Throttling Mechanism Research Articles

Regulation of throttling distribution and characteristic analysis for a microchannel Joule-Thomson (J-T) cooler

Miniature J-T coolers are applied extensively in electronic devices, cryosurgery and infrared detectors. The utilization of microchannels in miniature J-T coolers can induce a noticeable pressure drop through the recuperative structure, leading to modifications in the refrigeration mechanism. This study delves into the performance and coupling mechanism of throttling and heat exchange. Herein, a microchannel cooler with a noticeable throttling effect throughout the refrigeration process serves as a prototype. The mathematical model is proved with the experiments, thereby exposing limitations in the improvement of the throttling mechanism and the thermodynamic process. The analysis reveals that the backflow exhibits a significant pressure reduction (ΔPl); thus, the utilization ratio of the throttling effect is low. Additionally, further optimization of the thermodynamic process is possible by regulating throttling distribution. The performance and coupling mechanism of throttling and heat exchange with constant working conditions are investigated. The findings reveal that an optimal ratio of ΔPl (14.3 %) yields the lowest cold terminal temperature, which is reduced by up to 38.9 K. In this case, the J-T efficiency and the effectiveness of the recuperative process are observed to peak at 56.7 % and 83.8 %, respectively, indicating the optimal use of the throttling effect and interaction effects. The analysis also suggests that the thermodynamic process has been improved.

Investigation on the novel unsteady-liquid thin-walled cutting-edge throttling mechanism incorporated in the rotary valve design for a continuous wave pulse generator

The fundamental principle guiding the structural optimization design of the rotary valve in traditional continuous wave mud pulse generators is the steady-liquid thin-walled cutting-edge throttling mechanism (STCTM). However, due to the rotary valve's high-speed rotation, the muddy liquid's flow assumes an unsteady state. Therefore, this theory struggles to provide additional support for the high-speed design of the rotary valve. To address this issue, utilizing Bernoulli's equation as a foundation and considering three key factors: the unsteady flow of drilling mud, the two-stage constriction of fluid as it passes through the rotary valve, and the time-variant flow coefficient, an improved numerical model of the continuous wave pulse differential pressure signal is derived, and unsteady-liquid thin-walled cutting-edge throttling mechanism (UTCTM) of the rotary valve is revealed. Taking the design of a four-blade sector rotary valve port structure as an example, theoretical analysis and CFD experimental research are conducted based on both the STCTM and UTCTM. The results demonstrate that the simulated differential pressure generated by the rotary valve designed based on the UTCTM agrees more closely with the theoretical differential pressure in peak-to-peak value, indicating that the UTCTM better reflects the objective laws associated with continuous wave pulse differential pressure generation. This finding enriches the theoretical foundation for optimizing high-speed mud pulse pulser design and has significant applications in various engineering fields.

Effect of crossflow impinging type throttling mechanism on combustion characteristics of a strut-based scramjet combustor

Efficient mixing of fuel-air, improved combustion performance, and flame stabilization are the critical events for the successful operation of scramjets that must be realized within the short residence time. One of the significant concerns is flame blow-off during the start-up stage even with the presence of the flame holders. To counter it, an innovative mechanism of air-throttle injection has been proposed and investigated through computational fluid dynamics in the present study. In the proposed mechanisms, a strut is used as a base flame holder, and a provision is made to inject the air in the transverse direction behind the strut's base. Two- and three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations have been solved using the k-ω SST turbulence model for reacting and non-reacting flows. A finite-rate/eddy-dissipation combustion model is selected to include the effects of turbulence-chemistry interaction. It was observed from the simulations that the impingement of hydrogen jet and the transverse throttled jet generates the vortices and recirculation zones. Improved fluid-dynamics associated with the impinging action of the air-throttle has been studied by considering argon as a surrogate for air; also, the enriched oxygen (due to air throttling) around the hydrogen jet makes fuel-air mixture more flammable. These fluid dynamics and chemistry aspects are responsible for the superior performance of air-throttling mechanisms. The proposed mechanism showed 46 % reduction in combustor length to reach the combustion efficiency of more than 95 %. The maximum improvement of mixing efficiency is 48 % observed at downstream of the throttle base over the non-throttled condition. Further the effectiveness of the proposed throttling mechanism is demonstrated to show a promise for holding the flame even at a higher Mach number, i.e., M=4.5. The ignition is achieved at a shorter distance in the air-throttling case, resulting in 28 % reduction in ignition length. The air throttling within the two-shear layer may reduce the ignition delay associated, and the flame can be held immediately downstream of the injector. Additionally, a three-dimensional flow field was also analysed to study the flow characteristics around the transverse jet. In the 3-D flow field, the circulation profiles indicated that the stronger vorticity was generated during the air-throttling than without air-throttling.

