Analysis on Hydrodynamic Force Acting on a Catamaran at Low Speed Using RANS Numerical Method

Thi Loan Mai,Tien Thua Nguyen,Myungjun Jeon,Hyeon Kyu Yoon 한국항해항만학회 2020 한국항해항만학회지 Vol.44 No.2

This paper discusses the hydrodynamic characteristics of a catamaran at low speed. In this study, the Delft 372 catamaran model was selected as the target hull to analyze the hydrodynamic characteristics by using the RANS (Reynold-Averaged Navier-Stokes) numerical method. First, the turbulence study and mesh independent study were conducted to select the appropriate method for numerical calculation. The numerical method for the CFD (Computational Fluid Dynamic) calculation was verified by comparing the hydrodynamic force with that obtained experimentally at high speed condition and it rendered a good agreement. Second, the virtual captive model test for a catamaran at low speed was conducted using the verified method. The drift test with drift angle 0-180 degrees was performed and the resulting hydrodynamic forces were compared with the trends of other ship types. Also, the pure rotating test and yaw rotating test proposed by Takashina, (1986) were conducted. The Fourier coefficients obtained from the measured hydrodynamic force were compared with those of other ship types. Conversely, pure sway test and pure yaw test also were simulated to obtain added mass coefficients. By analyzing these results, the hydrodynamic coefficients of the catamaran at low speed were estimated. Finally, the maneuvering simulation in low speed conditions was performed by using the estimated hydrodynamic coefficients.

Establishment of empirical formulae for hydrodynamic derivatives of submarine considering design parameters

Mai Thi Loan,전명준,VO ANH KHOA,윤현규,Kim Seon-Hong,이주호 대한조선학회 2023 International Journal of Naval Architecture and Oc Vol.15 No.-

The hydrodynamic derivatives are necessary for assessing the dynamic characteristics, such as dynamic stability and maneuverability which are crucial in evaluating navigation safety and operational efficiency. Hence, it is required to compute the hydrodynamic derivatives precisely. This study nominates the new empirical formulae for predicting the hydrodynamic derivatives of a submarine. The proposed empirical formulae are derived from hydrodynamic forces and moments which are measured using Computational Fluid Dynamic (CFD) approach. Because the BB2 generic submarine is designed with an appropriate geometry and outstanding features, especially directionally stability, so, it is designated to establish the empirical formulae. The design parameters that have a significant impact on the maneuverability of the BB2 submarine, such as the length-to-diameter ratio, sail position, and sail height, are altered to fit different types of submarines for various purposes. Then, hydrodynamic derivatives of each change factor of the design parameter are taken using the least square method and assessed in relationship with the design parameters through correlation analysis. The high correlation values determine the independent variables which are the design parameters to form the empirical formulae for each hydrodynamic derivative based on multiple regression analysis. The applicability of the established empirical formulae is confirmed by applying them to calculate the hydrodynamic derivatives of BB2 and 2000 tons submarines, and comparing the calculation with the available data. The high precision implies that the established empirical formulae can be used to predict the hydrodynamic derivatives of similar profile submarines to the BB2 and 2000 ton submarines, and they can be extended to submarines in general at the designing phase.

Changes in the Hydrodynamic Characteristics of Ships During Port Maneuvers

Thi Loan Mai,VO ANH KHOA,전명준,윤현규 한국해양공학회 2022 韓國海洋工學會誌 Vol.36 No.3

To reach a port, a ship must pass through a shallow water zone where seabed effects alter the hydrodynamics acting on the ship. This study examined the maneuvering characteristics of an autonomous surface ship at 3-DOF (Degree of freedom) motion in deep water and shallow water based on the in-port speed of 1.54 m/s. The CFD (Computational fluid dynamics) method was used as a specialized tool in naval hydrodynamics based on the RANS (Reynolds-averaged Navier-Stoke) solver for maneuvering prediction. A virtual captive model test in CFD with various constrained motions, such as static drift, circular motion, and combined circular motion with drift, was performed to determine the hydrodynamic forces and moments of the ship. In addition, a model test was performed in a square tank for a static drift test in deep water to verify the accuracy of the CFD method by comparing the hydrodynamic forces and moments. The results showed changes in hydrodynamic forces and moments in deep and shallow water, with the latter increasing dramatically in very shallow water. The velocity fields demonstrated an increasing change in velocity as water became shallower. The least-squares method was applied to obtain the hydrodynamic coefficients by distinguishing a linear and non-linear model of the hydrodynamic force models. The course stability, maneuverability, and collision avoidance ability were evaluated from the estimated hydrodynamic coefficients. The hydrodynamic characteristics showed that the course stability improved in extremely shallow water. The maneuverability was satisfied with IMO (2002) except for extremely shallow water, and collision avoidance ability was a good performance in deep and shallow water.

