Search

This The IEEE 802.15.4 devices are proposed to operate in the 2.4 GHz industrial, scientific and medical (ISM) band. The other devices that use IEEE 802.11 b, g and n share the same frequency band. The interference caused by these technologies can degrade the performance of an IEEE 802.15.4 based wireless network. In this paper we study such degrading effects on a network equipped with IEEE 802.15.4 devices that is exposed to interference in turn with IEEE 802.11 b, g and n. The performance measure in this paper is the link Packet Receive Rate (PRR). Measurements are performed with real-life equipment, in order to quantify coexistence issues. We test all 16 channels of IEEE 802.15.4 in 2.4G band and the results show the decrease of PRR when suffering in close frequency with IEEE 802.11. The connection between energy detection and PRR is also exhibited in this paper.

A data center energy-saving system and method based on virtual IT technology resource distribution technology is proposed in this paper. Through monitoring virtual environment resources in data center, the limited IT resources can be dynamically migrated and the auxiliary equipment resources such as air conditioner can be rationally managed. Then the resources can be reasonably and efficiently allocated by monitoring the virtual environment. With a closed-loop feedback control mechanism, it effectively improves the utilization of data center resources, and ultimately achieves the operation and maintenance for data center of green energy-saving target. This method was implemented in a true data center for cloud computing. Test results show that the total energy consumption of this system can be reduced by 13%, and the power usage effectiveness drops to 1.5.

The theory of structural dynamic analysis is put forward firstly. Then the dynamic performance of HMC80 high-speed precision machining center column is analyzed by means of finite element method. The dynamic performance of the column is analyzed using structural dynamic optimization theory and variation analysis with the thickness of wall plate and the inner rib plates as the parameters thirdly. Based on the analysis results, the structure optimization scheme of the column is obtained. The structure optimization scheme is analyzed and the analysis results show that the dynamic performance of the column optimization scheme is improved obviously.

Based on the general geometrical model of scroll compression chamber for scroll fluid machine, the geometric characteristics of scroll compression chamber, such as width, length, volume, and comprehensive curvature radius at the mesh point, and their variation as well are comprehensively analyzed. It is shown by the analysis that among all of the geometric characteristics, the width variation is the most complicated one; the comprehensive variation of the width together with the length can be used to determine the deformation processes of the chamber. The variability of its length, volume, and comprehensive curvature radius at meshing points should be taken as its basic deformation characteristics. For a scroll compression chamber with involute of circle, its deformation efficiency is higher and dynamic stability is excellent. At the same time, the scroll wrap with involute of circle is easy to fabricate and the profile with involute of circle is used widely for the major part of the scroll profile.

Wind speed forecasting is critical for wind energy conversion systems. Adaptive and reliable methods and techniques of wind speed forecasting are urgently needed in view of the stochastic nature of wind resource, which is varying from time to time and from site to site. Multi-step-ahead speed forecasting is built with empirical mode decomposition (EMD) method and RBF neural network, which makes use of non-linear and non-stationary signal characteristics. Time series of original wind speed data is decomposed by EMD method. And RBF neural network is used to predict the decomposition of the various components. Experimental results show that the method effectively improves the accuracy and the reliability of wind speed forecasting.

The theory of structural dynamic analysis is put forward in this paper. The dynamic performance of a precision machine tool bed is analyzed by means of finite element method, and the analysis result shows that the natural frequency is too low is the main reason of the vibration of the bed. In order to improve the dynamic performance of the bed, the dynamic performance of the unit structure of the precision machine tool bed is analyzed. Based on the analysis of the unit structure, two structural optimization schemes for the machine tool bed are obtained. Furthermore, two optimization schemes are analyzed by means of finite element method too. Compared to the original machine tool bed, the dynamic performance of two structural optimization schemes is significantly improved.

Under deep and complex geological conditions, severe deformation occurs at intersection points of Y-type roadways with large cross sections during engineering projects in coal mines, especially at junction arches. Based on in-situ investigations and theoretical studies, we have summarized typical forms of destruction and identified high stress and unrestricted support at both sides of junction arch as its main causes. In this study, we also presented double-directional control bolt support technology for a large Y-type span intersection, applied to deep intersection engineering in the Jiahe Coal Mine, which has proved effective.

Construction of tunnels in urban areas requires assessment of the impact of tunneling on the stability and integrity of existing pile foundations. We have focused our attention to the analysis of the carrying capacity of pile foundations provided by the impact of construction of urban tunnels on adjacent pile foundations, under the engineering background of the construction of the # 2 Line of the Guangzhou subway. It is carried out using a fast Lagrangian analysis of a continuum in a 3D numerical code, which is an elastoplastic three-dimensional finite difference model, to simulate the response of piles under the entire process of metro tunneling (deactivation of soil element and activation of the lining). The adjacent stratum around the tunnel is classified into three regions: Zone I (upper adjacent stratum of tunnel), Zone II (45°-upper-lateral adjacent stratum of tunnel) and Zone III (lateral adjacent stratum of tunnel). In each region one typical pile is chosen to be calculated and analyzed in detail. Numerical simulations are mainly conducted at three points of each pile shaft: the side-friction force of the pile, the tip resistance of the pile and the axial loading of the pile. A contrasting analysis has been conducted both in the response of typical piles in different regions and from computer calculated values with site monitoring values. The results of numerical simulations show that the impact on carrying capacity of the piles lies mainly in the impact of construction of urban tunnels on the side-friction forces and the tip resistance of piles. The impact differs considerably among the different strata zones where the pile tips are located. The complicated rules of side-friction force and tip resistance of piles has resulted in complicated rules of pile axial loading thus, in the end, it impacts the carrying capacity of pile-foundations. It is necessary to take positive measures, such as stratum grouting stabilization or foundation underpinning, etc, to deal with the carrying capacity and the settlement of pile-foundations. The results are of value to similar engineering projects.

In the wireless sensor networks with multiple mobile sinks, the movement of sinks or failure of sensor nodes may leads to the breakage of existing routes. In order to repair broken path with lower communication overhead in terms of both energy and delay, we propose an efficient routing recovery protocol with endocrine cooperative particle swarm optimization algorithm to establish and optimize the alternative path. With this method, the alternative path from source nodes to the sink with the optimal QoS parameters can be selected. Simulation results demonstrate that ECPSOA can adapt to rapid topological changes with multiple mobile sinks, while decreasing communication overhead and efficiently reducing the energy consumption.