Throttling Effect on the Performance and Emissions of a Multi-Cylinder Gasoline Fuelled Spark Ignition Engine

The throttle mechanism, a regulatory technique of engine output, is accompanied by a loss of some energy. The effect of intake air throttling on the performance and emissions of a multi-cylinder spark ignition gasoline engine was experimentally investigated. The engine was coupled to a hydraulic dynamometer equipped with a customized cooling system for both the engine and dynamometer. Experimental tests were performed for various engine speeds and air-fuel ratios at the WOT and POT conditions with optimized ignition timing. The acquired results recorded that a better engine operation could be achieved with WOT in terms of bmep, bsfc, ηb, CO, CO2 and UHC compared to POT. At the same time, the worst trend at WOT was noticed for the NOx concentration due to the higher conversion efficiency of fuel combustion. In terms of engine speed for both WOT and POT conditions, operating at 3000 rpm represents the minima of ϕ, bsfc, CO and UHC; and the maxima of ηb, CO2 and NOx with some fluctuation on both sides of this point. Maximum recorded values of ηb were about 30.55% and 28. 55%, while the minimum values of bsfc were about 274 and 293 g/kW.h for the WOT and POT conditions, respectively. The maximum bmep was obtained at 2500 rpm at WOT and POT conditions with values of about 940 kPa and 904 kPa, respectively. Maximum recorded values of NOx were about 1525 and 977 ppm for the WOT and POT conditions, respectively.

DALock: Password Distribution-Aware Throttling

Large-scale online password guessing attacks are widespread and pose a persistant privacy and security threat to users. The common method for mitigating the risk of online cracking is to lock out the user after a fixed number (K) of consecutive incorrect login attempts. Selecting the value of K induces a classic security-usability trade-off. When K is too large, a hacker can (quickly) break into a significant fraction of user accounts, but when K is too low, we will start to annoy honest users by locking them out after a few mistakes. Motivated by the observation that honest user mistakes typically look quite different from an online attacker’s password guesses, we introduce DALock, a distribution-aware password lockout mechanism to reduce user annoyance while minimizing user risk. As the name suggests, DALock is designed to be aware of the frequency and popularity of the password used for login attacks. At the same time, standard throttling mechanisms (e.g., K-strikes) are oblivious to the password distribution. In particular, DALock maintains an extra “hit count" in addition to “strike count" for each user, which is based on (estimates of) the cumulative probability of all login attempts for that particular account. We empirically evaluate DALock with an extensive battery of simulations using real-world password datasets. In comparison with the traditional K-strikes mechanism, our simulations indicate that DALock offers a superior simulated security/usability trade-off. For example, in one of our simulations, we are able to reduce the success rate of an attacker to 0.05% (compared to 1% for the 3strikes mechanism) whilst simultaneously reducing the unwanted lockout rate for accounts that are not under attack to just 0.08% (compared to 4% for the 3-strikes mechanism).

