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Igor Rychlik - One of the best experts on this subject based on the ideXlab platform.

  • Notes on the Prediction of Extreme Ship Response
    Journal of Offshore Mechanics and Arctic Engineering, 2013
    Co-Authors: Wengang Mao, Igor Rychlik
    Abstract:

    In this note the relation between two simple approaches to estimate the extreme Ship Response used when no, or a limited, amount of data are available is discussed. The first one employs the long term distribution of the local maxima of Ship Response while the second one uses the expected number of upcrossings of a level by the Response. It is mathematically demonstrated that the two approaches are equivalent. However, the upcrossing method is more straightforward and convenient for practical applications, particularly for non-Gaussian Responses. The full-scale measurements of a 2800 TEU container Ship during the first six months of 2008 are used in the comparisons.

  • Theoretical development and validation of a fatigue model for Ship routing
    Ships and Offshore Structures, 2012
    Co-Authors: Jonas W. Ringsberg, Igor Rychlik, Zhiyuan Li
    Abstract:

    Fatigue cracks are observed much earlier than expected in Ships and marine structures due to uncertainties in the fatigue design process, such as encountered sea environments and variability in S-N curves, etc. The current study presents the theoretical development and validation of a fatigue model useful for Ship routing which may contribute to better utilisation of the materials and structures by more wise operation of them. During the theoretical development of the Ship routing fatigue model, various models to estimate fatigue damage intensity, including both cycle counting calculations and spectral approximations, are reviewed. The proposed Ship routing fatigue model is a function of operation profiles, i.e., heading angle and Ship speed, as well as encountered wave environments (significant wave height), which are easily available in today’s commercial routing tool systems. Concerning the characteristics of Ship Response, the so-called narrow-band approximation is adopted and further simplified in order to estimate the fatigue damage in Ships under an arbitrary stationary sea state. Long-term fatigue damage is estimated by a summation of fatigue damages in all encountered sea states during, for example, one voyage or a period of several years. Further, fatigue damage due to wave-induced vibrations (whipping and springing) and fatigue damage caused by various stress components are also studied and discussed. A validation using Response from full-scalemeasurements and numerical analysis is presented. It shows that the proposed model works very well in comparison with the rainflow counting method. Finally, the proposed Ship routing fatigue model is applied on real case scenarios, where its applicability in Shipping industry is demonstrated.

  • Estimation of Extreme Ship Response
    Journal of Ship Research, 2012
    Co-Authors: Wengang Mao, Igor Rychlik
    Abstract:

    In practice the severity of Ship Response is measured by high quantiles of long-term distribution of the Response. The distribution is estimated by combining the short-term distribution of the Response with a long-term probability distribution of encountered sea states. The paper describes an alternative approach, the so-called Rice’s method, based on estimation of expected number of upcrossings of high levels by stress during 1 year. The method requires description of long-term variability of the standard deviation, skewness, kurtosis, and zero upcrossing frequency of Ship Response. It is assumed that the parameters are functions of encountered significant wave height, heading angle, and Ship speed. The relation can be estimated from the measured stresses or computed by dedicated software assuming rigid Ship hull model. Then Winterstein’s transformed Gaussian model is used to estimate the upcrossing rates of Response during a sea state. The proposed method is validated using the full-scale measurements of a 2,800 TEU container Ship during the first 6 months of 2008. Numerical estimation of 4,400 TEU container Ship extreme Response illustrates the approach when no measurements are available.

