Ship Motion Analysis Research Articles

Numerical Analysis of Ship Motion of Crew Boat with Variations of Wave Period on Ship Operational Speed

Seakeeping is influenced by several factors such as speed, ship hull shape, and the direction of the waves (heading angle). In this research, the crew boat is analyzed using the 3D Diffraction method to obtain the response of the ship's motion at regular waves. The study focused on analyzing the sea motion of the crew boat at different wave periods (2.58 s, 4.12 s, 5.67 s, and 7.22 s) and variation of ship speeds (0 Knot, 3 knots, 6 knots, 9 knots, 12 knots, 15 knots, and 18 knots). It used input data including the heading angle of the wave (μ) which is 180° and at a wave height of 0.5 m. The numerical analysis was carried out to determine the ship's seakeeping and compare it with NORDFORSK 1987 criteria, and also to identify the Motion Sickness Incidence (MSI) of the crews on board. Based on the results obtained, the seakeeping value of the ship accepted the criteria of NORDFORSK 1987 up to a speed of 9 knots, starting at a speed of 12 knots it does not accept the criteria. As for the operability, the comfort level of the crew while on board has an MSI index of 0% for 0 Knot, and an MSI index for 18 knots is 4.46% of the total crew of the ship namely only 1 person from 25 persons will likely feel sea sickness.

Analysis of Ship Motion in An Ice Ridge Field Based on Empirical Approach

Analysis of Ship Motion in An Ice Ridge Field Based on Empirical Approach

Deriving spatial wave data from a network of buoys and ships

The real-time provision of high-quality estimates of the ocean wave parameters at appropriate spatial resolutions are essential for the sustainable operations of marine structures. Machine learning affords considerable opportunity for providing additional value from sensor networks, fusing metocean data collected by various platforms. Exploiting the ship-as-a-wave-buoy concept, this article proposes the integration of vessel-based observations into a wave-nowcasting framework. Surrogate models are trained using a high-fidelity physics-based nearshore wave model to learn the spatial correlations between grid points within a computational domain. The performance of these different models are evaluated in a case study to assess how well wave parameters estimated through the spectral analysis of ship motions can perform as inputs to the surrogate system, to replace or complement traditional wave buoy measurements. The benchmark study identifies the advantages and limitations inherent in the methodology incorporating ship-based wave estimates to improve the reliability and availability of regional sea state information.

Prediction of Flooded Compartment Damage Locations in Ships by Using Spectrum Analysis of Ship Motions in Waves

Considering the nature of marine accidents, even a single accident can result in significant damage to the environment and property, as well as loss of life. Therefore, the initial response should be rapid and accurate, and various decision support systems have been developed to achieve this. Research on simulating progressive flooding on board immediately after an accident is being actively conducted, but this requires high levels of computing power. In this study, a methodology for converting simulated ship motion data into a ship motion database is presented. The model of a training ship from the Korea Institute of Maritime and Fisheries Technology and KRISO in-house code SMTP was used for ship motion computations. The short-time Fourier transform was used to convert time-series motion data into a spectrogram motion database. A methodology for deriving a predicted location of the damage center is presented. The candidate locations of the damage centers were obtained by comparing the root mean square error values of the ship motion database from the simulation and real-time ship motion data. Finally, a probability function was suggested to confirm the predicted location of the damage center. Using 100 randomly selected test cases, our method showed 95% accuracy.

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.

Practical evaluation of flows due to arbitrary singularity distributions in the 3D theory of ship motions in regular waves at [formula omitted

The 3D frequency-domain analysis of the flow around a ship advancing in regular waves, in deep water, via the Green-function and boundary-integral method requires a practical and reliable way of evaluating the flow due to an arbitrary distribution of singularities (sources and dipoles) over the (flat or curved, quadrilateral or triangular) panels that are commonly used to approximate a ship hull-surface. This crucial element of the Green-function method, also widely called panel method, in a 3D analysis of ship motions is classically performed via a two-step procedure that involves evaluation of the Green function G and its gradient ∇G as a first step, and their subsequent integration over hull-surface panels. This usual direct method, widely studied and applied in the literature, involves notorious well-documented mathematical and numerical complexities. A novel alternative method, based on the Fourier–Kochin approach, is expounded in the study. In this method, evaluation of G and ∇G is bypassed, i.e. G and ∇G are not evaluated, and the flow due to a distribution of singularities is evaluated directly, in the manner already expounded for the particular cases of steady flow around a ship advancing in calm water and diffraction-radiation of regular waves by an offshore structure or a ship at zero forward speed. The method expounded in these previous studies and extended here is based on an analytical representation of the flow due to a distribution of singularities (including the special case of a Green function and its gradient) that yields a formal decomposition into a wave component, given by single Fourier integrals along the dispersion curves associated with the dispersion relation, and a non-oscillatory local-flow component given by a double integral that has a smooth integrand mostly dominant within a compact region of the Fourier plane. An important aspect of this analytical flow decomposition is that the wave and local-flow components are smooth, unlike the wave and local-flow components in the expressions for G and ∇G given in the literature. Moreover, the analytical representation of the flow due to a distribution of singularities given in the study provides a practical mathematical basis that is well suited for accurate and efficient numerical evaluation, as is demonstrated via the illustrative applications reported previously for steady flow around a ship advancing in calm deep water and diffraction-radiation of regular waves by an offshore structure in deep water, and reported here for the more general case of a ship advancing in deep water at a constant speed V through regular waves of frequency ω in the regime τ≡Vω∕g<1∕4 where g denotes the acceleration of gravity.

