비선형 특성을 갖는 파이프 연결부에 대한 안전성

조재웅(Jae-Ung Cho),한문식(Moon-Sik Han) 한국기계가공학회 2007 한국기계가공학회지 Vol.6 No.2

Nonlinear property and contact matter are analyzed about the pipe applied with internal pressure through this study. The weakest part and its safety can be examined. Maximum equivalent stress is shown at the contact surface between bolt and nut. The value of contact stress with the pressure of 12㎫ is increased 1.4 times as large as that with no pressure. The maximum contact pressure is shown at the clamp corner of the external surface on pipe. The value of contact pressure with the pressure of 12㎫ is increased 1.4 times as large as that with no pressure. The radial deformation with no pressure is also increased greatly at the middle part of internal surface on pipe. But this maximum deformation on pipe with the pressure of 12㎫ is shown at the part far away the support of pipe. This value is increased 5.7 times as large as that value with no pressure. As contact status, the sticking occurs most at the external surface of pipe. It also tends to occur at the contact surface between bolt and nut. At the external surface of pipe, the sticking in case of the pressure of 12㎫ occurs more than that in case of no pressure.

당뇨 환자 보행 시 발 형태와 당뇨 수준에 따른 발바닥 부위별 족압 특성

김재원(Kim, Jae-Won),강윤희(Kang, Youn-Hee),홍영선(Hong, Young-Sun),권오란(Kwon, Oran),김은주(Jin, Yin-Zhu),이경옥(Yi, Kyung-Ock) 한국웰니스학회 2022 한국웰니스학회지 Vol.17 No.4

본 연구의 목적은 당뇨 환자의 보행 시 발 형태별, 당뇨 단계별, 발바닥 부위별 족압의 차이를 분석하는 것이다. 연구 대상은 만 40-79세의 당뇨병성 신경병증이 있는 사람 83명과 당뇨병이 없는 사람 98명의 총 181명이다. 이들은 당화혈색소를 기준으로 1) 당뇨 정상유지(4.0-6.9%) 2) 당뇨 양호(7.0-7.9%) 3) 당뇨 조절요함(8.0-10.9%) + 절대조절(≥11.0%), 그리고 4) 당뇨가 없는 정상인으로 분류하였다. 발 형태는 기립시 종골기립각도(RCSP)를 기준으로 정상족(±2°), 편평족(≤-3°), 요족(≥+3°)으로 구분하였다. 족저압력은 노블(Novel)사의 족압분포 측정기(EMED-LE Measurement system)를 이용하였고, 서울 소재 E 대학 운동 역학 실험실과 부속 병원 내 8m의 보행 주로 위에서 5번째 걸음을 3회 이상 측정하였다. 보행속도는 100bpm으로 통제하였다. 발 부위는 후족, 중족, 5개 발허리 뼈, 5개 발가락의 총 12부위로 나누었다. 족압 변인은 발바닥 부위별 피크압력(kPa), 접지시간(%ROP), 압적((kPa)*s)으로 설정하였다. 자료처리는 크로스컬 월리스(Kruska-walls)와 맨 휘트니 U 검정(Mann-Whitney U test)을 이용하였다(p<.05). 당화혈색소 수치에 따라, 발형태별로, 발바닥 부위별로 피크압력과 접지시간, 그리고 압적이 다르게 나타났다. 당화혈색소 수준에 따른 보행 시 피크압력과 접지시간, 압적을 같이 비교해 본 결과 피크압력도 크지만, 주로 접지시간이 길어 압적이 커지는 것을 알 수 있었다. 당뇨단계가 가장 낮은 당뇨 정상유지 단계부터 피크압력이 크고, 발허리뼈, 발가락의 접지시간이 길고, 압적이 높게 나타나 중족과 발허리뼈, 발가락까지 길고 강하게 내리누르는 보행을 하고 있었다. 그러므로 당화혈색소는 정상으로 잘 유지되더라도, 발바닥의 압력은 이미 달라지고 있다는 것을 의미한다. 이것은 발목관절의 배/저굴, 외/내번, 내/외전 능력이 부족하여 중족, 발허리뼈, 발가락까지 동시에 사용하여 지면과 접지하기 때문이다. 그러므로 당뇨 정상유지 단계부터 발목 관절의 세가지 배/저굴, 내/외번, 내/외전 기능 향상을 위한 보행 훈련이 필요하며, 이에 관한 연구는 추후 과제로 한다. The purpose of this study was to analyze the difference in foot pressure by foot type, diabetes stage, and plantar area when walking in diabetic patients. The subjects of this study were 181 people aged 40-79 years, 83 people with diabetic neuropathy and 98 people without diabetes. Based on the glycated hemoglobin, 1) diabetes normal maintenance stage (4.0-6.9%) 2) diabetes good stage (7.0-7.9%) 3) diabetes need control stage (8.0-10.9%) + absolute control stage (≥11.0%), and 4) were classified as a non-diabetic group. Foot type was classified into Pes Rectus (±2°), Pes Planus (≤-3°), and Pes Cavus (≥+3°) based on the RCSP when standing. For plantar pressure, Novels EMED-LE Measurement system was used, and the fifth step was measured three or more times in the 8m walking path in the E University Kinesiology Laboratory in Seoul and the affiliated hospital. The walking speed was controlled at 100 bpm. The foot area was divided into 12 areas: hindfoot, midfoot, 5 metatarsal bone, and 5 toes. Foot pressure variables were set as peak pressure(kPa), contact time(%ROP), and pressure((kPa)*s) for each sole part. For statistics, Kruskal-walls and Mann-Whitney U test (p<.05) were used. According to the glycated hemoglobin level, the peak pressure, contact time, and pressure-time integral were different for each foot type and sole area. As a result of comparing the peak pressure, contact time, and pressure-time integral during walking according to the glycated hemoglobin level, it was found that the pressure-time integral was increased because the contact time was mainly longer than the peak pressure. From the diabetic normal maintenance stage, the lowest diabetic stage, the peak pressure of the midfoot was large, the contact time of the metatarsal bone and toes was long, and the pressure-time integral was high. Therefore, even if the glycated hemoglobin remains normal, it means that the pressure on the soles of the feet is already changing. This is because the ankle joint lacks dorsi/plantar flexion, inversion/eversion, and adduction/abduction abilities, so the mid foot, metatarsal bones, and toes are simultaneously used to contact the ground. Therefore, gait training is required to improve the three functions of the ankle joint from the normal maintenance stage of diabetes, and research on this is a future task.

