Science and Technology Development Journal
The official jornal of Viet Nam National University Ho Chi Minh City http://vn.scienceandtechnology.com.vn/
Vietnam National University Hochiminh City
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A control method for parallel inverters in Microgrid based on sliding mode and droop controls
Robust control and flexible operation are the major objectives of islanded microgrid. A microgrid can have different configurations with linear loads and nonlinear loads. The harmonic current caused by nonlinear loads make Proportional Integral (PI) or Proportional Integral Derivative (PID) voltage controller far beyond excellent performance in case of microgrid operating in islanded mode. Additionally, the robustness of the PID closed loop system can not be guaranteed. The voltage control by using Proportional resonant (PR) controller are recommended. Although PR controller has the ability to sinusoidal signals. However, PR controller has a slight deviation of the frequency of selected harmonic component. This paper presents a Sliding Mode Control (SMC) for voltage control of parallel inverters operating in islanded microgrid. This controller can enhance the robustness of control system and reduced-state tracking error. The stability of the closed-system is verified by means of Lyapunov stability criterion. The control structure is based on the inner sliding mode closed-loop and the outer droop control loop. The main aim of this paper is to design inner controllers to enhance the dynamics of the microgrid. The results obtained from the simulation of Matlab
Optimal surface roughness of die steels in powder mixed electrical discharge machining using titan powder
This paper introduces the research results of surface roughness of steel molds after roughing and fine machining by PMEDM using titanium powder. The influence of the concentration of titanium powder mixed dielectric fluid to the surface roughness (Ra) is surveyed in roughing machining, and the regression equation to describe this relationship and the optimal value Ra (Ratoiuu) also be established. The process parameters: electrode material, workpiece material, electrode polarity, pulse on time, pulse of time, current and concentration of titanium powder is used in research on SR of fine machining. The influence of the process parameters to R through the average value of R and its ratio S/N has given By Taguchi method. Results indicated that: current, electrode material, pulse on time, electrode polarity and the interaction between the electrode material with powder concentration greatest impact to Ra and the optimal value Ratoiuu is 1.73 ±0.39µm.
Study on correlation coefficient to design body basic block for various Vietnam women’s somatotype by 3D V- Stitcher
This paper presents results from research on correlation coefficient to design body basic block for various Vietnam women’s stomatotype by 3D V- Stitcher. The study was conducted on 67 female students with chest measurements ranged from 80±0.5cm. 7 body types were divided as the results of main component analysis, cluster analysis, discriminant analysis and ANOVA test on SPSS. In those 7 groups, choosing one group which has the highest percentage to design basic block. This basic block was simulated for 7 different body groups with the purpose of finding the adjustment coefficient in design formulas for various somatotype. The study evaluated sample fit through simulation software through the different colors on the tension map and pressure map beside expert assessment and samples wearer assessment. These evaluation results were tested reliability by Cronbach's Alpha. This research results meet the urgent needs of garment manufacturers and Vietnamese consumers.
Development of INCAT-GC-MS for analysis of metabolites in urine
This paper aims to develop a non-solvent microextraction technique using INCAT (Inside Needle Capillary Adsorption Trap) for GC-MS analysis of volatile metabolites in urine. INCATs with different sorbents were tested, resulting in an INCAT with 3 sorbent layers Chromosorb W+ 20% SE-54, Carbopack X and Carboxen 1000 (1 : 1 : 1), which proved to be the most suitable for differentiating and identifying volatile metabolites in urine samples of patients from those of healthy people.
