• 복합신소재구조학회 논문집
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• 제1권1호
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• pp.34-45
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• 2010

This paper describes the design, manufacturing process, testing, application, and assessment of capacity-ratings of the first all advanced composites bridge on a public highway system. In order to verify the bridge design prior to the field application, a sub-scale bridge superstructure was built and tested in the laboratory. The field load test results were compared with those of the finite element analysis for the verification of validity. To investigate its in-service performance, field load testing and visual inspections were conducted under an actual service environment. The paper includes the presentation and discussion for advanced composites bridge capacity rating based on the stress modification coefficients obtained from the test results. The test result indicates that the advanced composites bridge has no structural problems and is structurally performing well in-service as expected. Since these composite materials are new to bridge applications, reliable data is not available for their in-service performance. The results may provide a baseline data for future field advanced composites bridge capacity rating assessments and also serve as part of a long-term performance of advanced composites bridge.

• Wind and Structures
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• 제30권3호
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• pp.245-260
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• 2020

Wind load and responses are the major factors which govern the design norms of tall buildings. Corner modification is one of the most commonly used minor shape modification measure which significantly reduces the wind load and responses. This study presents a comparison of wind load and pressure distribution on different corner modified (chamfered and rounded) Y plan shaped buildings. The numerical study is done by ANSYS CFX. Two turbulence models, k-epsilon and Shear Stress Transport (SST), are used in the simulation of the building and the data are compared with the previous experimental results in a similar flow condition. The variation of the flow patterns, distribution of pressure over the surfaces, force and moment coefficients are evaluated and the results are represented graphically to understand the extent of nonconformities due to corner modifications. Rounded corner shape is proving out to be more efficient in comparing to chamfered corner for wind load reduction. The maximum reduction in the maximum force and moment coefficient is about 21.1% and 19.2% for 50% rounded corner cut.

• 한국자동차공학회논문집
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• 제12권3호
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• pp.109-121
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• 2004

This paper presents an optimal design method for structure-borne durability of a vehicle body structure. Structure-borne durability design requires a new design that can increase fatigue lives of critical areas in a structure and must prohibit transition phenomenon of critical areas that results from modification of the structure at the same time. Therefore, the optimization problem fur structure-borne durability design are consists of an objective function and design constraints of 2 types; type 1-constraint that increases fatigue lives of the critical areas to the required design limits and type 2-constraint that prohibits transition phenomenon of critical areas. The durability design problem is generally dynamic because a designer must consider the dynamic behavior such as fatigue analyses according to the structure modification during the optimal design process. This design scheme, however, requires such high computational cost that the design method cannot be applicable. For the purpose of efficiency of the durability design, we presents a method which carry out the equivalent static design problem instead of the dynamic one. In the proposed method, dynamic design constraints for fatigue life, are replaced to the equivalent static design constraints for stress/strain coefficients. The equivalent static design constraints are computed from static or eigen-value analyses. We carry out an optimal design for structure-borne durability of the newly developed bus and verify the effectiveness of the proposed method by examination of the result.

• Structural Engineering and Mechanics
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• 제12권5호
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• pp.527-540
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• 2001

A new sort of learning algorithm named whole learning algorithm is proposed to simulate the nonlinear and dynamic behavior of RC members for the estimation of structural integrity. A mathematical technique to solve the multi-objective optimization problem is applied for the learning of the feedforward neural network, which is formulated so as to minimize the Euclidean norm of the error vector defined as the difference between the outputs and the target values for all the learning data sets. The change of the outputs is approximated in the first-order with respect to the amount of weight modification of the network. The governing equation for weight modification to make the error vector null is constituted with the consideration of the approximated outputs for all the learning data sets. The solution is neatly determined by means of the Moore-Penrose generalized inverse after summarization of the governing equation into the linear simultaneous equations with a rectangular matrix of coefficients. The learning efficiency of the proposed algorithm from the viewpoint of computational cost is verified in three types of problems to learn the truth table for exclusive or, the stress-strain relationship described by the Ramberg-Osgood model and the nonlinear and dynamic behavior of RC members observed under an earthquake.

