• Tunnel and Underground Space
• /
• v.6 no.4
• /
• pp.335-341
• /
• 1996

This fundamental study analyzes the relationship between rock thermal properties and psychrometric properties in underground space and has a ultimate goal to develope technologies for predicting major environmental variables. The study is divided into 2 subjects (1) developement of a basic model for predicting temperature and humidity, (2) analysis of the validity of the model through application to a local underground storage space for military supplies. The basic model is built for the network of tunnel-shaped underground spaces. The model takes into account rock thermal properties and changes in moisture content in the air due to condensation/evaporation on the rock surface. Using lumped-parameter analytical method, heat flux from or to the surrounding rock is calculated and then the psychrometric properties(air quantity, pressure, temperature, humidity) are estimated through network simulation. The model can be utilized regardless of the tunnel type. The study site is a local storage space built in rock, mainly granite gneiss and quartz-porphyry. It is a U-shaped tunnel, 593.5m long and 6x6.5m wide. Relative humidity inside has to be strictly controlled under 55% to avoid erosion of a certain types of supplies stored in 6 chambers with the capacity of 300~1.000 ton. The thermal conductivity varies between 2.734 and 2.779W/m$^{\circ}C$ and the thermal diffusivity is in the range of 1.119 and $1.152{\times}10^{-6}\;m^2/s$ the specific heat between 910 and $920\;J/kg^{\circ}C$. Relative errors of the predicted values of dry/wet temperature and relative humidity are 0.8~3.0%, 0~7.5% and 0~7.0%, respectively. Apparent errors associated with the rock surface temperature seems to be partly due to the intrinsic limitations in the infrared thermometer used in this study.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.43 no.1
• /
• pp.43-54
• /
• 2023

Due to climate change, drought and flood occurrences have been increasing. Accurate projections of watershed discharges are imperative to effectively manage natural disasters caused by climate change. However, climate change and hydrological model uncertainty can lead to imprecise analysis. To address this issues, we used two lumped models, IHACRES and GR4J, to compare and analyze the changes in discharges under climate stress scenarios. The Hapcheon and Seomjingang dam basins were the study site, and the Nash-Sutcliffe efficiency (NSE) and the Kling-Gupta efficiency (KGE) were used for parameter optimizations. Twenty years of discharge, precipitation, and temperature (1995-2014) data were used and divided into training and testing data sets with a 70/30 split. The accuracies of the modeled results were relatively high during the training and testing periods (NSE>0.74, KGE>0.75), indicating that both models could reproduce the previously observed discharges. To explore the impacts of climate change on modeled discharges, we developed climate stress scenarios by changing precipitation from -50 % to +50 % by 1 % and temperature from 0 ℃ to 8 ℃ by 0.1 ℃ based on two decades of weather data, which resulted in 8,181 climate stress scenarios. We analyzed the yearly maximum, abundant, and ordinary discharges projected by the two lumped models. We found that the trends of the maximum and abundant discharges modeled by IHACRES and GR4J became pronounced as changes in precipitation and temperature increased. The opposite was true for the case of ordinary water levels. Our study demonstrated that the quantitative evaluations of the model uncertainty were important to reduce the impacts of climate change on water resources.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.20 no.2
• /
• pp.585-593
• /
• 1996

According to the considerable increase of the length of belt conveyors, the dynamic analysis of systme becomes necessary to consider the variation of tensions and transient motion of components during starting and stopping of conveyor. The mathematical model of system is derived using the lumped parameter method. The input driving force is represented with two functions of time and pulley speed to count the characteristics of motor and fluid coupling. An example system was studied with 14 km in the distance of carrying. At head, it has two drivers and one gravity take-up and at tail ond driver and one power winch take-up. In the example, the transient tensions and responses, calculated using two cases of driving force, are mutually compared in starting mode. Also, the position of maximum tension and the braking force of take-up are obtained in stopping mode.

• Earthquakes and Structures
• /
• v.4 no.2
• /
• pp.203-217
• /
• 2013

In recent decades, it has been realized that increasing the lateral stiffness of structure subjected to lateral loads is not the only parameter enhancing safety or reducing damage. Factors such as ductility and damping govern the structural response due to lateral loads. Despite the significant contribution of damping in resisting lateral loads, especially at resonance, there is no accurate mathematical representation for it. The main objective of this study is to develop a damping identification procedure for linear systems based on a mixed numerical-experimental approach, assuming viscous damping. The proposed procedure has been applied to a laboratory experiment associated with a numerical model, where a hollow rectangular steel cantilever column, having three lumped masses, has been fixed on a shaking table subjected to different exciting waves. The modal damping ratio has been identified; in addition, the effect of adding filling material to the hollow specimen has been studied in relation to damping enhancement. The results have revealed that the numerically computed response based on the identified damping is in a good fitting with the measured response. Moreover, the filling material has a significant effect in increasing the modal damping.

• Journal of Institute of Control, Robotics and Systems
• /
• v.14 no.4
• /
• pp.385-391
• /
• 2008

To effectively cope with a complexity of kinematic metrology due to workspace enlargement of the planar stage, the linear induction motor is suggested as its new driving source. Especially, the linear induction motor under uniform plate type of secondary doesn't inherently have a periodical force ripple which is generally shown in the brushless DC motor. But, it presents a poor transient characteristic at zero or low speed zone owing to time delay of flux settling, resulting in slow response. To improve the servo property of linear induction motor and apply successfully it to the precision stage, this paper discusses a modified vector control methodology. The controller has a novel input form, fixed d-axis current, q-axis current and forward-fed DC current, to control thrust force and normal force of the linear induction motor independently. Influence of the newly introduced input and the feasibility of controller are validated experimentally.

