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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.

The temperature dependence of the Flory-Huggins interaction parameter χ for poly(

A new design method for trajectory shaping guidance laws with the impact angle constraint is proposed in this study. The basic idea is that the multiplier introduced to combine the equations for the terminal constraints is used to shape a flight trajectory as desired. To this end, the general form of impact angle control guidance (IACG) is first derived as a function of an arbitrary constraint-combining multiplier using the optimal control. We reveal that the constraint-combining multiplier satisfying the kinematics can be expressed as a function of state variables. From this result, the constraint-combining multiplier to achieve a desired trajectory can be obtained. Accordingly, when the desired trajectory is designed to satisfy the terminal constraints, the proposed method directly can provide a closed form of IACG laws that can achieve the desired trajectory. The potential significance of the proposed result is that various trajectory shaping IACG laws that can cope with various guidance goals can be readily determined compared to existing approaches. In this study, several examples are shown to validate the proposed method. The results also indicate that previous IACG laws belong to the subset of the proposed result. Finally, the characteristics of the proposed guidance laws are analyzed through numerical simulations.

본 연구에서는 해양사고로 인해서 손상된 선박의 예인 특성에 대해서 살펴보고자 하며, 이를 위해서 선박의 동적 해석을 수행할 수 있는 KIMAPS (KRISO Integrated Multi-body And Positioning Simulation system)프로그램을 사용하여 예인 시뮬레이션을 수행하였다. 선박의 예인 특성을 살펴보기 위해서 예선, 부선 및 예인삭을 수치 모델링하였다. 부선의 운동은 MMG 모델 및 횡유동 모델(cross-flow model)을 적용하여 모사하였으며, 두 모델의 결과를 비교하였다. 두 모델은 예인 불안정상태에서 운동 진폭 및 진동주기에서 다소 차이는 있었지만 전반적인 경향은 동일하였으며, 예인 안정상태에서의 예인 특성 값 및 예인가능성에 대한 판단은 거의 동일하였다. 따라서 빠른 판단이 필요한 긴급구난 상황에서는 비교적 단순한 횡유동 모델을 실용적인 관점에서 사용할 수 있을 것으로 생각된다. 또한 손상선박의 상태를 모사하기 위해서 상용 CFD 해석 프로그램인 StarCCM+를 사용하여 횡경사가 있는 상태에서의 조류하중계수를 추정하였으며, 이를 횡유동 모델에 적용하여 손상선박의 자세(횡경사 유무)에 따른 예인 특성을 확인하였다. 횡경사가 존재함으로 인해서 비대칭 유체력이 발생하였으며, 부선의 불안정한 운동 진폭 및 최대 장력이 증가함을 확인하였다.

This article suggests closed-loop analysis results for both classical and incremental backstepping controllers considering model uncertainties. First, transfer functions with each control algorithm under the model uncertainties, are compared with the ones for the nominal case. The effects of the model uncertainties on the closed-loop systems are critically assessed via investigations on stability conditions and performance metrics. Second, closed-loop characteristics with classical and incremental backstepping controllers under the model uncertainties are directly compared using derived common metrics from their transfer functions. This comparative study clarifies how the effects of the model uncertainties on the closed-loop system become different depending on the applied control algorithm. It also enables an understanding of the effects of additional measurements in the incremental algorithm. Third, case studies are conducted assuming that the uncertainty exists only in one aerodynamic derivative estimate while the other estimates have true values. This facilitates systematic interpretations on the impacts of the uncertainty on the specific aerodynamic derivative estimate to the closed-loop system.

Operations involving small Unmanned Aerial Systems (sUAS) in urban environments are occurring ever more frequently as recognized applications gain acceptance, and new use cases emerge, such as urban air mobility, medical deliveries, and support of emergency services. Higher demands in these operations and the requirement to access urban airspace present new challenges in sUAS operational safety. The presence of Detect and Avoid (DAA) capability of sUAS is one of the major requirements to its safe operation in urban environments according to the current legislation, such as the CAP 722 in the United Kingdom (UK). The platform or its operator proves a full awareness of all potential obstacles within the mission, maintains a safe distance from other airspace users, and, ultimately, performs Collision Avoidance (CA) maneuvers to avoid imminent impacts. Different missions for the defined scenarios are designed and performed within the simulation model in Software Tool Kit (STK) software environment, covering a wide range of practical cases. The acquired data supports assessment of feasibility and requirements to real-time processing. Analysis of the findings and simulation results leads to a holistic approach to implementation of sUAS operations in urban environments, focusing on extracting critical DAA capability for safe mission completion. The proposed approach forms a valuable asset for safe operations validation, enabling better evaluation of risk mitigation for sUAS urban operations and safety-focused design of the sensor payload and algorithms.

