• 대한기계학회논문집A
• /
• 제32권1호
• /
• pp.29-34
• /
• 2008

The efforts of reflecting the system's uncertainties in design step have been made and robust optimization or reliability-based design optimization are examples of the most famous methodologies. In their formulation, the mean and standard deviation of a performance function and constraints expressed by probability conditions are involved. Therefore, it is essential to effectively and accurately calculate them and, in addition, the sensitivity results are required to obtain when the nonlinear programming is utilized during optimization process. We aim to obtain the new and efficient sensitivity formulation, which is based on integral form, on statistical moments such as the mean and standard deviation, and probability constraints. It does not require the additional functional calculation when statistical moments and failure or satisfaction probabilities are already obtained at a design point. Moreover, some numerical examples have been calculated and compared with the exact solution or the results of Monte Carlo Simulation method. The results seem to be very satisfactory.

• 대한기계학회논문집
• /
• 제17권1호
• /
• pp.11-20
• /
• 1993

본 연구에서는 준 해석적 방법에 촛점을 맞추어 전개를 하려 한다. 대개의 최적설계방식이 그렇듯 준 해석적 방법도 치수변수에 관해 응용이 이루어졌는데 그 정 확도에 문제가 나타나지는 않는다. 그러나 최근 형상변수에 대해 응용을 할 경우 오 차가 큰 것이 발견되었다. 물론 치수변수에 관해서도 준 해석적 방법에서 오차가 존 재한다는 보고 있으나 그 절대량이 크지 않으므로 그다지 심각하지 않다고 사료된다. 여기서는 준해석적 방법의 오차의 과정이 수학적으로 전개될 것이며, 설정된 구조물에 대한 수치적 계산결과가 논의 될 것이다. 해석의 대상 구조물로는 엄밀해가 존재하 여 비교분석이 용이한 2차원 외팔보가 선택되었으며, 여러가지 방법과의 비교로서 준 해석적 방법이 논의되고 효과적인 방법선택이 제안될 것이다.

• 대한기계학회논문집A
• /
• 제29권11호
• /
• pp.1494-1502
• /
• 2005

Fatigue life and notch sensitivity of the ultrafine grained pure Ti produced by ECAP was investigated. The ECAPed sample with the true strain of 460$\%$ showed near equiaxed grains with an average size of about 0.3 $\mu$m. After ECAP, the ultimate tensile strength was increased by 60$\%$, while the tensile ductility was decreased by 31$\%$. The ECAPed ultrafine grained pure Ti samples showed high notch sensitivity and significant improvement of high cycle fatigue limit by a factor of 1.67. The ECAPed samples also show high notch sensitivity (K$_{f}$/K$_{t}$ = 0.96). It can be concluded that ECAP is the effective process for achieving high fatigue strength in Ti by increasing its tensile strength through grain refinement

• 대한기계학회논문집A
• /
• 제29권11호
• /
• pp.1527-1533
• /
• 2005

Three methods for design sensitivity analysis such as finite difference method(FDM), direct differentiation method(DDM) and adjoint variable method(AVM) are well known. FDM and DDM for design sensitivity analysis cost too much when the number of design variables is too large. An AVM is required to compute adjoint variables from the simultaneous linear system equation, the so-called adjoint equation. Because the adjoint equation is independent of the number of design variables, an AVM is efficient for when number of design variables is too large. In this study, AVM has been extended to the eigenproblem of damped systems whose eigenvlaues and eigenvectors are complex numbers. Moreover, this method is implemented into a commercial finite element analysis program by means of the semi-analytical method to show applicability of the developed method into practical structural problems. The proposed_method is compared with FDM and verified its accuracy for analytical and practical cases.

• 대한기계학회논문집A
• /
• 제28권11호
• /
• pp.1760-1767
• /
• 2004

Sequential sampling approaches of a metamodel that sampling points are updated sequentially become a significant consideration in metamodeling technique. Sequential sampling design is more effective than classical space filling design of all-at-once sampling because sequential sampling design is to add new sampling points by means of distance between sampling points or precdiction error obtained from metamodel. However, though the extremum points can strongly reflect the behaviors of responses, the existing sequential sampling designs are inefficient to approximate extremum points of original model. In this research, new sequential sampling approach using the sensitivity of Kriging model is proposed, so that new approach reflects the behaviors of response sequentially. Various sequential sampling designs are reviewed and the performances of the proposed approach are compared with those of existing sequential sampling approaches by using mean squared error. The accuracy of the proposed approach is investigated against optimization results of test problems so that superiority of the sensitivity approach is verified.

