Pontoon Type Research Articles

폰툰식 VLFS의 초기구조설계에 관한 연구

In general the loads due to ocean wave are considered as main design parameters governing the global structural safety of VLFS (Very Large Floating Structure). In order to predict design wave loads accurately, hydro-elastic analysis must be conducted considering the initial global flexural rigidity of VLFS. However, in order to determine the structural scantling of major members (deck, bottom, side panels and longitudinal / transverse BHD etc.), static load and design wave loads must be given as explicit form generally. Therefore in order to determine a proper structural arrangement and scantlings of VLFS at initial design stage, both calculations of structural scantling and hydro-elastic analysis for wave conditions must be conducted iteratively and the convergence of their results must be checked. On this paper, based on the case design of a 500×300 m size's floating marina resort, the details of structural design technique using hydro-elastic analysis are explained and discussed. At first, the environmental conditions and the system requirements of the design of marina resort are described. The scantling formulas for the major members of pontoon type VLFS are proposed from the local and global design points of view. Considering the design wave loads as well as static design loads, the structural safety is checked iteratively.

연직판형 부소파제의 수리학적 특성과 동적거동

In order to develop a floating breakwater, which can efficiently control long period waves, vertical plates are attached in pontoon. Wave control and dynamic behaviors of the newly developed vertical plates type are verified from numerical analysis and hydraulic experiment. As a result, for the wave control and energy dissipation, the newly developed vertical plates type is more efficient than the conventional pontoon type. For the floating body motion, the wave transmission, depending on incident wave period, is decreased at the natural frequency. Dimensionless drift distance has similar trend of the reflection rate of wave transformation near natural frequency except maximum and minimum values. Dimensionless maximum tension is 17 percent of the weight of floating breakwater in case of the conventional pontoon type and 18 percent or 14 percent in case of the newly developed vertical plates type. Thus, it is shown that the wave control is improved by the vertical plates type. In addition, by adjusting the interval of the front and back vertical plate, we would control proper wave control.

불균일 강성을 갖는 폰툰형 구조물의 유탄성 응답 특성에 관한 실험 연구

Very Large Floating Structure(VLFS) is regarded as one of promising candidates for the future utilization of ocean space. VLFS has the merits of small environmental effect. short construction term, easiness for extension and removal. It is well known that hydroelastic response is one of major design concerns of such a huge structure. Most of studies on the hydroelastic analysis of VLFS assumed uniform mass and bending stiffness. In case of a floating hotel where noticeable change of mass and stiffness at the hotel part is expected. it is necessary to investigate the effect of nonuniform mass and bending stiffness on the hydroelastic response. A model test of a pontoon type VLFS with nonuniform bending stiffness carried out for performance evaluation of a floating marina-hotel-convention center is described in this paper. Through investigation of model test results and comparison with numerical analysis using eigenfunction method, effect of the variation of bending stiffness is discussed.

弾性変形を考慮したポンツーン型浮体に作用する変動波漂流力の解析

A pontoon type Very Large Floating Structure (VLFS) is expected to be implemented in the near future. Design of mooring system of VLFS requires an estimate of slowly-varying wave drift force. However, slowly-varying wave drift force on elastic VLFS has not been precisely computed yet. Slowly-varying wave drift force is second order wave force with respect to the wave height. Computation of second order wave force is very complicated and difficult because it requires computation of second order velocity potential. The authors have resolved this problem by using assistant radiation potential method, restricting the model for analysis to a pontoon type VLFS. In this paper, computation of slowly-varying wave drift force on elastic VLFS has been made, and comparison between direct computation and well-known approximation (Newman's approximation) is presented.

해수순환 방파제를 고려한 폰툰형 구조물의 유탄성응답 해석

Ocean space utilization using VLFS(Very Large Floating Structures) can provide environmental impact free space by allowing sea water flow freely through the floating structure. Use of Pontoon type VLFS for that purpose needs employment of breakwaters for reduction of wave effects. Therefore, in order to maximize advantage of environmental impact free structure, the breakwater should be the one that can allow water flow freely through it, too. In this paper hydroelastic response of a pontoon type structure is analyzed considering breakwaters which allow water flow through its opening at bottom of the breakwaters. Mode superposition technique is used for solving equation of flexible body while interactions between the pontoon and breakwaters is considered based on generalized mode concept. Bi-quadratic nine node higher-order boundary element method is adopted for more accurate numerical treatment near sharp edged body shape. Performance of various combinations of breakwaters is investigated.

