• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.109-112
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• 2006

In this study, an approach that installs seismic isolation bearings was proposed for the seismic retrofit of the existing bridges. The method that replaces all existing bearings with seismic isolators was proposed already. However, in this study, we recommend to utilize the existing bearings for the benefit of safety and cost. According to our proposal, the seismic isolators do not support vertical loads but they just function as the period shifter and the horizontal damper. To verify this approach experimentally, the real scale bearings and isolators for the real highway bridges were designed and fabricated. And the responses of this isolated bridges to the assumed earthquakes were determined by the pseudo dynamic test scheme. The test results were also compared to the responses computed by the well known structural analysis software to check the reliability of the test. From the test results, we found that the retrofitted bridges using the proposed method showed stable performances under earthquakes.

• Journal of Power System Engineering
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• v.16 no.2
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• pp.66-74
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• 2012

In this paper, the authors propose a new approach to control a barge type surface vessel. It is based on the Dynamic Positioning System(DPS) design. The main role of barge ship is to carry and supply the materials to the floating units and other places. To carry out this job, it should be positioned in the specified area. However sometimes the thrust systems are installed on it, and in general the rope control by mooring winch system is used. It may be difficult to compare the control performances of two types. If we consider this problem in point of usefulness, we can easily find out that the winch control system is more useful and applicable to the real field than the thrust control system except a special use. Therefore, in this paper we consider a DPS design problem which can be extended to the many application fields. The goal of this paper is twofold. First, the sliding mode controller (SMC) for positioning the our vessel is proposed. Especially, in this paper, a robust stability condition is given based on descriptor system representation. In the result, the sliding mode control law guarantees to keep the vessel in the defined area in the presence of environmental disturbances. And second, the thrust allocation problem is solved by using redistributed pseudo-inverse (RPI) algorithm to determine the thrust force and direction of each individual actuator. The proposed approach has been simulated with a supply vessel model and found work well.

• Journal of the Korea Concrete Institute
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• v.27 no.2
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• pp.147-155
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• 2015

A new SRCF (Steel Reinforced Concrete Frame) external connection method for seismic strengthening of medium-and low-rise reinforced concrete buildings is reported in this paper. The SRCF method, proposed in this study, is capable of carrying out the seismic retrofitting construction while residents can live inside building. The method is one of the strength design approach by retrofit which can easily increase the ultimate lateral load capacity of concrete buildings controlled by shear. The pseudo-dynamic test, designed using a existing school building in Korea, was carried out in order to verify the seismic strengthening effects of the proposed method in terms of the maximum load carrying capacity and deformation. Test results revealed that the proposed SRCF strengthening method installed in RC frame enhanced conspicuously the strength and deformation capacities, and the method can resist markedly under the large scaled earthquake intensity level.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.7
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• pp.774-781
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• 2014

The radar measurements are composed of range, Doppler and angles which are expressed as polar-coordinate components. An approach to match the measurements with the states of target dynamics which are modeled in cartesian coordinates is to use the pseudo-measurements or the extended Kalman filter in order to solve the mismatching problem. Another approach is that the states of dynamics are modeled in polar coordinates and measurement equation is linear. However, this approach bears that we have to deal with a time-varying dynamics. In this study, it is proposed that the states of dynamics are expressed as polar-coordinate component and the system matrix of the dynamic equation is modeled as a time-invariant. Nonlinear terms that appear due to the proposed modeling are regarded as a system input. The results of a series of simulation runs indicate that the tracking filter that uses the proposed modeling is viable from the fact that the Doppler measurement is easy to be augmented in the measurement equation.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.2
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• pp.264-277
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• 2015

This article investigates various transcription techniques for the Legendre pseudospectral (PS) method to compare the pros and cons of each approach. Eight combinations from four different types of collocation points and two discretization methods for dynamic constraints, which differentiate Legendre PS transcription techniques, are implemented to solve a carefully selected test set of nonlinear optimal control problems (NOCPs). The convergence property and prediction accuracy are compared to provide a useful guideline for selecting the best combination. The tested NOCPs consist of the minimum time, minimum energy, and problems with state and control constraints. Therefore, the results drawn from this comparative study apply to the solution of similar types of NOCPs and can mitigate much debate about the best combinations. Additionally, important findings from this study can be used to improve the numerical efficiency of the Legendre PS methods. Three PS applications to the aerospace engineering problems are demonstrated to prove this point.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.2
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• pp.204-213
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• 2016

A differential game theory based approach is used to develop an automated maneuver generation algorithm for Within Visual Range (WVR) air-to-air combat of unmanned combat aerial vehicles (UCAVs). The algorithm follows hierarchical decisionmaking structure and performs scoring function matrix calculation based on differential game theory to find the optimal maneuvers against dynamic and challenging combat situation. The score, implying how much air superiority the UCAV has, is computed from the predicted relative geometry, relative distance and velocity of two aircrafts. Security strategy is applied at the decision-making step. Additionally, a barrier function is implemented to keep the airplanes above the altitude lower bound. To shorten the simulation time to make the algorithm more real-time, a moving horizon method is implemented. An F-16 pseudo 6-DOF model is used for realistic simulation. The combat maneuver generation algorithm is verified through three dimensional simulations.

