The leg chord of truss type leg has a complex rack structure, and its hydrodynamic analysis is usually based on cylindrical approximation or experience, resulting in the deviation of the results from the reality. In order to improve the accuracy of the results, CFD is used to simulate the flow field around the chord with rack structure. The case study shows that the hydrodynamic coefficient Cd of chord is related to the form and size of chord rack and flow direction. This method can be also used to determine the hydrodynamic coefficients of other slender structures.


Ship and offshore engineering structures are in the flow field which contains sea water and air. The effect of the fluid on the structure shows strong nonlinear characteristics. Among them, slender structures are common in the field of ship and marine engineering, such as marine risers, spar platforms, etc., which can be called blunt bodies. The wake characteristics produced by the flow around the bluff body are directly related to the stress state of the bluff body. Unreasonable design will reduce the engineering life and even lead to the occurrence of engineering accidents.

Jack up platform is one of the most widely used offshore platforms. It depends on the pile leg to stand on the sea floor. The pile leg bears the weight of the platform main body and the external environmental load, which plays an important role in the safety of the whole platform. Compared with other types of pile legs, truss pile legs have higher safety and material utilization ratio, and are more commonly used in large-scale jack up platform.

As shown in Fig. 1, a typical truss type pile leg of a jack up platform is shown on site.

The truss type pile leg is composed of chords and braces. Among them, each brace is a regular cylinder, but the profile of chord is in the form of cylinder + rack as shown in Fig.2.

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