Flow Control

Perforated walls and transpiration flow play an important role in aerodynamics due to an increasing interest in application of flow control by means of blowing and/or suction. An experimental study was carried out which has led to the determination of a transpiration flow characteristics in the form of a simple formula that is very useful in modelling such flows. In connection to this relation a method of "aerodynamic porosity" determination has been proposed which is much more reliable than geometric description of the porosity. A theoretical analysis of the flow through a perforation hole was also carded out. The flow was considered as compressible and viscous. The gasdynamic analysis led us to a very similar result to the relation obtained from the experiment. The adequacy of the theoretical result is discussed in respect to the experiment.

Due to higher price, limited supply and negative impacts on environment by fossil fuel, automobile industries have
directed their concentrations in reducing the fuel consumption of vehicles in order to achieve the lower aerodynamic
drag. As a consequence, numerous researches have been carried out throughout the world for not only getting the
optimum aerodynamic design with lower drag penalty and but also other parameters that increase the fuel
consumption. In this regard, relevant experimental and numerical outcomes on vehicle drag reduction considering
various techniques such as active, passive and combined techniques in order to delay or suppress flow separation
behind the vehicles have been considered in this review paper. Furthermore, the effects of drag reduction and their
applicability on the vehicles are also illustrated in this paper. Therefore, it is conjectured that the drag reduction has
been improved as much as 20%, 21.2%, and 30% by using the active, passive and combined control systems,
respectively.

High penetration of renewable energy sources such as wind generation in microgrids (MGs) causes fluctuations of power flow and significantly affects the power system operation. This can lead to severe problems, such as system frequency oscillations, and/or violations of power lines capability. With the proper control, superconducting magnetic energy storage (SMES) is able to significantly enhance the dynamic security of the power system. In a SMES system, the power conditioning system (PCS) is the crucial component that directly influences the validity of the SMES in the dynamic control of the power system. This paper proposes the use of an improved SMES controller for the stabilization and control of the power flow of wind-hybrid MGs. In this sense, the design and implementation of a novel high performance PCS scheme of the SMES is described. Moreover, a detailed model of the SMES unit is derived and a novel three-level control scheme is designed, comprising a full decoupled current control strategy in the d-q reference frame and an enhanced power system frequency controller. The dynamic performance of the proposed systems is fully validated by computer simulation.

The efficient implementation of collective communication patterns in a parallel machine is a challenging design effort, that requires the solution of many problems. In this paper we present an in-depth description of how the Quadrics network supports both hardware-and softwarebased collectives. We describe the main features of the two building blocks of this network, a network interface that can perform zero-copy user-level communication and a wormhole routing switch. We also focus our attention on the routing and flow control algorithms, deadlock avoidance and on how the processing nodes are integrated in a global, virtual shared memory. Experimental results conducted on 64-node AlphaServer cluster indicate that the time to complete the hardwarebased barrier synchronization on the whole network is as low as 6 ¡ s, with very good scalability. Good latency and scalability are also achieved with the software-based synchronization, which takes about 15 ¡ s. With the broadcast, similar performance is achieved by the hardware-and software-based implementations, which can deliver messages of up to 256 bytes in 13 ¡ s and can get a sustained asymptotic bandwidth of 288 Mbytes/sec on all the nodes. The hardware-based barrier is almost insensitive to the network congestion, with 93% of the synchronizations taking less than 20 ¡ s when the network is flooded with a background traffic of unicast messages. On the other hand, the software-based implementation suffers from a significant performance degradation. With high load the hardware broadcast maintains a reasonably good latency, delivering messages up to 2KB in 200 ¡ s, while the software broadcast suffers from slightly higher latencies inherited from the synchronization mechanism. Both broadcast algorithms experience a significative performance degradation of the sustained bandwidth with large messages.

In recent years, many extensive studies have been performed that have attempted to improve the performance of TCP for wireless networks. The common assumptions made by TCP for wired networks definitely do not hold for wireless networks. TCP with its semantics such as end-to-end flow control, a congestion control mechanism and error recovery provide reliability in wired networks. Wireless communication has significantly different characteristics compared to wired networks such as higher bit error rates, higher latency, limited bandwidth, multi-path fading of the signals and handoff. In this paper, we propose an enhancement to TCP that will be referred to as E-TCP, which improves upon conventional TCP congestion and flow control in a wireless environment. Our simulation results show significant improvements to TCP performance can be achieved.

A new gigabit ATM photonic switching architecture is here presented and first experimental results are reported. The matrix is based on wavelength encoding of cells and on the broadcast-and-select principle for routing. A suitable management of fibre delay lines allows alloptical output queueing inside each switching element. These output buffered switching elements are then interconnected in a multi-stage Clos architecture and different design options are discussed in order to achieve a terabit capacity and simultaneously meet the ATM switching requirements. In particular, the feasibility of interstage flow control is proved and its benefits on system performance evaluated.

