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Effect of boattail angle on near-wake flow and drag of axisymmetric models: a numerical approach
The Hung Tran,Hoang Quan Dinh,Hoang Quan Chu,Van Quang Duong,Chung Pham,Van Minh Do 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.2
Flow behavior around axisymmetric boattail surface was studied by numerical methods. A wide range of boattail angles from 0° to 24° was investigated to find the drag trend of the model. Numerical simulation was validated by experimental results with the same flow conditions. Results showed that the use of boattail model always has a positive effect on drag reduction. Total drag showed minimum value at boattail model of around 14°. Length of the recirculation after body decreases with increasing boattail angle up to 14° and then becomes constant at higher angle. The trend of boattail pressure drag showed similar to previous studies for high-speed flow. However, base drag showed different trend to previous observation. The base drag showed to be the most important parameter to determine drag trend of the model. The effect of flow fields around boattail on pressure distribution and drag is discussed in detail.
The Hung Tran,Cong Truong Dao,Dinh Anh Le,Van Khiem Pham,Van Minh Do,Trang Minh Nguyen 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.12
This study examines the drag trend and flow behavior of axisymmetric models with conical boattails under subsonic and supersonic conditions by using a numerical approach. Mach numbers ranging from 0.1 to 3.0 and boattail angles varying from 0° to 24° are investigated. The numerical results are validated by experimental data under identical flow conditions. The flow behavior around the boattail body, the total drag, and the pressure distribution are analyzed in detail. The drag components acting on the boattail surface are examined to determine the reason for the change in drag due to different boattail angles and Mach number conditions. Results show that the minimum drag is around 14° for subsonic flow, but this value suddenly decreases to around 7° for supersonic flow. Formalization of the expansion and oblique shocks on the boattail is the main cause of changes in the pressure distribution on the surfaces, which in turn affect the drag trend. Moreover, the relationships among boattail angle, flow conditions, and four flow types on the boattail surface are presented in detail.
Factors Affecting the Internal Audit Effectiveness of Steel Enterprises in Vietnam
The Hung DINH,Duc Cuong PHAM,Tuan Thi NGUYEN 한국유통과학회 2021 The Journal of Asian Finance, Economics and Busine Vol.8 No.1
This article provides empirical evidence on factors of internal audit (IA) characteristics affecting the internal audit effectiveness in steel enterprises in Vietnam. The study uses data from survey obtained from 114 responses representing owners, managers, and internal auditors from 38 steel enterprises in Vietnam for period from 2018 to 2019. Data collected is firstly checked with Cronbach’s Alpha, then the EFA test, and the model linear regression is used to test the relationship between internal audit characteristics and internal audit effectiveness. Results reveal that internal audit effectiveness in steel enterprises in Vietnam is influenced by various internal factors, including the size of internal audit, the scope of internal audit, the capacity of internal auditors, the independence of internal auditor, and the operational bases and methods of internal audit. Based on the research results, the paper makes six recommendations: strengthening operational basis of IA; increasing the independence of IA; increasing the size and capacity of IA staff; expanding and not underestimate the scope of IA; and reforming the internal governance structure. These proposed recommendations could be applied, not only for steel companies in Vietnam, but also for other companies in Vietnam or other companies in jurisdictions that have similar conditions.
DINH, Hung The,PHAM, Cuong Duc Korea Distribution Science Association 2020 The Journal of Asian Finance, Economics and Busine Vol.7 No.9
This study investigates the effect of capital structure on the financial performance of pharmaceutical enterprises which are listing on Vietnam's stock market. The study builds the regression using ROE as dependent variable and four independent variables, including self-financing, financial leverage, long-term asset and debt to assets ratios. In addition, we use other variables as controlling ones, such as firm size, fixed asset rate and growth. We collect data for the period from 2015 to 2019 of all 30 pharmaceutical enterprises which are currently listing on Vietnam's stock market. The least square regression (OLS) is used to test the effect of capital structure to the firms' financial performance. The analysis results show that the financial leverage ratio (LR), long-term asset ratio (LAR) and debt-to-assets ratio (DR) have positive relationship with firm performance, meanwhile the self-financing (E/C) affects negatively to the return on equity (ROE). Upon the findings we suggest that the Vietnamese government should focus on stabilizing macro environment to create favorable environment for enterprises. And the pharmaceutical enterprises should build more reasonable capital structure with higher debt proportion than equity, diversifying loan mobilization channels such as issuing long-term bonds. Additionally, the firms should expand the scale appropriately to maintain development and ability to pay debts.
Impact of Corporate Social Responsibility Disclosures on Bankruptcy Risk of Vietnamese Firms
NGUYEN, Soa La,PHAM, Cuong Duc,NGUYEN, Anh Huu,DINH, Hung The Korea Distribution Science Association 2020 The Journal of Asian Finance, Economics and Busine Vol.7 No.5
This study investigates the nexus between the level of Corporate Social Responsibility Disclosures (CSRD) and Risk of Bankruptcy of companies that are listing in the Stock Exchanges of Vietnam. To investigate that relationship, this study collected secondary data from annual audited financial statements from 2014 to 2018 of listing companies. Applying two different regression models with two dependent variables and six independent and control variables, we find out that Vietnamese firms with higher level of CSRD performance can rapidly reduce their risk of bankruptcy. This phenomenon happens in the current year and in the coming years in all firms in the research sample. This result may be that the disclosures of social responsibility information can bring financial and non-financial benefits to the firms. In addition, the results also point out that there is a difference in risk of bankruptcy between the group of companies, which discloses and the one which does not disclose corporate social responsibility on their annual reports. This might be from the effects of various factors such as business size, financial leverage, market to book ratio, return on assets, cash flow from operations, etc. Our research results can be applied to other firms in Vietnam and in other similar jurisdictions.
Won-Shik Chu,Malik Muhammad Shehroze,Ngoc Giang Tran,The-Hung Dinh,Sung-Tae Hong,Doo-Man Chun 한국정밀공학회 2024 International Journal of Precision Engineering and Vol.25 No.5
This review study provides an overview of superhydrophobic surface fabrication techniques based on laser surface texturing that are environmentally friendly. There are many prospective applications for superhydrophobic surfaces, including self-cleaning, anti-icing, oil–water separation, anti-corrosion, and anti-biofouling. Except for hydrophobic nanoparticle coating procedures, superhydrophobic surface manufacturing methods have not been sufficiently developed or commercialized. Among the various fabrication techniques, laser surface texturing is an important process that is different from superhydrophobic surface coating processes. This technique can be used to fabricate superhydrophobic surfaces in an eco-friendly manner and can process selected regions without the use of a mask. This review study is intended to improve our understanding of these laser surface texturing technologies for fabricating superhydrophobic surfaces and to open up new research areas. In this review, procedures, materials, and parameters for creating superhydrophobic surfaces using laser processing and environmentally friendly post-processing are analyzed and summarized. Because they involve the use of hazardous chemicals, common laser processes with fluorination or silanization coatings were not included. Finally, we provide an overview of the study trends and offer conclusions based on this review.