Dynamic Backpressure Research Articles

Suppression and utilisation of aeroelastic behaviour in turbine-based combined cycle inlet

This study develops a two-way loosely coupled aeroelastic analysis framework based on a finite-volume fluid solver, a nonlinear finite-element solid solver and the Mesh-based parallel Code Coupling Interface. Research focuses on aeroelastic behaviour in a turbine-based combined cycle inlet after verifying the fluid solver and the coupling strategy through three benchmarks consisting of the inlet experimental model, the classical panel flutter problem and the deformation of a cantilever plate subjected to a shock tube flow. Coupling calculation shows that structural damping is limited only to the vibration suppression of deformable components under constant backpressure but exerts no evident influence on flow field oscillation induced by splitter plate vibration or perturbation from downstream dynamic backpressure. Interestingly, panel deformation (or forced vibration) has a positive impact on the stabilisation of the flow field. The use of a flexible panel with low thickness (e05) successfully prevents the shock train from transitioning, stabilising the performance profiles at the outlet even under dynamic backpressure. Pressure adjustment in the potentially unstable region through panel deformation is assumed to be the solution to weakening the disturbance from splitter plate vibration, which differs from the energy transfer theory under dynamic backpressure that is often found in the literature.

NFVnice: Dynamic Backpressure and Scheduling for NFV Service Chains

Managing Network Function (NF) service chains requires careful system resource management. We propose NFVnice, a user space NF scheduling and service chain management framework to provide fair, efficient and dynamic resource scheduling capabilities on Network Function Virtualization (NFV) platforms. The NFVnice framework monitors load on a service chain at high frequency (1000Hz) and employs backpressure to shed load early in the service chain, thereby preventing wasted work. Borrowing concepts such as rate proportional scheduling from hardware packet schedulers, CPU shares are computed by accounting for heterogeneous packet processing costs of NFs, I/O, and traffic arrival characteristics. By leveraging cgroups, a user space process scheduling abstraction exposed by the operating system, NFVnice is capable of controlling when network functions should be scheduled. NFVnice improves NF performance by complementing the capabilities of the OS scheduler but without requiring changes to the OS's scheduling mechanisms. Our controlled experiments show that NFVnice provides the appropriate rate-cost proportional fair share of CPU to NFs and significantly improves NF performance (throughput and latency) by reducing wasted work across an NF chain, compared to using the default OS scheduler. NFVnice achieves this even for heterogeneous NFs with vastly different computational costs and for heterogeneous workloads.

Lifetime-Aware Backpressure—A New Delay-Enhanced Backpressure-Based Routing Protocol

Dynamic backpressure is a highly desirable family of routing protocols known for their attractive mathematical properties. However, these protocols suffer from a high end-to-end delay making them inefficient for real-time traffic with strict end-to-end delay requirements. In this paper, we address this issue by proposing a new adjustable and fully distributed backpressure-based scheme with low queue management complexity, named Lifetime-Aware Backpressure (LTA-BP). The novelty in the proposed scheme consists in introducing the urgency level as a new metric for service differentiation among the competing traffic flows in the network. Our scheme not just significantly improves the quality of service provided for real-time traffic with stringent end-to-end delay constraints, but interestingly protects also the flows with softer delay requirements from being totally starved. The proposed scheme has been evaluated and compared against other state-of-the-art routing protocol, using computer simulation, and the obtained results show its superiority in terms of the achieved end-to-end delay and throughput.

A pneumatic sensor for grinding wheel condition monitoring

This paper presents the proof-of-concept of a pneumatic sensor for monitoring the performance of grinding wheels. The system concurrently considers the static and dynamic components of the back pressure signal, which refer to the position and topography of the functional wheel surface, respectively. Auxiliary experiments and numerical simulations are presented to demonstrate that the dynamic back pressure variations do indeed correspond to wheel topographic features. The performance of the sensor is evaluated with respect to wheel dressing, progressive wheel wear and grinding burn. The monitoring capability of the sensor is confirmed to be not compromised by the application of a flood coolant.

