This article was downloaded by: [Tech Univ of Lisbon Polo Ist], [Mr Carlos Guedes Soares] On: 05 July 2011, At: 04:34 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Ships and Offshore Structures Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tsos20
Product data model of hull structures and digital prototyping system for basic structural design a
a
J. M. Varela , Manuel Ventura & C. Guedes Soares
a
a
Centre for Marine Technology and Engineering (CENTEC), Technical University of Lisbon, Instituto Superior Técnico, Lisbon, Portugal Available online: 18 Feb 2011
To cite this article: J. M. Varela, Manuel Ventura & C. Guedes Soares (2011): Product data model of hull structures and digital prototyping system for basic structural design, Ships and Offshore Structures, 6:1-2, 3-14 To link to this article: http://dx.doi.org/10.1080/17445302.2010.480900
PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan, sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
Ships and Offshore Structures Vol. 6, Nos. 1–2, 2011, 3–14
Product data model of hull structures and digital prototyping system for basic structural design J.M. Varela, Manuel Ventura and C. Guedes Soares∗ Centre for Marine Technology and Engineering (CENTEC), Technical University of Lisbon, Instituto Superior T´ecnico, Lisbon, Portugal
Downloaded by [Tech Univ of Lisbon Polo Ist], [Mr Carlos Guedes Soares] at 04:34 05 July 2011
(Received 20 January 2010; final version received 20 February 2010) This work describes a computer system developed for the fast parametric generation of a 3D model of ship hull structure. The system is intended to be used as a tool for generating an initial product model of the hull structures at the basic design stage. The model provides not only the geometry of the hull and the main structural systems but also data describing the arrangement of plates and stiffeners of the component panels, including scantlings, spacing and materials. The objective of the system is to generate and help to evaluate alternative structural configurations, producing information on total or partial weights and centres of gravity at different levels of detail. For the intended purpose, the ease and speed of generation of a model is much more relevant than a high geometric accuracy, and so it was adopted as a simplified geometric modelling, representing curved shapes with polygonal approximations. The modelling concepts and methodology are discussed and the architecture of the system is presented, describing the main components. Finally, some results are shown from the partial modelling of a real ship that was used for testing and validation of the system. Keywords: data model; ship product; digital prototyping
Introduction Existing Computer Aided Design (CAD) systems present some limitations concerning the generation of product data models (PDM). Generic CAD systems can produce detailed geometric models at the cost of extensive interactive work but without all the associated product data. On the other hand, specific PDM systems used in shipbuilding are mainly oriented to production and must provide high accuracy (Ventura et al. 1999). Therefore, these systems demand a lot of detailed and extensive input, which is not compatible neither to the time constrains nor to the degree of design development for their application during the basic design stage. A system targeting the initial stages of ship design should be able to produce a 3D PDM of the hull with reduced input. It should also be flexible enough to allow minor alterations of the hull form maintaining the same structural configuration or to evaluate alternative structural arrangements for the same hull form. This type of system can serve different type of applications, including for basic ship structural design, and it is necessary to ensure that there is a standard way of transferring the PDM to other applications (Guedes Soares and Brooda 1999). For example, such a system could provide much better estimates of the hull weight by comparison to the usual statistics-based empiric formulas from bibliographic references or to the accumulated historic data of the designer. Better estimates than the statistical ones result from two
∗
Corresponding author. Email:
[email protected]
ISSN: 1744-5302 print / 1754-212X online C 2011 Taylor & Francis Copyright DOI: 10.1080/17445302.2010.480900 http://www.informaworld.com
main reasons: first, they can take into consideration the actual configuration of the hull (number of bulkheads, number of decks, frame spacings, etc.) instead of only a set of main dimensions and a few additional parameters used in the correlation formulas; second, they would not be dated, i.e. dependent of the age and the configuration of the ships’ sample on which the statistics were based. In addition, they would provide the capability to divide the weights in several categories (by structural system, by plates and profiles, by planar and curved, by mild steel and high tensile steel, etc.). This type of analysis allows much improved production cost estimates of both material and labour. Research on the development of 3D models of hull structures during the basic design started more than 20 years ago with systems such as the BRITSHIPS2 developed by British Ship Research Association and Swan Hunter shipyards for the structural design (Forrest and Parker 1983). Since then many other systems have been developed for different applications such as evaluation of labour during the production stages (Bong et al. 1990), design and analysis of the structures (Jingen and Jensen 1982; Na et al. 1994), generation of models for finite element analysis (Kawamura et al. 1997), data exchange for class approval (Hwanga et al. 2004) and block division and process planning (Roh and Lee 2006). This work describes a computational system developed for the fast generation of a 3D PDM of a part or the totality
Downloaded by [Tech Univ of Lisbon Polo Ist], [Mr Carlos Guedes Soares] at 04:34 05 July 2011
4
J.M. Varela et al.