  • On estimation of extreme Ship Response using upcrossing spectrum
    2011
    Co-Authors: Wengang Mao, Igor Rychlik
    Abstract:

    In this paper a simple method is proposed to estimate extreme Ship Response, which is defined by the upcrossing spectrum of the Responses at high levels. The method requires limited statistical information about Shipping and the corresponding Responses. Since the real Ship Responses are often non-Gaussian, a transformed Gaussian approach using the cubic Hermite polynomials is employed. The parametric transformation is a function of the standard deviation, skewness, kurtosis and zero up-crossing frequency of a Response which mainly varies with changing sea conditions and operation conditions. Parameters needed in the transformation are computed from their relations with encountered waves, characterized by the significant wave height here. The relations are derived from the measurements, but can be also computed by theoretical analysis. Finally, this method is compared and validated with the typical engineering approach, based on the full-scale measurements of a 2800 TEU container Ship during the first six months of 2008. If no measured Responses are available, the parameters of the transformation can be estimated using simple numerical analysis.

  • Assessment of Full-Scale Measurements With Regard to Extreme Hogging and Sagging Condition of Container Ships
    2011
    Co-Authors: Wengang Mao, Jonas W. Ringsberg, Zhiyuan Li, Igor Rychlik
    Abstract:

    In the design of a vessel's ultimate strength the extreme hogging condition is of great concern. Due to special properties of container Ship structures, such as large bow flare and overhanging stern, wave-induced slamming makes the Ship Responses more skewed to sagging conditions. In particular in large sea states, the ratio between maximum sagging and hogging can be quite high. Hence, the sagging condition might be very crucial with respect to a Ship's ultimate strength. In this study, the extreme Response caused by hogging and sagging is derived from upcrossing spectrums of Ship Responses. The Weibull fitting method and Rice's formula for the computation of the upcrossing spectrum are discussed using full-scale measurements from a container vessel on the North Atlantic trade. The extreme Ship Responses are therefore predicted using the long-term upcrossing spectrum. In the case where the Ship Response can be approximately treated as a series of stationary Gaussian processes, the corresponding upcrossings are computed by the explicit Rice's formula. For the non-Gaussian Ship Response, it is shown that the 4-moment Hermite transformation is an efficient approach to compute the corresponding upcrossing spectrums. The parameters in the transformation mainly depend on the wave environments and operation profiles. The relations between these parameters and the wave environments are needed if no measurement is available. However, according to the full-scale measurements, it is not possible to find general formulas to estimate the parameters in terms of wave environments or operation profiles for the practical applications. Copyright © 2011 by ASME.

B. C. Khoo - One of the best experts on this subject based on the ideXlab platform.

  • A fully coupled Ship motion and sloshing analysis in various container geometries
    Journal of Marine Science and Technology, 2012
    Co-Authors: S. Mitra, L. V. Hai, L. Jing, B. C. Khoo
    Abstract:

    In the present study a novel modeling approach is presented to solve the combined internal sloshing and sea-keeping problem. The model deals with interesting effects arising due to the coupled interaction between the sloshing in partially filled containers of several geometries and the Ship motion. The study is very important for the liquid cargo carrier operating in rough sea or under different environmental conditions. The resulting slosh characteristics that include transient pressure variation, free surface profiles and hydrodynamic pressure over the container walls have been reported in this study. In addition, the effects of coupled Ship Response and sloshing on Ship motion parameters have also been investigated. The equations of motion of fluid, considered inviscid, irrotational, and partially compressible, are expressed in terms of the pressure variable alone. A finite difference-based iterative time-stepping technique is employed to advance the coupled solution in the time domain. Several parameters of interest, including the container parameters, level of liquid, thrusters modeling and some important environmental factors are investigated.

Wengang Mao - One of the best experts on this subject based on the ideXlab platform.

  • Notes on the Prediction of Extreme Ship Response
    Journal of Offshore Mechanics and Arctic Engineering, 2013
    Co-Authors: Wengang Mao, Igor Rychlik
    Abstract:

    In this note the relation between two simple approaches to estimate the extreme Ship Response used when no, or a limited, amount of data are available is discussed. The first one employs the long term distribution of the local maxima of Ship Response while the second one uses the expected number of upcrossings of a level by the Response. It is mathematically demonstrated that the two approaches are equivalent. However, the upcrossing method is more straightforward and convenient for practical applications, particularly for non-Gaussian Responses. The full-scale measurements of a 2800 TEU container Ship during the first six months of 2008 are used in the comparisons.