In a today's internet end system, the congestion and flow control of every TCP connection is done separately. This means that every TCP sender of the TCP connections of an end system has to determine current information about the network for itself and independently from other TCP senders. Due to TCP's congestion control and timer management, i.e., the slow start algorithm and timeout timer calculation, this can lead to suboptimal network utilization. In addition, separate control reduces fairness between simultaneous TCP connections. Both effects are caused by several TCP senders' different perception of current network conditions. Therefore, it might be an interesting idea to reuse network information in an end system: information collected by existing TCP connections could be used to initialize control variables of new TCP connections with more up-to-date values. This can improve the overall network utilization of and the fairness between the TCP connections of an end system.

Statically exploring the inter-procedural control flow of objectoriented applications is often difficult because of the use of abstraction, polymorphism, and dynamic binding. To ease this problem, in this tool demonstration, we present a new profiler that dynamically explores the inter-procedural control flow of Java applications while they are executing. Our profiler visualizes the complete Calling Context Tree (CCT) with various dynamic metrics, such as method invocations, executed bytecodes, or allocated objects, and enables efficient navigation in large CCTs comprising up to several millions of nodes. We show that our tool can render data quite fast with response times in the range of 14-204ms upon user interactions. Thanks to a carefully tuned incremental data representation, the profiling data produced by a running application can be updated several times per second on a standard laptop. The visualization can also show recently active parts of the application. The collection of profiling data uses an aspect-based dynamic program analysis technique that simplifies extension and customization of the tool.

The work reported here is part of the PROGRES (PROgrammed Graph Rewriting Systems) project. PROGRES is a very high level multi paradigm language for the specification of complex structured data types and their operations. The data structures are modelled as directed, attributed, node and edge labelled graphs (diane graphs). The basic programming constructs of PROGRES are graph rewriting rules (productions and tests) and derived relations on nodes (paths and restrictions). These basic operations may be combined to build partly imperative, partly rule based, complex graph transformations by special control structures which regard the nondeterministic nature of graph rewriting rules. PROGRES offers its users a convenient, partly textual, partly graphical concrete syntax and a rich system of consistency checking rules for the underlying calculus of programmed diane-graph rewriting systems. This paper presents the key techniques used for the execution of PROGRES programs. We will discuss...

We propose a novel explicit rate-flow-control algorithm intended for available-bit-rate (ABR) service on an ATM network subject to loss and fairness constraints. The goal is to guarantee low cell loss in order to avoid throughput collapse due toretransmission by higher level protocols. The mechanism draws on measuring the current queue length and bandwidth availability, as well as tracking tile current number of active sessions contending for capacity, to adjust an explicit bound on the source transmission rates. We identify the factors that affect queue overflows and propose simple design rules aimed at achieving transmission with controlled loss in a dynamic environment. We also discuss how conservative design rules might be relaxed by accounting for statistical multiplexing in bandwidth sharing among bursty ABR sources and variable-bit-rate (VBR) sources. Index Terms-ABR service, ATM networks, delay differential equations, explicit rate flow control. |. INTRODUCTION A SYNCHRONOUS transfer mode (ATM) networks are geared at supporting and integrating a variety of communication services. These services may be divided into those based on reservation, e.g., constant-and variable-bit-rate (CBR, VBR) services, and best effort services, such as unspecified-bit-rate (UBR) and to some extent available-bit-rate (ABR) services. Among the latter, ABR service promises to play an important role in supporting high-bandwidth data as well as Internet traffic, such as TCP traffic. The rationale for including ABR is to provide an economical and flexible way to carry data traffic, as might be needed to simplify adoption of ATM to support delay adaptive real-time applications [6]. From the service provider's point of view, ABR traffic can be used to enhance utilization by directing sources to make the most of the network's available capacity subject to minimum cell rate and cell loss guarantees. It has been shown in [22], [23] that TCP performs poorly over ATM networks when congestion leads to lost ATM cells which in turn result in multiple corrupted IP packets. Significant performance degradation results from corrupted IP packets since

This paper investigates communication in distributed memory multiprocessors to support tasklevel parallelism for real-time applications. It is shown that wormhole routing, used in second generation multicomputers, does not support task-level pipelining because its oblivious contention resolution leads to output inconsistency in which a constant throughput is not guaranteed. We propose scheduled routing which guarantees constant throughputs by integrating task specifications with flow-control. In this routing technique, communication processors provide explicit flowcontrol by independently executing switching schedules computed at compile-time. It is deadlock-free, contention-free, does not load the intermediate node memory, and makes use of the multiple equivalent paths between non-adjacent nodes. The resource allocation and scheduling problems resulting from such routing are formulated and related implementation issues are anal yzed. A comparison with wormhole routing for various generalized hyp ercubes and tori shows that scheduled routing is effective in providing a constant throughput when wormhole routing does not and enables pipelining at higher input arrival rates.

