Structural design for shipbuilding is generally divided into three stages: the basic, detailed, and production designs, of which the production design is the most frequently revised among the three design stages. The revision involved in production design department was approximately 61% of the total 4,211 revision members and approximately 56% of the total 710 revision cases in the survey on the number of design revisions for nine ships. In this study, members and drawings with a high revision rate were investigated, and related design departments were identified. In addition, the work contents of the design department were analyzed to reduce the number of design revisions and three tasks are very frequently revised were selected. A survey was conducted with engineers engaged in the production design, after which, standards were proposed for the method of aggregating bills of materials, to employ macros to calculate the length of members and that of profile input data when reviewing drawings. Via the study, it was determined that the major causes of design revision are simple mistakes by engineers or lack of understanding on structural arrangement of basic members more than intricacies of prior design and high level specification. As a result of applying the proposed standards, it was confirmed that the design revision was reduced by approximately 40%.
{"title":"Study on Standardization Methods for Reducing Revision Rate of Hull Production Design","authors":"T. An, Tak-Kee Lee","doi":"10.26748/ksoe.2021.088","DOIUrl":"https://doi.org/10.26748/ksoe.2021.088","url":null,"abstract":"Structural design for shipbuilding is generally divided into three stages: the basic, detailed, and production designs, of which the production design is the most frequently revised among the three design stages. The revision involved in production design department was approximately 61% of the total 4,211 revision members and approximately 56% of the total 710 revision cases in the survey on the number of design revisions for nine ships. In this study, members and drawings with a high revision rate were investigated, and related design departments were identified. In addition, the work contents of the design department were analyzed to reduce the number of design revisions and three tasks are very frequently revised were selected. A survey was conducted with engineers engaged in the production design, after which, standards were proposed for the method of aggregating bills of materials, to employ macros to calculate the length of members and that of profile input data when reviewing drawings. Via the study, it was determined that the major causes of design revision are simple mistakes by engineers or lack of understanding on structural arrangement of basic members more than intricacies of prior design and high level specification. As a result of applying the proposed standards, it was confirmed that the design revision was reduced by approximately 40%.","PeriodicalId":315103,"journal":{"name":"Journal of Ocean Engineering and Technology","volume":"56 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130459420","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Thi Loan Mai, Anh Khoa Vo, Myungjun Jeon, Hyeong-Kyu Yoon
To reach a port, a ship must pass through a shallow water zone where seabed effects alter the hydrodynamics acting on the ship. This study examined the maneuvering characteristics of an autonomous surface ship at 3-DOF (Degree of freedom) motion in deep water and shallow water based on the in-port speed of 1.54 m/s. The CFD (Computational fluid dynamics) method was used as a specialized tool in naval hydrodynamics based on the RANS (Reynolds-averaged Navier-Stoke) solver for maneuvering prediction. A virtual captive model test in CFD with various constrained motions, such as static drift, circular motion, and combined circular motion with drift, was performed to determine the hydrodynamic forces and moments of the ship. In addition, a model test was performed in a square tank for a static drift test in deep water to verify the accuracy of the CFD method by comparing the hydrodynamic forces and moments. The results showed changes in hydrodynamic forces and moments in deep and shallow water, with the latter increasing dramatically in very shallow water. The velocity fields demonstrated an increasing change in velocity as water became shallower. The least-squares method was applied to obtain the hydrodynamic coefficients by distinguishing a linear and non-linear model of the hydrodynamic force models. The course stability, maneuverability, and collision avoidance ability were evaluated from the estimated hydrodynamic coefficients. The hydrodynamic characteristics showed that the course stability improved in extremely shallow water. The maneuverability was satisfied with IMO (2002) except for extremely shallow water, and collision avoidance ability was a good performance in deep and shallow water. Received 13 February 2022, revised 22 March 2022, accepted 8 April 2022 Corresponding author Hyeon Kyu Yoon: +82-55-213-3683, hkyoon@changwon.ac.kr c 2022, The Korean Society of Ocean Engineers This is an open access article distributed under the terms of the creative commons attribution non-commercial license (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
为了到达一个港口，一艘船必须通过一个浅水区，在那里海底效应改变了作用在船上的水动力。在港内航速为1.54 m/s的条件下，研究了自主水面舰艇在深水和浅水三自由度运动下的机动特性。CFD (Computational fluid dynamics)方法是舰船流体力学研究的一种专用工具，它基于reynolds -average Navier-Stoke求解器进行机动预测。为了确定船舶的水动力和力矩，在CFD中进行了静态漂移、圆周运动和圆周运动与漂移相结合等多种约束运动的虚拟圈养模型试验。此外，还在方形槽中进行了深水静态漂移试验模型试验，通过水动力和力矩的对比验证了CFD方法的准确性。结果表明，在深水和浅水中，水动力力矩和水动力力矩发生了变化，浅水中，水动力力矩和水动力力矩显著增大。速度场显示，随着水的变浅，速度变化越来越大。通过区分水动力模型的线性模型和非线性模型，采用最小二乘法求解水动力系数。根据估算的水动力系数，对飞机的航向稳定性、机动性和避碰能力进行了评价。水动力特性表明，在极浅水中，航道稳定性得到改善。除极浅水外，其机动性均满足IMO(2002)的要求，在深水和浅水均有良好的避碰能力。通讯作者Hyeon Kyu Yoon: +82-55-213-3683, hkyoon@changwon.ac.kr c 2022, The Korean Society of Ocean Engineers这是一篇开放获取的文章，根据创作共用归属非商业许可(http://creativecommons.org/licenses/by-nc/4.0)的条款分发，该许可允许不受限制的非商业使用，分发和在任何媒介上复制，只要原始作品被适当引用。