  • Estimation of Extreme Ship Response
    Journal of Ship Research, 2012
    Co-Authors: Wengang Mao, Igor Rychlik
    Abstract:

    In practice the severity of Ship Response is measured by high quantiles of long-term distribution of the Response. The distribution is estimated by combining the short-term distribution of the Response with a long-term probability distribution of encountered sea states. The paper describes an alternative approach, the so-called Rice’s method, based on estimation of expected number of upcrossings of high levels by stress during 1 year. The method requires description of long-term variability of the standard deviation, skewness, kurtosis, and zero upcrossing frequency of Ship Response. It is assumed that the parameters are functions of encountered significant wave height, heading angle, and Ship speed. The relation can be estimated from the measured stresses or computed by dedicated software assuming rigid Ship hull model. Then Winterstein’s transformed Gaussian model is used to estimate the upcrossing rates of Response during a sea state. The proposed method is validated using the full-scale measurements of a 2,800 TEU container Ship during the first 6 months of 2008. Numerical estimation of 4,400 TEU container Ship extreme Response illustrates the approach when no measurements are available.

  • On estimation of extreme Ship Response using upcrossing spectrum
    2011
    Co-Authors: Wengang Mao, Igor Rychlik
    Abstract:

    In this paper a simple method is proposed to estimate extreme Ship Response, which is defined by the upcrossing spectrum of the Responses at high levels. The method requires limited statistical information about Shipping and the corresponding Responses. Since the real Ship Responses are often non-Gaussian, a transformed Gaussian approach using the cubic Hermite polynomials is employed. The parametric transformation is a function of the standard deviation, skewness, kurtosis and zero up-crossing frequency of a Response which mainly varies with changing sea conditions and operation conditions. Parameters needed in the transformation are computed from their relations with encountered waves, characterized by the significant wave height here. The relations are derived from the measurements, but can be also computed by theoretical analysis. Finally, this method is compared and validated with the typical engineering approach, based on the full-scale measurements of a 2800 TEU container Ship during the first six months of 2008. If no measured Responses are available, the parameters of the transformation can be estimated using simple numerical analysis.

  • Assessment of Full-Scale Measurements With Regard to Extreme Hogging and Sagging Condition of Container Ships
    2011
    Co-Authors: Wengang Mao, Jonas W. Ringsberg, Zhiyuan Li, Igor Rychlik
    Abstract:

    In the design of a vessel's ultimate strength the extreme hogging condition is of great concern. Due to special properties of container Ship structures, such as large bow flare and overhanging stern, wave-induced slamming makes the Ship Responses more skewed to sagging conditions. In particular in large sea states, the ratio between maximum sagging and hogging can be quite high. Hence, the sagging condition might be very crucial with respect to a Ship's ultimate strength. In this study, the extreme Response caused by hogging and sagging is derived from upcrossing spectrums of Ship Responses. The Weibull fitting method and Rice's formula for the computation of the upcrossing spectrum are discussed using full-scale measurements from a container vessel on the North Atlantic trade. The extreme Ship Responses are therefore predicted using the long-term upcrossing spectrum. In the case where the Ship Response can be approximately treated as a series of stationary Gaussian processes, the corresponding upcrossings are computed by the explicit Rice's formula. For the non-Gaussian Ship Response, it is shown that the 4-moment Hermite transformation is an efficient approach to compute the corresponding upcrossing spectrums. The parameters in the transformation mainly depend on the wave environments and operation profiles. The relations between these parameters and the wave environments are needed if no measurement is available. However, according to the full-scale measurements, it is not possible to find general formulas to estimate the parameters in terms of wave environments or operation profiles for the practical applications. Copyright © 2011 by ASME.

