The ultimate approach for General Arrangement Definition

Transcription

1 The ultimate approach for General Arrangement Definition Rodrigo Perez (M) and Veronica Alonso 1 1. SENER, Madrid/Spain General Arrangement Drawing is a communication language that uses graphics to represent principally: volumes, spaces, compartments, bulkheads, hull forms, decks and main equipments. The general arrangement of a vessel can be defined as the allocation of volumes for all the crucial functions/operations, correctly synchronized for position and access. The well-organized operation of a ship depends upon the proper arrangement of each individual volume/space and the most efficient interrelationships among all compartments. It is vital that the general arrangement of a ship be usefully, practically and cost-effectively developed with respect to key factors that influence construction and operation cost, in particular the manpower required to operate the vessel. It is essential for those who are involved in shipbuilding industry to understand new tools for this kind of vessel drawing and know how to draw them, saving time for the rest of the process of ship design. In this paper it is showed, for first time in a conference, a new module dedicated to definition and management the compartment arrangement of a ship. Compartment arrangement of a vessel is based on the definition of its spaces. Each space is represented by its 3D model. Spaces contain further information than the geometric one, been able to set different user attributes to them or to their limits. 3D model of the spaces is generated taken as reference the surfaces of the ship as well as auxiliary geometry. It is also possible the definition of spaces from 2D drawing in a specific definition environment. Finally, this compartment arrangement is available for hydrostatic and stability calculations. KEY WORDS: Ship design, CAD System, General Arrangement. NOMENCLATURE CAD CS GA FGA Computer Aided Design Classification Societies General Arrangement FORAN General Arrangement INTRODUCTION The ship general arrangement is one of the main tasks of the initial design. Designers must meet all functional and operational requirements and, at the same time, comply with all applicable regulations. Most of the cost related to manufacturing and operation of a ship is committed in this early stage, therefore it is paramount to define the most reasonable ship general arrangement with the highest accuracy possible. This rational process of finding the better design requires the evaluation of multiple feasible alternatives. So it is very important to use a fast, flexible and reliable design tool. This paper describes the tool developed by SENER, based on its dual experience as ship designer and shipbuilding CAD developer, as well as on the feedback from its customers. FUNCTIONAL REQUIREMENTS Regarding the definition of the general arrangement and the reuse of data, different concepts are required during the stages of the design and operation of the ship. Early Design Stage Traditionally, the compartments have been treated by CAD systems as basic geometric data to make naval architecture calculations (volumes, hydrostatics, ) and evaluate loading and flooding conditions, adding generally just a few attributes (permeability, filling percentage, cargo density, ). Nowadays, to allow the seamless integration throughout the ship design cycle, other concepts must also be taken into account at this stage, including: Tight correspondence between ship functions and compartments Assessment of design by multiple criteria Space reservation and weight management Use of compartment geometry for analysis, simulation and virtual prototyping tools (noise propagation, fire control, evacuation routes, ) Creation and handling of user-defined attributes (firefighting, insulation, vulnerability, ) In addition, the integrated approach to compartment management should be used for an early estimate of material and production cost, and concepts such as volume, weight, painting areas, welding lengths, insulation must be addressed. So the easier definition of compartments taking in mind multiple considerations, and the possibility to handle intelligent data about them are the key requirements at this stage. Basic and Detail Design Stage During the detail design stage, the most important requirement is the reutilization of early design work to create the ship 3D Perez The ultimate approach for General Arrangement Definition 1

