• 대한기계학회논문집
• /
• 제14권2호
• /
• pp.298-309
• /
• 1990

In this paper, a new method is suggested to analyze impulsive stresses at loading poing of concentrated impact load under certain impact conditions determined by impact velocity, stiffness of plate and mass of impact body, etc. The impulsive stresses are analyzed by using the three dimensional dynamic theory of elasticity so as to analytically clarify the generation phenomenon of cone crack at the impact fracture of fragile materials (to be discussed if the second paper). The Lagrange's plate theory and Hertz's law of contact theory are used for the analysis of impact load, and the approximate equation of impact load is suggested to analyze the impulsive stresses at the impact point to decide the ranage of impact load factor. When impact load factors are over and under 0.263, approximate equations are suggested to be F(t)=Aexp(-Bt)sinCt and F(t)=Aexp(-bt) {1-exp(Ct)} respectively. Also, the inverse Laplace transformation is done by using the F.F.T.(fast fourier transform) algorithm. And in order to clarity the validity of stress analysis method, experiments on strain fluctuation at impact point are performed on a supported square glass plate. Finally, these analytical results are shown to be in close agreement with experimental results.

• 한국화재소방학회논문지
• /
• 제24권5호
• /
• pp.115-121
• /
• 2010

이 연구에서는 암모늄염을 처리한 리기다 소나무의 연소성을 시험하였다. 실온에서 3종류의 암모늄염 즉, 황산암모늄, 제1인산암모늄, 그리고 제2인산암모늄의 20wt% 수용액에 각각 리기다 소나무를 함침시켜 건조시킨 후 콘칼로리미터(ISO 5660-1)를 이용하여 그의 연소성을 시험하였다. 암모늄염으로 처리한 시험편은 처리하지 않은 시험편에 비하여 그의 연소성을 감소 시켰다. 이것은 연소 억제성이 순수 리기다 소나무 시험편에 처리한 암모늄염 때문에 향상된 것으로 생각된다. 또한 암모늄염으로 처리한 시험편은 처리하지 않은 시험편에 비해 낮은 최대열방출률과 낮은 총방출열량을 나타내었다.

• 한국응용과학기술학회지
• /
• 제33권3호
• /
• pp.540-548
• /
• 2016

sodium bis-(2-ethylhexyl)sulfosuccinate-water 라멜라 액정의 비뉴톤 유동곡선을 cone-plate 레오메타를 사용하여 여러 농도와 온도 조건에서 얻었다. 이러한 비뉴톤 유동곡선을 비뉴톤 유동식에 적용하여 유동파라메타를 구하였다. 특별히 주목할 점은 액정시료의 전단속도에 대한 전단응력은 증가와 감소에서 틱소트로피와 다일레턴시 현상을 보여 hysteresis loop를 나타내고 있다는 점이다. sodium bis-(2-ethylhexyl)sulfosuccinate-water 라멜라 액정은 작은 전단속도에서는 약한 젤 현상을 보이지만 응력이 한계 응력 이상에서는 비 선형 점탄성 성질을 나타낸다. 전단속도 감소에서 분산계는 전단속도가 증가할 때 측정된 값 보다는 큰 구조변화와 전단응력을 유지하고 있다.

• 대한기계학회논문집B
• /
• 제27권4호
• /
• pp.466-475
• /
• 2003

The gun-type gas burner adopted in this study is generally composed of eight slits and swirl vanes. Thus, this paper is studied to investigate the effect of slits and swirl vanes on the turbulent flow fields in the horizontal plane of gas swirl burner with a cone type baffle plate measured by using X-probe from hot-wire anemometer system. This experiment is carried out at flow rate 450 $\ell$/min in the test section of subsonic wind tunnel. The axial mean velocity component in the case of burner model with only swirl vanes shows the characteristic that spreads more remarkably toward the radial direction than axial one, it does, however, directly opposite tendency in the case of burner model with only slits. Consequently. both slits and swirl vanes composing of gun-type gas burner play an important role in decrease of the speed near slits and increase of the flow speed in the central part of a burner because the biggest speed spurted from slits encircles rotational flow by swirl vanes and it drives main flow toward the axial direction. Moreover, the turbulent intensities and turbulent kinetic energy of gun-type gas burner are distributed with a fairly bigger size within X/R<0.6410 than burner models which have only slits or swirl vanes because the rotational flow by swirl vanes and the fast jet flow by slits increase flow mixing, diffusion, and mean velocity gradient effectively.

