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Concept design is the first part of basic design, followed by preliminary design. It turns the mission requirements into the characteristics of the systems, developing two or more design alternatives from which a design is selected in accordance with specified criteria.
Development of performance requirements, or system capabilities, from the mission requirements.
Determination of the principal characteristics of the systems required to achieve these capabilities, which enable new construction systems to be designed and existing systems to be selected and altered if necessary.
Estimation of capital and operating costs of the systems.
Identification of one or a few mission systems from among a series of alternatives which optimally meet performance requirements to the extent possible considering design constraints acting.
The system discussed here includes the total system which is also called the mission system and its supporting systems. The supporting systems provide the submersible with shore-based facilities, housing maintenance, repair and administrative activities, transportation, launching and retrieval services, navigation, and even with land-transport vehicles, air-transport vehicles, seafloor-based transponders, and submarines. The submersible itself and other systems should coordinate with each other in order to achieve the mission in the most effective manner. Therefore, it is important to consider the series of individual systems as a whole and take their interaction into account.
It is often convenient to describe a system as isolated from its environment by a boundary for the purpose of studying its internal behavior and interaction with its environment. A mission system is designed to serve one or more underwater missions. The boundary of the mission system encloses individual or systems, each enclosed by its own boundary, illuminating the fact that the mission is completed by a submersible supported by other systems.
Many mission systems are designed in the beginning with most of the potential systems already existing and some nonexisting. Existing systems require from no to extensive alterations to convert them to systems, within equivalent amounts of design effort, construction, and costs involved. As for nonexisting systems, they must be designed and constructed “from scratch” and are expensive among all the systems.
There are many design constraints imposed on the mission system and its individual systems. These constraints can be categorized into three kinds including mission external design constraints, mission internal design constraints, and design criteria.
Mission external design constraints (MEDC) come from outside and are external to the boundary of the mission system, which means that they are independent of all mission considerations. The sources of MEDCs may include environmental, technological, economical, legal, sociological, physiological, and psychological. Some of MEDCs cannot be changed by designers, for example, environmental factors like the speed of current and the height of wave cannot be determined by the engineers. Some of them, however, can be controlled by designers. For example, during the process of designing the hull, the material, one of the technological factors, can be selected by the designer. Once the material has been determined, the following stages will be constrained by its characteristic.
Some of sources of MEDC will change as time goes by. For instance, the technology or the policy of the law at the stage of construction may be different from which when being designing. Some of these changes will have a great impact on the procedure of design. Therefore, it will be better for a designer to take it into account.
Mission internal design constraints (MIDC) come from inside and are internal to the boundary of the mission system or any lower-level system. The sources of MIDC are the interaction between the systems that influence each other. Some constraints between two systems are weak, but some are strong.
Design criteria (DC) afford standards for judgments regarding design procedures and for selecting system components (Allmendinger 1990). The use of specific structural formulas and the requirements of critical system components based on state-of-the-art technology are examples. The examples of design criteria also include the basis for optimization, cost-effectiveness, or minimum weight. And these design criteria may be formulated by the owner, the designer, or the classification society.
Concept design turns the mission requirements into the characteristics of the systems. It includes feasibility studies and completion of the optimum designs. Feasibility studies are concerned with the development of those performance requirements and associated system characteristics, which have significant impact on the cost-effectiveness optimization process. Completion of the optimum design, however, involves developing other major performance requirements and characteristics which are essential in defining systems but do not have significant impact on the optimization process (Allmendinger 1990).
Feasibility studies produce a series of mission system alternatives, all of which meet the demand of mission requirements and are technically feasible. One or some of these alternatives will be chosen to be the input of preliminary design stage. The number of the alternatives depends on the complexity of the task and the implication of optimizing techniques. Each alternative is composed of a unique combination of systems, each of which has its unique capabilities, characteristics required to achieve these capabilities, and cost associated with providing these characteristics. Certain unique systems may appeal in more than one combination, but individual combinations are not duplicated in other alternatives. Combinations of systems that make up the mission system alternatives may vary in number, capability, and state, all of which are related to the functions required to fulfill the mission tasks, the time for accomplishing these tasks, and even the economic benefits.
Approaches and Techniques
As is shown in Fig. 2, the design spiral consists of spokes and loops. The spokes stand for design considerations including performance requirements, arrangement, geometry displacement, hull structure, propulsion plant, electrical plant, command and surveillance, auxiliary systems, outfit and furnishings, energy summary, weight displacement, cost-estimate, and so on. The loops represent design iterations with the refinement of the design increasing as the loops spiral inward. The points identified alphanumerically stand for certain stages. For example, 2B means the arrangement in the second loop.