{"title":"Changes in the Hydrodynamic Characteristics of Ships During Port Maneuvers","authors":"Thi Loan Mai, Anh Khoa Vo, Myungjun Jeon, Hyeong-Kyu Yoon","doi":"10.26748/ksoe.2022.004","DOIUrl":"https://doi.org/10.26748/ksoe.2022.004","url":null,"abstract":"To reach a port, a ship must pass through a shallow water zone where seabed effects alter the hydrodynamics acting on the ship. This study examined the maneuvering characteristics of an autonomous surface ship at 3-DOF (Degree of freedom) motion in deep water and shallow water based on the in-port speed of 1.54 m/s. The CFD (Computational fluid dynamics) method was used as a specialized tool in naval hydrodynamics based on the RANS (Reynolds-averaged Navier-Stoke) solver for maneuvering prediction. A virtual captive model test in CFD with various constrained motions, such as static drift, circular motion, and combined circular motion with drift, was performed to determine the hydrodynamic forces and moments of the ship. In addition, a model test was performed in a square tank for a static drift test in deep water to verify the accuracy of the CFD method by comparing the hydrodynamic forces and moments. The results showed changes in hydrodynamic forces and moments in deep and shallow water, with the latter increasing dramatically in very shallow water. The velocity fields demonstrated an increasing change in velocity as water became shallower. The least-squares method was applied to obtain the hydrodynamic coefficients by distinguishing a linear and non-linear model of the hydrodynamic force models. The course stability, maneuverability, and collision avoidance ability were evaluated from the estimated hydrodynamic coefficients. The hydrodynamic characteristics showed that the course stability improved in extremely shallow water. The maneuverability was satisfied with IMO (2002) except for extremely shallow water, and collision avoidance ability was a good performance in deep and shallow water. Received 13 February 2022, revised 22 March 2022, accepted 8 April 2022 Corresponding author Hyeon Kyu Yoon: +82-55-213-3683, hkyoon@changwon.ac.kr c 2022, The Korean Society of Ocean Engineers This is an open access article distributed under the terms of the creative commons attribution non-commercial license (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.","PeriodicalId":315103,"journal":{"name":"Journal of Ocean Engineering and Technology","volume":"191 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122807609","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Computational fluid dynamics, Fully submerged depth, Froude number ABSTRACT: This paper presents the minimum submergence depth of an underwater vehicle that can remove the effect of free surface on the resistance of the underwater vehicle. The total resistance of the underwater vehicle in fully submerged modes comprises only viscous pressure and friction resistances, and no wave resistance should be present, based on the free surface effect. In a model test performed in this study, the resistance is measured in the range of 2 to 10 kn (1.03 – 5.14 m/s) under depth conditions of 850 mm (2.6D) and 1250 mm (3.8D), respectively, and the residual resistance coefficients are compared. Subsequently, resistance analysis is performed via computational fluid dynamics (CFD) simulation to investigate the free surface effect based on various submergence depths. First, the numerical analysis results in the absence of free surface conditions and the model test results are compared to show the tendency of the resistance coefficients and the reliability of the CFD simulation results. Subsequently, numerical analysis results of submergence depth presented in a reference paper are compared with the model test results. These two sets of results confirm that the resistance increased due to the free surface effect as the high speed and depth approach the free surface. Therefore, to identify a fully submerged depth that is not affected by the free surface effect, case studies for various depths are conducted via numerical analysis, and a correlation for the fully submerged depth based on the
摘要:本文提出了消除自由水面对水下航行器阻力影响的最小潜水深度。基于自由面效应，水下航行器在完全淹没模式下的总阻力仅包括粘性压力阻力和摩擦阻力，不应存在波浪阻力。在本研究进行的模型试验中，分别在850 mm (2.6D)和1250 mm (3.8D)的深度条件下，在2 ~ 10 kn (1.03 ~ 5.14 m/s)范围内测量了阻力，并比较了剩余阻力系数。随后，通过计算流体动力学(CFD)模拟进行阻力分析，研究不同淹没深度下的自由面效应。首先，将无自由面条件下的数值分析结果与模型试验结果进行对比，显示阻力系数的变化趋势和CFD模拟结果的可靠性。随后，将参考文献中给出的淹没深度数值分析结果与模型试验结果进行了比较。这两组结果证实了当高速和深度接近自由表面时，阻力由于自由表面效应而增加。因此，为了确定不受自由面效应影响的完全淹没深度，通过数值分析对不同深度进行了案例研究，并基于
