Applied Mechanics and Materials Vols. 52-54

Abstract: Designing a new control strategy for a moon lander to achieve an optimal soft landing, is the main purpose of this paper. For the dynamical system of the propeller to achieve the lowest level of fuel consumption, the problem of soft landing is presented as an optimal control one. Representing this into a variational form, transferring to an optimization problem on a measure space and then determining the optimal solution via a linear programming problem is the new solution path. This method has some important advantages in compare with the other, which are explain within a numerical simulation.

Abstract: It is difficult to obtain the correct criteria weights with uncertain information in the multicriteria decision-making. Many methods depend on the subjective estimate. Therefore, a method is presented to evaluate the samples ranking only need the importance order of criteria. It evaluates firstly the overall ranking scores of samples based on the graphical classification and multicriteria hierarchical integrated methods. Subsequently, the relation model between the criteria scores and overall ranking scores of samples is built by linear regression. Finally, a fincial credit loan decision-making problem is presented to describe the way of the multicriteria decisiion making process. The analysis to compare with the AHP method illustrates the proposed method is objective and effective.

Abstract: This study is to measure the impact pressure of high-speed water jet injected in water at the stand-off distance from the nozzle exit. The high-speed water jets are generated by the impact of a projectile, which known as impact acceleration method, launched by Horizontal Single Stage Power Gun. The maximum averaged jet velocity of about 374.24 m/s in water was generated in this experiment. The impact pressure of high-speed water jet in water at the stand-off distance 15, 20, 30 and 40 mm from the nozzle exit was measured by the PVDF pressure sensor. Moreover, the impact phenomena of the jet were visualized by a high-speed video camera with shadowgraph optical arrangement. From the pressure sensor, two peak over-pressures are always observed in this experiment. From visualization, it was found that the two peak over-pressures of 24 GPa and 35 GPa at x = 15 mm were generated by the jet and the bubble impact, respectively. The peak over-pressure decreases exponentially as the stand-off distance between the PVDF pressure sensor to the nozzle exit increases. Moreover, the jet and the bubble impact on the PVDF pressure sensor, shock waves, and bubble deformation were obviously observed in this study.

Abstract: The paper focuses on the enhancement of heat and mass transfer by adding active agent to lithium bromide aqueous solution. Through absorption experiments with local optical measurement, the qualitative analysis of the causes of the absorption enhancement with the surface-active agent is carried out with a view to further understand the absorption enhancement mechanism of surface-active agent. It is concluded that the Maragoni instability is mainly responsible for enhanced mixing, thereby enhancing absorption.

Abstract: Metal and Metal oxide nanofibers have different potential to play an essential role in a series of application, among them copper and copper oxide nanostructures is a promising semiconductor material with potential applications in many field. In this paper, electrospinning method via sol-gel was used to fabricate copper and copper oxide nanofibers. Synthesize of copper and copper oxide nanofibers and also effect of calcinations temperature on morphology investigated by thermal gravimetric analysis, scanning electron microscopy (SEM), Transmission electron microscopy, x-ray diffraction(XRD), Fourier transform infrared spectroscopy (FTIR) and Brunauer Emmett and Teller (BET).

Abstract: Machining error of a NC machining system is a kind of comprehensive error in dynamically machining process; especially it is of errors with non-linear characteristics. In this paper, we will set up a kind of model of comprehensive errors analysis for a NC machining system and present an error compensation for high-precision a NC machining system by a dynamic feedback neural network embedded in a NC machine tool. The results obtained shows that this approach can effectively improve compensation precision and real time of error compensation on machine tools.

Abstract: A similarity analysis is performed for a steady laminar boundary layer stagnation-point flow of an electrically conducting fluid in a porous medium subject to a transverse non-uniform magnetic field past a non-linear stretching sheet. A scaling group of transformations is applied to get the invariants. Using the invariants, a third order ordinary differential equation corresponding to the momentum is obtained. We show the existence and uniqueness of convex and concave solutions for the power law exponent, according to the values of magnetic parameter, permeability parameter and velocity ratio parameter.

Abstract: The common determination method of pile point and pile bearing capacity always depends on the practical experiences. The accuracy of pile survey data should be verified in the field. To predict the pile point and pile bearing capacity, a prediction model based on support vector regression algorithms has been developed. The friction resistance around piles and the static-load settlement are the inputs. The pile point bearing capacity characteristic value and the characteristic value of pile bearing capacity are the outputs. The prediction model is trained by the data in the adjacent block and validated by the field data in the project. The calculations of 40mm settlement and the prediction of other piles in the project can then be acquired. Compared to the survey data, the predicted values has 16% surplus. This will be beneficial to reduce construction work significantly and to save about 5% foundation cost.

Abstract: The Realizable k-ε Reynolds averaged Navior-Stokes (RANS) turbulence models and SST k-w detached eddy simulation (DES) models are investigated for simulation of external flow and trailing vortex around Ahmed body. The 3-D N-S equations are solved with central finite volume scheme and half-implicit SIMPLE method. The time average parameters of the DES results, such as the pressure, velocity field and drag coefficient Cd, are verified by comparing with RANS and experiment data. The vortex structures of vertical, horizontal plane and cross-section, along with the turbulent kinetic energy of tail vortex are studied in details. The results show that for time averaged parameters both models can get reasonable results, while for capturing the instant flow structure, DES shows advantage over RANS model.

Abstract: Adaptive hysteresis band current control(AHB CC) is used to control the three-phase grid currents by means of grid side converter in wind power generation system in this paper. AHB has reached the good purpose with PLL (Lock phase loop). First the mathematical models of each part are given. Then the control strategy of grid side converter-based wind power generation system is given in detail mainly including ABH CC and PI controllers of DC-link voltage, active power, reactive power. Finally the simulation model is set up which consists of power circuits, such as the grid side converter, LCL filter, transformer and grid, and control parts, etc. The simulation results have verified that the control strategy is feasible to fit for control of gird currents, active power, reactive power and DC-link voltage in wind power generation system.