DSpace collection: 第19卷第3期

A Fuzzy Based Adaptive Gateway Discovery Algorithm for Hybrid Multi-hop Wireless Networks

title: A Fuzzy Based Adaptive Gateway Discovery Algorithm for Hybrid Multi-hop Wireless Networks abstract: The portable devices such as mobile phones, laptops or personal digital assistants (PDAs) are used by mobile ad hoc networks (MANETs) for communication establishment in a spontaneous manner. For fulfilling the coverage requirements of future 4G we need integration of mobile ad hoc network with Internet to enhance the pervasiveness and flexibility of networks. It is necessary for mobile nodes to identify and choose an optimal gateway among multiple gateways for Internet access. Therefore, a mechanism for gateway discovery is needed. The adaptive gateway discovery can be configured by dynamically adjusting its TTL value (proactive area) on the basis of several parameters like number of active source nodes, traffic load at the gateway and link changes. Existing schemes involve inaccurate estimation of optimal proactive area, hence they suffer from large routing overhead which ultimately affects the network performance and throughput. This paper aims to develop a novel and efficient adaptive gateway discovery algorithm focusing on optimal TTL value by utilizing the potential and capability of Fuzzy logic, which makes a significant impact on routing overhead during gateway discovery. The proposed scheme also incorporates efficient handover in the situation of multiple gateways so that single gateway will not become a bottleneck. The proposed approach is evaluated using computer simulation and also analytically validated. Results show our approach outperforming existing ones.

An Efficient Adaptive Image Enhancement Method in Wavelet Domain for Handwritten Document

title: An Efficient Adaptive Image Enhancement Method in Wavelet Domain for Handwritten Document abstract: In this study, a new method, called adaptive image enhancement (AIE), is used to enhance handwritten document images, such as historical documents. An AIE method is proposed to denoise handwritten documents in a wavelet domain, which differs from others methods in two aspects: Firstly, modified contrast limited adaptive histogram equalization (MCLAHE) is used to equalize the contrast of an image by cutting the histogram at some threshold, and then equalization is used. Secondly, the image is improved by using directional discrete wavelet transform (D2 WT) enhancing for foreground and interfering strokes, respectively. As a result, this method not only removes the interfering strokes or visible watermarks in the background information, but also significantly increases the readability of handwritten document images.

Parallel Processing-Oriented Hybrid Scheduling of Virtual Machines in Cloud

title: Parallel Processing-Oriented Hybrid Scheduling of Virtual Machines in Cloud abstract: In cloud computing environment, parallel applications generally run on symmetric multiprocessing (SMP) virtual machine (VM). Since this type of application requires synchronous operations between processes/threads, all virtual CPUs (vCPUs) of a parallel VM (i.e., the VM running parallel application) should be online simultaneously. At present, relevant studies have been intensively conducted from the perspective of vCPU co-scheduling in virtual machine monitor (VMM). However, the existing co-scheduling methods have the problems of unrestricted preemptions between parallel VMs, which probably results in negative impact on the performance of parallel applications in these VMs. To address the above problems, in this paper, we first analyze the deficiencies of the existing co-scheduling approaches in virtualized environment. Then we propose an enhanced co-scheduling algorithm to improve the performance of parallel application in SMP VM.

Improving Wi-Fi Indoor-Positioning Accuracy by Using AP Selection and Adaptive Pattern Matching

title: Improving Wi-Fi Indoor-Positioning Accuracy by Using AP Selection and Adaptive Pattern Matching abstract: This study proposes a method based on access point (AP) selection and adaptive pattern-matching for Wi-Fi indoor positioning (ASAPM). In the proposed ASAPM, a box plot algorithm is used to remove received signal strength (RSS) outliers in samples received from APs in order to smooth the RSS. Subsequently, we analyzed the RSS variations for selecting the top-N APs with the least interference. Moreover, we analyzed the history of the positioning results to estimate the direction and distance of users in subsequent positions in order to reduce the pattern-matching time and computational overhead of the positioning system. The simulation results revealed that the average positioning error, average maximum positioning error, and average pattern-matching times of ASAPM were 36%, 51%, and 57% lower than the three compared strategies, respectively. These findings show that ASAPM could reduce the computational overhead; moreover, it is suitable as an indoor-positioning service for mobile devices.