of the hull structure of a new or an existing ship. The system works with a minimal set of input data, and the resulting model has the level of details required for the intended purpose. Most of the system development was done in the context of being able to serve the purpose of supporting the activity of planning ship inspections, collecting automatically inspection data and being able to communicate with more detailed ship PDM (Cabos et al. 2008). In fact, inspection data may be used to update the data models existing in the classification societies and may even be required for subsequent repair activities in which case data exchange also needs to be considered (Ventura and Guedes Soares 2007). The paper is organised as follows. Section 2 presents the software system architecture including the main actors, their roles and relationships. Section 3 describes the simplified geometry kernel which defines the basic features to model efficiently the geometry of the hull structures. Section 4 describes the structural modelling kernel, including the main structural systems modelled and the high-level functions required and implemented to generate them parametrically. Section 5 describes the database used to store the generated data and how it can be used to perform data queries and analysis within the scope of the initial design phase. Section 6 discusses the benefits of using scripting features to generate automatically most of the hull structures. Section 7 describes the graphics user interface (GUI). Section 8 presents the results of the tests in a real scenario using a prototype of the software system. Finally, Section 9 discusses the conclusions and future work. System architecture The system has a modular architecture providing a set of functionalities identified in the use-case diagram of Figure 1. The identified functionalities can be grouped and assigned to independent system modules with a specific role. As shown in Figure 1, these modules may be divided into two main groups according to their role: system basic modules and client modules. Basic modules are the core of the system in which all the fundamental information is stored and functions to generate the model are defined. These are the simplified geometry kernel, the structural modelling kernel and the ship database. The remaining modules work as clients of the basic modules using their functions to get information or to perform specific calculations. The application user accesses the functions and data defined and stored in the system through the client modules. The diagram also emphasises the two fundamental features that must exist in the process: the ship structure generation and the ship data storage and management. The following sections describe the main characteristics of the system modules.
The system is based on the object-oriented concept and was entirely implemented in C++ programming language. To increase the flexibility of its future use, open source components were used as much as possible, without compromising the functionalities and performance of the system. Standards were used where possible, namely for the database (SQL), for the data model (STEP) and data exchange (XML, IGES, DXF) and for graphical representation (OpenGL). The system is intended to work either interactively or in batch mode, reading a command and data files and producing some output files. This latter behaviour is required to be able to be used as a part of some optimisation processes.