Energy and exergy estimation for a combined cycle of solid CO2 production and NH3-H2O single effect absorption chiller
In order to reduce the compression power, to use an integrated thermal-driven cycle, and to mitigate the CO2 content in the air, a new combined cycle of absorption chiller and vapor-compression refrigeration cycle to produce carbon dioxide dry ice was devised and analyzed. In this study, the energy and the exergy analyses of the combined cycle were presented. The combined cycle simulation was carried out by using EES (Engineering Equation Solver) program. The CO2 condensation pressure and the generator temperature were considered as key parameters. Results show that the total compression and pumping power using the present combined cycle can be reduced remarkably, amounting to 44.4 %, in comparison with that in the conventional ammonia cooling system. Most of the irreversibility occur in the absorption system and the irreversibility of the absorber has the largest portion. The temperature reduction of the solution or increase in the cooling water temperature can improve the irreversibility of the absorber. However, the latter decreases the irreversibility more than the former
Constructing texture maps using enhanced Beltrami method
Image quality enhancement is a crucial requirement in many applications of digital image and video processing. Removing artifacts which are suffered from image compression will lose simultaneously image texture components. This paper combines Beltrami method and the window derivative to construct the texture map in an attempt to preserve image details during filtering artifacts. Texture map enhancement is also proposed. Simulation results show that the texture map is robust to noise and matches to real texture components of image.
Influence of Viet Nam climatic condition on ampacity of overhead power transmission lines
Based on our previous paper –[1], in which we have computed the ampacity of overhead power transmission lines with considering the influence of environmental conditions such as wind velocity, wind direction, temperature, and radiation coefficient on the typical line of ACSR, we continue in this paper to investigating the influence of Viet Nam climatic condition on the ampacity of overhead power transmission lines in twelve months of the year. The results obtained by the finite element method are compared with those computed by the IEEE standard have been shown the high accuracy and applicability of the finite element method. In particular, the comparison between our calculated results and the maximum current given by the design standard has been shown that if we monitor well the climatic condition, we can operate the real overhead transmission lines with the maximum current that is higher than the original design about several hundred amperes.
Analyses of the power generation performance and the non-equilibrium plasma of a disk MHD generator
Recently, closed cycle MHD power generation system studies have been focused on improving the isentropic efficiency and the enthalpy extraction ratio. By reducing the cross-section area ratio of the disk MHD generator, it is believed that a high isentropic efficiency can be achieved with the same enthalpy extraction. In this study, the results relating to a plasma state which takes into account the ionization instability of non-equilibrium seeded plasma is added to the theoretical prediction of the relationship between enthalpy extraction and isentropic efficiency. As a result, the electron temperature, which reaches the seed complete ionization state without the growth of ionization instability, can be realized at a relatively high seed fraction condition. However, the upper limit of the power generation performance is suggested to remain lower than the value expected in the low seed fraction condition. It is also suggested that a higher power generation performance may be obtained by implementing the electron temperature range, which reaches the seed complete ionization state at a low seed fraction.
A New Model for Discovering Communities of Users on Social Network
The trend of technological development and increasing varieties of social media lead to the changes in people’s behaviors in society and forming online communities. Changes of human’s behaviors make many models of business, marketing, services and even the field of education, security, politicsl change from approaches to user management. Community of users on social networks influence behaviors, habits of each user involved in the community. Therefore, exploring community on social networks from many different data sources via analyzing exchanged contents will help know the user community’s behaviors which are reflected in the content and topics that users are interested in discussing in messages. In this paper, we propose a new model of discovering communities of users on social networks based on the topic model combined with Kohonen network. In the proposed model, we focus on discovering communities of users on social networks and analyzing the interested topics change of online community in each period of time. The proposed model is experimented with a set of vectors in interested topics of online users in higher education field.
Optimization of affecting factors to glucuronic acid production in mature coconut fermentation
The process of mature coconut water fermentation by the complex of two bacteria strains Gluconacetobacter nataicola and Lactobacillus acidophilus in order to get high glucuronic acid concentration was studied. A Blackett – Burman matrix was designed to study the factors that affect glucuronic acid formation. After screening, four factors included G. Nataicola density, L. acidophilus density, sucrose concentration and temperature that have strongly contributed to glucuronic acid formation was selected to design a matrix for modeling optimal point. The result of Response surface methodology (RSM) with Central composite design (CCD) showed the maximum value of glucuronic acid concentration 94.23mg/l at 4.79 logCFU/ml G. Nataicola density, 5.34 logCFU/ml L. acidophilus density, 8.99 % sucrose and incubation at 31.96oC, respectively. The highest value of glucuronic acid concentration in the practical model was 94.23 mg/l.
