• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.303-312
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• 2003

This paper suggests a fuzzy expert system for fault diagnosis of rotating machinery, based on modulated databases. In the proposed system, alarm and trip levels are set based on ISO, considering operating condition, machinery type and maintenance history. Input signals for diagnosis, such as sub- and super-harmonic components of vibration and mean value, are normalized from 0 to 1 under the threshold level and otherwise equal to one so that chronic faults slightly below the threshold level can be monitored. The database for diagnosis consists of two modules: the well-known Sohre's chart module and if-then type rules. The Sohre's chart is utilized for the most common problems of high-speed turbomachinery, while the rule-based module, which was collected from many papers and reports, is for diagnosing peculiar faults according to the type of machinery. To infer the results from two modules, a fuzzy operation of Yager sum was adopted. Using a simulator constructed in laboratory, experimental verification was performed for the cases of resonance and housing looseness which were intended. The experimental results show that the proposed fuzzy expert system has feasibility in practical diagnosis of rotating machinery.

• 한국생산제조학회지
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• 제7권1호
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• pp.51-57
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• 1998

In order to minimize vibration problems of rotating machinery rotors have been assembled through balancing machines. Since perfect balancing is impossible, residual unbalances cause serious vibration while the rotor is in high speed region. To minimize unbalance effects of magnetic bearing systems (AMB) during rotation on-line balancing methodology was studied. Unbalances were considered as disturbances of the system. The disturbance observer was used to estimate unbalance force from measurable state and input variables. Balancing inputs computed according to LQR and outputs of the observer were applied to eliminate unbalances during high speed rotation of the AMB. the effectiveness of the on-line balancing was verified through numerical simulations.

• 한국정밀공학회지
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• 제17권12호
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• pp.151-156
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• 2000

A vibration in a high-speed machine may lead to machinery malfunction and even catastrophic failure. So solving the vibration problem is a fundamental requirement for the stability of the high-speed machine. The flywheel energy storage system using superconducting magnetic bearings is a device to store electrical energy as rotational kinetic energy by motor and to convert it to electrical by generator when necessary. The high-speed rotating flywheel has large amplitude at a critical speed. And it has an unstable behavior by the electric torque at the first stage of the energy generation. In this paper, the stability analysis is performed with an analytical model and equations of motion-which is considered the effect of the electric torque-to identify the stable driving condition and the dynamic behavior.

• Tribology and Lubricants
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• 제21권1호
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• pp.8-15
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• 2005

In this study a general Galerkin FE lubrication analysis method is utilized to analyze the complex lubrication performance of a spiral groove seal, which is being designed and developed for a high-speed flying object application operating at a high-speed of over 50,000 rpm. As at the equilibrium seal clearance the axial stiffness of the seal is predicted to have almost such a constant high value of $1.04\times10^8\;N/m$ regardless of a rotating speed, the seal is expected to maintain a stable thickness of lubrication film under a certain external excitation acting. Also, as even at an ultra high-speed of 80,000 rpm the axial damping of the seal is shown to have a rotatively high value of 5,775 N-s/m, the dynamic stability of the seal system at the axial degree of freedom is assured well enough.

• Tribology and Lubricants
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• 제21권2호
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• pp.53-62
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• 2005

In this study a general Galerkin FE lubrication analysis method was utilized to analyze the complex lubrication performance of a spiral groove seal having an additional inner circular groove, which was designed for a chemical process mixer operating at a low speed of the maximum 500 rpm. Equilibrium seal clearance analyses under varying outer pressure revealed that the seal maintains a certain levitation seal clearance under the outer pressure of more than about 1.5 bar, regardless of a rotating speed. Also, under the normal outer pressure of 11 bar, the axial stiffness of the seal was predicted to have a high value of more than 7.0 e + 07 N/m, regardless of a rotating speed and thereby, the seal is expected to maintain a stable thickness of lubrication film under a certain external excitation acting. A seal levitation test rig was designed and constructed. Experimental results at 500 rpm agreed well with analytical predictions and the applied lubrication analysis method was verified.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.513-517
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• 2005