Simplified geometry kernel Because the required geometric accuracy of the model for the intended purpose is not high, a simplified geometry concept was adopted that consists in using linear approximations of the shapes, replacing curves by polygonal lines and surfaces by polygonal grids. In spite of this simplified geometry concept, the hull form can be imported from generic CAD applications into the system. Crosssectional curves can be imported into the system and converted into polylines. Surfaces can also be imported into the system and cross section can be computed from intersections with a set of parallel planes. In either case, a 3D mesh will be generated from the set of polygonal cross sections and it will represent the outer boundary of the hull. Basically, the geometric model of the ship is composed of panel-sets. A panel-set is a topological association of panels, each defined by a plane and a closed polygonal contour, as shown in Figure 2. An example of the subdivision into panel sets, panels and contours is also presented in Figure 2 for the case of a corrugated bulkhead. The bulkhead is composed of three panel sets: the upper stool, the lower stool and the corrugate. The corrugate is composed of several adjacent panels from portside to starboard (which do not correspond to the plates) and each panel has a closed contour. In order to improve the performance and robustness of the geometric operations required to generate the model (which are described ahead), panel sets are implemented with topology in the form of half-edge data structures described by Kettner (1998). The kernel was developed to provide only the elementary modelling operations for the generation of panel-sets. After an extensive survey of the typical hull structure configuration and of the existent methods for parametric generation of surfaces and polygonal meshes used in 3D modelling, three of those were identified as fundamental
Ships and Offshore Structures
5
Ship generation
Applying
Generates structural systems geometry
Applying
Downloaded by [Tech Univ of Lisbon Polo Ist], [Mr Carlos Guedes Soares] at 04:34 05 July 2011
> Simplified geometry kernel
Generates plates and stiffeners geometry Using Generates structural systems
> Scripting engine
Using > Structural modelling functions
Generates plates and stiffeners
Ship storage and management
> User
From Visualises data Into
> Graphics User Interface
Updates data
Into/From > Ship database
Imports/Exports HCM Models in XML format
> XML processor Figure 1. Use-case diagram and associated system modules.
and sufficient for building the simplified geometric model of the ship:
r sweeping, r intersection and r trimming. The sweeping method was selected as the most appropriate to generate the geometry of the structural systems parametrically. In fact, this method is very flexible because it uses free 3D lines for the generation of the meshes which are not restricted to any rules. By sweeping one or more cross sections along a path line, any existent geometry in
the ship can be created as long as the shapes of the cross sections and the path are defined correctly. As an example, the forward zone of the main deck generation is considered using this method. The user defines the sheer line along the ship which is used as the path line of the sweeping method, and a set of transversal lines are defined and positioned along the sheer to define the deck camber. These are used as the cross sections along the path as shown in Figure 3. Grey tonalities correspond to different panels generated by the method. As can be seen between Section 2 and Section 3, the sweep method between corresponding segments of two adjacent cross sections may
Downloaded by [Tech Univ of Lisbon Polo Ist], [Mr Carlos Guedes Soares] at 04:34 05 July 2011
6
J.M. Varela et al.
Figure 2. The geometric model of the ship is composed of a set of panel-sets, panels and closed contours. (This figure is available in colour online.)
generate more than one panel because the segments may not be coplanar. Simplified versions of the method using straight lines as paths and only one cross section are normally used to generate other structural systems such as transversal bulkheads or plain decks. Intersections between panels and panel-sets are mainly used to define path lines for the sweeping method. Simple path lines or lines which are defined by design parameters such as the sheer or the deck camber are not generated by intersections. However, trace lines of stiffeners or deck beams can only be calculated by intersections with the shell and the main deck, respectively.
Finally, the trimming feature is fundamental to remove the non-existing geometry adapting the shape to the defined boundaries. As a rule to avoid incomplete geometry and to simplify the generation process from the user point of view, the sweeping method always generates geometries that go beyond their boundaries. The trimming process is then applied using the boundaries as the cutting objects in order to achieve the final geometry. This feature is applied for almost all the panel-sets because their parametric definition normally includes a set of boundaries. The shell may also (and often is) be a boundary and hence a cutting object as shown in Figure 4 for the case of a longitudinal bulkhead, where the sequence of trims is presented in order to obtain the final structure.
Structural modelling kernel
Figure 3. Main deck generation applying the sweep method with a multi-segment path line and three cross sections. (This figure is available in colour online.)
