On the effective viscosity of fresh concrete: A homogenization approach

Two new homogenization schemes together with the classical generalized self-consistent scheme (GSC) and its extension are proposed to deal with the effective viscosity of fresh concrete. All these models exploit the composite sphere morphology of suspension made of a viscous fluid and spherical particles. They differ from each other by the ways the extra fluid zone (EFZ) located in between the composite sphere are treated. The comparison with experimental data shows that the GSC provides very good result for a well arranged particle size scale that allows mapping the whole medium by composite spheres of different size scales. However, the GSC cannot be used for a suspension with a non negligible volume of the EFZ. For such a case, extensions of the GSC those take into account the contribution of the EFZ to the overall viscous behavior of the system is necessary to fit with experimental data. Two of them work very well for non-cohesive particles and the other can be employed for suspension with cohesive particles such as the case of fresh cement paste

Propagation de fissures et endommagement par microfissures des matériaux viscoélastiques linéaires non vieillissants

Most of France's energy is nuclear. The reactor building comprises a internal and external containment. The internal containment is prestressed to limit the flow of leakage in the internal-external space. The prestress decreases during time by the creep of concrete. It may propagate the cracks by the accidental internal pressure. So we define two research problems : propagation of macrocracks in viscoelastic structure ; effective behavior of microcracked viscoelastic material. Firstly, we develop a Burger viscoelastic model of concrete with two approaches: numerical and analytical. Then we solve the problem of single cracks in developing thermodynamically the concept of energy release rate. In the third part we develop a viscoelastic model to study the effective behavior of microcracked materials in the case without propagation. The problem of propagation of microcracks is then studied by a numerical approach based on the "representative pattern morphology". These studies are finally applied to solve the problems of crack propagation and damage of containment under accidental internal pressureLa plupart de l'énergie en France est d'origine nucléaire. Le bâtiment de réaction comporte une enceinte interne et une externe. L'enceinte interne est en béton précontraint, pour limiter le débit de fuite dans l'espace interne-ence inte. La précontrainte diminue au cours du temps à cause du fluage du béton. Il risque de se propager des fissures par une pression accidentelle interne. On pose alors deux problèmes de recherche : propagation de macrofissures dans une structure viscoélastique ; comportement effectif d'un matériau viscoélastique microfissuré. On développe tout d'abord un modèle viscoélastique de Burger pour le béton avec deux approches de calcul numérique et analytique. On traite ensuite le problème de fissure unique en développant thermodynamiquement la notion du taux de restitution d'énergie. Dans la troisième partie, on établit un modèle viscoélastique pour modéliser le comportement effectif des matériaux microfissurés dans le cas sans propagation. Le problème de propagation de microfisures est étudié ultérieurement par une approche numérique basée sur le "motif morphologique représentative". Ces études sont finalement appliquées pour traiter les problèmes de propagation de fissure et endommagement d'une enceinte de confinement sous l'application d'une pression accidentelle intern

Overall viscoelastic properties of 2D and two-phase periodic composites constituted of elliptical and rectangular heterogeneities

International audienceThis paper presents analytical solutions for the effective rheological viscoelastic properties of 2D periodic structures. The solutions, based on Fourier series analysis, are derived first in the Laplace-Carson (LC) space for different inclusion shapes (rectangle or ellipse) and arrangements. The effective results are obtained in the form of rational functions of the LC transform variable. Two inversion methods are used to find the relaxation behavior. The first one is based on the exact inverse of the LC transform while the second approximates the overall behavior by using a Standard Linear Solid model, which yields very simple analytical formulas for the coefficients entering the constitutive equations. Results of the two methods are compared in the case of an application to real materials