Behaviors of a Very Large Floating Structure Supported with Dolphins under Earthquake Loading

Researches and developments of VLFSs for airport use and so on have been carried out for recent years. There is a VLFS which has a pontoon type floating structure supported with many dolphins and it is important to investigate sufficiently the behaviors of such VLFS under earthquake loading.In this paper, a floating structure supported with 49 dolphins was modeled as both a horizontally elastic plate and rigid plate supported with springs and dashpots through gap elements. The time history response analyses of the structure when the gaps between fenders and dolphins were equal to zero were performed with varying the period and the velocity of the applied sinusoidal waves as an earthquake loading and the following conclusions have been obtained.1. The floating structure oscillates transversely with their natural periods of sway and yaw irrespective of the periods of sinusoidal earthquake wave applied, though the transverse oscillation is overlapped with an oscillation, of which period is the same as that of sinusoidal earthquake wave applied.2. The floating structure has resonance with the sinusoidal earthquake wave not only in the modes of sway and yaw but also in the modes of two and more nodes elastic vibration due to the horizontal elasticity of the structure. The fender, dolphin and ground also have resonance.3. When the sinusoidal earthquake wave velocity is relatively low, the resonance in the mode of yaw appears and the fender and dolphin reaction forces in the mode of yaw become larger than those in the mode of sway.4. An equation is proposed to estimate the sinusoidal earthquake wave velocity that the strong resonance of the floating structure with the sinusoidal earthquake wave in the mode of yaw and two and more nodes elastic vibration of the floating structure.5. Resonance periods of the fender, dolphin and ground are obtained accurately from the vibration equation on spring and dashpot and the resonance period of floating structure in the mode of sway is obtained as equal to that of fender.6. Within the low period region where dolphin and ground have resonance with the sinusoidal earthquake wave, the fender and dolphin reaction forces are not affected by the horizontal elasticity of the floating structure and the sinusoidal earthquake wave velocity.

A Fundamental Study on Hydroelastic Behavior of Flexible Floating Structures Supported by Several Aircushions in Regular Waves

Hydroelastic behavior of a flexible floating structure supported by several aircushions arranged in a lattice is discussed in this paper. The modified pressure distribution method, which can consider influence of the aircushion, is applied to a prediction of the hydrodynamic forces.A general pontoon type and four aircushion models are used for the prediction of elastic behavior. From the results, it is possible to reduce the response even if unit aircushion is a small scale. And also the aircushion type is useful to reduce the response of the structure in oblique waves.

흘수가 폰툰형 초대형 구조물의 유탄성 응답에 미치는 영향 해석

본 논문에서는 고차경계요소법을 사용하여 폰툰형 초대형 구조물의 유탄성 응답을 해석하였다. 폰툰형 구조물의 설치가 예상되는 천수심 해역에서 유탄성 응답 해석에서 흘수의 영향을 고찰하였다. 초대형 구조물인 경우 실제 해상파의 파장 범위인 단파장 구간일 때 흘수의 영향을 무시한 해석은 구조물의 유탄성 응답과 상대파고를 과소평가 하는 것으로 나타나 폰툰형 구조물에서도 흘수 영향을 고려한 해석이 중요함을 보였다. Present study aims to investigate draft effects on hydro-elastic response of pontoon type VLFS(Very Large Floating Structure). A three dimensional higher-order boundary element method(HOBEM: Hong et al;1999, Choi, Hong and Choi; 2001) is extended to analyze elastic response of structures. Intensive numerical calculations were carried out for box type structure to investigate the draft effect on hydrodynamic forces on pontoon type VLFS. Main attention was paid to wave run-up along the waterline for various cases of draft scantling. It is found that the draft effects on the hydro-elastic response of pontoon type VLFS are important especially in short wave range and shallow water region.