A group of functions to model the basic geometry of each of the structural systems from a set of design parameters was developed on the top of the simplified geometric kernel. The main five types of structural systems considered are the shell, deck, bulkhead, web frame and girder. Modelling these systems is a two-step process: first, a generic structural system definition is specified and, next, instantiations of that system can be generated according to the definition and providing the required location(s). As presented in Figure 5, structural system definitions have two main different layers: the geometric definition and the stiffened panel(s) definition.
Downloaded by [Tech Univ of Lisbon Polo Ist], [Mr Carlos Guedes Soares] at 04:34 05 July 2011
Ships and Offshore Structures
7
Figure 4. The trimming feature is applied to remove the non-existent geometry of the transversal bulkhead that goes beyond the shell and the main deck.
Common data of geometric definitions for all structural systems’ definitions are the list of boundary elements, a list of opening definitions and the required parameters to apply the sweeping method on their generation, namely the path and section(s). An additional basic structure may also be provided if the path defined by the user is to be projected into this structure generating then the real path to be used by the sweeping. Paths and sections are defined in a local 2D coordinate system and then reoriented and translated to the final location depending on the type of structural system that is being generated. The remaining data provided by the geometric definition depend on the structural system being defined. Therefore, each type of structural system has its own definition template which is an extension of the generic structural system definition. The simplest cases of the specific geometry definitions are the deck and shell definitions. In fact, no additional information is required to the generic structural system definition. The girder definition requires an additional parameter that indicates the orientation. Every stiffened panel that does not fit in the bulkhead, deck, shell or web frame definition is modelled as a girder. Bulkhead definitions also provide an orientation which may be longitudinal or transversal. In addition, three types
of bulkhead definitions are considered: plane, corrugated and sandwich. The corrugated bulkhead definition provides a corrugate definition and two optional stool definitions whose parameters are according to the Hull Condition Model (HCM) described by Jaramillo and Cabos (2007). From the geometric point of view, web frames are subdivided into four transverse panels (Figure 6): portside and starboard panels, floor and deck beam. Each of these has its own definition, which is also an extension of the generic structural system definition. Where there are no physical boundaries defined by a limiting structural member, a boundary line is explicitly defined. The exception is the shell for which the base-moulded surface is a polygonal mesh generated from a set on input cross sections, each defined by one or more polygonal lines. Regarding the specification of the stiffened panels, the model defines the direction of the layout of the plates and the direction of the stiffening. Along each of these directions, sets of cross sections are defined, each associated with the respective plate-set or stiffener-set. Plate-set definitions define groups of adjacent plates with the following common attributes:
r quantity, r breadth,
8
J.M. Varela et al. Structural system definition
Geometric definition
Outer boundary definitions
Downloaded by [Tech Univ of Lisbon Polo Ist], [Mr Carlos Guedes Soares] at 04:34 05 July 2011
Openings definitions
Stiffener-set definitions define groups of adjacent stiffeners with the following common attributes:
r r r r r r r r
quantity, section type (flat bar, bulb, T bar, L bar, etc.), dimensions (which depend on the type of stiffener), spacing (between stiffeners), web direction, flange direction (when applicable), material and edge-cutout type.
Edge cutout definitions
Stiffened panel definition
Plate-set definitions
Stiffener-set definitions
Flange definitions
Figure 5. The structural system definition has two main layers: the geometric definition and the stiffened panel(s) definition. (This figure is available in colour online.)
r thickness and r material. Each plate-set definition may have several different groups with the same length given by the cross-sectional length.
Similar to plate-set, stiffener-set definitions may have several groups of stiffeners with the same characteristics. Also, the length of each stiffener-set is given by its cross section. An edge-cutout type can be associated with each stiffener-set. Edge cutouts are defined as closed polygonal shapes. The actual cutouts are generated on the panels crossed by the stiffeners. The final shape of those panels is obtained by polygon clipping (Figure 7). Figure 8 shows the most intuitive case of applying the concept for the case of the plates, which is in the cargo zone of the side shell structure. Normally, in this zone each cross section represents a column of plates to which is applied a plate-set definition with different groups of equal plates. The four plate sets have the same length which is defined by the cross section. The plate breadths of the first set are smaller than the second one. The plates of the second and third sets have the same breadth; however, their thicknesses are different. Finally, the fourth set which is composed of a single plate has different breadth and thickness. Naturally, this concept is also applied to the hull inner structure. Flanges are a minor structural part, but they can have a sensitive impact in the global weight. Therefore, flange
Figure 6. Web frames are composed of four panel sets: the portside and starboard panel sets, the deck beam and the floor.
