• 소성∙가공
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• 제19권8호
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• pp.480-485
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• 2010

In this work, the closing behavior of cylindrical-shaped voids was experimentally investigated according to various parameters such as reduction ratio in height, initial void size and billet rotation during hot open die forging process. The reduction ratio in height, number of path, and billet rotation were chosen as key process parameters which influence the void closing behavior including the change of void shape and size. On the other hand, values of die overlapping and die width ratio were set to be constant. Void closing behavior was estimated by microscopic observation. Based on the observations, it was confirmed that application of billet rotation is more efficient to eliminate the void with less reduction ratio in height. The experimental results obtained from this study could be helpful to establish the optimum path schedule of open die forging process.

• 소성∙가공
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• 제20권5호
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• pp.339-343
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• 2011

This paper presents methods for analyzing the extent of cylindrical-shaped void closure. In addition, a quantitative relationship between change in void fraction and height reduction ratio of a compressed specimen is proposed. The height reduction ratio, number of deformation steps and billet rotation were chosen as key process parameters influencing the void closing behavior, namely, the changes in void shape and size during hot open die forging of a large ingot. The extent of void closure was analyzed from microscopic observations and estimated from tensile test results. The tensile strengths of specimens with closed voids and those without were compared for various reduction ratios in height. The results confirmed that void closure occurs at reduction ratios greater than 30 %. The void closing behavior could be expressed as a hyperbolic tangent function of reduction ratio in height, number of paths, and billet rotation. The knowledge presented in this paper could be helpful for optimizing deformation paths in open die forging processes.

• 대한치과교정학회지
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• 제30권3호
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• pp.367-375
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• 2000

하악전돌증(mandibular prognathism or mandibular prognathic patient) 환자의 경우 전후방과 수직적 악골(maxilla)의 부조화정도가 심하거나 안면측모(facial profile)에 대한 심미적 인식도가 클 때에는 교정치료만으로는 심미적으로 만족한 결과를 얻기가 어려우므로 악교정수술(orthognathc surgery)과 병행되어야만 한다. 이럴 경우 심미적인 개선은 환자의 치료결과에 대한 만족도에 중요한 요소가 되고 있지만 미에 대한 기준을 객관화하는데는 많은 문제점을 갖고 있어 그 평가도 환자자신의 주관적인 관점에 의하여 내려지게 된다. 우리나라의 경우 얼굴심미에 대한 기준이 서구인의 외형을 선호하는 경향이 있어 전통적인 둥그런 얼굴보다는 달걀형의 갸름한 얼굴모양을 선호한다. 이 연구는 하악전돌증으로 인한 악교정수술결과 술후 얼굴폭이 넓어져 수술전보다 얼굴의 모양이 둥그렇게 되었다고 호소하는 환자가 있어 시도하게 되었다. 악교정수술전후의 안모길이 및 폭경의 변화에 관한 연구를 위하여 하악전돌증을 주소로 악교정수술을 받은 총 14명 환자(남자 8명, 여자 6명)의 정모두부방사선사진 계측(skull PA analysis)과 설문조사를 통하여 수술후의 안모변화 및 환자의 만족도에 대한 분석을 시행하여 다음과 같은 결론을 얻었다. 1. 14명의 환자중 3명($21.4\%$)이 얼굴이 넓어졌다고 답하였다. 2. 악교정수술(orthognathic surgery)후 하악골폭경 (mandibular width)은 A군은 변화가 없었으며, B군은 0.7mm 감소하였고, 안면폭경 (zygomatic width)은 A군에서는 0.45mm, B군에서는 0.66mm의 증가를 보였다. 3. 악교정수술후 얼굴길이의 변화는 A군에서는 상안면 고경(upper facial height)이 0.52mm증가, 하안면고경(lower facial height)이 1.19mm감소, 하악골 고경(mandibular height)이 0.7mm감소하였으며, B군에서는 상안면 고경이 0.67mm 감소, 하안면고경이 3.66mm 감소, 하악골 고경이 5mn감소하였다. 4. 수술후 안면폭경에 대한 안면고경(facial height)의 비율은 A군에서 $1.5\%$, B군에서 ,$3.6\%$ 감소하였다. 5. 수술후 안면폭경에 대한 하악골 길이(mandibular height)의 비율은 A군에선 $1.3\%$, B군에서 $4.4\%$ 감소하였다. 6. 수술후 하악골폭경에 대한 하악골 길이(mandibular height)의 비율은 A군에서 $1.3\%$, B군에서 $4.3\%$ 감소하였다. 7. 수술로 인한 얼굴폭의 변화는 무시할만한 것으로 판단되나 수술후 얼굴의 길이가 짧아져 상대적으로 얼굴의 폭이 넓어보일 수 있으므로 수술시 이에 대한 충분한 고려 및 환자에 대한 설명이 있어야 한다.

