Ship Wave Loads Research Articles

CFD-FEM simulation of hydroelastic responses and slamming loads of a bow-flare ship advancing in head regular waves

ABSTRACT In this paper, the global motions and wave loads on a large bow-flare ship with the effect of hydro-elasticity, including whipping and springing, are numerically simulated by a CFD-FEM two-way coupled method. The simulation results of ship motions and wave loads by employing the numerical method are demonstrated by verification and validation studies including comparison with tank model experiment results. Additionally, the presented method is applied to study the motions, wave loads and slamming loads of the ship in different wave conditions. The vertical bending moment and vertical shearing force of different frequency components and their distribution along ship length are studied. The characteristics of slamming pressure and green water loads and their spatial distribution are studied. The simulation results indicate that the present numerical method well reproduces ship seakeeping and hydro-elasticity and has potential application values in the design and evaluation of ship wave loads.

Intelligent prediction of wave loads based on multi-source data-driven methods

ABSTRACT High-fidelity wave-load tests is pivotal in the design and development of modern ship structures. Nonetheless, the prohibitive cost of conducting such tests limits their applicability. A wave-load data fusion method was implemented using the model test data from a typical displacement-type ship to generalise the small sample test, and a multi-source data characterisation and model parameter optimisation method were established to achieve efficient wave-load (wave frequency and slamming superposition) prediction. Using multi-source data, a multi-fidelity wave-load prediction (MFWLP) model was constructed by combining numerical computation, regular wave tests (RWT), and irregular wave test (IWT) data based on transfer learning with a secondary correction wave load prediction under irregular wave conditions. The model was effectively employed in a ship wave-load engineering case. This study reveals that the adopted MFWLP model demonstrates adequate extrapolation and prediction capabilities, even with limited high-fidelity test samples. The discrepancy between the nonlinear wave load prediction and model test was found to be within 15%. Therefore, the proposed method can serve as a foundation for rapidly assessing ship wave loads across various sea conditions, especially under high sea states.

A design method for rock groynes exposed to overtopping from long-period ship wave loads

In German estuaries ship induced loads have increased in recent years due to the gradual change of the fleet structure towards bigger vessels. Groynes in particular are vulnerable to long-period primary ship wave loading due to an overtopping phenomenon which at some localities can lead to severe damages. While in recent years the hydraulic processes have been the focus of investigations, currently no validated rock sizing method existents for this special load case. To investigate this problem a prototype experiment with two optimized groyne designs was conducted. Associated monitoring recorded wave heights, flow velocities and structural changes over the course of 4 years. This paper conducts an analysis of this accumulated data. Relationships of primary wave heights and overtopping flow conditions and thus to rock movements are discussed. Similarities to weir flow and overflowing of riprap embankments are exploited by applying existing analytical and empirical formulae. This leads to good stone size predictions as validated against the observed riprap erosion data. From 28 observed erosive events, 23 could are predicted correctly. Ultimately, a rock sizing method for rock groynes against primary ship wave loads is proposed.

Numerical method for whipping response of ultra large container ships under asymmetric slamming in regular waves

In this paper, a 3-D nonlinear time-domain hydroelastic analysis method for ship wave loads considering asymmetric slamming is proposed, and a 3-D Rankine panel method is used to solve the seakeeping problem. To accurately predict the hydroelastic response of the hull girder, the interaction between the hull structure and the flow field is considered in the body boundary condition. The motions and sectional loads of the ship are expressed by the superposition of the modal, which is obtained by modal analysis on a 3-D finite element model of the hull. After calculating asymmetric slamming loads using the Modified Logvinovich Model (MLM), the hydroelastic response of a 21,000-TEU container ship is analyzed, which incorporates the horizontal bending-torsional coupling vibration. Furthermore, the hull motion, slamming force, and section load are analyzed in detail to properly identify the mechanism of the slamming-whipping phenomenon. The results show that asymmetric slamming significantly affects the horizontal-torsional whipping response of the hull, especially when the wave encounter frequency matches the natural frequency.

Uncertainty analyses on the CFD–FEA co-simulations of ship wave loads and whipping responses

In this paper, a fluid–structure interactions method which fully couples CFD and FEA solvers in a two-way manner is used to estimate ship wave loads and hydroelastic responses. The global motions, wave loads, and springing and whipping loads on a standard S175 containership model evaluated by the CFD–FEA coupling method are comprehensively investigated and related verification and validation studies are conducted. Verification and uncertainty analyses on the influence of fluid grid density, time step, fluid domain size, fluid viscosity and hull structural element number on the results of ship responses by the CFD–FEA coupling method are systematically conducted. The CFD–FEA co-simulated results of ship wave loads are further comprehensively compared with a series of existing results of S175 ship by potential flow theory, CFD simulation and tank model experiment as a benchmark and validation study. This study is the first specialized attempt of uncertainty analysis and benchmark study of ship motions, wave loads and hydroelastic responses predicted by CFD–FEA coupling method, which will provide valuable information regarding relative accuracy of the novel method used for wave loads prediction and hydroelastic analysis.

Slamming and green water loads on a ship sailing in regular waves predicted by a coupled CFD–FEA approach

A numerical simulation method is presented by integrating Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) solvers to predict ship wave loads and slamming loads taking into account hydroelastic effects. The interest of this study mainly lies in the slamming and green water pressures acting on a flexible ship investigated by the coupled CFD–FEA method. Firstly, verification and sensitivity analysis of the wave loads and slamming pressures on the S175 containership evaluated by the coupled CFD–FEA method is conducted by comparing the results using different mesh sizes and time step schemes. Discussion on the effect of hydroelasticity on impact pressures is also conducted. Then a comprehensive analysis on the global motions, wave loads, slamming and green water pressures of the ship in different regular wave conditions is undertaken. Finally, a simplified bow flare and bottom slamming pressure estimation method based on the seakeeping data of incident wave and ship global motions are proposed, which can reduce the computational burden of the two-way fluid-structure interaction simulations when impact pressure is concerned.

