• Structural Engineering and Mechanics
• /
• v.30 no.4
• /
• pp.427-444
• /
• 2008

A mathematical model for the nonlinear dynamics of a rotating beam with flexible root attached to a rotating hub with elastic foundation is developed. The model is developed based on the large planar and flexural deformation theory and the potential energy method to account for axial shortening due to bending deformation. In addition the exact nonlinear curvature is used in the system potential energy. The Lagrangian dynamics and the assumed mode method is used to derive the nonlinear coupled equations of motion hub rotation, beam tip deflection and hub horizontal and vertical displacements. The derived nonlinear model is simulated numerically and the results are presented and discussed for the effect of root flexibility, hub stiffness, torque type, torque period and excitation frequency and amplitude on the dynamic behavior of the rotating beam-hub and on its stability.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.21 no.2
• /
• pp.297-304
• /
• 1997

This paper presents a systematic design method of an anti-swing control law for overhead cranes. A velocity servo system for the trolley of a crane is designed based on the dynamics of the trolley and its load. The velocity servo system compensates for the effects of load swing on the trolley dynamics so that the velocity servo is independent of load swing. The velocity servo system is used for the design of a position servo system for the trolley via the loop shaping method. The position servo system and the swing dynamics of the load are then used to design an angle control system for load swing based on the root locus method. The combined position servo and the angle control systems constitute the overall control system. In the presence of low frequency disturbances, the proposed control law guarantees accurate position control for the trolley and fast damping for load swing. Furthermore, the performance of the proposed control law is independent of the mass of the load. Experimental results on a prototype crane show the effectiveness of the proposed anti-swing control law.

• Korean Journal of Soil Science and Fertilizer
• /
• v.45 no.3
• /
• pp.353-359
• /
• 2012

The identification of effective root zone would clarify dynamics of plant available water and soil water balance. Using the relationship between soil properties and electrical resistivity (ER) the purpose of this research is to identify soil zone affected by a plant root activity using electrical resistivity tomography (ERT) technique. Four plastic containers were prepared for two different soil textures (clay and sandy loam) and one container for each texture was selected for planting four corn seedlings (Zea mays L.) and the others were prepared for the blank. For ERT monitoring, we prepared 0.8 m plastic sticks with 17 electrodes installed with 5 cm space. The Ministing (AGI Inc., Texas) instrument for electrical resistivity measurement and semi-auto converter of electrode arrangement were set up for dipole-dipole array. During 2 months of the corns growing, ERT monitoring was made 3 to 4 days after the irrigation practice. Despite of the same amount water supplied into soils, two textures showed very different apparent resistivity values due to different clay content. The apparent electrical resistivity is consistently lower in clay loam comparing to sandy loam soil implying that plant root does not significantly alter the overall trend of resistivity. When plant root system, however, is active both soils with plants showed 2-7 times higher electrical resistivity and higher coefficient variation than soils without plant, implying the effect of root system on the resistivity, in which may caused by. This result suggests plant root activities regulating the soil water dynamics mainly control the variation of electrical resistivity over soil textural difference. Therefore the identification of water uptake zone would highly be correlated to plant root activities, thus ERT will be feasible approach to identify spatial characteristics of a plant root activity.

• Journal of the korean society of oceanography
• /
• v.39 no.4
• /
• pp.222-233
• /
• 2004

Using nitrogen as the limiting nutrient, the default version of a microplankton-detritus model linked chlorophyll concentration to the autotroph nitrogen. However, phosphorus dynamics were added to simulate the results of a microcosm experiment. Using standard parameter values with a single value of microheterotroph fraction in the microplankton taken from the observed range, the best simulation successfully captured the main features of the time-courses of chlorophyll and particulate organic carbon, nitrogen and phosphorus, with root-mean-square error equivalent to 29% of particulate concentration. A standard version of microbiological model assumes complete internal cycling of nutrient elements; adding a term for ammonium and phosphate excretion by microheterotrophs did not significantly improve predictions. Relaxing the requirement for constant microheterotroph fraction resulted in an autotroph-heterotroph model AH, with dynamics resembling those of a Lotka-Volterra predator-prey system. AH fitted the microcosm data worse than did MP, justifying the suppression of Lotka-Volterra dynamics in MP. The paper concludes with a discussion of possible reasons for the success of the simple bulk dynamics of MP in simulating microplankton behaviour.

