Time filter

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Houston, TX, United States

Murray J.,FloaTEC LLC
Hart's E and P | Year: 2011

FloaTEC LLC is working on a new approach to strake technology, providing longer life for spars. The technology provides solutions to the problem of stress that is exerted due to vortex-induced motions (VIM), leading to overstressing, buckling, brittle fractures, or fatigue. The concept is to modify the strake by attaching a hinge to the tip, allowing it to be folded during load-out. The new strake is designed to fold back to provide the required underside clearance gap for horizontal towing. Once the hull is uprighted at the installation site, the folded sections can be opened and secured so the resulting strake is the optimum size. The objective is to provide strakes that achieve their optimum performance in mitigating VIM on the hull without adding complexity to the load-out operation. Source

Yu X.,FloaTEC LLC | Falzarano J.,Texas A&M University
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2012

Cargo-transfer and underway replenishment are essentially important in long-term naval operations. The Office of Naval Research (ONR) initiated a technology development program in 2007 called STLVAST (Small to Large Vessel At-Sea Transfer). The goal of this program is to develop 'enabling capabilities' in the realm of logistic transfer (i.e. stores, equipment, vehicles) between a large transport vessel (e.g., the USNS Bob Hope) and a smaller T-craft ship, using a Deep Water Stable Crane (DWSC) spar between them. The DWSC spar consists of two entities, a catamaran craneship and a detachable spar. In this paper, a new numerical scheme to simulate time-domain motion responses of floating systems has been successfully proposed and applied to the motion response control of the DWSC spar. The equation of motions using the Impulse Response Function (IRF) is initially discretized into a new state-space model, where the first order and second order waves loads transfer functions are calculated from WAMIT. Two time steps affect the construction of this state-space model: the time step Δt used to estimate the IRF, and simulation step Δt. The LQR method is selected in this study. Firstly, the effects of both time step on the controlling efficiency is studied. Then various weighting factors (Q,R) for the LQR controller are further considered to study the robustness of the LQR method. Copyright © 2012 by the International Society of Offshore and Polar Engineers (ISOPE). Source

Chen B.,FloaTEC LLC | Nagarajaiah S.,Rice University
Structural Control and Health Monitoring | Year: 2013

The observer-based fault detection and isolation filter design method is a model-based method. By carefully choosing the observer gain, the residual outputs can be projected onto different independent subspaces. Each subspace corresponds to each monitored structural element, so that the projected residual will be nonzero when the associated structural element is damaged and zero when there is no damage. The key point of detection filter design is how to find an appropriate observer gain. This problem can be interpreted in a geometric framework and is found to be equivalent to the problem of finding a decentralized static output feedback gain. But it is a challenging task to find the decentralized controller by either analytical or numerical methods because its solution set is generally non-convex. In this paper, genetic algorithm is originally proposed to find the detection-filter-based decentralized controller, which can be applied in structural health monitoring. The numerical simulation and experimental results show that the developed method can successfully identify structural damage. Copyright © 2011 John Wiley & Sons, Ltd. Copyright © 2011 John Wiley & Sons, Ltd. Source

Jin J.,Texas A&M University at Galveston | Meng B.,FloaTEC LLC
Ocean Engineering | Year: 2011

Recent hurricanes have caused severe structural damages to a number of coastal highway bridges along the US coast of the Gulf of Mexico. A large amount of bridge superstructure sections were displaced or pushed off the substructure by storm surge and wave action. To prevent such structural failure of coastal bridges, wave loads on bridge superstructures need to be quantified. In this study, two different numerical models were used to analyze wave-structure interaction and compute wave loads. Computational Fluid Dynamics (CFD) Software Flow-3D was used to analyze the effects of green water loading and superstructure elevation on wave forces. A 2D potential flow model was developed for computation of wave loads on bridge superstructures fully submerged in water. Wave induced pressure on bridge superstructures was obtained by solving complex velocity potential from Laplaces equation and boundary conditions using finite difference method. The 2D potential flow model was validated by large-scale laboratory measurements, and then used to perform parametric study using a range of wave parameters, water depth and bridge superstructure width. Equations for calculating wave loads on bridge superstructures were developed using results of the parametric study. © 2011 Elsevier Ltd. All rights reserved. Source

Yang C.K.,FloaTEC LLC | Kim M.H.,Texas A&M University
Journal of Offshore Mechanics and Arctic Engineering | Year: 2010

This paper deals with a numerical model of top tension risers with hydropneumatic tensioner for Spar application in the Gulf of Mexico environment. The nonlinearity of the stiffness and the friction characteristics of the tensioner combined with stick-slip behavior of the riser keel joint are investigated. The relationship between tensions and strokes for the hydropneumatic tensioner is based on the ideal gas equation where the isotropic gas constant can be varied to achieve an optimum stroke design based on the tensioner stiffness. Challenges of modeling the coupling effects in the finite element (FE) method between the tensioner and hull motion are also presented. This new FE model is implemented into a fully-coupled time-domain coupled-dynamics-analysis program for floating bodies. The effect of nonlinearity of tensioner curve, tensioner friction, and riser keel friction is intensively investigated. The resultant global motion, TTR stroke, and tensions are systematically compared with those of a simple engineering approach, in which the nonlinear coupling effect is captured by linearization. © 2010 by ASME. Source

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