Study on Downhole Throttling Characteristics of High Water Content Gas

In order not to hinder gas production, we usually hope that the bottom hole effusion can be discharged to the surface with high-pressure natural gas. For the production data of high water content gas wells, the problems of insufficient water content and liquid-carrying capacity affecting gas well production should be considered. Based on the wellbore gas-liquid two-phase pipe flow theory and heat transfer theory, the temperature and pressure coupling prediction model of a high water-bearing gas well is established. Combined with the downhole throttling mechanism and gas-liquid two-phase homogeneous flow theory, the temperature and pressure field distribution model is established. The results show that compared with the Ramey model and Hassan and Kabir model, the temperature and pressure coupling prediction model of high water-bearing gas wells established in this study has the smallest coefficient of variation in the four groups of data tests. Based on this, the effects of different working conditions and choke diameter on downhole throttling characteristics of high water-bearing gas wells are analyzed. The findings of this study are helpful to better predict the wellbore temperature and pressure coupling of high water-bearing gas wells and provide more effective help for the smooth production of gas wells.

Managing surges in online demand using bandwidth throttling: An optimal strategy amid the COVID-19 pandemic

Managing supply chains requires quick access to the enterprise– and customer–facing online network applications and transparency of data across supply chains. While it is challenging to meet the rapidly growing demand for bandwidth to support supply chain applications in the Blockchain era, the COVID-19 pandemic has triggered bandwidth demand surges across all online services such as the internet, content delivery, e-platforms, and social media. A sudden demand surge may impel users to lose their access or have a poor online experience due to bandwidth throttling by their Online Service Providers (OSPs). Earlier work on optimal throttling mechanism under stochastic demand has overlooked such demand surges. In this paper, we recast the user demand to adequately capture the demand surges, such as home bandwidth demand surges during the COVID-19 pandemic. Specifically, we model the user demand as a geometric Lévy (jump–diffusion) process. Within our general setting, we show that it is optimal for the OSP to follow a modified control-band policy that encompasses the existing results as a special case. Our numerical study not only enhances the current insights about the optimal throttling mechanism by including demand surges but also provides new insights concerning the nature of demand surges. For example, our study suggests that OSPs should initiate demand throttling at relatively lower usage levels if the likelihood of having demand surges is high; furthermore, we find that when OSPs are exposed to demand surges with higher intensities, it is optimal for them to wait until the usage level reaches a relatively high level before throttling it.

Gini impurity based NDN cache pollution attack defence mechanism

Name Data Network (NDN) is a futuristic Internet architecture that delivers content based on strategically chosen names and caches content on intermediate routers in the content-delivery path, which is used to fulfill future requests for the same data. In-network caching significantly improves network throughput but also makes NDN vulnerable to revamp security attacks such as cache poisoning, cache pollution, and cache snooping. In this paper, we focused on content pollution attack, in which the attacker disrupts the cache locality by intelligently crafted fake requests. This paper introduce monitor metrics for quantitative anomaly detection of requests and proposed a scheme based on Gini Impurity to detect network under cache pollution attack. The paper also proposed an Interest throttling mechanism based on trust to reinforce network under cache pollution attacks. The proposed scheme is evaluated through various experiments on NdnSIM simulator.

Throttling strategies and optimization of the trigger-less streaming DAQ system in the CBM experiment

The Compressed Baryonic Matter experiment (CBM) operating at high heavy-ion interaction rates of up to 10 MHz excludes conventional, latency-limited trigger architectures. Instead, CBM opted for a trigger-less streaming readout. To be able to operate the experiment at highest interaction rates, despite beam intensity fluctuations introduced by the slow extraction of the SIS 100 synchrotron, a time-based throttling mechanism is investigated. To achieve a high number of complete readout events, different throttling strategies are compared and the throttling algorithms and parameters are optimized.