Determinants Influencing Management Competency of Small and Medium Enterprise Directors in Vietnam

Thi Mai Huong DOAN,Minh Thuy DO,Thanh Lan MAI,Vu Phuong Anh DO,Thi Loan NGUYEN 한국유통과학회 2021 The Journal of Asian Finance, Economics and Busine Vol.8 No.12

Currently, small and medium-sized enterprises (SMEs) are accounting for about 98% of the total number of enterprises in Vietnam. Each year, SMEs create over one million new jobs, utilize up to 51% of the labor force in the society, and contribute more than 40% of GDP to the country. The study aims to analyze factors affecting the management competency of directors in small and medium enterprises in Vietnam. To achieve these research objectives, quantitative and qualitative methods were used concurrently. 300 questionnaires were sent out, but only 276 were collected and used for the quantitative analysis through SPSS 20.0 software. Cronbach’s Alpha, EFA, and regression were used to further confirm the research findings. The research findings show that all four proposed factors have impacts on the management competency of SME directors, among which enterprise features and specific policies for entrepreneur development in the locality have the strongest impacts, followed by personal features and business environment. The findings of this study suggest that managers need to focus on factors affecting the management competency of directors. This paper also provides new insight into the management competency of directors. Based on the findings, some recommendations are given for SMEs to improve management competency.

Study on Pure Roll Test of a Ship Using CFD Simulation

Thi Loan Mai(마이티로안),Anh Khoa Vo(보안코아),Hyeon Kyu Yoon(윤현규) 대한조선학회 2022 大韓造船學會 論文集 Vol.59 No.6

Factors Influencing on Consumer's Decision on Vegetarian Diets in Vietnam

NGO, Vu Quynh Thi,VO, Thi Anh Dao,NGO, Anh Phung,NGUYEN, Do Mai Anh,LE, Minh Thu,TO, Thi Phuong Loan,NGUYEN, Thi Thuy Phi Korea Distribution Science Association 2021 The Journal of Asian Finance, Economics and Busine Vol.8 No.2

Recently, vegetarian diets have experienced a dramatic increase in popularity. The aim of the study is to explore and test the relationship between the factors influencing consumers' dietary decisions in Ho Chi Minh City, Vietnam. The questionnaire applied a five-point Likert scale to investigate factors that affect Ho Chi Minh City's citizens when they have a vegetarian diet. 497 respondents (68% female; 61.2% aged 18-22; 82.7% had regular vegetarian diets) living in Ho Chi Minh City took part in both online and offline surveys. The results were processed by SPSS 22.0 software. The reliability was checked by Cronbach Alpha and Exploratory factor analysis (EFA) to identify the underlying relationships between measured variables. The Correlation analysis was implemented to show how strong and degree of two variables are related to each other before the multivariate regression equation was analyzed. The result showed the Five factors that were motivating people in Ho Chi Minh City to decide on plant-based diets, such as Animal Welfare, Health, Religion, Mood, and Reference groups. The mood is the most influential variable that significantly influences people's food choices. Attitudes toward vegetarian diets are changing. Therefore, recognizing the trends in food consumption might help companies take advantage of investment opportunities and build their marketing strategies.

Determinants of Implementation of Enterprise Resource Planning System: A Case Study in Vietnam

Xuan Hiep NGUYEN,Thi Cam Loan NGUYEN,Xuan Dao MAI,Thi To Loan BUI,Thi Tra Giang TRAN,Thuy Trinh HO,Thi Huyen NGUYEN 한국유통과학회 2021 The Journal of Asian Finance, Economics and Busine Vol.8 No.4