• Imaging Science in Dentistry
• /
• 제52권1호
• /
• pp.75-82
• /
• 2022

Purpose: This cross-sectional study evaluated and categorized the tomographic sagittal root position (SRP) of the maxillary anterior teeth in a Brazilian population. Materials and Methods: Cone-beam computed tomographic scans of 420 maxillary anterior teeth of 70 patients (35 men and 35 women, mean age 25.2±5.9 years) were evaluated. The SRP was classified as class I, II, III, or IV. In class I, the root is positioned against the buccal cortical plate; in class II, the root is centered in the middle of the alveolar housing; in class III, the root is positioned against the palatal cortical plate; and in class IV, at least two-thirds of the root engage both the buccal and palatal cortical plates. Results: In total, 274 teeth (65.2%) were class I, 39 (9.3%) were class II, 3 (0.7%) were class III, and 104 (24.8%) were class IV. The frequency distribution over the teeth groups was different from the overall analysis. Important differences were found in the frequencies of classes I, II, and IV compared to other populations. Sex was not associated with the SRP classes (P=0.307). Age distribution was significantly different over the classes (P=0.004). Conclusion: The findings of this study on the distribution of SRP classes among the Brazilian population compared to other populations demonstrate that the SRP should be analyzed on a case-by-case basis for an accurate treatment plan in the maxillary anterior area.

• 구강회복응용과학지
• /
• 제31권3호
• /
• pp.169-177
• /
• 2015

목적: 한국인의 상악 전치부 순측골 두께와 치은 생체형(gingival biotype)의 분포 및 상관관계를 평가하는 것이다. 연구 재료 및 방법: 본 연구는 부산대학교치과병원에 내원한 57명의 환자, 335개의 치아를 대상으로 시행되었다. Cone Beam Computed Tomography (CBCT)를 이용하여 백악법랑경계로부터 4 mm, 6 mm, 8 mm 지점의 순측골 두께를 측정하였고, 치은 생체형은 치주탐침자를 이용하여 평가하였다. 결과: 대부분의 대상치아에서 1 mm 이하의 얇은 순측골(4 mm 지점 87%, 6 mm 지점 88%, 8 mm 지점 90%)이 우세하게 관찰되었고, 전체 대상자의 21%에서 얇은 치은 생체형이 확인되었다. 치은 생체형과 순측골 두께 사이의 유의한 상관관계는 존재하지 않았다. 결론: 성공적인 전치부 심미 임플란트 치료를 위해서는 치은 생체형 검사 같은 임상적 검사 이외에 순측골 평가를 위한 추가적 CBCT 등의 방사선 검사가 필수적이다.

• 대한조선학회논문집
• /
• 제52권4호
• /
• pp.305-314
• /
• 2015

In this paper, a numerical analysis is carried out to study the drag of conical cavitators, supercavity generation devices for the high-speed underwater vehicle. The realizable k-∊ turbulence model and the Schnerr-Sauer cavitation model are applied to calculate steady-state supercavitating flows around cones of various cone angles. The calculated drags of the cones are decomposed of the pressure and the friction parts and their dependency on the geometry and the flow conditions have been analyzed. It is confirmed that the pressure drag coefficients of the cones can be estimated by a simple function of both the cone angle and the cavitation number while the friction drag coefficients approximately by well-known empirical formulas, e.g., Schults-Grunow's for the drag of the flat plate. Finally a practical method for estimating the total drags of supercavitating cones is suggested, which can be useful consequently for the design of conical cavitaors.