Peak-Power-Aware Primary-Backup Technique for Efficient Fault-Tolerance in Multicore Embedded Systems

Multicore platforms offer great potential for task-level redundancy to achieve a degree of fault-tolerance/reliability in embedded systems by exploiting the idle cores. However, due to the Thermal Design Power (TDP) constraint, it may not be possible to simultaneously power-on all cores in a multicore chip at the full-throttle (e.g., in ARM's big.LITTLE architecture). Since TDP is the maximum sustainable power that a chip can dissipate safely (as per the specifications given by a chip vendor), violating TDP triggers a performance throttling mechanism (e.g., by lowering the operating voltage and frequency, or by power-gating with task migration) to avoid possible overheating problems. This can significantly affect the timeliness of the system, and hence, represents a serious challenge in using (off-the-shelf) multicore platforms in real-time embedded systems when exploiting it for full-scale reliability. That means only a few tasks can be afforded to run in a fully reliable mode under a given TDP constraint. In this article, at first, we study the power consumption of task-level redundancy running on multicore platforms. Then, to tackle the peak power problem, we propose a novel primary-backup scheme for power-aware scheduling of real-time tasks on core pairs in multicore systems. The proposed scheme aims at removing overlaps of peak power of concurrently executing tasks to keep the power consumption below the chip-level TDP constraint. This would facilitate higher reliability levels within a given power budget. To do this, considering the tasks' power profiles, we propose a task partitioning method along with maximum-peak-power-first (MPPF) and maximum-peak-power-last (MPPL) policies to schedule original and redundant copies of tasks, respectively. Our experiments show that our technique provides up to 50% (on average by 29.5%) peak power reduction compared to state-of-the-art schemes, while providing the same reliability level.

A Real-Time Application of Modified Inductor Coupled KY Converter Topology in Speed Control of E-Bikes

Congested road network and traffic jam lead to vehicle idling and fuel wastage. An E-bike which is a solution to this is often available with Thumb Throttle Mechanism and single speed operation. A motor controller with multiple output voltage levels and Click Throttle Mechanism is presented in this paper which provides variable speed operation, better power utilization and is highly economical. Proposed modified KY converter utilizes the turns ratio of an On-Line Tap Changer (OLTC) to generate multiple output voltages for variable speed commutation. This possess a stable continuous conduction mode throughout its operation and reduced switching transients when compared to the existing topologies. Mutually independent control variables namely turns ratio and duty ratio, are used here for voltage conversion, which facilitates the flexible transition between multiple output voltage levels. A 15 W prototype of the proposed modified inductor coupled KY converter is realized using Arduino Uno Board.

Wasted dynamic power and correlation to instruction set architecture for CPU throttling

Reducing dynamic power consumption is one of the major design goals in modern high-performance processor design. Throttling is a mechanism that reduces dynamic power at the expense of reduced throughput. Instruction profiling can identify a set of instructions suitable for fine-grained throttling without significant performance degradation. In this paper, an Electronic Design Automation (EDA) flow was developed to process pipeline trace at an early stage to identify the bottleneck. Using the developed EDA flow, this work identifies a set of instructions suitable for fine-grained CPU throttling to reduce wasted dynamic power in RISC-V architecture. To rank higher stall causing instructions in the instruction profile, a weight-based system was introduced. It was observed that independent of the workload and type, higher stall causing instructions were repeating across all the benchmark programs. The top 10 instruction profiles for each test suite identify probable throttling clock cycles for each pipeline stage for wasted dynamic power reduction at minimal performance loss. These results are expected to enable researchers to reduce wasted dynamic power by modifying existing architecture and effectively apply throttling mechanism without significant performance degradation.

Failure Analysis of Direct Liquid Cooling System in Data Centers

In this paper, the impact of direct liquid cooling (DLC) system failure on the information technology (IT) equipment is studied experimentally. The main factors that are anticipated to affect the IT equipment response during failure are the central processing unit (CPU) utilization, coolant set point temperature (SPT), and the server type. These factors are varied experimentally and the IT equipment response is studied in terms of chip temperature and power, CPU utilization, and total server power. It was found that failure of this cooling system is hazardous and can lead to data center shutdown in less than a minute. Additionally, the CPU frequency throttling mechanism was found to be vital to understand the change in chip temperature, power, and utilization. Other mechanisms associated with high temperatures were also observed such as the leakage power and the fans' speed change. Finally, possible remedies are proposed to reduce the probability and the consequences of the cooling system failure.