Downloaded by [Tech Univ of Lisbon Polo Ist], [Mr Carlos Guedes Soares] at 04:34 05 July 2011
Ships and Offshore Structures
Figure 7. Generation of cutouts on panels by crossing stiffeners.
entities can be defined and associated with both girders and openings.
Ship data management The structure model of a ship, even if simplified, has many components and different uses may pose queries that are beyond those made available by the system. For the proposed system, a relational database (MySQL 2005) that supports the standard SQL language (Date and Darwen 1996) was adopted.
9
In order to make the widest usage of the hull data generated, a data model was developed that takes into consideration both the STEP AP218 standard (ISO 2004) and the HCM (Jaramillo and Cabos 2007), oriented to hull maintenance data exchange. The database stores all the information specified in the PDM including the structures’ definitions and instances, the hull cross sections defining the hull form and general data such as the ship main dimensions and the frame spacing table. When generated by the structural modelling functions, geometry and structures are immediately sent to the database by using specific functions of each structure class to store the data in the corresponding module of the database. The data, the amount of which is often too large to be kept in memory, remains available in the database to be accessed and used on the generation of subsequent structures that depend on the previous generated ones. Therefore, during the generation of the ship, input functions and queries to database are constantly being called by the structure generation functions. The query of a ship instance also provides some parameters necessary to evaluate the cost of different alternatives under study. The parameters considered are the following:
r Weights and coordinates of the centres of gravity, separately for plates and stiffeners;
r Plates’ weight divided into flat, curved and corrugated, while stiffeners weight divided into straight and curved;
r Painting areas; r Lengths of welding seams.
Figure 8. In the cargo zone, the concept of cross section and plate-set definition is visualised as a column of a specific length with different adjacent groups of plates with the same characteristics.
Downloaded by [Tech Univ of Lisbon Polo Ist], [Mr Carlos Guedes Soares] at 04:34 05 July 2011
10
J.M. Varela et al.
The results are computed and displayed for the regions of the ship selected in the tree view. Hull data can be exchanged in XML format in accordance with the HCM, developed to provide support for the hull condition assessment (Jaramillo and Cabos 2007), providing support for the planning, viewing and analysing the results from thickness measurement campaigns (Jaramillo et al. 2005). Therefore, although the user is able to export the entire ship, including structure definitions, using the GUI, the information is filtered internally and only the data that can be mapped into the HCM are exported. The same happens when a HCM file is imported. The structural definitions are not known (the model may have even been generated in another modelling system) and the structure members are mapped into the available ones according to a mapping table defined by the designer. If no correspondence exists in the mapping table, structure members are mapped into the other members table of the database.
Scripting engine The development of a ship hull product model can be taken to different levels of detail, depending on the intended use. A complete modelling work of a ship requires a lot of repetitive tasks (for example, when generating web frames with similar arrangement and scantlings, but adapted to the local hull shape) that may be performed by programmed loop sequences with the appropriate parameters. Nevertheless, there are always exceptions that must be dealt with in an interactive way. Thus, in order to improve the efficiency of the modelling work it is important for the user to be able to automate some of these repetitive tasks, avoiding human interaction. Moreover, concerning the modelling approach described above, the sequence of tasks is relevant to model the ship correctly. Thus, a script stores not only the information required for modelling but also the sequence of function calls. For this purpose, the system is provided with a scripting capacity. The modelling process requires high-level customized commands, which can access both the system modelling functions to generate the structures and the database to store and retrieve data. For this purpose, the Python scripting language was adopted (Python 2005) and extended with a set of new commands. These new commands were developed to perform specific tasks in the modelling process and can be classified by their functionality in four main groups:
r definition of global ship data, r definition of typical structural systems’ shape configuration and scantlings,
r geometric modelling operations to obtain the shape from the topological boundaries specification and
r creation of the actual instances of the structural systems.
