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Item type:Publication, Access status: without files , Theoretical estimation of joint probability density function of roll angle and angular acceleration in beam seas using PDF line integral method(2022-03); ; ; ; So far, we have developed a calculation method for roll angular acceleration and its derivative, which is a jerk. In this study, using the probability density function (PDF) line integral method and the joint PDF (JPDF) of roll angle and angular rate, we obtain a theoretical method for the evaluation of the two properties. In particular, the estimation method of acceleration is considered crucial, as the angular acceleration is directly related to inertial forces or moments of onboard objects. Moreover, to consider the strength of container stacks, as well as the lashing strength of cargo and track on board, a separate evaluation of roll angle and roll angular acceleration is insufficient. Further, although the new-generation intact stability criteria for excessive acceleration have been discussed by the International Maritime Organization, the evaluation of JPDF of roll angle and roll angular acceleration could contribute to the efficient evaluation of the safety of crews on board. Meanwhile, no JPDF of roll angle or angular acceleration has been calculated for an arbitrary nonlinear system so far, and there is no doubt that it is a challenging problem. In this study, by applying and extending the idea of the PDF line integral method, we proposed a method for evaluating the JPDF of roll angle and angular acceleration.Publicationtype: Journal Article39 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Theoretical determination of asymmetric rolling amplitude in irregular beam seasA methodology for predicting the probability density function of roll motion for irregular beam seas is developed in the author’s previous research. In this paper, two methods for the prediction of the probability density function (PDF) of the rolling amplitude are examined. One of these methods is an approach based on a non-Gaussian PDF with the use of the equivalent linearization and the moment method, which has been used by Maki in the field of naval architecture. In the framework of this method, the instantaneous joint PDF of the roll and roll rate can be calculated. Thereby, the transformation from the joint PDF to the PDF of the total energy H is necessary. In this paper, the transformation from the joint PDF of instantaneous roll and rate to the PDF of H was conducted. The other method is the energy-based stochastic averaging method, whereby the PDF of the total energy H is determined from which the roll amplitude is calculated. It is noteworthy that the proposed theory aims to predict the PDF of the amplitude of the vessel due to wind or flooding. For such conditions, the restoring curve (GZ curve) has asymmetricity. To take into account this asymmetricity, a new theory for the transform of the PDF of the total energy H to the PDFof amplitude is proposed. The obtained theoretical results show almost complete agreement, and both of the two theoretical methods i.e., the energy-based stochastic averaging method and the non-Gaussian PDF method with the use of the equivalent linearization and moment method, show equivalent prediction performance even in the asymmetric condition.Publicationtype: Journal Article79 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Theoretical determination of roll angular jerk of ships in irregular beam seas using PDF line integral methodThe time derivative of acceleration is called a jerk, which is an important property to evaluate ride comfort in elevators, cars, and so on. Likewise, evaluation of motion sickness or ride comfort on a vessel could be achieved by this jerk property in the future. In this paper, we utilize the PDF Line Integral Method (PLIM), which was newly contrived in our previous research, for calculating not only roll angular acceleration but also roll angular jerk. The derivation of this theory, as well as numerical comparison with Monte Carlo simulation (MCS) results, are presented. Although the utilized restoring curve (GZ curve) exhibits strong asymmetricity, the proposed method successfully calculates roll angular jerk for such a condition. Since roll angular jerk is a high-order differential property, the biggest advantage of PLIM is that it only requires the information of roll and roll rate joint probability density function (PDF) to provide the PDF of jerk.Publicationtype: Journal Article83 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Theoretical estimation of roll acceleration in beam seas using PDF line integral method(2021-09); ; ; ; The prevention of excessive roll acceleration is one of the fundamental requirements of an oceangoing vessel at sea. In this paper, aiming at this requirement, we propose a new theoretical method for calculating roll angular acceleration, called “PDF line integral method.”. This paper presents the derivation of this method and a numerical comparison with Monte Carlo simulation (MCS) results; also, its validity is shown. Although the utilized GZ curve (restoring curve) exhibits strong asymmetricity, the proposed method can provide for such a condition. With only the information of roll and roll rate joint probability density function (PDF), this method can approximately calculate the roll angular acceleration, which is a high-order differential property. In addition, a relatively good agreement is achieved between the theory and MCS results.Publicationtype: Journal Article196