共查询到20条相似文献,搜索用时 13 毫秒
1.
The cross extension of hydraulic fracture and natural fracture is the key to realize the volume fracture in unconventional reservoir. Based on the non-continuum theory, with the help of numerical simulation algorithm, a mathematical model for in-situ stress about fracturing expansion when the hydraulic fracture intersects with a natural fracture is presented. Then, using two-dimensional linear elastic theory verify the validity of degenerate in-situ stress mode. So it makes the natural fissure error about natural fracture surface pressure less than 1%. As a result, the accuracy of the model was proved. On the basis of the above, considering fluid-structure coupling effect, the stress change rules on natural fracture surface are obtained during hydraulic fracture extension process. The calculation results are as follows: In the process of hydraulic fracture approaching natural fracture, the surface of natural fracture occurs shear deformation first, and then turns into open deformation. Under the influence of shear deformation, the direction of the maximum principal stress on natural fracture surface is the same as initial horizontal maximum principal geostress. Due to the expansion of hydraulic fracture and fracture tip concentration effect, the maximum principal stress appears in the hydraulic fracture tip, this two points may induce the natural fracture begin to extend. And for initial ground stress in a stratum, the smaller the difference, the greater the pressure required to open the natural fracture. At this time, the maximum principal stress on the surface of the natural fracture is less concentrated; multiple fracture initiations are easily formed. Under high pressure, when the approaching angle between natural fracture and hydraulic fracture closes to 45° hydraulic fracture is easier to activate natural fracture, the formed hydraulic fracture shape is more complicated. 相似文献
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Rana Kamlesh Kumar Tripathi Sachin Raw Ram Shringar 《Wireless Personal Communications》2020,110(3):1217-1235
Wireless Personal Communications - The Vehicular ad-hoc network (VANET) is an autonomous system mobile vehicle connected over a wireless link to transmit data packets in the network. It is... 相似文献
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Security is one of the most critical issues to Vehicular Ad-hoc Networks(VANETs) since the information transmitted is asynchronous and distributed.Vulnerability and instability are two of the challenges remain to be addressed by the research community and the industry. In this paper, we first proposed a trust reliability based model and extended the GPSR protocol to TM-GPSR protocol. Then, we improved the LET-GPSR protocol based on the link connection time prediction. On this basis, combined the... 相似文献
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A Mobicast Routing Protocol in Vehicular Ad-Hoc Networks 总被引:1,自引:0,他引:1
In this paper, we present a “spatiotemporal multicast”, called a “mobicast”, protocol for supporting applications which require
spatiotemporal coordination in vehicular ad hoc networks (VANETs). The spatiotemporal character of a mobicast is to forward
a mobicast message to vehicles located in some geographic zone at time t, where the geographic zone is denoted as zone of relevance (ZOR). Vehicles located in ZOR at the time t must keep the connectivity to maintain the real-time data communication between all vehicles in ZOR. The connectivity is
kept of all vehicles in ZOR through the vehicular ad hoc networks (VANETs). The connectivity of ZOR is lost if any vehicle
in ZOR suddenly accelerates or decelerates its velocity. The temporal network fragmentation problem is occurred such that
vehicle in ZOR cannot successfully receive the mobicast messages. To solve the problem, a new mobicast protocol is presented
in this work to successfully disseminate mobicast messages to all vehicles in ZOR via a special geographic zone, called as
zone of forwarding (ZOF). The main contribution of this work is to develop a new mobicast routing protocol to dynamically
estimate the accurate ZOF to successfully disseminate mobicast messages to all vehicles in ZOR. To illustrate the performance
achievement, simulation results are examined in terms of dissemination successful rate, packet overhead multiplication, packet
delivery delay, and throughput. 相似文献
5.
