Optimization of J-groove shape for the bulb turbine draft tube

Quang Huy Nguyen(응웬광휘),Viet Luyen Vu(부비엣루옌),Young-Do Choi(최영도) 한국유체기계학회 2019 한국유체기계학회 학술대회 논문집 Vol.2019 No.11

Assessment of Dynamic Response of 3D Ultra High Performance Concrete Frame Structure under High Explosion Using Johnson-Holmquist 2 Model

Viet-Chinh Mai,Ngoc-Quang Vu 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.3

Most of the 3D frame structures are not initially designed to resist blast loads. Due to the limitation of financial resources as well as the complex technical requirements, study the dynamic behavior of 3D frame structure under blast load, particularly for advanced materials like Ultra High Performance Concrete (UHPC), faces many challenges. Therefore, numerical simulation can be a good alternative. The objective of the research is to investigate the dynamic behavior of a UHPC building subjected to blast loading through a 3-D numerical model with the direct simulation of blast load. This building studied in this paper is a real, 6-story office building in Vietnam, which was originally designed for dead load, live load, wind, and earthquake. The building is subjected to surface blast of 500kg Trinitrotoluen (TNT) equivalent charge weight with close-in distance and a variable height of blast source. In this study, Johnson–Holmquist 2 damage model (JH-2) model is implemented to simulate the UHPC structures subjected to blast loading. Base on the theory of the JH-2 model, a subroutine, integrated with Abaqus software, is designed by the authors to calibrate the input parameters of UHPC material. A total of 8 cases of the explosion scenario are considered, in which the design of the original column is revised by using UHPC composite structure in external columns. The results indicate that there is a tremendous increase in response when the blast occurs at the mid-height of the building and the severe damage is observed in the external column in front of the explosion. The obtained result in terms of blast wave pressure during time history as well as peak deflections and damage of building under blast loading is assessed. The blast loading resistance effect of the revised design compared to the original design is also demonstrated as a beneficial alternative in blasting condition.

Behavior of composite CFST beam-steel column joints

엄순섭,Quang-Viet Vu,최지훈,George Papazafeiropoulos,김승억 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.32 No.5

In recent years, composite concrete-filled steel tubular (CFST) members have been widely utilized in framed building structures like beams, columns, and beam-columns since they have significant advantages such as reducing construction time, improving the seismic performance, and possessing high ductility, strength, and energy absorbing capacity. This paper presents a new composite joint - the composite CFST beam-column joint in which the CFST member is used as the beam. The main components of the proposed composite joint are steel H-beams, CFST beams welded with the steel H-column, and a reinforced concrete slab. The steel H-beams and CFST beams are connected with the concrete slab using shear connectors to ensure composite action between them. The structural performance of the proposed composite joint was evaluated through an experimental investigation. A three-dimensional (3D) finite element (FE) model was developed to simulate this composite joint using the ABAQUS/Explicit software, and the accuracy of the FE model was verified with the relevant experimental results. In addition, a number of parametric studies were made to examine the effects of the steel box beam thickness, concrete compressive strength, steel yield strength, and reinforcement ratio in the concrete slab on the proposed joint performance.

Stable vertical takeoff of an insect-mimicking flapping-wing system without guide implementing inherent pitching stability

Phan, Hoang Vu,Nguyen, Quoc Viet,Truong, Quang Tri,Truong, Tien Van,Park, Hoon Cheol,Goo, Nam Seo,Byun, Doyoung,Kim, Min Jun Springer-Verlag 2012 JOURNAL OF BIONICS ENGINEERING Vol.9 No.4

곤충 모방 날갯짓 비행체의 안정적인 수직 이륙 비행 구현

판호앙부(Hoang-Vu Phan),트롱쾅트리(Quang-Tri Truong),구옌쿠옥비엣(Quoc-Viet Nguyen),박훈철(Hoon Cheol Park),변도영(Doyoung Byun),구남서(Nam Seo Goo) 제어로봇시스템학회 2012 제어·로봇·시스템학회 논문지 Vol.18 No.2