• Journal of Korean Society of Forest Science
• /
• v.88 no.4
• /
• pp.454-461
• /
• 1999

The dynamics of root system in the fairy rings of Tricholoma matsutake was investigated in four zones divided into 'zone of decayed mycorrhizae', 'zone of mycorrhizae for fruiting', 'zone of physiologically active mycorrhizae' and 'zone of roots free from mycorrhizal infection'. The roots of Pinus densiflora in fairy rings, which occupied 70% of upper crown, comprised about 60% and 87% of total roots and alive roots, respectively. The ratio of fine-roots of P. densiflora over total roots was relatively higher than other species since that of P. densiflora was about 45% while that of the other species was about 13% on research of fine-roots. Especially, the roots of pine comprised about 70% of total root in the zone of mycorrhizae for fruiting and the zone of physiologically active mycorrhizae, which indicated that the pine roots were closely related to the fairy rings of T. matsutake. The fine roots of P. densiflora in the zone of physiologically active mycorrhizae was about 60.7%(1,087mg/100g soil) which was about twice compared to that of other zones. It allowed us to suppose that the fine roots of P. densiflora can make active growth in the zone of physiologically active mycorrhizae, and the growth was promoted by the fairy ring formation of T. matsutake. In addition, we found 3~5 times higher amount of fine roots than that of medium roots of P. densiflora in this zone, which indicated that the fairy rings of T. matsutake locate in the region of active growth of P. densiflora' roots.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.10 no.1
• /
• pp.209-215
• /
• 2002

A study of the guideway vehicle was made for a comparison of ride stabilities between its two primary steering types; one is the front wheel steering and the other the front-rear wheel. A numerical model as a closed loop system was built for an investigation of various factors to have an influence on the vehicular critical speed which is closely associated with ridabilities. It was shown that dynamics stabilities of the front steering type was much better over a large value of steering gain and the longer distance between front axle and guide link for both types provided better stabilities as well. A large steering gain ratio of the front to the rear significantly plays an important role in an improvement of stability in the front-rear steering. To observe a qualitative trend on stability behaviors, the root locus was obtained by considering a time lag which may be frequently caused by the complicated steering mechanism. In performing so, the appropriate selection of steering gain had a greater effect on the front-rear steering vehicle far more ride comfort. In addition, the dynamics model proposed here can be utilized for a more accurate evaluation on the vehicle design in lateral or yawing absorber and moreover expanded for the analysis of independent four-wheel steering vehicle.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.26 no.3
• /
• pp.248-257
• /
• 2016

Recently, researches on the free-piston Stirling engines(FPSEs) are actively investigated. FPSEs have merits in its light weight, simple structure, and little need for maintenance, thus becoming a promising solution for the power conversion of renewable energy and waste heat recycle. This paper presents the methodology that estimates damping coefficients using analytical models of linear and nonlinear dynamics for FPSEs, and validates the methodology by comparing with existing experimental results. The analysis model predicts an operable range of linear damping coefficients forming limit cycles by using the root locus, and time responses obtained by numerical integration determines nonlinear damping coefficients. The model predictions are compared with experimental results of the well-known FPSE B-10B. We also investigate the damping characteristics regarding heater temperatures and power piston motions.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.9 no.4
• /
• pp.384-388
• /
• 1999

This paper describes an approach for synthesizing a modularized gain scheduled PD type fuzzy logic controller(FLC) of nonlinear magnetic bearing system where the gains of FLC are on-line adapted according to the operating point. Specifically the systematic procedure via root locus technique is carried out for the selection of the gains of FLC. Simulation results demonstrate that the proposed gain scheduled fuzzy logic controller yields not only maximization of stability boundary but also better control performance than a single operating point (without gain scheduling)fuzzy controller.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.1
• /
• pp.263-270
• /
• 1995

The use of the shape memory alloy, Nitinol wire, is investigated as an actuator for enhancing the damping in structural vibration systems. The first-order mathematical model of the Nitinol wire is obtained from the experimental data for an actuator. Finite element method is utilized for the strain gage sensor model, which is installed at the root of cantilever beam. A simple system, cantilever beam, is built as a flexible structural system to implement a control law with the Nitinol wire actuator. The system model including sensor and actuator is derived, which agrees with the experimental results. The actuator dynamics is augmented with the system so as to design PI controller and the one of robust controllers, LQG/LTR controller, and the control laws are implemented experimentally. The experimental study shows the feasibility of utilizing the Nitinol wire as an actuator for the purpose of vibration control.

• Ocean Systems Engineering
• /
• v.8 no.4
• /
• pp.361-380
• /
• 2018

The dynamic performance of the wave energy converter (WEC) rotor with different geometric parameters such as depth of submergence and beak angle has been assessed by considering the linear potential flow theory using WAMIT solver and along with the computational fluid dynamics (CFD). The effect of viscous damping is incorporated by conducting numerical free decay test using CFD. The hydrodynamic coefficients obtained from the WAMIT, viscous damping from the CFD and estimated PTO damping are used to solve the equation of motion to obtain the final pitch response, mean optimal power and capture width. The viscous damping is almost 0.9 to 4.6 times when compared to the actual damping. It is observed that by neglecting the viscous damping the pitch response and power are overestimated when compared to the without viscous damping. The performance of the pitch WEC rotor in the Jeju western coast at the Chagwido is analyzed using Joint North Sea Wave Project (JONSWAP) spectrum and square-root of average extracted power is obtained. The performance of WEC rotor with depth of submergence 2.8 m and beak angle $60^{\circ}$ found to be good compared to the other rotors.