• 소성∙가공
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• 제3권3호
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• pp.291-301
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• 1994

In the simultaneous forward-backward extrusion the effects of some process variables including area reduction, stroke advance, materials(Al 2024 and commercial pure copper) on the extrusion load, plastic flow and height ratio of upper to lower extruded parts are experimentally investigated and analyzed. Grid-marking technique is employed to visualize the plastic flow. The influence of using split and original specimen on the extrusion load and height ratio is evaluated by experiments. Experimental results show that the plastic flow if oriented to the part of lower area reduction in the begining but it is usually variated during the overall process. The configurations of plastic deformation and plastic flow are dependent on the working materials and the lubricational conditions.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1994년도 춘계학술대회 논문집
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• pp.175-182
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• 1994

Effect of some process variables including area reduction, stroke advance, materials on the extrusion load, plastic flow and height ratio of upper to lower extruded parts in the cup-cup axisymmetric extrusion were experimentally investigated and analyzed. Deformed pattern is visualized by grid-marking technique using half-cut billets splitted. The influence of using split specimen and original specimen on the extrusion load and height ratio is examined by experiment.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.160-167
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• 2008

The effects of squealer rim height on three-dimensional flows and aerodynamic losses downstream of a high-turning turbine rotor blade have been investigated for a typical tip gap-to-chord ratio of h/c=2.0%. The squealer rim height-to-chord ratio is changed to be $h_{st}/c$=0.00(plane tip), 1.37, 2.75, 5.51, and 8.26%. Results show that as $h_{st}/c$ increases, the tip leakage vortex tends to be weakened and the interaction between the tip leakage vortex and the passage vortex becomes less severe. The squealer rim height plays an important role in the reduction of aerodynamic loss when $h_{st}/c{\leq}2.75%$. In the case of $h_{st}/c{\geq}5.51%$, higher squealer rim cannot provide an effective reduction in aerodynamic loss. The aerodynamic loss reduction by increasing $h_{st}/c$ is limited only to the near-tip region within a quarter of the span from the casing wall.

• 복합신소재구조학회 논문집
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• 제4권3호
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• pp.7-12
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• 2013

The demand for the structural system of reduction of story height increases because buildings are getting higher. The existing structural systems are not efficiency. Thus, it is hard to reduce the story height and existing methods cannot secure economics as expected. This study aims at developing the partially concrete-filled new type composite beam, which can efficiently resist against the end negative moment and central positive moment, also reduce deflection of beams. Through case studies on loading of concentrated load and uniformly distributed load to fixed beam, we could find the most efficient ratio of moment of inertia and the ratio ${\alpha}$(end beam length to span). The gap space between middle and end beam can be used as facilities installation, consequently the suggested Omega beam system is expected to get the effect of reduction in story height as well as reduction of quantity.

• 대한방사선기술학회지:방사선기술과학
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• 제45권4호
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• pp.313-320
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• 2022

Both angiography and interventional procedures accompanied by angiography provide many diagnostic and therapeutic benefits to patients and are rapidly increasing. However, unlike general radiography or computed tomography using the same X-ray, the amount of radiation is quite high, but the dose range can vary considerably for each patient and operator. The high sensitivity of the lens to radiation during cerebral angiography and neurointervention is already well known, and although there are many related studies, it is insufficient to easily reduce radiation in diagnosis and treatment. In this situation, in particular, by adding three-dimensional rotational angiography (3D-RA) to the existing two-dimensional (2D) angiography, it is now possible to make an accurate diagnosis. However, since this 3D-RA acquires images through projection of more radiation than before, the exposure dose of the lens may be higher. Therefore, we tried to analyze whether the radiation dose of the lens can be reduced by moving the lens out of the field range by adjusting the table height and magnification ratio during the examination using 3D-RA. The surface dose was measured using a rando phantom and a radiophotoluminescent glass dosimeter (PLD) and the radiation dose was compared by adjusting the table height and magnification ratio based on the central point. As a result, it was found that the radiation dose of the lens decreased as the table height increased from the central point, that is, as the lens was out of the field of view. In conclusion, in 3D-RA, moving the table position of about 2 cm in height will make a significant contribution to the dose reduction of the lens, and it was confirmed that adjusting the magnification ratio can also reduce the surface dose of the lens.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.114-117
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• 2009

In this work, closing behavior of the voids generated in a casting process was investigated for various parameters such as reductions in height void size and billet rotation during hot open die forging process. The reduction in height and path schedule including the number of paths and billet rotation were chosen as key process variables to express the change of geometrical void shape and void closing behavior. On the other hand, values of die overlapping and die width ratio were set to be constant. Extend of void closure was observed and evaluated using tensile test and microscope. Based on the experimental result, it is ensured that void closure do not occur at 15% and 30% reduction in height as well as one or two rotations of a billet. The useful datum obtained from this study could be utilized to establish an optimum path schedule in the open die forging process.

• Geomechanics and Engineering
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• 제2권1호
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• pp.29-44
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• 2010

Vertical vibration tests were conducted using model footings of different size and mass resting on the surface of finite sand layer with different height to width ratios which was underlain by either rigid concrete base, under both dry and saturated condition. The effect of saturation on the damping ratio of finite sand stratum underlain by a rigid base has been verified and compared with the results obtained for the case of finite dry sand stratum underlain by the rigid base. Comparison of results of the experimental study showed that the damping in both the cases is less than 10%. The damping ratio obtained for finite saturated sand stratum is marginally lower than that obtained on finite dry sand stratum at H/B ratio of 0.5. The difference between the two cases becomes significant when the H/B ratio increases to 3.0, indicating the significant influence of soil moisture on damping ratio of foundation- soil system with increase in the thickness of the finite sand stratum. Comparison of the predicted damping ratio for a homogeneous sand stratum with the experimental damping ratio obtained corresponding to the height to width ratio of 3.0 of the finite sand stratum underlain by the rigid concrete base indicates a significant reduction in damping ratio of the foundation-soil system for both the cases.