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Trajectory analyses of uncontrolled circular parachutes in random spatial wind fields
Thanh Dong Pham,Anh Tuan Nguyen,Vu Dan Thanh Le,Trung Kien Nguyen 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.8
The present paper explores the trajectories of two uncontrolled circular parachute models which differ in size and mass in random spatial wind fields. The wind velocity components were generated through three-dimensional inverse fast Fourier transforms; and the correlations of the simulation data compared with the theoretical functions to confirm the accuracy of the wind model. The parachute systems are modelled as six-degrees-of-freedom rigid bodies, on which the aerodynamic forces and moments are applied. The dynamics model was validated before being used to study the drop trajectories of the parachute systems in spatial wind fields. Analyzing the drop trajectories and the impact point dispersion characteristics of the two parachute systems, the paper shows that the smaller one oscillates at a higher frequency and is affected more strongly by the wind. While descending at low altitude, there could be resonance between the dynamics of the larger parachute model and the wind turbulence. Moreover, it is found that the use of simplified vertical wind profiles, which include only the variation of the wind velocity against the altitude, may cause significant error in the simulation results.
Tuan Anh Nguyen,Tuan Thanh Pham 한국도로학회 2018 한국도로학회 학술대회 발표논문 초록집 Vol.2018 No.05
Road network in the Mekong Delta is mostly coastal and river routes, then they are often flooded when the floods come in. As a result, the foundation and pavement are destroyed, reduced life expectancy, resulting in unsafety in traffic, cost of maintenance and repairs…. This paper establishes the technical conditions for the calculation on the flexible pavement working in the wet conditions (so flooded) based on the maximum usage of available materials in the provinces in the Mekong Delta. Simultaneously, we propose the flooded flexible pavement under the current climate change conditions.
Flapping flight in the wake of a leading insect
Anh Tuan Nguyen,Thanh Dong Pham,Quoc Tru Vu 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.7
This study explores the wake effects of an upstream leading insect on the flight performance of a following one. The potential-flow based aerodynamic model, which combines the unsteady panel and unsteady vortex-lattice methods, is used to compute aerodynamic loads and simulate wake structures. The accuracy of the current aerodynamic model was confirmed in this study. The paper shows that the following insect does not cause any noticeable impact on the leading insect aerodynamics, while unfavorable effects due to the presence of the leading insect were found on the following counterpart. Nonetheless, by choosing a proper wing kinematic phase, the following insect may absorb the energy of the leading insect’s trailing wake, and therefore mitigate these negative effects. The variations of the required mechanical power of the following insect against the wing kinematic phase difference were shown to be related to the travel of the leading insect’s downstroke starting vortex.
Tam-Thanh Pham,Anh-Tuan Dinh,Hong-Ha Tran,Dang-Khanh Le 대한전자공학회 2019 IEIE Transactions on Smart Processing & Computing Vol.8 No.3
In this paper, we consider a cooperative cognitive radio network with multiple relays under an eavesdropping attack. We first propose a novel relay selection scheme to improve network security and reliability. Then, we derive accurate closed-form expressions of the network outage and intercept probabilities. Finally, several representative simulation results are provided to validate our analyses. We show that network reliability is completely irrelevant to the channels’ statistical characteristics between relays and the eavesdropper, while network security is independent of the channel statistical characteristics for relays to the destination. We also point out that network security is first improved from increasing the number of relays; however, when the number of relays reaches a certain point, the increased network reliability is not proportional to the number of relays any more.
Nga Thanh DOAN,Trang Thu TA,Ha Thi Thanh CHU,Anh Thi Quynh LE,May Thi LE,Tuan Hoang PHAM,Thao Thu VUONG 한국유통과학회 2022 The Journal of Asian Finance, Economics and Busine Vol.9 No.2
The purpose of this study is to look at the precise direction and magnitude of cultural elements such as education, gender, power distance, and risk-taking proclivity on ethical decision-making. Data was collected from 194 interviewees in three groups: general business students, accounting major students, and professional auditors in Vietnam. The path analysis is used to test the impact of cultural factors on ethical awareness, ethical judgment, and ethical intention in different dubious scenarios at the personal level as independent variables, intermediate variables, and moderating variables. The metric is the percentage of respondents who believe a particular behavior is unethical based on a set of ethical principles. The researchers used SPSS AMOS software to conduct a confirmatory factor survey to evaluate the convergent and discriminant validity of latent variables. The results show differences between the two groups of students and professionals on these measures, suggesting that all of the four factors have an effect on ethical decision-making. Based on research results, some recommendations are proposed related to the four factors to improve the ethics of future generations of auditors in Vietnam. This study also contributes to the theory of culture in particular and cultural interference in general in the field of accounting-auditing in Vietnam in the process of international integration.
Quoc Tuan Hoang,Xuan Hien Pham,Anh Vu Le,Trung Thanh Bui 한국인터넷정보학회 2023 KSII Transactions on Internet and Information Syst Vol.17 No.3
Diagnosing breast diseases using ultrasound (US) images remains challenging because it is time-consuming and requires expert radiologist knowledge. As a result, the diagnostic performance is significantly biased. To assist radiologists in this process, computer-aided diagnosis (CAD) systems have been developed and used in practice. This type of system is used not only to assist radiologists in examining breast ultrasound images (BUS) but also to ensure the effectiveness of the diagnostic process. In this study, we propose a new approach for breast lesion localization and segmentation using a multi-scale pyramid of the ultrasound image of a breast organ and a convolutional semantic segmentation network. Unlike previous studies that used only a deep detection/segmentation neural network on a single breast ultrasound image, we propose to use multiple images generated from an input image at different scales for the localization and segmentation process. By combining the localization/segmentation results obtained from the input image at different scales, the system performance was enhanced compared with that of the previous studies. The experimental results with two public datasets confirmed the effectiveness of the proposed approach by producing superior localization/segmentation results compared with those obtained in previous studies.
Nguyen Duc Anh,Pham Van Thanh,Doan Tu Lap,Nguyen Tuan Khai,Tran Van An,Tran Duc Tan,Nguyen Huu An,Dang Nhu Dinh 한국인터넷정보학회 2022 KSII Transactions on Internet and Information Syst Vol.16 No.2
Forest fires inflict great losses of human lives and serious damages to ecological systems. Hence, numerous fire detection methods have been proposed, one of which is fire detection based on sensors. However, these methods reveal several limitations when applied in large spaces like forests such as high cost, high level of false alarm, limited battery capacity, and other problems. In this research, we propose a novel forest fire detection method based on image processing and correlation coefficient. Firstly, two fire detection conditions are applied in RGB color space to distinguish between fire pixels and the background. Secondly, the image is converted from RGB to YCbCr color space with two fire detection conditions being applied in this color space. Finally, the correlation coefficient is used to distinguish between fires and objects with fire-like colors. Our proposed algorithm is tested and evaluated on eleven fire and non-fire videos collected from the internet and achieves up to 95.87% and 97.89% of F-score and accuracy respectively in performance evaluation.