Vehicular ad-hoc networks (VANETs) is drawing more and more attentions in intelligent transportation system to reduce road accidents and assist safe driving. However, due to the high mobility and uneven distribution of vehicles in VANETs, multi-hops communication between the vehicles is still particularly challenging. Considering the distinctive characteristics of VANETs, in this paper, an adaptive routing protocol based on reinforcement learning (ARPRL) is proposed. Through distributed Q-Learning algorithm, ARPRL constantly learns and obtains the fresh network link status proactively with the periodic HELLO packets in the form of Q table update. Therefore, ARPRL’s dynamic adaptability to network changes is improved. Novel Q value update functions which take into account the vehicle mobility related information are designed to reinforce the Q values of wireless links by exchange of HELLO packets between neighbor vehicles. In order to avoid the routing loops caused in Q learning process, the HELLO packet structure is redesigned. In addition, reactive routing probe strategy is applied in the process of learning to speed up the convergence of Q learning. Finally, the feedback from the MAC layer is used to further improve the adaptation of Q learning to the VANETs environment. Through simulation experiment result, we show that ARPRL performs better than existing protocols in the form of average packet delivery ratio, end-to-end delay and number hops of route path while network overhead remains within acceptable ranges. 相似文献
6.
Wireless ad-hoc networks can experience significant performance degradation under fading channels. Spatial diversity has been
shown to be an effective way of combating wireless fading with the multiple-input multiple-output (MIMO) technique by transmitting
correlated information through multiple antennas. The virtual MIMO technique, which allows multiple wireless stations with
single antenna to form a virtual transmission array, is shown to be a viable solution from several recent studies. In this
paper, we propose a complete system framework for wireless ad-hoc networks utilizing two different cooperative relaying techniques
at the physical layer: the repetition coding and the space-time coding. In the data link layer, two medium access control
protocols are proposed to accommodate the corresponding physical layer cooperative diversity schemes. In the network layer,
diversity-aware routing protocols are proposed to determine the routing path and the relaying topology. Simulations with both
constant bit rate and TCP (transmission control protocol) traffic show significant performance gains of the proposed cooperative
relaying schemes. 相似文献
7.
Emerging Vehicular Ad-Hoc Networks (VANET) have the potential to improve the safety and efficiency of future highways. This paper reviews recent advances in wireless communication technologies with regard to their applications in vehicular environments. Four basic demands of future VANET applications are identified, and the research challenges in different protocol layers are summarized. Information dissemination is one of the most important aspects of VANET research. This paper also discusses the primary issues in information dissemination from an information-centric perspective, and provides two case studies. Finally, future research directions and possible starting points for new solutions are considered. 相似文献
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Ad Hoc网络路由协议研究及其性能比较 总被引:4,自引:0,他引:4
介绍和分析了当前Ad Hoc网络中的主要路由协议算法,在Linux下使用网络仿真软件NS2评价Ad Hoc路由协议中的距离矢量路由协议、临时排序路由算法、动态源路由协议和Ad Hoc按需距离矢量路由协议,编写了用于仿真实现的脚本程序,并对仿真结果进行了分析比较和性能评价,由此得出不同协议的特性及其适用范围。 相似文献
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无线Mesh网络路由协议研究 总被引:1,自引:0,他引:1
无线Mesh网络WMN(wireless mesh networks)是一种新型的无线网络,它融合了无线局域网(WLAN)和Ad Hoc网络的优势,成为宽带接入的一种有效手段。首先介绍了无线Mesh网的网络结构和特点.并在此基础上讨论了无线Mesh网络对路由协议的要求。无线Mesh网络的路由算法是Mesh领域的研究难点,通过分析比较4种针对WMN的路由协议,总结了现有的路由协议的优缺点,并对今后的研究方向做出了展望。 相似文献
12.
Ad Hoc网络路由协议性能分析 总被引:4,自引:4,他引:0
介绍了移动自组网的表驱动和按需驱动两类路由协议.提出了定量评估网络路由协议性能的六个基本指标.利用网络仿真器NS-2,对四种典型的路由协议(DSR、DSDV、AODV和TORA)建立仿真模型,配置仿真参数,并进行了仿真.对仿真过程产生的文档进行处理,分析,比较它们的性能指标.试验结果表明,模型仿真结果接近理论分析和实际情况,该方法在路由协议研究,设计与仿真方面具有较强的实用性和通用性. 相似文献
13.
