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Due to larger and larger diameter foundation piles with submerged conical shape are being used in the offshore industry, special driving issues will have to be considered such as the interaction with trapped and ambient water. This paper addresses the drivability of a submerged conical shaped pile, where water is internally displaced for each hammer blow resulting in the loss of driving energy. A numerical model quantifying the losses of driving energy has been developed and compared with the actual hammer driving log. Examples of driving large diameter piles with underwater conical sections have been analysed. It turns out that conical sections even with small slope cause significant energy loss. A 2.5=176; slope causes a 12% energy loss. Furthermore, the interaction during driving between surrounding water and appurtenances such as lifting trunnions is described. It is demonstrated that this interaction may result in resonant vibrations of appurtenances resulting in local high stress levels.
This study aimed to estimate tsunami vulnerability in South Korea where power plants, seaports and large-scale urban area have constantly developed. For the purpose, we estimated tsunami behavior using the FUNWAVE model and identified vulnerable factors from modified 3- round Delphi methods. The priorities order of the alternatives were ranked by assessments results of MCDM methods as TOPSIS and VIKOR. In addition, the tsunami vulnerability index was developed by combining the results. The approach can be provided to quantifying vulnerability to manage tsunami vulnerability in South Korea.
Zhenning-Wang, _ (Wuhan University of Technology) | Langxiong-Gan, _ (Hubei Inland Shipping Technology Key Laboratory) | Lei-Zhang, _ (Wuhan University of Technology) | Yuanzhou-Zheng, _ (Hubei Inland Shipping Technology Key Laboratory)
The safety of submarine pipelines which cross waterways is often threatened by objects falling from ships, such as anchors. In the process of dropping an anchor, an anchor penetrates the seabed, and most energy of the anchor was absorbed by seabed during the interaction process, which can reduce or even avoid damage to pipelines. In this paper, a non-linear finite element program(LS-DYNA/ANSYS) is used to analyze the dynamic response process of contact and collision between the anchor and seabed, as well as to simulate the velocity change and energy dissipation of the anchor in the soil during the penetration process. The results of numerical simulation can accurately display the energy dissipation and displacement deformation of the anchor in the seabed, in a way to determine the minimum burial depth of pipelines. The research results can provide the basis for the protection design of submarine pipeline.
Koh, Jian Hao (Nanyang Technological University) | Robertson, Amy N. (National Renewable Energy Laboratory) | Jonkman, Jason M. (National Renewable Energy Laboratory) | Driscoll, Frederick (National Renewable Energy Laboratory) | Ng, Eddie Yin Kwee (Nanyang Technological University)
Using data obtained from open-sea testing of the 1:6.5 scale prototype of the SWAY hybrid tension-leg spar-type floating wind turbine, a FAST model of the SWAY system was built and validated. Significant in the validation process were improvements to the FAST wind turbine simulation tool to incorporate wind loading on the turbine tower for floating systems. Simulations were performed with and without the new tower-load capability to examine its influence on the response characteristics of the system. This is important in situations when the turbine is parked in survival conditions. The simulation results were then compared to measured data from the SWAY system in both turbine operating and nonoperating conditions. Mixed results were observed when comparing the simulated system behavior to the measured data, but the tower wind loads improved the comparison for nonoperating conditions.
Submarine flexible pipes are subject to the impact of complex environment factors including waves and current particularly. A series of special dynamic phenomenon would occur due to these impacts. According to the wave-domain theory, waves can significantly affect the current, especially on the wave boundary layer near the bottom. Meanwhile, the combined action would significantly influence the dynamic response of pipelines. There are quite a few studies about velocity field analysis around pipes under a constant flow have been published in open literature. However, investigation on the combined action of wave and current seems to be inadequate and incomplete. Therefore, this paper will focus on this topic to conduct model test under both pure current action and wave-current joint action to illustrate the combined effect. Velocity data acquisition of several selected vertical section will be presented, analysis of velocity field variation (with and without waves) around pipes will be derived. Some general rules of velocity profile near pipes will be demonstrated showing the wave-current interaction mechanism.
A nonlinear response amplitude operator (NRAO) that is able to model a wide class of nonlinear systems and structures, usually found in maritime and offshore applications, is developed. Its functional scheme is of the Volterra-series type and its order is explicitly dictated from the order of nonlinearity of the actual dynamical system. In addition, the proposed method is not bounded by any amplitude or frequency constrains and it can compute the response of a nonlinear system even for multi-chromatic excitations that consist of modes with significantly, or not, different amplitudes and frequencies.
In this research, we strictly conducted experiments to clarify these factors aiming at obtaining findings about the relation between the wave energy and volume of an overtopping wave, and the characteristics of water fed by the water-level difference between the inside and around the tank, which varies depending on the volume of the overtopping wave. As a result, volume of overtopping was able to be formulized with the wave energy of the irregular wave.
Based on the multiple-cylinder diffraction solution, systematic calculations are made about multidirectional random wave loads on cylinders. The time series of multidirectional wave loads can be calculated. The effect of wave directionality on the wave run-up and wave loading on large-scale cylinders is investigated. For multidirectional random waves, as the wave directional spreading parameter s becomes small, the wave run-up on most of points around cylinders would be larger. This means that the wave run-up on multidirectional wave condition is larger than it for unidirectional wave. The effect of wave directionality on the transverse force is more obvious than on the normal force. The transverse force on the front cylinder is not always larger than that on the back cylinder, especially, for smaller s. As a consequence of the results, the engineering project design based on unidirectional waves cannot always give a conservative estimate.
This paper examines the development of rapid, real-time hurricane/storm risk assessment tools and their cyber-implementation. Kriging surrogate modeling is adopted to approximate storm responses, utilizing existing databases of high-fidelity simulations. Principal component analysis is considered to reduce the high dimensionality of the responses over large coastal region, contributing to significant improvement in computational efficiency (lower memory requirements and faster evaluations). The developed surrogate model can be then utilized for real-time predictions during incoming hurricanes, supporting a rapid probabilistic risk assessment. The cyber-implementation of these tools is also discussed. The overall approach is illustrated for hurricane risk estimation in the Hawaiian Islands.
By Physical experiment, the harbors wave height distribution and the wave overtopping of different wharf structural form were studied. With the example of one wharf extension project, the wave heights in harbors and the wave overtopping in different wharf surface elevation were compared between ordinary and perforated caisson wharf. The result shows that, the perforated caisson wharf has more advantages to control the wave height and reduce the wave overtopping than ordinary caisson wharf. The wharf surface elevation is an important influence factor for wave overtopping. In order to reduce the wave height and wave overtopping, the perforated caisson wharf should be preferentially considered, and the wharf surface elevation should be as much as possible under economic conditions available.