후판 4단 압연기에서 백업롤과 워크롤의 접촉응력에 관한 연구

김상록(S. R. Kim),송승호(S. H. Song),권용덕(Y. D. Kwon) 한국소성가공학회 2013 한국소성가공학회 학술대회 논문집 Vol.2013 No.10

We examined the contact pressure between back up roll surface and work roll surface in a 4-high plate-rolling mill and adopted submodeling method in order to predict contact pressure. This method was able to predict contact pressure distribution on barrel length and max contact pressure on local stress concentration region. We investigated the change of contact pressure according to change of the plate width and specific force. The result show that increase of plate width and specific force influenced the increase of overall contact pressure distribution on roll barrel length and max contact pressure. Change of plate width and specific force influenced contact pressure deviation between roll barrel center and chamfer starting point of back up roll.

Impact of contact pressure on output voltage of triboelectric nanogenerator based on deformation of interfacial structures

Seol, M.L.,Lee, S.H.,Han, J.W.,Kim, D.,Cho, G.H.,Choi, Y.K. Elsevier 2015 Nano energy Vol.17 No.-

A micro- and nano-structure at the contact interface of triboelectric nanogenerator (TENG) is an essential element enabling a remarkable performance improvement. Despite the various innovative inventions of interfacial structures, there has been little understanding about the analytical interpretation of the contact interface. Herein, the deformation behavior of interfacial micro- and nano-structures during the contact process is systematically analyzed to clarify the origin of the contact pressure to output voltage relationship of TENG. The visualization experiment, simulation, theoretical modeling, and electrical measurements are conducted for the comprehensive analysis. The results confirm that the deformation of interfacial structures directly determines the pressure-voltage relationship of TENG. The surface enlargement effect by interfacial nanostructure formation becomes completely valid only when the provided contact pressure is stronger than the certain threshold pressure to make the full-contact condition. Due to the correlation between contact pressure and output voltage, interfacial structure of the TENG should be carefully customized depending on the application environment. Based on the analyzed pressure-voltage relationship of the TENG, a hybrid circuit for energy scavenging and digital pressure sensing is designed and experimentally demonstrated.