2 model and to generate all the outputs for fabrication and assembly. At the beginning of the project the definition of the ship takes in consideration the operational point of view, distribution of compartments, volumes, spaces, etc. As the ship project evolves into the basic and detail stages, it is necessary to organize the information according to the build strategy, that is, by assembly or block to fit the shipyard production capabilities. However, once the ship has been assembled, the concept of construction block makes no sense anymore and the compartment is again the key concept to organize the ship data. Typically required concepts at these stages regarding the general arrangement definition refer to an intelligent generation of compartments that can be reused in the detail design stage. In addition, at this stage it is necessary a more accurate calculation of painting areas, welding characteristics, scheduling, checking of accessibility, etc Life Cycle Support The cost of designing and building a ship is relatively small compared with the cost of operation and maintenance throughout the ship s life cycle. In this regard, the integrated approach allows designing more efficient ships as a compromise solution of theoretically optimal solutions concerning cost, safety and performance. It also provides an excellent support to calculate removal paths, determine evacuation routes or train crew, to mention just a few applications. DESIGN APPROACHES Compartment design and definition of ship s general arrangement used to be done by using 2D drafting tools combined, but not integrated or poorly integrated, with other calculation and analysis tools. Recent evolution of the 3D CAD has led to a new approach for compartment design, based on the generation of an early 3D model of the ship, including ship compartments. One of the best advantages offered by FGA is the smart combination of those 2D and 3D approaches, as it will be described. The 2D Approach On the 2D or traditional approach, designers work with standard drafting tools on a set of views of the ship, typically an elevation view and several deck plant views, to draw the ship s general arrangement. Libraries of 2D views or symbols of equipment and accommodation items are also used. Figure 1: Basic Design: the 2D approach versus the 3D approach Some advantages of the 2D are the possibility of starting from scratch, or with very little information available, and the ease of small modifications, directly made on a drawing. Other advantage is that the 2D tools are widely used by all designers. Main drawbacks refer to the little intelligence associated to the compartments and general arrangement, and the lack of possibility to reuse or integrate the information with other calculation and analysis tools. The possibility of introducing errors and inconsistencies is another important drawback. The 3D Approach On this approach, the compartments are generated as solids, based on or referred to the main surfaces of the ship (hulls, decks and bulkheads). The objective is to define not only the geometry of the spaces, but a complete product model including the ship general arrangement and a hierarchical tree structure of ship compartments with associated attributes. 3D layout techniques are used in combination with libraries of predefined models of equipment and accommodation items, to complete the ship general arrangement. The main advantage is that the designers can build an accurate and practical 3D product model of the ship general arrangement from the very beginning, including intelligence and attributes associated to compartments. Most significant drawback is that the general arrangement definition is more time consuming in the initial stages, when it is necessary to perform many modifications in layout of compartments or when not too much 3D information is available for equipment and accommodation items. The FGA Approach As mentioned, FGA combines in a single tool the advantages of the 2D and the 3D approaches, removing most of their restrictions and drawbacks. This combination of 2D and 3D functionalities and techniques was already adopted in previous accommodation design modules of FORAN. The designers can work indistinctly in two different but synchronized environments, 2D (deck plant view) and 3D (ship model), switching from one to the other in accordance with their own preferences, availability of data, or particular ease of definition. Working in 2D, the 3D model will be built as the Perez The ultimate approach for General Arrangement Definition 2

3 consequence of a drawing; whereas working in the 3D space, the 2D environment will be kept coherent as a symbolic representation of the ship being defined. The 2D tools are used for quickly defining or modifying the limits of compartments and accommodation spaces on a deck plant view, or when there is not enough 3D information on equipment and accommodation items. It is relevant to mention that all data generated is stored in a single database in FORAN. This allows the reuse of information in further stages of the design. In addition, it is possible to work in a complex collaborative or distribute design environment. FGA COMPARTMENT DESIGN TOOLS The Ship Main Surfaces The normal starting point in the compartment definition by FGA is the ship surface model, made up of the molded surfaces of hulls, decks, bulkheads, appendages and superstructures. The geometrical representation for all these surfaces is a collection of trimmed NURBS and Bezier patches, ruled surfaces and implicit surfaces such as planes, cylinders, spheres, cones and torus. The surface model may have been created by FORAN surface definition modules (FSURF and FDESIGN) or imported from third-party systems by using proprietary or industry-standard formats, such as IGES or STEP AP-203 and AP-216. The preliminary compartment layout could be described by the internal volumes defined by the intersection of those molded surfaces. Inside these volumes, FGA allows the definition of auxiliary planes, limits and subdivisions to refine the compartment arrangement, thus creating all necessary locals and rooms. 