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Tran N. Hoa,S. Khatir,G. De Roeck,Nguyen N. Long,Bui T. Thanh,M. Abdel Wahab 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.25 No.4
This paper proposes a novel approach to model updating for a large-scale cable-stayed bridge based on ambient vibration tests coupled with a hybrid metaheuristic search algorithm. Vibration measurements are carried out under excitation sources of passing vehicles and wind. Based on the measured structural dynamic characteristics, a finite element (FE) model is updated. For long-span bridges, ambient vibration test (AVT) is the most effective vibration testing technique because ambient excitation is freely available, whereas a forced vibration test (FVT) requires considerable efforts to install actuators such as shakers to produce measurable responses. Particle swarm optimization (PSO) is a famous metaheuristic algorithm applied successfully in numerous fields over the last decades. However, PSO has big drawbacks that may decrease its efficiency in tackling the optimization problems. A possible drawback of PSO is premature convergence leading to low convergence level, particularly in complicated multi-peak search issues. On the other hand, PSO not only depends crucially on the quality of initial populations, but also it is impossible to improve the quality of new generations. If the positions of initial particles are far from the global best, it may be difficult to seek the best solution. To overcome the drawbacks of PSO, we propose a hybrid algorithm combining GA with an improved PSO (HGAIPSO). Two striking characteristics of HGAIPSO are briefly described as follows: (1) because of possessing crossover and mutation operators, GA is applied to generate the initial elite populations and (2) those populations are then employed to seek the best solution based on the global search capacity of IPSO that can tackle the problem of premature convergence of PSO. The results show that HGAIPSO not only identifies uncertain parameters of the considered bridge accurately, but also outperforms than PSO, improved PSO (IPSO), and a combination of GA and PSO (HGAPSO) in terms of convergence level and accuracy.
The Competitiveness of Soc Trang Ecotourism Associated with Khmer Culture
LONG, Nguyen Thanh Korea Distribution Science Association 2020 The Journal of Asian Finance, Economics and Busine Vol.7 No.10
Tourism is considered one of the key economic sectors in Vietnam as it helps to promote the economic development, increase foreign exchange earnings, create jobs, and improve the living standards of local people. So, this study aims to identify factors affecting the competitiveness of Soc Trang ecotourism associated with Khmer culture based on a combination of qualitative and quantitative research methods. Qualitative research was conducted through focus group discussions with experts, and quantitative research was conducted through direct interviews with visitors at ecotourism sites in Soc Trang province. The study involves questionnaire surveys and multivariate data analysis methods (Cronbach's Alpha test, EFA, CFA, SEM). Research results from 350 respondents demonstrate that all factors have a positive impact on the competitiveness of ecotourism associated with Khmer culture in Soc Trang province. It shows that the competitiveness of ecotourism associated with Khmer culture is influenced by five factors, including: (1) religious ritual customs of the Khmer people; (2) ecotourism infrastructure; (3) traditional festival activities of Khmer people; (4) culinary culture of Khmer people; and (5) folk ritual customs of the Khmer people. From these findings, the study offers some managerial implications to improve the competitiveness of Soc Trang ecotourism associated with Khmer culture.
Parametric Study on Fracture Behaviors of Non-aligned Twin Cracked Pipe Under Bending
Thanh-Long Nguyen,Myeong-Woo Lee(이명우),Yun-Jae Kim(김윤재) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
To analyze the fracture behavior of multiple cracks and their effect, researchers did some bending tests. However, tests could not be stopped to observe details of crack propagation path and interaction due to the limitation of numbers of the test. Therefore, from test geometries in the previous studies, non-aligned twin cracked pipe simulation was performed by applying the FE damage model which based on stress modified fracture strain. In this paper, crack behaviors and the interaction effects between non-aligned twin cracks on the maximum bending stress were investigated.
Thanh Long Nguyen,권형안 한국신뢰성학회 2021 한국신뢰성학회 학술대회논문집 Vol.2021 No.11
전자장치가 사용되는 현장환경에서 진동부하 크기는 매우 다양하고 편차가 크다. 예를 들면 0.001 g²/Hz에서 1 g²/Hz 로 수십에서 수천배차이가 있다. 미 공군의 통계에 따르면 전자장치의 고장 중에 20%는 진동고장이며(Steinberg D.S. Vibration analysis for electronic equipment. John Wiley & Sons, 2000) 고장까지의 걸리는 시간은 진동부하에 매우 민감하다. 자동차, 항공, 국방등에서 활용되는 전자장치는 진동부하에 상시로 노출될 수 있어, 수일 또는 수주일 걸리는 진동시험을 통해 빠르게 현장신뢰성을 미리 평가해 볼 수 있다. 하지만 앞에서 언급한 대로 다양한 유형의 현장진동환경을 시험만으로 모두 모사하여 신뢰성검증을 하기는 어렵다. 예를 들면, MIL-HDBK-810G는 3가지 제조유형, 8가지 운송분류, 12가지 운영분류, 2가지 보조분류를 하고 있어(단순조합 3*8*12*2=576 가지), 시험을 통한 철저한 진동부하평가를 하려면 시간과 비용이 많이 들기 때문에 시뮬레이션을 통한 수명분석의 효용성과 가치는 매우 높다. 금번 연구에서는 이러한 사업적 필요성을 충족할 수 있는 시나리오를 정하고 기술적인 RPA 수명예측결과를 진동부하관점에서 비교분석하여, 구체적이고 현실적인 선택과 결정에 도움이 될 수 있는 방안을 제시한다. 이러한 방안을 적용하게 되면, 제조시 ESS 를 얼마나 오래해야 할 것인지, 거리와 비용에 따른 운송수단을 어떤 것을 선택해야 하는지, 고객이 구매한 제품을 어떻게 운영하고 사용하는 지에 따라 목표수명기간동안 고장률을 얼마나 보장해 주어야 하는 지를 평가하고 검증하는 데 도움을 받을 수 있다.
Nguyen Huu Nhan,Truong Thi Nhan,Le Thi Phuong Ngoc,Nguyen Thanh Long 경남대학교 기초과학연구소 2021 Nonlinear Functional Analysis and Applications Vol.26 No.1
In this paper, we investigate an initial boundary value problem for a nonlinear pseudoparabolic equation. At first, by applying the Faedo-Galerkin, we prove local existence and uniqueness results. Next, by constructing Lyapunov functional, we establish a sufficient condition to obtain the global existence and exponential decay of weak solutions.