一种基于动态流控的多信道媒体接入控制算法

文中提出一种基于动态流控的多信道媒体接入控制算法(Multi-channel MAC with Dynamic Flow Control,MMAC-DFC)。通过动态流控,可以根据控制信道的繁忙状况动态地调整每次传输的数据分组的数量,实现了对特定控制信道多信道MAC算法的增强。仿真结果表明,MMAC-DFC相比于其他多信道MAC算法能有效地提升网络的吞吐量和端到端时延。

基于源抑制的内网流量自适应控制算法研究

针对源抑制机制在内网流量控制中存在的带宽利用率不高的问题,提出一种基于源抑制的内网流量自适应控制算法。该算法在网关上监视网络流量,当总流量小于阈值时,不执行流量控制;当总流量超过阈值时,开始统计每个用户的流量,找出流量较大的用户,对于下载流量直接在网关上限速,对于上传流量通知接入交换机控制用户流量。在Linux中实现基于源抑制的内网流量自适应控制算法,并对其进行测试,结果表明该算法能够有效控制内网流量,实现带宽公平和高效利用。

基于FC-SCSI的多通道高速信号采集与实时存储系统

传统的多通道信号采集与存储系统面对庞大的数据采集任务,缺乏足够的传输带宽以及实时存储能力。为此,提出一种以光纤通道-小型计算机系统接口(FC-SCSI)为核心的实时采集存储方案。运用链式查找表结构以及动态流控技术,提高FC-SCSI软件协议存储速率,解决多通道同步采集的大容量流数据实时落盘问题,实现具备大数据量采集、实时可靠存储、便携性能好的综合数据处理存储系统。实验结果表明,在2.125 Gb光纤通道条件下,该系统可靠稳定存储速率为186.6 MB/s,达到2.125 Gb光纤通道理论速率的94.7%,与传统FC-SCSI存储方案的167.1 MB/s速率相比提升了11.7%。

Multi-model Predictive Control of Ultra-supercritical Coal-fired Power Unit

The control of ultra-supercritical(USC) power unit is a difficult issue for its characteristic of the nonlinearity, large dead time and coupling of the unit. In this paper, model predictive control(MPC) based on multi-model and double layered optimization is introduced for coordinated control of USC unit. The linear programming(LP) combined with quadratic programming(QP) is used in steady optimization for computation of the ideal value of dynamic optimization. Three inputs(i.e. valve opening, coal flow and feedwater flow) are employed to control three outputs(i.e. load, main steam temperature and main steam pressure). The step response models for the dynamic matrix control(DMC) are constructed using the three inputs and the three outputs. Piecewise models are built at selected operation points. Double-layered multi-model predictive controller is implemented in simulation with satisfactory performance.

Dynamic Control of a Flexible Shaft Mounted in Adaptive or Active Bearing

The dynamic behavior of rotors is highly influenced by bearing characteristics. In previous works, the authors have shown that it may be beneficial to adapt the bearing behavior to the shaft behavior. Several adaptive and active components will be developed in this paper in order to control the shaft dynamical amplitude. Different models of hydrodynamic bearings behavior are described. The Reynolds equation resolution may be done by numerical or analytical solutions. A physical analysis of the equation of thin films will identify the most sensitive parameters. The shaft flexibility is taking into account by a modal approach. The fluid-structure coupling process is a simulation, step by step, of the rotor behavior. At each step, the nonlinear fluid force is numerically calculated to obtain the unbalanced shaft response. The results, presented in this paper, concern the dynamic response of unbalanced shaft mounted in adaptive or active bearings： bearings with variable clearance, variable viscosity or variable housing speed. It is shown that the fluid bearing parameters must be adapted to the rotor speed （in particular near or far a critical speed）. Then, the paper presents a new kind of active bearing. It works with a mechanical control of the housing position. Several parameters are tested and compared. The robustness of the dynamic control parameters is presented. In conclusion, the bearing adaptation could be very useful to control the shaft dynamic. This limits the effect of the critical speed, in particular by diminishing the shaft amplitude and the dynamic forces transmitted to the housing.

Cavity flow regime for spillway aerators

It is well known that the effect of air entrainment for cavitation damage controls is related not only to the air discharge into aerator devices but also the flow regime of the cavity below them.On the basis of the hydraulic characteristics of the flow,the aerator devices were for the first time classified.The theoretical considerations were performed about the jet length and cavity flow regime with the influencing factors.Comparing with the behavior of the flow through the aerator of discharge tunnels,the flow regimes of the cavity below spillway aerators were experimentally investigated,and the empirical expressions were presented to identify the conversions of the cavity flow regimes,including fully filled cavity,partially filled cavity,and net air cavity.Some issues of the design of the aerator devices were suggested in the present work.

Periodical shedding of cloud cavitation from a single hydrofoil in high-speed cryogenic channel flow

In order to explain criteria for periodical shedding of the cloud cavitation, flow patterns of cavitation around a piano-convex hydrofoil were observed using a cryogenic cavitation tunnel of a blowdown type. Two hydrofoils of similarity of 20 and 60 mm in chord length with two test sections of 20 and 60 mm in width were prepared. Working fluids were water at ambient temperature, hot water and liquid nitrogen. The parameter range was varied between 0.3 and 1.4 for cavitation number, 9 and 17 m/sec for inlet flow velocity, and -8° and 8° for the flow incidence angle, respectively. At incidence angle 8°, that is, the convex surface being suction surface, periodical shedding of the whole cloud cavitation was observed on the convex surface under the specific condition with cavitation number and inlet flow velocity, respectively, 0.5, 9 m/sec for liquid nitrogen at 192℃ and 1.4, 11 m/sec for water at 88℃, whereas under the supercavitation condition, it was not observable. Periodical shedding of cloud cavitation occurs only in the case that there are both the adverse pressure gradient and the slow flow region on the hydrofoil.