3D Hydroelasticity Research Articles

A frequency-domain hydroelastic analysis of a membrane-based offshore floating photovoltaic platform in regular waves

This study presents an approach for analyzing the hydroelastic response of membrane-based floating photovoltaic (PV) platforms. The structural deformation of the platform’s main components, including a floater and a membrane, is further described through a comprehensive set of in-plane and out-of-plane modes. This analysis employs potential flow theory and 3D hydroelasticity theory to evaluate the hydrodynamic loads. Additionally, the Morison equation is utilized to express the drag term associated with the floater’s in-plane motion. Addressing the connection between the floater and the membrane is achieved through the Lagrange multiplier method. Ultimately, this study establishes a frequency-domain coupled dynamic equation for the platform. The response results provide modal amplitudes and displacement data for test points, revealing that under low-frequency conditions, the flexible floater and the membrane conform to wave profiles. As the frequency increases, the impact of the floater’s stiffness becomes prominent, resulting in a substantial three-dimensional interaction effect. In addition, this study examines various structural parameters, specifically the membrane pretension, elastic modulus, and the bending stiffness of the floater, to illustrate their influence on the motion and deformation of the platform. This work contributes to a deeper comprehension of membrane-based floating PV systems and their practical applications.

Fully 3D ship hydroelasticity: Monolithic versus partitioned strategies for tight coupling

This paper analyzes the partitioned and monolithic strategies to simulate tightly coupled hidroelastic problems. The seakeeping hydrodynamics solver used is based on a first-order linear time-domain FEM model with forward speed and double-body linearization. The structural dynamics solver is based on a full 3D time-domain FEM with corotational shell elements accounting for the geometric non-linearity. Both solvers are implemented under the same programming framework, which allows to implement the monolithic strategy, and to minimize the communication overheads of the partitioned strategy. Two case studies are used to test and compare the partitioned and monolithic coupling: a flexible catamaran in oblique waves, and a large floating reticulated structure made of fiber reinforced plastic. In both cases, the monolithic strategy is between three and four times faster than the partitioned strategy.This project has been developed under the H2020 project FIBRESHIP aimed at developing the technology to design and build the structure of large-length vessels in fiber reinforced polymers.

Experiment and numerical investigation on structural response of a FMRC hexagon enclosed platform in waves

Hexagon Enclosed Platform (HEP) provides life accommodation, ship docking and marine replenishment for many ocean-going vessels in deep ocean. The HEP is composed of six trapezoidal floating modules connected by six rigid connectors and has characteristic of heteromorphic mat-type so that its hydroelastic response is critical. Therefore, this paper proposes a FMRC (Flexible modulus Rigid Connector) HEP model and studies its hydroelastic response by means of numerical simulations and model experiment. Firstly, a scaled model of HEP which is also made up of six trapezoidal structural modules constructing with a steel layer and foam layer is designed and fabricated for model experiment. Secondly, the model experiment of HEP is performed in a number of tank waves. Thirdly, 3D hydroelasticity method is used to calculate the load and structural responses of HEP model. Finally, numerical results and experimental results involving frequency-domain and time-domain results are obtained and compared, and the structural response mechanism of FMRC HEP is analysed. It is found that experimental results and numerical results have accordant matching and hydroelastic response of HEP is generated indeed based on research results. The research results and conclusions obtained in the paper are used to guide conceputal design of a HEP structure.

Investigation of connector loads of a 3-module VLFS using experimental and numerical methods

The connector loads of a 3-module VLFS (Very Large Floating Structure) deployed in the shallow water areas have been investigated by experimental and numerical methods. For the numerical method, a simplified analysis procedure has been built based on 3D hydroelasticity theory and RMFC (Rigid Module Flexible Connector) model, and the effect of the uneven seabed can be included in this procedure. The model tests of the 3-module VLFS considering the complicated seabed topography and wave environment have been finished. Some key technologies for the model tests have been solved, such as the simulations of the complicated seabed topography and the connector model. A lot of the first-hand model test results have been discussed and compared with the numerical results. Some useful conclusions were obtained, which can provide reference basis for the preliminary and conceptual design of VLFS and its connectors.

Time-domain numerical and segmented model experimental study on ship hydroelastic responses and whipping loads in harsh irregular seaways

In this paper, wave-induced motions and loads of a bow flare ship advancing in harsh irregular waves are investigated both numerically and experimentally. A 3D time-domain hydroelasticity theory that includes memory-effect function considering Froude–Krylov nonlinearity is developed to predict ship motions, wave loads and slamming loads in long-crested irregular waves. In the hydroelasticity algorithm, the wave memory effects and forward speed effects are addressed by retardation function method to improve the computing efficiency and provide opportunity for short-term statistical analysis of ship responses in irregular waves. In addition, segmented model tank tests are conducted to experimentally investigate the motions and loads of ship sailing in long-crested irregular waves and also validate the numerical results. To further understand the nonlinear wave loads behavior of ship in short-crested waves, large-scale segmented model sea trials are performed in realistic sea waves. The numerical results and experimental results are systemically analyzed and compared using time series, spectral and probability statistical analysis methods.

