• International Journal of Precision Engineering and Manufacturing
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• 제8권2호
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• pp.32-37
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• 2007

This paper proposes a dual-mode ultra precision positioning system for machine tools and measuring machines. The objective was to position a machine table with a picometer order of resolution, i.e., pico-positioning. A twist-roller friction drive (TFD) was used in coarse-mode positioning. The TFD, which was driven by an AC servomotor, is a kind of lead screw in mechanical terms, and several centimeters of machine table movement was controlled with a nanometer order of positioning resolution. To eliminate lateral vibration caused by the TFD, an active aerostatic coupling driven by piezoelectric actuators was inserted between the TFD and the machine table. This active aerostatic coupling was also applied as a feed drive device for fine-mode positioning; in the fine mode, the positioning resolution was 50 pm. Factors influencing pico-positioning, such as how noise from displacement sensors and vibrations in the aerostatic guideway affect positioning resolution, are discussed.

• Geomechanics and Engineering
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• 제18권6호
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• pp.567-574
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• 2019

In order to study the effect of stress and water pressure on the permeability of fractured rock mass under three-dimensional stress conditions, a single fracture triaxial stress-seepage coupling model was established; By using the stress-seepage coupling true triaxial test system, large-scale rock specimens were taken as the research object to carry out the coupling test of stress and seepage, the fitting formula of permeability coefficient was obtained. The influence of three-dimensional stress and water pressure on the permeability coefficient of fractured rock mass was discussed. The results show that the three-dimensional stress and water pressure have a significant effect on the fracture permeability coefficient, showing a negative exponential relationship. Under certain water pressure conditions, the permeability coefficient decreases with the increase of the three-dimensional stress, and the normal principal stress plays a dominant role in the permeability. Under certain stress conditions, the permeability coefficient increases when the water pressure increases. Further analysis shows that when the gob floor rock mass is changed from high stress to unloading state, the seepage characteristics of the cracked channels will be evidently strengthened.

• Nuclear Engineering and Technology
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• 제55권6호
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• pp.1974-1987
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• 2023

The load-following operation of small modular reactors (SMRs) requires accurate prediction of transient behaviors that can occur in the balance of plants (BOP) and the nuclear steam supply system (NSSS). However, 1-D thermal-hydraulics analysis codes developed for safety and performance analysis have conventionally excluded the BOP from the simulation by assuming ideal boundary conditions for the main steam and feed water (MS/FW) systems, i.e., an open loop. In this study, we introduced a lumped model of BOP fluid system and coupled it with NSSS without any ideal boundary conditions, i.e., in a closed loop. Various methods for coupling boundary conditions at MS/FW were tested to validate their combination in terms of minimizing numerical instability, which mainly arises from the coupled boundaries. The method exhibiting the best performance was selected and applied to a transient simulation of an integrated NSSS and BOP system of a SMART. For a transient event with core power change of 100-20-100%, the simulation exhibited numerical stability throughout the system without any significant perturbation of thermal-hydraulic parameters. Thus, the introduced boundary-condition coupling method and BOP fluid system model can expectedly be employed for the transient simulation and performance analysis of SMRs requiring daily load-following operations.

• International Journal of Automotive Technology
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• 제7권4호
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• pp.423-439
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• 2006

This paper proposes a hybrid analytic method for the prediction of vibrational and acoustic responses of reverberant system in the medium-to-high frequency ranges by using the PFA(Power Flow Analysis) algorithm and SEA(Statistical Energy Analysis) coupling concepts. The main part of this method is the application of the coupling loss factor(CLF) of SEA to the boundary condition of PFA in reverberant system. The hybrid method developed shows much more promising results than the conventional SEA and equivalent results to the classical PFA for various damping loss factors in a wide range of frequencies. Additionally, this paper presents applied results of hybrid power flow finite element method(hybrid PFFEM) by formulating the new joint element matrix with CLF to analyze the vibrational responses of built-up structures. Finally, the analytic results of coupled plate structures and an automobile-shaped structure using hybrid PFFEM were predicted successively.

