• 대한기계학회논문집
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• 제18권5호
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• pp.1126-1133
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• 1994

When designing an internal gear. the bending strength around pitch point as well as that at tooth root fillet should be considered because the bending stress around pitch point may occur as high as that at tooth root fillet. In this study, including stress state around pitch point, the bending strength (tensile side and compressive side) of internal gear tooth is investigated by the use of the finite element method(FEM) with regarding many influencing factors of cutter and gear geometries. Then, the critical sections around pitch point and at tooth root fillet are determined, and the simple formulae based on nominal stresses(bending, compressive, and shear) are derived for the calculations of actual stresses as the functions of tooth thicknesses and radii of curvatures of involute and fillet curve at those critical sections. The stresses calculated by the formulae agree well with those by the FEM. And the bending stresses around pitch point and at tooth root are easily estimated by the use of those formulae, therefore, those formulae are useful for the purpose of the design or the bending strength estimation of internal gear.

• 대한기계학회논문집B
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• 제29권7호
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• pp.784-794
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• 2005

In the very low specific speed range ($n_s=0.24$ < 0.25, non-dimensional), the efficiency of centrifugal pump designed by a conventional method is very low in common. Therefore, positive-displacement pumps have long been used widely. Recently, since the centrifugal pumps are becoming higher in rotational speed and smaller in size, there expects to develop a new centrifugal pump with a high performance to replace the positive-displacement pumps. The purpose of this study is to investigate the internal flow characteristics of a very low specific speed centrifugal pump and to examine the effect of internal flow pattern on pump performance. The results show that the theoretical head definition of semi-open impeller should be revised by the consideration of high slip factor in the semi-open impeller, and the leakage flow through the tip clearance results in a large effect on the impeller internal flow. Strong reverse flow at the outlet of semi-open impeller reduces the absolute tangential velocity considerably, and the decreased absolute tangential velocity increasese the slip factor with the reduction of theoretical head.

• 한국소음진동공학회논문집
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• 제25권2호
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• pp.116-123
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• 2015

This paper proposed a new formula for predicting acoustic power transmission loss of simple expansion chamber with two internal partitions. Seventeen cases of computational results were performed and the database was constructed for the TL according to the various positions of internal partitions. Using this database, firstly, the formula for the peak values of TL at certain frequencies was developed using the least square estimation. Secondly, the formula for the TL curve could be obtained automatically with the input data of the positions of two internal partitions. The formula of TL developed in this paper showed good agreement with computational results. This formula will be helpful for the positioning of internal partitions to improve TL at target frequencies.

• 한국자동차공학회논문집
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• 제21권1호
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• pp.36-42
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• 2013

Recently, the automobile of the future will be able to substitute an electric vehicle for an internal combustion engine, so the following research is actively in the process of advancing. A traction motor is one of the core parts which compose the electric vehicle. Especially, it is difficult to connect cooling water piping to an in-wheel motor because the in-wheel motor is located within the wheel structure. This structure has disadvantage for closed type and air cooling, so the cooling design of motor housing and internal in-wheel motor is important. In this study, thermo-flow analysis of the in-wheel motor for vehicles was performed in consideration of ram air effect. In order to improve cooling efficiency of the motor, we variously changed geometries of housing and internal shape. As a result, we found that the cooling efficiency was most excellent, in case the cooling groove direction was same with air flow direction and arranged densely. Furthermore, we investigated the cooling performance enhancement with respect to variable geometries of internal in-wheel motor.

• 한국소음진동공학회논문집
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• 제22권10호
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• pp.1010-1019
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• 2012

Non-contact detection of internal defects in a rail using ultrasonic waves is discussed in this paper. Cracks in a rail may be the cause of a serious railway accident such as derailment if left undetected. Concurrent rail inspection method based on ultrasonic testing using piezoelectric transducers has several limitations as it should keep physical contact with the rail. This work suggests a non-contact detection of internal defects in a rail using ElectroMagnetic Acoustic Transducers (EMAT) which can produce and measure ultrasonic waves in a rail without any couplant. The EMATs for rail inspection are designed and fabricated and their working performance is verified through a series of experiments on various types of internal defects in test rails. The effect of lift-off between the transducers and the rail on the generated signals is also discussed.

