Applied Mechanics and Materials Vols. 448-453

Abstract: The transport sector is considered one of the sectors that cause serious environmental impacts and, being strongly associated to development, it is important to choose more energy efficient transport modes. With the growing environmental problems sustainability becomes essential in the transport sector by reducing energy consumption and pollutant emissions in the atmosphere. Accordingly, through the case study of soybean transport from Sorriso, state of Mato Grosso, to Santos, state of Sao Paulo, this study aims to define which mode of transport, unimodal or multimodal, may provide greater efficiency in the use of energy from fossil source, in both direct and indirect ways. The method evaluates the energy consumption in the life cycle of transport vehicles, ie, consumption and supply of fuel and energy embedded in fabrication. The analysis verifies the efficiency of the multimodal transport.

Abstract: The stress state of a rock anchor reinforced concrete (RC) foundation of a wind driven generator located in the new constructed wind power station in Guodian Tieling Development Zone of China is numerically analyzed in this paper by using the large general-purpose finite element analysis (FEA) software ABAQUS, to discuss the mechanical characteristics of the rock anchor RC foundation, and validate the safety of normal use of the rock anchor foundation, and compare the developed rock anchor foundation with the traditional gravity one. The results show that the new-type RC foundation has greater advantage than the traditional one and it can completely replace the traditional gravity foundation in the condition of rock soil environment in the future.

Abstract: The pullout test of an anchor bolt is very important for the anchorage technology. Adopting enlarged bottom anchor bolts to wind turbine foundations can not only take advantage of the mechanical property of rock mass, but also have good security and economical efficiency. The finite element analysis software ANSYS is used in this paper to numerically analyze a single enlarged bottom anchor bolt under pullout loading, to research the performance and failure pattern of the anchor bolt. The anchor bolt side friction is extracted to understand the stress distribution of the bolt. By the analysis of the bearing capacity of anchor's enlarged head and the change of plastic zone form, the ultimate strength and destruction form of the anchor blot are clearly understood. The results also show that the bearing capacity of the proposed enlarged bottom anchor bolt can obviously increased, resulting in a cone-shape failure pattern of soil.

Abstract: For the effective use of wind resources, and in order to decrease the wake effect on the performance of wind turbine, a numerical simulation has carried out to the aerodynamic interaction between two rotors coaxial arrangement. At last the numerical simulation results are verified by experiment. The results show that downstream turbine makes the upstream diverging wake to be converged when coaxial arrangement, and the output of downstream turbine is affected by upstream wake when the distance is less than 5D.The wake field become more diffused after pass the downstream turbine, the area of diverging wake become larger than the wake of upstream turbine mainly due to the increase of turbulence intensity. The greater fatigue load will impact on the downstream turbine. At last the simulation results are in well agreement with the experimental results.

Abstract: At different wind speeds, in order to study the impact of obstacle size and distance to the bottom of the hill on wind farm, using Pro / E generates the model of hills and upstream obstacle, sinusoidal model was selected to the hill contour, then Fluent was adopted to analyze the flow field, turbulence model select the SSK k-ω, inlet boundary condition was exponential function. Wind speed distribution and wind pressure distribution of hill surface at each case were depicted by the simulation results; the obstacle of conducive for wind farms was obtained by comparing flow field distribution of each case.

Abstract: A computational method based on nonlinear wake model was established for horizontal axis wind turbines aerodynamic performance prediction. This method makes use of finite difference method to solve the integral differential equation of the model, the induced velocity of wake vortex can be calculated from equations and compared with the induced velocity of wake vortex in linear model. The comparison between the calculated results of wind turbine under axis flow condition, including tip vortex geometry and aerodynamic performance, and available experimental data shows that this method is suitable for wind turbine aerodynamic performance analysis. Finally, a series of numerical calculations were made to investigate the change of wake geometry and aerodynamic performance of the wind turbine when yawing and pitch angle increasing, which provide foundations for aerodynamic optimization design of horizontal axis wind turbines.

Abstract: Accurate wind power predicting is helpful for the dispatch and safety operation of grid, so as to increase wind power penetration, Two representative prediction models, based on gray theory and time series forecasting method respectively, were selected, the farm measured data were input to the models and their own prediction results were obtained respectively. Finally, the prediction results of the combined model were compared with the two individual models, verifying the feasibility of the combined model to wind farm generation capacity forecast. It is concluded that the combined forecast model can predict more accurately than the individual forecast model.

Abstract: The DC bus voltage is key variable for the operation of converter system in a wind power system. When grid voltage drops, a control of the DC bus voltage is needed to keep the smoothness of DC bus voltage for avoiding generator cutting off grid. A combined control method based on the grid voltage information feedforward with a crowbar circuit is proposed for a direct-drive wind power system in the paper. The unbalanced energy of the DC bus can be unleashed by the crowbar circuit during the dropping of grid voltage. At the same time, the output power of motor-side converter can be controlled to decrease according to the grid-side voltage information, and the mechanical speed of wind turbine and generator can be suppressed by the pitch angle regulation when the output power reduces. Thus, the DC-bus voltage can keep smooth. Results based on Matlab/Simulink simulation shows that this method not only improves dynamic response performance of DC bus voltages control, but also reduces the action time of crowbar circuit. It is benefit to the ability of the wind power system riding through the grid fault.

Abstract: This paper analyses the characteristics of large-scale offshore wind farm collection network and the impact of the medium voltage collection system optimization,while from the electrical technology point,it proposes the short circuit current of the collection network computational model and algorithms,based on the principle of equivalent circuit.Taking a wind power coolection system planned for a certain offshore wind farm planning for example, the validity of the model and algorithm is verified.

Abstract: As a kind of new renewable energy, wind power has been used in power systems more and more. Wind power has a installed capacity more than 10% of the power grid’s where the wind resources are abundant in our country. Because the wind power has the characteristics of randomness, intermittence, uncontrollability and so on, we can’t be sure about the continuity and stability. With the increase of the wind power installed capacity, the influence of wind power is expanding. By applying the PSCSD, this paper analyse the power gird’s stability of different wind power proportion and different access points.