A new wave spectrum resembling procedure based on ship motion analysis

A new wave spectrum resembling procedure, based on two subsequent steps, is developed to detect the sea state parameters, namely the wave peak period, the significant wave height and the wave spectrum shape parameter, based on the analysis of heave and pitch motion time series, obtained by onboard measurements. The outlined procedure is applied to the S175 containership, assumed as reference vessel, and a set of basic conditions, with different vessel speeds, heading angles and sea state parameters, is preliminarily investigated. In this respect, heave and pitch motion time histories were obtained by time-domain simulations, based on theoretical wave spectra, in order to systematically investigate the reliability of the proposed procedure. Subsequently, a wide benchmark study is carried out, based on random generation of wave peak periods, significant wave heights and vessel speeds at four heading angles, equally spaced from head to following seas, in order to investigate the incidence of time duration on resembled sea state parameters. Finally, the statistics of errors on wave peak periods and significant wave heights are analysed to select the proper time duration of onboard measurements that allows balancing the reliability of resembled data with the need of an almost real-time sea state monitoring.

Moored ship motion analysis in Paradip port under the resonance conditions using 3-D boundary element method

Loading and unloading of moored ship is difficult task during the extreme wave oscillation in a port during the seasonal weather conditions. Therefore, a mathematical model is developed based on Laplace equation to analyze the six different modes (surge, sway, heave, roll, pitch, and yaw) of the moored ship motion under resonance conditions utilizing the 3-D boundary element method (BEM). The domain of interest is divided as bounded (port region), unbounded (open sea) and ship region. The equation of motion with six degree of freedom is solved to analyze the moored ship motions with variable water depth. The present numerical scheme is validated with existing well-known studies. The current numerical model is implemented on realistic Paradip port to determine the resonance frequency for the moored ship motion at key location. In additional, the wave field with different resonance modes is also estimated inside the Paradip port. The safe locations inside the Paradip port are identified for the moored ships under the resonance conditions.

Study on sloshing simulation in the independent tank for an ice-breaking LNG carrier

As the LNG carrier operates in ice covered waters, it is key to ensure the overall safety, which is related to the coupling effect of ice-breaking process and internal liquid sloshing. This paper focuses on the sloshing simulation of the ice-breaking LNG carrier, and the numerical method is proposed using Circumferential Crack Method (CCM) and Volume of Vluid (VOF) with two main key factors (velocity vx and force Fx). The ship motion analysis is carried out by CCM when the ship navigates in the ice-covered waters with a constant propulsion power. The velocity vx is gained, which is the initial excitation condition for the calculation of internal sloshing force Fx. Then, the ship motion is modified based on iterative computations under the union action of ice-breaking force and liquid sloshing load. The sloshing simulation under the LNG tank is studied with the modified ship motion. Moreover, an ice-breaking LNG ship with three-leaf type tank is used for case study. The internal LNG sloshing is simulated with three different liquid heights, including free surface shape and sloshing pressure distribution at a given moment, pressure curves at monitoring points on the bulkhead. This present method is effective to solve the sloshing simulation during ice-breaking process, which could be a good reference for the design of the polar ice-breaking LNG carrier.

An Analysis of Rolling Damage Ship Motion Caused by the Wave Load on Bulk Carrier Vessels

Stabilitas menjadi syarat utama kapal yang laik layar. Artikel ini memuat analisa gerakan rolling pada kapal bulk carrier yang mengalami kebocoran ketika dikenai beban gelombang dengan sudut heading 90⁰ dan 270⁰ dan tinggi gelombang maksimum. Kapal berada pada kondisi muatan full load saat simulasi dan analisa dilakukan dengan skenario terjadi kebocoran pada ruang muatnya. Karena kapal dengan kebocoran kompartemen mengalami kondisi trim dan oleng maka hasil gerakan rolling menunjukkan perbedaan pada setiap arah datang gelombang. 3D diffraction panel method digunakan untuk mendapatkan gerakan rolling kapal sebagai fungsi waktu. Hasil penelitian tanpa efek sloshing menunjukkan bahwa kapal bulk carrier memiliki resiko tenggelam jika terdapat kebocoran pada dua ruang muatnya.