{"title":"Effect of Free Surface Based on Submergence Depth of Underwater Vehicle","authors":"T. Youn, Min-Jae Kim, Moon-Chan Kim, J. Kang","doi":"10.26748/ksoe.2021.077","DOIUrl":"https://doi.org/10.26748/ksoe.2021.077","url":null,"abstract":"Computational fluid dynamics, Fully submerged depth, Froude number ABSTRACT: This paper presents the minimum submergence depth of an underwater vehicle that can remove the effect of free surface on the resistance of the underwater vehicle. The total resistance of the underwater vehicle in fully submerged modes comprises only viscous pressure and friction resistances, and no wave resistance should be present, based on the free surface effect. In a model test performed in this study, the resistance is measured in the range of 2 to 10 kn (1.03 – 5.14 m/s) under depth conditions of 850 mm (2.6D) and 1250 mm (3.8D), respectively, and the residual resistance coefficients are compared. Subsequently, resistance analysis is performed via computational fluid dynamics (CFD) simulation to investigate the free surface effect based on various submergence depths. First, the numerical analysis results in the absence of free surface conditions and the model test results are compared to show the tendency of the resistance coefficients and the reliability of the CFD simulation results. Subsequently, numerical analysis results of submergence depth presented in a reference paper are compared with the model test results. These two sets of results confirm that the resistance increased due to the free surface effect as the high speed and depth approach the free surface. Therefore, to identify a fully submerged depth that is not affected by the free surface effect, case studies for various depths are conducted via numerical analysis, and a correlation for the fully submerged depth based on the","PeriodicalId":315103,"journal":{"name":"Journal of Ocean Engineering and Technology","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125528867","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Wang-Geun Lee, Sang-Hyun Kim, Doojin Jung, Sooyeon Kwon
: In general, the effect of roll motion is not considered in the study on maneuverability in calm water. However, for high-speed twin-screw ships such as the DTMB 5415, the coupling effects of roll and other motions should be considered. Therefore, in this study, the estimation of maneuverability using a 4-degree-of-freedom (DOF; surge, sway, roll, yaw) maneuvering mathematical group (MMG) model was conducted for the DTMB 5415, to improve the estimation accuracy of its maneuverability. Furthermore, a study on the change in turning performance according to the fin angle was conducted. To accurately calculate the lift and drag forces generated by the fins, it is necessary to consider the three-dimensional shape of the wing, submerged depth, and effect of interference with the hull. First, a maneuvering simulation model was developed based on the 4-DOF MMG mathematical model, and the lift force and moment generated by the side fins were considered as external force terms. By employing the CFD model, the lift and drag forces generated from the side fins during ship operation were calculated, and the results were adopted as the external force terms of the 4-DOF MMG mathematical model. A 35° turning simulation was conducted by altering the ship’s speed and the angle of the side fins. Accordingly, it was confirmed that the MMG simulation model constructed with the lift force of the fins calculated through CFD can sufficiently estimate maneuverability. It was confirmed that the heel angle changes according to the fin angle during steady turning, and the turning performance changes accordingly. In addition, it was verified that the turning performance could be improved by increasing the heel angle in the outward turning direction using the side fin, and that the sway speed of the ship during turning can affect the turning performance. Hence, it is considered necessary to study the effect of the sway speed on the turning performance of a ship during turning.
{"title":"Change in Turning Ability According to the Side Fin Angle of a Ship Based on a Mathematical Model","authors":"Wang-Geun Lee, Sang-Hyun Kim, Doojin Jung, Sooyeon Kwon","doi":"10.26748/ksoe.2021.099","DOIUrl":"https://doi.org/10.26748/ksoe.2021.099","url":null,"abstract":": In general, the effect of roll motion is not considered in the study on maneuverability in calm water. However, for high-speed twin-screw ships such as the DTMB 5415, the coupling effects of roll and other motions should be considered. Therefore, in this study, the estimation of maneuverability using a 4-degree-of-freedom (DOF; surge, sway, roll, yaw) maneuvering mathematical group (MMG) model was conducted for the DTMB 5415, to improve the estimation accuracy of its maneuverability. Furthermore, a study on the change in turning performance according to the fin angle was conducted. To accurately calculate the lift and drag forces generated by the fins, it is necessary to consider the three-dimensional shape of the wing, submerged depth, and effect of interference with the hull. First, a maneuvering simulation model was developed based on the 4-DOF MMG mathematical model, and the lift force and moment generated by the side fins were considered as external force terms. By employing the CFD model, the lift and drag forces generated from the side fins during ship operation were calculated, and the results were adopted as the external force terms of the 4-DOF MMG mathematical model. A 35° turning simulation was conducted by altering the ship’s speed and the angle of the side fins. Accordingly, it was confirmed that the MMG simulation model constructed with the lift force of the fins calculated through CFD can sufficiently estimate maneuverability. It was confirmed that the heel angle changes according to the fin angle during steady turning, and the turning performance changes accordingly. In addition, it was verified that the turning performance could be improved by increasing the heel angle in the outward turning direction using the side fin, and that the sway speed of the ship during turning can affect the turning performance. Hence, it is considered necessary to study the effect of the sway speed on the turning performance of a ship during turning.","PeriodicalId":315103,"journal":{"name":"Journal of Ocean Engineering and Technology","volume":"46 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123066543","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Brazilian