• Bulletin of the Society of Naval Architects of Korea
• /
• v.26 no.4
• /
• pp.44-56
• /
• 1989

Recently the residual strength of damaged tubulars under axial compression has extensively been investigated. However, in spite of the possibility of damage onto underwater members of offshore structures as results of collisions, dropped objects and other accidental impacts occurring in service or during fabrication or installation, no research works on the structural behaviour of damaged tubulars under combined loadings including hydrostatic pressure have been reported in the literature. In this paper, a numerical method has been proposed to estimate the residual strength of damaged tubulars under combined loadings, and then the proposed method has been substantiated with corresponding test data. A simple design equation has been derived based upon the results of the parametric study using the proposed method. The accuracy of the predictions using the derived equation is found to be a 10.1% COV(Coefficient of Variation) together with an 1. 037 mean comparing with the test data.

• Journal of Environmental Science International
• /
• v.22 no.4
• /
• pp.481-492
• /
• 2013

In this study, the use survey of domestic and international weather information on coastal regions and the demand survey (e.g. general and in-depth surveys) for customer needs with coastal industries were carried out to design customized coastal weather contents. The general demand survey showed that most of the customers working in the coastal industries were interested in a short-term forecast, such as a general weather outlook (approximately 29% of the total respondents) and typhoon information (19%), and they preferred to be given the forecast information from new media such as the internet web-pages (36%) and mobile utilities (23%) rather than old media such as TV (16%) and radio (11%). In addition, only 31% of the total respondents were found to be satisfied with the use of the current coastal weather service. This low percentage might mainly be a result of lack of information accuracy (about 64%) and diversity (28%). From in-depth survey with site visiting, the need of coastal weather contents, such as weather elements, data form, a tool of communication, and forecast interval, differed with the working stages in three coastal industries (e.g. shipbuilding, maritime trade, and passenger transport industries).

• Journal of the Korean Society of Hazard Mitigation
• /
• v.9 no.4
• /
• pp.21-28
• /
• 2009

Most of domestic shipyards are located at coastal regions which are affected by typhoons nearly every year. For effectiveness of shipbuilding, shipyards contain many facilities which are light-weighted and affected dominantly by wind. In the present paper, we analyze various wind fields over a shipyard including surrounding topology and structures to evaluate the structural safety of the facilities posed in the strong wind. Extreme wind speed for a study region was estimated by typhoon Monte Carlo simulation and then used for inlet wind speed for CFD analysis for wind load on the facilities. Considering geometrical wind effects, we assess the surface pressure of the elements as the pressure factor, the ratio of surface pressure to dynamic pressure. The results show that the simulated wind speed is greater than the design wind speed for the some facilities because of the shipyard's geometry. It also shows that surrounding topography in coastal area is needed to be considered and adjustment for design wind speed at wind load standard application is necessary for mooring ship and industry facilities.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.31 no.2
• /
• pp.157-164
• /
• 2011

This work is devoted to the technique application of lock-in infrared Thermography in the shipbuilding and ocean engineering industry. For this purpose, an exploratory study to find the optimized test conditions is carried out by the design of experiments. It has been confirmed to be useful method that the phase contrast images were quantified by a reference image and weighted by defect hole size. Illuminated optical intensity of lower or medium strength give a good result for getting a phase contrast image. In order to get a good phase contrast image, lock-in frequency factors should be high in proportion to the illuminated optical intensity. The integration time of infrared camera should have been inversely proportional to the optical intensity. The other hand, the difference of specimen materials gave a slightly biased results not being discriminative reasoning.

• Journal of Advanced Research in Ocean Engineering
• /
• v.1 no.3
• /
• pp.157-167
• /
• 2015

In order to provide simple and accurate wave theory in design of offshore structure, an analytical approximation is introduced in this paper. The solution is limited to flat bottom having a constant water depth. Water is considered as inviscid, incompressible and irrotational. The solution satisfies the continuity equation, bottom boundary condition and non-linear kinematic free surface boundary condition exactly. Error for dynamic condition is quite small. The solution is suitable in description of breaking waves. The solution is presented with closed form and dispersion relation is also presented with closed form. In the last century, there have been two main approaches to the nonlinear problems. One of these is perturbation method. Stokes wave and Cnoidal wave are based on the method. The other is numerical method. Dean's stream function theory is based on the method. In this paper, power series method was considered. The power series method can be applied to certain nonlinear differential equations (initial value problems). The series coefficients are specified by a nonlinear recurrence inherited from the differential equation. Because the non-linear wave problem is a boundary value problem, the power series method cannot be applied to the problem in general. But finite number of coefficients is necessary to describe the wave profile, truncated power series is enough. Therefore the power series method can be applied to the problem. In this case, the series coefficients are specified by a set of equations instead of recurrence. By using the set of equations, the nonlinear wave problem has been solved in this paper.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.16 no.4
• /
• pp.248-254
• /
• 2013

Recently, contra-rotating propellers (CRP) having higher efficiency draw much attention since the EEDI regulation of IMO has been enforced. In this paper a numerical method based on the vortex lattice potential theory with a wake model and an experimental procedure with a newly built measuring device, specifically focusing on CRPs, are introduced. And they are applied to a series of CRP known to be designed for the purpose of improving EEDI. The numerical and experimental results showed good agreement explaining the characteristics of the CRP properly. The proposed method is believed to be effectively used for various CRP related studies.

