Rectangular Pontoon Research Articles

Hydraulic Model Tests for a Pontoon-Type Floating Structure with a Horizontal Damping Plate

In this study, hydraulic model tests were conducted to investigate the effect of a horizontal damping plate on the motion of the pontoon-type floating structure. The floating structures with and without the horizontal damping plates were fabricated with the scale of 1/20 and their motion responses to the regular and irregular wave conditions were investigated. From the comparison for the responses of each model with 16 wave conditions, it could be known that the damping plate made the response of the the pontoon to be smaller by about 5 to 10 % compared with the normal rectangular pontoon.

Comparison of different fidelity hydrodynamic-aerodynamic coupled simulation code on the 10 MW semi-submersible type floating offshore wind turbine

This study aimed to analyze and examine the precision of a middle-fidelity simulation tool by performing load analysis using CFD and middle-fidelity analysis tools. The analysis was performed on a fully coupled system including turbine, platform, and mooring system under the severe operating state. Grid sensitivity tests were performed on the turbine and floater to increase the precision of CFD results. The results showed that the mid-fidelity analysis tool had a high error rate in surge and pitch load responses due to failure in considering the current load caused by wind. Moreover, potential flow-based analysis tools can be less accurate for complex-shaped structures such as the rectangular pontoon used in this study. To determine the extent to which the viscosity effect, dependent on the wet body shape, affects the accuracy of the results, this study compared the accuracy of potential flow-based analysis tools and CFD. This study contributes to the development of research in this field by providing new insights and undiscovered results for analyzing a FOWT with an unstructured shape.

Simplified analytical solutions to the yaw dynamics of modular floating structures

Climate change has necessitated the development of modular floating structures (MFS) as a sustainable solution to enhance the resiliency of coastal cities against flooding and sea level rise. Hence, it is imperative that simplified methods of analysis are introduced to the design community. This technical note presents closed-form expressions parameterizing the response amplitude operators (RAO) of rectangular pontoons subject to yaw (rotation about the vertical z axis) to complement solutions derived by Wang (2022) for the five remaining degrees of freedom. Following validation, a parametric investigation was implemented to assess the influence of pontoon geometry on the yaw response of an idealized MFS exposed to realistic sea states. It was identified that pontoons exhibiting a characteristic width smaller than the wavelength are generally more resistant to yaw excitation as they become squarer in shape. Conversely, while larger pontoons are less sensitive to geometric effects, they exhibit heightened sensitivity to changes in wave conditions. The simplified analytical approach thus provides an accessible pathway towards the structural or architectural design of floating structures as a precursor to detailed computational modeling.

Analytical solutions for the dynamic analysis of a modular floating structure for urban expansion

Modular floating structures (MFS) offer a sustainable alternative over traditional land reclamation for the expansion of coastal megalopolises in the context of climate change adaptation. Yet, there are currently no guidelines for structural engineers pertaining to their analysis and design. This work presents analytical solutions readily accessible for the dynamic analysis of MFS utilizing conventional rectangular pontoons subject to regular or irregular waves. Closed-form formulations utilizing linear wave theory proved capable in capturing the response amplitude operators (RAO) for sway, heave, and roll when compared against smoothed particle hydrodynamics (SPH) simulations for a typical MFS to which appropriate damping ratios were obtained. A parametric study was subsequently implemented to examine the contribution of building slenderness and superstructure-to-pontoon mass ratios on critical accelerations induced by different sea states. It was revealed that structural configurations beneficial to static stability may result in larger dynamic effects under wave excitation thus compromising occupant comfort delineated via various international standards. Ultimately, this paper represents a significant step towards the realization of MFS for urban expansion by providing structural engineers with an accessible methodology for the dynamic analysis of floating structures as a precursor to detailed computational modeling.