3D Definition Methods The basis of the 3D compartment definition is the selection of a set of surfaces or limits that enclose a particular volume. If the surfaces may define more than one volume, the user can choose the intended solution by means of a bounding or enclosing box, selecting a reference face, an edge or an inside reference point. In most cases, the compartments are limited by six surfaces oriented as per ship s reference system: aft and fore on the x axis; port and starboard on the y axis; and lower and upper on the z axis; for instance, a hold limited by two transverse bulkheads, a longitudinal bulkhead, the inner hull, the double bottom and the main deck. Yet FGA permits to define any kind of compartment by using a set of general surfaces, for instance, a fore peak limited by the external hull, the main deck and the collision bulkhead. In any case, the intersection curves are calculated to obtain the compartment edges, which trim the surfaces to give as a result the compartment faces. This definition method is particularly useful when the space dimensions must be modified frequently: not only the parametric surface, but also the adjacent surfaces, and all model affected, are automatically readapted to the new parameters. 2D Definition Method According to the traditional way of working, the compartments are defined on plan views of existing decks. For this purpose, FGA uses the concept of working deck, which may be either the whole deck surface or a part of it. When the working deck is created, FGA requires the selection of an upper deck or a height value as a reference; if needed, several decks can compose this upper limit. Using these working decks also permits several designers to work concurrently on the same ship s deck. Having as a reference the fixed geometry, that is, the deck contour and the bulkhead intersection lines, the user can define auxiliary geometry as the reference for other compartment limits. Thus, the compartment definition becomes an easy process: in most cases by a single click to select a closed 2D contour on the working deck. The geometrical definition of a compartment can be enriched by assigning a set of user-defined attributes, for instance type or functionality. Topological Links The compartment definition is based on the ship molded surfaces, which compose a fully topological surface model. Any modification in these surfaces can be automatically propagated to the definition of compartments. FGA recalculates the compartment geometry, starting with the deck contour and the bulkhead intersection lines, stored on the working decks, and then, following a top-down process, the user-defined auxiliary geometry. The Solid Model As a geometric and topological object, the compartment is represented with as solid model internally defined by a boundary representation (B-rep), the limits of the solid model being a set of connected trimmed surfaces. The faces of the solid are given by the ship molded surfaces and the rest of compartment limits defined with auxiliary geometry. The edges of the solid model correspond to the intersection of the selected surfaces as limits of the compartment. Parametrical Spaces Vertical trunks, staircases, tunnels are examples of special types of space that can be defined by FGA using predefined parametrical objects such as boxes, cylinders, spheres and cones. Perez The ultimate approach for General Arrangement Definition 3

4 This is usually made by positioning existing 3D models, previously created, in the compartments and deck areas of the vessel. If only 2D information is available, it is also possible to perform a preliminary layout of the existing 2D equipment views on the corresponding deck areas. FORAN includes multiple functions to define accurately and quickly 3D models of equipment and other items: by combining parametric objects (cylinders, cones, nozzles ), by sweeping operations (of an object along any space curve), by transformations, or by importing from other systems or directly from manufacturer s catalogues. Figure 2: View of compartments in the solid model From the solid model defined by the boundary representation, FGA triangulates every face. A special treatment is used for connecting the triangles on the calculated edges in order to avoid gaps on face limits. The solid model is a powerful basis for advanced visualization, accurate naval architecture calculations derived from geometrical properties, and searching (for instance, compartment where a given structural, outfitting, or accommodation element is located). Graphic Interface FGA features an advanced graphic user interface, including multiple views, projections and rendering methods such as wireframe, shading and hidden lines removal or dotted, and different levels of translucency / transparency for every object. A general conic view allows the user to walk through the compartments to check the design, a feature particularly useful when equipment and accommodation elements are visible in the scene. In the graphical 3D environment multiple elements can be selected and highlighted for further application of any kind