• 동력기계공학회지
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• 제7권3호
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• pp.48-53
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• 2003

This paper deals with the control of a horizontally placed flexible rotor levitated by electromagnets in a multi-input/multi-output (MIMO) active magnetic bearing(AMB) system. AMB is a kind of novel high performance bearing which can suspend the rotor by magnetic force. Its contact-free manner between the rotor and stator results in it being able to operate under much higher speed than conventional rolling bearings with relatively low power losses, as well as being environmental-friendly technology for AMB system having no wear and no lubrication requirements. In this MIMO AMB system, the rotor is a complex mechanical system, it not only has rigid body characteristics such as translational and slope motion but also bends as a flexible body. Reduced order nominal model is computed by consideration of the first 3 mode shapes of rotor dynamics. Then, the $H_{\infty}$ control strategy is applied to get robust controller. Such robustness of the control system as the ability of disturbance rejection and modeling error is guaranteed by using $H_{\infty}$ control strategy. Simulation results show the validation of the designed control system and the modeling method to the rotor.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.430-440
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• 2009

Top-Base Foundation(TBF) was developed in Japan as a factory made concrete product. It is actively used in 6,000 sites by the end of 1980s in Japan and applied for a domestic patent in 1985. It is a shallow foundation whose effectiveness is proven by many relevant researchers and engineers. TBF was introduced to Korea in 1991 and has been applied mainly to architectural structures to date. Currently, the effectiveness in bearing capacity and settlement of TBF is being underestimated for civil engineering structures. Characteristics of Top-Base Foundation studied in Japan and Korea is known as follows: (1) as concrete part and crushed stone behave together, they perform the function of rigid mat; (2) the conical part and pile part of TBF disperses load by interaction with the crushed stone; (3) by preventing lateral strain and differential settlement on lower ground, it improves bearing capacity and constrains settlement at the same time. In Korea, it is used mostly in clayey soft grounds. The formula of bearing capacity and settlement of TBF suggested in Japan give the values of the underestimated. bearing capacity while its settlement is overestimated in comparison with the values measured from the field loading test. Therefore, in this study, the stress delivery mechanism of Top-Base Foundation developed in Japan and Floating Top Base developed in Korea is investigated through numerical analysis and laboratory model test.

• 한국기계가공학회지
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• 제11권6호
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• pp.164-168
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• 2012

In this paper, a manufacturing process for a ball bearing outer race is studied by experiments and predictions, which is composed of four hot forging stages and the final hot or warm profile ring rolling stage. An analysis model and some assumption to simulate the profile ring rolling process is introduced. The entire process including the forging stages and ring rolling stage is simulated using a rigid-thermoviscoplastic finite element method and the predictions are compared with the experiments in terms of major dimensions, showing that they are quantitatively very close to each other.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 기초기술학술발표회
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• pp.77-89
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• 2002

To analyze a bearing capacity for pile groups, a number of model tests have been done and theoretical methods studied. In the case of design of group pile bearing capacity is calculated with only pile capacity. But uncertainty of bearing capacity and behavior of foundation cap(raft) leads to conservative design ignoring bearing effects of foundation cap. In the case of considering bearing capacity of foundation cap, the simple sum of bearing capacity of foundation cap and pile groups cannot be the bearing capacity of total foundation system. Since cap-pile-soil interaction affects the behavior of pile groups. Thus, understanding cap-pile-soil interaction is very important in optimal design. In this paper, the piled raft behavior is studied through model tests of 2$\times$2, 2$\times$3, 3$\times$3 pile group. Changes of behavior of pile group foundation by touching effects of foundation cap with soil are studied. Also changes of spacing between piles. Foundation cap is made of rigid steel plate and piles are made steel pipes. From this model tests, the changes of behavior changes of pile groups by touching effects of foundation cap with soil are studied.

• Tribology and Lubricants
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• 제30권2호
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• pp.116-123
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• 2014

The objective of this study is to model and simulate the nonlinear lubrication performance of the sliding part between the piston and cylinder wall in a hydrostatic swash-plate-type axial piston pump. A numerical algorithm is developed that facilitates simultaneous calculation of the rotating body motion and fluid film pressure to observe the fluid film geometry and power loss. It is assumed that solid asperity contact, so-called mixed lubrication in this study, invariably occurs in the swash-plate-type axial piston pump, which produces a higher lateral moment on the pistons than other types of hydrostatic machines. Two comparative mixed lubrication models, rigid and elastic, are used to determine the reaction force and sliding friction. The rigid model does not allow any elastic deformation in the partial lubrication area. The patch shapes, reactive forces, and virtual local elastic deformation in the partial lubrication area are obtained in the elastic contact model using a simple Hertz contact theory. The calculation results show that a higher reaction force and friction loss are obtained in the rigid model, indicating that solid deformation is a significant factor on the lubrication characteristics of the reciprocating piston part.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2001년도 춘계학술대회 논문집
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• pp.426-431
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• 2001

