Effects of laser power density on static and dynamic mechanical properties of dissimilar stainless steel welded joints

The mechanical properties of laser welded joints under impact loadings such as explosion and car crash etc. are critical for the engineering designs. The hardness, static and dynamic mechanical properties of AISI304 and AISI316L dissimilar stainless steel welded joints by CO2 laser were experimentally studied. The dynamic strainstress curves at the strain rate around 103 s-1 were obtained by the split Hopkinson tensile bar （SHTB）. The static mechanical properties of the welded joints have little changes with the laser power density and all fracture occurs at 316 L side. However, the strain rate sensitivity has a strong depen- dence on laser power density. The value of strain rate factor decreases with the increase of laser power density. The welded joint which may be applied for the impact loading can be obtained by reducing the laser power density in the case of welding quality assurance.

Parametric study on single shot peening by dimensional analysis method incorporated with finite element method

Shot peening is a widely used surface treatment method by generating compressive residual stress near the surface of metallic materials to increase fatigue life and re- sistance to corrosion fatigue, cracking, etc. Compressive re- sidual stress and dent profile are important factors to eval- uate the effectiveness of shot peening process. In this pa- per, the influence of dimensionless parameters on maximum compressive residual stress and maximum depth of the dent were investigated. Firstly, dimensionless relations of pro- cessing parameters that affect the maximum compressive residual stress and the maximum depth of the dent were de- duced by dimensional analysis method. Secondly, the in- fluence of each dimensionless parameter on dimensionless variables was investigated by the finite element method. Fur- thermore, related empirical formulas were given for each di- mensionless parameter based on the simulation results. Fi- nally, comparison was made and good agreement was found between the simulation results and the empirical formula, which shows that a useful approach is provided in this pa- per for analyzing the influence of each individual parameter.

Application of deep learning method to Reynolds stress models of channel flow based on reduced-order modeling of DNS data

Recently,the methodology of deep learning is used to improve the calculation accuracy of the Reynolds-averaged Navier-Stokes (RANS) model.In this paper,a neural network is designed to predict the Reynolds stress of a channel flow of different Reynolds numbers.The rationality and the high efficiency of the neural network is validated by comparing with the results of the direct numerical simulation (DNS),the large eddy simulation (LES),and the deep neural network (DNN) of other studies.To further enhance the prediction accuracy,three methods are developed by using several algorithms and simplified models in the neural network.In the method 1.the regularization is introduced and it is found that the oscillation and the overfitting of the results are eflectively prevented.In the method 2,y^+ is embedded in the input variable while the combination of the invariants is simplified in the method 3.From the predicted results,it can be seen that by using the first two methods,the errors are reduced.Moreover,the method 3 shows considerable advantages in the DNS trend and the smoothness of a curve.Consequently,it is concluded that the DNNs can predict effectively the anisotropic Reynolds stress and is a promising technique of the computational fluid dynamics.

Numerical simulation of bubble detachment at submerged orifice and analysis of interface stability

This paper presents the experimental and numerical results of the bubble detachment from a submerged orifice at a constant gas flow rate.The compressible large eddy simulation combined with the volume of fluid method is adopted in the simulation and is validated by experiment.The transition criterion from the elongation stage to the detachment is obtained.In the detaching stage in the simulation,the distributions of the pressure and the surface tension on the cylindrical bubble neck are obtained.The Rayleigh-Plesset equation in the cylindrical coordinate frame is used to describe this process.Based on the comparison between the numerical results and the equation analysis,a reference value of the uncertain integral parameter in the equation is determined.

Numerical simulation of dynamic characteristics of a water surface vehicle with a blended-wing-body shape

The blended-wing-body shape vehicle is a new type of water surface vehicle with a large square coefficient. The interference of the wave systems under a high speed condition is more significant for the blended-wing-body shape vehicle and the dynamic characteristics of the new type vehicle are very different from that of a traditional vehicle. In this paper, the implicit volume of fluid（VOF） method is adopted to simulate the wave resistance of the high speed blended wing body vehicle, and a semi-relative reference frame method is proposed to compute the maneuvering coefficients. The effects of the navigation speed, the drift angle and the rotating radius are studied. The dimensional analysis method is used to assess the influence of Fr and L/R on the results. The wave making resistance coefficient against the speed sees a large fluctuation because of the serious wave interference. The lateral rotation maneuvering characteristics under the surface navigation condition is nonlinear and more complex than under the under water condition, which is quite different to control.