Review and Evaluation of Agricultural Policies in Years 2015-2017

This journal article describes main results of the OECD Annual Report published in 2018, titled “Review and evaluation of agricultural policy in 2017” for 51 selected countries in the world, including Vietnam. The report is closely prepared by MARD and OECD experts. The journal article emphasizes more on Vietnam by updating and adjusting data, information and policies in 2017 and 2018. The description presents the changing trend of agricultural policies applied in the world, considering whether this trend is in the direction of achieving sustainable productivity growth, environmental protection, and adaptation to climate change. On average in the last 20 years, trend of world policies has been better but far to catch above purposes. The development of international trade has made the commodity movement more freely and price gaps narrowed between countries and regions. This trend made agricultural markets developed more toward reflecting the scarcity of good and services. Average level of total agricultural supports has been reducing. Consequently, the world price indices and the total support have been converted between countries and commodities. However, the total agricultural support reduction is mainly in developed countries like OECD countries. Emerging and developing countries have increased their agricultural supports. Relative to GDP, the level of the total agriculture support in Vietnam has been reducing.Inside the total agricultural support, producer supports accounted 78% while general service support accounted only for 14%. Inside the producer support, market price support accounted for more than 50% in many countries. Payments based on outputs and inputs also accounted more than 50% in many countries. In Vietnam, the producer support is very small, negative level in 2015 and 2016 and became positive in 2017 and 2018. The agricultural producer support in 2017 is about 900 million USD. In the overall service support, many countries mainly invest in infrastructure construction, for example in Japan and Vietnam over 70%, while investments in other items are too small, for example that in Vietnam is only about 16%.In conclusion, OECD suggests that market price support should be reduced and finally eliminated. Similarly, output and input payments should be reduced and eliminated. Future policies should focus on general support service that helps producers to achieve sustainable productivity growth in the context of a changing and uncertain climate. OECD especially emphasizes on appropriate investments in research, together with efforts to ensure that the outputs of this research reach farmers. OECD also emphasizes on research that help producers to better manage risks including business risk, weather risk, and climate changes. Agricultural production and climate changes are strongly interacted. Future research should be the better co-operation between public and private sectors with the leading role of public sector. The future research should be co-operated more strongly between countries and regions because of the differences in histories, cultures, geology and climate

On finite-time output feedback sliding mode control of an elastic multi-motor system

In this paper, the tracking control scheme is presented using the framework of finite-time sliding mode control (SMC) law and high-gain observer for disturbed/uncertain multi-motor driving systems under the consideration multi-output systems. The convergence time of sliding mode control is estimated in connection with linear matrix inequalities (LMIs). The input state stability (ISS) of proposed controller was analyzed by Lyapunov stability theory. Finally, the extensive simulation results are given to validate the advantages of proposed control design

RELATIONSHIP BETWEEN CLIMATIC CONDITION AND MANGROVE FOREST STRUCTURE ON NORTHERN COAST OF VIETNAM

The differences in mangrove forest structure, climate, and the linear relationship between climate and mangrove forest structure on the northern coast of Vietnam were analyzed using mangrove forest data measured in 28 sample plots (Dong Rui-8, Xuan Thuy National Park-12 and Lach Sung-8) and climate data collected at the meteorological stations near the study sites (Dong Rui-Tien Yen station, Xuan Thuy National Park-Van Ly station and Lach Sung-Thanh Hoa station) in the period of 1994 - 2012. Results showed that the differences in mangrove forest structure (stem diameter, biomass and basal area) and climate (temperature and rainfall) among study sites were significant (p 0.05). Stem diameter, tree height, basal area and biomass had positive linear relationship with annual average temperature and January average temperature, and negative linear relationship with annual rainfall. A consistently low regression coefficient of less than 0.66 was found among the variables. However, all the regression models were statistically significant (p 0.05). The results could be used to develop multiple linear regression models to predict the change of mangrove ecosystems.The differences in mangrove forest structure, climate, and the linear relationship between climate and mangrove forest structure on the northern coast of Vietnam were analyzed using mangrove forest data measured in 28 sample plots (Dong Rui-8, Xuan Thuy National Park-12 and Lach Sung-8) and climate data collected at the meteorological stations near the study sites (Dong Rui-Tien Yen station, Xuan Thuy National Park-Van Ly station and Lach Sung-Thanh Hoa station) in the period of 1994 - 2012. Results showed that the differences in mangrove forest structure (stem diameter, biomass and basal area) and climate (temperature and rainfall) among study sites were significant (p 0.05). Stem diameter, tree height, basal area and biomass had positive linear relationship with annual average temperature and January average temperature, and negative linear relationship with annual rainfall. A consistently low regression coefficient of less than 0.66 was found among the variables. However, all the regression models were statistically significant (p 0.05). The results could be used to develop multiple linear regression models to predict the change of mangrove ecosystems

