• Journal of the Society of Naval Architects of Korea
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• v.41 no.3
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• pp.35-40
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• 2004

Since the scale of vessels is growing up recently, some troubles between the shaft and after bush bearing are frequently reported. Generally, mean pressure on bush bearing is used as a design criterion. However, in some case of the long bearing such as after bush bearing of the propulsion shaft, it might be liable to be locally under high pressure. As for the main engine bearings and the intermediate shaft bearing, it is reasonable to take the mean pressure as a design criterion. But, in case of after bush bearing, it is not sufficient because of the possibility of high pressure caused by local contact. In this study, Hertzian contact condition was applied to evaluation of the local pressure for after bush bearing. To reduce the local maximum pressure, the height of the after bush bearing was controlled. It was found that local maximum pressure could be reduced effectively by taking a partial slope on the white metal of the aft bush bearing.

• 제어로봇시스템학회:학술대회논문집
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• 1988.10a
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• pp.315-320
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• 1988

This paper considers modelling and control of ABS(Anti-skid Brake System) which avoids dangerous wheel locking due to excessive brake pressure during the vehicle braking. The brake pressure is controlled by on and off's of solenoid valves via the variation of the wheel circumferential deceleration measured using tacho-sensors. The dynamic model between the brake pressure and the wheel acceleration of a vehicle is mathematically derived. The computer simulation shows that the threshold value of the on-off control is critical to the performance of the ABS.

• 한국가시화정보학회:학술대회논문집
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• 2003.11a
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• pp.111-114
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• 2003

Drop size is one of the most important parameters which are control the performance of the engine using liquid fuel/oxidizer and drop formation is mainly controlled by aerodynamic force caused by ambient gas. Because of this, empirical data and correlation acquired under standard ambient condition are not valid. So experiments under high ambient pressure condition to measure the drop size using image processing method And find the empirical correlation between SMD and chamber pressure(density), injection velocity.

• Korean Journal of Clinical Pharmacy
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• v.26 no.2
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• pp.163-171
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• 2016

Objective: A meta-analysis was performed to determine effect of ginseng on blood pressure. Methods: The databases of PubMed, Embase, Cochrane Library, RISS, DBpia, KISS, and Koreamed were searched for all published studies from inception to January 2016. The following terms were used: "ginseng", "hypertension", and "blood pressure". Using the Review Manager 5, mean differences (MDs) were pooled to measure the effect of ginseng on blood pressure compared to that of placebo. Results: Eleven randomized controlled trials were included. In this meta-analysis, ginseng treatment significantly lowered systolic blood pressure (SBP) in a dose-independent way (MD: -1.99, p = 0.04). In subgroup analysis, 8-12 week consumption of ginseng achieved significantly greater reduction in SBP (MD: -3.14, p = 0.03), while single administration of ginseng failed to show BP-lowering effect. When ingested over 8-12 weeks, ginseng significantly lowered diastolic blood pressure (DBP) (MD: -1.96, p = 0.03). No significant association was found between ginseng dose and the magnitude of BP-lowering effect. However, a significant positive relationship was observed between baseline SBP level and the magnitude of SBP reduction (r = 0.848, p = 0.033). Such a relationship was not seen in DBP. Conclusion: Consumption of ginseng for 8-12 weeks achieved significant reductions in SBP and DBP in a dose-independent way. There was a significant positive relationship between baseline SBP level and the magnitude of SBP reduction.

• Journal of ILASS-Korea
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• v.4 no.1
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• pp.34-44
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• 1999

The purposes of this study were to evaluate engine performance and to analyze smoke emission characteristics for varied injection pressures and engine operating conditions of an electronically-controlled ultra high pressure fuel injection system(UHPFIS). It was discovered that the engine performance with the present UHPFIS was far better than what was initially expected. And the UHPFIS permitted engine operation at air/fuel ratios richer than 20 : 1 without increasing smoke emissions. It was discovered that the indicated mean effective pressure was increased, while the specific fuel consumption and the amount of soot were decreased, as the fuel rail pressures were improved atomization of the fuel spray. As the intake air temperature was increased from $38\sim205^{\circ}C$ in 38 degree increments, the indicated mean effective pressure was dropped while the specific fuel consumption was increased.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.5
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• pp.140-147
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• 2001