The structure of a typical script is shown in Figure 9. Although an interpreted scripting language such as Python can be extremely useful for this type of modelling tasks, if not used correctly, it may become a severe bottleneck of the application and the user may experience many difficulties before even modelling a small part of the ship. This happens mainly because of the absence of efficient parsers to detect syntax errors or debuggers to monitor the tasks being performed on run-time. In order to minimise the drawbacks of using the scripting language, composed scripts are used to model the ship. This means that the user is able to divide the full script that models the entire ship into smaller scripts that may be called maintaining the same sequence. This approach also allows the user to test the smaller scripts and more easily detect eventual errors. Some rough script debug functionalities were also developed by writing messages to a log file, with the tasks being performed by the application while running each script. Extended scripting functions are used as wrappers for the structural modelling functions that are written in the application development language, which is C++. Thus, parameters provided by the user into the Python scripting functions are very similar to the ones provided internally to the structure generation functions. Graphics user interface Because of the eventual large amount of the components, the visualisation of a complete 3D model can be not only very time-consuming but also very difficult to perceive by the user, even with the shading capabilities. Therefore, the capability to display only the selected items and to control the type of representation is relevant when browsing the model. Plates and stiffeners allow different types of graphical representation, as polygonal lines (wireframe representations) or as their basic surfaces (surface representation), without thickness. Plates can be represented either by their boundary contour or by polygonal surface meshes. Stiffeners can be represented either by their trace lines or by a polygonal mesh. Another type of representation is available, in which the plates and stiffeners are represented with the respective thicknesses as meshed solids. Currently, this option is only implemented as a file export capability based on the DXF industrial standard format (Autodesk 2007). The 3D solid model can be imported in most of the existing CAD systems and provides the basis for the initial study of the layout of equipment and piping systems. Similar to the other modules or subsystems of the application, the GUI is naturally centred in the database where all the data are stored. Briefly, it allows the user to access, visualise, change and store the information contained in the database.
Ships and Offshore Structures
11
Start
Input main dimensions frame table
Downloaded by [Tech Univ of Lisbon Polo Ist], [Mr Carlos Guedes Soares] at 04:34 05 July 2011
Import hull form
Define templates of the main structural systems
Ship database
Define actual instances of the structural systems
Compute local geometry
Generate plates and stiffeners and store in database
End Figure 9. Logical structure of a generating script.
Three main types of visualisation and management of the database content are provided:
r 3D viewer, r 2D viewer and r hierarchical tree of the structural systems. The 3D window is a typical fly-through viewer in which objects with 3D graphical representation are displayed. The following types of objects are displayed in this viewer:
r r r r
hull form sections, structure members geometry, structures (plates and stiffeners) and measured points.
Figure 10 presents screen captures of the four types of objects displayed by the 3D viewer. As can be seen in Figure 10 as well as in Figures 12 and 13, different tonalities are applied to each plate and
stiffener to allow an easier perception of the structures that really interest for this type of application. Selecting structures (plates or stiffeners) in the viewer through the mouse cursor triggers queries in the database and gets additional information about the structure, displayed in tables, pictures, forms, etc. A typical drawing which is widely used in naval architecture to identify plates, stiffeners trace lines is the hull expansion. Therefore, the system provides the 2D viewer that represents the plates and stiffeners of the ship outer shell. For this purpose, the shell shape is expanded in the ship transverse direction, using the concept commonly used in the naval architecture drawings. A mirror of the data contained in the database is presented in a hierarchical tree allowing the user to visualise and manage all the existent objects. Even objects that do not have graphical representation such as the structural system definitions are visualised and accessed from the tree. OpenGL (Shreiner et al. 2005) was selected as the base engine for the graphic representation of the system.