Three-dimensional hydroelasticity theory of ships in waves and ocean-acoustic environment with applications

The three-dimensional (3D) hydroelasticity theory of floating structures established in 1984 embodies the predictions of seakeeping behaviors, structural loads, dynamic strength, fatigue, and vibration of a surface ship or an underwater vehicle travelling in the sea in a unified generalized fluid-structure interaction theory. After more than thirty years of development, this theory has been further extended to two main branches: the 3D hydroelasticity theories for examining the wave excited dynamic responses of ships, and the 3D hydroelasticity theories for investigating the machinery or propeller excited vibrations and underwater acoustic radiations of a ship. The latter is also called the 3D sono-elasticity theory of ships. Drawn by the momentum gained from the comprehensive demand of marine applications, China Ship Scientific Research Center (CSSRC) has been devoted to the systematic innovative research in creating the linear and non-linear 3D hydroelasticity theories of ships, the 3D hydroelasticity theory of floating structures deployed in complicated ocean geographical environment near islands and reefs, the 3D sono-elasticity theory of ships in ocean acoustic environment etc. together with developing the numerical methods and corresponding software. These have been extensively employed to solve the key technical problems, such as motion and structural response predictions, behavior and safety assessment, design check and optimization of surface ships, underwater vehicles and other marine structures, This paper is not to present the state of the art of the worldwide development of hydroelasticity theories, but to concisely described the concept and framework of the 3D hydroelasticity and sono-elasticity theories of ships which are mainly developed by the research group of CSSRC. Typical application examples of the hydroelastic analyses of a 500000 DWT ultra large ore carrier and an 8-module very large floating structure, as well as the sono-elastic analysis of a simplified submarine model are also briefly illustrated. Finally, simply mentioned are the important directions of future research in the field of hydroelasticity and sono-elasticity of ships.

Springing Responses Analysis and Segmented Model Test on a 550,000 Dead Weight Tonnage Ore Carrier

In hydroelastic model tests, segmented ship models are usually used to make sure that the model scale and the full size ship satisfy the similarity law of structural natural frequency and distribution of ship bending stiffness. However, springing barely occurs in those tests because the natural frequency of segmented ship models is too high for the regular waves required to be generated in a tank. In order to investigate the springing effect, three sets of backbone of variable cross section are adopted in the test. One set of backbones satisfies the similarity law of natural frequency, and two extra sets of low stiffness backbones are used so that the springing effect can appear and be measured. Experimental results show that the springing occurs when the wave encounter frequency coincides with the first elastic natural frequency of the ship, or with half or one-third of it. A good agreement has also been obtained between the experimental and the numerical results by a three-dimensional (3D) hydroelasticity method. Based on these results, the contribution of the springing responses to the fatigue damage of the ship is estimated and analyzed.

Investigation of hydroelastic ship responses of an ULOC in head seas

Investigation of hydroelastic ship responses has been brought to the attention of the scientific and engineering world for several decades. There are two kinds of high-frequency vibrations in general ship responses to a large ocean-going ship in its shipping line, so-called springing and whipping, which are important for the determination of design wave load and fatigue damage as well. Because of the huge scale of an ultra large ore carrier (ULOC), it will suffer seldom slamming events in the ocean. The resonance vibration with high frequency is springing, which is caused by continuous wave excitation. In this paper, the wave-induced vibrations of the ULOC are addressed by experimental and numerical methods according to 2D and 3D hydroelasticity theories and an elastic model under full-load and ballast conditions. The influence of loading conditions on high-frequency vibration is studied both by numerical and experimental results. Wave-induced vibrations are higher under ballast condition including the wave frequency part, the multiple frequencies part, the 2-node and the 3-node vertical bending parts of the hydroelastic responses. The predicted results from the 2D method have less accuracy than the 3D method especially under ballast condition because of the slender-body assumption in the former method. The applicability of the 2D method and the further development of nonlinear effects to 3D method in the prediction of hydroelastic responses of the ULOC are discussed.

Nonlinear vertical accelerations of a floating torus in regular waves

The longitudinal motions and vertical accelerations of a floating torus as well as wave motion inside the torus are studied by model tests in regular deep-water waves. Comparisons are made with linear and partly with second-order potential-flow theory for the smallest examined experimental wave height-to-wave length ratio 1/120. Reasonable agreement is obtained, in particular for the linear problem. The importance of 3D flow, hydroelasticity and strong hydrodynamic frequency dependency is documented. Experimental precision errors and bias errors, for instance, due to tank-wall interference are discussed. Numerical errors due to viscous effects are found to be secondary. Experiments show that the third and fourth harmonic accelerations of the torus matter and cannot be explained by a perturbation method with the wave steepness as a small parameter.