of operation or calculation procedure. Calculation of Properties The calculation of compartment properties takes advantage of the solid model definition and the advanced triangulation of faces. As a result, typical values such as volume, inertia, center of gravity coordinates, and surface area of boundary surfaces are calculated with very high accuracy. In case of special spaces like tanks, the benefits of the use of a triangulation method is shown in the free surface effects at intact ship stability when inertias are calculated. The solid model can be intersected and subdivided by a plane for the calculation of the main properties of the resultant volumes. PRELIMINARY LAYOUTS Apart from the definition of ship compartments, to complete the ship general arrangement it is also necessary to carry out the preliminary layout of main equipment and accommodation items. Figure 3: Preliminary layouts The 3D model of equipments can be defined with different levels of detail or representation, simpler for initial design, more complex for detail design, and are organized into hierarchical libraries applicable to different projects. Dismounting, safety or operational areas can be included as part of the model definition and can be switched on or off during the design process. A macro language is also available to facilitate the definition of systematic series of models. The layout of equipment and accommodation items is simply made by selecting a model in the library and positioning it on the corresponding compartment or deck area. The equipment items can be topologically positioned as regards other ship elements, such as the frame system or decks. Space reservations can also be made by means of geometrical macros. In addition, it is possible to perform a preliminary layout of the ship main distributor systems by defining the geometry of the pipes and ducts. If needed, other FORAN modules can supplement the information generated by FGA by incorporating into the ship model auxiliary structures such as foundations, ladders, gratings or non-structural tanks, which can be easily defined as a combination of plate and profile parts or by using a macro language. These auxiliary structures are also stored in hierarchically organized libraries open to different projects. FGA has specific features for accommodation layout, allowing a fast and topological definition and modification of walls, panels, rooms, cabins, windows, holes and many other characteristic objects. As noted, FGA builds a 3D solid representation of the objects based on their 2D layout on the decks and the height Perez The ultimate approach for General Arrangement Definition 4

5 between decks. Actually, FGA will supersede the previous FORAN accommodation design modules. DRAWINGS GENERATION Drawings for all design disciplines in FORAN (initial design, hull, outfitting and electrical) are managed by FDESIGN module. FDESIGN generates drawings based on FGA entities, either to represent a single compartment, a group of compartments, for instance engine room arrangement, or the complete ship general arrangement. The drawing may contain any combination of selected elements of the 3D model of the ship and that can be represented by means of: Main orthogonal projections Sections by any plane Perspective views with any orientation A set of user defined templates permits to customize the views generation and the final aspect of the drawings. Combining a scripting language based on the standard ECMAScript and FORAN intrinsic functionality, FDE allows the designer to create and use new commands, access the product model database, and generate fully customized reports and other documents. In parallel with the development of FGA, the development environment has been enhanced to permit the access to space and compartment trees and associated data. The most important compartment-related functionalities available within FDE can be divided into three main groups: Geometric spaces: including not only the purely geometric characteristics, such as volume, center of gravity, area of boundary surfaces, but also hierarchical or relational dependencies, such as topology, volume addition or subtraction. Compartments: the values of any user-defined attributes may be inquired and modified by user programming. General arrangement elements and space reservation, which are defined in a parametric way and therefore easy to be handled by scripts. One of the main functional requirements of FGA has been the fast verification of design in accordance with the rules of classification societies, IMO and flag administrations, as a further step towards the so-called rule-based design. The FGA user may, by combining the different features of FDE, obtain tailor-made reports with compartment related data, for example a document with the volume and center of gravity of spaces grouped by type of cargo. Figure 4: Drawing generation in FDESIGN Drawings are generated directly from the 3D product model. The 2D entities that represent the product model elements are linked to the 3D elements and are always updated with the latest version of the product model. A symbolic representation is possible and different visualization methods are available. Additional information (labels, dimensions, including ship reference, bill of materials, texts) can be added drawings but remaining linked to the product model elements. Drawings can be regenerated automatically after changes have been made in the 3D model, including labels and dimensioning. DEVELOPMENT ENVIRONMENT With the main goal of allowing users to customize the system, add new capabilities and automate processes frequently repeated, FORAN features an integrated development environment, called FORAN developed environment (FDE). FDE was conceived keeping in mind the ease of use in order to be practical and efficient for users of different levels. REUSE OF DATA There is a tight integration of all FORAN modules for end-toend creation and management of compartments. Ship designers can take advantage of FGA to integrate the objects created with this new module within a highly productive and intuitive design environment. Model Refinement Main FORAN modules such as FHULL, FPIPE and FCABLE can access the compartment trees and feature a set of common commands to perform compartment-related actions, including: Reading compartments selected from the trees Visualizing the compartment 3D solid model and its name Selecting compartment, either from the tree or from the graphic area Getting information about the compartment boundaries and characteristics Editing user-defined attributes Associating and disassociating elements to a compartment Retrieving information of a compartment pointing to one of its elements Including the compartment concept as an additional hierarchy in the build strategy Reuse of information in further stages: Basic and Perez The ultimate approach for General Arrangement Definition 5

6 Detail Design The generation of the general arrangement in a smart tool integrated with the rest of disciplines benefits the overall design process. As regards hull structure, the handling of FGA compartments provides more accurate painting area calculations and automatic assignment of welding procedures based on compartment characteristics, among other great advantages. All compartments can be visualized which is helpful when the detail design of structure is performed. Most elements included in the ship model during the preliminary layout, can be reused in later stages when developing outfitting and electrical detail layouts or coordination drawings, because any element positioned during the general arrangement definition is there in further stages. The equipment associated to compartments in the preliminary layout can be fully reused for subsequent assignment to zones and systems. Additional attributes can be entered at any time for a full definition of equipment. Equipment models could be also refined by using the different levels of representation. And this capability of reusing data is even more evident in the case of accommodation design, which, as mentioned, will be carried out integrally with FGA. REFERENCES Pérez, R. y Toman, M. (2014). An Innovative Approach for Hull Surface Fairing stages. COMPIT 2014 (13th International Conference on Computer Applications and Information Technology in the Maritime Industries). Redworth, United Kingdom of May. Pérez, R.; Alonso, V. y Valderrama, A. (2013). The use of a 3D CAD System for early design in shipbuilding. SPS 2013 (Ship Production Symposium). Bellevue, WA, USA. 6-8 of November. Doo-Jin Lee; Cebollero, A. y Pérez, R. (2013). New Approach to Design Transition in Korean Production Environment. ICCAS Busan, South Korea of September. Alonso, V.; Gonzalez, C. y Pérez, R. (2013). Efficient use of 3D tools at early design stages. COMPIT Cortona, Italy of April. CONCLUSIONS As described in this paper, FGA has been conceived with several main objectives in mind: To reduce the design time and improve quality in the early design stages avoiding errors and inconsistencies To facilitate the analysis and study of different design alternatives The general arrangement of a ship will evolve during the definition and production stages. A smart and integrated design tool facilities the task of introduce changes and keep it update to allow the reuse of data in other design stages FGA can be considered not only as a specific application for integrated management of ship compartments, but also as a complete general arrangement tool. FGA combines the advantages of designing in 2D and 3D environments, thus facilitating the design tasks in the early stages of design when the available information is poor or scarce. FGA provides specific functions for definition and management of ship compartments, together with other capabilities oriented to equipment and accommodation layout, all of them working on an advanced modelling and visualization environment. Combined with FDE, the integrated FORAN Development Environment, FGA permits to develop new functions and commands, from generating tailor-made reports through to implementing rule-based design capabilities. One relevant characteristic of FGA is the integration within FORAN shipbuilding CAD system, thus taking full advantage of other initial design modules, such as hull form definition and naval architecture calculations, and facilitating the reuse of data in other design stages. Perez The ultimate approach for General Arrangement Definition 6