S. Mitra - One of the best experts on this subject based on the ideXlab platform.

  • A fully coupled Ship motion and sloshing analysis in various container geometries
    Journal of Marine Science and Technology, 2012
    Co-Authors: S. Mitra, L. V. Hai, L. Jing, B. C. Khoo
    Abstract:

    In the present study a novel modeling approach is presented to solve the combined internal sloshing and sea-keeping problem. The model deals with interesting effects arising due to the coupled interaction between the sloshing in partially filled containers of several geometries and the Ship motion. The study is very important for the liquid cargo carrier operating in rough sea or under different environmental conditions. The resulting slosh characteristics that include transient pressure variation, free surface profiles and hydrodynamic pressure over the container walls have been reported in this study. In addition, the effects of coupled Ship Response and sloshing on Ship motion parameters have also been investigated. The equations of motion of fluid, considered inviscid, irrotational, and partially compressible, are expressed in terms of the pressure variable alone. A finite difference-based iterative time-stepping technique is employed to advance the coupled solution in the time domain. Several parameters of interest, including the container parameters, level of liquid, thrusters modeling and some important environmental factors are investigated.

Toshio Iseki - One of the best experts on this subject based on the ideXlab platform.

  • Extracting clearer tsunami currents from Shipborne Automatic Identification System data using Ship yaw and equation of Ship Response
    Earth Planets and Space, 2020
    Co-Authors: Daisuke Inazu, Tsuyoshi Ikeya, Toshio Iseki, Takuji Waseda
    Abstract:

    We have explored tsunami current signals in maritime Automatic Identification System (AIS) data during the 2011 Tohoku, Japan, tsunami. The AIS data were investigated in detail taking into account Ship motion and Response to tsunami current. Ship velocity derived from AIS data was divided into two components in terms of the Ship heading: heading-normal and heading-parallel directions. The heading-normal velocity showed good agreement with the simulated tsunami current, as mentioned in our former research. Here, we found the heading-normal velocity was contaminated by non-tsunami noises that were mostly related to the Ship yaw motion around the pivot point. The noises due to the yaw motion were reasonably corrected in the heading-normal velocity. The corrected heading-normal velocity clearly showed better agreement with the simulated tsunami current. Although the heading-parallel velocity is basically the navigation speed, and is mostly controlled by Ships’ captain, we could find the heading-parallel velocity was also drifted by tsunami currents. The corrected heading-normal velocity was still a Ship Response to the tsunami current. Based on an equation of a Ship Response to tsunami currents, we numerically estimated tsunami current from the corrected heading-normal velocity. We could find very slight improvements in estimating the tsunami currents, which indicated that this operation possibly worked as a secondary correction. Tsunami currents of tens of centimeters per second are expected to be suitably detected using AIS based on discussion on detection limit.

  • Real-Time Estimation of Directional Wave Spectra Using Non-Stationary Ship Motion Data
    Volume 6: Materials Technology; C.C. Mei Symposium on Wave Mechanics and Hydrodynamics; Offshore Measurement and Data Interpretation, 2009
    Co-Authors: Toshio Iseki
    Abstract:

    The Bayesian modeling procedure is modified for real-time estimation of directional wave spectra using non-stationary Ship motion data. The assumption of stationary stochastic processes is applied to the seaway, but not to Ship Response because it also depends on Ship maneuvers. Ship Response is strongly affected by changes in the encounter angle and frequency of waves. Therefore, it is need to be a real-time algorithm that can deal with non-stationary stochastic processes and estimate the directional wave spectra. In the proposed algorithm, the iterative calculations of the non-linear equations were optimized and the convergence was not achieved at every time step, but was achieved gradually over several time steps. In order to examine the reliability of the proposed method, real-time estimation was conducted by using the data of onboard experiments. Comparisons between the results of the proposed algorithm and a wave monitoring radar system show good agreements.Copyright © 2009 by ASME