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In this study, numerical simulations are conducted in order to analyze the capsizing of roll-on/roll-off passenger ship, Sewol, which occurred on 16 April 2014. Since little is known about the reason of ship capsize, numerical simulation aims to the finding of possible scenarios which can cause this tragic accident. To this end, 4-degree-of-freedom (surge, sway, yaw, and roll motions) maneuvering equations are solved. The hydrodynamic coefficients obtained from a similar ship are applied and the WISH-Maneuver program of Seoul National University is used to perform the numerical simulation. The present analysis utilizes the probabilistic approach, which considers various physical variables and involves the simulation of a large number of cases using different combinations of the variables. The total number of simulation cases is over 70 millions, and the simulation results that are close to the conditions of the actual accident situation are selected. Through this process, the effects of the simulation variables are investigated and the potential causes of the accident are identified. The results show the hydrostatic instability of the ship in the operational condition owing to cargo overload and insufficient ballast water, which raised the vertical center of gravity. The reduced stability combined with large starboard steering angle and cargo movement during large heel may have been the decisive reason of capsizing. [ABSTRACT FROM AUTHOR]

In the present study, a Rankine panel method, which is based on the potential theory and a Cartesian-grid method, which solves the Euler equation directly, are applied to calculate ship motion and added resistance. In the Rankine panel method, a near-field method which calculates added resistance by integrating the second-order pressure on a body surface is adopted. In the Cartesian grid method, the wave-body interaction problem is considered as a multiphase problem, and volume fraction functions are defined in order to distinguish each phase in a Cartesian grid system. The added resistance is calculated by subtracting the steady surge force from the mean surge force measured in motion problems. This study focuses on added resistance under short wave conditions. Calculation capacities of the Rankine panel method and Cartesian grid method in short wavelength are systematically analyzed for several models, including Series 60 hulls (CB=0.7, 0.8), S175 containerships and KVLCC2 hulls. In addition, established asymptotic methods in short wavelength are examined. [ABSTRACT FROM AUTHOR]

In this study, a model test was carried out to evaluate the station-keeping performance of Korea Research Institute of the Ships and Ocean Engineering (KRISO) standard semi-submersible, K-Semi in the Deep Ocean Engineering Basin (DOEB). The test was performed using a 1/50 scaled model with 12 mooring lines. The water depth was set to 3.2 m using a moveable bottom structure and truncated mooring lines. The dynamic behavior of the K-Semi was examined using a free decay test and regular wave as well as irregular wave tests of 1800. Large surge, heave and pitch due to drift motion from second-order effect were observed. The reason for the excessive low-frequency pitch motion is attributed to the restoring force and moment related to the mooring system as excessive surge occurred. The numerical model of K-Semi with the truncated mooring system was tuned and calibrated using model test results such as free decay and regular wave tests. Through numerical analysis, the motion characteristics of the K-Semi were compared with irregular model test results. In the case of a semi-submersible using a mooring system, it is observed that excessive pitch motion due to vertical restoring force and moment may occur when large horizontal displacement occurs. The effect of low-frequency pitch motion related to surge motion is an important factor in upwell estimation as well as second-order motion in referred DNV-GL OTG13.

We investigated the segregation behavior of a molten diblock copolymer, poly(n-butyl acrylate)-b-poly(methyl methacrylate-r-styrene) (PBA-b-P(MMA-r-S)), wherein styrene (S) is incorporated as a comonomer in the second block to modulate the effective interaction between homopolymer and a random copolymer block. The temperature dependence of the effective interaction parameter χeff between n-butyl acrylate (BA) and the average monomer of the MMA-r-S random block was evaluated from small-angle X-ray scattering (SAXS) analysis using the random phase approximation (RPA) approach. The calculated χeff, as a function of the styrene fraction in the random copolymer block, shows a good agreement with the mean-field binary interaction model. This consistency indicates that the effective interaction between component BA and the average monomer of the random copolymer block is smaller than the interactions between pure components (χBA,MMA,χBA,S). The present study suggests that the introduction of a random copolymer block to a block copolymer can effectively reduce the degree of incompatibility of the block copolymer system without altering the constituent species, which may serve as a viable methodology in designing novel thermoplastic elastomers based on triblock or multiblock copolymers.

In this study, the coupled motion of a mooring system and multifloating cranes were analyzed. For the motion analysis, the combined equations of motions of the mooring line and multifloating cranes were introduced. The multibody equations for floating cranes were derived from the equations of motion. The finite element method (FEM) was used to derive equations to solve the stretchable catenary problem of the mooring line. To verify the function of mooring simulator, calculation results were compared with commercial mooring software. To validate the analysis results, we conducted an experimental test for offshore operation using two floating crane models scaled to 1:40. Two floating crane models and a pile model were established for operation of uprighting flare towers. During the model test, the motion of the floating cranes and tensions of the mooring lines were measured. Through the model test, the accuracy of the mooring analysis program developed in this study was verified. Therefore, if this mooring analysis program is used, it will be possible to perform a mooring analysis simulation at the same time as a maritime work simulation.

This paper deals with a soil moisture retrieval model design with airborne measurements for remote monitoring of soil moisture level in large crop fields. A small quadrotor unmanned aerial vehicle (UAV) is considered as a remote sensing platform for high spatial resolutions of airborne images and easy operations. A combination of multispectral and infrared (IR) sensors is applied to overcome the effects of canopies convering the field on the sensor measurements. Convolutional neural network (CNN) is utilized to take the measurement images directly as inputs for the soil moisture retrieval model without loss of information. The procedures to obtain an input image corresponding to a certain soil moisture level measurement point are addressed, and the overall structure of the proposed CNN-based model is suggested with descriptions. Training and testing of the proposed soil moisture retrieval model are conducted to verify and validate its performance and address the effects of input image sizes and errors on input images. The soil moisture level estimation performance decreases when the input image size increases as the ratio of the pixel corresponding to the point to estimate soil moisture level to the total number of pixels in the input image, whereas the input image size should be large enough to include this pixel under the errors in input images. The comparative study shows that the proposed CNN-based algorithm is advantageous on estimation performance by maintaining spatial information of pixels on the input images.