• 한국해양공학회지
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• 제32권6호
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• pp.492-501
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• 2018

The following results were obtained from a series of studies to accumulate data to reduce the coefficient of friction for press dies by performing tribological tests before and after the UNSM treatment of SM45C. The UNSM-treated material had a nano-size surface texture, high surface hardness, and large and deep compressive residual stress formation. Even when the load was doubled, the small amount of abrasion, small weight of the abrasion, and width and depth of the abrasion did not increase as much as those for untreated materials. When loads of 5 N, 7.5 N, and 10 N were applied to the untreated material of SM45C, the coefficient of friction was approximately 0.76-0.78. With the large specimen, a value of 0.72-0.78 was maintained at a load of 50 N despite the differences in the size of the wear specimen and working load. Tribological tests of large specimens of SM45C treated with UNSM under tribological conditions of 100 N and 50 N showed that the frictional coefficient and time constant stably converged between 0.7 and 0.8. The friction coefficients of the small specimens treated with UNSM showed values between 0.78 and 0.75 under 5 N, 7.5 N, and 10 N. The friction coefficients of the SM45C treated with UNSM were comparable to each other.

• Tribology and Lubricants
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• 제40권3호
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• pp.84-90
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• 2024

This study investigates the effect of the surface microstructure on the tribological characteristics of glass substrates. Chemical etching using hydrofluoric acid and ammonium hydrogen fluoride was employed to create controlled asperity structures on glass surfaces. By varying the etching time from 10 to 50 min, different surface morphologies were obtained and characterized using optical microscopy, surface roughness measurements, and water contact angle analysis. Friction tests were performed using a stainless steel ball as the counter surface to evaluate the tribological behavior of the etched specimens. The results showed that the specimen etched for 20 min exhibited the lowest and most stable friction coefficient, which was attributed to the formation of a uniform and dense asperity structure that effectively reduced the stress concentration and wear at the contact interface. In contrast, specimens etched for shorter (10 min) or longer (30-50 min) durations displayed higher friction coefficients and accelerated wear owing to nonuniform asperity structures that led to local stress concentration. Optical microscopy of the wear tracks further confirmed the superior wear resistance of the 20-minute etched specimen. These findings highlight the importance of optimizing the etching process parameters to achieve the desired surface morphology for enhanced tribological performance, suggesting the potential of chemical etching as a surface modification technique for various materials in tribological applications.

• Wind and Structures
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• 제35권1호
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• pp.55-66
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• 2022

Tall buildings are often subjected to steady and unsteady forces due to external wind flows. Measurement and mitigation of these forces becomes critical to structural design in engineering applications. Over the last few decades, many approaches such as modification of the external geometry of structures have been investigated to mitigate wind-induced load. One such proven geometric modification involved the rounding of sharp corners. In this work, we systematically analyze the impact of rounded corner radii on the reducing the flow-induced loading on a square cylinder. We perform 3-Dimensional (3D) simulations for high Reynolds number flows (Re=1 × 105) which are more likely to be encountered in practical applications. An Improved Delayed Detached Eddy Simulation (IDDES) method capable of capturing flow accurately at large Reynolds numbers is employed in this study. The IDDES formulation uses a k-ω Shear Stress Transport (SST) model for near-wall modelling that prevents mesh-induced separation of the boundary layer. The effects of these corner modifications are analyzed in terms of the resulting variations in the mean and fluctuating components of the aerodynamic forces compared to a square cylinder with no geometric changes. Plots of the angular distribution of the mean and fluctuating coefficient of pressure along the square cylinder's surface illustrate the effects of corner modifications on the different parts of the cylinder. The windward corner's separation angle was observed to decrease with an increase in radius, resulting in a narrower and longer recirculation region. Furthermore, with an increase in radius, a reduction in the fluctuating lift, mean drag, and fluctuating drag coefficients has been observed.