Stability of floating barges with trapezoidal and pentagonal sections

The issues of stability of the symmetrical equilibrium position of floating barges in liquid, which have trapezoidal and pentagonal sections, are discussed in the paper. The basic principles of static analysis necessary for studying the stability of floating bodies are given. The exact expression for the potential energy of a floating body is constructed and its quadratic approximation is calculated near the investigated equilibrium state for both problems under consideration. Stability conditions are obtained in terms of dimensionless parameters on the basis of these expressions, and each of the problems under discussion has three such parameters. It is checked that for particular variants of a rectangular pontoon and a triangular boat, the previously known results follow from the found stability conditions in both problems. The found solutions are illustrated as a series of stability regions on the plane of two dimensionless parameters when the value of the third parameter varies. This graphical interpretation allows to establish the main qualitative and quantitative features of the constructed solutions and draw key conclusions. The obtained results are interesting from a theoretical point of view and may be of some practical value.

An experimental study on vortex-induced motion responses of a moored semi-submersible with and without riser

This article presents an experimental study on the “vortex-induced motion” responses of a moored “semi-submersible without catenary riser” and “semi-submersible with catenary riser.” An eight-point catenary mooring system is adopted for the study in which eight rollers are installed on the pontoons for guiding the mooring lines and the semi-submersible design is of two rectangular pontoon and two circular columns on each of the pontoons. To replicate the real-world scene, the experiments are conducted in wave-cum-current flume with five directions of current (i.e. 0°, 30°, 45°, 60°, and 90°) to study the vortex-induced motion under the surge and sway degrees of freedom at high dimensionless reduced velocities (i.e. 6< Urs<50.86). Along with the surge and sway degrees of motion, the roll and pitch degrees of motion are investigated too with their paths for semi-submersible (i.e. amplitude traces). A “stainless steel flexible braided hose” with an aspect ratio of 157 till the touchdown point is used as a catenary riser. Results are presented with the definitions of degrees of freedom with respect to the axes defined at the center of gravity of semi-submersible and show that above the reduced velocity of 25 for the sway and surge degrees of freedom, the vortex-induced motion responses show a complex variation without any monotonicity. Furthermore, it is observed that (1) in traces there are no eight-shaped trajectories; (2) for both the semi-submersible without catenary riser and semi-submersible with catenary riser, the higher responses occur along the diagonals; (3) there are couplings of the pitch with surge, and roll with sway dofs; (4) the catenary riser reduces the vortex-induced motion responses for most of the current directions; and (5) galloping instabilities may be occurring and higher amplitudes may be related to them. Finally, it is shown that the vortex-induced motion response of semi-submersible reduces the vortex-induced vibration response of riser and that the motions in pitch and roll are likely to become critical and they demand a detailed analysis to be addressed in future to improve the operational range of semi-submersible and catenary riser in deep water depths under harsh marine environment of high current velocities.

Investigating the Response Amplitude Operator of a Heaving Pontoon under the Influence of a Submerged Trapezoidal Breakwater

Although breakwaters are of great importance to damp the wave energy and protect floating vessels/facilities, they are not fully successful in reducing the waves’ height. Therefore, special attention should be paid to accurately investigate the performance of breakwaters. In this paper, the efficiency of a submerged trapezoidal breakwater in the vicinity of a floating pontoon is numerically investigated. First, different simulations are conducted to calibrate the numerical model to achieve an optimum mesh size. Next, a test case is presented for simulation of regular waves passing over a submerged breakwater. Subsequently, the heave response amplitude operator (RAO) of a rectangular pontoon facing an incoming regular wave is studied. A comparison of the obtained results in both test cases with experimental data shows good compliance. Ultimately, the heave motion of a rectangular pontoon behind four different submerged trapezoidal breakwaters facing a regular wave is investigated and different parametric studies are conducted to assess the geometrical effect of the breakwaters. This is the main novelty of the present work which studies the effect of a breakwater on the response amplitude operator (RAO) of a floating structure. In fact, a new version of RAO is presented which includes both incident and transferred wave (which pass over the breakwater) affecting the floating body. Based on the acquired results, the modified RAO of the heaving pontoon shows that breakwater has no effect on the responding frequency, but it does reduce the amplitude of the exciting wave up to 30%.