Periodic forcing of a shock train in a scramjet inlet-isolator at overspeed condition

Unsteady viscous numerical simulations are performed to explore the response of a shock train to downstream backpressure forcing in a scramjet inlet-isolator at the overspeed condition. A sinusoidal dynamic backpressure is applied at the exit of the isolator, thus leading a forced shock train oscillation. The results show that the shock train travels along a different path for the upstream and downstream movements. There is a clear hysteresis loop during the shock train oscillation. Under the low forcing frequency, the shock train travels in a clockwise loop. While it travels in a counter-clockwise loop under the high forcing frequency. Moreover, there is a lag between the shock train oscillation and the fluctuating backpressure. Especially for the high forcing frequency, the phase of the shock train oscillation is opposite to the fluctuating backpressure. The effects of the amplitude and frequency of the periodic fluctuating backpressure on the oscillation range of the shock train are also investigated. With the amplitude of the fluctuating backpressure increasing, the oscillation range of the shock train increases. With the frequency of the fluctuating backpressure increasing, the oscillation range of the shock train increases first and then decreases under high frequency.

Effects of dynamic backpressure on shock train motions in straight isolator

A numerical study of an oscillating shock train under different types of sinusoidal backpressure in a straight isolator is conducted. In comparison, the shock train location and structure under steady backpressure are explored at first. The results reveal that the shock train moves upstream in a nonlinear way with the increasing backpressure and it keeps nearly the same structure in the process of moving upstream under a certain range of backpressure. Secondly, the typical characteristic of shock train motions under dynamic backpressure is investigated from many aspects. When subjected to sinusoidal backpressure, the shock train undergoes a consistent and repeatable periodic motion, which is similar to the simple harmonic motion. Moreover, the impacts of frequency, amplitude and the average of dynamic backpressure on shock train motions are discussed systematically in this paper. It is found that the average backpressure has a great influence on the location of shock train oscillating region, which moves upstream as the average backpressure is increased. The amplitude of dynamic backpressure has a noticeable effect on the size of shock train oscillating region, which is positively correlated with the amplitude. The frequency affects both the location and size of shock train oscillating region. As the frequency increases, the oscillating region becomes smaller and closer to the exit of the isolator.

Practical Opportunistic Data Collection in Wireless Sensor Networks with Mobile Sinks

Wireless Sensor Networks with Mobile Sinks (WSN-MSs) are considered a viable alternative to the heavy cost of deployment of traditional wireless sensing infrastructures at scale. However, current state-of-the-art approaches perform poorly in practice due to their requirement of mobility prediction and specific assumptions on network topology. In this paper, we focus on low-delay and high-throughput opportunistic data collection in WSN-MSs with general network topologies and arbitrary numbers of mobile sinks. We first propose a novel routing metric, Contact-Aware ETX (CA-ETX), to estimate the packet transmission delay caused by both packet retransmissions and intermittent connectivity. By implementing CA-ETX in the defacto TinyOS routing standard CTP and the IETF IPv6 routing protocol RPL, we demonstrate that CA-ETX can work seamlessly with ETX. This means that current ETX-based routing protocols for static WSNs can be easily extended to WSN-MSs with minimal modification by using CA-ETX. Further, by combing CA-ETX with the dynamic backpressure routing, we present a throughput-optimal scheme Opportunistic Backpressure Collection (OBC). Both CA-ETX and OBC are lightweight, easy to implement, and require no mobility prediction. Through test-bed experiments and extensive simulations, we show that the proposed schemes significantly outperform current approaches in terms of packet transmission delay, communication overhead, storage overheads, reliability, and scalability.

