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Characterization of random stress fields obtained from polycrystalline aggregate calculations using multi-scale stochastic finite elements

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Frontiers of Structural and Civil Engineering 2015年第2期9卷 121-140页

作者： Bruno SUDRET hung xuan DANG Marc BERVEILLER Asmahana ZEGHADI Thierry YALAMAS Risk Safety and Uncertainty Quantification ETH Zurich Stefano-Franscini-Platz 5 Zurich CH-8093 Switzerland Phimeca Engineering S.A. Centre d'affaires du Zenith 34 rue de Sarlieve Cournon F-63800 France EDF R&D Dept. of Materials and Mechanics of Components Site des Renardieres Moret-sur-Loing Cedex 77250 France

The spatial variability of stress fields resulting from polycrystalline aggregate calculations involving random grain geometry and crystal orientations is investigated. A periodogram-based method is proposed to identify the properties of homogeneous Gaussian random fields (power spectral density and related covariance structure). Based on a set of finite element polycrystalline aggregate calculations the properties of the maximal principal stress field are identified. Two cases are considered, using either a fixed or random grain geometry. The stability of the method w.r.t the number of samples and the load level (up to 3.5% macroscopic deformation) is investigated.

关键词： polycrystalline aggregates crystal plasticity random fields spatial variability correlation structure Random CRYSTAL PLASTICITY multi-scale stress fields FINITE ELEMENT aggregates arithmetic

Assessment of soil quality indicators under different agricultural land uses and topographic aspects in Central Vietnam

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International Soil and Water Conservation Research 2018年第4期6卷 280-288页

作者： Tung Gia Pham hung Trong nguyen Martin Kappas Cartography GIS and Remote Sensing DepartmentGottingen UniversityGeorge August University of GoettingenGoldschmidstr.537077 GoettingenGermany University of Agriculture and Forestry Hue UniversityVietnam Ministry of Natural Resources and Environment Vietnam

Soil quality assessment is valuable for agricultural production. In this research, 155 soil samples at two soil depths were collected from four land use types in an agricultural area of the A Luoi district in the Central Vietnam. Differences of soil organic carbon, total nitrogen in soil and soil pH under different land use types and topographic aspects were compared. Soil organic carbon contents in arable land and plantation forest are higher than those in natural forest and grassland (p < 0.05). Conversely, the total nitrogen in natural forest was significantly lesser in comparison to other land use types. Meanwhile there were no significant differences of the total nitrogen content (p < 0.05) among arable land, plantation forest, and grassland. The soil of grassland, natural and plantation forests land use types were more significantly acidic than those of the soils of the arable land use type. Soil organic carbon and total nitrogen showed a decreasing trend while soil depth increased in all land use types. The soil pH in plantation forest and arable land use types showed no significant change in relation to soil depth. Significant differences were not found in topographic aspects and soil organic carbon content;however, the different changing trends of soil organic carbon content between land use types and aspects were found. The impact of slope, elevation, farming system or soil texture accounted for the differences in these soil indicators under different land use types in the A Luoi district.

关键词： Central Vietnam Land use type Hilly area Soil quality Topographic aspects

Analysis of an Ar plasma jet in a dielectric barrier discharge conjugated with a microsecond pulse

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Plasma Science and Technology 2019年第9期21卷 73-81页

作者： Duc Ba nguyen Quang hung TRINH Won Gyu LEE Young Sun MOK Department of Chemical and Biological Engineering Jeju National University Jeju 63243 Republic of Korea Center for Advanced Chemistry Institute of Research and Development Duy Tan University 03 Quang Trung Da Nang Vietnam Division of Chemical Engineering and Bioengineering Kangwon National University Chuncheon Kangwon 24341 Republic of Korea

In this work, an Ar plasma jet generated by an AC-microsecond-pulse-driven dielectric barrier discharge reactor, which had two ring-shaped electrodes isolated from the ambient atmosphere by transformer oil, was investigated. By special design of the oil insulation, a chemically active Ar plasma jet along with a safe and stable plasma process as well as low emission of CO and NOxwere successfully achieved. The results indicated that applied voltage and frequency were basic factors influencing the jet temperature, discharge power, and jet length, which increased significantly with the two operating parameters. Meanwhile, gas velocity affected the jet temperature in a reverse direction. In comparison with a He plasma jet, the Ar plasma jet had relatively low jet temperature under the same level of the input parameters, being preferable for bio-applications. The Ar plasma jet has been tested to interact with human skin within 5 min without the perception of burnt skin and electrical shock.