multinational petroleum corporation Petrobras and partners are developing the Buzios oil field, which is approximately 210 km offshore of Brazil. The Floating production storage and offloading (FPSO) is spread-moored in a maximum water depth of 2,030 m and has facilities to receive oil from sub-sea wells. It also has production plant facilities to process fluids, stabilize them, and separate produced water and natural gas, which is re-injected into a dedicated reservoir. Processed liquids are metered, stored in the FPSO cargo storage tanks, and offloaded to export tankers. The design life of the FPSO is 30 years. The relative water depth is defined as , where is the wave number, is the angular frequency, is the wavelength, is the wave period, is water depth, and is gravity. According to DNV (2010a), it is normally not necessary to investigate wave periods longer than 18 s. Therefore, the relative water depth is greater than 25 for the project. When the relative water depth is greater than 2, deep-water wave theories are applicable (Chakrabarti, 1987; DNV, 2010b; Shin, 2019). Well-known wave theories include Airy theory, Stokes theory, Dean’s stream function theory, Fenton’s theory, and trochodial (Gerstner) theory for deep-water waves in offshore structure design. Trochodial theory is an exact solution of the Euler equation with vorticity. The first rotational solution was described by Gerstner in 1802 and was independently rediscovered later by Rankine (1863). A mathematical analysis of trochodial theory was performed by Constantin (Henry, 2008). The wavelength is independent of the trochoidal wave’s height, unlike in Stokes’ wave theory and observations. The trajectories of a water particle are closed circles, in contrast with the usual experimental observation of Stokes drift associated with wave motion. Therefore, trochodial theory is of limited use for offshore structure design. Airy theory, Stokes theory, Dean’s stream function theory, and Fenton’s theory are irrotational wave theories, unlike Trochodial theory. The wavelength is also independent of Airy wave’s height, and Airy theory is applicable for ≤ (Chakrabarti, 1987), where is the wave height. Therefore, Airy theory is unsuitable for describing waves near the Miche limit (DNV, 2010b); i.e., , where is the wavelength calculated by Airy theory. Journal of Ocean Engineering and Technology [ARTICLE IN PRESS] https://doi.org/10.26748/KSOE.2021.092 pISSN 1225-0767 eISSN 2287-6715
{"title":"A Fourier Series Approximation for Deep-water Waves","authors":"JangRyong Shin","doi":"10.26748/ksoe.2021.092","DOIUrl":"https://doi.org/10.26748/ksoe.2021.092","url":null,"abstract":"The Brazilian multinational petroleum corporation Petrobras and partners are developing the Buzios oil field, which is approximately 210 km offshore of Brazil. The Floating production storage and offloading (FPSO) is spread-moored in a maximum water depth of 2,030 m and has facilities to receive oil from sub-sea wells. It also has production plant facilities to process fluids, stabilize them, and separate produced water and natural gas, which is re-injected into a dedicated reservoir. Processed liquids are metered, stored in the FPSO cargo storage tanks, and offloaded to export tankers. The design life of the FPSO is 30 years. The relative water depth is defined as , where is the wave number, is the angular frequency, is the wavelength, is the wave period, is water depth, and is gravity. According to DNV (2010a), it is normally not necessary to investigate wave periods longer than 18 s. Therefore, the relative water depth is greater than 25 for the project. When the relative water depth is greater than 2, deep-water wave theories are applicable (Chakrabarti, 1987; DNV, 2010b; Shin, 2019). Well-known wave theories include Airy theory, Stokes theory, Dean’s stream function theory, Fenton’s theory, and trochodial (Gerstner) theory for deep-water waves in offshore structure design. Trochodial theory is an exact solution of the Euler equation with vorticity. The first rotational solution was described by Gerstner in 1802 and was independently rediscovered later by Rankine (1863). A mathematical analysis of trochodial theory was performed by Constantin (Henry, 2008). The wavelength is independent of the trochoidal wave’s height, unlike in Stokes’ wave theory and observations. The trajectories of a water particle are closed circles, in contrast with the usual experimental observation of Stokes drift associated with wave motion. Therefore, trochodial theory is of limited use for offshore structure design. Airy theory, Stokes theory, Dean’s stream function theory, and Fenton’s theory are irrotational wave theories, unlike Trochodial theory. The wavelength is also independent of Airy wave’s height, and Airy theory is applicable for ≤ (Chakrabarti, 1987), where is the wave height. Therefore, Airy theory is unsuitable for describing waves near the Miche limit (DNV, 2010b); i.e., , where is the wavelength calculated by Airy theory. Journal of Ocean Engineering and Technology [ARTICLE IN PRESS] https://doi.org/10.26748/KSOE.2021.092 pISSN 1225-0767 eISSN 2287-6715","PeriodicalId":315103,"journal":{"name":"Journal of Ocean Engineering and Technology","volume":"63 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129061283","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A water-jet can be used as one of the propulsion systems for ships and marine life. When a jet is injected to obtain thrust, a vortex ring is formed at a nozzle and then propagated downstream (Krueger et al., 2008). Furthermore, a vortex ring is generated due to volcanic eruption or nuclear explosion (Akhmetov, 2009). The flow of a