The paper presents the design and evaluation of PECOS, a PreEmptive COntrol Signature technique for on-line detection of control flow errors. The technique uses assertions that can be embedded in the assembly language code and that are triggered by control flow instructions in the code. The PECOS target error model is any corruption that causes the application to take an incorrect control flow path. This includes corrupted control flow instructions as well as any other corruption that subsequently affects the control flow. The proposed technique is shown to handle both static and dynamic control flow constructs. PECOS is evaluated through software-based error injection-both directed control flow injections and random injections into the text segment of the running application. The injected errors model the impact of failures in the address and data lines between a processor and memory. The effectiveness of PECOS is illustrated on a real application: the Dynamic Host Configuration Protocol (DHCP) server. It is shown that PECOS detects more than 87% of control flow errors, reducing the incidence of fail-silence violations from 3.6% to 0.1% and of process crashes from 54.6% to 7.1%. Performance studies show a degradation of 15-29% with instrumentation of the entire DHCP server, and a degradation of 5-13% with instrumentation of only the critical DHCP protocol engine.

Network on Chip is an efficient on-chip communication architecture for SoC architectures. It enables the integration of a large number of computational and storage blocks on a single chip. The router is the basic element of NoC with multiple, connecting to other router and to a local IP core. This router architecture can be used later for building a NoC with standard or arbitrary topology with low latency and high speed and High maximal peak performance. The low latency and high speed is achieved by allowing for each input port a routing function which runs in parallel with Link controler and with distributed arbiters. To evaluate our approach, A wormhole input queued 2-D mesh router was created to verify the capability of our router. Various parameterized designs were synthesized to provide a comparative study with other implementations in FPGA thechnology, with different flit size.

1st International Conference on Managing Rivers in the 21st Century: Issues & Challenges ... River Restoration Through Bank Stabilization Using FLUVIAL-12: Case Study of Raia River, Ipoh, Perak ... AHMAD DARUS, River Engineering Section, Department of Irrigation and ...

This paper presents a clock selection algorithm for control-flow intensive behaviors that are characterized by the presence of conditionals and deeply-nested loops. Unlike previous works, which are primarily geared towards data-dominated behaviors, this algorithm examines the effects of branch probabilities and their interaction with allocation constraints.

In optimistic parallel simulations, state-saving techniques have been traditionally used to realize rollback. In this article, we propose reverse computation as an alternative approach, and compare its execution performance against that of statesaving. Using compiler techniques, we describe an approach to automatically generate reversible computations, and to optimize them to transparently reap the performance benefits of reverse computation. For certain fine-grain models, such as queuing network models, we show that reverse computation can yield significant improvement in execution speed coupled with significant reduction in memory utilization, as compared to traditional state-saving. On sample models using reverse computation, we observe as much as three-fold improvement in execution speed over traditional state-saving.

In this paper some theoretical and experimental results concerning the modeling and control of rectangular natural circulation loops are presented. These thermo-fluid-dynamic systems are used to refrigerate heat sources by means of natural circulation of a fluid without mechanical pumping. Despite the structural simplicity of these systems, they can exhibit unstable behaviour, resulting in wide and dangerous oscillations. A non-linear lumped parameter model was derived by using a truncated Fourier series expansion of a suitable set of variables. The performance of the model was compared with a set of experimental data. Then a set of controllers, corresponding to different equilibrium points, was designed and tested both in simulation and experimentally. In all cases the controllers were capable of stabilising the system to the desired equilibrium condition. #

The aim of this experimental study is the implementation of a practical and efficient closed-loop feedback control of the turbulent flow over a NACA-4412 airfoil equipped with leading-edge zero-net-mass-flux actuators. By using prior computation of correlations between particle image velocimetry data and multiple surface pressure measurements, real-time instantaneous low-dimensional estimates of the velocity field over the wing are then computed from the unsteady surface pressure. From such estimates, a direct knowledge of the state of the flow above the airfoil is obtained (i.e., attached, incipient separation, or fully separated flow). We first show the effectiveness of the low-dimensional modeling approach in extracting and estimating the underlying large-scale structures in a turbulent flow, using the proper orthogonal decomposition and the modified linear/quadratic stochastic measurements. We then show how such an approach is used successfully in a simple, but practical, proportional feedback loop to delay the separation of the flow over the wing at high angles of attack. The benefits of closed-loop vs open-loop control are then discussed. These fundamental results validate the use of low-dimensional modeling techniques for further, more sophisticated, closed-loop feedback control algorithms.

The authors describe and solve a Markov model or the lealey bucket ATM generic 110w control mechanism. The model has a space carclinality which grows quiclely with its parameters and is challenging to solve. Exploiting the cyclic nature of the model, the authors develop a methoclology which allows them to enïciently solve instances of the mocle! with 3905 134 states and 53869532 transitions using 29.8 Mbyte of memory and 222Mbyte of disc storage. The cru utilisation is high (between 70'1" and 90%). The methoclology is new and can be easily extended to any leind of linite cyclic Markov models.

