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

• Smart Structures and Systems
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• 제26권2호
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• pp.253-262
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• 2020

In this paper, a new higher order shear deformation model is developed for static analysis of functionally graded beams with considering porosities that may possibly occur inside the functionally graded materials (FGMs) during their fabrication. The model account for higher-order variation of transverse shear strain through the depth of the beam and satisfies the zero traction boundary conditions on the surfaces of the beam without using shear correction factors. The present work aims to study the effect of the distribution forms of porosity on the bending of simply supported FG beam. Based on the present higher-order shear deformation model, the equations of motion are derived by the principle of virtual works. Navier type solution method was used to obtain displacement and stresses, and the numerical results are compared with those available in the literature. A comprehensive parametric study is carried out to assess the effects of volume fraction index, porosity fraction index, and geometry on the bending of imperfect FG beams. It can be concluded that the proposed model is simple and precise for the resolution of the behavior of flexural FGM beams while taking into account the shape of distribution of the porosity.

• 방사선산업학회지
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• 제12권4호
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• pp.297-302
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• 2018

The wedge filter has two movements, fixed and dynamic. In this study, the depth dose distribution was analyzed to determine the stability of the dose distribution and dose volume histograms obtained by evaluating the usability of the critical normal tissue dose around the tumor dose. The depth dose was analyzed from the dose distribution from a Linac (6 MV and 10 MV irradiation field of energy $20{\times}20cm^2$, wedge filter with a SSD of 100 cm and $15^{\circ}$, $30^{\circ}$, $45^{\circ}$ Y1-in (Left -7 cm), Y2-out(Right +7 cm). To analyze the fluctuations of the depth dose, a fixed wedge and dynamic wedge toe portion was examined according to the energy and angle because the size of the fluctuations was included in the error bound and did not show significant differences. The neck, breast, and pelvic dosimetry in tumor tissue are measured more commonly with a dynamic wedge than a fixed wedge presumably due to the error range. On the other hand, dosimetry of the surrounding normal tissue is more common using a fixed wedge than with a dynamic wedge.

• 도시과학
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• 제11권2호
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• pp.9-17
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• 2022

The purpose of this study is to develop an index for evaluating the function of a new motorway using the travel distance frequency distribution (TLFD) calculated using the vehicle travel route big data, and to overcome the limitations of the evaluation through the existing traffic volume. The mobility evaluation index of motorways was developed by applying it to the TLFD data table in 2019. The smaller the value of the mobility evaluation index of the link is calculated, the more it is a link with mainly short-distance travel, and the higher the value of the mobility evaluation index, the more it means a link with mainly long-distance travel. The accessibility evaluation index was calculated through the result of the mobility evaluation index of all motorways developed, and all motorways were grouped into three groups using K-means clustering. Group A was found to exist inside a large city and consisted of motorways with many short-distance traffic, Group B was investigated as acting as an arterial between groups, and Group C was classified as a motorway consisting mainly of long-distance traffic connecting large cities and large cities. This study is significant in developing a new motorway function evaluation index that can overcome the limitations of motorway function evaluation through the existing traffic volume. It is expected that this study can be a reasonable comprehensive indicator in the operation and planning process of motorways.

• Steel and Composite Structures
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• 제33권2호
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• pp.195-208
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• 2019

Based on a four-variable shear deformation shell theory, the free vibration analysis of functionally graded graphene platelet-reinforced composite (FGGPRC) doubly-curved shallow shells with different boundary conditions is investigated in this work. The doubly-curved shells are composed of multi nanocomposite layers that are reinforced with graphene platelets. The graphene platelets are uniformly distributed in each individual layer. While, the volume faction of the graphene is graded from layer to other in accordance with a novel distribution law. Based on the suggested distribution law, four types of FGGPRC doubly-curved shells are studied. The present shells are assumed to be rested on elastic foundations. The material properties of each layer are calculated using a micromechanical model. Four equations of motion are deduced utilizing Hamilton's principle and then converted to an eigenvalue problem employing an analytical method. The obtained results are checked by introducing some comparison examples. A detailed parametric investigation is performed to illustrate the influences of the distribution type of volume fraction, shell curvatures, elastic foundation stiffness and boundary conditions on the vibration of FGGPRC doubly-curved shells.