The solenoid valve in ABS hydraulics, modulator is a two directional on-off valve and is controlled by around 100Hz high speed pulse width modulation. When the inlet valve is switched from open state to closed state, there are braking force degration, noise and vibration due to pressure surge phenomena in the hydraulic line and wheel cylinder. In this study, identifies pressure surge phenomenon in the braking process of a ABS, and investigates the way to reduce the phenomenon. For the purpose theoretical analysis on the pressure surge in the closed state hydraulic line, characteristic curve method based on wave equation was utilized. During this analysis, we could find pressure surge characteristics change due to hydraulic line change and PWM control conditions. In conclusion, by using the results of this study for the pressure surge prediction and reduction method, we could expect braking performance enhancement in Anti-Lock Braking System.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.505-508
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• 1995

This paper suggests new hydraulic circuit to control the pressure of clutches and brakes which has several advantages than conventional hydraulic circuit in automatic transmissions. In conventional hydraulic circuit, the pressures of all friction elements are controlled by only one pressure control valve and accumlators. So, controllable range is limited and it is unable to control the friction elements independently. Therefore, we can not do the fine control of timing between apply clutch and release clutch which is needed in clutch-to clutch shifting automatic transmissions. To overcome these faults, we designed the direct-acting hydraulic circuit where one pressure control valve and pressure control solenoid valve are allocated to each friction element and control that independently. Through this structural improvement of hydraulic circuit, we can achieve elaborate aontrol to clutch pressure. Specially, We can control the timing between apply clutch and release clutch delicately which is needed in clutch-to-clutch shifting.

• International Journal of Precision Engineering and Manufacturing
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• v.8 no.3
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• pp.8-13
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• 2007

A hybrid fuzzy PID controller for a pneumatic chamber is proposed in this paper. First, a mathematical model of a pneumatic pressure servocontrol system was developed where separate implementations of a PID controller and a fuzzy controller were made. The experimental results using a step input signal revealed that the PID controller accurately controlled the steady-state pressure but did not robustly handle parameter variations in the system while the fuzzy controller provided a fast rise time and low overshoot of the pressure in the system. In order to attain the advantages of both the fuzzy and PID controllers, a hybrid control scheme was developed. The experimental results show that the hybrid fuzzy PID controller proposed in this study does indeed possess the advantages of both PID and fuzzy controllers. Hence, it can be concluded that the hybrid fuzzy PID controller is suited for high-precision control of pressure in a pneumatic chamber.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.3
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• pp.192-200
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• 2002

Semi-active suspension systems are greatly expected to be in the mainstream of future controlled suspensions for passenger cars. In this study, a continuous variable damper for a passenger car suspension is developed, which is controlled actively and exhibits high performance with light weight, low cost, and low energy consumption. To get fast response of the damper, reverse damping mechanism is adapted, and to get small pressure change rate after blow-off, a pilot controlled proportional valve is designed and analyzed. The reverse continuous variable damper is designed as a HS-SH damper that offers good body control with reduced transferred input force from tire, compared with any other type of suspension system. The damper structure is designed, so that rebound and compression damping force can be tuned independently, of which variable valve is placed externally. The rate of pressure change with respect to the flow rate after blow-off becomes smooth when the fixed orifice size increases, which means that the blow-off slope is controllable using the fixed orifice size. The damping force variance is wide and continuous, and is controlled by the spool opening, of which scheme is usually adapted in proportional valves. The reverse continuous variable damper developed in this study is expected to be utilized in the semi-active suspension systems in passenger cars after its performance and simplicity of the design is confirmed through real car test.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.8
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• pp.2480-2490
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• 1996

This paper presents a new type of hydraulic servo chllinder which is characterized by its simple construction and an ubtegrated feedback mechanism. Piston position of the cylinder is controlled by eletrical input and mechamical feedback deduced from its own structure. Hydraulic pressure in each cylinder room is controlled by a poppet valve. The poppet is activated by a solenoid and is linked to the piston. Solenoid input current pulls up the poppet, which results in pressure drop and thus piston motion. The piston motion generates pull down force on the poppet by the linkage and the motion stops at equilibrium. In that way the piston position is controlled by an expernal input current. Characteristics of the servo cylinder is verified by stability analysis, tranient vehavior and steady state positing for step input. Design parameter analyses have been executed by derivation of analytical approximate solutions and by computer simulations. A prototype hydraulic servo cylinder is developed and tested. The experimental results show successful function of the servo cylinder and consistency with the theoritical results.