• 한국정밀공학회지
• /
• 제32권2호
• /
• pp.167-172
• /
• 2015

In order to prevent crack in thick weld zones, the preheating process such as induction and gas torch heating needs to be applied. Among them induction heating is the most effective heat source because it has rare thermal effect and very rapid heating characteristics. In this paper, when the induction heating method is used to improve arc welding, the temperature distribution and magnetic field density of the welding zones are analyzed by simultaneously solving heat transfer and electromagnetic field equation. In particular, cone and flat type coils are designed and induction heating effects of each type are compared to identify heating characteristics on a V-groove weld joint. As a result, a cone shape coil is more efficient in the preheating process. When induction heating and arc welding system is designed for thick plate with V-groove weld joint, the results in this paper could be applied.

• Imaging Science in Dentistry
• /
• 제37권4호
• /
• pp.197-203
• /
• 2007

Purpose: To provide diagnostic information by evaluation of the positional relationship between the mandibular third molar and the mandibular canal. Materials and Methods: Eighty-nine mandibular third molars were classified as mesioangular, horizontal, vertical, distoangular groups. The distances between the mandibular third molar and the mandibular canal were measured in cone-beam computed tomographs. The height and width ratios of distances from the mandibular third molar and the mandibular canal to the mandibular inferior border and to the lingual cortical plate were calculated. Results: The vertical and buccolingual distances between the mandibular third molar and the mandibular canal were 0.03 mm, 2.96 mm in the mesioangular, 0.37 mm, 3.38 mm in the horizontal, -1.50 mm, 1.38 mm in the vertical, -1.10 mm, 4.20 mm in the distoangular group. There were significant differences in vertical (P < 0.05), but not in buccolingual (P>0.05). The height and width ratios of distances on the mandibular third molar were 47.1 %, 36.1 % in the mesioangular, 47.4%, 34.4% in the horizontal, 37.0%, 46.7% in the vertical, 40.9%, 37.4% in the distoangular group. There were significant differences between the mesioangular and the vertical group, and the horizontal and the vertical group in height ratio (P < 0.05), and also between the mesioangular and the vertical group in width ratio (P < 0.05). The height and width ratios of distances on the mandibular canal showed no significant differences between groups (P > 0.05). Conclusion : The mesioangular group showed the nearest distance between the mandibular third molar and the mandibular canal vertically. The root apex of the mandibular third molar was positioned more buccally in the vertical group than in the mesioangular group.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 추계학술대회논문집B
• /
• pp.341-346
• /
• 2001

The gun-type gas burner adopted in this study is generally composed of some slits and swirl vanes. Therefore, this paper is studied to investigate the effect of slits and swirl vanes on the turbulent flow fields in the horizontal plane of gas swirl burner with a cone type baffle plate measured by using X-probe from hot-wire anemometer system. This experiment is carried out at flow rate $450\;{\ell}/min$, which is equivalent to the combustion air flow rate necessary for heat release 15,000 kcal/hr in gas furnace, in the test section of subsonic wind tunnel. When the burner has only swirl vanes, the axial mean velocity component shows the characteristic that spreads more remarkably toward radial direction than axial one, but when it has only slits, that is developed spreading more toward axial direction than radial one. Therefore, because the biggest speed is spurted in slits and it derive main flow toward axial direction encircling rotational flow that comes out from swirl vane that is situated on the inside of slits, both slits and swirl vanes composing of cone type gas burner act role that decreases the speed near slits and increases the flow speed in the central part of a burner. Moreover, because rotational flow by swirl vanes and fast jet flow by slits increase turbulent intensities effectively coexisting, the turbulent kinetic energy is distributed with a bigger size fairly near slits than burner models which have only slit or swirl vanes within X/R<0.6410.