기계학습기반의 근사모델을 이용한 선박 횡동요 운동 예측

Seakeeping safety module in Korean e-Navigation system is one of the ship remote monitoring services that is employed to ensure the safety of ships by monitoring the ship's real time performance and providing a warning in advance when the abnormal conditions are encountered in seakeeping performance. In general, seakeeping performance has been evaluated by simulating ship motion analysis under specific conditions for its design. However, due to restriction of computation time, it is not realistic to perform simulations to evaluate seakeeping performance under real-time operation conditions. This study aims to introduce a reasonable and faster method to predict a ship’s roll motion which is one of the factors used to evaluate a ship’s seakeeping performance by using a machine learning-based surrogate model. Through the application of various learning techniques and sampling conditions on training data, it was observed that the difference of roll motion between a given surrogate model and motion analysis was within 1%. Therefore, it can be concluded that this method can be useful to evaluate the seakeeping performance of a ship in real-time operation

Motions of an unmanned catamaran ship with fixed tandem hydrofoils in regular head waves

Hydrofoils are approved of having the ability to help the propulsion of ships, and have been applied to many ships as an auxiliary propulsion system. However, in this paper, a novel unmanned catamaran ship completely driven by hydrofoils is proposed, which could navigate in the sea for a very long time at low speed as a mobile ocean observation platform. The hydrodynamics of this ship is systematically investigated through numerical simulations. First, the potential theory and the CFD method based on FLUENT for ship motion analysis are introduced. Second, the validation of the two numerical methods is carried out by comparing the results of heave and pitch motions for the case of the unmanned ship without hydrofoils. Finally, the CFD model of this unmanned ship is established and analyzed, and the interactions between the ship and hydrofoils are considered. The effects of the hydrofoils on ship motion under different wave conditions with low forward speed are analyzed. The results show that the horizontally fixed hydrofoils can significantly reduce the ship’s heave and pitch motions within a certain encountered wavelength range. It indicates that this unmanned catamaran ship with the horizontally fixed hydrofoils has good seakeeping performance.

Integrated method of analysis, visualization, and hardware for ship motion simulation

Abstract Traditionally, graphs were the only way to show the results of ship motion analyses. They did not usually impose any feeling about how fast the ship could move or how large the positions of the ship changed. Currently, integrated simulations combining physics-based analyses with IT technologies, such as virtual reality (VR), motion platforms, or other hardware, can offer a potential solution. In ship motion analyses, the dynamic ship response can be obtained by considering the environmental loads, such as ocean waves, and VR technology can be used to visualize the analysis results in the virtual world. We can see the ship motion relative to textures of real objects, including the water and sky, as if in the real world. The results calculated from the ship motion analysis can also be transferred to the motion platform to generate realistic movements. However, it is not easy to integrate three different technologies in one system because they have different purposes and have been developed individually. To solve this problem, an integrated simulation framework based on three different technologies is proposed. The proposed framework can be used to synchronize the simulation time and exchange the data through the middleware using a standardized data structure. Furthermore, we can easily add new components or remove the existing components in the simulation. To verify the efficiency and applicability of the proposed framework, the motion simulation of a drillship is applied. Highlights We propose an integrated simulation framework for analysis, visualization, and hardware. Multibody dynamics is used for the motion analysis. We perform the integrated motion simulation of a drillship. The motion analysis, visualization, and motion platform of a drillship are perfectly synchronized.

Simulation of whipping response of a large container ship fitted with a linear generator on board in irregular head seas

There is plenty of energy contained in the ocean waves, and great efforts have been made over recent decades to make full use of these sustainable energy resources. As a novel device to utilize ocean wave energy, the authors propose in this paper a whipping energy converter, which utilizes a linear generator extracting power from ship’s whipping and springing (hull girder 2-node vibration) responses. The device is designed resonant to the hull girder 2-node vibration frequency. Numerical simulation of the responses of the whipping energy converter was carried out under irregular head sea condition, using time domain ship motion analysis by Rankine source method and subsequent three-dimensional whole ship FE analysis, and the main parameters of the whipping energy converter was studied. A 14,000 TEU large container ship was utilized in this study, because large container ship is prone to constant whipping and springing responses in real seas. As a result, it was found that the whipping energy converter can effectively generate power from the whipping and springing responses, and at the same time, the whipping energy converter functions as a dynamic damper. With the piston weight of 5–10 tons, the whipping vibration is visibly reduced, while if the piston weight is about 100 tons, the spectral peak is reduced to less than one-third. This implies that the whipping energy converter contributes to the prevention of fatigue damage due to whipping and springing, which is an imminent concern in the design of large container ships. It was also found that larger power generation can be expected as the piston weight is heavier, and the bow is the most effective location for this device.