Kamlesh Chandra Purohit Sushil Chandra Dimri Sanjay Jasola 《Wireless Personal Communications》2017,97(4):5099-5114
Vehicular Ad-hoc network (VANET) is a self-organized ad hoc network. VANET becomes a most challenging research area as it has several issues related to routing protocols, quality of service, security, etc. Vehicular communication is critically unsafe to several kinds of active and passive routing attacks. This paper analyzes the impact of a compromised node (vehicle) on zone routing protocol and ad-hoc on-demand distance vector, and recommends a suitable solution called secure vehicular on demand routing to find out and mitigate the black hole attack. The given study analyses the effect of vehicle density on the average throughput, packet delivery ratio, end-to-end delay, normalized routing load and average path length. 相似文献
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Herman Fernández Lorenzo Rubio Juan Reig Vicent M. Rodrigo-Peñarrocha Alejandro Valero 《Mobile Networks and Applications》2013,18(6):755-765
Vehicular communications are receiving considerable attention due to the introduction of the intelligent transportation system (ITS) concept, enabling smart and intelligent driving technologies and applications. To design, evaluate and optimize ITS applications and services oriented to improve vehicular safety, but also non-safety applications based on wireless systems, the knowledge of the propagation channel is vital. In particular, the mean path loss is one of the most important parameters used in the link budget, being a measure of the channel quality and limiting the maximum allowed distance between the transmitter (Tx) and the receiver (Rx). From a narrowband vehicular-to-vehicular (V2V) channel measurement campaign carried out at 5.9 GHz in three different urban environments characterized by high traffic density, this paper analyzes the path loss in terms of the Tx-Rx separation distance and fading statistics. Based on a linear slope model, values for the path loss exponent and the standard deviation of shadowing are reported. We have evaluated the packet error rate (PER) and the maximum achievable Tx-Rx separation distance for a PER threshold level of 10 % according to the digital short-range communications (DSRC) specifications. The results reported here can be incorporated in an easy way to vehicular networks (VANETs) simulators in order to develop, evaluate and validate new protocols and systems architecture configurations under realistic propagation conditions. 相似文献
16.
随着移动自组网络的快速发展,对距离矢量按需路由协议(AODV)的服务质量提出了越来越高的要求.为了提升AODV在无线传感器网络通信中的表现,文章提出了一种新型的基于AODV的多度量无线路由协议(MWR-AODV).MWR-AODV综合考虑了对路由协议性能影响重大的最小跳数、剩余能量、能量流失率和网络节点密度这四个因素,并且引入了一种低成本且高效的本地修复策略.通过Network Simulator-2仿真平台对MWR-AODV与标准AODV、DSDV协议的表现进行了仿真分析.结果表明,所提出的MWR-AODV能为无线传感器网络提供更好的通信服务,并且在均衡能量消耗延长网络寿命和平衡网络通信负载方面也有上佳表现. 相似文献
17.
Pau Arce Juan C. Guerri Ana Pajares Oscar Lázaro 《Mobile Networks and Applications》2008,13(3-4):324-336
A performance evaluation of real time services (such as video streaming) over mobile ad-hoc networks using both hierarchical and flat routing protocols is shown in this paper. A variety of workload and scenarios, as characterized by mobility, load and size of the ad hoc network have been simulated using NS-2. We use OLSR (Optimized Link State Protocol) as the flat routing protocol and our own implementation of HOLSR (Hierarchical OLSR)—which uses HNA (Host and Network Association) messages—as the hierarchical one, modifying other previous HOLSR version and maintaining the maximum compatibility with the flat OLSR. We carry out a complete comparison between these protocols focused on video evaluation. The simulation lets us compare the quality of service (QoS) of the video streaming paying attention to objective parameters (PSNR, packet delivery ratio, packet delay and interruptions). Some drawbacks of the hierarchical environment are also analyzed, as the link load between cluster heads and the lack of QoS-state-aware in HOLSR design. Quantitative results indicate that the protocol overhead is reduced (more than 40% in larger networks) and the video quality is improved (from 1 to 6 dB in certain cases) using hierarchical protocols. 相似文献
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天基综合信息网是未来卫星网络的发展趋势,与国家利益联系日益紧密,也是人们关注的热点问题。文中首先介绍了卫星网络的划分模式及种类,其次,针对天基综合信息网分别描述了其系统构成和主要特点,然后对天基综合信息网所面临的攻击威胁进行了分析,并就基于信任机制及认证机制的路由协议和抗毁路由协议等从原理和性能方面进行了阐述和安全分析,最后对天基综合信息网的安全路由协议进行了总结。综合利用各种卫星资源,提高卫星网络的综合利用效率,提高整个空间网络的安全性。 相似文献