vortex ring is formulated with the Helmholtz vorticity equation in inviscid and incompressible fluids (Batchelor, 1967). A steady vortex ring was first reported by Helmholtz (1867) who examined a vortex ring of an small circular cross section, while a spherical vortex was first analyzed by Hill (1894). Norbury (1973) analyzed a vortex ring in a steady state for general circumstances, which is referred to as the Norbury–Fraenkel family (N-F family) of vortex rings. A dynamic analysis is required for analyzing the instability due to the disturbance or interaction between vortex rings. A contour dynamics (CD) method for fluid velocity is used for analyzing the complex evolution of the contour of a vortex core. The CD method is a two-dimensional or axisymmetric flow analysis method due to the isolated vorticity in an inviscid, incompressible, and irrotational flow field (Pullin, 1992; Smith et al., 2018). The CD method can drastically reduce the burden of computations because the computation is performed in the form of line integrals on the boundary contour of the vorticity region. The fluid velocity on the contour is calculated using the CD method and then applied with time integrals to estimate the dynamic changes in the shape of the vortex core. Zabusky et al. (1979) introduced the CD method in dynamic analysis of two-dimensional vortex patches. Various examples of dynamic analysis for threedimensional axisymmetric vortex rings are provided in the study by Shariff et al. (1989). In this study, the CD method was applied to the analysis of the N-F family of vortex rings which are flows in steady state. Choi (2020) combined the CD method for a stream function (Shariff et al., 1989) and the direct shape-calculation method, and thus obtained results that were superior that those reported by Norbury (1973) wherein surface integrals and Fourier analysis were used. As a follow-up study to Choi (2020), in this study, we analyzed the N-F family of vortex rings using the CD method for fluid velocity examined in studies by Shariff et al. (1989) and Shariff et al. (2008). A stream function has been mostly used for analyzing a vortex ring in a steady state (Batchelor, 1967; Fraenkel, 1970; Fraenkel, 1972; Norbury 1973). In this study, we examined whether the CD method for fluid velocity, which is used in dynamic analysis, can also be applied to the analysis of a vortex ring in Journal of Ocean Engineering and Technology [ARTICLE IN PRESS] https://doi.org/10.26748/KSOE.2021.070 pISSN 1225-0767 eISSN 2287-6715
水射流可用作船舶和海洋生物的推进系统之一。当射流注入以获得推力时，在喷嘴处形成旋涡环并向下游传播(Krueger et al.， 2008)。此外，火山喷发或核爆炸也会产生漩涡环(Akhmetov, 2009)。用亥姆霍兹涡度方程(Batchelor, 1967)表示了无粘性和不可压缩流体中的涡环流动。Helmholtz(1867)首先报道了稳定涡环，他研究了一个小圆形截面的涡环，而Hill(1894)首先分析了球形涡环。Norbury(1973)分析了一般情况下稳态下的涡环，称之为涡环的Norbury - fraenkel族(N-F族)。由于涡旋环之间的干扰或相互作用而引起的不稳定性需要进行动力学分析。采用流体速度的轮廓动力学方法分析了涡核轮廓的复杂演化过程。CD方法是一种二维或轴对称流动分析方法，由于在无粘、不可压缩和无旋转的流场中存在孤立的涡量(Pullin, 1992;Smith et al.， 2018)。CD方法以线积分的形式在涡度区边界轮廓上进行计算，大大减少了计算量。采用CD法计算轮廓上的流体速度，并结合时间积分估计涡核形状的动态变化。Zabusky et al.(1979)将CD方法引入二维涡旋斑块的动态分析。Shariff et al.(1989)的研究提供了三维轴对称涡环动力分析的各种实例。本文将CD方法应用于稳态流动的N-F族涡环的分析。Choi(2020)结合了流函数的CD方法(Shariff et al.， 1989)和直接形状计算方法，从而获得了优于Norbury(1973)报告的结果，其中使用了表面积分和傅里叶分析。作为Choi(2020)的后续研究，在本研究中，我们使用Shariff et al.(1989)和Shariff et al.(2008)研究中检验的流体速度的CD方法分析了N-F族涡环。流函数主要用于分析稳定状态下的涡环(Batchelor, 1967;Fraenkel, 1970;Fraenkel, 1972;Norbury 1973)。在这项研究中，我们研究了用于动力分析的流体速度的CD方法是否也可以应用于涡环的分析，海洋工程与技术杂志[ARTICLE In PRESS] https://doi.org/10.26748/KSOE.2021.070 pISSN 1225-0767 eISSN 2287-6715
{"title":"Analysis of Steady Vortex Rings Using Contour Dynamics Method for Fluid Velocity","authors":"Yoon-Rak Choi","doi":"10.26748/ksoe.2021.070","DOIUrl":"https://doi.org/10.26748/ksoe.2021.070","url":null,"abstract":"A water-jet can be used as one of the propulsion systems for ships and marine life. When a jet is injected to obtain thrust, a vortex ring is formed at a nozzle and then propagated downstream (Krueger et al., 2008). Furthermore, a vortex ring is generated due to volcanic eruption or nuclear explosion (Akhmetov, 2009). The flow of a vortex ring is formulated with the Helmholtz vorticity equation in inviscid and incompressible fluids (Batchelor, 1967). A steady vortex ring was first reported by Helmholtz (1867) who examined a vortex ring of an small circular cross section, while a spherical vortex was first analyzed by Hill (1894). Norbury (1973) analyzed a vortex ring in a steady state for general circumstances, which is referred to as the Norbury–Fraenkel family (N-F family) of vortex rings. A dynamic analysis is required for analyzing the instability due to the disturbance or interaction between vortex rings. A contour dynamics (CD) method for fluid velocity is used for analyzing the complex evolution of the contour of a vortex core. The CD method is a two-dimensional or axisymmetric flow analysis method due to the isolated vorticity in an inviscid, incompressible, and irrotational flow field (Pullin, 1992; Smith et al., 2018). The CD method can drastically reduce the burden of computations because the computation is performed in the form of line integrals on the boundary contour of the vorticity region. The fluid velocity on the contour is calculated using the CD method and then applied with time integrals to estimate the dynamic changes in the shape of the vortex core. Zabusky et al. (1979) introduced the CD method in dynamic analysis of two-dimensional vortex patches. Various examples of dynamic analysis for threedimensional axisymmetric vortex rings are provided in the study by Shariff et al. (1989). In this study, the CD method was applied to the analysis of the N-F family of vortex rings which are flows in steady state. Choi (2020) combined