We investigate piston-mode fluid resonance within the narrow gap formed by two identical fixed barges in a side-by-side configuration, utilizing a two-dimensional fully nonlinear numerical wave tank. The focus is on examining the effects of uniform and shear currents. Under ‘wave+uniform-current’ conditions, a certain current speed is identified, beyond which the gap resonance reduces dramatically and monotonically with the current speed. This reduction is attributed to a stronger increase in damping compared to wave excitation, qualitatively explained by a linearized massless damping lid model. Furthermore, we study the effects of waves propagating on shear currents, maintaining an identical ambient current speed at the gap depth. Complementary to previous studies on this topic, our study reveals that the velocity profile of the studied shear current has an insignificant effect on the resonant gap amplitudes. The ambient current velocity at the gap depth is a more important key parameter to consider when assessing wave-induced gap responses, leading to a non-negligible increase in the resonant gap response. Consequently, disregarding the influence of currents in engineering practices is not a conservative approach.
Ship-to-ship (STS) bunkering of liquid fuel, e.g., LNG, has emerged as a more practical way to ensure high bunkering volumes and good access without regional restrictions and upgrading of existing infrastructures at the port. Wave resonance in the narrow gap between side-by-side receiving vessel and bunkering vessel happens when the wave frequency is close to the natural frequency of the gap flow. Large wave elevation in the gap and hydrodynamic forces on the
ships are expected, thus reducing the time window of the bunkering operation and even risking the safety of the crew. It is well known that the wave frequency and amplitude can be affected by the presence of current. Correspondingly, the waves and loads on marine structures will be somewhat different from the scenario without current, which will have significant influence on the bunkering operation. However, few previous studies have reported in the literature for wave resonance considering current effect. In the present work, the finite-amplitude fluid resonance inside the gap between two ship cross-sections in side-by-side configuration is studied under combined waves and currents. Both a uniform current and a shear current with constant vorticity are considered. A fully nonlinear numerical wave tank is established based on the commercial CFD package STAR-CCM+. The unsteady Reynolds averaged Navier-Stokes turbulence model is applied to consider viscous dissipation. The volume of fluid method is applied to capture the free surface, and the flow field analytically obtained from the stream function method is specified in the forcing zones at upstream and downstream boundaries, respectively, by the user-defined wave elevation and velocity. The influence of following current on the wave amplitude in the gap and hydrodynamic load on the cross-sections is investigated by comparison with the cases without current. The relation between the wave or force amplitude and the vorticity of the shear is further analysed. The present study may provide useful results about gap resonance and hydrodynamic loads on two approaching marine structures during the bunkering operation in wave-current environment.
Coupled piston-mode fluid response and the heave motion of two identical barges in side-by-side configuration is studied under finite-depth and shallow-water waves using a two-dimensional fully nonlinear numerical wave tank. To understand possible critical responses of the gap flow and the floating barge, regular-wave conditions which are able to excite up to 5th-order nonlinear gap resonance and also the resonant heave motion of the barge are considered. In shallow-water waves, high-frequency oscillations, featured by secondary peaks in the time histories, are observed for both wave elevation in the gap and the heave motion of the barge. The shallow-water wave-induced 4th- or 5th-order gap resonance can be equally crucial as the 1st- and 2nd-order resonances due to finite-depth waves. At higher-order gap resonance, the higher-harmonic heave motion of the barge is negligibly small, in contrast to the gap-flow response. Compared with fixed barges, the free-heave motion of an upstream barge tends to increase the wave elevation in the gap in most of the resonant conditions, except at 1st-order gap resonance where the gap response is greatly reduced. When the resonant heave motion of a floating barge, either located upstream or downstream, is excited, significant barge motion is observed. However, the relative motion between the gap flow and the floating barge is seen to be very small, ascribed by small phase difference between the two. The present study suggests that the effects of heave motion and water-depth should be carefully considered in the design of side-by-side marine operations, and hiding the small bunkering ships behind the large receiving ships is regarded as a preferred arrangement during the bunkering operations in offshore and coastal environments.
Ship collision and grounding events constitute a major hazard for ship operations, and ship collision risk analyses have to be carried out for installations such as offshore structures for extraction of hydrocarbons, offshore wind farms, and bridges spanning waterways. This book provides assessment procedures for ship collision and grounding analysis and includes probabilistic methods for collision and grounding risk assessment, estimation of the energy released during collisions, and prediction of the extent of damage on the involved structures.