• Coupled systems mechanics
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• 제13권2호
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• pp.115-132
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• 2024

This paper introduces an improved shear deformation theory for analyzing the buckling behavior of functionally graded plates subjected to varying temperatures. The transverse shear strain functions employed satisfy the stress-free condition on the plate surfaces without requiring shear correction factors. The material properties and thermal expansion coefficient of the porous functionally graded plate are assumed temperature-dependent and exhibit continuous variation throughout the thickness, following a modified power-law distribution based on the volume fractions of the constituents. Moreover, the study considers the influence of porosity distribution on the buckling of the functionally graded plates. Thermal loads are assumed to have uniform, linear, and nonlinear distributions through the thickness. The obtained results, considering the effect of porosity distribution, are compared with alternative solutions available in the existing literature. Additionally, this study provides comprehensive discussions on the influence of various parameters, emphasizing the importance of accounting for the porosity distribution in the buckling analysis of functionally graded plates.

• 한국분무공학회지
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• 제9권4호
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• pp.17-23
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• 2004

Spray characteristics of a twin-hole air shrouded nonle designed for gasoline injectors was investigated by using laser diffraction particle analyzer (LDPA) and tomography reconstruction- A confined spray chamber which is optically accessible through a pair of glass windows was made to simulate the fuel injection condition in intake manifold of gasoline engine. The measurement was applied to the twin hole injector with and without an air shroud. It demonstrates that for the case with an air shroud, fine atomization is achieved and there exists a large number of fine droplets between the region of the main spray streams, which conforms with the spray visualization. The drop size distribution was investigated as a function of elapse time after fuel injection. The distribution was greatly affected by the measurement position from the injector exit. Also, the spatially resolved spray volume fraction and Sauter Mean Diameter (SMD) from line-of-sight data of the LDPA are tomographically reconstructed by Convolution Fourier transformation under the steady injection condition.

• Journal of Biosystems Engineering
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• 제26권5호
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• pp.431-440
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• 2001

Generated agri-chemical droplets by orchard sprayers are evaporated regenerated and transported along wind streams. The droplets are deposited to targets after changing their sizes, affecting the retention of droplets. An orchard sprayer, designed for spraying grapevines was studied on the spatial distribution of droplet size. The experimental variables were spray direction (0, 22.5, 45, 67.5 and 90˚), distance(2.5, 3.0 and 3.5 m) and fan speed (2,075 and 3,031 rpm). Droplet sizes were converted and analyzed from spray stains, sampled using water sensitive papers. The number median diameter (NMD) increased with an increase of the distance due to disappeared fine droplets (<50 ㎛): however, the volume median diameter (VMD) decreased due to shrunken large droplets (>100 ㎛). Fast fan speed delivered large droplets to 3.5 m, but the spatial distributions of NMD and VMD were not uniform. Slower fan speed decreased the possibility of evaporation and drift; therefore, plenty of droplets were maintained up to 3.0 m. The upward blasting distance was limited within 3 m, but the limit to the ground level was extended to 3.5 m. Concentrated wind and droplets to the ground level should be redistributed to upper canopy direction, leading more uniform deposits. High speed wind and system pressure should be avoided because of generating fine droplets, which would be disappeared and drifted away.

• Coupled systems mechanics
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• 제9권6호
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• pp.499-519
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• 2020

The effect of porosity on the thermo-mechanical behavior of simply supported functionally graded plate reposed on the Winkler-Pasternak foundation is investigated analytically in the present paper using new refined hyperbolic shear deformation plate theory. Both even and uneven distribution of porosity are taken into account and the effective properties of FG plates with porosity are defined by theoretical formula with an additional term of porosity. The present formulation is based on a refined higher order shear deformation theory, which is based on four variables and it still accounts for parabolic distribution of the transverse shearing strains and stresses through the thickness of the FG plate and takes into account the various distribution shape of porosity. The elastic foundation is described by the Winkler-Pasternak model. Anew modified power-law formulation is used to describe the material properties of FGM plates in the thickness direction. The closed form solutions are obtained by using Navier technique. The present results are verified in comparison with the published ones in the literature. The results show that the dimensionless and stresses are affected by the porosity volume fraction, constituent volume fraction, and thermal load.

• Composites Research
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• 제17권2호
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• pp.34-39
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• 2004

본 연구에서는 폐쇄형 발포금속의 인장 특성을 이해하기 위하여 수정된 단위모델을 제시하였다. 또한 발포금속의 밀도는 가우스 분포에 의거하여 확률적으로 분포한다고 가정하고 본 연구에서 제시된 수정 단위 모델을 조합하여 유한요소 모델을 제안하였다. 이 모델은 실제 인장 시험과 유사한 변형거동을 보이는 것을 확인하였고, 적절한 밀도 분포와 내부 기공을 고려하게 되면, 해석에서 구해진 최대 인장 강도가 근사적으로 실험결과와 일치하는 것을 볼 수 있었다. 또한, 발포 알루미늄의 최대 인장 강도는 밀도 분포의 표준편차보다는 내부 기공 부피분율에 더 민감하게 변하는 것으로 밝혀졌다.