Enhancing the Delay Performance of Dynamic Backpressure Algorithms

For general multi-hop queueing networks, delay optimal network control has unfortunately been an outstanding problem. The dynamic backpressure (BP) algorithm elegantly achieves throughput optimality, but does not yield good delay performance in general. In this paper, we obtain an asymptotically delay optimal control policy, which resembles the BP algorithm in basing resource allocation and routing on a backpressure calculation, but differs from the BP algorithm in the form of the backpressure calculation employed. The difference suggests a possible reason for the unsatisfactory delay performance of the BP algorithm, i.e., the myopic nature of the BP control. Motivated by this new connection, we introduce a new class of enhanced backpressure-based algorithms which incorporate a general queue-dependent bias function into the backpressure term of the traditional BP algorithm to improve delay performance. These enhanced algorithms exploit queue state information beyond one hop. We prove the throughput optimality and characterize the utility-delay tradeoff of the enhanced algorithms. We further focus on two specific distributed algorithms within this class, which have demonstrably improved delay performance as well as acceptable implementation complexity.

Effects of Dynamic Backpressure on Pseudoshock Oscillations in Scramjet Inlet-Isolator

To estimate the effects of combustion-induced backpressure on the pseudoshock oscillation within a scramjet inlet isolator, a computational-fluid-dynamics code was used to study the motions of pseudoshock under different sinusoidal dynamic backpressures. The relations of the pseudoshock oscillation with the pressure histories, standard deviation, and spectral density distributions were explored. Second, the impact of frequency and amplitude of dynamic backpressure on the pseudoshock oscillation was investigated. The results show that the leading edge of the oscillating pseudoshock is not at the place where maximum values of standard deviation and spectral density occur because sinusoidal dynamic backpressure is applied at the exit of the isolator. Moreover, the frequencies of dynamic backpressure have minor influence on the maximum upstream position of the pseudoshock leading edge with the increase of frequency. In comparison, the amplitudes of the dynamic backpressures have great impact on the maximum upstream and downstream locations of the pseudoshock leading edge. It was also revealed that, although the flowfields as well as the locations of pseudoshock leading edge are quite different, the standard deviation and spectral density distributions are nearly the same for the case of sinusoidal backpressure applied.

Trust-based backpressure routing in wireless sensor networks

In this paper, we apply a vector autoregression (VAR) based trust model over the backpressure collection protocol (BCP), a collection mechanism based on dynamic backpressure routing in wireless sensor networks (WSNs). The backpressure scheduling is known for being throughput optimal. In the presence of malicious nodes, the throughput optimality no longer holds. This affects the network performance in collection tree applications of sensor networks. We apply an autoregression based scheme to embed trust into the link weights, so that the trusted links are scheduled. We have evaluated our work in a real sensor network testbed and shown that by carefully setting the trust parameters, substantial benefit in terms of throughput can be obtained with minimal overheads. Our results show that even when 50% of network nodes are malicious, VAR trust offers approximately 73% throughput and ensures reliable routing, with a small trade–off in the end–to–end packet delay and energy consumptions.

A NOVEL ANION-EXCHANGE RESIN SUITABLE FOR BOTH DISCOVERY RESEARCH AND CLINICAL MANUFACTURING PURPOSES

Strong ion-exchange protein chromatography is one of the most powerful and most common steps for protein purification in both discovery research and manufacturing. However, the demands on protein purification of early drug discovery and later stage manufacturing are quite different. In order to shorten the time of developing a purification process for new protein drug candidates, there is a need for a strong ion-exchange resin that will be optimum for both stages. This article details a novel anion-exchange resin suitable for research, as well as for clinical manufacturing. In this study, a novel Q resin anion-exchange prototype was evaluated and compared to the GE Healthcare Q Sepharose® Fast Flow (QFF) and Q Sepharose® High Performance (QHP) resins. This study specifically focused on the following: resolution, dynamic binding capacity, flow rate, back pressure, and scale up. The evaluation was performed in both small- and large-scale experiments. From all the comparable data, the prototype resin is adaptable for both discovery research and manufacturing. Its wide-range operation suitability could potentially shorten the time required to develop conventional purification protocols for clinical manufacturing.