Application of Transformerless High Gain DC/DC Converter for Grid-connected Offshore Windfarms

title: Application of Transformerless High Gain DC/DC Converter for Grid-connected Offshore Windfarms abstract: In this paper, operation and control of an offshore wind farmusing typical configuration is considered. Commonly, the offshore wind farms are connected to the grid using HVDC transmission system in order to decrease power losses and voltage sag. In the proposed configuration a new cascaded structure of transformerless high gain DC/DC converter is appliedinstead of a power transformer. The proposed DC/DC converter can boost voltage level and regulate DC link voltage in output of permanent magnet synchronous generator (PMSG). By adjusting DC link voltage in a suitable value, the maximum active power can be received from PMSG. The main advantage of the proposed configuration is that there aren’t anypower transformer and back-to-back converter inoutput of PMSG. The simulation results confirm good operation of the proposedconfiguration in various wind speeds. Also experimental results of the introduced prototype of the DC/DC converter show the effectiveness of this converter in high gain mode.

Experimental Study on Uniform Mobility Displacement Method for Heterogeneous Reservoir

title: Experimental Study on Uniform Mobility Displacement Method for Heterogeneous Reservoir abstract: Reservoir heterogeneity is the most important reason for low recovery and early excess water production. Experimental study on uniform mobility displacement was conducted to improve conformance and reduce water channeling for heterogeneous reservoir. The principle and mechanism were founded using a heterogeneous stratified reservoir model. For this model, injection slugs matching different permeable layers can flow simultaneously and achieve a piston-like flow. Mobility contour was proposed to screen polymer concentration. Displacement experiments were conducted in heterogeneous cores to estimate the EOR effect. The results show that uniform mobility displacement can improve oil recovery greater than polymer flooding and ASP flooding. This may provide a new EOR method to reduce water production for heterogeneous reservoir.

Convection of Cu-water Nanofluid in a Partially Active Porous Cavity with Internal Heat Generation

title: Convection of Cu-water Nanofluid in a Partially Active Porous Cavity with Internal Heat Generation abstract: In this study, the effect of internal heat generation for Cu-water nanofluid on natural convection heat transfer in a fluid saturated porous cavity with partially active walls has been numerically investigated. The governing non-dimensional Darcy-Brinkman-Forchheimer equations are solved using the finite volume approach together with SIMPLE algorithm. Benchmark results are compared with present study which furnish that the present results are to be reliable. The addition of nanoparticles produces an augmented heat transfer rate for low values of internal heat generation. On the other hand, the base fluid water induces the maximum heat transfer rate than the nanofluid for high values of internal heat generation parameter. This means that in the presence of high internal heat generation, there is no need to add nanoparticles inside the cavity to generate the augmented heat transfer rate.

A Review on Role of Processing Parameter in Determining Properties of Silicon Carbide Reinforced Metal Matrix Nanocomposites

title: A Review on Role of Processing Parameter in Determining Properties of Silicon Carbide Reinforced Metal Matrix Nanocomposites abstract: The present paper reports a review on study of various processing routes and related mechanical properties of silicon carbide reinforced Metal Matrix Nanocomposites (MMNCs). Physical and mechanical properties that can be obtained with Metal Matrix Nanocomposites (MMNCs) have made them potential candidate for use in aerospace and automobile applications. MMNCs are made by dispersing a ceramic material into a metallic matrix. MMNCs have attracted attention as a result of their low costs and enhanced properties. Various reinforcements used are carbides, nitrides, and oxides. MMNCs manufacturing can be broken into three types - solid, liquid and vapor. Solid state methods include powder metallurgy, liquid state method includes stir casting and squeeze casting whereas vapor state method includes physical vapor deposition and chemical vapor deposition. In comparison with conventional polymer matrix composites, MMNCs are resistant to fire, can operate in wider range of temperatures, do not absorb moisture, have better electrical and thermal conductivity, are resistant to radiation damage, and do not display outgassing. It is expected that the silicon carbide reinforced metal matrix nanocomposites will be a potential candidate for heavy duty applications.

