Data enhancement for sharing of ship design models
Introduction
In order to develop a CIM (computer integrated manufacturing) system, or a CALS (commerce at light speed) project, different CAD/CAM systems must be connected and the data exchanged between them. A new international standard, STEP, is in the process of being developed together with related research 1, 2for the exchange of design data and manufacturing information.
The geometric data of a CAD system is represented by its own scheme geared to function and performance. In terms of the topology, each CAD system has different data representations such as 2D graphic entities, 3D wireframes, surface models, or solid models. Furthermore, the geometric entities are incompletely constructed in accordance with the levels of design detail. Therefore, a data exchange problem requires data enhancement in addition to simple data translation between different data formats.
Fig. 1 shows a flow of the information among different CAD systems in the ship structural design office at Hyundai Heavy Industry of Korea. Different CAD systems are used by different design departments, and the design result is usually delivered as paper drawings. The 2D structural design data, which is designed by the AutoCAD system, is manually re-modeled as a 3D finite element model within an FEM pre-processor, and a 3D hull model is manually re-constructed by the AutoDef system for the production design. This situation requires a data enhancement strategy that involves data exchange including topological changes of geometric models.
This paper describes an enhancement strategy applied to a complex design environment. The enhancement strategy entails the following: (1) implementation of a ship product model by the STEP [3]methodology, (2) recognition of shipbuilding features to keep design intentions during a data exchange process, (3) use of the non-manifold 4, 5modeler, ACIS, to accommodate topological changes of geometric models and to generate models valuable to downstream applications. The implemented product model contains shipbuilding features so that the information from an earlier design stage can be utilized at a later design stage.
A product data model should be consistent in order to manage heterogeneous data throughout the product's life cycle [6]. It must support various data representation schemes of each CAD/CAE system. A systematic methodology to represent a product model is required. The STEP methodology [7]can be used for the data exchange between CAx systems. STEP is organized as a series of parts, and these parts fall into one of the following series: description methods (10s), implementation methods (20s), conformance testing methodology and framework (30s), integrated generic resources (40s), integrated application resources (100s), application protocols (200s), and abstract test suites (300s), and application interpreted constructs (500s). Implementation methods such as Part 21 (the physical file format [8]) and Part 22 (the method of storing and retrieving STEP data in a general database management system), are combined with an application protocol to form the basis of an actual STEP implementation.
Section snippets
Related work and problem scope
The product model implemented for the data exchange is created by recognizing shipbuilding features from 2D AutoCAD data. Most previous feature-recognition research has been concerned with the determination of manufacturing features from a 3D solid model, because a 3D solid model has complete geometric information. Design features are quite different from manufacturing features. Some research has been reported on the subject of feature recognition from 2D representations. Aldefeld [9]cited the
Representation of shipbuilding CAD data
Every CAD system has its own data format to maximize the performance based on its usage scenario and functions required within the target domain. As the result, there are many kinds of data structures and data representation schemes. For example, geometric information is stored in 2D or 3D, a wireframe model, or a solid model. A solid model can be represented by the B-Rep (boundary representation) method or the CSG (constructive solid geometry) method. Therefore, to share a CAD data model among
3D model construction from 2D drawings
The ship structural design department of Hyundai Heavy Industry of Korea produces 2D drawings using the AutoCAD. As shown in Fig. 5, this geometric information is different from the 3D production model in many aspects. Scaled-down drawings of the real model (100:1) are such that the drawings contain simplified geometric information. Many geometric entities are omitted where precise shapes are not needed. Modifications are required if a real 3D model is re-constructed from 2D drawings. For
Step data enhancement system
To handle the midship schema that is composed of EXPRESS constructs, the STEP toolkit ST-Developer [21]has been used. C++ classes generated by the EXPRESS compiler of this toolkit have member data and member functions that are supplied by the ROSE system in addition to the member data defined in the midship schema. These classes use the ROSE library to handle the STEP data, and refers to the ROSE database that holds information on the corresponding schema when a STEP entity is instantiated. A
Conclusion
A shipbuilding CAD data set has been enhanced using STEP methodology and a non-manifold modeler. The information modeling language EXPRESS, has been utilized in this process. Using a non-manifold modeler the geometry data, represented differently for each CAD/CAE system, has been enhanced to a valid data set for downstream applications. Such a data enhancement system can solve the data exchange problems which occur when each CAD/CAE system has different functions and topologies. Simply
Yongjae Shin is a PhD student at the Korea Advanced Institute of Science and Technology (KAIST). He received BS and MS degrees in naval architecture from the Seoul National University of Korea. His current research interests include product model, STEP standard, and feature modelling.
Dr Soon-Hung Han is an Associate Professor in the Department of Mechanical Engineering at the Korea Advanced Institute of Science and Technology. He received BS and MS degrees in the Department of Naval
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Yongjae Shin is a PhD student at the Korea Advanced Institute of Science and Technology (KAIST). He received BS and MS degrees in naval architecture from the Seoul National University of Korea. His current research interests include product model, STEP standard, and feature modelling.
Dr Soon-Hung Han is an Associate Professor in the Department of Mechanical Engineering at the Korea Advanced Institute of Science and Technology. He received BS and MS degrees in the Department of Naval Architecture of SNU and a PhD from the University of Michigan. He has work experience at the Korea Research Institute of Ships and Ocean Engineering. His current research interests include geometric modelling kernel, intelligent CAD, and STEP standards.
Dr Soon-Hung Han is an Associate Professor in the Department of Mechanical Engineering at the Korea Advanced Institue of Science and Technology. He received BS and MS degrees in the Department of Naval Architecture of SNU and a PhD from the University of Michigan. He has work experience at the Korea Research Institute of Ships and Ocean Engineering. His current interests include geometric modelling kernel, intelligent CAD, and STEP standards.