Numerical analysis of ship motion under linear and nonlinear waves

Simulating physical phenomena by applying mathematical and numerical modeling has been increasingly used during the different stages of research and development and innovation projects. The purpose of this study is to present results about translational motion (x, y, z), angular motion (α, β, γ) and trajectories obtained using a numerical model developed to study ship dynamics under the influence of linear and nonlinear waves. The results indicated that translational motion, surge and sway, is mostly influenced by thrust in the studied scenario. The translational motion (heave) displayed curves which can be related with wave patterns before 0.1 hr. The angular motion distributions displayed a variation that can be related with wave forces. However, at 0.4 hr the curves depicted smaller variations that is explained by the increased engine thrust pattern. In both simulations, the distance of 20.582 km and 20.342 km for linear and nonlinear simulations were calculated, respectively. Once both simulations yielded similar values for travel distance, the wave patterns used in this study were shown to generate variations at the displacement from 0 to 0.4 hr. After 0.4 hr, the ship displacement depicted linear curves but the engine thrust was able to overcome the external forces.

Simulation-Based Analysis of Ship Motions in Short-Crested Irregular Seas

Simulation-Based Analysis of Ship Motions in Short-Crested Irregular Seas

쇄빙연구선 ARAON호의 빙하중 추정을 위한 6자유도 운동계측 및 스트레인 게이지 데이터의 비교 분석

This study focuses on the comparison of measured data from 6-DOF motion sensor and strain gauge installed in the IBRV ARAON during 2015 summer voyage in the Arctic. Procedures to calculate the global ice load from MotionPak II inertial measurement system and the local load from stain gauge system are discussed. The ship's speed and peak load are determined in the concept of an ice collision "event". It is found that the peak values in the global ice calculated form whole ship motion analysis fall in the range of 1.5~3 times of the local ice load based in strain gauge measurement.

Sloshing design load prediction of a membrane type LNG cargo containment system with two-row tank arrangement in offshore applications

This paper addresses the safety of two-row tank design by performing the extensive sloshing model tests. Owing to the uncertainties entangled with the scale law transforming the measured impact pressure up to the full scale one, so called comparative approach was taken to derive the design sloshing load. The target design vessel was chosen as 230 K LNG-FPSO with tow-row tank arrangement and the reference vessel as 138 K conventional LNG carrier, which has past track record without any significant failure due to sloshing loads. Starting with the site-specific metocean data, ship motion analysis was carried out with 3D diffraction-radiation program, then the obtained ship motion data was used as 6DOF tank excitation for subsequent sloshing model test and analysis. The statistical analysis was carried out with obtained peak data and the long-term sloshing load was determined out of it. It was concluded that the normalized sloshing impact pressure on 230 K LNG-FPSO with two-row tank arrangement is higher than that of convectional LNG carrier, hence requires the use of reinforced cargo containment system for the sake of failure-free operation without filling limitation.

유탄성 효과를 고려한 완전통계 피로해석 프로그램 개발을 위한 기초 연구

The purpose of this research is to develop a full-spectral fatigue analysis program, based on rigid-body ship motion analysis, in order to perform a full-spectral fatigue analysis that considers hydroelasticity effects. To gain credibility, fatigue anal ysis results of two ship types, performed by the developed program, were compar ed with those of a classification society, and it was found that both are identical. Full-spectral fatigue analysis considering hydroelasticity effects would be developed in further studies by including flexible-body ship motion analysis results and by supplementing the developed program with a wide-band fatigue damage model.

Coupled analysis of nonlinear sloshing and ship motions

A coupled numerical model considering nonlinear sloshing flows and the linear ship motions has been developed based on a boundary element method. Hydrodynamic performances of a tank containing internal fluid under regular wave excitations in sway are investigated by the present time-domain simulation model and comparative model tests. The numerical model features well the hydrodynamic performance of a tank and its internal sloshing flows obtained from the experiments. In particular, the numerical simulations of the strong nonlinear sloshing flows at the natural frequency have been validated. The influence of the excitation wave height and wave frequency on ship motions and internal sloshing has been investigated. The magnitude of the internal sloshing increases nonlinearly as the wave excitation increases. It is observed that the asymmetry of the internal sloshing relative to still water surface becomes more pronounced at higher wave excitation. The internal sloshing-induced wave elevation is found to be amplitude-modulated. The frequency of the amplitude modulation envelope is determined by the difference between the incident wave frequency and the natural frequency of the internal sloshing. Furthermore, the coupling mechanism between ship motions and internal sloshing is discussed.