monument to the quality work done in its preparation for the basin campaign,” he stresses. “The focus is essentially on executing the required test programme in a tight slot for the basin while achieving the highest quality results that we expect and here the basin crew excel.”

But the tests are only the externally visible part of the test campaign, he stresses. The foundations are laid behind MARIN’s closed doors by a large number of MARIN personnel including the project engineers, instrumen- tation and workshop technicians and data analysts who make significant contributions towards our high quality results that we can reliably use. “Here I thank all involved in tests for us who contribute towards our successful sequence of quality tests at MARIN, and long may it continue!”

South Arne platform

tests in a calibration role. After all, computers only do what we instruct them to do using the assumptions we make, and model tests help us with a bit of a reality check.”

In recent years, 3D CAD drawings and PVC as a construction material have become the standard at MARIN for building semi-sub- mersible and TLP models. Does HESS con- sider this an advantage for its own projects? Joel certainly considers that there have been tremendous improvements by using both 3D CAD drawings and (weldable) PVC. “With 3D CAD models we fully represent our design intent and it has allowed us to improve models in the Offshore Basin for wind loads, for example.” The one area in particular that has improved compared to a decade ago, is an ability to more accurately replicate wind loads from the wind tunnel tests in the Offshore Basin and the use of a common 3D CAD model is a significant contributing factor, he points out.

“With PVC constructions the quality of the models compared to a decade ago is a magnitude higher and many historical issues, like leakage, just don’t happen these days and this is due to the improved construction offered by PVC. And because we can use

8 report

transparent sections we can place cameras inside the model looking outwards. This gives us a view that we did not have before.”

High-speed cameras This also touches on an area that has significantly improved the model tests and that is digital video and high-speed cameras, he adds. “A large part of model testing is the delivery of visual results and we can now capture local events at high resolution. This allows us to study the event in great detail particularly when comparing it to the measured time series of motions, wave elevations and loads.”

Stampede TLP project HESS recently visited MARIN for model tests on the Stam- pede TLP. More details of this successful model test campaign are outlined on the adjacent page. Stampede was in a relatively long line of tests at MARIN for different projects. The Stampede TLP is a conventional TLP and so in itself, the test campaign was relatively straightforward both in scope and execution. But Joel explains, with each new model test campaign HESS sees a trend of increasing complexity in the model construction and associated instrumentation and Stampede followed this trend. “The Stampede model was one of the best built for us and it is a

With each test campaign HESS has always used the lessons learnt from previous cam- paigns and incorporated new developments. But Joel says he considers the high-speed camera aspects of the Stampede tests as a particular success. “While we used this system in the Offshore Basin in the previous test campaign at MARIN our techniques benefited from this experience to provide excellent visual results for Stampede.”

Extreme conditions One of the important aspects for the design of semi-submersibles and TLPs is the deck clearance. What does HESS consider the main issues when addressing the platform response in extreme wave conditions? “The clearance between the deck of a floating facility and the instan- taneous local wave elevation is a highly complex one in terms of the underlying physics and really is a subject of a workshop and certainly beyond a simple answer. It is one where there is still some debate and I am not sure that all the contributing physics involved in this structure-wave-current in- teraction is fully understood.” However, he adds: “What I can say is I see model tests as extremely valuable in identifying and capturing these extreme events for subsequent assessment. While today’s numerical models help screen these local events we still need high quality representative model tests for this aspect for design.” Joel adds that over the next few years he would like to see the further development of CFD tools to improve on air gap prediction methodology for design. “And MARIN is well placed to make a significant contribution in this field!”

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