We report a method to directly introduce a hydroxyl group at the omega chain end of polystyrene prepared by atom-transfer radical polymerization. To achieve the quantitative conversion of the bromine group to a hydroxyl group, the transfer reaction of a carbocation with water was exploited. This transfer reaction is a well-known reaction in cationic polymerization. The quantitative conversion and chemical structures of the hydroxyl-terminated PS were characterized using 1H nuclear magnetic resonance spectroscopy, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and high-performance liquid chromatography. In addition, alcohol-based compounds were used to introduce acetonide and propane groups into PS-Br. We introduce a facile method to convert the bromine end of the polymer into a hydroxyl group. For this, bromine-terminated polystyrene (PS-Br) was prepared by atom transfer radical polymerization. The bromine groups of the PS-Br could be directly converted to hydroxyl groups by using Ag+ as the Lewis acid in water/acetone. The conversion yield was investigated by 1H nuclear magnetic resonance spectroscopy, high-performance liquid chromatography, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

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.

In this study, experimental and numerical methods were applied to estimate surge and sway wave drift forces and yaw drift moment acting on KVLCC2, advancing in oblique wave. An experiment was carried out in the ocean engineering basin of the Korea Research Institute of Ships and Ocean Engineering (KRISO). A series of regular wave tests under various heading conditions were conducted to investigate ship motion responses and wave drift forces. A Rankine panel method based on potential flow was adopted in the numerical analysis, and the direct pressure integration method that integrates second-order pressure on the hull surface was applied to compute wave drift force. Through this study, validation data of wave drift force acting on KVLCC2 was established, and the computation capability of the potential-based numerical method was systematically analyzed.

This paper deals with the modeling of soil moisture retrieval from multispectral and infrared (IR) images using convolutional neural network (CNN). Since it is difficult to measure the soil moisture level of large fields, it is essential to retrieve soil moisture level from remotely sensed data. Quadrotor unmanned aerial vehicle (UAV) is considered as sensing platform in order to acquire data with high spatial resolution at anytime by non-experts. With considerations both on the availability of sensors for the platform and the information needed to overcome the effects of the canopies covering soil, IR and multispectral images are selected to be used for soil moisture retrieval. In order to prevent information loss by the calculation of parameters from measurements and enhance the applicabiliy for online operations, CNN is applied for the construction of soil moisture retrieval model to use the sensor measurement images directly as input data. Training and testing are conducted for the proposed CNN-based soil moisture retrieval model using the data from actual quadrotor flight over an agricultural field.

This paper deals with a strategic deconfliction of heterogeneous multiple unmanned aerial vehicles (UAVs) via trajectory optimization. A trajectory optimization problem for multiple UAVs with different specifications is defined with constraints to accomplish deconfliction between UAVs and avoidance against obstacles in the environment and the objective function to minimize the total control effort of the UAVs. The takeoff and landing times of UAVs are considered as optimization parameters and the optimization problem is constructed with multiple phases defined with take-off and landing times of UAVs. Gauss pseudospectral optimization method considered in this paper decides not only the guidance commands for UAVs but also the take-off and landing times of UAVs by determining the durations of phases to minimize the objective function. A case study is performed to illustrate how a given strategic deconfliction problem is defined as a trajectory optimization problem for Gauss pseudospectral optimization method and to show the example result of the strategeic deconfliction with trajectory optimization.

This work builds on a robust decentralized task allocation algorithm to address the multiple unmanned aerial vehicle (UAV) surveillance problem under task duration uncertainties. Considering the existing robust task allocation algorithm is computationally intensive and also has no optimality guarantees, this paper proposes a new robust task assignment formulation that reduces the calculation of robust scores and provides a certain theoretical guarantee of optimality. In the proposed method, the Markov model is introduced to describe the impact of uncertain parameters on task rewards and the expected score function is reformulated as the utility function of the states in the Markov model. Through providing the high-precision expected marginal gain of tasks, the task assignment gains a better accumulative score than the state of arts robust algorithms do. Besides, this algorithm is proven to be convergent and could reach a prior optimality guarantee of at least 50%. Numerical Simulations demonstrate the performance improvement of the proposed method compared with basic CBBA, robust extension to CBBA and cost-benefit greedy algorithm.

