• 한국소음진동공학회논문집
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• 제19권2호
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• pp.138-145
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• 2009

Structural vibration and noise are hot issues in underwater vehicles such as submarines for their survivability. Therefore, active vibration and noise control of submarine, which can be modeled as hull structure, have been conducted by the use of piezoelectric materials. Traditional piezoelectric materials are too brittle and not suitable to curved geometry such as hull structures. Therefore, advanced anisotropic piezocomposite actuator named as Macro-Fiber Composite(MFC), which can provide great flexibility, large induced strain and directional actuating force is adopted for this research. In this study, dynamic model of the smart hull structure is established and active vibration control performance of the smart hull structure is evaluated using optimally placed MFC. Actuating performance of MFC is evaluated by finite element analysis and dynamic modeling of the smart hull structure is derived by finite element method considering underwater condition. In order to suppress the vibration of hull structure, Linear Quadratic Gaussian(LQG) algorithm is adopted. After then active vibration control performance of the proposed smart hull structure is evaluated with computer simulation and experimental investigation in underwater. Structural vibration of the hull structure is decreased effectively by applying proper control voltages to the MFC actuators.

• Ocean Systems Engineering
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• 제10권4호
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• pp.373-397
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• 2020

Heave compensation is a vital part of various marine and offshore operations. It is used in various applications, including the transfer of cargo between two vessels in the open ocean, installation of topsides of an offshore structure, offshore drilling and for surveillance, reconnaissance and monitoring. These applications typically involve a load suspended from a hydraulically powered winch that is connected to a vessel that is undergoing dynamic motion in the ocean environment. The goal in these applications is to design a winch controller to keep the load at a regulated height by rejecting the net heave motion of the winch arising from ship motions at sea. In this study, we analyze and compare the performance of various control algorithms in stabilizing a suspended load while the vessel is subjected to changing sea conditions. The KCS container ship is chosen as the vessel undergoing dynamic motion in the ocean. The negative of the net heave motion at the winch is provided as a reference signal to track. Various control strategies like Proportional-Derivative (PD) Control, Model Predictive Control (MPC), Linear Quadratic Integral Control (LQI), and Sliding Mode Control (SMC) are implemented and tuned for effective heave compensation. The performance of the controllers is compared with respect to heave compensation, disturbance rejection and noise attenuation.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.367-375
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• 2020

This paper presents an integrated analysis about dynamic performance of a Floating Offshore Wind Turbine (FOWT) OC4 DeepCwind with semi-submersible platform under real sea environment. The emphasis of this paper is to investigate how the wave mean drift force and slow-drift wave excitation load (Quadratic transfer function, namely QTF) influence the platform motions, mooring line tension and tower base bending moments. Second order potential theory is being used for computing linear and nonlinear wave effects, including first order wave force, mean drift force and slow-drift excitation loads. Morison model is utilized to account the viscous effect from fluid. This approach considers floating wind turbine as an integrated coupled system. Two time-domain solvers, SIMA (SIMO/RIFLEX/AERODYN) and FAST are being chosen to analyze the global response of the integrated coupled system under small, moderate and severe sea condition. Results show that second order mean drift force and slow-drift force will drift the floater away along wave propagation direction. At the same time, slow-drift force has larger effect than mean drift force. Also tension of the mooring line at fairlead and tower base loads are increased accordingly in all sea conditions under investigation.

• 한국산업융합학회 논문집
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• 제25권2_2호
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• pp.271-278
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• 2022

The solar energy has been widely used to reduce the fossil fuel and prevent the environmental pollution. The renewable energy including solar heat tends to spread due to carbon neutrality for main country of the world. Targets of solar collector are usually acquisitions of hot water or hot air. Especially, air-heating collector using solar heat is known as the technology for obtaining hot air. This study aims to investigate of characteristics of thermal flow when the hot air by air-heating collector using solar heat flows inside of indoor space. The thermal flow of heating indoor space was simulated using ANSYS-CFX program and thus the behaviors of hot air in indoor space were evaluated with standard k-𝜀 turbulence model. As the results, as the inlet velocity was increased, the behaviors of hot air became simple, and temperature range of 25~75℃ had almost no effect on behavior of flow. As the inlet temperature was increased, the temperature curve of indoor space from bottom to top was changed from linear to quadratic. Furthermore, it was confirmed that inlet velocity as well as inlet temperature also should be considered to heat indoor space equally by air-heating collector using solar heat.