Under the pressure of business competition and effectiveness, more and more organizations in the world are likely to apply modern software such as enterprise resource planning (ERP) which can help them to create better organizing practice, better managing capabilities of administrators, and better operations of personnel. In Vietnam, many firms are afraid to install it and the number of firms adopting this software is limited mainly due to the insufficient scientific evidence of the successful implementation of ERP. This study aims to identify and measure the factors influencing the successful implementation of ERP of firms in Vietnam. Qualitative research methodology combined with quantitative research methodology is used. The data are surveyed with 343 administrators of 45 organizations that have successfully deployed ERP in Ha Noi and Ho Chi Minh cities. Of these 19 were excluded from analyses due to unsatisfactory responses, and only 324 were used for statistical processing. The collected data were processed by using the SPSS software. The result of the study shows that there are six factors affecting the successful implementation of ERP of firms in Vietnam, (ranked in descending order of importance), they are top management commitment and support, business process re-engineering, user involvement, project management board, vendor support, and suitability of software and hardware.

Numerical Investigation of Motion Response of the Tanker at Varying Vertical Center of Gravities

Van Thuan Mai,Thi Loan Mai,Hyeon Kyu Yoon 한국해양공학회 2024 韓國海洋工學會誌 Vol.38 No.1

The vertical center of gravity (VCG) has a significant impact on the roll motion response of a surface ship, particularly oil tankers based on the oil level in the tanker after discharging oil at several stations or positional changes, such as changes in the superstructure and deck structure. This study examined the motion response of the Korea very large crude carrier 2 (KVLCC2) at various VCGs, especially roll motion when the VCG changed. The potential theory in the Ansys AQWA program was used as a numerical simulation method to calculate the motion response. On the other hand, the calculations obtained through potential theory overestimated the roll amplitudes during resonance and lacked precision. Therefore, roll damping is a necessary parameter that accounts for the viscosity effect by performing an experimental roll decay. The roll decay test estimated the roll damping coefficients for various VCGs using Froude’s method. The motion response of the ship in regular waves was evaluated for various VCGs using the estimated roll-damping coefficients. In addition, the reliability of the numerical simulation in motion response was verified with those of the experiment method reported elsewhere. The simulation results showed that the responses of the surge, sway, heave, pitch, and yaw motion were not affected by changing the VCG, but the natural frequency and magnitude of the peak value of the roll motion response varied with the VCG.

Evaluation of Dynamic Characteristics for a Submerged Body with Large Angle of Attack Motion via CFD Analysis

Myungjun Jeon,Thi Loan Mai,Hyeon Kyu Yoon,Jaekwan Ryu,Wonhee Lee,Pyungmo Ku 한국해양공학회 2021 韓國海洋工學會誌 Vol.35 No.5

A submerged body with varied control inputs can execute large drift angles and large angles of attack, as well as basic control such as straight movement and turning. The objective of this study is to analyze the dynamic characteristics of a submerged body comprising six thrusters and six control planes, which is capable of a large drift angle and angle of attack motion. Virtual captive model tests via were analyzed via computational fluid dynamics (CFD) to determine the dynamic characteristics of the submerged body. A test matrix of virtual captive model tests specialized for large-angle motion was established. Based on this test matrix, virtual captive model tests were performed with a drift angle and angle of attack of approximately 30° and 90°, respectively. The characteristics of the hydrodynamic force acting on the horizontal and vertical surfaces of the submerged body were analyzed under the large-angle motion condition, and a model representing this hydrodynamic force was established. In addition, maneuvering simulation was performed to evaluate the standard maneuverability and dynamic characteristics of large-angle motion. Considering the shape characteristics of the submerged body, we attempt to verify the feasibility of the analysis results by analyzing the characteristics of the hydrodynamic force when the large-angle motion occurred.

Experimental Investigation of the Hydrodynamic Characteristics of a Ship due to Bank Effect

Anh Khoa Vo,Thi Loan Mai,전명준,윤현규 한국항해항만학회 2022 한국항해항만학회지 Vol.46 No.2

When a ship moves in the proximity of the lateral bank, bank suction forces are generated due to bank effects. Thus, hydrodynamic forces can significantly impact the ship’s maneuverability and navigation safety. In this study, model tests were performed to investigate the hydrodynamic forces exerted on a ship, especially suction forces caused by bank effects, using captive model and bank effect tests. A low-speed condition was selected in this study, because of the perilous situation as the ship moves close to the bank. The accuracy of the hydrodynamic forces exerted on the hull was verified, by comparing the results of the static drift test with the results obtained from other institutes at design speed. The straight simulation caused by bank effects was then implemented using estimated hydrodynamic coefficients.