• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.7
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• pp.500-511
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• 2007

The Optimal solutions of the design variables in internally finned tubes have been obtained for three-dimensional periodically fully developed turbulent flow and heat transfer. For a trapezoidal fin profile, performances of the heat exchanger are determined by considering the heat transfer rate and pressure drop, simultaneously, that are interdependent quantities. Therefore, Pareto frontier sets of a heat exchanger can be acquired by integrating CFD and a multi-objective optimization technique. The optimal values of fin widths $(d_1,\;d_2)$, fin height(h) and helix angle$(\gamma)$ are numerical1y obtained by minimizing the pressure loss and maximizing the heat transfer rate within ranges of $d_1=0.5\sim1.5mm$, $d_2=0.5\sim1.5mm$, $h=0.5\sim1.5mm$, and $\gamma=0\sim20^{\circ}$. For this, a general CFD code and a global genetic algorithm(GA) are used. The Pareto sets of the optimal solutions can be acquired after $30^{th}$ generation.

• Journal of the Korean Society of Safety
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• v.22 no.1 s.79
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• pp.13-18
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• 2007

Structural integrity assessment of thin-walled pipes and pipe items has become one of the major issues in the nuclear power plant. ASME Section XI Code Case N-597-2 provides a criterion for acceptance of the pipes. But the code case has several limitations for application and sometimes gives too conservative or non-conservative results. So it is necessary to understand fully the technical bases of the code case. In the code case N-597, the allowable local thicknesses of thinned straight pipes are given for three different cases. Because of the different technical base, each case gives different thickness values and sometimes gives contradictory values. In this paper attempts were made in order to propose a unified rule for the allowable local thickness and in order to remove or relax the restrictions on the application of the code case. For this purpose elastic stress analyses were made using the finite element method and the stress results were examined. Based on the obtained bending stress results, a very simple procedure was proposed to obtain the consistent allowable local thickness for the thinned straight pipes.

• Journal of Korean Society for Quality Management
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• v.37 no.4
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• pp.61-70
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• 2009

This paper introduces quantitative tools for evaluating the relative efficiency of Career & Counseling Jobs in universities. As tools, it uses Data Envelopment Analysis (DEA) developed by Charnes and Cooper. It finally selects 29 DMUs which are listed on the Ministry Of Education, Science And Technology(http://academyinfo.go.kr). We measures the technical efficiency of each DMU with the use of DEA-CRS, rather then DEA-VRS because DEA-CRS not only compares relative efficiencies but also implicitly considers economies of scale based on the assumption of linearity. We run a linear programming model Frontier Analyst Program for the estimation of the relative efficiencies of each DMU. The model also indicates the precise amount of inefficiencies for each input, which mean how much inputs are wasted for a given output and how much the university is inefficiently operated. This analysis helps to give guideline for the organization to construct a futureoriented operational strategy and also to show clear picture of contents of mismanagement for the past. The details of mismanagement are to be identified, analysed and finally corrected.

• Journal of Radiation Protection and Research
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• v.45 no.4
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• pp.147-153
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• 2020

Background: Malawi's 2018 National Energy Policy includes nuclear power as an energy option with an operational 100 MW targeted for 2035. Materials and Methods: This paper challenges the scope of the policy on nuclear power by reviewing its implementation strategy and comparing it to: the strategy established for coal in the same policy; some experiences from other countries; and documents by the International Atomic Energy Agency (IAEA) relating to establishing a national position on nuclear power and infrastructural requirements for a nuclear power program. Results and Discussion: It is found that the pro-nuclear position is uninformed, and targets are unrealistic owing to a lack of understanding of nature of nuclear power including the requirements for safety, security and safeguards, and nuclear infrastructure. It is apparent that neither consultation nor a proper analysis were comprehensively conducted for nuclear. Though the national energy policy suggests a national position for nuclear energy, the content does not demonstrate that the position was arrived at knowledgeably. Conclusion: Thus, nuclear power may presently be viewed as a potential energy option that is yet to be seriously considered. It is important to build an appropriate level of literacy on nuclear science and technology for policy makers, key stakeholders, and the public to be better positioned for strategizing on nuclear power.

• Advances in nano research
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• v.10 no.3
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• pp.263-270
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• 2021

The present manuscript focuses the effects of suction on the flow of the dusty fluid along permeable exponentially stretching cylinder. Derived PDEs for this work are changed into ODEs by adopting right transformations. Numerical procedure is carried out for the obtained resultant equations by Shooting Technique in accordance with Runge-Kutta (RK-6) technique. Obtained results for the parameters namely, particle interaction parameter, suction parameter and Reynold number parameters are probed thoroughly. Some salient points are: (a) Fluid velocity decreases and the dust phase velocity rises for the higher values of particle interaction parameter; (b) more suction produces retarding velocities for both the phases; (c) high Reynold number slows down the fluid velocity while the speed of dust phase and (d) skin friction coefficient goes high for all these parameters.

