bravo zulu 1/2008 - GL Group

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gaS EXploSIon. The rigs enable real world tests to be conducted at large scale. separate test facilities are maintained and constantly being developed to simulate most of the hazards that the oil and gas industries could experience. All the test rigs include advanced data acquisition systems for comprehensive analysis. The Spadeadam test site has a wide range of existing facilities and test rigs with specialized instrumentation. In addition scientists and engineers can design and construct experimental test rigs tailored to satisfy specific test requirements. Major projects have involved joint industry projects in support of the oil and gas industry and testing new designs and processes for a range of industries. These include oil and gas exploration, production and transmission, water processing and distribution, and ballistics and defence systems among many others. Full-scale fracture propagation of transmission-pipe and long-term high-pressure sour-gas corrosion testing of process equipment have established the site’s credentials for accurate and reliable data capture over periods of milliseconds or months. Gas distribution pipes in polyethylene are intensively tested to measure the resistance of material to rapid crack propagation. Operating conditions can range from – 20°C and pressures to 30 bar. The effect of intense jet fires on structures is met by two flame impingement test facilities. The test rigs enable full-scale tests to be conducted with nominal flame 2 bravo zulu 01/2008 aREa. Bird‘seye view of the test site. capacity up to 2,000 MW, long-term testing (longer than one hour) can be sustained at 300 MW. Heat-flux densities and internal temperature gradients can be readily provided along with film or video recording for later analysis. The effect of gas explosions on structures are investigated over a wide range of conditions on a large scale. Fire pressure transients from explosions can be recorded of conditions such as variable confinement or congestion. Alternatively, site engineers have developed unique facility to enable pressure transients to be accurately produced by gas explosions. These pressure transients can be tailored from 0 to 7 bar and with periods of 5 ms to 1 second. high-sea Testing on dry land This remote, land-locked location in the North of England seems an unlikely setting for maritime tests. But over the years a great deal of work for the marine sector has been carried out at Spadeadam and it is still a feature of current and future trial activity. Spadeadam has carried out several ship- to-ship and ship-to-shore tests looking at vapour ignition and rapid-phase transition effects as well as fuel fires and the effects of blasts against ship structures whilst alongside a dock. “The GL Industrial Services large-scale test site is certainly worth serious consideration if any planned maritime tests or trials have a significant hazardous component,” says Brown. The site is currently exploring the possibility of a series of compartment fire tests with GLIS. This involves using a representative ship superstructure whilst keeping a weather-eye on novel and future fuel technology. ■ For further information: David Brown, General Manager, Phone: +44 1697749138 E-Mail: david.brown@advanticagroup.com www.advanticagroup.com/spadeadam technology special FIGURE 8. Aerodynamic flow simulation for frigates.
SImUlaTIon-BaSEd dESIgn Virtual Experience for navy Ships TEchnology SpEcIal Simulation-based design increasingly replaces traditional experience-based design. an overview of techniques now used in advanced industry practice, with particular focus on navy applications by Volker Bertram Ship design is increasingly supported by sophisticated analyses. Traditionally, ship design is based on experience. This is still true to some extent, but we increasingly rely on “virtual experience” from dedicated and well chosen simulations. Scope and depth of these simulations guiding our decisions in design and operation of ships have developed very dynamically over the past decade. Described is the state of the art as reflected in the work, but now with particular focus on applications for navy ships. 1. Structural analyses 1.1 Finite-element analysis (FEa) FEA for global strength within the elastic material domain have been standard for a long time, see Fig. 1. These simulations were the starting point for more sophisticated analyses, e.g. fatigue strength assessment, ultimate strength assessment, etc. Until 1998, the SOLAS regulations on subdivision and damage stability specified damage stability requirements only for cargo ships longer than 100 m. Since 1998, this limit has been lowered to 80 m for new cargo ships. Additional transverse bulkheads to fulfil damage stability requirements are costly and restrict operations. However, the new SOLAS regulations allow alternative arrangements for some ships, provided that at least the “same degree of safety” is achieved. This notation allows some flexibility of structural designs supported by advanced simulations. For example, a structural design with increased collision resistance, thus reducing the probability of penetration of the inner hull, could eliminate the need for additional bulkheads. Based on extensive FEA simulations for ship collisions, GL has developed an approval procedure which provides the first such standard for evaluation and approval of alternative solutions for design and construction of these ships, see Fig. 2. The basic philosophy of the approval procedure is to compare the critical deformation energy in case of side collision of a strengthened structural design to that of a reference design complying with the damage stability requirement described in the SOLAS regulation. FEA require load specifications which for ships often involve frequently external hydrostatic and hydrodynamic loads. GL ShipLoad supports efficient load generation for global FEA of ship structures. Hydrostatic and hydrodynamic computations are integrated into the program. GL Ship- Load supports the generation of loads from first principles (realistic inertia and wave loads for user supplied wave parameters), but the program is also helpful in the selection of relevant wave situations for the global strength assessment based on bending moments and shear forces according to GL’s rules. The result is a small number of balanced load cases that are sufficient for the dimensioning of the hull structure. 1.2 Vibration analyses Advances in computer methods have made three-dimensional FEA today the standard choice for ship vibration analyses today. The computations require longitudinal mass and stiffness distribution as input. The mass distribution considers the ship, the cargo and the hydrodynamic ‘added’ mass, see Fig. 3. The added mass reflects the effect of the surrounding water and depends on the frequency. One can either use estimates based on experience or employ sophisticated hydrodynamic simulations. For local vibration analyses, see Fig. 4, added mass needs to be considered if the structures border on tanks or the outer hull plating. Because of the high natural frequencies of local structures, FEA models must be detailed enough to include also the bending stiffness of structural elements. 1.3 acoustics FIgURE1. global strength analysis; grid and stresses for frigates. FIgURE 2. FEa for collision of two ships. For very high frequencies (structure-borne noise), the standard FEA approach to vibration analyses is impossible due to excessive computational requirements. For a typical passenger vessel for a frequency of 1,000 Hz, an FEA vibration model would lead to several million degrees of freedom. However, the very fact that information is required only averaged over a frequency band allows an alternative, far more efficient approach based on statistical energy analysis. GL’s Noise Finite Element Method (GL NoiseFEM) is based on a related approach. GL NoiseFEM predicts the propagation of noise by analysing the exchange of energy between weakly coupled subsystems. Validation with full-scale measurements shows that the accuracy of GL NoiseFEM is sufficient for typical structure-borne sound predictions for the frequency range between 80 Hz and 4,000 Hz. While further development is still needed, struc- bravo zulu 01/2008 3
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bravo zulu 1/2008 - GL Group

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