The main feature of the book is that it encapsulates reliable and fast analysis methods for collision and grounding assessment and the methods have been extensively validated with experimental and numerical results. In addition, all the described analysis methods include realistic calculation examples so as to provide confidence in their use to eventually conduct the required assessment according to the rules and design codes. The book is intended as a handbook for professionals and researchers in the industry dealing with design and analysis of ships and offshore structures. The book can also be used as a text book for postgraduate courses orientated towards the design and analysis of ship and offshore structures.
To clean the produced water is always a challenging critical issue in the offshore oil & gas industry. By employing the plant-wide control technology, this paper discussed the opportunity to optimize the most popular hydrocyclone-based Produced Water Treatment (PWT) system. The optimizations of the efficiency control of the de-oiling hydrocyclone and the water level control of the upstream separator are discussed and formulated. Some of our latest research results on the analysis and control of slugging flows in production well-pipeline-riser systems are also presented. The ultimate objective of this research is to promote a technical breakthrough in the PWT control design, which can lead to the best environmental protection in the oil & gas production, without sacrificing the production capability and production costs.
Due to the harsh weather conditions, severe spatial limitations and extremely high safety requirements, the indoor climate control for offshore oil & gas production platforms is much more challenging than any on-shore situations. For instance, the indoor pressure of man-board quarters should be kept all the way above the ambient pressure according to safety regulations. Meanwhile, the indoor air needs to be regularly changed in order to guarantee the indoor air quality. Both requirements could be possibly achieved by automatically manipulating either the throttle valve located at the terminal of the inlet channel in the considered Heating Ventilation and Air-Condition (HVAC) system, or the pressurization system located inside the inlet channel, or both of them in a coordinated way. A Model-Predictive Control (MPC) solution to control the inlet throttle has been proposed in our previous work. This paper proposes a set of control solutions to regulate the variable speed pressurization fan system such that the energy efficiency of the considered HVAC system can be explicitly considered. A combined feed-forward with a PI-based feedback control solution, and an MPC solution are proposed based on derived simple system models. Some preliminary simulation results show that both control solutions can keep the indoor pressure and the air circulation in a very satisfactory and robust manner, even subject to the presence of severe disturbances.
Our recent experimental investigations of flexible side-by-side blades under both steady and unsteady flows have observed flutter in both scenarios. Flutter significantly impacts blade kinematics and the hydrodynamic drag experienced by the blades. Our numerical approach [1], utilizing the reactive force model, successfully reproduces flutter phenomena. In contrast, the traditional Morison’s equation fails to trigger flutter. In the static regime where flutter does not occur, the bulk drag coefficients calibrated from experiments in steady and unsteady flows can be unified through an effective Cauchy number, allowing for the use of analytical models developed for steady flows in unsteady flows. In the flutter regime, using the bulk drag coefficient from steady flows underestimates the drag load in oscillatory flow.
This work is part of the ongoing implementation of hydroelastic solution for ships inside the OceanWave3D-seakeeping code. This solver has been developed by the Maritime Group at DTU- Department of Civil and Mechanical Engineering based on linearized potential flow theory. The numerical implementation has been conducted on overlapping grids using a high-order finite difference method. A Fast Fourier Transform (FFT) has been employed to transform the time-domain hydrodynamic solutions to frequency-domain solutions. A pseudo-impulse tailored to the desired frequency range is used as the forcing for the time-domain solution. In previous work, a preliminary implementation of hydroelastic solutions was implemented in OceanWave3D-seakeeping with an Euler-Bernoulli beam model to represent the eigenmodes of the flexible ship hull. However, shear effects are ignored by this beam theory, even though the shear effect is very important to acurately predict the structural deformation especially for a thick beam model. In this work, ship hulls have been treated using the Timoshenko beam model includ- ing shear effects. The influence of shear effects are also discussed through a couple of numerical test cases. Good agreement with reference solutions illustrates the effectiveness of the numerical implementation. The current work focuses on zero speed, and work is also in progress to validate the implementation at forward speeds
This work is part of the ongoing implementation of generalized modes for ship hydroe- lasticity inside the OceanWave3D-seakeeping solver. The solver has been developed by the Mar- itime Group at DTU- Civil & Mechanical Engineering based on solving the linearized potential flow problem using a high-order finite difference method on overlapping grids. The focus of this paper is a comparison between the hydroelastic solutions obtained using two different implementations of the hydrostatic restoring force coefficients. The first hydrostatic model is according to Newman, and the second model is based on Malenica and Bigot. These two hydrostatic models agree for the rigid modes, but are slightly different for the flexible modes. The results are validated using both numerical and experimental solutions for two different ship geometries at zero forward speed.