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This paper introduces a novel approach to deal with the multi-objective optimization of a two-stage bevel helical gearbox by applying the Taguchi method and Grey Relation Analysis (GRA). The goal of the study is to find optimal main design factors that minimize the gearbox volume and maximize the gearbox efficiency. To accomplish this, five main design parameters were selected: the coefficients of wheel face width (CWFW) of the bevel and the helical gear sets, the allowable contact stresses (ACS) of the first and the second stages, and the gear ratio of the first stage. Furthermore, two single targets were investigated: minimum gearbox volumes, and maximum gearbox efficiency. Also, the multi-objective optimization problem is solved through two steps: Step 1 for closing the gap between variable levels and Step 2 for determining the optimal main design factors. The study’s findings were used to introduce the optimum values of five major design parameters for designing a two-stage helical gearbox.

In this work, activity of radioactive isotopes in some offshore seawater samples at vicinity areas of three islands has been investigated Phu Quy (Binh Thuan province), Phu Quoc (Kien Giang province), and Bach Long Vy (Hai Phong province). The ranges of radioactivity 226Ra, 238U, 137Cs, 90Sr, and 239,240Pu in seawater at three offshore islands are 2.09 ÷ 4.77 mBq/L, 2.33 ÷ 4.95 mBq/L, 0.98 ÷ 1.45 mBq/L, 1.22 ÷ 1.49 mBq/L, and 0.0045 ÷ 0.0066 mBq/L, respectively. These values show that the radioactivities of the above-mentioned radionuclides differ between monitoring periods and between three offshore islands of Vietnam, but which is equal to or lower than the corresponding value according to others seas in Vietnam and Asia – Pacific. The correlation between radioisotopes and properties of seawater (pH, conductance, and salinity) is also shown in this study to assess their impact on the fluctuations of the above radinuclides.

Control of local governments in countries around the world is very diverse,but mainly divided into two categories: 1) control of state agencies (central government control, court control, control of local power representations); 2) control of social institutions including political party control over local government, control of organizations and public associations, control of the media, and control of the people. The paper focuses on analysing the controlling local governments in some countries, thereby giving reference values for Vietnam.

In mechanism design with symmetrical or asymmetrical motions, obtaining high precision of the input path given by working requirements of mechanisms can be a challenge for dimensional optimization. This study proposed a novel hybrid-combined differential evolution (DE) and Jaya algorithm for the dimensional synthesis of four-bar mechanisms with symmetrical motions, called HCDJ. The suggested algorithm uses modified initialization, a hybrid-combined mutation between the classical DE and Jaya algorithm, and the elitist selection. The modified initialization allows generating initial individuals, which are satisfied with Grashof’s condition and consequential constraints. In the hybrid-combined mutation, three differential groups of mutations are combined. DE/best/1 and DE/best/2, DE/current to best/1 and Jaya operator, and DE/rand/1, and DE/rand/2 belong to the first, second, and third groups, respectively. In the second group, DE/current to best/1 is hybrid with the Jaya operator. Additionally, the elitist selection is also applied in HCDJ to find the best solutions for the next generation. To validate the feasibility of HCDJ, the numerical examples of the symmetrical motion of four-bar mechanisms are investigated. From the results, the proposed algorithm can provide accurate optimal solutions that are better than the original DE and Jaya methods, and its solutions are even better than those of many other algorithms that are available in the literature.

This study is to deal with unwanted current harmonics in rotating (d-q) frames of a 7-phase non-sinusoidal permanent magnet synchronous machine (PMSM) in a wye-connected winding topology. The machine is supplied by a 7-leg voltage source inverter (VSI) fed by a DC-bus voltage. In control, current responses are expected to properly track their references. However, several unwanted harmonics of the non-sinusoidal back electromotive force (back-EMF) and the inverter nonlinearity generate unwanted harmonic components in d-q currents. These current harmonics cannot be nullified by controllers such as conventional proportional-integral (PI) controllers. Consequently, the current responses cannot track their references. In this study, a combination of conventional PI controllers and simple adaptive linear neurons (ADALINEs) is proposed to eliminate these current harmonics, improving current control quality of the drive. The effectiveness of the proposed control structure is verified by experimental results. Thai Nguyen University of Technology and CE2I project

For the multiscale simulation of advanced materials with hierarchical, heterogeneous, and random microstructures such as fibrous composites by finite element method, mathematical homogenization method has been extended to the stochastic multiscale method. In this paper, a stochastic perturbation-based homogenization method was used to predict homogenized properties of short fiber reinforced composites with random fiber length, random orientation, and random mechanical properties of fiber and matrix resin. For demonstration, a random short fiber reinforced plastic was investigated considering thirteen random physical parameters and two ways of approximation of statistically measured fiber length distributions. The influences of each uncertainty factor on the homogenized properties of the material were observed. The results show that the homogenization properties are likely orthotropic even though the fiber and matrix are considered as isotropic materials. The material is stronger in the direction where the fibers are mostly longitudinal. Each component of the homogenized properties is resulted in a probability density function under the influence of the random physical parameters. Besides, the scatter of the properties was predicted due to very slight difference between two fiber length distributions.

The dimensional synthesis of the four-bar mechanism has been solved by using many meta-heuristic approaches such as genetic algorithm (GA), differential evolution (DE), and/or particle swarm optimization (PSO) However, the performance of a symbiotic organisms search (SOS) for the dimensional synthesis of the four-bar mechanism has not been investigated so far. Thus, this study aims to investigate the applicability of SOS in the optimal dimensional design of a four-bar mechanism by comparing the results gotten by SOS with those of DE, GA, and PSO. The results of SOS for the dimensional synthesis of the four-bar mechanism show that the SOS has a good exploitation ability for a fast converge rate but it has a limited exploration capability to find accurate solutions.

A combined differential evolution (DE) and Jaya algorithm, named CDJ, for size and shape truss optimization under frequency constraints is suggested in this paper. In CDJ, a combined operator of the original DE and Jaya are used to achieve both the global and local searching abilities. Then, the elitist selection technique is used in the selection stage. As a result, the CDJ can generate good solutions with a small computational effort in comparison with two original methods and some other optimization algorithms in the literature. To validate its feasibility, two numerical examples of shape and size optimization and size optimization are performed.

Improving quality of life (QOL) is an important objective. This study measured the QOL of farmers in rural areas in Vietnam using the WHOQOL-BREF. 600 farmers from 5 provinces in Vietnam participated in the study. Farmers reported low QOL, with psychological dimension had the highest QOL score and environmental dimension had lowest QOL. Male, young, well-educated, married, healthy farmers and farmers who had average living standard, living in small families, living with having less than 3 working members, and have savings were more likely to have higher QOL. However, only 3 factors predicted QOL: education, living standard and number of working members. Implications on Vietnamese family culture and the role of agriculture in modern society were discussed.

In cam design process, synthesizing the motion curves is very important because of the effect of motion curves to cam size, force, and vibration. Thus, improving the kinematics of cam curves is significant. This paper presents a general synthesis of motion curves of cam mechanisms. A Non Uniform Rational B-Spline (NURBS) is used to improve the kinematics. The linear system of equations is established to determine motion curves for arbitrary boundary conditions of displacement, velocity, acceleration, and jerk. By controlling the weight parameters of NURBS, the peak values of acceleration and jerk can decrease. Several examples are presented to demonstrate this research. The results are also compared with traditional motion curves.