Analysis and design of new droop control scheme for three-phase parallel inverters in standelone Microgrid
This paper presents a new load sharing technique for parallel-connected three-phase inverters in Standelone Microgrid. The paper proposed improvements droop controller to accurate load share by ratio with rated power of the inverter. In addition, the proposed scheme ensures reduced load voltage droop due to the load and droop. In the paper, the active power and reactive power are divided by voltage regulation under reference voltage in conditions of stark difference between line impedances, In addition the paper presents the ability to overcome the disadvantages of traditional droop scheme. The proposed model is simulated by Matlab-Simulink for 3 parallel-connected three-phase inverters. The simulation results proved the technical soundness and advantages of the proposed in comparision with a tradition scheme even if the output impedance is resistance reactance in power sharing and load voltage drop reduce problems.
Controlling the morphology of polycaprolactone microparticles produced by electrospraying
Electrospraying is an effective method to produce polycaprolactone microparticles for drug or protein carrier application. In this study, some factors which influenced the morphology of polycaprolactone (PCL) particles were investigated by Scanning Electron Microscopy (SEM), such as polymer concentration, solvent and distance from tip to the collector. The SEM micrographs indicated that the low concentration (1 %) of PCL solution created in wrinkled and hollow semi-spheres while wrinkled spheres were formed by using higher polymer concentration (4 %). The spherical morphology was obtained when the polymer concentration was high enough (4 %) to create significant chain entanglements. In addition, chloroform and dichloromethane were good solvents to fabricate electrosprayed microspheres. Solvent mixtures such as acetone and chloroform or Dimethylformamide (DMF) and chloroform were unsuitable for electrosprayed particles since they caused unstable and heterogeneous shape. This research demonstrated that the morphology of microparticles was controlled by adjusting parameters of electrospraying to have a homogeneous and stable morphology.
Effect of Temperature and Porosities on Dynamic Response of Functionally Graded Beams Carrying a Moving Load
The effect of temperature and porosities on the dynamic response of functionally graded beams carrying a moving load is investigated. Uniform and nonlinear temperature distributions in the beam thickness are considered. The material properties are assumed to be temperature dependent and they are graded in the thickness direction by a power-law distribution. A modified rule of mixture, taking the porosities into consideration, is adopted to evaluate the effective material properties. Based on Euler-Bernoulli beam theory, equations of motion are derived and they are solved by a finite element formulation in combination with the Newmark method. Numerical results show that the dynamic amplification factor increases by the increase of the temperature rise and the porosity volume fraction. The increase of the dynamic amplification factor by the temperature rise is more significant by the uniform temperature rise and for the beam associated with a higher grading index.
A family of modified Newton iteration method for solving nonlinear algebraic equations
In this study, a modified Newton iteration version for solving nonlinear algebraic equations is formulated using a correction function derived from convergence order condition of iteration. If the second order of convergence is selected, we get a family of the modified Newton iteration method. Several forms of the correction function are proposed in checking the effectiveness and accuracy of the present iteration method. For illustration, approximate solutions of four examples of nonlinear algebraic equations are obtained and then compared with those obtained from the classical Newton iteration method.
Generalized Knaster-Kuratowski-Mazurkiewicz type theorems and applications to minimax inequalities
Knaster-Kuratowski-Mazurkiewicz type theorems play an important role in nonlinear analysis, optimization, and applied mathematics. Since the first well-known result, many international efforts have been made to develop sufficient conditions for the existence of points intersection (and their applications) in increasingly general settings: G-convex spaces [21, 23], L-convex spaces [12], and FC-spaces [8, 9]. Applications of Knaster-Kuratowski-Mazurkiewicz type theorems, especially in existence studies for variational inequalities, equilibrium problems and more general settings have been obtained by many authors, see e.g. recent papers [1, 2, 3, 8, 18, 24, 26] and the references therein. In this paper we propose a definition of generalized KnasterKuratowski-Mazurkiewicz mappings to encompass R-KKM mappings [5], L-KKM mappings [11], T-KKM mappings [18, 19], and many recent existing mappings. Knaster-KuratowskiMazurkiewicz type theorems are established in general topological spaces to generalize known results. As applications, we develop in detail general types of minimax theorems. Our results are shown to improve or include as special cases several recent ones in the literature..