This brief introduces a new design methodology for impact angle control guidance (IACG) laws. The proposed methodology can extend any proven homing guidance laws to their impact angle control versions if the expressions of the estimated terminal flight path angles under those guidance laws are given. The time derivatives of the estimated terminal flight path angles are obtained as functions of the guidance commands. The IACG versions of the homing guidance laws are derived from those functions and the desired error dynamics of the estimated terminal flight path angle. The guidance law of each IACG version has two terms: the first term maintains the characteristics and capturability of the original guidance law and the second term drives the estimated terminal flight path angle to converge to the specified flight path angle. When a well-understood homing guidance law for a certain combination of target and missile models is given, an IACG law for that combination is easily derived without reformulating the guidance problem again. The usefulness of the proposed method is demonstrated by several examples, deriving new IACG laws for various target and missile models.

This paper performs a numerical computation of ship maneuvering performance in waves. For this purpose, modular-type model (MMG (Mathematical Modeling Group) model) is adopted for maneuvering simulation and wave drift force is included in the equation of maneuvering motion. In order to compute wave drift force, two different seakeeping programs are used: AdFLOW based on Wave Green function method and SWAN based on Rankine panel method. When wave drift force is calculated using SWAN program, not only ship forward speed but also ship lateral speed are considered. By doing this, effects of lateral speed on wave drift force and maneuvering performance in waves are confirmed. The developed method is validated by comparing turning test results in regular waves with existing experimental data. Sensitivities of wave drift force on maneuvering performance are, also, checked.

It is important to predict the actual RPM and engine power of a ship because it helps the ship builder and seafarer understand the actual performance of the ship. However, a precise prediction is difficult because it is closely connected to the ship design, resistance, seakeeping, maneuvering performance, etc., synthetically. In this paper, we propose a new approach to predict the actual RPM and engine power of an LNGC from full-scale measurement data considering the described performance. The sea route, speed over ground and environmental conditions obtained from the measured data are additionally used to simulate sailing of the ship from the coast of southern Taiwan to the coast of Madagascar for 14 days. The results of the simulation are qualitatively reviewed by comparing the calculated time histories of the RPM and the power with the measured RPM and power. The results are quantitatively analyzed by comparing the time histories of errors between the measured values and calculated values. Finally, the power increment due to the environmental load is estimated by comparing the predicted power considering the environmental load with the predicted power, not considering the environmental load.

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.

The motion responses of ships carrying liquid cargo are affected not only by external wave excitation, but also by internal sloshing-induced forces and moments. Sloshing flow is coupled with the ship motion. This means the added resistance in waves may change when sloshing occurs inside the tank of the ship. In this study, the motion responses and added resistance of a ship, coupled with the sloshing-induced internal forces and moments are considered by using the linear potential theory. The three-dimensional Rankine panel method, in which the physical quantities are represented by using B-spline basis function, is applied. The sloshing flow of inner tanks is also simulated by using the Rankine panel method and linearized boundary value problem. To study the added resistance, a near-field method, which integrates the second-order pressure on a body surface, is applied. The model ship is a blunt modified Wigley model with two inner tanks. Numerical results obtained without inner tanks are compared with the experimental data, and then the effect of filling ratio of inner tanks on ship motion and added resistance are observed. The components that induce added resistance are examined, and the effects of surge motion on sloshing flow and added resistance are briefly considered. This study shows that the sloshing flow inside the inner tanks may significantly influence not only the motion responses, but also added resistance, especially, when the incident wave frequency approaches the resonance frequency of the sloshing flow.

In this study, ship's maneuvering performance in waves is evaluated using numerical computation. To this end, three degrees-of-freedom (3DOF) planar motions are considered, and modular-type maneuvering model (maneuvering modeling group model (MMG model)) is applied. As external force of the equation of motion, hull force, propulsion force, rudder force, and wave drift force are adopted. In order to calculate wave drift force, seakeeping program which is based on a higher-order Rankine panel method is used by considering wave frequency, wave heading, ship's forward speed, and ship's lateral speed. This wave drift force is pre-calculated, made into database, and used in time domain simulation. The developed simulation program is validated by comparing the computation results of a turning test in regular waves with experimental data. Using this program, turning performance in irregular waves is evaluated and sensitivities for time signal of wave elevation are investigated. Through this study, it is confirmed that the simplified method based on the MMG model including wave drift force can provide good agreement with experimental data in a practical point of view. It can be observed that the simulation results considering the lateral speed show better agreement with the experimental data than those without consideration. In the case of irregular wave condition, the turning performance can be affected by wave random phases. When the ship encounters the beam sea during the turning operation, the wave elevations at that time play an essential role in the change of ship speed and turning trajectory.