The Distributed Computing Software project at Oxford University is using formal specification techniques to explore the design of services in a distributed operating system. Our goal is to construct and publish the specification of a loosely-coupled distributed operating system consisting of a number of autonomous services. Some design principles have been proposed from consideration of conventional business practice. Several services have already been designed and implemented according to these principles.

The current approach for testing a program is, in principle, quite primitive. Some small sample of the data that a program is expected to handle is presented to the program. If the program produces correct results for the sample, it is assumed to be correct. Much current work focuses on the question of how to choose this sample. We propose that a program can be more effectively tested by executing it "symbolically". Instead of supplying specific constants as input values to a program being tested, one supplies symbols. The normal computational definitions for the basic operations performed by a program can be expanded to accept symbolic inputs and produce symbolic formulae as output. If the flow of control in the program is completely independent of its input parameters, then all output values can be symbolically computed as formulae over the symbolic inputs and examined for correctness. When the control flow of the program is input dependent, a case analysis can be performed producing output formulae for each class of inputs determined by the control flow dependencies. Using these ideas, we have designed and implemented an interactive debugging/testing system called EFFIGY.

A variety of different types of actuators have been previously investigated as flow control devices. Potential applications include the control of boundary layer separation in external flows, as well as jet engine inlet and diffuser flow control. The operating principles for such devices are typically based on either mechanical deflection of control surfaces (which include MEMS flap devices), mass injection

Human intervention in the hydrologic basin of the Colorado River has eliminated water discharge and sediment supply to the river's mouth and its delta. After ∼95 years of applying strong flow control policies, the previous sedimentary budget in the delta has changed, the delta now being entirely exposed to the hydrodynamic forces in its basin. In order to assess the anthropogenic impact of water diversion on deltaic sedimentary processes and short-term delta geomorphic evolution, textural and mineralogical analyses were performed on 68 sediment samples collected from the river, estuary, beach, continental shelf, delta plain and desert. The results show a consistent NE to SW textural gradient on the shallow-marine platform adjacent to the Colorado River delta (an area known as the Upper Gulf of California), and a net cross-basinal sediment transport occurring in the same direction. Two opposing littoral transport components exist along the Sonoran and Baja Californian coasts: (1) net sediment transport from SE to NW along the Sonoran coast delivers sediments from the ocean into the estuarine basin through the Sonora channel of the deltaic system of the Colorado River; and (2) sediment transport from N to S along the Baja Californian coast removes sediments from the estuarine basin of the Colorado River into the Northern Gulf of California (NGC). The residual sediment transport pattern observed suggests a counterclockwise path of exchange of materials between the estuarine basin of the Colorado River and the NGC. Multivariate cluster and factor analyses of the heavy-mineral data reveal the existence of a sedimentary system dominated by two end-members, representing two heavy-mineral sedimentary provinces: (1) the Sonora province is characterized by a heavy-mineral suite of garnet and zircon (G–Z), whose sediment supply originates from the sandy sediments of the Sonora Mesa deposits and Sonora's Gran Desierto; and (2) the Baja California province is characterized by a hornblende–epidote–pyroxene (H–E–P) suite, whose sediments originate from the earlier supply of the Colorado River. Since the Colorado River is no longer supplying sediments from its drainage basin, the H–E–P-rich sediments now actively dispersed in the system have mainly originated through intense reworking of the delta. Moreover, G–Z-rich sediments are starting to invade areas previously dominated by H–E–P sediments. On the basis of the prevailing hydraulic regime, textural and mineralogical characteristics of the sediments, and hydrographic and bathymetric information from the region, a hypothetical sediment dynamics model for the delta region is proposed, in which the tidally influenced, wave-dominated, sediment-reworked, slightly eroding Sonoran coast changes into a tide-dominated, depositional, very slowly prograding Baja Californian coast. This study shows that human intervention of the hydrologic basin of the Colorado River is not only responsible for inducing drastic hydrologic changes in its estuary (i.e., from brackish to hypersaline), but also for inducing drastic changes in the hydrographic circulation of the receiving basin (i.e., from long-basinal to cross-basinal). These changes are ultimately responsible for the relocation of massive volumes of the delta's sediment inventory, and for the serious ecological impact of habitat loss of indigenous species, such as the now endangered Totoaba (Totoaba macdonaldi) and Vaquita (Phocoena sinus).

Java 2 Micro-Edition Connected Limited Device Configuration (J2ME CLDC) is the platform of choice when it comes to running mobile applications on resourceconstrained devices (cell phones, set-top boxes, etc.). The large deployment of this platform makes it a target for security attacks. The intent of this paper is twofold: First, we study the security architecture of J2ME CLDC, then we provide a vulnerability analysis of this Java platform. The analyzed components are: Virtual machine, CLDC API and MIDP (Mobile Information Device Profile) API. The analysis covers the specifications, the reference implementation (RI) as well as several other widely-deployed implementations of this platform.

