It is well known that at certain discrete frequencies the conventional boundary integral equation formulation of free surfacc fluid-structure interaction analyses breaks down. At such 'irregular' frequencies the BIE method fails to provide either an acceptable or a unique solution. Having established the existence of irrcgular frequencies, a review of the different approaches adopted to remedy this problem is presented.A very simple modification of the BIE method is also presented to eliminate the irregular frequency problem. The proposed procedure, designated the combined boundary integral equation method (CBIEM), can be categorized as a modified integral domain method. A description of the CBIEM formulation is presented and its ability to provide a unique solution at all frequencies is demonstrated. Predictions of 3D hydrodynamic reactive coefficients of addcd mass and fluid damping for a Series 60 hull form and an ellipsoid based on the CBIEM procedure are presented. These predictions are compared with results generated using conventional integral equation methods. The numerical studies demonstrate that the CBIEM is both a practical and effective method of suppressing irregular frequencies. In particular, the procedure is easy to implement in existing BIE computer codes with minimal additional computational effort.
KF.Y WORDS Combined boundary integral equation method Fluid-structure interaction Irregular frequencies
This paper is concerned with the effects of wave drift damping upon the motions of a moored tanker and a moored offshore barge. The assignment of wave drift damping coefficients, whether predicted or measured. has a significant effect upon the excursions of the moored structure and hence upon the associated line tensions experienced by the mooring system.Procedures for simulating the random sea and determining the Quadratic Transfer Functions of second order wave effects are discussed in the context of including such effects in the time domain simulation of a moored vessel.
This paper is concerned with the formulation and simplifications of the general fluid structure interaction analysis for an advancing oscillating vessel in waves to provide alternative 3D hydrodynamic models to determine first and second-order wave-induced fluid loadings, and, hence, the prediction of low-frequency wave damping coefficients. Heuristic arguments which lead to the Added Resistance Gradient (ARG) method of calculating low-frequency damping coefficients together with two 3D-based calculation procedures are presented. Predictions of added resistance and motion responses are compared with other published data. The intermediate hydrodynamic coefficient predictions based on 2D and 3D hydrodynamic models are compared. Low-frequency damping coefficient predictions based on the two proposed 3D calculation procedures are compared with experimental measurements and earlier published generalized strip theory values. Assessment of the applicability of the procedures, the result of their application, and further possible generalizations of the methods are discussed.
A noble lateral buckling design mitigation scheme involving combined vertical and lateral offsets incorporated in a conventional sleeper concept has been developed [1]. This so called Zero-Radius-Bend (ZRB) method significantly improves the buckle initiation reliability and its effectiveness has been field proven on many recent projects. This paper first describes the ZRB buckle mitigation method, its unique characteristics and ensuing advantages over the conventional sleeper method, followed by specific design and analysis considerations for deepwater application using reel-lay or J-lay installation method to create the lateral offset. Other considerations for lateral buckling such as post-reel response and cyclic lateral buckling-axial walking interaction response are also discussed.
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