Trans RINA, Vol 154, Part C1, Intl J Marine Design, Jan - Jun 2012
provide data for decision support for possible design changes required performance; and
to achieve
anticipate consequences of requested design changes.
The design-space may be as broad or as narrow as the designer desires, provided that it can be described numerically and that adequate numerical tools
are
available to meaningfully assess designs within the design-space. For example one scenario might be the assessment
of the speed, number, size and type
(monohull, catamaran, etc.) of vessels that should be used on a ferry route. On the other hand, a more specific design brief might have the vessel type specified as well as a preferred range of primary dimensions. Provided that the required performance measures can be reasonably computed from the chosen design parameters, and that these parameters can be automatically varied in a manner so as to produce viable design variants, it is feasible to undertake a design-space exploration.
The design-space investigation thus comprises four main tasks: identification of the performance measures of interest and the tools available to compute them (in this case, hydrostatics, resistance and sea- keeping);
definition of a suitable parametric model which can be used to generate feasible design variants from a small number of key parameters; numerical analysis of these variants
using
simulation tools to provide an assessment of the vessel performance characteristics of interest; the tools should be capable of providing sufficiently reliable data within available time and computational resource constraints; and automation of design variant
secondly to systematically vary desired the design,
control the analyses and collate the results for all the design variants.
Table 1: Principal particulars of the proposed vessel. min.
Length between perpendiculars [m] Beam on DWL [m]
Design Waterline, DWL [m] Maximum speed [kts] max.
68.00 72.00 14.00 14.25 3.9
Displacement: seawater @ DWL [tonnes] approx. 2200 Cruise speed [kts]
16.0 20.0
What is of interest and importance to the designer will depend on the individual project being undertaken. In this example, static stability as well as resistance and also passenger comfort when the vessel is under the influence of waves have been considered. The vessel’s calm water resistance was estimated using SHIPFLOW [2], whilst sea-keeping characteristics and hydrostatic stability were predicted using Seakeeper (SK) and Hydromax (HM) [3].
2. METHODOLOGY
In this section we shall look, in some detail, at the numerical methods
used different for the design-space
investigation. The key concept to take from this paper is the methodology;
substituted and different performance measures will be appropriate for different projects.
2.1 PERFORMANCE MEASURES generation,
analysis, results gathering and post-processing tasks.
Once the design-space exploration has been completed, the results are stored in response surfaces which may then be used for optimisation or as a basis for design decisions.
1.1 EXAMPLE APPLICATION
In this paper, the design-space exploration methodology is elaborated by an example application to the initial design of a luxury motor-yacht. The design requirements are for a twin-screw, displacement monohull vessel with principal particulars as given in Table 1.
The FRIENDSHIP-Framework (FFW) [1] has been used to:
firstly define the hull geometry in a parametric manner which can then be systematically varied; and
The first step is to determine the key performance characteristics that are pertinent to the design brief. Depending on the nature of the project this may include: calm
water resistance and powering; sea-keeping
performance; static stability; life-cycle cost, economic viability and return on investment; environmental impact; etc. During this step it is also important
to
establish whether there are suitable computational tools available to estimate these performance characteristics in the time available and the design parameters and level of design detail required by the selected tools.
2.2 PARAMETRIC MODELLING
The second step is to determine the parameters that are relevant to the design task and which adequately define the design-space allowing it to be explored to an appropriate level of detail. At this stage it is also important to bear in mind the performance measures which have been identified and the analysis methods which will be used because they can have a significant influence on the parameters that are of importance (there is no point in including the number of propeller blades as a parameter if this parameter is not required for the resistance / propulsion model being used). Furthermore, the number of parameters should be kept sensibly low to
C-18 ©2012: The Royal Institution of Naval Architects analysis software can be
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