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Numerical Calculation of Hip Squeak Over the Normal Gait Cycle
강재영 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.12
This paper present the numerical and analytical hip squeak model using the normal gait data acquired from the experiment. The axis of the ground reaction force is defined on the hip joint at the successive position of the right hip during the gait cycle. The contact pressure and its distribution on the ball are calculated by the Hertz theory at the corresponding cycle. The eigenvalue sensitivity analysis is conducted at the quasi-static state of the successive position of the right hip for both the full lubrication and the mixed lubrication. For the full lubrication case, the hip joint system becomes dynamically unstable only when the hip extends. In the mixed lubrication, the 2nd bending mode has the very high squeak propensity and its frequency drastically varies with the gait cycle.
두 번의 연속적 뇌경색에 의한 Hemimedulla 증후군
강재영 대한뇌졸중학회 2000 Journal of stroke Vol.2 No.1
Background : Two major vascular syndromes of the medulla oblongata are the medial and lateral medullary syndrome. Combination of the two syndromes may occur by obstruction of vertebral artery, but the report about hemimedullary syndrome caused by consecutive infarction with its MRI scan is rare. Case report : 1st admission; A 59-year-old hypertensive man developed abrupt weakness and tingling sensation of his right limb. He also noted dizziness and speech disturbances. On neurologic examination, he had dysarthria, nystagmus, left hypoglossal nerve palsy, and right hemiparesis without facial weakness. Carotid doppler sonography results showed findings suggestive of occlusion of the left vertebral artery. Brain MRI revealed left anteromedial medullary lesion. 2nd admission (after 1 month); The patient our hospital again because of newly developed hoarseness, tingling sensation of the left face, and recurrent right hemiparesis. Neurologic examinations revealed dysarthria, vocal cord paralysis, Honer’s syndrome, nystagmus, facial palsy and hypesthesia, absent gag reflex, hypoglossal nerve palsy, cerebellar ataxia on the left side, and hemiparesis, and sensory disturbance on the right hemibody. Repeat brain MRI revealed left hemimedullary infarction. Conclusion : Hemimedullary syndrome may be caused by two consecutive medullary infarcts.Korean Journal of Stroke 2000;2(1): 103~107
Experimental investigation of friction noise in lead screw system under mode-coupling
강재영,서강숙,김기선 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.12
This study experimentally investigated the friction noise in the lead screw system. The mechanism involved in the friction noise wasanalyzed on basis of the mode-coupling characteristics. Therefore, the frequency separation between two modes near the squeak frequencywas traced with the location of nut. It was found that the friction noise of the lead screw was generated only at the nut locationwhere the frequencies of the axial and torsion modes were met. It indicated that the friction noise in the lead screw system was caused bythe mode coupling between the torsion and axial modes.
Finite element modeling for stick-slip pattern of squeal modes in disc brake
강재영 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.10
This paper provides the finite element modeling for describing the nonlinear stick-slip response of squealing modes in a disc brake system. The analytical nonlinear contact kinematics is applied to each contact node of the finite element disc and pads. Numerical resultsshow that a portion of the contact area can undergo the stick-slip oscillation. Depending on the size of the stick-slip zone, the correspondingsqueal vibration can be either the pure harmonic or periodic oscillation. Particularly, the squeal mode arising from the pad rigid modegenerates the periodic stick-slip limit cycle in its steady-squealing response, as opposed that the disc squeal modes become the pure harmonicresponse.
강재영,김대호,이동구,김인섭,전민구,이재득,김익휘,이상현 한국잔디학회 2013 Weed & Turfgrass Science Vol.2 No.1
Seven medicinal plant extracts were tested for antifungal activities against six species of the major turfgrass pathogenic fungi (Colletotrichum graminicola, Pythium spp., Rhizoctonia cerealis, Rhizoctonia solani AG1-1, Rhizoctonia solani AG2-2, and Sclerotinia homoeocarpa) using paper disk diffusion method. Three medicinal plant extracts, including Pinus densiflora showed antifungal activities. In suppression of mycelium growth test, on medium adding P. densiflora extract showed that inhibition rate of mycelium growth were above 80% in 10 mg/10 ml concentration of the extract. The inhibition rate of Pythium spp. was 100% and C. graminicola was 84.3% in 10 mg/10 ml concentrations of P. densiflora extract, respectively. In particularly, the inhibition rate of Pythium spp. was 89.5% in 2 mg/10 ml concentrations of P. densiflora extract. As a result, P. densiflora extract showed high antifungal activity to Pythium spp. and C. graminicola of the turfgrass pathogen in in vitro test. 본 연구에서는 7종의 약용식물(송절, 지구목, 측백, 대풍자, 유백피, 은행잎, 참오동나무)을 사용하여 잔디의 주요병원균 6종(R. solani AG 2-2(IV), R. solani AG-1 IB,Pythium sp., S. homoeocarpa, R. cerealis, C. graminicola)을대상으로 항진균 활성을 실험하였다. 디스크 확산법으로항진균 활성이 있는 약용식물 추출물을 선발하였고, 선발된 추출물을 사용하여 균사생육 억제 효과를 검정하였다. 디스크 확산법으로 실험 한 결과 7종의 약용식물 중 송절,측백, 유백피 등 3종의 추출물에서 항진균 활성이 있는 것으로 나타났다. 송절 추출물 1,000배 처리에서 Pythium sp. 에 대하여 100%, C. graminicola에 대하여 84.3%의 균사생육 억제율을 나타내었으며, 특히 Pythium sp.에 대해서는 5,000배 처리에서도 89.5%의 균사생육 억제율을 나타내었다.
Lyapunov exponent of friction-induced vibration under smooth friction curve
강재영 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.8
This paper studies the nonlinear behavior of the friction-induced vibration by using spring-mass model subject to the smooth frictionvelocity curve. The nonlinearity and instability of the friction may produce the chaotic vibration depending on the friction curve. In order to show this, the Lyapunov exponents are calculated for a variety of the slope and magnitude in the smooth friction curve. In turn, the dependency of the friction curve on the chaotic attractor is illustrated.