Seismic performance of base isolated rigid-mass model were studied through shaking table tests. Friction pendulum systems (FPS), pure-friction systems with laminated rubber bearing (LRB) were selected for the comparison of performance. Performance of specially designed isolation systems were tested statically using actuator and dynamically using shaking table. Numerical methods were developed to simulate the nonlinear behavior of the frictional base isolation systems. Two models were considered. one is modified Bouc-Wen model considering breakaway coefficient of friction and the other is classical Coulomb model. The results of numerical methods are found to be in very good agreement with test results.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 추계학술대회 논문집
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• pp.440-445
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• 2002

The characteristic equation for regenerative chatter loop including a delay element replaced by a rational function is presented by a linear differential-difference equation, accounting for the dynamics of the AMB controllers, the uncut chip thickness equation and the cutting process as well as the rigid spindle dynamics itself. The chatter stability analysis of a rigid milling spindle suspended by 5-axes active magnetic bearings(AMBs) is also performed to investigate the influences of the damping and stiffness coefficients of AMBs on the chatter free cutting conditions, as they are allowed to vary within the stable region formed by the AMB control gains. Several cutting tests varying the derivative gains of the AMB were performed to investigate the regenerative chatter vibrations, and it was concluded that the theoretical analysis results are in good consistency with the test results.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2003년도 봄 학술발표회 논문집
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• pp.439-446
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• 2003

In this paper the model tests have been conducted and the results are compared with those by the theoretical methods to study the behaviors of the piled raft. The size of model box is 2.2m${\times}$2m${\times}$2m. The raft is made of rigid steel plate and piles made of steel pipes. Generally the bearing capacity of group piles is designed with only the pile capacities, and the bearing capacity of raft is ignored. But the uncertainty of pile-raft-soil interaction leads to conservative design ignoring the bearing effects of raft. In the case of considering the bearing capacity of raft, the simple sum of bearing capacity of raft and that of each pile cannot be the bearing capacity of piled raft. Because the pile-raft-soil interaction affects the behavior of piled raft. Thus the effects of pile-raft-soil interaction are very important in the optimal design. In this paper, the behaviors of piled raft are studied through model tests of 2${\times}$2, 2${\times}$3, and 3${\times}$3 pile groups. The spacing between piles is changed in the model tests. And the behaviors of free standing and piled raft are also studied.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 가을 학술발표회 논문집
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• pp.358-365
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• 2002

In this paper the model tests have been conducted and the results were compared with those by the theoretical methods to study the behaviors of the piled raft. The size of model box is 2.2m${\times}$2m${\times}$2m. The raft is made of rigid steel plate and piles are made of steel pipes. Generally the bearing capacity of group piles is designed with only the pile capacities, which is Ignored the bearing capacity of raft. But the uncertainty of pile-raft-soil interaction leads to conservative design ignoring the bearing effects of raft. In the case of considering the bearing capacity of raft, the simple sum of bearing capacity of raft and that of each pile cannot be the bearing capacity of piled raft. Because the pile-raft-soil interaction affects the behavior of piled raft. Thus the effects of pile-raft-soil interaction are very important in the optimal design. In this paper, the behaviors of piled raft are studied through model tests of 2${\times}$2, 2${\times}$3, and 3${\times}$3 pile groups. The spacing between piles is changed in the model tests. And the behaviors of free standing and piled raft are also studied.

• Journal of Advanced Marine Engineering and Technology
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• 제10권4호
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• pp.31-40
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• 1986

With the tendency toward high speed and high pressure in centrifugal pumps, the problem of sub-synchronous vibration has arisen, caused by the hydraulic forces of the working fluid, such as wearring, balance piston, impeller, etc.. These forces can drastically alter the rotor critical speeds and stability characteristics, and can be acted significant destabilizing forces. For preventing such self-excited vibration, the desing of the rotor system needs, which would secure the stability of the machine. In this paper, a procedure is presented for dynamic modeling of rotor-bearing-seal-impeller systems which consist of rigid disks, distributed parameter finite rotor elements and discrete bearings, seals and impellers. A finite element model including the effects of rotatory inertia and gyroscopic moments is developed using the consistent matrix approach. The technique of dynamic matrix reduction is applied to the shaft matrices to reduce them to a set of matrices of dynamic of significantly fewer degrees of freedom. The representation of bearing, seal and impeller elements is in term of linearized stiffness and damping matrices by reasonably small perturbations from equilibrium. The stability behavior of a typical double suction centrifugal pump is presented. Results show the influence of clearance and flow conditions on running speeds and stability characteristics.