• International Journal of Automotive Technology
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• 제8권5호
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• pp.599-603
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• 2007

An efficient optimum design process has been developed and applied to systematically design a lock-up clutch system for a torque converter used in an automatic transmission. A simulated annealing algorithm was applied to determine the parameters of the compressive helical damper springs in the clutch. The determination of the number, location, a number of turns, and deflection of damper springs plays an important role in reducing vibration and noise in the lock-up system. Next, FE-based shape optimization was coded to find the shape of the clutch disk that would satisfy the strength, noise and vibration requirements. Using the optimum code, parametric studies were performed to see how spring diameters and frequencies of clutch systems changed as the damper spring traveling angles and the torques were varied. Based on the optimum results, five different designs for clutches with different springs were fabricated and vibration analyses and tests were conducted to validate the accuracy of the proposed method. Results from the two methods show a good correlation.

• 한국정밀공학회지
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• 제32권4호
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• pp.377-386
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• 2015

Joint force/torque estimation by inverse dynamics is a traditional tool in biomechanical studies. Conventionally for this, kinematic data of human body is obtained by motion capture cameras, of which the bulkiness and occlusion problem make it hard to capture a broad range of movement. As an alternative, inertial motion sensing using cheap and small inertial sensors has been studied recently. In this research, the performance of inertial motion sensing especially to calculate inverse dynamics is studied. Kinematic data from inertial motion sensors is used to calculate ground reaction force (GRF), which is compared to the force plate readings (ground truth) and additionally to the estimation result from optical method. The GRF estimation result showed high correlation and low normalized RMSE(R=0.93, normalized RMSE<0.02 of body weight), which performed even better than conventional optical method. This result guarantees enough accuracy of inertial motion sensing to be used in inverse dynamics analysis.

• Steel and Composite Structures
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• 제42권2호
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• pp.221-241
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• 2022

Perfobond rib connectors are widely used in composite structures to achieve the composite action between the steel and the concrete, and empirical expressions for their strength and secant stiffness have been obtained by numerical simulations or push-out tests. Since perfobond connections are generally in an elastic state in the service process and the structural analysis are always based on the elastic properties of the members, the secant stiffness is not applicable for the normal structural analysis. However, the tangent stiffness of perfobond connections has not been introduced in previous studies. Moreover, the perfobond connections are bearing tension and shear force simultaneously when the composite beams subjected to torque or local loads, but the current studies fail to arrive at the elastic stiffness considering the combined effects. To resolve these discrepancies, this paper investigates the initial elastic stiffness of perfobond connections under combined forces. The calculation method for the elastic stiffness of perfobond connections is analyzed, and the contributions of the perfobond rib, the perforating rebar and the concrete dowel are investigated. A finite element method was verified with a high value of correlation for the test results. Afterwards, parametric studies are carried out using the reliable finite element analysis to explore the trends of several factors. Empirical equations for predicting the initial elastic stiffness of perfobond connections are proposed by the numerical regression of the data extracted by parametric studies. The equations agree well with finite element analysis and test results, which indicates that the proposed empirical equations reflect a high accuracy for predicting the initial elastic stiffness of perfobond connections.

• 한국재료학회지
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• 제33권8호
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• pp.323-329
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• 2023

There are many types of foam molding methods. The most commonly used methods are the pressure foaming method, in which foam resin is mixed with a foaming agent at high temperature and high pressure, and the normal pressure foaming method, which foams at high temperature without pressure. The polymer resins used for foaming have different viscosities. For foaming under normal pressure, they need to be designed and analyzed for optimal foaming conditions, to obtain resins with low melt-viscosity or a narrow optimal viscosity range. This study investigated how changes in viscosity, molding temperature, and cross-link foaming conditions affected the characteristics of the molded foam, prepared by blending rubber polymer with biodegradable resin. The morphologies of cross sections and the cell structures of the normal pressure foam were investigated by SEM analysis. Properties were also studied according to cross-link/foaming conditions and torque. Also, the correlation between foaming characteristics was studied by analyzing tensile strength and elongation, which are mechanical properties of foaming composites.