• International Journal of Aeronautical and Space Sciences
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• v.8 no.1
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• pp.10-20
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• 2007

For spacecraft attitude control, reaction wheel (RW) steering laws with more than three wheels for three-axis attitude control can be derived by using a control allocation (CA) approach.1-2 The CA technique deals with a problem of distributing a given control demand to available sets of actuators.3-4 There are many references for CA with applications to aerospace systems. For spacecraft, the control torque command for three body-fixed reference frames can be constructed by a combination of multiple wheels, usually four-wheel pyramid sets. Multi-wheel configurations can be exploited to satisfy a body-axis control torque requirement while satisfying objectives such as minimum control energy.1-2 In general, the reaction wheel steering laws determine required torque command for each wheel in the form of matrix pseudo-inverse. In general, the attitude control command is generated in the form of a feedback control. The spacecraft body angular rate measured by gyros is used to estimate angular displacement also.⁵ Combination of the body angular rate and attitude parameters such as quaternion and MRPs(Modified Rodrigues Parameters) is typically used in synthesizing the control command which should be produced by RWs.¹ The attitude sensor signals are usually corrupted by noise; gyros tend to contain errors such as drift and random noise. The attitude determination system can estimate such errors, and provide best true signals for feedback control.⁶ Even if the attitude determination system, for instance, sophisticated algorithm such as the EKF(Extended Kalman Filter) algorithm⁶, can eliminate the errors efficiently, it is quite probable that the control command still contains noise sources. The noise and/or other high frequency components in the control command would cause the wheel speed to change in an undesirable manner. The closed-loop system, governed by the feedback control law, is also directly affected by the noise due to imperfect sensor characteristics. The noise components in the sensor signal should be mitigated so that the control command is isolated from the noise effect. This can be done by adding a filter to the sensor output or preventing rapid change in the control command. Dynamic control allocation(DCA), recently studied by Härkegård, is to distribute the control command in the sense of dynamics⁴: the allocation is made over a certain time interval, not a fixed time instant. The dynamic behavior of the control command is taken into account in the course of distributing the control command. Not only the control command requirement, but also variation of the control command over a sampling interval is included in the performance criterion to be optimized. The result is a control command in the form of a finite difference equation over the given time interval.⁴ It results in a filter dynamics by taking the previous control command into account for the synthesis of current control command. Stability of the proposed dynamic control allocation (CA) approach was proved to ensure the control command is bounded at the steady-state. In this study, we extended the results presented in Ref. 4 by adding a two-step dynamic CA term in deriving the control allocation law. Also, the strict equality constraint, between the virtual and actual control inputs, is relaxed in order to construct control command with a smooth profile. The proposed DCA technique is applied to a spacecraft attitude control problem. The sensor noise and/or irregular signals, which are existent in most of spacecraft attitude sensors, can be handled effectively by the proposed approach.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.12
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• pp.647-655
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• 2020

This study introduced income mobility analysis using pseudo-longitudinal panel data from Family Income and Expenditure Survey (FIES) to consider the dynamic process of individual's well-being through time. Since there is no comprehensive measurement of income mobility because of its dynamic process, various income mobility indices such as Chi-square, Average Jump Index, Atkinson et al. Mobility Ratio, and Shorrocks' Mobility Index were used. These indices revealed that Filipino households' income movements are more mobile than expected, and their income status improved from 2000 to 2015. As income mobility takes place, income inequality is reduced by 91.80 percent (91.80%). Furthermore, the growth effect is the main factor of income mobility. This indicates that households took the economic opportunities from economic growth to earn more. However, income mobility due to transfer effect (transfer of income from one household to another through lottery winning and borrowing) increased when the economy is not good. The higher income mobility due to growth effect compared to transfer effect, whether the economy is good or bad, means that households learned how to use their income in savings, investments, and entrepreneurship. This is the result of a successful financial literacy program of the government wherein households realized financial stability and security.

• Membrane and Water Treatment
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• v.6 no.6
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• pp.451-476
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• 2015

Membrane distillation (MD), which can utilize low-grade thermal energy, has been extensively studied for desalination. By incorporating solar thermal energy, the solar membrane distillation desalination system (SMDDS) is a potential technology for resolving the energy and water resource problems. Small-scale SMDDS (s-SMDDS) is an attractive and viable option for the production of fresh water for small communities in remote arid areas. The minimum-cost design and operation of s-SMDDS are determined by a systematic method, which involves a pseudo steady state approach for equipment sizing and the dynamic optimization using overall system mathematical models. The s-SMDDS employing three MD configurations, including the air gap (AGMD), direct contact (DCMD) and vacuum (VMD) types, are optimized. The membrane area of each system is $11.5m^2$. The AGMD system operated for 500 kg/day water production rate gives the lowest unit cost of $5.92/m^3$. The performance ratio and recovery ratio are 0.85 and 4.07%, respectively. For the commercial membrane employed in this study, the increase of membrane mass transfer coefficient up to two times is beneficial for cost reduction and the reduction of membrane heat transfer coefficient only affects the cost of the DCMD system.

• Journal of the Earthquake Engineering Society of Korea
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• v.26 no.6
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• pp.237-246
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• 2022

Based on the random-vibration-theory methodology, dynamic responses of nuclear facilities subjected to obliquely incidental and incoherent earthquake ground motions are calculated. The spectral power density functions of the 6-degree-of-freedom motions of a rigid foundation due to the incoherent ground motions are obtained with the local wave scattering and wave passage effects taken into consideration. The spectral power density function for the pseudo-acceleration of equipment installed on a structural floor is derived. The spectral acceleration of the equipment or the in-structure response spectrum is then estimated using the peak factors of random vibration. The approach is applied to nuclear power plant structures installed on half-spaces, and the reduction of high-frequency earthquake responses due to obliquely incident incoherent earthquake ground motions is examined. The influences of local wave scattering and wave passage effects are investigated for three half-spaces with different shear-wave velocities. When the shear-wave velocity is sufficiently large like hard rock, the local wave scattering significantly affects the reduction of the earthquake responses. In the cases of rock or soft rock, the earthquake responses of structures are further affected by the incident angles of seismic waves or the wave passage effects.