Downloaded by [Tech Univ of Lisbon Polo Ist], [Mr Carlos Guedes Soares] at 04:34 05 July 2011
12
J.M. Varela et al.
Figure 12. 3D model of the tank generated for validation purposes in a measurement campaign simulation.
Figure 10. The 3D viewer displays four types of objects with graphical representation.
by their types. The selection of entities on the tree is the beginning of most operations carried out by the system. The selection of an entity on the tree implies the selection of all the child entities.
The user interface is of a typical windows-based application where commands can be given from hierarchical menus. Data associated with elements selected interactively on the graphic display can be viewed and edited through dialogue boxes. The main window of the application shows a tree view, which displays all the contents of the database organised
Validation and testing For the validation of the developed system, a set of test cases were prepared, specifying typical structural arrangements of the cargo area of two merchant ships, namely an oil tanker and a bulk carrier. Each of these ship types was selected because of some specific aspects of the inner structure shape and arrangements. The oil tanker modelled, a SuezMax with a double hull, allows checking the correctness of the generation of the web
Figure 11. The corrugated bulkhead is one of the structure members that requires specific modelling functions incorporated in the scripting language.
Figure 13. The large number of points measured by the crawler in the shell are imported to the system through an XML file and represented in the 3D model.
Downloaded by [Tech Univ of Lisbon Polo Ist], [Mr Carlos Guedes Soares] at 04:34 05 July 2011
Ships and Offshore Structures frames provided with openings. The longitudinal bulkheads can have horizontal or vertical knuckles. A typical bulk carrier was also modelled in order to test the modelling functionalities with some specific aspects such as the existence of corrugated bulkheads with upper and lower stools (Figure 11), as well as of the hopper and wing tanks composed of panels inclined in both the transversal and longitudinal directions. Finally, the system modelling, visualisation and data exchange capabilities were tested in a different context – the representation of an existing hull. This type of application sets a higher level of requirements because it is expected to reproduce some particularities of the structural arrangement in order to guarantee the correct mapping between the model and the existing plates and stiffeners. In the scope of the project ‘CAS – Condition Assessment of Aging Ships for Real-Time Structural Maintenance Decision’ (Cabos et al. 2008), a partial model of an existing tanker was developed to support the recording and visualisation of data from a thickness measurement campaign that was carried out in the real ship. Analysing the structural drawings and writing the Python scripts to conclude this task took about 3 days. However, modelling the complete cargo zone would take only a few hours more because of the similarity of the cargo tanks. On a PC the script runs in about 5 minutes, and the final result is presented in Figure 12. Measurements were performed using two different methods. For the inner structure, thicknesses were measured manually with an ultrasonic probe at pre-established locations. These points were introduced into the system by the user in real time immediately after the measurement. For the outer shell, a crawler robot was used to measure thicknesses, which were stored in an XML file and then imported to the system. Figure 13 presents the visualisation of the measured points for the second case.
Conclusions A system for the generation of simplified 3D models of ship hull structures was developed. The system, intended to be used as a basic design tool, was designed with a limited level of detail and accuracy in order to gain in terms of speed of visualisation and actualisation of the model. The prototype system demonstrated that for the level of detail required in this type of application, the geometry kernel may be very simple, composed of small subset of the features that are normally used in commercial 3D modelling applications. The hull model can be mostly generated automatically, by running a script file that populates the database. The resulting structures can be viewed either in wireframe or in surface representations or exported as a solid model.
13
Future developments of the system will increase the detail of the model both by adding new entities (e.g. flanges, brackets, compartments, etc.) and by further detailing the existing ones (e.g. adding attributes to the information on welding seams). Data exchange capabilities of the system will also be improved for possible interface with dimensioning systems based on classification society rules. Acknowledgements The present paper has been partially funded by the project ‘Condition Assessment of Aging Ships for Real-Time Structural Maintenance Decision (CAS)’, financed by the European Union through the Sustainable Surface Transport programme of the sixth framework programme under contract TST4-CT-2005-516561. The first author was funded by the Portuguese Science and Technology Foundation, through grant SFRH/BD/39312/2007.