关键词： Ar plasma jet atmospheric pressure plasma jet OES of Ar gas emission of Ar plasma jet transformer oil

Double-loop Control Structure Using Proportional Resonant and Sequence-decoupled Resonant Controllers in Static Coordinates for Dynamic Voltage Restorer

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Chinese Journal of Electrical Engineering 2019年第3期5卷 10-19页

作者： Vu Thai hung Hongchun Shu Le Ngoc Giang nguyen Duc The School of Electric Power Engineering Kunming University of Science and TechnologyKunming 650500China AD-AF Academy of Viet Nam Son TayHa Noi 100000Viet Nam

Among incidents on grids,the sag/swell voltage is considered as the most frequent *** solve this problem,custom power devices are *** particular,the dynamic voltage restorer(DVR)is a modern and efficient customer *** are used to mitigate voltage sag/swells and harmonics on the load bus,thus protecting the sensitive *** DVR is a serial compensator that applies a voltage to the point of common coupling to maintain the voltage of sensitive load at the nominal *** improve the performance of DVRs,in this study,the control strategy of the two-stage loop circuit is *** external voltage control loop uses a sequence-decoupled resonant(SDR)controller,and the inner current-control loop uses the proportional resonant(PR)controller implemented in the stationary frameαβ.

关键词： Dynamic voltage restorer PR controller SDR controller nonlinear load

EXISTENCE AND STABILITY OF PERIODIC AND ALMOST PERIODIC SOLUTIONS TO THE BOUSSINESQ SYSTEM IN UNBOUNDED DOMAINS

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Acta Mathematica Scientia 2022年第5期42卷 1875-1901页

作者： Thieu Huy nguyen Truong xuan PHAM Thi Ngoc Ha VU The Sac LE School of Applied Mathematics and Informatics Hanoi University of Science and Technology Vien Toan ung dung va Tin hocDai hoc Bach khoa Hanoi 1DaiCoVietHanoiVietnam Department of Mathematics Faculty of Information TechnologyThuyloi university Khoa Cong nghe Thong tinBo mon ToanDai hoc Thuy loi175 Tay SonDong DaHa NoiViet Nam Thuyloi University Dai hoc Thuy Loi175 Tay SonDong DaHanoiViet Nam

In this paper we investigate the existence and stability of periodic solutions(on a half-line R_(+))and almost periodic solutions on the whole line time-axis R to the Boussinesq system on several classes of unbounded domains of R^(n) in the framework of interpolation *** the linear Boussinesq system we combine the L^(p)—L^(q)-smoothing estimates and interpolation functors to prove the existence of bounded mild ***,we prove the existence of periodic solutions by invoking Massera’s *** also prove the existence of almost periodic *** we use the results of the linear Boussinesq system to establish the existence,uniqueness and stability of the small periodic and almost periodic solutions to the Boussinesq system using fixed point arguments and interpolation *** results cover and extend the previous ones obtained in[13,34,38].

关键词： Boussinesq systems periodic solutions almost periodic solutions unbounded domains smoothing estimates dual estimates interpolation spaces stability

Evaluation of Weathering Performance of Rosin-Copper Based Treated Wood

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Journal of Renewable Materials 2022年第11期10卷 2765-2780页

作者： Thi Thanh Hien nguyen Nho Quyet Tran Thi Minh Nguyet nguyen Hien Mai Trinh xuan Phuong Le Trong Kien nguyen College of Wood Industry and Interior Design Vietnam National University of ForestryHa NoiViet Nam College of Economics and Management Northeast Forestry UniversityHarbinChina

This study aimed to evaluate the effect of natural weathering on some surface characteristics and mechanical properties of Styrax wood treated with mixtures of 1.0%,2.0%,or 4.0%rosin sizing agent and 3%copper *** samples after treatment were exposed to outdoor conditions for one year and changes in color,glossiness,weight loss,compression strength parallel to grain(CSPG),modulus of rupture(MOR),and modulus of elasticity(MOE)were investigated after 6 and 12-month of natural *** results showed that rosin-copper treatment could improve color stability and gloss of samples after *** losses of all rosin-copper treated samples after 12 months of exposure were negligible compared with the untreated control *** addition,rosin-copper treatment enhanced the CSPG compared to untreated controls,but slightly decreased the MOR and MOE of Styrax wood before *** weathering factors induced a reduction for all strength properties,however,the decrease rate for strength properties of rosin-copper treated samples was negligible compared with the untreated control samples after 12-month natural weathering *** FTIR and SEM-EDX confirmed that the use of the rosin-copper formulations to impregnate wood could decrease the hazard of the copper preservative leaching into the environment,while also enhancing more resistance against weathering factors and other biotic factors.

