• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.224-229
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• 2008

With the wide use of mobile phones, a paging signal by a sound transducer acts as an environmental noise on many occasions, thus necessitating an alternative paging signal by a vibration motor. Conventional vibration motors employ three-phase windings with mechanical brushes for commutation. In this paper, a new one-phase brushless and sensorless vibration motor is introduced utilizing digital signal processor chips in cell-phones. For electromagnetic field analysis, two-dimensional modeling can be implemented to determine the back electromotive force using axisymmetric boundary conditions. Geometric design parameters, such as coil pitch and magnet pitch. are considered for performance optimization. Through the experiments, it is shown that the proposed design has the equivalent performance with reduced number of parts, thus enhancing manufacturing productivity and reducing manufacturing cost.

• The KSFM Journal of Fluid Machinery
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• v.6 no.3 s.20
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• pp.7-14
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• 2003

It is addressed that the turbulent broadband sound power from a sirocco fan can be modeled by the trailing edge noise. The trailing edge noise is usually influenced by inflow turbulence, separation, and boundary layer thickness on the blade. The design parameters such as solidity (c/s) and stagger angle are specified to predict performance and noise level because the separation and slip velocity are strongly affected by them along with the flow coefficient. This paper reports the effects of the stagger angle upon the trailing edge noise for various trailing edge shapes. It is believed that the serrated trailing edge provides break-up mechanism for organized convecting vortices, thereby reduce the overall noise level for every case of stagger angle.

• Proceedings of the KIEE Conference
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• 2001.11c
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• pp.420-423
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• 2001

In this paper, the Multi-FNNs(Fuzzy-Neural Networks) architecture is identified and optimized using HCM(Hard C-Means) clustering method and genetic algorithms. The proposed Multi-FNNs architecture uses simplified inference and linear inference as fuzzy inference method and error back propagation algorithm as learning rules. Here, HCM clustering method, which is carried out for the process data preprocessing of system modeling, is utilized to determine the structure of Multi-FNNs according to the divisions of input-output space using I/O process data. Also, the parameters of Multi-FNNs model such as apexes of membership function, learning rates and momentum coefficients are adjusted using genetic algorithms. An aggregate performance index with a weighting factor is used to achieve a sound balance between approximation and generalization abilities of the model. To evaluate the performance of the proposed model we use the time series data for gas furnace and the NOx emission process data of gas turbine power plant.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.4
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• pp.662-669
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• 1988

The acoustical characteristics of silencer has been investigated by experimental methods. The relations between various geometrical parameters, i.e. length, diameter, offset and twisting angle of silencers and transmission loss have been studied. The effect of mean flow on the transmission loss was also investigated. Results show that experimental decomposition of flow and sound is possible. Experimental results which take into account for the effect of mean flows provide the accurated data which have not been found in the literature.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.8 s.239
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• pp.921-926
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• 2005

In the idealized model problem of the interaction between a planar travelling shock and a symmetric vortex, the physics of shock distortion and quadrupole sound generation are well known to many researchers. However, the authors have distinguished the weak waves reflected and transmitted by the complicated photograph images obtained from a shock tube experiment. In this paper, we introduces a parametric study based on Navier-Stokes simulation and Rankin vortex model to see the difference of shock deformation shapes. Four combination of the strength of shock and vortex are respectively selected from a parameter plane of shock and vortex strength extended to the strong vortex region. The result shows clearly discernable wave morphology for the main parameters, which is not yet explicitly mentioned by other researchers.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.6
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• pp.740-745
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• 2006

This study suggested the occurrence source of weld-defects and its solution methods in a welding of Electrolyte injection hole by pulsed Nd:YAG laser. In experiment, the ramp down was used in order that solidification crack was removed. Furthermore. shrinkage stress and heat input were reduced by changing of weld trajectory and defocused distance. As a results of a experiment, a sound weld bead shape and crack-free weld bead can be obtained. In conclusion this show that the welding stability is greatly affected by modulation of laser pulse shape for the same laser energy and welding parameters.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1998.10a
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• pp.90-96
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• 1998

There are various noises generated by friction. Among the rest, eliminating squeal noise generated during braking is an important task for the improvement of vehicle passengers' comfort. The parameters affecting brake squeal noise are the material properties of the braking pad, the dynamic properties of the brake parts and the dimensions of the brake assemble etc. Also, the squeal noise changes its inherent form(i.e. its sound pressure level and its frequency) with the normal load and sliding speed. In this study, the characteristics of brake squeal noise generated by friction is analyzed experimentally. The experiment focused on the analysis of friction self-excited vibrationand squeal noise level. Friction self-excited vibration is caused by the dry friction between pads and rotor, and occurs as a function of their relative sliding speeds. And Friction self-excited vibration is raised the brake squeal noise.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.967-972
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• 2001

An axial fan design code, called iDesignFan$^{TM}$, was developed. In this code, three major loss models were used to predicted the aerodynamic performance of a fan. The overall sound pressure level, predicted from steady blade loading, is also used as an input parameter from the third loop of the designing process to acquire most silent fan for the given aerodynamic performance parameters. With this kind of inverse design concept used in this code, the period of designing a fan, which has given aerodynamic performance with minimal acoustic noise, is significantly shortened. The experimental results of a prototype fan, designed by this code, showed that aerodynamic and acoustic performance of an axial fan is reasonably well predicted. Thus, one can design/develop an axial fan in a short time by using the code.e.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.393-398
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• 2001

Pulsations, vibration and stress are the basic dynamic phenomena in power plant piping systems which directly affect system reliability. These phenomena are both acoustical and mechanical in nature and are closely interrelated. It was noticed that thermodynamic parameters were changed after replacing with new type tube bundles of reheat exchanger. It was reported later that the drain piping connecting the new bundle header with the associated drain tank is regularly pulsating at about every 3 second with 13.4㎐ and 7.5mm, p-p in amplitude. This amplitude is about 6 times higher than reference level of sound piping. The results of finite element analysis of the pipeline showed that its dominant natural frequency is 13.4㎐. The soundness is predicted whether the bending dynamic stress evaluated excesses the maximum allowable high cycle fatigue stress or not by the measured amplitude of vibration.

• The Journal of the Acoustical Society of Korea
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• v.16 no.1E
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• pp.49-56
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• 1997

Ultrasonic cleaning at high frequency around 1 MHz, called megasonic cleaning, is commonly used to remove particles less than 1 ㎛ by generating high frequency accelerations on the cleaning objects. Cleaning is performed in an ultrasonically-excited liquid contained in a double-structured container. Ultrasonic waves generated by piezoelectric transducers propagate in the outer container and are transmitted through the inner container. The bottom of the inner container is inclined to make oblique incidence of the ultrasonic wave in order to raise the efficiency of the transmission through the bottom plate. This work deals with the efficiency of the transmission, which directly affects the cleaning performance. The transmission characteristics of the ultrasonic wave in the megasonic cleaner have been obtained analytically and numerically for the variations of some parameters, such as the thickness and inclined angle of the bottom plate of the inner container and the chemical ratio and temperature of the cleaning liquid. The calculated results have yielded the optimum cleaning condition in terms of the sound power transmitted into the cleaning liquid.