• 대한치과교정학회지
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• 제40권3호
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• pp.167-175
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• 2010

Periotest$^{(R)}$는 보철용 임플랜트 식립 3 - 4개월 후 골유착 정도를 평가하기 위해 사용되는 동요도 측정 기기로 교정용 미니임플랜트 안정성 평가에 적용가능성이 높다. 본 연구는 교정용 미니임플랜트의 안정성 평가를 위해 Periotest$^{(R)}$의 유효성을 검증하고자 하였다. 성견 다섯 마리의 상악, 하악 협측골에 교정용 미니임플랜트를 식립하고, 식립 시 식립토오크와 동요도를 측정하고 12주 동안 교정력을 부여한 후, 제거 시 제거 토오크와 동요도를 측정하였다. 동요도 (Periotest$^{(R)}$ value, PTV) 측정은 재현성을 위해 동일 부위에 2회 측정하였다. PTV와 다른 변수와의 상관성 분석을 위해 모든 실험견은 CT 촬영 후 식립 부위의 골밀도와 피질골 두께를 계측하였다. 동요도 측정에 대한 재현성은 0.96의 상관계수를 나타내 매우 높았으며 (p < 0.001) 골밀도와 피질골 두께에 있어 하악골 협측치조골이 상악골에 비해 유의하게 컸다 (p < 0.05). 12주 동안 PTV 값은 -3.2에서 4.8의 범위를 나타내며 모든 임플랜트는 임상적으로 안정적이었다. 식립 시 PTV 값은 하악에서 식립 토오크(-0.51), 골밀도(-0.48), 피질골 두께(-0.42)와 상관성이 있었으나 (p < 0.05), 상악에서는 상관성이 없었다. 제거 시 PTV 값은 하악에서 제거 토오크(-0.66)와 상관성이 있었으며(p < 0.05), 상악에서는 상관성이 없었다. 이상의 결과는 Periotest$^{(R)}$를 이용하여 교정용 미니임플랜트의 안정성을 간접적으로 평가할 수 있으나 골밀도가 높고 피질골이 두꺼운 부위에서 제한적으로 응용할 수 있음을 시사한다.

• International Journal of Automotive Technology
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• 제7권4호
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• pp.441-448
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• 2006

In-cylinder flows such as tumble and swirl play an important role on the engine combustion efficiencies and emission formations. The tumble flow, which is dominant in current high performance gasoline engines, is able to effect fuel consumptions and emissions under a partial load condition in addition to the volumetric efficiency under a wide open throttle condition. Therefore, it is important to optimize the tumble ratio of a gasoline engine for better fuel economy, lower emissions, and maximum volumetric efficiency. First step for optimizing a tumble ratio is to measure a tumble ratio accurately. For a tumble ratio measurement, many different methods have been developed and used such as steady flow rig, PIV, PTV, and LDV. However, it is not well known about the relations among the measured tumble ratios using different methods. The purpose of this research is to correlate the tumble ratios measured using three different methods and find out merits and demerits of each measurement method. In this research the tumble flow was measured, compared, and correlated using three different measurement methods at the same engine: steady flow rig; 2-dimensional PIV; and 3-dimensional PTV water flow rig.

• 한국정밀공학회지
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• 제26권7호
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• pp.142-149
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• 2009

The aim of this study was to identify both the mechanical and reflex properties associated with spasticity in hemiplegic patients. Ten hemiplegic patients were included in this study. Multiple pendulum tests were executed for each subject, and knee joint angle and EMG of Rectus Femoris muscle were measured. The neuromusculoskeletal system model was developed from generally accepted mechanism and identified through minimization of the error in the model-predicted pendulum trajectories. The identification was successful in terms of small error in simulated kinematics and high sensitivity and precision of simulated torque against EMG activity. The reflex threshold showed significant difference between different clinical scores (p<0.01) and significant negative correlation (r=-0.93) with the EMG duration. It is expected that the suggested method may help in understanding mechanisms underlying spasticity.