the CD method for a stream function (Shariff et al., 1989) and the direct shape-calculation method, and thus obtained results that were superior that those reported by Norbury (1973) wherein surface integrals and Fourier analysis were used. As a follow-up study to Choi (2020), in this study, we analyzed the N-F family of vortex rings using the CD method for fluid velocity examined in studies by Shariff et al. (1989) and Shariff et al. (2008). A stream function has been mostly used for analyzing a vortex ring in a steady state (Batchelor, 1967; Fraenkel, 1970; Fraenkel, 1972; Norbury 1973). In this study, we examined whether the CD method for fluid velocity, which is used in dynamic analysis, can also be applied to the analysis of a vortex ring in Journal of Ocean Engineering and Technology [ARTICLE IN PRESS] https://doi.org/10.26748/KSOE.2021.070 pISSN 1225-0767 eISSN 2287-6715","PeriodicalId":315103,"journal":{"name":"Journal of Ocean Engineering and Technology","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116435103","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
: There are many different types of tanks on ships that meet various requirements. Each tank is required to undergo hydrostatic testing according to the Ship Safety Act after being installed onboard. In some hydrostatic tests, excessive deformation may occur. The overpressure of the air in the tank generated during testing is one of the possible causes of deformation. Based on the dimensions of the tank, nozzle, and pipes installed, it was confirmed that the overpressure of the air can cause problems with the structure, according to the Bernoulli equation. Additionally, finite element analysis (FEA) was performed on the tank structure to confirm the deformation and the stress occurring in the structure. From the perspective of deformation, the maximum deflection limit was set based on the criteria provided by the Eurocode and DNV. From the perspective of stress, the structural safety assessment was performed by comparing the allowable stress and equivalent stress generated in the structure. To determine whether the behavior of the actual structure was well implemented via FEA, beam theory was applied to the tank structure and compared with the FEA results. As a result of the analysis, severe deformation was found in some cases. This means that the overpressure of the air may be the cause of actual deformation. It was also confirmed that permanent deformation may occur.
{"title":"Preliminary Study on Deformation During Hydrostatic Testing in a Deep Tank","authors":"Geuntae Kim, T. An, Tak-Kee Lee","doi":"10.26748/ksoe.2021.075","DOIUrl":"https://doi.org/10.26748/ksoe.2021.075","url":null,"abstract":": There are many different types of tanks on ships that meet various requirements. Each tank is required to undergo hydrostatic testing according to the Ship Safety Act after being installed onboard. In some hydrostatic tests, excessive deformation may occur. The overpressure of the air in the tank generated during testing is one of the possible causes of deformation. Based on the dimensions of the tank, nozzle, and pipes installed, it was confirmed that the overpressure of the air can cause problems with the structure, according to the Bernoulli equation. Additionally, finite element analysis (FEA) was performed on the tank structure to confirm the deformation and the stress occurring in the structure. From the perspective of deformation, the maximum deflection limit was set based on the criteria provided by the Eurocode and DNV. From the perspective of stress, the structural safety assessment was performed by comparing the allowable stress and equivalent stress generated in the structure. To determine whether the behavior of the actual structure was well implemented via FEA, beam theory was applied to the tank structure and compared with the FEA results. As a result of the analysis, severe deformation was found in some cases. This means that the overpressure of the air may be the cause of actual deformation. It was also confirmed that permanent deformation may occur.","PeriodicalId":315103,"journal":{"name":"Journal of Ocean Engineering and Technology","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129182781","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In recent years, various studies have been conducted on oscillating-water-column-type wave energy converters (OWC-WECs) with multiple chambers with the objective of efficiently utilizing the limited space of offshore/onshore structures. In this study, a numerical investigation based on a numerical wave tank was conducted on single, dual, and triple OWC chambers to examine the hydrodynamic performances and the energy conversion characteristics of the multiple water columns. The boundary value problem with the Laplace equation was solved by using a numerical wave tank based on a finite element method. The validity of the current numerical method was confirmed by comparing it with the measured data in the previous experimental research. We undertook a series of numerical simulations and observed that the water column motion of sloshing mode in a single chamber can be changed into the piston motion of different phases in multiple OWC chambers. Therefore, the piston motion in the multiple chambers can generate considerable airflow at a specific resonant frequency. In addition, the division of the OWC chamber results in a reduction of the time-dependent variability of the final output power from the device. As a result, the application of the multiple chambers leads to an increase of the energy conversion performance as well as a decrease of the variability of the wave energy converter.
