Figure 2: File Sizes with JT.
• JT Simplified Geometry is used for significantly improving performance
storing an arbitrary number of faceted representations with varying LODs.
• Ultra-Lightweight Precise (ULP) format provides a lighter weight surface
in large assemblies. It provides for every assembly and sub-assembly to be represented by its external surfaces only rather than the full detail of all the individual part surfaces. The assembly loads initially in as little as 1/10th the time for the full assembly. The individual part JT files are then loaded either on demand at the request of the user, or when needed for operations like measurement or cross sectioning. Simplified Geometry is ideal for shipbuilding where very large assemblies need to be loaded before users can navigate to the area where they need to work.
representation of the 3D geometry with file sizes significantly smaller (Figure 2). ULP has built in IP protection as it is accurate enough for most supplier interaction use cases but does not provide the exact surface definition (like BREP) and therefore can not be used for reverse engineering. Te ULP format makes it easier to share data across low bandwidth connections. Small file size is important as the shipbuilding collaboration network extends to countries with inadequate telecom infrastructure. JT data can be contained in a single or multiple files. Each file can contain any relevant JT information. By properly managing the allocation of information to a given physical file, if source data changes, only the JT file corresponding to that information would need to be recreated or updated. PLM solutions like Teamcenter can manage the JT files relative to their CAD originals and synchronise the creation of a new JT for every CAD revision.
PLM XML PLM XML is a XML based PLM format. PLM XML schema describes a model’s geometry, structure, features, ownership, and visualisation. PLM XML allows for
The Naval Architect January 2012
Figure 3: Use Cases
a single logical product model to have several different geometric representations, tailored to different purposes. Metadata of several different types like mass, material, PMI, application specific data, etc. can be attached to logical parts of the model or specific geometric representations. File sizes can be reduced using a reference-instance mechanism and by splitting out various sections of data into separate files (so that data not needed for a particular purpose need not be transmitted). As well as approximating and separating data, PLM XML also supports mechanisms for restricting access to parts of the model data on the basis of person, organisation or place.
Use Cases
• Visualisation & Digital Mock-up (DMU): JT is primarily used for 3D viewing by any
stakeholder who does not need to edit the geometry (Figure 3). Once a ship model is converted to JT, a JT viewer can display the product structure, perform measurements, conduct interference/clearance analysis, display properties (metadata), etc. A JT viewer can be coupled with a Virtual
• Documentation & Archiving: The most important requirement relating
Reality (VR) system that projects the image in stereo so that the user with the aid of stereo glasses can see the model in real-time 3D. It is possible to create JT files that contain structure, metadata and geometry, or alternatively the material and metadata can be imported from a PLM system. In DMU, collision checks for assembly/ disassembly and design space checks are carried out.
to the documentation and archiving of engineering data is that all relevant information be stored in a standardised format that can be read irrespective of a specific IT infrastructure and aſter a long period of time. Since the life cycle of ships can vary from 20+ years to 40+ years depending on whether they are commercial or naval, long-term data retention (LTDR) of ship product information is a serious issue. With continuous improvements in CAD technology and end of life for some of the CAD soſtware traditionally
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