Influence of Payloads on the Hydrodynamic Response of Semi Submersible Platform

The hydrodynamic analysis of the semi submersible platform was carried out for height. with and without mooring condition by changing the metacentric A physical model of scale 1 in 100 was tested in 1m width and 30 m long regular wave flume at CWR (Centre for Water Resource) Laboratory. The model has four rectangular columns and two rectangular pontoons along with mooring. The natural heave, pitch and roll periods of the semi-submersible have greatest impact on the downtime of platform operation.This paper focus on the influence of payloads on the hydrodynamic behavior semisubmersible platform. On the basis of present work, the configuration of Semi-submersible having four rectangular columns and two rectangular pontoons has been arrived at for the proposed desalination plant.

An experimental study of double-row floating breakwaters

A preliminary experimental study on the hydrodynamic behaviors of double-row floating breakwaters is carried out in a wave flume under regular wave action. The floating breakwater chosen as the experimental subject is a dual rectangular pontoon floating breakwater. The hydrodynamic behaviors of the floating breakwater are validated through the calculation of the wave transmission coefficients, the wave reflection coefficients, the motion responses of the floating breakwaters and the mooring forces for different waves and structural parameters. The dynamic responses of single-row floating breakwater as a control group are also examined in the present experiments. The results indicate that double-row floating breakwaters significantly reduces the transmission coefficients as compared with single-row floating breakwater, especially for short-period wave, which is attributed to dissipation caused by eddies and moon-pool effect. However, the reflection performance is almost identical between two types. It is also found that the motion responses of the single-row and double-row floating breakwaters are similar. Spacing distance between double-row floating breakwaters has a significant influence on the windward mooring tension of the model at the upstream location, which always keeps the largest level in all mooring forces.

Parametric study on the vortex-induced motions of semi-submersibles: Effect of rounded ratios of the column and pontoon

The vortex-induced motions (VIMs) of semi-submersibles have emerged as an important issue in offshore engineering, as they pose a threat to safe and reliable operations and severely affect the fatigue lives of risers and mooring systems. The VIM response depends on the shape of the submerged structure and thus is significantly influenced by the design parameters related to the columns and pontoons. Numerical simulations by the detached Eddy simulation method are validated by experimental data and then used for parametric analysis of the VIM performance of various semi-submersibles with different column rounded ratios (Rc/L) and pontoon rounded ratios (Rp/Lp). The results show that the transverse amplitudes of a semi-submersible with circular columns at a 0° current heading are twice as large as those at a 45° current heading. However, the semi-submersible with rounded square columns shows more significant transverse motions at a 45° current heading than at a 0° current heading. Furthermore, at the 45° current heading, the transverse amplitudes of the semi-submersibles show a rapid increase as the column radius increases in the range of Rc/L<0.1. The peak values remain roughly the same for 0.1≤Rc/L≤0.2 and then decrease as the column radius increases (Rc/L≥0.3). In addition, the effect of the pontoon shape on the transverse response is negligible for semi-submersibles with sharp square columns, while for semi-submersibles with rounded square columns or circular columns, the sharp rectangular pontoons greatly mitigate the VIM response.

Time-domain hydrodynamic analysis of pontoon-plate floating breakwater

The hydrodynamic behaviors of a floating breakwater consisting of a rectangular pontoon and horizontal plates are studied theoretically. The fluid motion is idealized as two-dimensional linear potential flow. The motions of the floating breakwater are assumed to be two-dimensional in sway, heave, and roll. The solution to the fluid motion is derived by transforming the governing differential equation into the integral equation on the boundary in time domain with the Green's function method. The motion equations of the floating breakwater are established and solved with the fourth-order Runge-Kutta method to obtain the displacement and velocity of the breakwater. The mooring forces are computed with the static method. The computational results of the wave transmission coefficient, the motion responses, and the mooring forces of the pontoon-plate floating breakwater are given. It is indicated that the relative width of the pontoon is an important factor influencing the wave transmission coefficient of the floating breakwater. The transmission coefficient decreases obviously as the relative width of the pontoon increases. The horizontal plates help to reduce the wave transmission over the floating breakwater. The motion responses and the mooring forces of the pontoon-plate floating breakwater are less than those of the pontoon floating breakwater. The mooring force at the offshore side is larger than that at the onshore side.