{"title":"Numerical Analysis for Hydrodynamic Performance of OWC Devices with Multiple Chambers in Waves","authors":"Jeong-Seok Kim, B. Nam","doi":"10.26748/ksoe.2021.091","DOIUrl":"https://doi.org/10.26748/ksoe.2021.091","url":null,"abstract":"In recent years, various studies have been conducted on oscillating-water-column-type wave energy converters (OWC-WECs) with multiple chambers with the objective of efficiently utilizing the limited space of offshore/onshore structures. In this study, a numerical investigation based on a numerical wave tank was conducted on single, dual, and triple OWC chambers to examine the hydrodynamic performances and the energy conversion characteristics of the multiple water columns. The boundary value problem with the Laplace equation was solved by using a numerical wave tank based on a finite element method. The validity of the current numerical method was confirmed by comparing it with the measured data in the previous experimental research. We undertook a series of numerical simulations and observed that the water column motion of sloshing mode in a single chamber can be changed into the piston motion of different phases in multiple OWC chambers. Therefore, the piston motion in the multiple chambers can generate considerable airflow at a specific resonant frequency. In addition, the division of the OWC chamber results in a reduction of the time-dependent variability of the final output power from the device. As a result, the application of the multiple chambers leads to an increase of the energy conversion performance as well as a decrease of the variability of the wave energy converter.","PeriodicalId":315103,"journal":{"name":"Journal of Ocean Engineering and Technology","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130867477","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Seo, Gyeong-Seon Yeom, Changmin Lee, Woo-Dong Lee
Generally, tsunamis are generated by the rapid crustal movements of the ocean floor. Other factors of tsunami generation include landslides on coastal and ocean floor slopes, glacier collapses, and meteorite collisions. In this study, two numerical analyses were conducted to examine the formation, propagation, and deformation properties of landslide tsunamis. First, LS-DYNA was adopted to simulate the formation and propagation processes of tsunamis generated by dropping rigid bodies. The generated tsunamis had smaller wave heights and wider waveforms during their propagation, and their waveforms and flow velocities resembled those of theoretical solitary waves after a certain distance. Second, after the formation of the landslide tsunami, a tsunami based on the solitary wave approximation theory was generated in a numerical wave tank (NWT) with a computational domain that considered the stability/steady phase. The comparison of two numerical analysis results over a certain distance indicated that the waveform and flow velocity were approximately equal, and the maximum wave pressures acting on the upright wall also exhibited similar distributions. Therefore, an effective numerical model such as LS-DYNA was necessary to analyze the formation and initial deformations of the landslide tsunami, while an NWT with the wave generation method based on the solitary wave approximation theory was sufficient above a certain distance.