• Journal of Advanced Research in Ocean Engineering
• /
• v.2 no.3
• /
• pp.150-157
• /
• 2016

When blocks are supported on a dock, huge reaction forces concentrated at the supports cause structural damage owing to local stress concentrations. Thus, the supports should be arranged to avoid local failure from the reaction forces by redistributing those forces. Docking analyses to determine the proper blocks and their support arrangements are introduced so that the local stresses are minimized to warrant the safety of the docking supports. Local stresses enforced by the support arrangement should be evaluated by finite element analysis (FEA). However, it is difficult to consider an accurate 3D geometry of the blocks in the finite element model because the structural design information is too complicated to determine within several days using the FEA model. This paper presents a simplified FE model to evaluate the safety of the arrangement of supports using a simplified grillage element. The grillage element can be efficiently used to obrain the reaction forces in docking analysis becasuse the reaction forces at the supports are enough to assess the safety of block. Since a simplified grillage model of the entire ship cannot accurately calculate the local stresses, an optimized modeling method based on the grillage element was introduced. The local reaction forces obtained by the proposed approach and three-dimensional FEA were discussed for typical types of ships. It is shown that the reaction forces obtained by the present grillage model are in reasonably good agreement with the FEA model.

• Wind and Structures
• /
• v.19 no.1
• /
• pp.1-14
• /
• 2014

Rail-mounted cranes can be easily damaged by a sudden gust of wind while working at a running speed, due to the large mass and high barycenter positions. In current designs, working rail-mounted cranes mainly depend on wheel braking torques to resist large wind load. Regular brakes, however, cannot satisfactorily stop the crane, which induces safety issues of cranes and hence leads to frequent crane accidents, especially in sudden gusts of wind. Therefore, it is necessary and important to study the braking performance of working rail mounted cranes under wind load. In this study, a simplified mechanical model was built to simulate the working rail mounted gantry crane, and dynamic analysis of the model was carried out to deduce braking performance equations that reflect the qualitative relations among braking time, braking distance, wind load, and braking torque. It was shown that, under constant braking torque, there existed inflection points on the curves of braking time and distance versus windforce. Both the braking time and the distance increased sharply when wind load exceeded the inflection point value, referred to as the threshold windforce. The braking performance of a 300 ton shipbuilding gantry crane was modeled and analyzed using multibody dynamics software ADAMS. The simulation results were fitted by quadratic curves to show the changes of braking time and distance versus windforce under various mount of braking torques. The threshold windforce could be obtained theoretically by taking derivative of fitted curves. Based on the fitted functional relationship between threshold windforce and braking torque, theoretical basis are provided to ensure a safe and rational design for crane wind-resistant braking systems.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.19 no.1
• /
• pp.71-77
• /
• 2013

Smart work has been gaining more popularity recently. Smart work means that employees perform their works anytime and anywhere as utilizing the information and communication technology. It can be divided into four categories; the mobile office, the home office, the work-at-center and the tele-cooperation. Among them, the mobile office based on tablet personal computers(PCs) or smart phones, employees can exchange information with tablet PCs or smart phones via mobile radio communication networks and portable terminals. Smart devices such as tablet PCs and smart phones help to access intranet system for requests, approvals, information search whenever employees need. This mobile office system for real-time HSE managing can contribute to improve the productivity and work efficiency in a shipyard. In this study, the main goal is to design the specialized mobile application for the HSE management system on the shipbuilding industry. The mobile application including 10 functions is designed based on ooCBD(object-oriented Component Based Development) methodology.

• Journal of the Society of Naval Architects of Korea
• /
• v.29 no.2
• /
• pp.140-149
• /
• 1992

The new method, termed the substructural eigensensitivity synthesis method, utilizes the computational merits of the component mode synthesis technique and of sensitivity analysis for the design sensitivities of the dynamic characteristics of substructurally combined structures. It is shown that the eigensensitivities of the entire structure can be obtained by synthesizing the substructural eigensolution and the sensitivities of the eigensolution for the design variables of the modifiable substructure. The sensitivities of the eigenvalues and eigenvectors obtained by the new method are compared to exact eigensolutions in terms of accuracy and computational efficiency. The small errors in eigensensitivity due to the truncation of higher modes remain within a manageable and permissible range for further analysis. The advantage of the newly proposed method as compared to the direct application of sensitivity analysis of the whole structure is demonstrated through examples.