• 대한기계학회논문집B
• /
• 제32권10호
• /
• pp.800-809
• /
• 2008

Scanning Thermal Microscope (SThM) is the tool that can map out temperature or the thermal property distribution with the highest spatial resolution. Since the local temperature or the thermal property of samples is measured from the extremely small heat transferred through the nanoscale tip-sample contact, improving the sensitivity of SThM probe has always been the key issue. In this study, we develop a new design and fabrication process of SThM probe to improve the sensitivity. The fabrication process is optimized so that cantilevers and tips are made of thermally grown silicon dioxide, which has the lowest thermal conductivity among the materials used in MEMS. The new design allows much higher tip so that heat transfer through the air gap between the sample-probe is reduced further. The position of a reflector is located as far away as possible to minimize the thermal perturbation due to the laser. These full $SiO_2$ SThM probes have much higher sensitivity than that of previous ones.

• Nutrition Research and Practice
• /
• 제17권6호
• /
• pp.1255-1266
• /
• 2023

BACKGROUND/OBJECTIVES: This study aimed to predict the association between nutritional intake and diabetes mellitus (DM) by developing an artificial neural network (ANN) model for older adults. SUBJECTS/METHODS: Participants aged over 65 years from the 7th (2016-2018) Korea National Health and Nutrition Examination Survey were included. The diagnostic criteria of DM were set as output variables, while various nutritional intakes were set as input variables. An ANN model comprising one input layer with 16 nodes, one hidden layer with 12 nodes, and one output layer with one node was implemented in the MATLAB^® programming language. A sensitivity analysis was conducted to determine the relative importance of the input variables in predicting the output. RESULTS: Our DM-predicting neural network model exhibited relatively high accuracy (81.3%) with 11 nutrient inputs, namely, thiamin, carbohydrates, potassium, energy, cholesterol, sugar, vitamin A, riboflavin, protein, vitamin C, and fat. CONCLUSIONS: In this study, the neural network sensitivity analysis method based on nutrient intake demonstrated a relatively accurate classification and prediction of DM in the older population.

• Tribology and Lubricants
• /
• 제28권5호
• /
• pp.203-211
• /
• 2012

Atomic force microscopy (AFM) has been used as a tool, not only for imaging surfaces, but also for measuring surface forces and mechanical properties at the nano-scale. Force calibration is crucial for quantitatively measuring the forces that act between the AFM probe of a force sensing cantilever and a sample. In this work, the lateral force calibrations of a V-shaped cantilever were performed using the finite element method, multiple pivot loading, and thermal noise methods. As a result, it was shown that the multiple pivot loading method was appropriate for the lateral force calibration of a V-shaped cantilever. Further, through crosschecking of the abovementioned methods, it was concluded that the thermal noise method could be used for determining the lateral spring constants as long as the lateral deflection sensitivity was accurately determined. To obtain the lateral deflection sensitivity from the sticking portion of the friction loop, the contact stiffness should be taken into account.

• Journal of Mechanical Science and Technology
• /
• 제19권7호
• /
• pp.1449-1459
• /
• 2005

This paper shows the results of local flow speed measurement using tunable AC thermal anemometry, which is suitable for the accurate measurement of wide range flow speed. The measurement accuracy is verified through the comparison between the measurement data and the analytic solution of the sensor temperature oscillation in stationary fluid. The relation between the phase lag and the flow speed is experimentally investigated at various conditions. The measurement sensitivity for low flow speed improves in a low frequency region and that for high flow speed improves in a high frequency region. Also, the sensitivity increases with decreasing thermal conductivity of the surrounding fluid. The local flow speed could be measured as low as 1.5 mm/s and the highest measurement resolution was 0.05 mm/s in the range of 4.5 $\~$5.0 mm/s at 1 Hz in this experiment.

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
• /
• pp.281-282
• /
• 2002

To reduce the spin-off of lubricants on a magnetic disk, which is caused by the radial component of shear force between the disk and air, we analyzed the air-velocity distribution and the air-shear force by three-dimensional large-eddy simulation (LES). This sensitivity analysis, on five design parameters, showed that disk/arm clearance and arm thickness have a greater effect on the mean radial air-shear force than the other parameters. The force on a disk optimized according to the optimum parameters is 12% less than the force on a conventional disk.