{"title":"Numerical Analyses on the Formation, Propagation, and Deformation of Landslide Tsunami Using LS-DYNA and NWT","authors":"M. Seo, Gyeong-Seon Yeom, Changmin Lee, Woo-Dong Lee","doi":"10.26748/ksoe.2021.089","DOIUrl":"https://doi.org/10.26748/ksoe.2021.089","url":null,"abstract":"Generally, tsunamis are generated by the rapid crustal movements of the ocean floor. Other factors of tsunami generation include landslides on coastal and ocean floor slopes, glacier collapses, and meteorite collisions. In this study, two numerical analyses were conducted to examine the formation, propagation, and deformation properties of landslide tsunamis. First, LS-DYNA was adopted to simulate the formation and propagation processes of tsunamis generated by dropping rigid bodies. The generated tsunamis had smaller wave heights and wider waveforms during their propagation, and their waveforms and flow velocities resembled those of theoretical solitary waves after a certain distance. Second, after the formation of the landslide tsunami, a tsunami based on the solitary wave approximation theory was generated in a numerical wave tank (NWT) with a computational domain that considered the stability/steady phase. The comparison of two numerical analysis results over a certain distance indicated that the waveform and flow velocity were approximately equal, and the maximum wave pressures acting on the upright wall also exhibited similar distributions. Therefore, an effective numerical model such as LS-DYNA was necessary to analyze the formation and initial deformations of the landslide tsunami, while an NWT with the wave generation method based on the solitary wave approximation theory was sufficient above a certain distance.","PeriodicalId":315103,"journal":{"name":"Journal of Ocean Engineering and Technology","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122800270","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
With the advancement of intelligent vehicles and unmanned systems, there is a growing interest in underwater surveys using autonomous marine vehicles (AMVs). This study presents an automated planning strategy for a long-term survey mission using a fleet of AMVs consisting of autonomous surface vehicles and autonomous underwater vehicles. Due to the complex nature of the mission, the actions of the vehicle must be of high-level abstraction, which means that the actions indicate not only motion of the vehicle but also symbols and semantics, such as those corresponding to deploy, charge, and survey. For automated planning, the planning domain definition language (PDDL) was employed to construct a mission planner for realizing a powerful and flexible planning system. Despite being able to handle abstract actions, such high-level planners have difficulty in efficiently optimizing numerical objectives such as obtaining the shortest route given multiple destinations. To alleviate this issue, a widely known technique in operations research was additionally employed, which limited the solution space so that the high-level planner could devise efficient plans. For a comprehensive evaluation of the proposed method, various PDDL-based planners with different parameter settings were implemented, and their performances were compared through simulation. The simulation result shows that the proposed method outperformed the baseline solutions by yielding plans that completed the missions more quickly, thereby demonstrating the efficacy of the proposed methodology. Received 13 December 2021, revised 10 January 2022, accepted 10 January 2022 Corresponding author Jinwhan Kim: +82-42-350-1519, jinwhan@kaist.ac.kr c 2022, The Korean Society of Ocean Engineers This is an open access article distributed under the terms of the creative commons attribution non-commercial license (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
随着智能车辆和无人系统的发展，人们对使用自主海洋车辆(amv)进行水下调查的兴趣越来越大。本研究提出了一种用于长期调查任务的自动化规划策略，该策略使用由自主水面航行器和自主水下航行器组成的amv舰队。由于任务的复杂性，车辆的动作必须是高度抽象的，这意味着这些动作不仅表示车辆的运动，还表示符号和语义，例如与部署、冲锋和调查相对应的符号和语义。在自动化规划方面，采用规划域定义语言(PDDL)构建任务规划器，实现了功能强大、灵活的规划系统。尽管能够处理抽象行为，但这种高级规划人员在有效优化数值目标方面存在困难，例如在给定多个目的地的情况下获得最短路线。为了缓解这一问题，还采用了运筹学中一个广为人知的技术，该技术限制了解决方案的空间，使高层规划人员能够制定有效的计划。为了对所提方法进行综合评价，实现了不同参数设置的基于pddl的规划器，并通过仿真对其性能进行了比较。仿真结果表明，所提方法优于基准解，生成的计划能更快地完成任务，从而证明了所提方法的有效性。通讯作者Jinwhan Kim: +82-42-350-1519, jinwhan@kaist.ac.kr c 2022, The Korean Society of Ocean Engineers这是一篇开放获取的文章，根据创作共用归属非商业许可(http://creativecommons.org/licenses/by-nc/4.0)的条款分发，该许可允许在任何媒介上不受限制的非商业使用、分发和复制，前提是原始作品被适当引用。
{"title":"Mission Planning for Underwater Survey with Autonomous Marine Vehicles","authors":"Junwoo Jang, Haggi Do, Jinwhan Kim","doi":"10.26748/ksoe.2021.097","DOIUrl":"https://doi.org/10.26748/ksoe.2021.097","url":null,"abstract":"With the advancement of intelligent vehicles and unmanned systems, there is a growing interest in underwater surveys using autonomous marine vehicles (AMVs). This study presents an automated planning strategy for a long-term survey mission using a fleet of AMVs consisting of autonomous surface vehicles and autonomous underwater vehicles. Due to the complex nature of the mission, the actions of the vehicle must be of high-level abstraction, which means that the actions indicate not only motion of the vehicle but also symbols and semantics, such as those corresponding to deploy, charge, and survey. For automated planning, the planning domain definition language (PDDL) was employed to construct a mission planner for realizing a powerful and flexible planning system. Despite being able to handle abstract actions, such high-level planners have difficulty in efficiently optimizing numerical objectives such as obtaining the shortest route given multiple destinations. To alleviate this issue, a widely known technique in operations research was additionally employed, which limited the solution space so that the high-level planner could devise efficient plans. For a comprehensive evaluation of the proposed method, various PDDL-based planners with different parameter settings were implemented, and their performances were compared through simulation. The simulation result shows that the proposed method outperformed the baseline solutions by yielding plans that completed the missions more quickly, thereby demonstrating the efficacy of the proposed methodology. Received 13 December 2021, revised 10 January 2022, accepted 10 January 2022 Corresponding author Jinwhan Kim: +82-42-350-1519, jinwhan@kaist.ac.kr c 2022, The Korean Society of Ocean Engineers This is an open access article distributed under the terms of the creative commons attribution non-commercial license (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.","PeriodicalId":315103,"journal":{"name":"Journal of Ocean Engineering and Technology","volume":"37 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124943084","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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