Performance improvement of water-cooled screw chiller under part load operation conditions by the paralleling throttle mechanism

Currently, water-cooled screw chiller is widely applied in commercial and industrial buildings, and the energy consumption of water chiller even could cover 70% of air-conditioning energy consumption in the most adverse operating conditions. Moreover, a number of chillers are running at a low rate under part-load state. In order to reduce the energy consumption of water-cooled screw chillers under part-load state, the paper presents the paralleling throttle mechanism. Through experimental study, under part-load state, it can be found that the by-pass tube diameter ?16 has the most positive effect on the performance of water-cooled screw chiller in four by-pass tube diameters. The oblique access mode is better than the vertical access mode, while the spiral access mode has little influence on the chiller performance. Because of paralleling throttle using, the exergetic loss of the evaporator and chiller is able to be reduced by 3.4%-15.5% and 0-6.7%, respectively. Meanwhile, the coefficient of performance of chiller can be enhanced by 0.2%-1.6%, and discharge temperature can be reduced by 0.4-2.7?C. In addition, the economic and environmental benefits of the advanced water-cooled screw chiller are more evident than the conventional water-cooled screw chiller's.

On the Impacts of Greedy Thermal Management in Mobile Devices

As mobile system-on-chips incorporate multicore processors with high power densities, high chip temperatures are becoming a rising concern in mobile processors. Modern smartphones are limited in their cooling capabilities and employ CPU throttling mechanisms to avoid thermal emergencies by sacrificing performance. Traditional throttling techniques aim at achieving maximum utilization of the available thermal headroom so as to minimize the performance penalty at a given time. This letter demonstrates that such greedy techniques lead to fast elevation of temperature on other system components and cause substantially suboptimal performance over increased durations of phone activity. Through experiments on a commercial smartphone, we characterize the impact of application duration on throttling-induced performance loss and propose quality-of-service (QoS) tuning as an effective way of providing the mobile system user with consistent performance levels over extended application durations. The proposed QoS-aware frequency capping technique achieves up to 56% improvement in performance sustainability.

Bypass Rotary Magnetorheological Damper for Automotive Applications

A novel concept of bypass rotary Magneto-rheological (MR) damper is studied in the automotive suspension application. The proposed design is developed based on a vane-type damper structure with an MR control valve located outside of the damper. The design is intended to enhance the ease of maintenance and to reduce the thermal effect from the coil to the MR fluid. The valve is the key component of the damper that exploits the advance characteristics of MR fluid in which have sensitive rheological properties to magnetic field. The ability of the valve to modify the strength of magnetic field has given an advantage that the valve can be operated without any moving parts. The elimination of these parts in the throttling mechanism of the valve will provide benefit in terms of product lifetime and responsiveness. The main objective of this paper is to elaborate the advantages of the bypass rotary MR damper and to demonstrate the damper performance through force-velocity characteristics. The analytical model of the damper is developed and used in the determination of the force-velocity curves and the equivalent damping coefficients.

Experimental Investigation on Flow Characteristic of Stepped Capillary Tube for Heat Pump Type Air Conditioner with R410A

A stepped capillary tube consisting of two serially connected capillary tubes with different diameters is invented to replace the conventional expansion device. The mass flow rate of refrigerant R410A in stepped capillary tubes with different size were tested. The model of stepped capillary tube is proposed, and its numerical algorithm for tube length and mass flow rate is developed. The experimental results show that the performance comparing between stepped capillary tube system and capillary tube assembly system, the cooling capacity is reduced by 0.3%, the energy efficiency ratio (EER) is equal to each other, the heating capacity is increased by 0.3%, the coefficient of performance (COP) is decreased by 0.3%. That is to say, the performance index of the two kinds of throttle mechanism is almost identical. It indicates that the stepped capillary tube can replace the capillary tube assembly in the R410A heat pump type air conditioner absolutely. The model is validated with experimental data, and the results show that the model can be used for sizing and rating stepped capillary tube.