Control Status and Strategy of VOCs from Gasoline Filling Stations in China

Tightness, dynamic back pressure and air to liquid volume ratio (A/L) of vapor recovery system of gasoline filling stations were detected, VOCs was analyzed by GC, in-station diagnostic operation status was inspected by site investigation. The results denoted that the modification of gasoline filling stations was not complete and the installed vapor recovery systems didn’t operate under normal state. Insufficient understanding on vapor recovery control, poor management and unsuitable regulations resulted in these problems. Some solutions such as enhancing the propaganda, making preferential policies, holding training for the connected staffs, maintenance in time, and revising the unsuitable regulations were proposed. This study has positive significance in promoting vapor recovery control developed in China.

Tradeoff Analysis of Delay-Power-CSIT Quality of Dynamic Backpressure Algorithm for Energy Efficient OFDM Systems

In this paper, we analyze the fundamental power-delay tradeoff in point-to-point OFDM systems under imperfect channel state information quality and non-ideal circuit power. We consider the dynamic back- pressure (DBP) algorithm, where the transmitter determines the rate and power control actions based on the instantaneous channel state information (CSIT) and the queue state information (QSI). We exploit a general fluid queue dynamics using a continuous time dynamic equation. Using the sample-path approach and renewal theory, we decompose the average delay in terms of multiple unfinished works along a sample path, and derive an upper bound on the average delay under the DBP power control, which is asymptotically accurate at small delay regime. We show that despite imperfect CSIT quality and non-ideal circuit power, the average power (P) of the DBP policy scales with delay (D) as P = O(Dexp(1/D)) at small delay regime. While the impacts of CSIT quality and circuit power appears as the coefficients of the scaling law, they may be significant in some operating regimes.

A Dynamic Fluid Property Model for the Engineering Design of Hydraulic Dampers

To improve accuracy in the engineering design of hydraulic dampers, a dynamic mathematic model for its working fluid density, viscosity, modulus and stiffness is established. The dynamic flow loss due to volumetric change and pressure leakage is also formulated, wherein the dynamic back pressure in the air chamber is coupled. Simulation results show that most of the fluid properties change obviously when the damper is subjected to external excitations, they are not constant values. The viscosity would drop 74.68% and the flow loss would soar 298.68% with the increase of fluid temperature; the modulus and the stiffness would also drop over 20% when the entrapped air ratio increases, but the density is relatively robust to both variations. The established mathematic model gives a dynamic representation of the fluid property under real service conditions, it has already been applied to the engineering design of several hydraulic damper products in industry, and the effectiveness is validated by pertinent product experiments.

Backpressure-based routing protocol for DTNs

In this paper we consider an alternative, highly agile In this paper we consider an alternative, highly agile approach called backpressure routing for Delay Tolerant Networks (DTN), in which routing and forwarding decisions are made on a per-packet basis. Using information about queue backlogs, random walk and data packet scheduling nodes can make packet routing and forwarding decisions without the notion of end-to-end routes. To the best of our knowledge, this is the first ever implementation of dynamic backpressure routing in DTNs. Simulation results show that the proposed approach has advantages in terms of DTN networks.

Cross-layer scheduling with infrequent channel and queue measurements

The downlink scheduling problem in multi-queue multi-server systems under channel uncertainty is considered. Two policies that make allocations based on predicted channel states are proposed. The first is an extension of the well-known dynamic backpressure policy to the uncertain channel case. The second is a variant that improves delay performance under light loads. The stability region of the system is characterised and the first policy is argued to be throughput optimal. A recently proposed policy of Kar et al has lesser complexity, but is shown to be throughput suboptimal. Further, simulations demonstrate better delay and backlog properties for both our policies at light loads.