파랑 입사각이 장방형 플로팅 함체와 상부 골조에 미치는 효과

파랑하중의 입사각의 변화가 직사각형 콘크리트 플로팅 함체 위에 있는 3층 철골 모멘트 연성골조의 모멘트에 미치는 영향을 알아보기 위하여, 파도 주기 5초부터 15초까지 2초 간격으로 동적 유체해석을 수행하였다. 길이방향에 대하여 입사각이 <TEX>$0^{\circ}$</TEX>, <TEX>$30^{\circ}$</TEX>, <TEX>$60^{\circ}$</TEX>, <TEX>$90^{\circ}$</TEX>로 증가함에 따라 RAO-Roll에 의한 영향이 증가하는 것으로 나타났다. 파압에 의하여 입사각이 <TEX>$0^{\circ}$</TEX>인 경우 길이방향의 골조 모멘트가 크게 증가하였으며, 입사각이 증가함에 따라 파압에 의한 모멘트가 감소하는 것으로 나타났다. 또한 함체의 피칭과 롤링에 의하여 발생되는 가속도 성분에 의하여 상부 철골 모멘트 연성 골조의 모멘트를 산정하였으며, 입사각이 <TEX>$90^{\circ}$</TEX>로 작용한 경우에 모멘트의 증가량이 입사각 <TEX>$0^{\circ}$</TEX>의 경우보다 크게 나타났다. To find the influence of incident angle of wave on the moment of 3 storied steel moment resisting frame which is placed on the concrete rectangular pontoon, the fluid dynamic analysis is carried out, varying the period of wave from 5 to 15 second by 2 seconds. As increasing incident angle of wave to longitudinal axis, the influence of RAO-rolling is increased. The moment of longitudinal frame is increased apparently by the wave pressure when the incident angle is <TEX>$0^{\circ}$</TEX>. And the moment of the frame due to the wave pressure is decreased as the incident angle is increased. But the moment of frame due to acceleration caused from pitching and rolling is increased. It is shown that the increased moment when incident angle is <TEX>$90^{\circ}$</TEX> is much greater than that of incident angle <TEX>$0^{\circ}$</TEX>.

Optimal planning of cargo operations at bunkering tankers with respect to dynamical character of their parameter restrictions

The present paper is devoted to the problem of bunkering tankers' optimal cargo planing. The brief analysis of existing approaches for solving the multiple-criterion optimisation problem is fulfilled with respect to specific features of the bunkering control processes. The complex three-component non-linear criteria taking into account restrictions at both cargo tanks capacity and tanker's loading conditions is developed. The solution of the non-linear mathematical programming problem for the model of the tanker in the form of rectangular pontoon is presented and confirms efficiency of the suggested criterion. The necessity of dynamical character of restrictions applying is proved for the problem. The fuzzy system for the restrictions issuing is also developed.

Semi-Analytical Hydrodynamics and Motions for a TLP Structure—Part I: Enhancement of Pontoon Results Using Two of Haskind’s Theorems

Abstract A semi-analytical solution procedure for the derivation of first-order wave forces, added mass, and damping terms is presented for rectangular pontoons which may be floating, submerged, or resting on the seabed. The development is based on a solution matching technique for the scattered and radiated wave potentials and gradients across common boundaries of the subdivided solution domain. The final expressions are true for waves of arbitrary angle of incidence and singularities due to the case of normal incidence are eliminated. The approach is also generalized for the case where the pontoon is a unit of a TLP offshore production system by referring all quantities to a global coordinate system. Numerical results are extracted for a number of benchmark problems and compared with independent values where available in the literature. Excellent agreement is obtained for wave forces, added mass, and damping Values for cases involving floating, submerged, and bottom-founded pontoon configurations.