• Journal of Advanced Marine Engineering and Technology
• /
• v.17 no.4
• /
• pp.87-99
• /
• 1993

Nowadays, the cartridge valve can be controlled proportionally in remote place by adopting proportional solenoid and it becomes widely used as control component in hydraulic systems. Especially, multi stage proportional valve is attractive because it consumes less input power though its characteristics might slightly be defected. But, the system parameter should be carefully chosen to obtain optimistic characteristics. This study concerning three stage proportional throttle control valve is purposed to examine the influences of paameters to the dynamic characteristics. The typical transient and frequency responses of proportional throttle control valve were inspected through the experiments and compared to those derived from the theoritical analyses. And it was confirmed that the analyses are appropriate. Then the influences of various system parameters to the dynamic characteristics were examined by means of simulations. For the analyses, the basic equations derived from lumped model were linearized and the linearized equations were transformed to the transfer functions between inputs and outputs. Then the transient responses and frequency responses were obtained from transfer functions. 1. It is appropriate to estimate the dynamic characteristics of valve which has relatively sophisticated structure by means of system analyses using linearized equations. 2. Though the valve has two pilot stages, fairly good characteristics can be obtained by carefully choosing system parameters. 3. Main valve very quickly follows the movement of second pilot valve when the parameters of main valve(the oil supply passage and discharge passage fpr second pilot valve) are appropriately chosen.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.8 no.5
• /
• pp.416-424
• /
• 1984

A numerical and experimental investigation was carried out on the single-phase natural circulation system. This study is concerned with the multiloop system which is relevant to the primary system of the pressurized water reactor. For numerical analysis, five time-dependent governing equations were derived using the one-dimensional lumped parameter model. These equations were discretized by the space-time integration technique, and a simplified computer program, SIMFARS, was developed to solve those discretized equations. Experiments were performed for two purposes-one is to validate the developed code, and the other is to understand the qualitative behavior of the natural circulation loop. Comparison of the computational results with experiments, and several experimental and numerical results are presented in this article.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.3 s.174
• /
• pp.728-734
• /
• 2000

An asymmetric actuator can be used to reduce the distance between the reflective mirror and objective lens of a small optical disk drive for use in the notebook-sized personal computer data storage devices. However, this asymmetric actuator is very sensitive to the subsidiary resonance which is caused by its rigid body motion. In this paper, an analytical approach using a simple lumped parameter system model is presented with a physical insight to investigate why the subsidiary resonance occurs. The finite element method is used to figure out the force and torque characteristics of the asymmetric actuator which are essential to understand the subsidiary vibration characteristics. The frequency responses are presented to examine how the subsidiary resonance is altered for various situations of having different thickness of a yoke and permanent magnet and of having a different magnet circuit. Finally, the design guidelines to avoid the subsidiary resonance will be presented.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2001.09a
• /
• pp.117-124
• /
• 2001

A simplified method fur the eigenpair sensitivities of damped system with multiple eigenvalues is presented. This approach employs a reduced equation to determine the sensitivities of eigenpairs of the damped vibratory systems with multiple natural frequencies. In the proposed method, adjacent eigenvectors and orthonormal conditions are used to compute an algebraic equation whose order is (n+m)x(n+m), where n is the number of coordinates and m the number of multiplicity of multiple natural frequencies. The proposed method is an improved Lee and Jung's method which was developed previously. Two equations are used to find eigenvalue derivatives and eigenvector derivatives in Lee and Jung's method. A significant advantage of this approach over Lee and Jung's method is that one algebraic equation newly developed is enough to compute such eigenvalue derivatives and eigenvector derivatives. This method can be consistently applied to both structural systems with structural design parameters and mechanical systems with lumped design parameters. To demonstrate the theory of the proposed method and its possibilities in the case of multiple eigenvalues, the finite element model of the cantilever beam and 5-DOF mechanical system in the case of a non-proportionally damped system are considered as numerical examples. The design parameter of the cantilever beam is its height. and that of the 5-DOF mechanical system is a spring.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2001.10a
• /
• pp.515-522
• /
• 2001

A simplified method is presented for the computation of eigenvalue and eigenvector derivatives associated with repeated eigenvalues. In the proposed method, adjacent eigenvectors and orthonormal conditions are used to compose an algebraic equation whose order is (n+m)x(n+m), where n is the number of coordinates and m is the number of multiplicity of the repeated eigenvalue. One algebraic equation developed can be computed eigenvalue and eigenvector derivatives simultaneously. Since the coefficient matrix of the proposed equation is symmetric and based on N-space, this method is very efficient compared to previous methods. Moreover the numerical stability of the method is guaranteed because the coefficient matrix of the proposed equation is non-singular, This method can be consistently applied to both structural systems with structural design parameters and mechanical systems with lumped design parameters. To verify the effectiveness of the proposed method, the finite element model of the cantilever beam and a 5-DOF mechanical system in the case of a non-proportionally damped system are considered as numerical examples. The design parameter of the cantilever beam is its width, and that of the 5-DOF mechanical system is a spring.