A CFD–FEA two-way coupling method for predicting ship wave loads and hydroelastic responses

This paper presents a co-simulation method for numerical prediction of nonlinear hydroelastic response of ship advancing in severe wave conditions. Two-way coupling of CFD and FEA solvers is applied where the external fluid pressure exported from the CFD simulation is used to derive the structural responses in the FEA solver and the structural deformations are fed back into the CFD solver to deform the mesh. Violent free surface flow such as slamming and green water on deck is well captured by the RANS and VOF techniques in the CFD solver. The nonlinear whipping and springing responses can be accurately simulated by the structural solver through the dynamic 3D FEA of the hull. By conducting co-simulations with a standard S175 containership, the developed fully coupled method was proved to be capable and reliable in accurate simulating almost all the physical characteristics of interests within the scope of ship seakeeping and hydroelasticity, which include large-amplitude motions, accelerations, wave loads, slamming loads, green water loads and whipping and springing responses of the hull in waves.

Ultimate strength analysis of longitudinal bending of hull girder based on image analysis

In the traditional code, the allowable stress method is used to check the total longitudinal strength of hull girder, which has the characteristics of simple and quick calculation. However, this method is based on the assumption of elastic materials, and can not truly reflect the actual bearing capacity of the structure. Based on image analysis, a practical method for calculating the ultimate longitudinal strength of ship hull is studied. The average stress-strain relationship of the elements constituting the cross section of the hull girder under axial pressure is given, and the progressive collapse behavior of the hull girder in longitudinal bending is analyzed. Finally, the reliability analysis method for the ultimate strength of the hull girder in longitudinal bending is put forward, and a real ship example is given. The research results show that the proposed method is not only suitable for the safety assessment of ship structures in the conceptual design stage, but also meets the requirements of rapid prediction of real ship wave loads and structural strength reliability analysis.

OPTIMIZED ROCK GROYNE DESIGN FOR LONG-PERIODIC SHIP WAVE LOADS

Increased severity of damage to estuarine rock structures have been observed across the major German estuaries during the past two decades. These damages are predominantly caused by long-period primary ship waves, which can result in load cases that are particularly erosive to the rock armour layer. To date no design methods exists to dimension structures for long-period ship wave loads. This study presents an innovative groyne design optimized for resistance to ship-induced waves. During a field trial data were collected which allow for the characterisation of wave-structure-interaction as well as loads and damage parameters for the future development of validated design methods.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/FnrU8AKBITo

Computational and experimental study on local ship loads in short and steep waves

Currently, little information exists on the validity of interface-capturing methods in predicting local ship wave loads in short and steep waves. This study compares computational and experimental results in such a case (kA = 0.24, L wave /L ship = 0.16). The results allow the variation of wave loading between ten locations in the bow area of the ship to be observed. The computations were performed with an unstructured RANS solver that models free-surface flows with a volume-of-fluid method. In the model tests, the wave loads were measured with pressure sensors. The analysis of the results focuses on the wave conditions and on the pressure histories of the local wave loads. The computational and experimental results are in good qualitative agreement and encourage the further use of the computational results.

Numerical Analysis of Ship Wave Loads and Structure Strengthen Analysis on a Wind Power Installation Ship

In a typical load condition of wind power equipment Installation ship, using the three-dimensional potential flow theory to prediction the long-term response of wave induced loads. then using the main load control parameters as a basis for the design wave selection, then application of DNV's SESTRA program make the wave-induced directly to the structure to finite element simulation. The results show that the hull structural design can meet the requirements.

Variability in spatial patterns of long nonlinear waves from fast ferries in Tallinn Bay

Abstract. High-speed ferries are known to generate wakes with unusually long periods, and occasionally large amplitudes which may serve as a qualitatively new forcing factor in coastal regions that are not exposed to a sea swell. An intrinsic feature of such wakes is their large spatial variation. We analyze the variability of wake conditions for the coasts of Tallinn Bay, the Baltic Sea, a sea area with very intense fast ferry traffic. The modelled ship wave properties for several GPS-recorded ship tracks reasonably match the measured waves in terms of both wave heights and periods. It is shown that the spatial extent of the wake patterns is very sensitive to small variations in sailing conditions. This feature leads to large variations of ship wave loads at different coastal sections with several locations regularly receiving high ship wave energy. The runup of the largest ship wakes on the beach increases significantly with an increase in wave height whereas shorter (period <2–5 s) waves merge into longer waves in the shoaling and runup process.

Simulation of patterns of wakes from high-speed ferries in Tallinn Bay

We analyse spatial patterns and far field properties of the long-wave part of wakes of fast ferries in Tallinn Bay with the use of the B oussinesq-type shallow-water model COULWAVE, forced by realistic ship motions. The calculated he ights of ship waves exhibit substantial spatial variability. The largest waves were created when the ship, sailing to Talli nn, entered into super- critical regime when moving over the coastal slope. The maximum wave height eventually reached 3 m, whereas along other sections of the track the wave height was about 1 m. The highest waves hit the area of Pirita Beach that apparently has much larger ship wave loads than the adjacent sections of the Viimsi Peninsula.