics
The preliminary design is also meant to provide a greater level of detail especially identifying and defining those features which have a significant effect on other characteristics of the vessel including cost For example, a calculation of the longitudinal strength of the hull and the development of the midship cross-section permit a more accurate calculation of the weight and centre of gravity of the vessel This in turn permits a more accurate calculation of draft, deadweight capability and stability, etc
The preliminary design should provide sufficient detail to permit verification of both the technical and economic feasibility of the vessel This level of detail is sufficient to permit a construction cost estimate to be made This usually requires just the principal dimensions, weight estimate and type of main engines Any special features which significantly affect the construction also need to be identified These include such features as cargo handling equipment, stabilisation systems, etc The preliminary design also provides sufficient detail to permit a reasonably accurate operating cost estimate to be made The operating cost estimate relies on such information as crew number, fuel and lubricating oil consumption and an estimate
of maintenance costs based on the outfitting and coating systems used
Design work for the specific vessel begins in earnest in the preliminary design phase and the size
of the design team and the cost of the design effort significantly increases The objectives of this phase include the following:
requirements
During this phase formal trade-off studies are performed on design issues that have an effect on vessel size, overall configuration, performance, cost or risk The study of issues that do not have
a major impact on these parameters should be deferred to the following phase Some examples
of pertinent issues for trade-off studies in this phase include the following:
more seriously and with more force or effort than before
small change in sth
the act of balancing two things that are opposed to each other
delay
appropriate to a particular situation
the bottom of the ship which is immerse in water
= goal : sth that you are trying to achieve
Trang 7● Propulsion plant type (diesel type, diesel-electric, hybrid system, etc.)
The preliminary design is developed beyond the initial concept design in all technical areas regardless of whether they are subject to formal trade-off studies In design areas not subject to the investigation of design alternatives a reasonable baseline concept is selected and defined to the appropriate level of detail For many vessel systems this is the identification and approximate sizing of major system components and the development of a single one-line diagram (schematic) of the system Major emphasis is placed on the performance prediction to validate that the stated performance requirements have been satisfied These predictions may include speed, sea-keeping, station keeping, acoustic performance, cargo load/discharge rates, etc If the hull form is unusual and hydrodynamic performance is critical, limited model testing may be done to validate performance estimates More often model testing is deferred to the subsequent phase
Products of the design team during the preliminary design phase would include the following:
according to a fixed plan or pattern
less important
a set of standard dimensions for parts of a structure
according to a fixed plan or pattern
Trang 86 Contract Design
The third design stage involves the preparation of both contract specification and the contract drawings, the primary purpose of which is to create a set of documents which accurately describe the vessel and can be used as basis for agreement between the buyer (owner) and the constructor (shipyard) The level of specificity at this stage is not fixed by industry practice, rather, it depends on a number of factors including the size and complexity of the vessel, presence of novel features and contractual risks in dealing with certain shipyards, etc
The level of detail in the specification and drawings should be just sufficient for both parties to fully understand the requirements of the other The specifications are meant to be a companion document to the contract plans and the contract itself In the event that there are contradictions between contract, specifications and drawings, the generally accepted hierarchy is that the contract terms prevail, followed by the specifications and lastly the drawings This is usually explicitly stated in the contract and specification
The specifications and drawings should be prepared to thoroughly describe the vessel and those features which the owner needs or desires However, the owner should realise that excessive specificity could inhibit the ingenuity of a constructor and perhaps produce a more costly vessel
During both the preliminary and contract design efforts a great many calculations are performed
These do not usually form part of the contract package, however, if provided to the constructor they should be treated formally, carefully checked and documented and remain with the design package While many shipyards or preparers of the working drawings prefer to re-do these calculations, some do not and therefore in their case, the calculations are useful in simplifying or verifying ongoing design work As most contracts place full responsibility for performance of the vessel on the constructor, it is essential they re-do the calculations for their own protection
The principal objectives of the contract design phase are:
Extensive additional engineering effort is required to achieve the first objective Emphasis is placed on the development and refinement of systems throughout Trade-off studies deferred from the previous stage due to their lesser impact are now undertaken The technical portion of the bid package is developed by the design team and consists of a vessel specification, drawings and other vessel descriptive data (e.g., the weight estimate)
For each system the following tasks must be performed:
requirements
the quality of being specific
a system that is organized into different level of importance
clear and easy to understand
to prevent sth from happening
the ability to invent sth
the development
Trang 9● Completed engineering on selected systems
The hull form including appendage definition and general arrangement are further refined Arrangement drawings for many internal and deck spaces are developed (e.g., anchoring and mooring areas and equipment, navigation and control spaces, helideck and hangar facilities, etc.) Technical specifications for long lead equipment and materials are developed All aspects of the vessel’s performance are analysed and the stated performance requirements validated A full program of hydrodynamic model tests is typically performed for naval vessels, some of which support the propeller design
The vessel specification is arguably the most important product of the contract design which is obviously essential if the owner plans to have constructors bid for the detail design and construction phase The specification includes the testing and trials requirements for the new vessel as well as acceptance criteria for each test and trial requirement These criteria must be met for the owner to accept the vessel The specification also contains requirements for the documentation that must be delivered with the vessel to properly support the vessel throughout its life Because of the importance of the specification and the drawings referenced in it, it is carefully reviewed prior to the completion of the design phase In this review process, specification and drawing integration is emphasised to ensure that there are no conflicting requirements between sections of the specification and/or the various drawings
Products of the design team during the contract design phase would include the following:
making small changes
Trang 10● Accommodation space arrangements
The design phase requires proper planning Many designs are commenced on ad hoc basis and there is little or no opportunity for formal planning For each subsequent phase, however, formal planning before the start of the phase is essential The work effort in each task area must be defined including the approach to be taken, the inputs required from other task areas, the deliverables or products to be created, the work schedule including dates for inputs, outputs and intermediate milestones and finally the labour hours and resources required Resources may include computers, facilities, funds for model construction and testing, etc
An overall top-level design schedule needs to be created which must address intermediate project milestones at which the design baseline will be formally updated as well as the dates for major reviews of the entire design Individual plans for each task area must be integrated within this overall plan and with each other Emphasis must be placed on the interfaces between the various elements The dates for the exchange of interface data must be scheduled such that there is sufficient time to complete the design of the affected elements
A Gantt chart or similar means of scheduling tool needs to be developed and regularly updated in response to any irrecoverable losses of time or to milestones being reached ahead of schedule
The design project’s critical path needs to be identified which will determine the probable entire timeline for the design project
A very effective design programme control tool is the in-process design review At these formal reviews the individual responsible for a specific element of the design presents the design approach, status and current design configuration In attendance is the project management nucleus and other members from the project team responsible for the design of elements or subsystems that interface with the element under review Frequently misunderstandings regarding the interfaces between elements are identified and resolved immediately, or the approach modified The project manager has the opportunity in such reviews to verify that the subject design effort is on track and that no attractive design options are being overlooked
not prepare thoroughly
the point where subject meet and affect each other
likely to happen
centre part of sth