Investigation of the mechanical behavior of a flexible solid metal seal for a cryogenic butterfly valve

Ahn, Jun-Tae,Lee, Kyung-Chul,Lee, Kwon-Hee,Han, Seung-Ho 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.9

Seat tightness at the fully shut position should be a consideration in the development of a butterfly valve for use in a liquefied natural gas (LNG) vessel. A flexible solid metal seal offers sufficient tightness of the butterfly valve and meets the specifications for cryogenic temperature. In the present study, characteristics for a cryogenic butterfly valve, such as the flow coefficient and the pressure loss coefficient, were estimated by numerical fluid analysis carried out to simulate 3-D flow and to study performance as it was affected by the opening angles of the valve disc. A design criterion to ensure the seat tightness of the butterfly valve at the fully shut position was proposed, in which the contact pressure between the metal seal and the valve disc would be compared with the fluid pressure. Numerical structural analysis showed that the contact pressure can be calculated by simulation of the frictional contact behavior on the surface of the metal seal and the valve disc. As a result, an adequate flexibility of the metal seal and the valve disc was required in order to accomplish a contact pressure that would be high enough to satisfy the seat tightness requirement. Under cryogenic temperature, thermal shrinkage caused the metal seal to adhere closely to the valve disc periphery at both sides and raised the contact pressure to a relatively high value, though there was no contact across a small area at the center position, which is susceptible to leakage. An additional displacement of the metal seal and the valve disc appeared at an operating fluid pressure of 6.9 bar and produced sufficient contact pressure at the no-contact area. This was verified by experimental leakage tests performed at room and cryogenic temperatures.

Contact behavior analysis of elastomeric x-ring under uniform squeeze rate and internal pressure before and after forcing-out using the photoelastic experimental hybrid method

Alunda Ouma Bernard,황재석,신동철,Bai Dong 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.5

Many different types of elastomeric rings have been developed to suit various needs in industry. The X-ring was introduced as a resultof the limitations of O-rings that twist, especially during dynamic application. A better understanding of the behavior and the stressdistribution of the X-ring under a uniform squeeze rate and internal pressure is needed. We analyzed the contact stresses and internalstresses developed in an X-ring before and after forcing-out by using the photoelastic experimental hybrid method, ascertained thepacking ability of an X-ring, and studied the failure criterion of an X-ring under uniform squeeze rate and internal pressure. Forcing-outin the X-ring occurred when the internal pressure was 3.92 MPa. After forcing-out, at an internal pressure of 5.88 MPa, the two lobes onthe upper contact surface merged one contact side of the upper side immensely. Even after extrusion of the X-ring, the X-ring can be usedto effectively contain the fluid. This is because the effects of extrusion on the X-ring affected the stress distribution of only two lobesclose to the assembly gap and the two lobes are merge into one lobe. In addition, our experimental results show that the maximum shearfailure criterion is suitable for the prediction of failure in X-ring seals.

실런트 접합부 누유 검토를 위한 초기 면압에 대한 연구

서정호(Jongho Seo),정재연(Jaeyun Jung) 한국자동차공학회 2011 한국자동차공학회 학술대회 및 전시회 Vol.2011 No.11

This study is stated that the initial contact pressure by the bolt tightening force is important for the prevention of the leakage in the sealant connection. The maintenance of the initial contact pressure will be able to prevent the leakage of between the front retainer and T/M case for using the sealant and this paper is mentioned the leakage case and discuss the improved case using the parameter study for the contact pressure. The most important factor to maintain the initial contact pressure is the distance between bolts and the second order is the width of face between the bolted distance and next order is the tighten torque. The method to examine the leakage on the driven condition was introduced in this study. The method is the distance between contact parts.

비 공기압 타이어의 회전 시 접지압

김승혜(Seunghye Kim),김두만(Doo-man Kim),최석주(Seok-ju Choi) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10

Rolling contact pressure is an important parameter to evaluate tire performance; rolling resistance, traction, handling, and wear of tread. Especially, Non-pneumatic tire(NPT) is necessary to know the characteristics of the rolling contact pressure. The NPT is modeled as elastic structure with hexagonal honeycomb spokes. Rolling contact pressure of NPT is expected irregular distribution. This paper investigates the rolling contact pressure of a non-pneumatic tire with hexagonal honeycomb spokes. Finite element (FE) based numerical simulation of 3D contact pressure of NPT is carried out using ABAQUS. Using this result, the rolling contact pressure of NPT is compared with that of a conventional pneumatic tire.