• 한국식품과학회지
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• 제38권3호
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• pp.337-341
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• 2006

다시마를 Vibrio sp.로 분해하여 제조한 SCD를 첨가하여 수산 연제품을 만들어 그 특성을 분석하였다. 원료의 최적 배합 비율을 구하기 위하여 mixture program의 modified distance design을 적용하였다. 수리미와 SCD의 첨가량이 증가할수록 hardness와 cohesiveness 값은 감소 후 증가하였다. SCD의 첨가량이 증가할수록 hardness의 값은 증가 후 감소하였으나 cohesiveness 값은 감소 후 증가하였다. 수리미와 물의 첨가량이 증가할수록, SCD의 첨가량이 감소할수록 gumminess와 brittleness의 값은 증가하였다. SCD의 첨가량이 증가할수록, 물의 첨가량이 감소할수록 수분보유력과 백색도의 값은 증가하였다. 수리미의 첨가량이 증가할수록 백색도의 값은 증가한 반면, 수분보유력은 감소하였다. ANOVA 분석에 의한 다시마 SCD 어육 gel의 Hardness 및 cohesiveness는 nonlinear model(Quadratic model)이 결정되었으며, gumminess, brittleness, 수분보유력 및 백색도는 linear model이 결정되었다. Constraint coefficient 값의 분석 결과 수리미는 hardness 및 백색도에 가장 큰 영향을 미쳤고, cohesiveness, gumminess, brittleness에서는 SCD가, 수분보유력에서는 물이 가장 큰 영향을 미쳤다. Hardness는 surimi-SCD의 상호작용이 있었으며 cohesiveness에서는 surimi-water의 상호작용이 나타났다. Modified distance design에 의한 다시마 SCD 어육 gel의 수리미, 물 및 SCD의 최적배합 비율은 각각 36.80, 57.05 및 4.14%이었다.

• 한국항공운항학회지
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• 제9권1호
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• pp.59-69
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• 2001

복합재로 된 회전날개깃을 상자보로 모델링하고 수동/능동 감쇠를 주기 위해 ACL(Active Constrained Damping Layer)을 상하양면에 부착하고 복합변위이론에 기초한 유한요소방법을 이용하여 구조해석을 수행하였다. 이 이론은 ACL내의 복합재와 점탄성층 그리고 압전층의 전단변형효과를 정확하게 모델링하는데 효과적이다. Hankel 의 특이값을 이용해 축차모델을 유도하였으며 축차모델과 측정된 출력에 기초한 LQG 제어기를 설계하였다. 그러나 LQG 제어기는 공칭 운전속도에서는 좋은 성능을 보여주었으나 운전속도가 변하는 상황에 대해서는 강인안정성을 보여주지 못했다. 이 LQG제어기의 강인안정성을 개선하기 위하여 루프전달회복을 통한 강인한 제어기를 설계하였다. 수치 예를 통해 제시된 제어기가 회전날개깃의 공기역학적인 안정성을 개선하는데 효과적이며 동체모드와 연계된 리드-래그 모드감쇠를 증가시켜 회전날개깃의 진동을 효과적으로 억제하는 것을 보였다.

• 한국식품조리과학회지
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• 제30권4호
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• pp.454-462
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• 2014

This study aimed at the optimization and development of rice snack by response surface methodology (RSM). The effect of rice soaking time and additional ratio of soybean milk on physicochemical properties and sensory evaluation of dried rice flour for non-fried snack was studied. After soaking for 0 to 12 days, Baekjinju rice was milled and then air-dried. A quadratic model was selected for weight, volume, hardness, taste and appearance. Two-factor interaction model was selected for expansibility, color and overall preference. A linear model was selected for yellowness and flavor. Weight, hardness and appearance were increased and decreased thereafter as rice soaking time increased, but the volume was reversed. Expansibility, color, taste and flavor were decreased as rice soaking time increased, but yellowness was reversed. Weight and overall preference decreased as additional ratio of soybean milk increased, but volume, expansibility and yellowness were reversed. Hardness, taste and appearance were increased after initial decrease as additional ratio of soybean milk increased, color and flavor were not changed by additional ratio of soybean milk. The optimum conditions of each factor were set to where the rice soaking time and additional ratio of soybean milk were at their minimum. Weight, volume, expansibility, yellowness, hardness, color, taste, flavor, appearance and overall preference were established at maximum level where the objective of the optimum was in level. Our data indicated the statistically predicted values of the highest desirability was 1.24 day of rice soaking time and 15.80% of additional ratio of soybean milk.