• Smart Structures and Systems
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• v.30 no.2
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• pp.135-143
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• 2022

The object of this paper is to investigate the free vibration behavior under the effect of carbon nanotube distribution in functionally graded carbon nanotube-reinforced composite (FG-CNTRC) by using higher-order shear deformation theories. In this work, we present a novel distribution method for carbon nanotubes in the polymer matrix by using a new exponential power law distribution of carbon nanotube volume fraction. It is assumed that the SWCNTs are aligned along the beam axial direction and the distribution of the SWCNTs may vary through the thickness of the beam with different patterns of reinforcement. The rule of mixtures is used in order to obtain material properties of the CNTRC beams. Hamilton's principle is used in deriving the equations of motion. The validity of the free Vibration results is examined by comparing them with those of the known data in the literature. The results that obtained indicate that the carbon nanotube volume fraction distribution play a very important role on the free vibrations characteristics of the CNTRC beam.

• Nuclear Engineering and Technology
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• v.54 no.9
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• pp.3215-3224
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• 2022

Latest studies found that for 316LN austenitic stainless steel (ASS), its LCF life decreased noticeably in high temperature water containing a great amount of dissolved oxygen (DO) (2 ppm DO), compared with that in the water containing 50 or 100 ppb DO. This finding is different from previous studies about ASSs. This study confirmed that the 316L had similar behavior to 316LN. The LCF life of 316L in water containing 1000 ppb DO water was considerably shorter than that in the water containing 50 ppb DO. Addition of boric acid & lithium hydroxide and pre-soaking did not display noticeable effects on the LCF life of this material in the water with 1000 ppb DO, indicating the discrepancy between the latest studies and previous studies was not caused by the boric acid & lithium hydroxide and pre-soaking. This study also confirmed that similar to 316LN, when a certain amount of DO was added into the water, the amount of hydrogen absorbed into the material decreased significantly compared with that when the DO was less than 5 ppb.

• Advances in nano research
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• v.12 no.5
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• pp.489-499
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• 2022

Nanofluids have recently triggered a substantial scientific interest as cooling media. However, their stability is challenging for successful engagement in industrial applications. Different factors, including temperature, nanoparticles and base fluids characteristics, pH, ultrasonic power and frequency, agitation time, and surfactant type and concentration, determine the nanofluid stability regime. Indeed, it is often too complicated and even impossible to accurately find the conditions resulting in a stabilized nanofluid. Furthermore, there are no empirical, semi-empirical, and even intelligent scenarios for anticipating the stability of nanofluids. Therefore, this study introduces a straightforward and reliable intelligent classifier for discriminating among the stability regimes of alumina-water nanofluids based on the Zeta potential margins. In this regard, various intelligent classifiers (i.e., deep learning and multilayer perceptron neural network, decision tree, GoogleNet, and multi-output least squares support vector regression) have been designed, and their classification accuracy was compared. This comparison approved that the multilayer perceptron neural network (MLPNN) with the SoftMax activation function trained by the Bayesian regularization algorithm is the best classifier for the considered task. This intelligent classifier accurately detects the stability regimes of more than 90% of 345 different nanofluid samples. The overall classification accuracy and misclassification percent of 90.1% and 9.9% have been achieved by this model. This research is the first try toward anticipting the stability of water-alumin nanofluids from some easily measured independent variables.

• Advances in nano research
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• v.12 no.5
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• pp.441-455
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• 2022

This study explores the linear and nonlinear solutions of sigmoid functionally graded material (S-FGM) nanoplate with porous effects. A size-dependent numerical solution is established using the strain gradient theory and isogeometric finite element formulation. The nonlinear nonlocal strain gradient is developed based on the Reissner-Mindlin plate theory and the Von-Karman strain assumption. The sigmoid function is utilized to modify the classical functionally graded material to ensure the constituent volume distribution. Two different patterns of porosity distribution are investigated, viz. pattern A and pattern B, in which the porosities are symmetric and asymmetric varied across the plate's thickness, respectively. The nonlinear finite element governing equations are established for bending analysis of S-FGM nanoplates, and the Newton-Raphson iteration technique is derived from the nonlinear responses. The isogeometric finite element method is the most suitable numerical method because it can satisfy a higher-order derivative requirement of the nonlocal strain gradient theory. Several numerical results are presented to investigate the influences of porosity distributions, power indexes, aspect ratios, nonlocal and strain gradient parameters on the porous S-FGM nanoplate's linear and nonlinear bending responses.

• Earthquakes and Structures
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• v.24 no.4
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• pp.237-245
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• 2023

Based on novel Galerkin's technique, the theoretical study gives a prediction to estimate the vibrations of FG rotating cylindrical shell. Terms of ring supports have been introduced by a polynomial function. Three different laws of volume fraction are utilized for the vibration of cylindrical shells. Variation frequencies with the locations of ring supports have been analyzed and these ring supports are placed round the circumferential direction. The base of this approach is an approximate estimation of eigenvalues of proper functions which are the results of solutions of vibrating equation. Each longitudinal wave number corresponds to a particular boundary condition. The results are given in tabular and graphical forms. By increasing different value of height-to-radius ratio, the resulting backward and forward frequencies increase and frequencies decrease on increasing length-to-radius ratio. There is a new form of frequencies is obtained for different positions of ring supports, which is bell shaped. Moreover, on increasing the rotating speed, the backward frequencies increase and forward frequencies decreases.