On the prediction method of a hydroelastic responses of a VLFS considering a seabed topography

In recent years, there are a lot of researches on hydroelastic responses of a Very Large Floating Structure (VLFS) which has several kilometers both in length and width. In the most of these researches, a geometric shape of the model is pontoon-type rectangle VLFS and it assumes that the sea depth is constant. But if we have a plan to construct such large structure in actual coastal area, it is quite difficult to find a vast flat bottom of the sea in Japan. So, in this paper we propose a prediction method on a hydroelastic behavior of VLFS extending the eigen functions expansion method to that including the sea bottom topographical effects. In the analyses the hydroelstic effect of the VLFS is also analyticaly taken into account. One of the improve points of the present method is that the problem of any supportive type of VLFS (i.e. pontoon supportive, column-supportive etc.) can be analyzed by this method. In other words, we can treat the pontoon type problem as a box-like shape column supportive type.Finally, some numerical results are carried out and discussions on the validity of the present method and the effects of seabed topography are made in this paper.

The hydroelastic response of very large floating structure suppoted by footing-columns (2nd report)

A Very Large Floating Structure (VLFS) is expected as a new utilization of the ocean space. Rigidity of VLFS is, however, relatively small, so that an hydroelastic response of VLFS in waves should be considered. Many researchers studied on the elastic response of a pontoon type VLFS, in addition, on that of column support type VLFS. The VLFS supported by columns shows the smaller elastic response than that of the pontoon type VLFS. In the 1st report of this paper, we have discussed about hydrodynamic responses of a column with footing which has a wave-free frequency on wave exciting force and also examined the hydroelastic responses of a VLFS supported by a large number of the columns in regular waves.In this paper, we investigate on the charcteristics of hydroelastic behaviors of a VLFS supported by a large number of footing-columns which have two wave-free frequencies. And then, we disccuse about the hydroelastic behaviors of a VLFS in irregular seas based on spectral analyses. Furthermore we compare the hydroelastic responses of VLFSs among supported by columns without wave-free frequency, supported by columns with one wave-free frequency and supported by columns with two wave-free frequencies. In the analyses, the hydrodynamic forces of the single column are calculated by using 3-dimensional source sink method, and the hydrodynamic characteristics of VLFS are obtained by using hydro interaction theory.

Study on Critical Condition of VLFS with Large Aspect Ratio

In recent years, many researchers investigated the structural response of pontoon type VLFS (Very Large Floating Structure). They made clear, that the waves often excite the structure outstandingly in the specific wave directions. For the design of VFLS, we have to understand sufficiently the relation between the structural response and incident wave angles.In this paper, the structural response of the VFLS, which has a rectangular plane configuration with large aspect ratio, is examined. In the results, the critical condition, that induces peak strain energy of the floating body, is presented.

A Study on the Hydroelastic Behavior of a Pontoon Type Large Floating Disk

The solution method to the problem of a floating elastic disk subject to a train of plane waves is presented. This method is based on Stoker (1957) 's work and Ohkusu & Namba (1998) 's method using the assumptions of linear long wave theory, shallow draft approximation and Bernoulli-Euler equations for a thin plate. Solving an extended differential equation of Bessel in the disk domain, its velocity potential is matched to the exterior solution in the water domain. Some numerical results using this semi-analytical method are shown for a rigid or flexible disk relative to the length.

DYNAMIC MOVEMENT OF PONTOON TYPE FLOATING STRUCTURE WITH FLAT PLATES

Pontoon type floating structure with submerged flat plate has been studied in this paper. Wave response analyses of the pontoons have been performed for several different attached positions of flat plate and the stability of the pontoons were examined. Furthermore, the characteristics of the hydrodynamics such as the reflection and a transmission ratio were examined.It was verified that the flat plate have worked effectively for mitigation of the heaving motion, especially it is obvious to the plate area of 2 times of surfaces area at the water line and 0.02 or more wave steepness. It was confirmed that the dimension and attaching depth of flat plates important factor for motion control of a floating pontoon. The possibility of the stable improvement and the effective wave control by the size and position of the flat plate were shown.