Petri nets (PN) are useful for the modelling, analysis and control of hybrid dynamical systems (HDS) because PN combine in a comprehensive way discrete events and continuous behaviours. On one hand, PN are suitable for modelling the discrete part of HDS and for providing a discrete abstraction of continuous behaviours. On the other hand, continuous PN are suitable for modelling the continuous part of HDS and for working out a continuous approximation of the discrete part in order to avoid the complexity associated with the exponential growth of discrete states. This paper focuses on the advantages of PN as a modelling tool for HDS. Investigations of such models for diagnosis and control issues are detailed.

We provide a new method for the selective surface patterning of microfluidic chips with hydrophobic fluoropolymers which is demonstrated by the fabrication of hydrophobic valves. It enables efficient optical quality control for the surface patterning thus permitting the lowcost production of highly reproducible hydrophobic valves. Specifically, a fluoropolymer-solvent-dye solution based on carbon black (CB) is presented which creates superhydrophobic surfaces (contact angle = 157.9°) on chips made from cyclic olefin copolymer (COC). It further provides good visibility for the quality control (QC) in polymer labs-on-a-chip and increases the burst pressure of hydrophobic valves. Finally, an application which aims for the amplification of mRNA on-chip and relies on the defined flow control by hydrophobic valves is presented. Here, the QC in combination with the Teflon-CB coating improves the average standard deviation of the burst pressures from 14.5% down to 6.1 % compared to solely Teflon-coated valves.

This review compiles personal and indoor microenvironment particulate matter (PM) monitoring needs from recently set research objectives, most importantly the NRC published ''Research Priorities for Airborne Particulate Matter (1998)''. Techniques and equipment used to monitor PM personal exposures and microenvironment concentrations and the constituents of the sampled PM during the last 20 years are then reviewed. Development objectives are set and discussed for personal and microenvironment PM samplers and monitors, for filter materials, and analytical laboratory techniques for equipment calibration, filter weighing and laboratory climate control.

The effectiveness of a sensor configuration for feedback flow control on the wake of a circular cylinder is investigated in both direct numerical simulation as well as in a water tunnel experiment. The research program is aimed at suppressing the von Kármán vortex street in the wake of a cylinder at a Reynolds number of 100. The design of sensor number and placement was based on data from a laminar two-dimensional simulation of the Navier-Stokes equations for the unforced condition. A low-dimensional proper orthogonal decomposition (POD) was applied to the vorticity calculated from the flow field and sensor placement was based on the intensity of the resulting spatial eigenfunctions. The numerically generated data was comprised of 70 snapshots taken over three cycles from the steady state regime. A linear stochastic estimator (LSE) was employed to map the velocity data to the temporal coefficients of the reduced order model. The capability of the sensor configuration to provide accurate estimates of the four low-dimensional states was validated experimentally in a water tunnel at a Reynolds number of 108. For the experimental wake, a sample of 200 particle image velocimetry (PIV) measurements was used. Results show that for experimental data, the root mean square estimation error of the estimates of the first two modes was within 6% of the desired values and for the next two modes was within 20% of the desired values. This level of error is acceptable for a moderately robust controller.

Nowadays more and more business activities are operated through web and the web plays a vital role in the interests of both businesses and their shareholders. However, the very good features of web such as its popularity, accessibility and openness, has provided more opportunities for security breaches by malicious users. That is why the rate of successful attacks on web and web applications are increasing. Many approaches have been introduced so far to reduce the rate of successful attacks of many kinds. Any technique that can detect these vulnerabilities and mitigate the security problems of web applications is useful to organizations seeking for more reliability from the security viewpoint. In this paper we first introduce the control flow tampering attack, which is one of the notable attacks against web applications, and present our approach for countering this attack using web application firewall.

The single dielectric barrier discharge plasma actuators (PAs) are known to be effective for flow control process. This study investigated the winglet-type thin and small PAs, which were suspended in the quiescent air flow. We conducted the PIV measurements and flow computations for the PA induced flow. The induced flow was discussed on three regions: a sink-like flow to the electrode, a shear flow over the winglet surface, and a jet-like flow downstream from the winglet. When the electrode
was located at the leading edge of the winglet PA, the sink-like flow was effectively enhanced. On the other hand, when the electrode was located at the trailing edge, the friction loss was minimized for the near-wall high shear flow over the winglet, and thus the highest momentum integral was obtained for the downstream jet-like flow. From these results, the most effective flow actuation was suggested to be achieved by the short winglet that had the exposed electrode at a leading edge and the covered
electrode at a trailing edge.