Inverse Dynamic Analyzing of Flexible Link Manipulators with Translational and Rotational Joints
Inverse dynamic problem analyzing of flexible link robot with translational and rotational joints is presented in this work. The new model is developed from single flexible link manipulator with only rotational joint. The dynamic equations are built by using finite element method and Lagrange approach. The approximate force of translational joint and torque of rotational joint are found based on rigid model. The simulation results show the values of driving forces at joints of flexible robot with desire path and errors of joint variables between flexible and rigid models. Elastic displacements of end-effector are shown, respectively. There are remaining issues which need be studied further in future work because the error joints variables in algorithm to solve inverse dynamic problem of flexible with translational joint has not been mentioned yet.
Extended finite element method for simulating the mechanical behavior of multiple random holes and inclusions in functionally graded material
Analysis of mechanical behavior of a structure containing defects such as holes and inclusions is essential in many engineering applications. In many structures, the discontinuities may have a significant influence on the reduction of the structural stiffness. In this work, we consider the effect of multiple random holes and inclusions in functionally graded material (FGM) plate and apply the extended finite element method with enrichment functions to simulate the mechanical behavior of those discontinuous interfaces. The inclusions also have FGM properties. Numerical examples are considered and their obtained results are compared with the COMSOL, the finite element method software.
Approximations of Variational Problems in Terms of Variational Convergence
We show first the definition of variational convergence of unifunctions and their basic variational properties. In the next section, we extend this variational convergence definition in case the functions which are defined on product two sets (bifunctions or bicomponent functions). We present the definition of variational convergence of bifunctions, icluding epi/hypo convergence, minsup-lop convergnece and maxinf-lop convergence, defined on metric spaces. Its variational properties are also considered. In this paper, we concern on the properties of epi/hypo convergence to apply these results on optimization proplems in two last sections. Next we move on to the main results that are approximations of typical and important optimization related problems on metric space in terms of the types of variational convergence are equilibrium problems, and multiobjective optimization. When we applied to the finite dimensional case, some of our results improve known one.
Design and enhance the vein recognition using near infrared light and projector
The difficulty of intravenous access in patients is an important clinical issue. Recently, many studies and several devices have been developed to assist physicians, nurses and surgeons in finding veins. Amongst them, near infrared imaging technology is one of the new technologies being widely used in the biomedical. NIR imaging allows visualizing veins underneath the skin of those having non-visibility of veins problem, mapping the normal and abnormal veins in treating disorders, or diagnosing related diseases. In this paper, we will introduce a portable device which can help doctors and nurses visualize blood vessel maps of their patients. On basic of combining a vein infrared imaging method and a projector system, this vein instrument can be optimally designed for viewing veins in the monitor or displaying vessel maps of patients directly on their skin.
Design, manufacture and test of a dental camera using fluorescence technique
Dental caries is a major oral health problem in most industrialised countries and is still a major cause of tooth loss. The early diagnostics of caries is of great importance for children and adults to facilitate the treatment and prevention of the diseases. In this study, a fluorescence camera was designed and manufactured for this purpose. This device includes a 380-nm LED, which stimulates porphyrins - metabolic products of the life cycle of caries-inducing bacteria to emit fluorescence, and a compact camera recording fluorescence images in real time. The device is connected to computer via usb cable. An archiving software helps save shots as image or video. The weight and size of this device are suitable for the visual inspection in oral cavity and can be used in daily dental practice. The test results showed that this fluorescence camera can detect some types of carious lesions including dental plaque, dental caries, hidden caries and early caries. Besides, this tool has a number of advantages such as non-invasiveness, safety (non-ionizing radiation), mobility, rapid test time, and economical..
