• Structural Engineering and Mechanics
• /
• 제85권4호
• /
• pp.445-459
• /
• 2023

The current investigation is the first endeavor to apply the full layerwise finite element method (FEM) in free vibration analysis of functionally graded (FG) composite plates reinforced with graphene nanoplatelets (GPLs) in thermal environment. Unlike the equivalent single-layer (ESL) theories, the layerwise FEM focuses on all three-dimensional (3D) effects. The GPLs weight fraction is presumed invariable in each layer but varies through the plate thickness in a layerwise model. The modified Halpin-Tsai model is employed to acquire the effective Young's modulus. The rule of mixtures is applied to specify the effective Poisson's ratio and mass density. First, the current method is validated by comparing the numerical results with those stated in the available works. Next, a thorough numerical study is performed to examine the influence of various factors involving the pattern of distribution, weight fraction, geometry, and size of GPLs, together with the thickness-to-span ratio, thermal environment, and boundary conditions of the plate, on its free vibration behaviors. Numerical results demonstrate that employing a small percentage of GPL as reinforcement considerably grows the natural frequencies of the pure epoxy. Also, distributing more square-shaped GPLs, involving a smaller amount of graphene layers, and vicinity to the upper and lower surfaces make it the most efficient method to enhance the free vibration behaviors of the plate.

• Advances in aircraft and spacecraft science
• /
• 제11권1호
• /
• pp.55-81
• /
• 2024

This paper presents the exact solutions and closed forms for of nonlinear stability and vibration behaviors of straight and curved beams with nonlinear viscoelastic boundary conditions, for the first time. The mathematical formulations of the beam are expressed based on Euler-Bernoulli beam theory with the von Karman nonlinearity to include the mid-plane stretching. The classical boundary conditions are replaced by nonlinear viscoelastic boundary conditions on both sides, that are presented by three elements (i.e., linear spring, nonlinear spring, and nonlinear damper). The nonlinear integro-differential equation of buckling problem subjected to nonlinear nonhomogeneous boundary conditions is derived and exactly solved to compute nonlinear static response and critical buckling load. The vibration problem is converted to nonlinear eigenvalue problem and solved analytically to calculate the natural frequencies and to predict the corresponding mode shapes. Parametric studies are carried out to depict the effects of nonlinear boundary conditions and amplitude of initial curvature on nonlinear static response and vibration behaviors of curved beam. Numerical results show that the nonlinear boundary conditions have significant effects on the critical buckling load, nonlinear buckling response and natural frequencies of the curved beam. The proposed model can be exploited in analysis of macrosystem (airfoil, flappers and wings) and microsystem (MEMS, nanosensor and nanoactuators).

• Computers and Concrete
• /
• 제25권3호
• /
• pp.215-224
• /
• 2020

In the present study, according to the important of porosity in low specific weight in comparison of high stiffness of carbon nanotubes reinforced composite, buckling and free vibration analysis of sandwich composite beam in two configurations, of laminates using differential quadrature method (DQM) is studied. Also, the effects of porosity coefficient and three types of porosity distribution on critical buckling load and natural frequency are discussed. It is shown the buckling loads and natural frequencies of laminate 1 are significantly larger than the results of laminate 2. When configuration 2 (the core is made of FRC) and laminate 1 ([0/90/0/45/90]_s) are used, the first natural frequency rises noticeably. It is also demonstrated that the influence of the core height in the case of lower carbon volume fractions is negligible. Even though, when volume fraction of fiber increases, the critical buckling load enhances smoothly. It should be noticed the amount of decline has inverse relationship with the beam aspect ratio. Investigating three porosity patterns, beam with the distribution of porosity Type 2 has the maximum critical buckling load and first natural frequency. Among three elastic foundations (constant, linear and parabolic), buckling load and natural frequency in linear variation has the least amount. For all kind of elastic foundations, when the porosity coefficient increases, critical buckling load and natural frequency decline significantly.

• 대한영양사협회학술지
• /
• 제7권3호
• /
• pp.295-306
• /
• 2001

The purpose of the study was to develop an internet nutritional counseling program using an expert system to assist obese people to lose weight through behavior modification. The internet counseling program for weight loss was developed by the accumulation of knowledge dealing with eating habits and exercising behaviors in expert system tool, Knowledge Engineering Agent (KEA) by a dietitian without any help of computer expert. To accumulate knowledge into KEA, survey was performed in 150 obese people, dietitians reviewed and consulted each survey case, and the consulted contents were learned and accumulated into KEA. Survey questionnaire was the same as that of the internet consulting program, and it included general characteristics, dietary habits, lifestyle, and exercise patterns related to obesity. Also, the dietitian selected proper factors inferred from the survey questionnaire of each case, and added the conclusions for them. Conclusions were made for helping clients to correct bad eating behaviors and accumulate good behaviors to lose weight. Counseling was divided into two parts; a two-week part and a daily part. Two-week counseling was performed based on 4 step questionnaires, and daily counseling was done for daily food consumption and physical activity. When clients answered survey questionnaires in a counseling internet program, the recommendations on how to eat, to exercise and to deal with stress in a real time for each case, was given. In conclusion, a counseling internet program for weight reduction can be used to give advices how to deal with obesity in a man-to-man way in a real time using KEA where nutritional knowledge based on behavior modification for weight loss was accumulated.