Stream restoration, or more properly rehabilitation, is the return of a degraded stream ecosystem to a close approximation of its remaining natural potential. Many types of practices ͑dam removal, levee breaching, modified flow control, vegetative methods for streambank erosion control, etc.͒ are useful, but this paper focuses on channel reconstruction. A tension exists between restoring natural fluvial processes and ensuring stability of the completed project. Sedimentation analyses are a key aspect of design since many projects fail due to erosion or sedimentation. Existing design approaches range from relatively simple ones based on stream classification and regional hydraulic geometry relations to more complex two-and three-dimensional numerical models. Herein an intermediate approach featuring application of hydraulic engineering tools for assessment of watershed geomorphology, channel-forming discharge analysis, and hydraulic analysis in the form of one-dimensional flow and sediment transport computations is described.

Results are reported of an experimental investigation into the motion of a heavy cylinder free to move inside a water-filled drum rotating around a horizontal axis. The cylinder is observed to either co-or, counter intuitively, counter-rotate with respect to the rotating drum. The flow was measured with particle image velocimetry (PIV), and it was found that the inner cylinder significantly altered the bulk flow field from the solid-body rotation found for a fluid filled drum. In the counter-rotation case, the generated lift force allowed the cylinder to freely rotate without contact with the drum wall. Drag and lift coefficients of the freely counter-rotating cylinder were measured over a wide range of Reynolds numbers, 2,500 < Re < 25,000, dimensionless rotation rates, 0.0< α <1.2, and gap to cylinder diameter ratios 0.003 < G/2a < 0.5. Drag coefficients were consistent with previous measurements on a cylinder in a uniform flow. However, for the lift coefficient considerable larger values were observed in the present measurements. We found the enhancement of the lift force to be mainly caused by the vicinity of the wall. arXiv:0911.4535v2 [physics.flu-dyn]

A flow visualisation study was performed to investigate a periodic flow instability in a bifurcating duct within the tip of the flares at the Shell refinery in Clyde, NSW, to verify the trigger of a combustion-driven oscillation proposed in Part A of this study, and to identify its features. The model study assessed only the flow instability, uncoupled from the

Small switch buffers, high-speed links, short round-trip times and the composite nature of the traffic in data center networks (DCN) lead to several congestion problems that are not handled well by traditional congestion control mechanisms such as TCP. In this paper we design a simple switch-driven, flow-aware, congestion control algorithm to deal with such congestion issues. The basic idea of the proposed mechanism is reminiscent of classic congestion control in flow-aware networks such as ATM-ABR, where the switch sets a field in packet headers to enforce the sending rate at the source; less classic though are the challenges faced in designing such flow-awareness in the flow-aversive IP environment without modifying the TCP sender and receiver algorithm, to enable deployment in public data centers. We discuss in this paper our algorithm, two implementations (as a Linux kernel module or as an added feature to OpenVSwitch) and finally give numerical results from NS-2 simulations to show its effectiveness in achieving high throughput overall, a good fairness and short flow completion times for delay-sensitive flows.

The vortex shedding characteristics and the drag force acting on a circular cylinder, attached with an oscillating splitter plate, are investigated by solving the two-dimensional Navier–Stokes equations. The splitter plate is forced to exhibit harmonic oscillation about its attachment point, and the Reynolds number (Re) of the flow is 100. In order to facilitate easy handling of the plate oscillations inside the computational domain, the equations are solved in a Cartesian grid, and the concept of immersed boundary method is used to impose the boundary conditions on the body surface. The characteristic feature of this problem is the complex interaction between the vortices shed from the splitter plate and the cylinder. Three different patterns of vortex shedding are observed in the wake of the circular cylinder depending upon the frequency and amplitude of plate oscillation: normal shedding, chain of vortices and shedding from splitter plate. It is found that the inverse relationship between the vortex formation length and Strouhal number is not applicable when the splitter plate is subjected to oscillation. Additional related interesting fluid dynamics features are also presented.► Three shedding patterns: normal shedding, chain of vortices and shedding from plate. ► To completely suppress shedding oscillating plate can be much shorter than fixed one. ► Inverse relationship between vortex formation length and St is not applicable. ► Drag coefficient is less than that of fixed plate configuration. ► Use of immersed boundary method to model plate oscillations in fixed Cartesian grid.

We investigate linear-quadratic dynamical systems with energy preserving quadratic terms. These systems arise for instance as Galerkin systems of incompressible flows. A criterion is presented to ensure long-term boundedness of the system dynamics. If the criterion is violated, a globally stable attractor cannot exist for an effective nonlinearity. Thus, the criterion represents a minimum requirement for a physically justified Galerkin model of viscous fluid flows. The criterion is exemplified e.g. for Galerkin systems of twodimensional cylinder wake flow models in the transient and the post-transient regime, the Lorenz system, and for physical design of a Trefethen-Reddy Galerkin system. There are numerous potential applications of the criterion, for instance system reduction and control of strongly nonlinear dynamical systems.