Model of colposcopy using polarized light and effective early
Cervical disease is one of the common diseases, it occurs in women and has a growing tendency. In particular, cervical cancer is one of the most common diseases. The disease can be cured if it is detected early and treated under the guidance of a physician. The usual cervical examination methods are biopsies, and colposcopy. Recently, many studies have applied imaging techniques in the analysis and evaluation of cervical pathology characteristics [1-3]. In this study, we improved the traditional colposcopy with a polarized light source, and captured images with high resolution. Based on the image obtained, we developed image processing algorithms, initially analyzed and evaluated some of the common features of cervical disease.
A novel numerical approach for fracture analysis in orthotropic media
This paper presents a novel approach for fracture analysis in two-dimensional orthotropic domain. The proposed method is based on consecutive-interpolation procedure (CIP) and enrichment functions. The CIP were recently introduced as an improvement for standard Finite Element method, such that higher-accurate and higher-continuous solution can be obtained without smoothing operation and without increasing the number of degrees of freedom. To avoid re-meshing, the enrichment functions are employed to mathematically describe the jump in displacement fields and the singularity of stress near crack tip. The accuracy of the method for analysis of cracked body made of orthotropic materials is studied. For that purpose, various examples with different geometries and boundary conditions are considered. The results of stress intensity factors, a key quantity in fracture analysis, are validated by comparing with analytical solutions and numerical solutions available in literatures.
Seismic Analysis of AP1000 Nuclear Island Structure by Using the Finite Element Software ANSYS
Seismic analysis of AP1000 nuclear island structure by using the commercial finite element software ANSYS is presented. Using the ANSYS Workbench, a sophisticated three-dimensional finite element model of the structure is created and employed in the analysis. Dynamic response of the structure to both the one-directional and three-directional acceleration time histories are considered in the analysis. The time histories for the relative displacement, velocity and absolute acceleration of the structure are obtained for various earthquakes, including American El Centro, Japanese Kobe and Vietnamese Dien Bien earthquakes. The numerical results show that the dynamic characteristics obtained by using one-directional and thee-directional acceleration time histories are different, and the three three-directional acceleration time histories should be employed in the seismic analysis. The result also reveals that the nuclear island is safer in Dien Bien earthquake that it is in El Centro and Kobe earthquakes. The distribution of the von Mises stresses of the structure according to the maximum displacement at the top point is also examined and highlighted.
Nonlinear analysis of thermal behavior for a small satellite in Low Earth Orbit using many-node model
In this paper, nonlinear thermal responses of a small satellite in Low Earth Orbit (LEO) are analyzed using many-node model. The main elements of primary structure of the satellite include six rectangular cover plates and a solar array linking with satellite's body. These elements can be modeled as different lumped thermal nodes. We use an eight-node model for estimating temperatures at nodal elements i.e. six nodes for cover plates, and two nodes for front and rear surfaces of the solar array. The nodes absorb three major heat energy sources from the space environment consisting of solar irradiation, Earth’s albedo and infrared radiation. The established system of thermal balance equations for nodes is nonlinear and is solved by a numerical algorithm. For simulation purpose, it is assumed that the satellite always remains Earth-pointing attitude during motion. Temperature evolutions of nodes in time are explored in details. The obtained results show that the predictive temperature values of nodes are within the allowable temperature limit range of the satellite.