• 대한지역사회영양학회지
• /
• 제16권6호
• /
• pp.672-682
• /
• 2011

This study was conducted to examine the differences in perceived body weight and image and various lifestyles based on the self-rated health of university students when gender was adjusted. Five hundred fifty-five participants were asked their perceived health condition, and 58, 289, 160 and 48 students answered themselves as "very healthy", "healthy", "normal", and "unhealthy", respectively. As compared to the other 3 groups, "unhealthy" group showed higher proportions in dissatisfaction of body weight and negative perception of body image (P < 0.01). As health related lifestyles, "very healthy" group reported longer sleeping time than "unhealthy" group (P < 0.05), and had a higher proportion of people with regular exercise. Among the dietary behaviors, the frequencies of followings significantly different among the groups: "Regularity of meal time" (P < 0.01), "Eat protein foods more than twice a day" (P < 0.001), "Eat vegetables" (P < 0.01), "Eat fruit and fruit juice" (P < 0.01), "Eat vegetable oil added foods" (P < 0.01), "Eat seaweed" (P < 0.01), "Eat breakfast" (P < 0.01), "Modulation in animal fat and high in cholesterol intake" (P < 0.01). Particularly, higher proportion of subjects answered "very healthy" had higher frequencies (6-7 times/week) of these dietary behaviors. Overall results suggest that healthy lifestyle including adequate sleeping time, regular exercise, and good dietary behaviors might be potential factors affecting positive perception of health. In addition, positive perception of body weight and image were related with positive perception of health.

• 한국환경복원기술학회지
• /
• 제8권3호
• /
• pp.21-32
• /
• 2005

In Incheon metropolitan city, the urban open space areas are deficient and it is nearly impossible to obtain newly the land for parks by reason of the risk of the land value, the budgetary deficit and so forth. Therefore, it seems to be urgent to consider how to manage the established urban natural park efficiently to enhance the quality of recreational experiences of the public. The organization for the urban natural parks management is to be completely put in good order, for the objects to manage is changeable as well as diverse and what users need should be full satisfied. The purpose of this study is to investigate the differences of urban natural park's management suggest the improvement and development directions in urban natural park by group(professionals and Users). To do this, data were collected in the typical regions by urban natural park for this study, using the questionnaires. In these urban natural park, the on-site survey was carried out the users of these urban natural park during October in 2004. Also The analysis was done with the valid questionnaires of user's 644 and professional's 146. The questionnaires contained three of categories : openspace types' satisfaction and urban natural park's satisfaction, and management, and park user's socioeconomic characteristics and behaviors. Data collected from respondents were analysized by descriptive statistics, T-test, factor analysis and regression analysis. The results of this study can be summarized as follows; The evaluation of urban natural park management is predicted the operation management. So, one can draw a conclusion that user's needs is likely to be increased correspondingly as urban natural park planning and design, management which meets the overall satisfaction. Using the results of this study, we can make a guideline for a park management program, market positioning, standards and provisions of urban natural park by group.

• Environmental Engineering Research
• /
• 제19권1호
• /
• pp.1-8
• /
• 2014

Natural organic matter (NOM) is a primary component of fouling in low-pressure membrane filtration, either solely, or in concert with colloidal particles. Various preventive measures to interfere with NOM fouling have been developed and extensively tested, such as coagulation, oxidation, ion exchange, carbon adsorption, and mineral oxide adsorption. Therefore, this article aims to conduct a literature review covering the topics of low-pressure membrane processes, NOM characteristics and fouling behaviors, and diverse fouling control strategies. In-depth explanations and discussion are made regarding why some treatment options are able to remove NOM from source water, but do not reduce fouling. This review provides insight for hybridized membrane processes with respect to NOM removal and fouling mitigation in water treatment.

• Journal of Advanced Marine Engineering and Technology
• /
• 제30권6호
• /
• pp.724-730
• /
• 2006

Fracture behavior of brittle solids is closely related to microcracking. A meso-scale analysis method using the natural element method is proposed for the analysis of brittle microcracking solids. The microcracking is assumed to occur along Voronoi edges in the Voronoi diagram generated using the nodal points as the generators. The mechanical effect of microcracks is considered by controlling the material constants in the neighborhood of the microcracks. The meso-analysis method is applied to the simulation of the microcracking behaviors of brittle solids subjected to tensile macrostress. The method is also applied to the analysis of the propagation of a macrocrack accompanied by the coalescence with microcracks formed near the macrocrack-tip.

• 대한기계학회논문집B
• /
• 제22권12호
• /
• pp.1796-1804
• /
• 1998

A numerical investigation has been performed to discuss the radiation-affected steady-laminar natural convection induced by a hot inner cylinder under a large temperature difference in the annuli filled with a gray gas. To examine the effects of thermal radiation on thermo-fluid dynamic behaviors in the eccentric geometry, the generalized body-fitted coordinate system is introduced while the finite volume method (FVM) is used for solving the radiative transport equation. After validating the numerical results for the case without radiation, the detailed radiation effect has been discussed. Based on the results of this study, when there exists a large temperature difference between two cylinders, the existence of radiatively participating medium is found to incur a distinct difference in fluid dynamic as well as thermal behavior.

• 한국수학교육학회지시리즈D:수학교육연구
• /
• 제5권1호
• /
• pp.1-12
• /
• 2001

Generating fractal images by graphing calculators such as TI_92 combines several important features, which convey the excitement of a living, changing mathematics appropriate to secondary or post-secondary students. The topic of fractal geometry can be illustrated using natural objects such as snowflakes, leaves and ferns. These complex and natural forms are often striking fantastic and beautiful. The examples highlight the fact that complex, natural behaviors can result from simple mathematical rules such as those embodied in iterated function systems(IFS). The visual splendor beauty of fractals, in concert with their ubiquity in nature, revels the intellectual beauty of nonlinear mathematics in a compelling way. The window is now open for students to experience and explore some of the wonder of fractal geometry.