• The Journal of Asian Finance, Economics and Business
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• 제8권2호
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• pp.223-230
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• 2021

The concept of Shariah-based internal audit has received increasing attention from researchers in recent times especially since Islamic financial institutions have been developing in several Asian countries like Bangladesh. To avoid financial irregularities and to maintain Shariah-based financial transactions, an effective Shariah-based internal audit system is extremely important for Islamic financial institutions such as Islamic banks. Hence, the objective of this study is to determine the factors that influence the effectiveness of the Shariah-based audit system. Study data has been gathered from Shariah auditors, members of the Shariah board and audit committee of six private Islamic banks in Dhaka, Bangladesh. A total of 210 survey questionnaires were sent and finally 136 responses were retained, indicating a final sample size of n=136, with a survey feedback rate of 65%. The study adopted a quantitative measure and collected only primary data, followed by convenience sampling. SPSS has been used to run necessary statistical interpretation. Results reveal that auditor's work autonomy, level of competency, and work performance significantly impact the Shariah-based internal audit effectiveness. The study findings can be adopted as guidelines to improve the overall effectiveness of the Shariah-based internal audit system in Islamic financial institutions.

• 대한기계학회논문집A
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• 제35권10호
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• pp.1243-1248
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• 2011

내부결함은 주조제품의 강도 및 피로 수명에 있어 상당한 영향을 미치기 때문에 주조공정에서 주요 관심사 이다. 일반적으로 내부결함은 응력집중을 발생시키며 균열의 시작점이 되므로 피로 수명과 같은 기계적 거동에 있어 수축공과 같은 결함을 이해하는 것이 중요하다. 본 논문에서는 내부결함을 고려한 인장시편에 대해 피로시험을 수행하고 주조결함을 고려할 때의 특정하중피로노치 계수를 산정하였다. 실제 내부결함은 산업용 CT 장비를 통해서 확인하였으며 확인된 결함은 형상단순화법에 의해 타원체로 단순화 하고 응력해석과 피로해석을 수행하였다. 그 결과 우리가 제안한 방법이 기계적 거동에 있어 내부결함의 영향을 조사하고 피로수명 등을 예측함에 있어 유용함을 확인할 수 있었다.

• 대한기계학회논문집
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• 제15권2호
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• pp.436-444
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• 1991

A computational method has been developed to analyze the bone-remodeling induced by external fixator. The method was based on the Finite Element Method (FEM) in combination with numerical formulation of adaptive bone-remodeling theories. As a feed-back control variable, compressive strain and effective stress were used to determine the surface remodeling and internal (density) remodeling respectively. Surface remodeling and internal remodeling were combined at each time step to predict the rel situation. A noticeable shape and density change were detected at the region between two pins and density change was decreased with time increment. At final time step, the shape and density distribution were converged closely to its original intact bone model. Similar change was detected in stress distribution. The altered stress distribution due to the pin and external fixator converged to the intact stress distribution with time.

• 한국자동차공학회논문집
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• 제9권5호
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• pp.82-88
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• 2001

The EGR is needed fur one of various strategies to reduce NOx emission. But to get the proper EGR rate, the intake and exhaust system become complicated. That is a reason why we consider using the internal EGR system. The internal EGR is a system which reduces NOx by controling the residual gas fraction in cylinder by changing valve timing and valve lift of intake and exhaust. In this paper, characteristics of volumetric efficiency and residual gas fraction in cylinder were investigated for various engine speeds by changing valve timing and valve lift of intake and exhaust in the 4 stroke-cycle diesel engine. Volumetric efficiency and residual gas fraction were calculated by the method of characteristics. As the results, residual gas fraction and volumetric efficiency in cylinder by variable valve timing were visualized.

• 대한기계학회논문집B
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• 제30권12호
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• pp.1196-1202
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• 2006

A MEMS methanol reformer was fabricated and its performance was evaluated in the present study. Catalytic steam reforming of methanol was selected because the process had been widely applied in macro scale reformers. Conventional Cu/ZnO catalyst that was prepared by co-precipitation method to give the highest coating quality was used. The reactor structure was made by bonding three layers of glass wafers. The internal structure of the wafer was fabricated by the wet-etching process that resulted in a high aspect ratio. The internal surface of the reactor was coated by catalyst and individual wafers were fusion-bonded to form the reactor structure. The internal volume of the microfabricated reactor was $0.3cm^3$ and the reactor produced exhaust gas with hydrogen concentration at 73%. The production rate of hydrogen was 4.16 ml/hr that could generate power of 350 mW in a typical PEM fuel cell.