Nguyen Manh Hung

Study of separation phenomenon in transonic flows produced by interaction between shock wave and boundary layer

For compressible flows, the transonic state depends on the geometry, Mach number and the incidence. This effect can produce shock wave. Some studies showed that the interaction between shock wave and boundary layer concerns separation phenomenon. Studies in this report demonstrate conditions of separation in transonic flow and that it is not any interaction between shock wave and boundary layer which can cause boundary layer separation. The studies also show that maximum Mach number in the local supersonic region is not a unique factor influencing the separation, and the separation in transonic flows can occur at the incidence of 0o. For the calculation of viscous transonic flows, we use Fluent software with serious treatment of application operation based on the physical nature of phenomenon and the technique of numerical treatment. For the calculation of invicid transonic flows, we built a code solving the full potential equation with verification for accuracy. Results calculated from Fluent have been seriously compared with results of present program and published results in order to assure the accuracy of application operation in the domain of investigation.

Experiments and numerical calculation to determine aerodynamic characteristics of flows around 3D wings

The report presents method and results of experiments in wind tunnel to determine aerodynamic characteristics of 3D wings by measuring pressure distribution on the wing surfaces. Simultaneously, a numerical method by using sources and doublets distributed on panel elements of wing surface also is carried out to calculate flows around 3D wings. This computational method allows solving inviscid problems for wings with thickness profile. The experimental and numerical results are compared to each other to verify the built program that permits to extend the range of applications with the variation of wing profiles, wing planforms, and incidence angles.

Storm wave modeling with swan comparison of measurement data and modeling results for the storm MUIFA 11/2004

With the average of 4-5 storms hitting the Vietnamese coastline every year, our country is suffering from great damage of infrastructures and lost of human life. Most storms induce significant waves which, especially in the coastal zones, can destroy houses, coastal structures and move large amounts of sand from beaches to offshore resulting in shoreline erosion. Therefore modeling of storm waves is an important task of engineers, scientists, weather forecasting specialists of our country. In order to meet the need of mitigation storm effects, to improve the storm wave forecasting capability in general and to study the coastal evolution in the Red River Delta (RRD) in particular, the authors have developed the S\i\TAN model for the storm wave calculation in the East Sea. In the paper some formulations of the model has been used to get the best agreement with the measured wave field in the storm MUIFA 11/2004. The wind and wave data at the oil platform MSPl and wave height field over the sea were used to compare the model results . The obtained results afford the promising of using the SWAN model in research and weather forecast .

EXPERIMENTAL STUDY OF LAMINAR SEPARATION PHENOMENON COMBINING WITH NUMERICAL CALCULATIONS

The separation is much more sensitive for laminar flow than for turbulent flow. These remarks have been attested for both subsonic and supersonic flows. However, they are not applicable to transonic flows when there are interactions between boundary layer and shock wave. Along with the Reynolds number, the Mach number is a necessary dimensionless parameter for the condition and the mechanism of separations. The report presents one part of studies on laminar separation with Mach number of incompressible flow. The laminar regimes correspond to flows through wind turbine blades. Our ex- perimental work for laminar separation phenomenon was carried out in a subsonic open circuit wind tunnel by taking photographs. The accuracy of experimental results basically depends on the accuracy of wind tunnel and the quality of smoke on density and con- stitutive materials. Experimental results permit to determine the position of separation and the form of turbulent region followed from the separation point. Numerical studies were simultaneously realized. Based on obtained experimental and numerical results, the report presents also the comparison between the laminar separation and the turbulent separation.

Static and free vibration analyses of laminated composite shells by cell-based smoothed discrete shear gap method (CS-DSG3) using three-node triangular elements

A cell-based smoothed discrete shear gap method (CS-DSG3) using three-node triangular elements was recently proposed to improve the performance of the discrete shear gap method (DSG3) for static and free vibration analyses of isotropic Reissner-Mindlin plates and shells. In this paper, the CS-DSG3 is further extended for static and free vibration analyses of laminated composite shells. In the present method, the first-order shear deformation theory (FSDT) is used in the formulation due to the simplicity and computational efficiency. The accuracy and reliability of the proposed method are verified by comparing its numerical solutions with those of others available numerical results.

LONG SHORE SEDIMENT TRANSPORT COMPUTATION FOR HAI HAU BEACH-NAM DINH PROVINCE

Several stretches of shore line in the Red River Delta (RRD) are suffering from severe erosion, especially an area between too large river mouths Balat in the North and Day in the South, known as Hai Hau beach. Several different hypothesis have been put forward to explain this erosion. The cut off of the Ha Lan river mouth (in 1955) which discharged sediment at the upstream end of the beach, possibly affects Hai Hau beach. Also, the construction of Hoa Binh dam in the upstream part of Red river has reduced the sediment supply to the area. In this study, it is shown that the prevailing wave climate in connection with the complex topography of Balat river mouth and Hai Hau beach promotes erosion along the coastal line. A two dimensional random wave transformation model was used with 20-year time series of hindcast waves to compute the long shore sediment transport along the study beach.

LATERAL TURBULENT MIXING FORCES IN THE LONG SHORE CURRENT CALCULATION BY LONGUET-HIGGINS METHOD AND THEIR INFLUENCE ON LONG SHORE SEDIMENT TRANSPORT

Longuet - Higgins method for long shore current and Bijker method for sediment transport calculations are worldwide used mathematical model in the coastal engineering. When using them, we should image how work the methods and what is sensitivity and influence of each parameters on final results as sediment transport. In this paper, the influences of parameters N, P of lateral turbulent mixing forces on the long shore current and then on the sediment transport are estimated. The Bijker example is used and the computation results are compared with Bijker results for neglecting the lateral turbulent mixing. A field application with appropriate parameters N and P for Le Thuy beach is obtained for verification of long shore current and sediment transport.

A TWO DIMENSION NUMERICAL MODEL FOR WAVES INDUCED CURRENTS IN THE COASTAL ZONE

In this paper, the results of two dimension numerical model for waves induced currents in the coastal zone are presented. The model was adjusted and verified at Phan Ri-Binh Thuan zone. The results of the testing show a good agreement between the observed and computed values. Then the model is applied to calculation of the distribution of waves induced currents in Ly Hoa area.

On the Asymptotic Behavior of Solutions of the First Initial Boundary-Value Problems for Parabolic Equations

We consider the first initial boundary-value problem for a strongly parabolic system on an infinite cylinder with nonsmooth boundary. We prove some results on the existence, uniqueness, and asymptotic behavior of solutions as t → ∞.

On the Stability of Semilinear Nonautonomous Evolution Equations in Banach Spaces and Its Application to Strongly Parabolic Equations

The paper is concerned with the exponential stability of the zero solution of strongly nonautonomous parabolic equations. Conditions are found on time-dependent coefficients of a parabolic equation under which its solutions converge exponentially to 0 as t → ∞.