Roll Stiffness Optimization for Anti-roll Bar in Interconnected Air Suspension

title: Roll Stiffness Optimization for Anti-roll Bar in Interconnected Air Suspension abstract: Lateral Interconnected Air Suspension (hereinafter referred to as Interconnected Air Suspension or IAS) tends to deteriorate vehicle roll stability on the condition of steering while travelling in high speed, so interconnection state is generally closed when lateral acceleration of car body exceeds its designed threshold (0.4 g in this paper). In this paper, a roll stiffness optimization strategy of anti-roll bar in IAS based on genetic algorithm is proposed for better roll stiffness as well as better roll angle vibration characteristics both in the state of interconnection and non-interconnection. And the strategy is used to optimize the anti-roll bar of a passenger car equipped with IAS. In the optimization strategy, weighted sum of body roll angle’s mean value and standard deviation is originally determined as the objective function based on impact sensitivity analysis, i.e. the analysis of anti-roll bar roll stiffness’s influence on body roll angle’s mean value and standard deviation. Besides, totally 6 driving conditions are considered in the optimization to make it more realistic. The optimization result shows that optimal roll stiffness of front and rear anti-roll bar is 1998 N m/deg and 1402 N m/deg respectively. The proposed optimization strategy helps to resolve the problem of how to balance vehicle roll stability and roll angle vibration characteristics under different working conditions during the process of anti-roll bar roll stiffness matching for IAS vehicles. It can also be guidance or a reference for the matching of other parameters in IAS vehicles.

Characteristics of Wind Pressures on a Cooling Tower Exposed to Stationary and Translating Tornadoes with Swirl Ratio 0.54

title: Characteristics of Wind Pressures on a Cooling Tower Exposed to Stationary and Translating Tornadoes with Swirl Ratio 0.54 abstract: Current wind-resistant design of wind-sensitive structures including large-scale cooling towers is generally carried out with respect to synoptic boundary-layer-type strong winds. A swirling tornado can produce significantly different wind pressures than conventional boundary-layer wind. This paper presents both stationary and translating tornado effects on a cooling tower in a tornado vortex simulator developed at Tongji University, China. Wind pressures acting on the external surface of cooling tower model were measured at a fixed swirl ratio (S = 0.54) in the present study. Different radial distances between a cooling tower and stationary tornado vortex center were considered. Translating tornadoes with three different translation speeds (u = 0.04 m/s, 0.12 m/s and 0.2 m/s) were simulated. The results show that a tornado vortex can produce high negative wind pressures on a cooling tower surface due to the negative pressure drop accompanying a tornado. A cooling tower exposed to a tornado experiences combined effects of pressure drop accompanying a tornado and aerodynamic flow-structure interaction.

The Building Information Modeling and its Use for Data Transformation in the Structural Design Stage

title: The Building Information Modeling and its Use for Data Transformation in the Structural Design Stage abstract: As a processing technology of data and information, building information modeling (BIM) is often used for producing digital engineering model and promoting interoperability among participants involved in the Architecture, Engineering, and Construction (AEC) industry. The real values of BIM largely depend on effective information integrating and sharing among different stages or disciplines through the whole building lifecycle. To this day, although BIM has made a substantial contribution to the Chinese AEC industry, there are still some debates on its roles. Moreover, due to the complexity of structural design process, the weak link between structural model and BIM model makes its deep application even harder. To address these issues, this paper discusses the roles of BIM from the perspective of structural engineers through comparing with the traditional CAD. Then, the BIM structural model is studied by analyzing the model conformation, design mode, and Industry Foundation Classes (IFC)-format structural model. By comparing the differences between BIM physical model and structural mechanical model, an indirect method for the data transformation from BIM model to structural analysis model is proposed. An interface is developed based on the analysis of data formats and mapping rules. Three typical cases are adopted to demonstrate the data transfer efficiency by using the interface. The case study shows that the proposed method achieves higher efficiency for the data transformation from BIM model to structural analysis model.