• Journal of Community Nutrition
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• 제3권1호
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• pp.21-29
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• 2001

This study was conducted to examine factors with attendance in hyperlipidemia nutrition eduction program among 101 hyperlipidemic outpatients (38 males 63 females) at Samsung Medical Center We employed the Health Belief Model (HBM) as the theoretical framework The individual nutrition education and counseling program was scheduled with 4- half hour session sin 2 to 4 weeks intervals. Upon initiation of the program a trained dietitian surveyed HBM constructs and psychosocial factors. The following were included perceived susceptibility to cardiovascular disease(CVD) perceived severity to CVD percieved benefits to diet modification perceived barriers to persistence in maintaining therapy and self efficicacy and social support from family Sociodemographic data health factors stress level nutrition knowledge, and 24-hour dietary recall behavior were also surveyed All these data was analyzed according to the number of nutrition sessions attended The subjects were 55.9$\pm$9.4 year old and 24.6$\pm$kg/㎡ Sociodemographic factors were not associated with the number of nutrition sessions attended HBM constructs and psychosocial factors were significantly associated with the number of nutrition sessions attended. According to Spearman correlation coefficients. From stepwis regression analyses using HBM constructs as independent variables perceive barriers to persistence in maintaining diet therapy (negative) proved to be the strongest predictors for the number of nutrition sessions attended (partial R$^2$= 72.3%) followed by perceived severity to CVD and self efficacy (model R$^2$=76.6% The findings indicate that HBM constructs and psychosocial factors were closely associated with patient attendance It suggests that information and guidance to minimize patients perceived barriers to diet therapy might help to improve patients to scheduled appointments in nutrition education programs.

• 대한간호학회지
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• 제25권4호
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• pp.681-695
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• 1995

It has been noted that a genetic alteration of cells influenced by unhealthy lifestyle In addition to a series of other carcinogens increases various neoplasmic diseases. Therefore the importance of lifestyle that minimizes such impact on health should be emphasized. Since stomach cancer, the most common neoplasmic disease in Korea, is re-lated to the Korean lifestyle and as there's a possibility of its recurrence, people with stomach cancer need to lead a healthy lifestyle. The purpose of this study is to provide a basis for nursing intervention strategies to promote health promoting behaviors that are constructive to a healthy lifestyle. A multivariate model was constructed based on the fender's health promotion model and Booker's health belief model by including influential factors such as hope. The sample was composed of 164 patients with stomach cancer who visited outpatient clinics of a university hospital in Seoul. The following instruments were used in the study after some adaptation : Wallston and others' multidimensional health locus of control scale Laffrey's health conception scale, Lawston and others' health self- rating scale, Walker and others' health promotion lifestyle profile and Rogenberg's self esteem scale. In addition Moon's health belief scale was used with some modification. For self efficacy, the present author constructed a self-efficacy scale based on previous research. The above mentioned instruments were tested in a pilot study with 24 patients with stomach cancer. The reliabilities of instruments were tested with Cronbach's alpha(0.574∼0.949). Data were analyzed using a SAS program (or Pearson correlation coefficients, descriptive correlational statistics and stepwise multiple regression. The results are as follows : 1. The scores on the health promoting behavior scale ranged from 55 to 145 with a mean of 107.91 (S. D : 16.50). The mean scores(range 1-4) on the different dimensions were nutrition 3.14, exercise 2.48, stress management 2.69, health responsibility 2.65, interpersonal relationship 2.878E self actualization 2.85. 2. There were significant correlations among all the predictive variables & the health promoting behavior (r=.20-.55, p〈.01) 3. Stepwise multiple regression analysis showed that : 1) Hope was the main predictor and accounted for 29.8％ of the total variance. 2) Self efficacy, perceived barriers & self esteem accounted for an additional 14.6% of the total variance. 3) Hope, self efficacy, perceived barriers & self esteem altogether accounted for 44.3％ of the total variance. In conclusion, hope, self efficacy, perceived barriers & self esteem were identified as important variables that contributed to promote health promoting behavior.