This study considers the wave impact loads on the semi-submersible structure. To evaluate wave impact loads on the semi-submersible structure, a series of experiments are conducted in a 2D wave flume. In the experimental test, the semi-submersible half model is used, and 11 uniaxial force sensors are installed in deck side, column side, and deck bottom. Wave probes are, also, attached in the test model to measure the relative wave elevation. To generate horizontal and bottom wave impact on the test model, focusing wave is applied. The test model is fixed without any motion during each test, while the trim angle of the test model is changed to examine the effect of trim angle on wave impact load. Through this, the characteristics of the wave impact force at each position were investigated.

In this paper, closed loop system characteristics with an incremental backstepping controller are investigated through theoretical analysis when both measurement biases and model uncertainties exist. Incremental backstepping algorithm is proposed in previous studies to reduce model dependency of classical backstepping algorithm with additional measurements about state derivatives and control surface deflection angles. This research enables to have following critical understandings especially about the effects of biases on these additional measurements to system characteristics with incremental backstepping method. First, these biases do not affect a characteristic equation, so they do not have any influence about a condition for absolute stability. Second, these biases cause a steady state error, and model uncertainty in control effectiveness information starts to have an impact to it when these biases are additionally considered.

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.

Addressed here deals with the problem of weight and trajectory optimization for multi staged anti-air missile. By using the subsystem requirements, such as aerodynamic coefficients, thrust and structure, amount of propellant and weight of each stage can be optimized via appropriate optimization methods. In this paper, the weight and trajectory optimization results are obtained by using the commercial optimization tool, GPOPS-II. To investigate the effect of subsystem parameter and constraints on the optimization result, the sensitivity analysis is conducted.

In this paper, theoretical analysis on the incremental backstepping control is suggested especially under the existence of model uncertainties. This algorithm is proposed in the previous studies by modifying the backstepping method to reduce model dependency. Because this method is a type of nonlinear control and the model uncertainties are assumed to be considered, it is difficult to have theoretical analysis, which causes lack of understandings about this algorithm. Therefore, this paper suggests closed-loop analysis with simplified dynamics under the model uncertainty. Transfer function is derived and poles, stability condition, steady state error, and settling time are presented. In addition, the effects of model uncertainties and gains are identified through analysis. Proposed analysis is meaningful in terms of establishing critical understandings about the algorithm, even though the simplified dynamics is applied for analysis purpose.

This paper develops an approximation algorithm for maximization of monotone submodular reward function with a cardinality constraint. The main focus of our development is to enhances the level of guaranteed optimality, computational complexity or both compared with the well-known existing greedy based approaches. The proposed algorithm is called the greedily excluding algorithm. In this algorithm, an element is removed from the ground set to find the solution set and this allows the algorithm to improve both the optimality level and computational complexity for a problem with a high cardinality constraint. The characteristics of the proposed algorithm are mathematically analysed and compared with those of well-known greedy-based algorithms. A case study is also carried out to demonstrate the performance of the approximation algorithms developed.

This paper addresses the application of task allocation algorithm for agricultural remote sensing using a group of UAVs. A task allocation problem is formulated as a form of reward function maximization problem. The reward function is defined by considering the following three aspects. The first aspect is to assign tasks to UAVs with proper sensors to detect the most severe hazards for the crop raised in each field at the observation season. The minimization of the total operation time of UAVs is another aspect for short observation time and small fuel consumption. The last aspect is to assign tasks uniformly to the UAVs to prevent overloads on certain UAVs. In order to apply submodular maximization-based algorithm, the subexponential submodularity tester is applied to verify the submodularity of the defined reward function. A greedy algorithm-based task allocation method is applied to the designed task allocation problem as an example of submodular maximization-based algorithm. Simulations are conducted to show the characteristics of the designed reward function and to compare the results of the task allocation method with the optimal solutions.

This paper considers a numerical computation of ship maneuvering performance in waves. For this purpose, modular-type maneuvering model (MMG model) is adopted and wave drift forces and moments are included in maneuvering equation of motion. Wave drift forces ware calculated using a seakeeping program based on higher-order Rankine panel method. When calculating the wave drift force acting on a ship, the forward speed, wave heading, wave period and drift angle of the ship are considered as key parameters. It means that ship’s lateral speed is also included to calculate wave drift force. Numerical simulations are carried out in regular waves using S175 containership and computation results are validated by comparing them with results of free-running model test. Using the developed program, numerical simulation in irregular waves are, also, conducted and discussion is made on the sensitivities of time signal of wave elevation on turning performance.