Concept design feasibility studies are somewhat confined to the A and B loops of design spiral in the Fig. 2. The A loop is mainly considered with the approximate sizing of the submersible and utilize empirical formulations and similar design data extensively. Three major steps are involved in the sizing process. Firstly, select the geometry and the major elements of the SWBS (Ship Work Breakdown Structure) systems. Secondly, obtain first estimate of sizing data for these systems. Thirdly, summarize these data to estimate the size parameters of total weight and displacement in the neutral buoyancy condition and the total cubic.
Concept design procedure from 1A to 12B based on Fig. 2 will be discussed in the following part.
A loop Step 1 – Performance Requirements
- 1.Task site
Area of the world
Seafloor or water column site
Maximum operating depth
Point or separated points – site at one point or more than one point separated by certain distances
Line – site along lines of specified distances, as would be the case in a pipeline inspection mission
Area – site over an area of specified dimensions, as would be the case in a seafloor area mapping mission
- 2.Task work
- b.Work objects
General – a general description of the work object such as a buried pipe, an open-frame fixed platform, or a wet-well head
Specified – as extensive information as possible needed to formulate adequate maneuvering and mission subsystems performance requirements facilitating proper vehicle positioning, vehicle orientation, and mating of tools and other equipment – a critical mission requirement in affecting the productive time of a submersible
- c.Task description
Work to be performed – data to be acquired, nondestructive inspection to be performed, values to be replaced, and so forth
Loads to be transported – from water surface to site or site to water surface or both. These loads are part of the overall payload which also includes weights of all items used exclusively in performing mission task work
- d.On-board personnel – required to accomplish certain work
Type – one atmosphere or ambient pressure types
Response time – time allotted for the submersible to reach to the work site, if critical in performing mission tasks
A loop Step 2 – Arrangement
Firstly, the submersible may be considered as consisting of the pressure hull, envelope, and all other forms of structures comprising it. In this stage, the designer should determine the type and number of the pressure hull which includes one-atmosphere type and ambient pressure type, the type of envelope which includes enclosed one and non-enclosed one. And the location of other items should also be considered at this stage. Inside the pressure hull, there are personnel (in HOV) and all items of equipment to which they must have ready access. The items outside pressure hull include propulsion unit, high-pressure air bottles, main ballast tank, and so forth.
A loop Step 3 – Geometry
- 1.Pressure hull
If the designed submersible works in shallow depths, then its shape is governed by hydrodynamic and arrangement considerations.
If the designed submersible works in deep depths, then its shape is governed by structural considerations.
Dimensions are estimated from volume which pressure hull must enclose.
Enclosed envelope – envelope streamlined in direction of motion for relatively high forward or vertical speeds or both. If not streamlined, it should be a fair form to reduce the potential for entanglement and fouling
Open-frame envelope – shape usually approximates a rectangular prism
Dimensions – the dimensions of length L, breadth B, and depth D, which can initially be estimated from the similar designs
Displacement of submersible
Steps 4–9 in A loop are categorized as SWBS (ship work breakdown structure) groups. Two of the sizing procedures should be followed in this portion of the A loop: (1) select major components of systems to be used with the particular design alternative under study and (2) obtain first estimates of sizing data for the systems selected.
A loop Step 4 – Hull structure
Fixed ballast and buoyancy are included. These systems can provide for neutral buoyancy, zero trim, adequate stability, and a weight margin in design. The pressure hull is the main, pressure-resisting shell structure of the submersible. This hull is usually a ring-stiffened cylinder, closed with hemispherical heads, for shallow-depth submersible although other geometries may be used. An unstiffened sphere, or combination of spheres, is used for deep-depth submersibles.
A loop Step 5 – Propulsion plant
The propulsion plant is composed of all systems required to move the submersible in the ahead and astern directions under normal or emergency conditions. The propulsion power source which consists almost all of the batteries for untethered submersibles is included in this group.
A loop Step 6 – Electrical plant
The propulsion plant is composed of systems necessary to provide and distribute electric power to meet all of the submersible’s needs, excluding propulsion. It is the nonpropulsion power sources for auxiliary, including electrical power generation system, power distribution system, lighting systems, and some special purpose systems.
A loop Step 7 – Command and Surveillance
The nature and the extent of systems composing command and surveillance system vary greatly depending on demands placed on them by mission performance requirements. It includes command and control system, navigation system, communication system, surveillance system, and special purpose system.