A Study on the Hydroelastic Behavior of Pontoon Type Large Floating Structures

A Study on the Hydroelastic Behavior of Pontoon Type Large Floating Structures

Estimation Method of Slowly Varying Drift Motion and Elastic Behavior of Pontoon Type Very Large Floating Body in Irregular Waves

A real elastic motion of a very large floating structure is complicated because a field that a VLFS will be installed is random sea area. Then, it is important to predict horizontal motions too, because slowly varying drift motion may occur in irregular waves. So, the motion responses must be investigated in irregular waves.In this paper, one method in order to calculate a time series of wave drift forces is shown. The validity of that method and the estimation method of wave drift forces is confirmed by comparing with the corresponding experimental results. Then, the time histories of vertical and horizontal displacements are compared. And, this paper proposes the some examinations on the estimation method of the wave drift force. They are the effect of an interaction among directional angles of incident waves and the necessary term in order to predict it.

Hydroelastic Responses of Pontoon Type Very Large Offshore Structure

The authors consider a pontoon type flexible floating airport as the very large floating structure. In order to design this kind of structure, we have to investigate several key points in advance. Among those key points, estimation of the wave drift forces is very important in order to design of the mooring system. In this paper, the authors consider the square type flexible flat plate with shallow draft, exactly speaking, zero draft as the floating airport. The authors develop the computer code of the slowly varying wave drift force for an elastic floating structure with shallow draft based on the so called Near Field Method which is validated by both the Far Field Method and the corresponding Experiments.The authors conclude that even though the water depth is shallower, there is no big difference among the steady wave drift forces in each water depth, while the rigidity of the structure is smaller, more flexible, then, the steady wave drift forces or mooring forces are smaller.Finally, they showed the flexibility of a floating structure decreases not only steady wave drift forces but also slowly varying wave drift forces under the numerical time domain simulation of a very large floating structure with the multiple dolphins mooring system.

On the Hydroelastic Response of Box-Shaped Floating Structure with Shallow Draft

The research of VLFS (Very Large Floating Structure) for various applications such as floating airports is making a steady progress by the Technological Research Association of Mega-Float and others.The pontoon type structure with the length of 5 km, breadth of 1 km and draft of 1 m can be expected in the concept. This structure will be surrounded by the breakwaters for decreasing the influence of waves. Therefore the floating units of several hundred meters long should be connected together on offshore site instead of the construction in the dockyard.This paper deals with the wave induced connecting loads and the elastic behaviors of the box-shaped floating unit divided into three parts longitudinally. The 300 m long prototype structure used for atsea test by the Technological Research Association of Mega-Float has been modeled for the experiment. Three kinds of connecting conditions such as free condition without connection, pin-connection and beam connection have been considered.The numerical analysis code has been developed to estimate the elastic motions and the connecting loads. The analysis is based on FEM and the pressure distribution method using the zero-draft Green function. The authors have also carried out the tank tests using a 1/30 scale model for the validation of it. The test model has been designed on the basis of law of similitude concerning the stiffness and the mass of the structure.The calculated results show a quite satisfactory agreement with the experiment. It has been confirmed that the method has a sufficient accuracy for the practical use.

Study on Edge Shape of Very Large Floating Structures to Reduce Motion

In recent research, it has cleared that the motions of pontoon type very large floating structures (VLFS) are dominated by the dissipation wave that is induced by the floating structure and the fluid interaction. Incident wave excites the weather side of the structure, and then the deformation is propagated over all the structure. The deformation wave propagation to the main part of VLFS is not desirable, because the deformation requires the large area of high strength of the structures and the motion might affects the function of VLFS. In this study, the edge shape of VLFS that restrains the propagation of the deformation wave has been investigated. To evaluate the effect of the improved edge form, a program to calculate the response of VLFS that has arbitrary horizontal outline has been developed. Using the program, it has been confirmed that the notched edge reduces the deformation of the inner area of VLFS. In order to reduce the motion effectively, a relation between the edge form and the incident wavelength was found.

Hydroelastic Response Characteristics of a Pontoon Type VLFS in Waves

Hydroelastic Response Characteristics of a Pontoon Type VLFS in Waves

Hydroelastic Responses of Pontoon Type Very Large Floating Offshore Structure

Hydroelastic Responses of Pontoon Type Very Large Floating Offshore Structure