Science and Technology Development Journal

A novel numerical approach for fracture analysis in orthotropic media

Nguyen Ngoc Minh, Nguyen Thanh Nha, Bui Quoc Tinh, Truong Tich Thien — Wed, 23 May 2018 12:03:23 +0700

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

Nguyen Dinh Kien, Vu Lam Dong — Wed, 23 May 2018 14:26:31 +0700

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.

Effect of Temperature and Porosities on Dynamic Response of Functionally Graded Beams Carrying a Moving Load

Bui Van Tuyen — Wed, 23 May 2018 14:29:06 +0700

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

Nghiem Xuan Luc, Nguyen Nhu Hieu — Wed, 23 May 2018 14:44:34 +0700

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.

Inverse Dynamic Analyzing of Flexible Link Manipulators with Translational and Rotational Joints

Bien Xuan Duong, My Anh Chu, Khoi Bui Phan — Wed, 23 May 2018 14:49:23 +0700

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.

Forming limit curve determination of AA6061-T6 aluminum alloy sheet

Nguyen Huu Hao, Nguyen Ngoc Trung, Vu Cong Hoa — Wed, 23 May 2018 14:52:25 +0700

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

Dung Nguyen Thai, Hung Nguyen Van — Wed, 23 May 2018 14:55:54 +0700

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.

Nonlinear analysis of thermal behavior for a small satellite in Low Earth Orbit using many-node model

Pham Ngoc Chung, Nguyen Dong Anh, Nguyen Nhu Hieu — Wed, 23 May 2018 14:58:49 +0700

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.

Density Functional Theory Study of Hydrogen Electroadsorption on the Pt(110) surfaces

Tran Thi Thu Hanh — Wed, 23 May 2018 15:01:24 +0700

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.

Design, manufacture and test of a dental camera using fluorescence technique

Wed, 23 May 2018 15:07:19 +0700

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..

Design and enhance the vein recognition using near infrared light and projector

Wed, 23 May 2018 15:10:54 +0700

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.

Model of colposcopy using polarized light and effective early

Phan Ngoc Khuong Cat, Huynh Quang Linh, Nguyen Ngoc Quynh, Ly Cao Duong — Wed, 23 May 2018 15:14:00 +0700

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.

Approximations of Variational Problems in Terms of Variational Convergence

Dương Ton Dam, Dang Kien Cuong — Wed, 23 May 2018 15:17:42 +0700

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.

Approximations of Variational Problems in Terms of Variational Convergence

Huynh Thi Hong Diem — Wed, 23 May 2018 16:03:36 +0700

Short-term Flood Forecasting with an Amended Semi-parametric Regression Ensemble Model

Le Hoang Tuan, To Anh Dung — Wed, 23 May 2018 15:20:43 +0700

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

Le Xuan Dai, Nguyen Van Hung, Phan Thanh Kieu — Wed, 23 May 2018 15:27:40 +0700

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.

Generalized Knaster-Kuratowski-Mazurkiewicz type theorems and applications to minimax inequalities

Ha Manh Linh — Wed, 23 May 2018 15:31:06 +0700

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..

Extended finite element method for simulating the mechanical behavior of multiple random holes and inclusions in functionally graded material

Kim Bang Tran, The Huy Tran, Quoc Tinh Bui, Tich Thien Truong — Wed, 23 May 2018 15:48:32 +0700

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.