가파르게 처방된 소프트 콘택트렌즈 착용으로 인한 각막 굴절력, 눈물막 파괴시간, 안압의 변화

전영윤,박성종,이석주 대한시과학회 2015 대한시과학회지 Vol.17 No.4

목 적: 1일 착용용 소프트 콘택트렌즈의 가파르게 처방된 정도에 따른 각막굴절력의 변화, 눈물막 파괴시간의 변화, 안압의 변화와 상관관계를 알아보고자 하였다. 방 법: 대학생 24명(48안)을 대상으로 1일착용 렌즈를 8시간 착용시켜 8시간 경과 후 렌즈를 제거하고 각막굴절력, 눈물막 파괴시간 그리고 안압 측정을 시행하여 콘택트렌즈 착용전과 비교하였다. 결 과: 가파른 피팅을 함에 따라 각막굴절력은 +0.29±0.06 D 증가(t=-12.62, p<0.05)하였으며, 눈물띠 파괴시간(TBUT)은 –1.26±2.02sec 감소(t=5.04, p<0.05)하였으며 안압은 –2.19±2.15mmHg 감소(t=6.4, p<0.05)하였다. 가파른 피팅 정도에 따른 각막의 굴절력과의 상관관계(r=-0.98)는 강한 음의 상관관계를 가졌으며. TBUT와의 상관관계(r=-0.26)는 약한 음의 상관관계를 가졌으나 안압(r=-0.07)과는 상관관계가 없었다. 결 론: 각막의 곡률반경에 비하여 소프트 콘택트렌즈의 곡률반경이 0.3mm 이상 가파른 피팅되어 8시간 착용했을 때, 각막굴절력의 변화에 대한 강한 상관관계가 있으므로 소프트 콘택트렌즈 처방 시 가파른 피팅이 되지 않도록 유의해야 한다. Purpose: To study on cornea refractive power, TBUT, and Intra-ocular pressure after wearing daily wear soft contact lens fitted steep. Methods: 24 students(48 eyes) who was wearing daily contact lens for 8 hours. After 8 hours, taking off contact lens and then measuring the corneal refractive power, the tear film break-up time and intra-ocular pressure. The measurement was compared before and contact lens wear. Results: As a steep fitting, corneal refractive power was increased +0.29±0.06 D (t=-12.62, p< 0.05), tear break-up time (TBUT) was decreased -1.26±2.02 sec (t=5.04, p< 0.05) and IOP reduction was -2.19±2.15 mmHg (t=6.4, p< 0.05). Correlation of the corneal refractive power and the degree of the steep fitting (r=-0.98) had a strong negative correlation. TBUT Correlation (r= -0.26) had a weak negative correlation but intra-ocular pressure (r=-0.07) was no correlation. Conclusions: When the soft contact lens is at least 0.3mm steep fitting when worn 8 hours, it is a strong correlation between the changes in the corneal power and it should be noted that the steep fitting prescription is avoided.

Air-Bag 가압식 300 mm 웨이퍼 폴리싱 테이블의 가압 분포 해석

노승국,박종권,이상열,편도선 한국공작기계학회 2008 한국공작기계학회 춘계학술대회논문집 Vol.2008 No.-

In this paper, the contact pressure of the wafer and polishing pad were investigated through numerical analysis using FEM tool, ANSYS 9.0. The distribution of the contact pressure is one of main parameters affect on the flatness and surface roughness of polished wafers. Two types of air polishing head, a hard type head with ceramic disk and soft type head with air bag compression were considered. The effects of the table deformation and initial shape on the contact pressure and deformation were also examined. Both heads and tables were modeled as solid model and finite element model, and the material properties of polishing pads and rubber plate for the air-bag head were used based on the tensile tests. The distribution errors of the air-bag head were smaller than hard type head even when the table was convex or concave shape, so it could be concluded that the air-bag head is advantageous for the uniformity of the contact pressure.