• Tribology and Lubricants
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• 제33권4호
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• pp.141-147
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• 2017

The vibration data of bearings are very useful for monitoring and determining the condition of the bearings. The defect frequencies of ball bearings have been used for monitoring there condition. However, it is not easy to verify the defect frequencies as the wear progress. Therefore there is a need for an easy method to monitor the damages of bearings in real-time and to observe the variations in vibration characteristics as the wear progress. In this study, a bearing test equipment is constructed to diagnose the damage of bearings. The friction coefficient and vibration data are measured by using a torque sensor and an acceleration sensor, and the correlation between the measured data is analyzed to diagnose the condition of the bearing. We reached the following conclusions from the results. When the ball surface, inner and outer rings of a ball bearing are damaged, the friction coefficient increases to over 0.02 with an adhesion on the surface. Moreover this damage occurs more quickly with an increase in the number of revolutions. In the vibration characteristics, the amplitude of vibration wave appears high with an increase in the friction coefficient. In the high frequency range between 1000 and 2000 Hz, a wide range of frequency components with high amplitude occurs continuously irrespective of the number of revolutions.

• 대한화장품학회지
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• 제45권2호
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• pp.131-138
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• 2019

Carbonylated proteins (CPs)은 단백질의 염기성 아미노산 잔기들과 지질 과산화 중 생성되는 알데히드 화합물과의 화학적 반응을 통하여 만들어진다. CP는 UVA와 청색 광선 영역의 빛을 흡수하여 흥분하며, CP의 감광 반응을 통해 superoxide anion radicals ($^{\cdot}O_2{^-}$)이 생성되고 각질층(Stratum corneum, SC)에서 reactive oxygen species (ROS) 생성을 통해 새로운 protein carbonylation이 진행되는 것이 알려졌다. 또한, superoxide anion radicals이 SC에서 CP를 생성하며 색상과 수분 기능을 포함한 피부 상태에 영향을 미치는 것으로 보고되었다. 따라서, 본 연구의 목적은 피부 각질층에 존재하는 stratum corneum carbonylated protein (SCCP)의 생성량과 피부 탄력 개선의 상관정도를 알아보는 것이었다. 이를 위하여 46명의 건강한 피험자들을 대상으로 8주간 피부임상실험을 진행하였다. 8주간 진행한 피부임상시험은 피험자를 두 그룹으로 나누어, 한 그룹은 아무것도 함유하지 않은 크림을 사용하고, 다른 그룹은 탄력개선 원료가 함유된 크림을 사용하였다. 임상시험 측정 항목은 DUB scanner를 이용한 진피 치밀도 측정, Primos를 이용한 주름 측정을 진행하였으며 탄력 측정은 dermal torque meter (DTM310)와 Balistometer (BLS780)를 통해 진행하였다. SCCP측정은 피험자의 뺨에서cyanoacrylate를 이용한 skin surface biopsy (SSB)방법을 이용하여 각질을 채취한 후, 비침습적인 검출 방법을 이용해 SCCP의 양을 조사하였다. 측정은 0주, 4주, 8주 총 3회에 걸쳐서 진행하였으며 각 주차의 측정값을 각각 분석하여 종합적인 결과를 비교하였다. 그 결과, SC에 존재하는 CP의 양은 피부 주름 및 피부 탄력성과 관련된 생물학적 인자의 수치가 개선됨에 따라 감소하는 것을 확인하였다. 이를 통해 항노화 효과에 있어서 탄력 개선과 CP양의 상관관계를 확인하여, 차후 피부 항노화 시험방법에 응용할 수 있음을 확인하였다.