Automating Stressmark Generation for Testing Processor Voltage Fluctuations

Rapid current changes (large di/dt) can lead to significant power supply voltage droops and timing errors in modern microprocessors. To test a processor's resilience to such errors and determine appropriate operating conditions, engineers generally create manual di/dt stressmarks that have large current variations at close to the power distribution network's resonance frequency to induce large voltage droops. This process is time-consuming and might need to be repeated several times to generate appropriate stressmarks for different system conditions (for example, different frequencies or di/dt throttling mechanisms). Furthermore, generating efficient di/dt stressmarks for multicore processors is difficult because of their complexity and synchronization issues. In this article, the authors measure and analyze di/dt issues on state-of-the-art multicore x86 systems. They present an automated di/dt stressmark generation framework called Audit to generate di/dt stressmarks quickly and effectively for multicore systems.

A throttling mechanism sustaining a hole tone feedback system at very low Mach numbers

AbstractThis study investigates the sound produced when a jet, issued from a circular nozzle or hole in a plate, goes through a similar hole in a second plate. The sound, known as a hole tone, is encountered in many practical engineering situations. Direct computations of a hole tone feedback system were conducted. The mean velocity of the air jet was 10 m s−1. The nozzle and the end plate hole both had a diameter of 51 mm, and the impingement length between the nozzle and the end plate was 50 mm. The computational results agreed well with past experimental data in terms of qualitative vortical structures, the relationship between the most dominant hole tone peak frequency and the jet speed, and downstream growth of the mean jet profiles. Based on the computational results, the shear-layer impingement on the hole edge, the resulting propagation of pressure waves and the associated vortical structures are discussed. To extract dominant unsteady behaviours of the hole tone phenomena, a snapshot proper orthogonal decomposition (POD) analysis of pressure fluctuation fields was conducted. It was found that the pressure fluctuation fields and the time variation of mass flows through the end plate hole were dominantly expressed by the first and second POD modes, respectively. Integrating the computational results, an axisymmetric throttling mechanism linking mass flow rates through the hole, vortex impingement and global pressure propagation, is proposed.

Modular Design of Artificial Tissue Homeostasis: Robust Control through Synthetic Cellular Heterogeneity

Synthetic biology efforts have largely focused on small engineered gene networks, yet understanding how to integrate multiple synthetic modules and interface them with endogenous pathways remains a challenge. Here we present the design, system integration, and analysis of several large scale synthetic gene circuits for artificial tissue homeostasis. Diabetes therapy represents a possible application for engineered homeostasis, where genetically programmed stem cells maintain a steady population of β-cells despite continuous turnover. We develop a new iterative process that incorporates modular design principles with hierarchical performance optimization targeted for environments with uncertainty and incomplete information. We employ theoretical analysis and computational simulations of multicellular reaction/diffusion models to design and understand system behavior, and find that certain features often associated with robustness (e.g., multicellular synchronization and noise attenuation) are actually detrimental for tissue homeostasis. We overcome these problems by engineering a new class of genetic modules for ‘synthetic cellular heterogeneity’ that function to generate beneficial population diversity. We design two such modules (an asynchronous genetic oscillator and a signaling throttle mechanism), demonstrate their capacity for enhancing robust control, and provide guidance for experimental implementation with various computational techniques. We found that designing modules for synthetic heterogeneity can be complex, and in general requires a framework for non-linear and multifactorial analysis. Consequently, we adapt a ‘phenotypic sensitivity analysis’ method to determine how functional module behaviors combine to achieve optimal system performance. We ultimately combine this analysis with Bayesian network inference to extract critical, causal relationships between a module's biochemical rate-constants, its high level functional behavior in isolation, and its impact on overall system performance once integrated.