This paper demonstrates how to implement inherent pitching stability in an insect-mimicking flapping-wing system for vertical takeoff. Design and fabrication of the insect-mimicking flapping-wing system is briefly described focusing on the recent modification. Force produced by the flapping-wing systems is estimated using the UBET (Unsteady Blade Element Theory) developed in the previous work. The estimation shows that the wing twist placed in the modified system can improve thrust production for about 10 %. The estimated thrust is compared with the measured thrust, which proves that the UBET provides fairly good estimations for the thrust produced by the flapping-wing systems. The vertical takeoff test shows that inherent pitching stability can be implemented in an insect-mimicking flapping-wing system by aligning the aerodynamic force center and center of gravity.

Fully nonlinear inelastic analysis of rectangular CFST frames with semi-rigid connections

Van-Tuong Bui,Quang-Viet Vu,Viet-Hung Truong,Seung-Eock Kim 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.38 No.5

In this study, an effective numerical method is introduced for nonlinear inelastic analyses of rectangular concrete-filled steel tubular (CFST) frames for the first time. A steel-concrete composite fiber beam-column element model is developed that considers material, and geometric nonlinearities, and residual stresses. This is achieved by using stability functions combined with integration points along the element length to capture the spread of plasticity over the composite cross-section along the element length. Additionally, a multi-spring element with a zero-length is employed to model the nonlinear semi-rigid beam-to-column connections in CFST frame models. To solve the nonlinear equilibrium equations, the generalized displacement control algorithm is adopted. The accuracy of the proposed method is firstly verified by a large number of experiments of CFST members subjected to various loading conditions. Subsequently, the proposed method is applied to investigate the nonlinear inelastic behavior of rectangular CFST frames with fully rigid, semi-rigid, and hinged connections. The accuracy of the predicted results and the efficiency pertaining to the computation time of the proposed method are demonstrated in comparison with the ABAQUS software. The proposed numerical method may be efficiently utilized in practical designs for advanced analysis of the rectangular CFST structures.

Comparison of machine learning algorithms for regression and classification of ultimate load-carrying capacity of steel frames

Seung-Eock Kim,Quang-Viet Vu,George Papazafeiropoulos,Zhengyi Kong,Viet-Hung Truong 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.37 No.2

In this paper, the efficiency of five Machine Learning (ML) methods consisting of Deep Learning (DL), Support Vector Machine (SVM), Random Forest (RF), Decision Tree (DT), and Gradient Tree Booting (GTB) for regression and classification of the Ultimate Load Factor (ULF) of nonlinear inelastic steel frames is compared. For this purpose, a two-story, a six-story, and a twenty-story space frame are considered. An advanced nonlinear inelastic analysis is carried out for the steel frames to generate datasets for the training of the considered ML methods. In each dataset, the input variables are the geometric features of W-sections and the output variable is the ULF of the frame. The comparison between the five ML methods is made in terms of the mean-squared-error (MSE) for the regression models and the accuracy for the classification models, respectively. Moreover, the ULF distribution curve is calculated for each frame and the strength failure probability is estimated. It is found that the GTB method has the best efficiency in both regression and classification of ULF regardless of the number of training samples and the space frames considered.

Pressure effects on EXAFS Debye-Waller factor and melting curve of solid krypton

Khac Hieu Ho,Viet Tuyen Nguyen,Nguyen Van Nghia,Nguyen Ba Duc,Vu Quang Tho,Tran Thi Hai,Doan Quoc Khoa 한국물리학회 2019 Current Applied Physics Vol.19 No.1

The pressure effects on atomic mean-square displacement, extended X-ray absorption fine structure (EXAFS) Debye-Waller factor and melting temperature of solid krypton have been investigated in within the statistical moment method scheme in quantum statistical mechanics. By assuming the interaction between atoms can be described by Buckingham potential, we performed the numerical calculations for krypton up to pressure 120 GPa. Our calculations show that the atomic mean-square displacement and EXAFS Debye-Waller factor of krypton crystal depend strongly on pressure. They make the robust reduction of the EXAFS peak height. Our results are in good and reasonable agreements with available experimental data. This approach gives us a relatively simple method for qualitatively calculating high-pressure thermo-physical properties of materials. Moreover, it can be used to verify future high-pressure experimental and theoretical works.

