http://www.vliz.be/imisdocs/publications/230280.pdf

Wave run-up on cylindrical and cone shaped foundations for offshore wind turbines

Dynamic behaviour of square and triangular offshore tension leg platforms under regular wave loads

A small-scale experimental study was performed to investigate wave runup on rigid full-length and truncated circular cylinders under regular and random sea conditions. Wave elevations were measured around one-half of the cylinder circumference together with the total in-line wave force. The regular wave data were compared with predictions obtained using linear diffraction theory, and the results were consistent with the findings of earlier researchers. A regression analysis was performed on the regular wave data to obtain a relationship between the wave runup and the velocity head. The resulting empirical equation can be used to make preliminary estimates of wave runup on truncated circular cylinders. An approximate formula for predicting the time-dependent wave force on a truncated cylinder is presented. Transfer functions relating the enhanced wave-surface-elevation spectrum and the wave-force spectrum to the incident-wave spectrum are derived. The validity of the wave-force approximation and the adequacy of the linear transfer functions are examined in light of the new experimental data. As in the case of regular waves, the random-wave spectrum model does not adequately predict the root-mean-square (RMS) surface elevation at the front of the cylinder, but does provide a reasonably good estimate of the wave force on full-length and truncated cylinders. Extreme value estimates based on standard statistical procedures are compared with the experimental data and generally found to be conservative.

Wave Runup and Forces on Cylinders in Regular and Random Waves

Offshore compliant structures such as guyed platforms, tension leg platforms and articulated towers are economically attractive for deep water conditions because of their reduced structural weight compared to conventional platforms. The foundations of these kinds of structures do not resist lateral environmental loads forces; instead, restoring moments are provided by a large buoyancy force, a set of guylines or a combination of both. These structures have a fundamental frequency well below the ocean wave’s lower frequency-bound. As a result of the relatively large displacements, geometric nonlinearity is an important consideration in the analysis of such a structure. This paper presents a literature review on offshore compliant structures. The review focuses on the static and dynamic response of the structure due to various environmental conditions, such as wind, waves and current. Emphasis is placed on modeling techniques and methods of solution. Many modeling and analysis techniques are common to the aerospace and ocean engineering communities due to the similarities in structural and environmental complexities. For example, aerodynamic loads on offshore platforms are a significant part of any analysis. Also, fluid loading models bear great similarities to mechanistic wind loading models. It is in this vein that a review paper with the focus on offshore structures is included in a journal of aerospace engineering.

Dynamic Response of Compliant Offshore Structures—Review

Experimental study of interactions between multi-directional focused wave and vertical circular cylinder, part II: Wave force

Probabilistic collision model for a pair of flexible cylinders

A large-scale experimental study to investigate the dynamic response of a single flexible cylinder in waves is presented. The cylinder was designed to exhibit the dynamic characteristics of a TLP riser or tendon in approximately 1,000 m of water. Instrumentation provided detailed information on the inline and transverse curvature along the length of the cylinder. Wave loading mechanisms and the resulting response were investigated and compared with previous studies of rigid cylinders in oscillating flow. It was found that the complicated multifrequency response at large Keulegan-Carpenter numbers could be explained by introducing the depth dependence of the Keulegan-Carpenter number. The predicted inline response was shown to be reasonable for the wave frequency component of the measured inline response. Similarities between the measured transverse response and the high-frequency inline response were also shown. Probability density functions of the measured curvature were non-Gaussian, leading to significantly higher probabilities of curvature than would be predicted based on assuming a Gaussian process.

Dynamic Response of a Single Flexible Cylinder in Waves

This paper describes a method developed to estimate the three-dimensional displacement field of long, flexible cylinders subjected to wave loading. The method makes use of the relationship between curvature and displacement of a uniform beam. The technique was implemented in a large-scale experimental study to investigate the response of a pair of flexible cylinders in close proximity, with an emphasis on the collision behavior between them. The model cylinders were designed to be representative of risers or tendons of a tension-leg platform in approximately 1000 m of water. The cylinder models, approximately 17-m long and 0.03-m diameter, were instrumented to measure the cylinder curvature at discrete locations along their length. At each time step the displacement field was computed from the curvature measurements using a ‘shoot-to-fit’ numerical-integration scheme. This procedure yielded a complete description of displacement along the cylinder as a function of time. The number and location of the curvature measurements were optimized by simulating the wave-flexible cylinder interaction with a finite-element model that was also used to demonstrate the accuracy of the method. The effectiveness of the technique is demonstrated by results from the experimental program, and it appear to be feasible to adapt this approach for field experiments.

Estimation of Flexible Cylinder Displacements in Wave-basin Experiments

The results of a small scale experimental study to investigate the wave run-up and wave forces on a truncated cylinder, representing a single TLP leg are presented. The

A. S. Duggal

Papers

Wave Runup and Forces on Cylinders in Regular and Random Waves

Probabilistic collision model for a pair of flexible cylinders

Dynamic Response of a Single Flexible Cylinder in Waves

Estimation of Flexible Cylinder Displacements in Wave-basin Experiments

Wave Run-Up and Wave Forces on a Truncated Cylinder