Introduction : In the field of guidance technology, advanced guidance laws are being developed using various control theories such as optimal control [1,2], sliding mode control [3–6], H-infinity control [7], the state-dependent Riccati equation [8], the Lyapunov theory [9], the geometric control theory [10], predictive control [11,12], and feedback linearization control [13]. The general procedure of this approach is to first establish the guidance problem to be solved and to define the guidance geometry and kinematics equation corresponding to the guidance problem. A guidance law is then systematically designed in such a way that an appropriate control theory is applied to a predetermined guidance problem. The potential importance of this approach is that a number of advanced guidance laws can be newly developed, depending on the combinations of guidance problems and control theories. Therefore, recent trends in the design of guidance laws focus on finding a new combination of guidance problems and control theory to obtain a new guidance law that is superior to the conventional guidance law. Although previous research has focused more on the methodology and the design process itself, little effort has been made toward understanding the characteristics of the newly developed guidance laws.

This paper deals with the observability analysis and enhancement of target state variables and radome aberration estimation only with line-of-sight (LOS) angle measurement. The local observability conditions at an arbitrary time are derived, and a new maneuver algorithm, revised adaptive intermittent maneuver (RAIM), is introduced to enhance the estimation performance of the system. Simulations are conducted to verify the observability conditions and analyze the performance and characteristics of RAIM.

In this study, the added resistance of ships in short waves is systematically studied by using two different numerical methods - Rankine panel method and Cartesian grid method - and existing asymptotic and empirical formulae. Analysis of added resistance in short waves has been preconceived as a shortcoming of numerical computation. This study aims to observe such preconception by comparing the computational results, particularly based on two representative three-dimensional methods, and with the existing formulae and experimental data. In the Rankine panel method, a near-field method based on direct pressure integration 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 identify each phase in a Cartesian grid. The computational results of added resistance in short waves using the two methods ar e systematically compared with experimental data for several ship models, including S175 containership, KVLCC2 and Series 60 hulls (CB = 0.7, 0.8). The present study includes the comparison with the established asymptotic and empirical formulae in short waves.

Kinetic energy(KE) rod warhead system is a new interceptor which combines advantages of existing ones. This system is less dependant on a precision guidance than direct hit type warhead and gives high penetration rates than blast fragmentation type warhead. In this paper, isotropic KE rod warhead system is introduced with detonation/deployment model. A penetration effects of the deployed rods are calculated using TATE penetration equation. Also, an engagement performance analysis method is suggested. Finally, an optimal detonation time and engagement geometry is derived by Monte-Carlo simulation in various engagement situation using the performance analysis factor.

국제적으로 친환경에 대한 관심이 증가하고, 국제해사기구 (International Maritime Organization, IMO)가 선박의 온실가스 방출을 규제하기 위해서 2013년부터 선박연비제조지수 (Energy Efficiency Design Index, EEDI)를 도입하면서 조선 및 해운업계 에서는 선박의 운항 효율이 주요 관심사가 되었다. 선박의 운항 효율을 향상시키기 위한 많은 방법 중에 하나로 파랑 중 저항을 감소시키는 방법이 고려되고 있다. 부가저항이란 선박이 실제 해 상에서 운항하는 경우 바람이나 파랑에 의해 정수 중 저항보다 증가하는 저항을 말하며, 이러한 부가저항은 선박에 따라서 정수 중에서 운항하는 경우의 저항보다 15~30%까지 커지는 경우도 있다. 따라서 부가저항을 정확히 예측하고 이를 효과적으로 감소 시키고자 하는 연구들이 수행되고 있다. 본 논문에서는 최근 수행되었던 부가저항의 예측을 위한 수조 실험 및 수치계산 기법에 대한 연구들에 대하여 체계적으로 살펴 보고, 그 결과들을 비교하여 여러 기법들에 대한 검증과 장단점, 그리고 실선 적용에 대한 활용성 등을 다루고자 한다. 파랑 중 부가저항의 추정을 위해 실험 및 수치적 연구는 1970~1980년대에 많이 수행이 되었으나 한동안 주목을 받지 못 하다가 최근 그린쉽에 대한 관심이 고조되며 근래들어 여러 연구 들이 수행되고 있다. 부가저항의 초기 연구는 실험에 기반하여 진행되었다. 부가저항 실험은 1970년대부터 Series 60 선형 (Gerritsma & Beukelman, 1972; Storm-Tejsen, et al., 1973), S175 컨테이너선 모델 (Fujii & Takahashi, 1975; Nakamura & Naito, 1977), Wigley 모델 (Journee, 1992) 등에 대한 연구가 진행되었다. 최근 Kuroda, et al. (2011)은 컨테이너선 기본선형 을 기준으로 선수부의 형상을 다양하게 변화시켜가면서 이에 따 른 부가저항 변화를 살펴보았다. 또한, Lee, et al. (2013)도 최 pISSN:1225-1143, Vol. 51, No. 6, pp. 459-479, December 2014