References Autodesk Inc. 2007. Autocad 2008 DXF Reference. Available from: www.autodesk.com Bong H, Hills W, Caldwell J. 1990. Methods of incorporating design-for-production considerations into concept design investigations. J Ship Prod. 6(2):69–80. Cabos C, Jaramillo D, Stadie-Frohb¨os G, Renard P, Ventura M, Dumas B. 2008, April. Condition assessment scheme for ship hull maintenance. Proceedings of the Computer Applications and Information Technology in the Maritime Industries, (COMPIT’2008); Liege, Belgium. p. 222–243. Date CJ, Darwen H. 1996. A guide to the SQL standard. 4th ed. Boston (MA): Addison-Wesley Longman Publishing Co., Inc. Forrest P, Parker M. 1983. Steelwork design using computer graphics. Trans R Inst Nav Archit. 125:1–25. Guedes Soares C, Brodda, editors. 1999. Application of information technologies to the maritime industries. Lisbon: Edic¸o˜ es Salamandra, Lda. Hwanga H-J, Hana S, Kim Y-D. 2004. Mapping 2D midship drawings into a 3D ship hull model based on STEP AP218. Comput-Aided Des. 36:537–547. ISO. 2004. Industrial automation systems and integration – Product data representation and exchange. Part 218: Application Protocol: Ship Structures. ISO 10303-218. Geneva, Switzerland: ISO. Jaramillo D, Cabos C. 2007. Specification of HCM (hull condition data model). Deliverable report D1.3.1 from CAS Project. Jaramillo D, Cabos C, Renard P. 2005, Sep. Efficient data management for hull condition assessment. Proceedings of the International Conference on Computer Applications in Shipbuilding: ICCAS’2005; Pusan, Korea. Jingen G, Jensen J. 1982. A rational approach to automatic design of ship sections. Proceedings of Computer Applications in the Automation of Shipyard and Ship Design (ICCAS IV); 1982 June 7–10; Annapolis, Md.: New York, North Holland, p. 117–124. Kawamura Y, Ohtsubo H, Suzuki K. 1997. Development of a finite element modeling system for ship structures. J Mar Sci Technol. 2(1):35–51. Kettner L. 1998. Designing a data structure for polyhedral surfaces. Proceedings of 14th Annual ACM Symposium on Computer Geometry; Minneapolis, Minnesota. p. 146–154. MySQL 5.0 Reference manual [Internet]. 2005. Available from: www.mysql.com
14
J.M. Varela et al.
Downloaded by [Tech Univ of Lisbon Polo Ist], [Mr Carlos Guedes Soares] at 04:34 05 July 2011
Na S-S, Kim Y-D, Lee K-Y. 1994. Development of an interactive structural design system for the midship part of ship structures. Proceedings of the 8th International Conference on Computer Applications for Shipbuilding (ICCAS’94); Bremen, Germany. Python 2.5 Language reference [Internet]. 2005. Available from: www.python.org. Roh, M-I, Lee, K-Y. 2006. An initial hull structural modeling system for computer-aided process planning in shipbuilding. Adv Eng Softw. 37:457–476.
Shreiner D, Woo M, Neider J, Davis T. 2005. The OpenGL programming guide: the official guide to learning OpenGL, Version 2. 5th ed. New York: Addison-Wesley Publishing. Ventura M, Guedes Soares C. 2007. Application of STEP technology to ship repair data management. J Ship Prod. 23(4):231– 237. Ventura M, Vit´oria J, Guedes Soares C. 1999. Ship hull product model. In: Guedes Soares C, Brodda J, editors. Application of information technologies to the maritime industries. Lisbon: Edic¸o˜ es Salamandra, Lda. p. 147–162.