Comparison between matrix and back-to-back converter in flywheel energy storage systems

Flywheel energy storage systems (FESS) are considered as the grid integration of renewable energy sources due to their buit-in advantages such as fast response, long cycle life and flexibility in providing auxiliary services to the grid, such as frequency regulation, and voltage support. This paper introduces the structure and comparison results of matrix converter and back-to-back converter which integrated with axial flux permanent magnet motor (AFPM) in FESS. Two converters are functionally equivalent in terms of input power quality and energy regeneration capabilities but need to be compared in terms of performance testing with speed response. In this paper, the research results have been verified that matrix converters perform more effective than back-to-back converters

Controlling matrix converter in flywheel energy storage system using AFPM by processor-in-the-loop method

Flywheel energy storage systems are considered as the grid integration of renewable energy sources due to their inherent advantages such as fast response, long cycle life and flexibility in providing auxiliary services to the grid, such as frequency regulation, and voltage support. The article focuses on the design of the controller, then conducts processor-in-the-loop (PIL) simulation of the dynamics part using the axial flux permanent magnet (AFPM) motor with the matrix converter on MATLAB/Simulink combined with the controller on the TMS32F28377S microcontroller card of Texas Instruments to evaluate the efficiency of the energy storage system

Propagation de fissure et endommagement dans un milieu viscoélastique linéaire

La propagation d'une fissure est associée à un changement de nature des conditions aux limites sur la portion de frontière nouvellement créée. Cette situation interdit le recours à la transformation de Laplace pour la résolution des problèmes viscoélastiques linéaires. On développe donc une approche numérique en éléments finis permettant d'évaluer le taux de restitution d'énergie élastique, puis d'analyser la propagation. On aborde ensuite une extension à l'endommagement par microfissuration

ĐẶC ĐIỂM DÒNG CHẢY VEN BỜ BẮC TRUNG BỘ (HÀ TĨNH - THỪA THIÊN-HUẾ) THỜI KỲ 4/2016

This paper presents the modeled results of general current pattern (daily average value) in Northern Central Vietnam Coast (Ha Tinh - Thua Thien-Hue) during April 2016. Study results show that in general, current flowed from the North to the South with small and instable velocity (V ≈ 0.1 - 0.2 m/s). From 2nd to 6th April current flowed from the South to the North. From 7th to 29th April current flowed from the North to the South. During 13rd to 16th April current velocity was weak (V ≤ 0.1 m/s). In the southern region of Thua Thien-Hue province, the direction of current was instable (from 6th to 9th and from 20th to 22nd April current flowed from the South to the North). Current distribution pattern from modeled results was in accordance with the propagation characteristics of surface water temperatures in the studied area through data analysis of satellite images.Bài báo trình bày kết quả tính toán trường dòng chảy tổng hợp trung bình ngày cho khu vực ven bờ Bắc Trung Bộ (Hà Tĩnh - Thừa Thiên-Huế) thời kỳ 4/2016. Kết quả nghiên cứu cho thấy trong thời gian nghiên cứu nhìn chung dòng chảy tổng hợp trung bình ngày có hướng từ bắc xuống nam, tốc độ tương đối nhỏ V ≈ 0,1 - 0,2 m/s và không ổn định. Từ 2-6/4/2016 dòng chảy tổng hợp trung bình ngày ven bờ có hướng từ nam lên bắc. Từ 7-29/4/2016 dòng chảy ven bờ có hướng từ bắc xuống nam. Các ngày 13-16/4/2016 dòng chảy tổng hợp trung bình ngày có tốc độ nhỏ (V ≤ 0,1 m/s). Khu vực phía nam Thừa Thiên-Huế dòng chảy tổng hợp trung bình ngày có hướng bị biến động mạnh nhất (các ngày 6-9/4 và 20-22/4 hướng dòng từ nam lên bắc). Đặc điểm phân bố dòng chảy tính toán tương đối phù hợp với đặc điểm lan truyền nhiệt độ nước tầng mặt tại khu vực nghiên cứu qua số liệu phân tích ảnh vệ tinh