The condition monitoring of rotating machinery such as turbines, pumps and compressors, determine what repairs are needed to avoid shutdown and disassembly of the machine in an industrial plant Many diagnosis methods have been developed for use when the machine is running at steady state, the stationary condition. But much information can be gained about a rotor's condition during non-stationary conditions such as run-up and run-down. Order tracking analysis is a powerful tool for analyzing the condition of a rotating machine when its speed changes over time. Powerful OTA using digital signal processing has some advantages(cheap hardware, the powerful methods, the accurate post processing) and also some disadvantages(calculation time, high speed sampling). New OTA tool based on the chirplet transform is similar to the short time Fourier transform. But, it has good resolution at high speed like other OTA methods based STFT and more resolution for constant frequency components than re-sampling OTA.

• 한국유체기계학회 논문집
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• 제6권2호
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• pp.62-69
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• 2003

An oil-free turbo-compressor supported by compliant foil bearings which remove oil-contamination by elimination of a conventional ball bearing and oil lubrication systems is presented. Turbo-compressor makes two individual air compressions with two impellers at a operating speed of 39,000 rpm. In this study, the rotordynamic effects caused by aerodynamic instability were investigated with variable mass flow rates. Correlations between frequencies of pressure fluctuation in two diffusers and those of excitation forces on rotor were clearly observed in an aerodynamic unsteady region. Thus, these results show that it is beneficial to design high-speed rotating turbomachinery by considering coupling effect between aerodynamic instability and rotordynamic force.

• 한국유체기계학회 논문집
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• 제15권6호
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• pp.64-69
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• 2012

This paper deals with the study on repair case of journal shaft and bearing damage in 25MW industrial gas turbine caused by sudden blackout, operation mistake, and logic abnormal, etc. When a serious accident such as journal and bearing damage in a gas turbine occurs, the domestic local companies having the gas turbine are dependent on manufacturer for all maintenance and repair schedule until now. This case study shows that the damaged gas turbine is normally re-operated itself in domestic by establishing repair schedule in a short period of time, repairing damage journal shaft and tilting pad bearings, and performing rotating test for a reliability check. This paper can be regarded as the important case study of emergency test run experience of the refurbished 25MW gas turbine rotor.

• 한국유체기계학회 논문집
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• 제18권6호
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• pp.12-18
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• 2015

Recently, the development trend of turbomachinery is high capacity and high efficiency. Most of turbomachinery in the market are adopting ball bearings or air foil bearings. However, ball bearings have a limit for high speed product over $2.0{\times}10^6DN$(product of the inner diameter of the bearing in mm (D) and the maximum speed in rpm (N)). Air foil bearings have a limit for high axial load for high power products over 200~300 HP(horse power). Magnetic bearing is one of the solutions to overcome the limits of high speed and high axial load. Because magnetic bearings have no friction between the rotor and the bearings, they can reduce the load of the motor and make it possible to increase the rotating speed up to $5.0{\times}10^6DN$. Moreover, they can have high axial load capacity, because the axial load capacity of magnetic bearing depends on the capacity of the designed electromagnet. In this study, the radial and thrust magnetic bearings are designed to be applied to the 200 HP class turbo blower, and their performance was evaluated by the experiment. Based on the tests up to 26,400 rpm and 21,000 rpm under the no-load and load condition, respectively, it was verified that the magnetic bearings are stably support the rotor of the turbo blower.

• 한국유체기계학회 논문집
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• 제5권1호
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• pp.33-41
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• 2002

Low NPSH and high pressure pumps we widely used for turbopump systems, which have an inducer and operate at high rotating speeds. In this paper, a meanline method has been established for the preliminary design and performance prediction of pumps having an inducer for cavitating or non-cavitating conditions at design or off-design points. The method was applied for the performance prediction of a fuel pump. Predicted performances by the method are shown to be in good agreement with experimental results for cavitating and non-cavitating conditions. The established meanline method can be used for the performance prediction and preliminary design of high speed pumps which have a inducer, impeller and volute.