Este artículo presenta el diseño e implementación de una herramienta para facilitar la comprensión del funcionamiento de un servicio de audio/vídeo streaming. Su objetivo serán alumnos de carreras técnicas (informática y telecomunicaciones) que se adentran por primera vez con un servicio de características muy especiales, entre las que se encuentran: fuerte consumo de recursos, elementos para garantizar la calidad de servicio, protocolos independientes para control y transporte de la información, protocolos con estados, entre otras.

The authors present the design and implementation of an asynchronous remote operation execution facility, futures, that retains the benefits of the remote procedure call (RPC) abstraction but allows execution to proceed locally in parallel with remote execution and provides extensive support for managing replies. It is shown how this facility can be easily used to support many common interprocess communication

An experimental investigation on the flow separation in the corner (i.e., "corner separation") between a wall and a single wing in a windtunnel and in a highly loaded compressor cascade was performed. As a passive flow control device a single vortex generator placed in each corner on the wing or the guide vane reduces the corner separation considerably. The experiments with the single wing were carried out for Reynolds numbers of Re= 0.2 x10 6 to 1.2 x10 6 in the low speed windtunnel of the Hermann-Foettinger-Institut of the Technical University of Berlin. With flow visualisation techniques it was shown that a significant reduction of the corner separation and an improvement of the two-dimensionality of the flow can be achieved with vortex generators. Force measurements of the wing profiles with vortex generators showed a lift increase and a drag reduction. In order to extend the design of the vortex generators for an application in turbomachines, an experimental study is currently ongoing, which investigates the influence of the vortex generators on the loss behaviour of an aerodynamically highly loaded compressor cascade with NACA 65 K48 blades. Initial experiments with a compressor cascade at Ma = 0.67 and Re=0.56x10 6 show, using flow visualisation techniques, a significant reduction of the corner separation on the guide vane and the wall. δ u [°] camber angle ϕ VG [°] angle of inclination of the VG

This paper presents the development and design of a fractional PI controller for a first order system with delay. The proposed fractional controller is contrasted with two different design techniques of integer controllers, one of them based on the SIMC technique and the other one on the classic design of frequency response. Performing a discrete implementation fractional controller and the results show the fractional PI controller robustness against other design techniques

Most conventional methods for flow control during resin transfer molding have varied the applied pressure using pressure regulators. However, with this method it is difficult to control the flow far from the inlet or outlet points. The present study proposes a flow control scheme by monitoring and actuating flow/temperature using a thin multifunctional interdigital electrode array film. The film is used for estimation of resin impregnation and temperature distribution, and increases the resin temperature by dielectric heating at arbitrary positions on the film, thereby increasing the resin velocity at the required positions. Foam cored GFRP structures were impregnated with resin by VaRTM, and the effectiveness of the flow control scheme assessed. The occurrence of dry spots was effectively prevented.

LDV and wall static pressure measurements were performed to investigate the flow properties downstream of an asymmetric wide-angle diffuser controlled by perforated plates. The experimental results showed significant changes in the mean flow velocity and local fluctuating component properties downstream of the diffuser. The tests were undertaken in a system comprising half a conventional pyramidal diffuser connected to a chamber of rectangular cross-section. One of the lateral walls was parallel to the flow, and the opposite one had an opening angle of 45°. The total diffuser opening vertical angle delimited by the top and bottom walls was 60°, and the area ratio was equal to 7. A combination of four perforated plates with porosities of 45%, positioned within the diffuser, permitted the investigation of a total of seven different experimental configurations. While good flow uniformity could be achieved in symmetric diffusers with only two perforated plates, as reported in the literature, it has been found that an additional plate is needed for the best flow distribution in the studied asymmetric diffuser. Ó 2004 Elsevier Inc. All rights reserved.

Active flow control (AFC) relies on actuators’ control authority as a primary enabling technology for flow manipulation. The requirements from the actuation systems are revisited and tools for critical evaluation of actuators are offered. The application in mind is boundary layer separation control. Effective yet robust methods for coupling the excitation to unstable flow modes should be experimented. The recent introduction of the SaOB (steady Suction and Oscillatory Blowing) actuator concept to AFC and the use of similar no-moving parts oscillators have the potential to be both effective at higher speeds and overall efficient. To be accepted by industry, system efficiency should always be assessed, not only the improvement in aerodynamic performance. A few performance based criteria for comparing different actuation concepts are presented and discussed. The first criterion is the actuator conversion efficiency, from input energy (electric or fluidic) to mechanical energy. The second criterion evaluates the actuator based on its force or momentum generation capability as it operates in still fluid, while considering its weight, volume and power consumption. An additional, application dependent, criterion is the Aerodynamic Figure of Merit, an energy efficiency criterion, based on the improvement of the controlled performance (e.g., lift to drag ratio, wind turbine power production or drag reduction efficiency) of a certain application, when the power consumption (and possibly also the weight) of the actuation system are taken into account. Relevant recent separation control data are presented, compared and discussed. It was found that Piezo fluidic actuation is effective at low speeds while SaOB actuation is preferred at higher speeds. Mechanical or electromagnetic actuators are less effective mainly due to excessive weight while DBD Plasma actuators are orders of magnitude less efficient (0.1%). A minimal actuation efficiency requirement based on CFD results is also outlined.