关键词： Rosin-copper weathering color stability CSPG MOR MOE

Accuracy assessment of mine walls＇ surface models derived from terrestrial laser scanning

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International Journal of Coal Science & Technology 2018年第3期5卷 328-338页

作者： nguyen Quoc Long Michal M. Buczek La Phu Hien Sylwia A. Szlapinska Bui xuan Nam nguyen Viet Nghia Cao xuan Cuong Department of Mine Surveying Hanoi University of Mining and Geology Hanoi Vietnam Department of Mine Surveying AGH University of Science and Technology Kxakow Poland Department of Surveying and Spatial Data Analysis Hanoi University of Mining and Geology Hanoi Vietnam Department of Surface Mining Hanoi University of Mining and Geology Hanoi Vietnam

The monitoring of highwall slopes at open-pit mines is an important task to ensure safe mining. For this reason, several techniques such as total station, radar, terrestrial Light Detection and Ranging （LIDAR） can be employed for surface measurement. The objective of this study is to investigate mesh algorithms, which can be used to interpolate 3D models of pit walls. Experiments were carried out at Coc Sau open-pit mine at Quang Ninh province of Vietnam, and at experimental mine of Akademia Gtrniczo-Hutnicza University of Science and Technology in Cracow, Poland. First, 3D point cloud data for the study area was acquired by using terrestrial LIDAR, then was used to generate mesh surfaces using three algorithms--Delaunay 2.5D XY Plane, Delaunay 2.5D Best Fitting Plane, and Mesh from Points. After that, the results were rectified and optimized. Subsequently, the optimized meshes were used for generation of non-uniform rational basis spline （NURBS） surfaces. Then, the NURBS surface accuracy was assessed. The results showed that the average distance between surface and point cloud was within range of 5.6-5.8 mm with deviation of 6.2-6.8 mm, depending on the used mesh. Additionally, the quality of surfaces depends on the quality of input data set and the algorithm used to generate mesh network, and the accuracy of computed NURBS surfaces fitting into pointset was 4-5 times lower than that of optimized mesh fitting. However, the accuracy of the final product allows determining displacements on the level of centimeters.

关键词： Polygon mesh network NURBS surface LIDAR - Open-pit mine Highwall slope

Bubble-enhanced quadrilateral finite element formulation for nonlinear analysis of geotechnical problems

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Underground Space 2018年第3期3卷 229-242页

作者： T.Vu-Hoang T.Vo-Minh H.nguyen-xuan Department of Civil Engineering HCMC University of TechnologyHo Chi Minh CityViet Nam Department of Civil Engineering Hutech UniversityHo Chi Minh CityViet Nam Center for Interdisciplinary Research in Technology Hutech UniversityHo Chi Minh CityViet Nam

We investigate a new numerical procedure based on a bubble-enriched finite element formulation in combination with the implicit backward Euler scheme for nonlinear analysis of strip footings and stability of *** soil body is modeled as a perfect plastic Mohr-Coulomb *** displacement field is approximated by a 4-node quadrilateral element discretization enhanced with bubble *** loads and failure mechanisms in cohesive frictional soil are determined by solving a few Newton-Raphson *** results of the present approach are verified by both analytical solutions and other numerical solutions available in the literature.

关键词： Material nonlinear analysis Backward Euler scheme Bearing capacity Slope stability Bubble functions Finite elements

A Size-Dependent Functionally Graded Higher Order Plate Analysis Based on Modified Couple Stress Theory and Moving Kriging Meshfree Method

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Computers, Materials & Continua 2018年第12期57卷 447-483页

作者： T.D.Tran Chien H.Thai H.nguyen-xuan Faculty of Construction&Electricity Ho Chi Minh City Open UniversityHo Chi Minh CityVietnam Division of Computational Mechanics Ton Duc Thang UniversityHo Chi Minh CityVietnam Faculty of Civil Engineering Ton Duc Thang UniversityHo Chi Minh CityVietnam Center for Interdisciplinary Research in Technology Ho Chi Minh City University of Technology(HUTECH)Ho Chi Minh CityVietnam Department of Physical Therapy Graduate Institute of Rehabilitation ScienceChina Medical UniversityTaichung40402Taiwan

A size-dependent computational approach for bending,free vibration and buckling analyses of isotropic and sandwich functionally graded(FG)microplates is in this study *** consider both shear deformation and small scale effects through the generalized higher order shear deformation theory and modified couple stress theory(MCST).The present model only retains a single material length scale parameter for capturing properly size effects.A rule of mixture is used to model material properties varying through the thickness of *** principle of virtual work is used to derive the discrete system equations which are approximated by moving Kriging interpolation(MKI)meshfree *** examples consider the inclusions of geometrical parameters,volume fraction,boundary conditions and material length scale *** and effectiveness of the present method are confirmed through numerical results.

关键词： Modified couple stress theory isotropic and sandwich FGM plates moving Kriging meshfree method