Mitigation of Resonance for High Speed Train-bridge Systems Considering Overhanging Beam Effects

title: Mitigation of Resonance for High Speed Train-bridge Systems Considering Overhanging Beam Effects abstract: Short overhanging beams usually exist at both ends of a simply supported bridge. As a train passes through the overhanging beams of the bridge at high speeds, the overhanging beams would be subjected to intensive vibrations, from which the dynamic response of the train-bridge system would be built up. To mitigate the amplified response of the train-bridge system due to the overhanging beam effects, an end rotational spring to restrain the relative rotations is equipped between the free ends of the adjacent beams. By the vehicle-bridge interaction finite element analysis, the numerical studies indicated that the overhanging beams play a key role in amplifying the response of the train-bridge system. Even so, the proposed end restraintscan reduce the amplified response of the VBI system significantly

CFD Simulation in Helical Coiled Tubing

title: CFD Simulation in Helical Coiled Tubing abstract: According to hydrodynamic theory, based on CFD software-Fluent, the simulation for Newtonian fluid flow in helical coiled tubing was carried out to reveal the flow characteristics and pressure gradient of the helical section. Laminar and turbulent flow with different inlet velocities are considered. The results are compared with other published correlations. The results show that maximum velocity distributes in the outer side of the coiled tubing. The velocity in turbulent flow is more uniform than in laminar flow. It is shown that the faster the inlet velocity, the greater the pressure gradient increment. CFD simulation is in close agreement with the published correlations.

Daily Peak Load Forecasting Based on Fast K-medoids Clustering, GARCH Error Correction and SVM Model

title: Daily Peak Load Forecasting Based on Fast K-medoids Clustering, GARCH Error Correction and SVM Model abstract: Safe and economic operation of power system is based on load forecasting, and how to increase forecasting accuracy is the premise of power dispatching and economic analysis. Present paper establishes SVM (support vector machine) forecasting model based on fast K-medoids clustering algorithm and data accumulative pre-processing. FKM (fast K-medoids clustering algorithm) is applied to extract similar days by dividing all samples into k clusters, and respective forecasting of k clusters can realize the forecasting of a whole object. Before inputting the data into SVM system, the original data is preprocessed by accumulation to weaken the irregularity disturbance and strengthen sequence regularity. Due to existing unexplained component in forecasting error, GARCH (generalized autoregressive conditional heteroskedasticity) model is employed to forecast the error with non-white noise. According to its results, error correction is applied to the forecasted daily peak load. The forecasting effect of the proposed model is compared with other models in the given example, which verifies that SVM model based on fast K-medoids clustering algorithm and GARCH model has the characteristic of effectiveness, superiority and universality. The accuracy of daily peak load forecasting is enhanced significantly

A Two-Fluid Model for Herschel-Bulkley Fluid Flow through Narrow Tubes

title: A Two-Fluid Model for Herschel-Bulkley Fluid Flow through Narrow Tubes abstract: A two-fluid model of Herschel-Bulkley fluid flow through tubes of small diameters is studied. It is assumed that the core region consists of Herschel-Bulkley fluid and Newtonian fluid in the peripheral region. The analytical solutions for velocity, flow flux, effective viscosity, core hematocrit and mean hematocrit have been derived and the effects of various relevant parameters on these flow variables have been studied. It is found that the effective viscosity, core hematrocit and mean hematrocit for Newtonian fluid is less than that for Bingham fluid, power-law fluid and HerschelBulkley fluid. It has been observed that the effective viscosity and mean hematocrit increase with yield stress, power-law index, hematocrit and tube radius but the core hematocrit decreases with hematocrit and tube radius. Further, it is also noticed that the flow exhibits the anomalous Fahraeus-Lindqvist effect.