Short-term Flood Forecasting with an Amended Semi-parametric Regression Ensemble Model
Flood forecasting is very important research topic in disaster prevention and reduction. The characteristics of flood involve a rather complex systematic dynamic under the influence of different meteorological factors including linear and non-linear patterns. Recently there are many novel forecasting methods of improving the forecasting accuracy. This paper explores the potential and effect of the semi-parametric regression to modelize flood water-level and to forecast the inundation of Mekong Delta in Vietnam. The semi-parametric regression technique is a combination of a parametric regression approach and a non-parametric regression concept. In the process of model building, three altered linear regression models are applied for the parametric component. They are stepwise multiple linear regression, partial least squares solution and multi-recursive regression method. They are used to capture flood’s linear characteristics. The non-parametric part is solved by a modified estimation of a smooth function. Furthermore, some justified non-linear regression models based on artificial neural network are also able to obtain flood’s non-linear characteristics. They help us to smooth the model's non-parametric constituent easily and quickly. The last element is the model's error. Then the semi-parametric regression is used for ensemble model based on the principle component analysis technique. Flood water-level forecasting, with a lead time of one and more days, has been made by using a selected sequence of past water-level values and some relevant analytical method is utilized to build the model. Obtained empirical results indicate that the prediction by using the amended semi-parametric regression ensemble model is generally better than those obtained by using the other models presented in this study in terms of the same evaluation measurements. Our findings reveal that the estimation power of the modern statistical model is reliable and auspicious. The proposed model here can be used as a promising alternative forecasting tool for flood to achieve better forecasting accuracy and to optimize prediction quality further.
The Gap Function of a Parametric Mixed Strong Vector Quasivariational Inequality Problem
The parametric mixed strong vector quasivariational inequality problem contains many problems such as, variational inequality problems, fixed point problems, coincidence point problems, complementary problems etc. There are many authors who have been studied the gap functions for vector variational inequality problem. This problem plays an important role in many fields of applied mathematics, especially theory of optimization. In this paper, we study a parametric gap function without the help of the nonlinear scalarization function for a parametric mixed strong vector quasivariational inequality problem (in short, (SQVIP)) in Hausdorff topological vector spaces.
Forming limit curve determination of AA6061-T6 aluminum alloy sheet
The forming limit curve (FLC) is used in sheet metal forming analysis to determine the critical strain or stress values at which the sheet metal is failing when it is under the plastic deformation process, e.g. deep drawing process. In this paper, the FLC of the AA6061-T6 aluminum alloy sheet is predicted by using a micro-mechanistic constitutive model. The proposed constitutive model is implemented via a vectorized user-defined material subroutine (VUMAT) and integrated with finite element code in ABAQUS/Explicit software. The mechanical behavior of AA6061-T6 sheet is determined by the tensile tests. The material parameters of damage model are identified based on semi-experience method. To archive the various strain states, the numerical simulation is conducted for the Nakajima test and then the inverse parabolic fit technique that based on ISO 124004-2:2008 standrad is used to extracted the limit strain values. The numerical results are compared with the those of M-K, Hill and Swift analytical models.
Dynamic Analysis of Firing Mechanism of Underwater Pistol
The important problem of designing underwater pistol was analysed and calculated the dynamics of firing mechanism. On the basis of analyzing the performance of the underwater pistol, the paper presents a theoretical model for analysing the dynamics of firing mechanism of underwater pistol with the with the resistance of water acting on firing pin and slide. The result of this research can be applied to design the underwater pistol and underwater firearm.
Density Functional Theory Study of Hydrogen Electroadsorption on the Pt(110) surfaces
The hydrogen adsorption on the Pt(110) and Pt(110)-(1x2) electrode surfaces has been investigated. To gain insight into detailed atomistic picture on the equilibrium coverage and structure, we have constructed a lattice gas model by determining the on-site energy and the interaction parameters using the first principles total-energy calculation. Therein atop, fcc, short bridge, long bridge and R, T, F, F’ sites for H/Pt(110) and H/Pt(110)-(1x2) are covered by hydrogen atoms under various coverage conditions 0 ML < θ < 1 ML and the total-energy calculations are done for the (1x1) and (1x2) cells. The surface of (1×2) and (1×1) lateral unit cells. The convergence property with respect to the number of Pt layers and the k-point mesh are found. The comparison between different surface types are done. By comparing the calculated results with two different theoretical simulated data, SIESTA and VASP, we found good agreement between them.