Applied Mechanics and Materials Vols. 268-270

Abstract: For the optimal design of base bleed unit, a 2D-axisymmetric unsteady model was established and the effects of different exhaust nozzle diameters on the internal flow field were studied. Results show that the larger the exhaust nozzle is, the higher the depressurization rate and the mass flux are at the earlier stage of depressurization, and the lower the pressure, the temperature, the density in the base bleed unit and the flow rate at the nozzle outlet are. But at the later stage, the depressurization rate and the mass flux are smaller instead. The radial temperature is generally unchanged in most part far from the burning surface and increases near the burning surface at the earlier stage of depressurization, whereas it is lowest at the axis and rises up quickly along the radial direction at the later stage. The radial density distributes just oppositely.

Abstract: Contact surface of nanoscale sliding friction represent some new features that are different from the macro scale sliding friction, which need to seek new analysis methods. Molecular dynamics simulation is an effective method to describe microscopic phenomena. Therefore, Molecular dynamics method was used to study mechanical behavior of contact surface of nanoscale sliding friction. A molecular dynamics model of hemisphere sphere sliding on rectangular solid plane was built. State change of the micro contact area and friction force variation in the process of sliding friction were observed and analyzed after solution and simulation. The results show that, at the beginning position of the sliding, with different contact depth, contact action region of hemisphere and plane generated the atoms displacement, re-arranged and close-packed accumulation is also different. The deeper the contact depth is, the greater the atoms close-packed accumulation is, and the greater the contact deformation is. In the process of sliding friction, the contact surface of the basal body has produced lattice destruction, surface upheaval and silicon atoms close-packed accumulation, and then formed furrow scratches. At the same time the silicon atoms of the hemisphere generated atomic migration obviously and adhered on the basal body surface. The top of the hemisphere was torn and peeled, which resulted in wear. The deeper contact depth is, the more loss of the material of the hemisphere is, and wear become heavier. The curve of friction force and sliding displacement in different contact depths shows that the deeper contact depth is, the greater friction force is. The friction force increases quickly at the beginning of the sliding. Then the friction force remains steady relatively at stable sliding phase. In subsequent sliding process, due to hemisphere was worn and the original contact surface changed in size, shape and configuration state, friction force decreases obviously. Besides, in process of sliding friction, due to stick-slip effect, friction force appears obviously fluctuations. Moreover, if the sliding speed is large the changes of sliding speed have less effect on friction force when the nanoscale sphere sliding on the plane at the different speeds.

Abstract: Direct Numerical Simulation(DNS) was carried out for laminar-turbulent transition of an incompressible boundary layer on a flat plate based on disturbance Navier-Stokes(N-S) equation in spatial mode with Massage Passing Interface(MPI) technology. Study on breakdown mechanism of laminar-turbulent transition was carried on. The effect of mean flow distortion on the process of breakdown in laminar-turbulent transition was investigated. Results indicate that change of instability characteristic of mean flow profile plays a key role during process of breakdown.

Abstract: In this paper, by using complex variable function and conformal mapping technique, the author studies the stress concentration intensities of silo wall opening through predigesting the stress calculation of silo wall opening as a problem of plane calculation and obtains the stress concentration factor of opening. When simplified silo wall is subjected to in-plane tension or pressure, maximal stress concentration point around opening is at the corner of opening. this paper may provide some referenced value to the designers.

Abstract: Sphere-cylinder combined shell is one of the main pressure hull forms of submersible. This paper analyzes on edge stress of sphere-cylinder combined shell under external hydrostatic pressure. The edge models of cylindrical and spherical parts of combined shells are established by moment analysis and deformation compatibility. In the experiment, a ring-stiffened cylinder with hemispherical end is designed to verify edge models. The results of stress analysis are discussed in the paper.

Abstract: We study the weighted Monte Carlo method, which was proposed by Milchev, Heermann and Binder. First, we describe our method and the Monte Carlo procedure. Second, we apply the procedure to study the phase transitions of and Sine-Gordon models, respectively. The critical values of the parameters allow us to determine the phase diagram of the models.

Abstract: A simple geometrical and material nonlinear co-rotational planar beam element of field consistency is proposed. Herein the element which produces a local stiffness matrix of 3 by 3 other than 6 by 6 is developed. Material nonlinearity is taken into account on the base of yield function of element internal forces. By applying static equilibrium relationship of classic beam theory for the transferring of local element nodal force to global element nodal force, a new transformation matrix different from the nodal displacement transformation matrix is established. Although this results in an asymmetric global tangential stiffness matrix, the new transformation is simpler, and gives rise to field consistency and makes it possible to compute very large beam deflection without remeshing of the deformed structure. Computations of numerical example indicates that formulations for the nonlinear beam element are of validation and high efficiency

Abstract: Ignoring the deformation effect, the original size principle is normally used to calculate the internal force and deformations of the bars in Mechanics of Materials, the calculation error is not discussed in the textbooks, however. In order to show the adaptability of the original size principle to calculate the internal force of plane statically determinate truss, a case of the two-bar statically determinate truss was also given. The calculation error of the internal force and the angle deformations are quantitatively studied to make a comparison between the actual internal force and that calculated by the original size principle. The research showed that the relative error of angle deformations and the internal forces of the two rods are nonlinear dependent on the external forces (the given force), tensile stiffness and the initial angle of the plane truss. If the strength and tensile stiffness of the bars can meet the requirements of engineering, the original size principle can be used to calculate the internal force of metallic bar truss under the conditions of small deformations.

Abstract: In order to study the influence of gap to wind loads on the solar panel, aerodynamic performance of normal flat plate was simulated by various turbulence models with high Reynolds numbers. Time averaged mean drag coefficients and Strouhal numbers were analyzed and compared with other researchers' simulated and experimental results. The flow characteristics of 2D gapped flat plates with different gap sizes at high angle of attack were simulated based on Reynolds stress equation model. Time averaged mean pressure coefficients and Strouhal numbers of gapped flat plates with different gap sizes were compared. The corresponding influences of gap sizes to the pressure coefficients of gapped flat plates were obtained. The simulated results provide theoretical support for the engineering design of the solar panels.

Abstract: Assumed that the viscoelastic material of the beam obeys the Kelvin-Voigt fractional derivative constitutive relationship, the governing equation of the axially moving viscoelastic beam is established by the D ' Alembert principle. Based on Galerkin method, the fractional ordinary differential equations of simply supported beam are obtained. Then, Haar wavelet algorithm based on fractional integral operator matrix is employed to numerically solve the resulting equations. The effects of moving speed on the vibration behaviors of moving viscoelastic beams are investigated.