• Structural Engineering and Mechanics
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• 제9권4호
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• pp.383-396
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• 2000

A new structure-vibration-control approach is proposed which uses a passive coupling element between two parallel structures to reduce the seismic response of a system due to earthquake excitation. Dynamic characteristics of the two coupled single-degree-freedom systems subject to stationary white-noise excitation are examined by means of statistical energy analysis (SEA) techniques. Optimal parameters of the passive coupling element such as damping and stiffness under different circumstances are determined with an emphasis on the influence of the structural parameters of the system on the optimal parameters and control effectiveness. Numerical results including the root mean square values of the response due to the filtered white-noise excitation and the time-histories of response to El Centro 1940 NS excitation are presented.

• 대한기계학회논문집A
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• 제26권8호
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• pp.1480-1486
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• 2002

In this study, the cross-coupling control (CCC) with three new features is proposed to maintain contour precision in high-speed nonlinear contour machining. One is an improved contour error model that provides almost exact calculation of the errors. Another is the utilization of variable controller gains based on the instantaneous curvature of the contour and the variable command. For this scheme, a stability is analyzed. As a result, the stability region is obtained, and the variable gains are decided within that region. The other scheme in the proposed CCC is a real-time feedrate adaptation module to regulate cutting force fur better surface finish through regulation of material removal rate (MRR). The simulation results show that the proposed CCC system can provide better precision than the existing method particularly in high-speed machining of nonlinear contours.

• Journal of electromagnetic engineering and science
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• 제15권3호
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• pp.194-198
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• 2015

Magnetic resonant coupling is more efficient than inductive coupling for transferring power wirelessly over a distance. However, a conventional resonant wireless power transfer (WPT) system requires a transmitter and receiver pair in exactly coaxial positions. We propose a resonator that can serve as an omnidirectional WPT system. A magnetic field will be generated by the current flowed through the transmitter. This magnetic field radiates omnidirectionally in the x-y plane because of the crisscross structure characteristic of the transmitter. The proposed resonator is demonstrated by using a single port. To check the received S21 and transfer efficiency, we moved the receiver around the transmitter at different distances (50-350 mm). As a result, the transmission efficiency is found to be 48%-54% at 200 mm.

• 대한전기학회논문지
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• 제41권4호
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• pp.362-368
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• 1992

This paper presents a coupling scheme, which couples an analytical solution and the standard finite element, for analyzing the electromagnetic fields. The former is a solution of the magnetic field in free space, i.e., the outer region of boundary, and the latter represents the system with source currents and magnetic materials in the inner region of boundary. The proposed method retains the sparsity and symmetry of the final system matrix, the merits of the standard FEM. To verify the usefulness of the proposed algorithm, an example which can be solved analytically is chosen and analyzed. The results are compared with those of the standard FEM and the analytic solutions.

• 대한기계학회논문집A
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• 제25권4호
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• pp.555-563
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• 2001

Support dynamics are often important in rotordynamic analyses. It may well happen in real situation of machines such as centrifugal pumps or turbines operating on flexible structure. This paper presents the applications of the impedance coupling method and the improved rotor model for including the support effects on the interaction with the rotor. The impedance coupling techniques are based on the FRFs of each substructure. Its dynamic stiffness matrix can be assembled to generate the system matrix, which satisfy the constraint conditions in the connection coordinates. And, the improved rotor uses the simplified spring-mass models as support properties. The equivalent support models are directly incorporated into the finite element rotor model. To verify the suggested analytical procedures, the results are compared to those of the pump system.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.1034-1039
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• 2000

In turbo-machines operated at high speeds through gear speed increasers a precise coupled analysis of lateral and torsional vibrations is required to achieve highly reliable designs with low vibration and low noise levels, where the vibration coupling is due to the gear pair mesh stiffness. In this paper, applying the generalized coupled lateral-torsional finite element model of a gear pair element, has been analyzed a coupled lateral-torsional vibration of the prototype 800 RT turbo-chiller rotor-bearing system with a bull-pinion gear speed increaser. Results have shown that the coupled torsional natural frequencies have decreased due to the coupling effect of lateral vibration and particularly, the 2nd torsional natural frequency and its mode shape have had big changes. However, changes of lateral vibration characteristics have been noticed only at high lateral whirl natural frequencies above 15,000 rpm.