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Topology optimization using moving morphable bars for versatile thickness control
Hoang, Van-Nam,Jang, Gang-Won North-Holland Pub. Co 2017 Computer methods in applied mechanics and engineer Vol.317 No.-
<P><B>Abstract</B></P> <P>Topology optimization for minimum and maximum thickness control, uniform thickness control, and multiple thickness control is provided by using moving morphable bars formed of rectangles with semicircular ends. By employing the center coordinates of the semicircular ends and the thickness of a moving bar as design variables, the bar can float around the design domain while its shape morphs according to the design sensitivities. The overlapping of moving bars is allowed, and the element density is determined by the approximation of the Heaviside function by measuring the shortest distance from the boundaries of the bars. The minimum thickness of the members of an optimized structure is controlled by simply setting the lower bound of the thickness variables for the moving bars. No constraints or filtering techniques are required for the minimum thickness control. The maximum thickness is controlled for each moving bar through its corresponding constraint, which prevents an over-sized member due to the overlapping of moving bars. By solving benchmark problems, the validity of the method proposed for versatile thickness control is shown. It is also shown that the proposed method alleviates numerical difficulties for hinges when it is applied for compliant mechanism problems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Topology optimization for thickness control is provided using moving morphable bars. </LI> <LI> The minimum thickness is controlled by setting lower bound of thickness variables. </LI> <LI> The number of design variables is much smaller than those of conventional methods. </LI> <LI> The difficulty of hinge designs in compliant mechanism can be also resolved. </LI> </UL> </P>
Battery-less Pork Freshness Monitoring Based on High-Efficiency RF Energy Harvesting
( Nam Hoang Nguyen ),( Minh Binh Lam ),( Wan-young Chung ) 한국센서학회 2020 센서학회지 Vol.29 No.5
Food safety has emerged as a growing concern for human health in recent times. Consuming contaminated food may lead to serious health problems, and therefore, a system for monitoring food freshness that is both non-detrimental to the quality of food and highly accurate is required to ensure that only high-quality fresh food packages are provided to the customers. This paper proposes a method to monitor and detect food quality using a compact smart sensor tag. The smart tag is composed of three ultra-low-power sensors, which monitor four major indicators of food freshness: temperature, humidity, and the concentrations of ammonia and hydrogen sulfide gases. An RF energy scavenging circuit is integrated into the smart sensor tag to harvest energy from radio waves at a high frequency of 13.56 MHz to supply sufficient power to the tag. Experimental results show that the proposed energy harvester can efficiently obtain energy at a distance of approximately 40 cm from a 4W reader. In addition, the proposed smart sensor tag can operate without any battery, thereby eliminating the requirement of frequent battery replacement and consequently decreasing the cost. Meanwhile, the freshness of preserved pork is continuously monitored under two conditions-room temperature and refrigerator temperature--both of which are the most common temperatures under which food is generally stored. The food-monitoring experiments are conducted over a period of one week using the proposed battery-less tag. Based on the experimental results, the food assessment is classified into four categories: fresh, normal, low, and spoiled.
Network-less Power System Frequency Stability Assessment Tool Development
Nam-Du Nguyen-Hoang,Thanh Nguyen Nguyen,Duc Ngoc Nguyen,Jin Hur(허진),Jaegul Lee(이재걸),Solyoung Jung(정솔영),Oh Seungchan(오승찬),Jae Woong Shim(심재웅) 대한전기학회 2021 대한전기학회 학술대회 논문집 Vol.2021 No.4
This paper introduces software development for network-less power system frequency stability evaluation based on Python software using renewable energy resources, frequency-dependent load model, energy storage system (ESS). In this paper, the integration modeling of generators implements all the inertia constants presented in the system into one inertia constant based on a swing equation. The evaluation of the developed software performs using Python software with the Korean network 2022 and 2023 by comparing the generator model responses with the responses of the PSS/e data.
Nam Hoang NGUYEN,Minh Ngoc NGO 한국유통과학회 2021 The Journal of Asian Finance, Economics and Busine Vol.8 No.8
ASEAN Economic Community (AEC) was established in 2015 from 10 countries to realize the ultimate (adopted in 1997), which aimed to transform ASEAN into a stable, prosperous, and highly competitive region with equitable economic development, reduced poverty, and socioeconomic disparities. The purpose of this paper is to examine the effect of knowledge level on the AEC of Vietnamese small and medium enterprises (SMEs) in the textile and apparel industry towards attitudes, readiness, and performance. This study uses convenience sampling to get questionnaires from 150 SMEs in Hanoi, Vietnam. Then, the paper applies SPSS-AMOS 24 to process data. The empirical results show that AEC’s implementation only has a small impact on improving SME performance. However, SMEs have adequate knowledge, attitude, and readiness about AEC. The structural modeling findings indicate that the knowledge factor has an indirect effect on SMEs’ performance. This finding is to provide new insight into the roles of attitude and readiness in the case of Vietnam. These factors are needed to mediate the effect of attitudes and readiness in the relationship between knowledge and business performance, a framework strategy of business organizations, and can be used as a conceptual model to improve SMEs’ performance.
Perceived Risk and Intention to Use Credit Cards: A Case Study in Vietnam
Nam Hoang TRINH,Ha Hong TRAN,Quan Duc Hoang VUONG 한국유통과학회 2021 The Journal of Asian Finance, Economics and Busine Vol.8 No.4
This study aims to develop a theoretical model in order to determine factors affecting consumer intention to use credit cards by combining Theory of perceived risk and Technology acceptance model. Despite of perspective of consequences in prior studies on related research fields, this study focuses on the sources of perceived risk, including transaction, payment and credit risks, which are proposed and measured in a preliminary research. A measurement model and a structural model with the presence of perceived risk in sources are tested in a formal research with data collected from 538 bank customers. An analysis results show that payment risk, usefulness, transaction risk, ease of use, and credit risk influence significantly Vietnamese consumers’ intention to use credit cards in decreasing order of influence. These factors account for 64.6% of the variation in intended use. All three dimensions of perceived risk have a negative effect on the intention to use, with the total impact greater than the level of influence of the other two factors of usefulness and ease of use. These findings can be beneficial to banks in enacting policies to attract more consumers and to allocate resources for improving their credit card business.
Hoang Nam Nhat,Dinh Van Chau,Dinh Van Thuong,Nguyen Thi Hang 한국인터넷방송통신학회 2015 International Journal of Internet, Broadcasting an Vol.7 No.1
This paper presents the application of the bond valence method to estimate the valence charge distribution in several perovskite systems: La1xPbxMnO3 (x=0.1-0.5), La0.6Sr0. - xTixMnO3 (x=0.0-0.25) and La1xSrxCoO3 (x=0.1-0.5); the reviewing of their crystal structures is also incorporated. The results showed the failure of the elastic bonding mechanism in all studied systems and revealed the general deficit of the valence charge in their unit cells. This valence deficit was not associated with the structural defects and was not equally localized in all coordination spheres. As the content of substitution increased, the charge deficit declined systematically from balanced level, signifying the transfer of valence charge from the O6 to O12 spheres. This transfer depended on the valence deviation of spheres and the average reached near 2 electron per unit cell. The possible impact of the limitted accuracy of the available structural data on the bond valence results has also been considered.