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.

The observability of radome aberration estimation with line-of-sight (LOS) angle-only measurement is studied in this paper. When missile seeker can only measure LOS angle of target, target state variables are required to be estimated with this measurement for accurate missile guidance. Since LOS angle measurement contains error, caused by radome attached at missile nose and called radome aberration angle, the state estimation performance is degenerated. Thus, the radome aberration effects should be estimated and compensated for accurate target state variable estimation. The radome aberration angle is modeled as the product of radome slope and gimbal angle. The observability of state variables and radome slope estimation is analyzed for the relative dynamics with stationary target model in polar coordinate system. Simulations are conducted to verify the observability conditions obtained in this paper.

Recently, the design of commercial ships that produce less greenhouse gas has been of great interest in naval architecture fields. Ship designers are asked to find optimum hull forms with minimum resistance in ocean waves. An accurate computation of added resistance, therefore, is getting more important for the prediction of power increase in random ocean waves. This study focuses on a comparison of the computational results of added resistance on ships in waves. To calculate added resistance, three different numerical approaches are applied: the strip method, the Rankine panel method, and the Cartesian grid method, which solves the Euler equation. In order to predict added resistance, near- and far-field approaches are adopted in the strip and Rankine panel methods, while added resistance is calculated directly in the Cartesian grid method. The computational results are validated by comparing them with experimental data on Wigley hulls, Series 60 hulls, and the S175 containership, and show reasonable agreements for all models. The study is extended to the analysis of added resistance in short wavelengths; therefore, the established asymptotic methods for short waves are examined.

This paper presents a panel generation framework for seakeeping analysis of multiple bodies and offshore structures. The configurations of multiple bodies and offshore structures are different from those of a single ship. In particular, the topological structure of the free surfaces becomes complicated due to the multiple floating bodies, resulting in multiple classifications for the free surfaces based on their genus. The multi-body configuration consists of two floating bodies placed in two configurations, i.e., side by side and tandem, which would generate two holes in the free surface. For the offshore structure case, multiple holes are generated in the free-surface domain due to the legs of the offshore structure. In this work, strategies for generating body and free-surface panels are provided, and the results are analyzed. A software prototype that implements the proposed methods is developed to provide efficient panel generation for multiple bodies and offshore structures. Examples demonstrate that the proposed framework can be successfully used for seakeeping analysis of multiple bodies and offshore structures.

Recently, the design of commercial ships with less green-house gas is one of great interests in naval architecture fields. Ship designers are asked to find optimum hull forms with minimum resistance in ocean waves. The accurate computation of added resistance, therefore, is getting more important for the prediction of power increase in random ocean waves. This study focuses on the numerical computation of added resistance on ships with Ax-bow shapes which are designed to reduce added resistance. To this end, the time-domain Rankine panel methods based on weakly-nonlinear and weak-scatterer approaches are applied, which can reflect the influence of above-still-water bow shape. As computational models, KCS and KVLCC2 hull forms are considered. Each ship is combined with the three types of Ax-bow shape, and computational results are compared each other.

In the present study, the added resistance of a containership in parametric roll motion is investigated. The numerical simulation is carried out using a three dimensional Rankine panel method along with the weakly nonlinear formulation. The added resistance is evaluated by a near-field method, namely, the direct integration of the 2nd-order pressure on a body surface. To calculate the component resulting from the large-amplitude roll motion, the higher-order restoring and Froude-Krylov forces on wetted hull surfaces are taken into account. With or without parametric roll in regular waves, the components of added resistance classified with respect to integral terms are compared to figure out the important of each term. Through the investigation, the correlation between the added resistance and parametric roll is derived from coupling and decoupling the components of roll motion and vertical motions.