Flexural behavior of concrete-filled double skin steel tubes with a joint

Eom, Soon-Sub,Vu, Quang-Viet,Choi, Ji-Hun,Park, Ho-Hoon,Kim, Seung-Eock Elsevier 2019 Journal of constructional steel research Vol.155 No.-

<P><B>Abstract</B></P> <P>In the present study, concrete-filled double skin steel tubes (CFDSTs) with a joint, which are lighter and more economical than concrete-filled steel tubes (CFSTs), were developed. The CFDSTs are made of two steel tubes of different diameters with concrete filling the space between them. The length, the outer and inner diameters of a CFDST are 10 m, 914.4 mm, and 514.4 mm, respectively. Two types of shear connectors consisting of M16 and steel plate studs were used. A new type of connection in CFDSTs was developed to transfer the imposed load effectively. Four different specimens were made to test all possible combinations of the two different shear connectors (M16 studs, steel plate studs) and joints. The bending performance of the CFDSTs was investigated through 4-point loading experiments and finite element analysis (FEA). Finally, a comparison of design predictions and experiment results was made for these tubes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The accuracy of the developed FE model of the composite tubes was verified by comparing the test and the FEA results. </LI> <LI> M16 studs are more suitable than the steel plate studs. </LI> <LI> FEA and experiment results indicated that the joint has sufficient strength to connect these composite tubes. </LI> <LI> The developed CFDST members have sufficient flexural strength and they can be used for construction. </LI> </UL> </P>

Metabolic Syndrome and Insulin Resistance Syndrome among Infertile Women with Polycystic Ovary Syndrome: A Cross-Sectional Study from Central Vietnam

Minh Tam Le,Vu Quoc Huy Nguyen,Quang Vinh Truong,Dinh Duong Le,Viet Nguyen Sa Le,Ngoc Thanh Cao 대한내분비학회 2018 Endocrinology and metabolism Vol.33 No.4

Background: Polycystic ovarian syndrome (PCOS) is one of the most common endocrinopathies among reproductive-age women. Its metabolic features often overlap with those associated with metabolic syndrome (MS) and insulin resistance syndrome (IRS). Theobjective of this study was to determine the prevalence and predictors of MS and IRS in infertile Vietnamese women with PCOS. Methods: A cross-sectional study was conducted at a tertiary fertility centre at Hue University Hospital from June 2016 to November 2017. A total of 441 infertile women diagnosed with PCOS based on the revised 2003 Rotterdam consensus criteria were enrolled. MS and IRS were defined based on the National Heart, Lung, and Blood Institute/American Heart Association Adult Treatment Panel III 2005 and American College of Endocrinology IRS 2003 criteria, respectively. Complete clinical and biochemicalmeasurements of 318 women were available for analysis. Independent predictors of MS and IRS were identified using multivariatelogistic regression. Results: The overall prevalence of MS and IRS in women with PCOS was 10.4% and 27.0%, respectively. We identified older age(>30 years) and obesity as independent predictors of MS and IRS. Elevated anti-Müllerian hormone levels increased the risk of IRS,but not that of MS. Conclusion: MS and IRS are prevalent disorders among infertile Vietnamese women with PCOS. PCOS is not solely a reproductiveproblem. Screening and early intervention for MS and/or IRS based on anthropometric, metabolic, and reproductive hormone riskfactors should be an integral part of fertility care.