• 한국지능시스템학회논문지
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• 제26권1호
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• pp.16-22
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• 2016

세계적으로 수많은 로봇연구실에서 이륜 도립진자 이동로봇에 대한 연구가 진행되고 있다. 본 논문에서는 이런 이륜 도립진자 이동로봇이 평탄한 경사면에서 안정적으로 주행할 수 있도록 하는 강인 제어기를 개발하는 것으로 고려한다. 경사면에서 이륜 도립진자 이동로봇의 균형을 위해 3 자유도의 운동방정식에서 선회운동을 제한한 2 자유도 동력학식을 사용하며, 가변구조시스템 이론을 근간으로 하는 슬라이딩 모드 제어기를 제안하고 LQR 이론을 이용하여 슬라이딩 운동이 일어나는 슬라이딩 평면을 설계한다. 시뮬레이션을 위해 Mathworks사의 Simulink를 활용하여 이륜 도립진자 이동로봇의 2 자유도 모델을 실현하고, 슬라이딩 모드 제어기 또한 Simulink를 이용하여 구현한다. 시뮬레이션 결과를 통해 제안된 제어기가 경사면을 주행하는 이륜 도립진자 이동로봇을 효과적인 제어한다는 것을 보인다.

• Structural Engineering and Mechanics
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• 제54권3호
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• pp.501-520
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• 2015

Presence of torsional loadings can significantly affect the flow of internal forces and deformation capacity of reinforced concrete (RC) columns. It increases the possibility of brittle shear failure leading to catastrophic collapse of structural members. This necessitates accurate prediction of the torsional behaviour of RC members for their safe design. However, a review of previously published studies indicates that the torsional behaviour of RC members has not been studied in as much depth as the behaviour under flexure and shear in spite of its frequent occurrence in bridge columns. Very few analytical models are available to predict the response of RC members under torsional loads. Softened truss model (STM) developed in the University of Houston is one of them, which is widely used for this purpose. The present study shows that STM prediction is not sufficiently accurate particularly in the post cracking region when compared to test results. An improved analytical model for RC square columns subjected to torsion with and without axial compression is developed. Since concrete is weak in tension, its contribution to torsional capacity of RC members was neglected in the original STM. The present investigation revealed that, disregard to tensile strength of concrete is the main reason behind the discrepancies in the STM predictions. The existing STM is extended in this paper to include the effect of tension stiffening for better prediction of behaviour of square RC columns under torsion. Three different tension stiffening models comprising a linear, a quadratic and an exponential relationship have been considered in this study. The predictions of these models are validated through comparison with test data on local and global behaviour. It was observed that tension stiffening has significant influence on torsional behaviour of square RC members. The exponential and parabolic tension stiffening models were found to yield the most accurate predictions.

• Structural Engineering and Mechanics
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• 제56권6호
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• pp.959-982
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• 2015

In this study, a non-stationary random earthquake Clough-Penzien model is used to describe earthquake ground motion. Using stochastic direct integration in combination with an equivalent linear method, a solution is established to describe the non-stationary response of lead-rubber bearing (LRB) system to a stochastic earthquake. Two parameters are used to develop an optimization method for bearing design: the post-yielding stiffness and the normalized yield strength of the isolation bearing. Using the minimization of the maximum energy response level of the upper structure subjected to an earthquake as an objective function, and with the constraints that the bearing failure probability is no more than 5% and the second shape factor of the bearing is less than 5, a calculation method for the two optimal design parameters is presented. In this optimization process, the radial basis function (RBF) response surface was applied, instead of the implicit objective function and constraints, and a sequential quadratic programming (SQP) algorithm was used to solve the optimization problems. By considering the uncertainties of the structural parameters and seismic ground motion input parameters for the optimization of the bearing design, convex set models (such as the interval model and ellipsoidal model) are used to describe the uncertainty parameters. Subsequently, the optimal bearing design parameters were expanded at their median values into first-order Taylor series expansions, and then, the Lagrange multipliers method was used to determine the upper and lower boundaries of the parameters. Moreover, using a calculation example, the impacts of site soil parameters, such as input peak ground acceleration, bearing diameter and rubber shore hardness on the optimization parameters, are investigated.