웨이블릿 교차상관관계를 이용한 변형체 선박의 휘핑 응답 식별

Identification of the whipping response out of the combined wave-vibration response of a flexible sea going vessel is one of the most interesting research topic from ship designer's point of view. In order to achieve this goal, a novel methodology based on the wavelet cross-correlation technique was proposed in this paper. The cross-correlation of the wavelet power spectrum averaged across the frequency axis was introduced to check the similarity between the combined wave-vibration response and impulse response. The calculated cross-correlation of the wavelet power spectrum was normalized by the auto-correlation of the each spectrum with zero time lag, eventually providing the cross-correlation coefficient that stays between 0 and 1, precisely indicating the existence of the impulse response buried in the combined wave-vibration response. Additionally, the weight function was introduced while calculating the cross-correlation of the two spectrums in order to filter out the signal of lower frequency so that the accuracy of the similarity check becomes as high as possible. The validity of the proposed methodology was checked through the application to the artificially generated ideal combined wave-vibration signal, together with the more realistic signal obtained by running 3D hydroelasticity program WISH-Flex. The correspondence of the identified whipping instances between the results, one from the proposed method and the other from the calculated slamming modal force, was excellent.

3D Dynamic Hydroelasticity Analysis of Light Weight Pyramidal Sandwich Plates with Imperfection Subjected to Water Impact

The aim of this work is to investigate the hydroelastic responses of rectangular, clamped light weight pyramidal sandwich plate structures with imperfection (LWPSPS-IM) subjected to water impact via analytical prediction and numerical simulation. Firstly, the characteristics of impact pressure and structure deformation are computed by using FEM program LS-DYNA based on the proposed 3D multi-physics computational model. Numerical results show that the impact pressure of total fluid-solid interaction (FSI) surface for LWPSPS-IM is lower than that of the perfect LWPSPS. In the theoretical approach, a novel analytical method is proposed to calculate the elastic constants of LWPSPS-IM. Then an engineering estimation model to predict the maximum deformation of LWPSPS-IM is developed, in which the total deformation is divided into two parts, i.e. local field deformation and global field deformation and they are both computed using analytical approach. Good agreement between the numerical results and ones obtained from the proposed analytical model is achieved.

Dynamic analyses of floating fish cage collars in waves

An extended 3D hydroelasticity theory is used in the frequency domain to predict the dynamic response of 5 by 2 floating fish farm collars in regular waves. Hinge modes in two directions and flexible torsional modes are all considered in the analyses. The dry and wet resonant natural frequencies for each rigid relative motion and the flexible modes are also calculated. The results show that the modes, flexible bending and torsional modes, as well as their interactions, greatly contribute to the dynamic response of the floating collar system. From a design point of view, the effects of the connector rotational stiffness on the dynamic response of the structures are also analysed.

Advances in the three-dimensional hydroelasticity of ships

The study of hydroelasticity of ships first gained momentum in the late 1970s with the work of Bishop and Price, who established the two-dimensional (2D) hydroelasticity theory of ships. The concept and basic principle presented in their work to embody the structure and the surrounding fluid as a coupled entirety was further employed and extended in the creation of the general linear three-dimensional (3D) theory of hydroelasticity for an arbitrary shaped flexible marine structure travelling with a forward speed in a seaway in the middle of 1980s (Wu, 1984; Price and Wu, 1985a; Bishop et al., 1986). Since then, great progress has been achieved in the development and application of 3D hydroelasticity theories. These include the more rigorous methods of frequency-domain linear analysis accounting for the forward speed effect and the steady flow effect, the time-domain linear 3D theory, the non-linear 3D theory and the numerical methods for a floating structure travelling in rough seas with large motions, experimental techniques of 3D flexible ship models, the hydroelasticity-based design and safety assessment, etc. This paper presents an overview of these developments and achievements of linear and non-linear 3D hydroelasticity theories of ships, and the corresponding numerical and experimental techniques.

Ribbon bridge in waves based on hydroelasticity theory

For the design and operation of a floating bridge, the understanding of its hydroelastic behavior in waves is of great importance. This paper investigated the hydroelastic performances of a ribbon bridge under wave action. A brief introduction on the estimation of dynamic responses of the floating bridge and the comparisons between the experiments and estimation were presented. Based on the 3D hydroelasticity theory, the hydroelastic behavior of the ribbon bridge modeled by finite element method (FEM) was analyzed by employing the mode superposition method. And the relevant comparisons between the numerical results and experimental data obtained from one tenth scale elastic model test in the ocean basin were made. It is found that the present method is applicable and adaptable for predicting the hydroelastic response of the floating bridge in waves.

Composite 2D/3D Hydroelastic‐Analysis Method for Floating Structures

A new approach to the analysis of the wave‐induced, hydroelastic response of floating, slender structures is developed that combines a three‐dimensional structural model with fluid forces from two‐dimensional potential theory (strip theory). Because a three‐dimensional finite‐element model of the structure is used, the method allows direct computation of three‐dimensional structural response, such as individual member forces and stresses. However, because a two‐dimensional fluid model is used, the large computational effort of three‐dimensional hydroelasticity (primarily a result of three‐dimensional potential theory) is avoided. The composite 2D/3D method is verified by satisfactory agreement with results from full three‐dimensional hydroelasticity for a SWATH (small water‐plane area twin‐hull) ship. The results indicate that the method may be useful in design of large, slender structures, such as ships, because the computational effort is significantly less than required in 3D hydroelasticity.