An experimental study is conducted to characterize the performance of a pulsed-plasma jet (called a "spark jet" by other researchers) for potential use in supersonic flow control applications. A pulsed-plasma jet is a high-speed synthetic jet that is generated by striking an electrical discharge in a small cavity. The gas in the cavity pressurizes owing to the heating and is allowed to escape through a small orifice. To obtain an estimate of the relative strength of the pulsed-plasma jet, the jet is injected normally into a Mach 3 crossflow and the penetration distance is measured by using schlieren imaging. These measurements show that the jet penetrates 1.5 boundary-layer thicknesses into the crossflow and the jet-to-crossflow momentum flux ratio is estimated to be 0.6. A series of experiments was conducted to determine the characteristics of the pulsed-plasma jet issuing into stagnant air at a pressure of 35 torr. These results show that typical jet velocities of about 250 m=s can be induced with discharge energies of about 30 mJ per jet. Furthermore, the maximum pulsing frequency was found to be about 5 kHz, because above this frequency the jet begins to misfire. The misfiring appears to be due to the finite time it takes for the cavity to be recharged with ambient air between discharge pulses. The velocity at the exit of the jet is found to be primarily dependent on the discharge current and independent of other discharge parameters such as cavity volume and orifice diameter. Temperature measurements are made using optical emission spectroscopy and reveal the presence of considerable nonequilibrium between rotational and vibrational modes. The gas heating efficiency was found to be 10% and this parameter is shown to have a direct effect on the plasma jet velocity. These results indicate that the pulsed-plasma jet creates a sufficiently strong flow perturbation that holds great promise as a supersonic flow actuator. Nomenclature j = density of the pulsed-plasma jet 1 = freestream density u j = exit velocity of the pulsed-plasma jet u 1 = freestream velocity

We present a novel dynamic analysis technique that finds real deadlocks in multi-threaded programs. Our technique runs in two stages. In the first stage, we use an imprecise dynamic analysis technique to find potential deadlocks in a multi-threaded program by observing an execution of the program. In the second stage, we control a random thread scheduler to create the potential deadlocks with high probability. Unlike other dynamic analysis techniques, our approach has the advantage that it does not give any false warnings. We have implemented the technique in a prototype tool for Java, and have experimented on a number of large multi-threaded Java programs. We report a number of previously known and unknown real deadlocks that were found in these benchmarks.

A dielectric barrier discharge, operating at kHz and kV conditions, can generate largely isothermal surface plasma and induce wall-jetlike fluid flow. It can serve as an aerodynamic actuator, and has advantages of no moving parts. In order to better understand the mechanism of the momentum coupling between the plasma and the fluid flow, both computational modeling and experimental information are presented. Furthermore, the impact of such athermal, non-equilibrium plasma discharges on low-speed aerodynamics and heat transfer is discussed. The plasma and fluid species are treated as a two-fluid system exhibiting decades of length and time-scale disparities. For Reynolds numbers of 10 4 -10 5 , the time-scales ratios between those characterizing the discharge physics (convection, diffusion, and reaction/ionization) and the fluid flow mechanisms are separated by several decades, allowing the effect of plasma on the fluid dynamics modeled via a one-way body force treatment. At a phenomenological level, the plasma model can be established using a linearized force distribution to approximate the discharge structure. A high-fidelity approach using a first-principle-based hydrodynamicplasma model is also reviewed. Numerical techniques such as operating splitting are introduced in order to handle the computational stiffness resulting from the time and length scale variations. The goal is to use time-step sizes in the range of the fluid dynamics level while treating the fast varying ones statistically. The momentum coupling is discussed in the context of discharge chemistry; species transport properties, insulator and electrode materials, and dielectric barrier discharge (DBD) geometry. Parametric studies conducted on the operating variables such as voltage, frequency and geometric arrangements offer substantial insight into the plasma physics, as well as a basis to explore thermal management and flow control applications. r

This article traces the unstable semantics of use cases from Jacobson to UML 1.3. The UML 1.1 metamodel formally defined the «uses» and «extends» use case relationships as stereotypes of generalisation, yet both received interpretations that varied between inheritance and composition, reflecting a large degree of confusion among developers. The recently revised UML 1.3 has quietly dropped these in favour of new «include» and «extend» relationships, which are styled instead as kinds of dependency. Despite this change, the deployment of use case diagrams encourages analysts to conceptualise and develop models which conceal arbitrary jumps in the flow of control, corresponding to goto and comefrom statements, and in which unpleasant non-local dependencies exist across modules. A discussion of examples reveals how a conscientious designer must disassemble use case models completely to produce properly-structured code. A radical solution is proposed.