Human systems (especially in HOV) – It is composed of crew and noncrew and personal effects brought on board.
Air, gas, and miscellaneous fluid systems, which are required to expel seawater from ballast tank and to provide hydraulic power.
Static control systems – Care must be taken that items associated with these systems which vary during the dive, such as seawater in the main ballast tank, are accounted for as loads under load to submerge.
Dynamic control systems – Only thrust-producing systems used exclusively for maneuvering are included in this subgroup.
A loop Step 9 – Outfit and furnishings
The weight and displacement are minute in these systems compared with others. And the space requirements of them should also be carefully considered. The size of ladders, lockers, seats, and hull insulation has great influence on the pressure hull volume and, hence, has a cascading effects on other design considerations.
A loop Step 10 – Energy Summary
The power-energy requirements for the SWBS systems should be summarized and the sizing data for the electrical and pneumatic energy storage systems should be estimated. At this point, the following should be considered: dive profile, bottom-work time, endurance, power users, power requirements, power totals and time, reserve energy, emergency energy storage, and energy storage capacity.
A loop Step 11 – Weight-Displacement-Center Summary
At this point, summarize weights and displacements of SWBS systems and their loads and achieve the submerged design condition criterion of neutral buoyancy, in which total weight is equal to the displacement.
A loop Step 12 – Cost Estimate Summary
Summary of cost estimates is deferred until Point 12B.
Above is the complete procedure of the A loop. The B loop procedures begin to develop the submersible and its SWBS systems in detail in order to refine sizing data, obtain cost estimates, and obtain assurance that design condition criteria of neutral buoyancy, zero time, and adequate stability can be acquired.
B loop Step 1 – Performance Requirements
Examine performance requirements according to sizing data created in the A loop. The requirements should remain the same unless these data indicate that certain requirements are excessive and may lead to unfeasible design. In this case, the designer should consult with the owner to make some changes to the requirements.
B loop Step 2–3 – Arrangement and Geometry
At this stage, the first definitive view of the submersible is obtained, and the major components of the SWBS systems are located for the first time. These procedures are promoted by considering the two points together.
B loop Step 4–9 – The SWBS System Groups
These steps develop systems in sufficient detail to permit refinement of sizing data and close estimates of cost data to be made. More precise formulations and direct calculations are used in this portion of the B loop, which begin to analyze each system, breaking it down into its parts for study, increasing in detail as the design progress through the inner loops of the spiral.
B loop Step 10 – Energy Summary
It refines electrical power-energy profile and pneumatic storage system based on more precise B loop SWBS data.
B loop Step 11 – Weight-Displacement-Center Summary
Using the more refined sizing data, it obtain a more accurate estimate of fixed ballast or buoyancy, a check on the vertical distribution of weights and displacement necessary for adequate stability, and a check on the longitudinal distribution of weights and displacements required for zero trim.
B loop Step 12 – Cost Estimate Summary
It summarizes estimates of first and annual operating costs associated with the SWBS systems selected for a particular design alternative (Allmendinger 1990).
Systematic Parametric Analysis Approach – Optimization Programs
These programs permit a very large number of concept design alternatives to be investigated, which increases the probability that the optimum concept design will be identified. Design procedures are formalized by establishing mathematical relationships between dependent design variables and independent design variables or parameters. These relationships or parameter equations in the program permit rapid evaluation of design parameter changes on the dependent variables. And the explicitness of optimization program is useful in facilitating discussion between owners and designers regarding any aspect of the mission requirements or the design in question.
Concept design is an irreplaceable step of the design of submersible. Christ and Wernli (2014) dis reviewed the technology of ROV and then delve into the theoretical basis for ROV operations (including stability and drag computations) and also reviewed the standards surrounding the industry in general. Correa et al. (2015) introduced architecture for the conceptual design of remotely operated vehicles (ROV). Guo and Lin (2011) developed an underwater vehicle which can adjust its attitude freely by changing the direction of propulsive forces. Li et al. (2011) introduced the design of P-SURO AUV which is a test-bed for developing underwater technologies. The team of biologists and engineers considered the concept design of a bionic autonomous underwater vehicle (AUV) that uses the pectoral fins to achieve high maneuverability (Fish et al. 2003). ARV, a hybrid kind of submersible, can be considered as the combination of ROV and AUV. The design of Nereus (Bowen et al. 2008) is an important attempt of the design of ARV.
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