Turbocharger surge behavior for sudden valve closing downstream the compressor and effect of actuating variable nozzle turbine

Surge is an unstable phenomenon appearing when a valve closing reduces the compressor flow rate. This phenomenon is avoided for automotive turbochargers by defining a surge margin during powertrain system design. This surge margin established with measurements in steady state testing regime limits the maximal engine torque at low levels of output. An active control of the compressor could reduce the surge margin and facilitate a transient compressor operation for a short time in surge zone. In this paper, an experimental study of the transient operation of a turbocharger compressor entering the surge zone is performed. Control of the turbocharger speed is sought to avoid unsteady operation using the variable geometry turbine (VGT) nozzle actuator. From a given stable operating point, surge is induced by reducing the opening of a valve located downstream of the compressor air circuit. The effect of reducing the speed of rotation by controlling the VGT valve is investigated, as this should lead to more stable compressor operation. The rotation speed of the turbocharger is controlled to avoid an unstable operating point using servo-actuator of variable geometry turbine. From a stable operating point, the surge appearance is caused by closing a butterfly valve downstream the air circuit of the compressor. The effect on the compressor rotation speed when the opening of variable geometry turbocharger valve is modified is studied. Measurements have been conducted for different control profiles of the VGT valve placed downstream the compressor. This article presents the means used to carry out these tests as well as the results of the measurements of the instantaneous signals of pressure, temperature, flow rate and rotation speed, allowing the analysis of the surge phenomenon.

Reduction in DC-Drift in LiNbO3-Based Electro-Optical Modulator

This study involves the results of research on short-term and long-term DC-drifts in electro-optical modulators based on annealed proton exchange waveguides in LiNbO3 crystals after wafer pre-annealing. The relaxation time of the DC-drift of the operating point for a short-term drift is measured in minutes, and for a long-term drift it is measured in hours and days. DC-drift was measured by applying bias voltage and changing crystal temperature. The obtained results show significant impact on the stability of operating point in EO-modulators after treatment of defective structure of the near-surface layer of a LiNbO3 crystal. Treatment of the disturbed near-surface layer of a LiNbO3 crystal results in the simultaneous reduction in short-term DC-drift and increase in operation stability of electro-optical modulators during long-term measurement of temperature by activation energy calculation.

Gas Turbine Compressor Configuration Analysis for Production and Efficiency Optimization at PT Saka Indonesia Pangkah Ltd.

Gas Turbine Compressors are used by Saka Indonesia Pangkah Ltd. in upstream oil and gas facilities either to boost hydrocarbon products to downstream facilities or to lift liquid hydrocarbon as a common artificial method. As production rate declining leads to gas supply deficiency to the compressors, the operating point move to surge line away from the best efficiency point. Gas feed shortage affecting the compressor’s performance which contributed to head and flow capacity. This condition is then calculated and simulated using UNISIM Design Simulator to get optimum configuration results. The simulation was performed at the same gas turbine shaft power output of each compressor. Two cases of centrifugal compressors configuration with different functions and performance are studied. Due to process dynamic conditions, constraint parameter is considered as per desired operating point. This paper also analyses techno-economic aspects between individual and serial pipelines arrangement of the two compressors by evaluating operational data and design calculation. Subsequently, this study produces assessment observations associated with the compressor performance both in individual and serial configuration and eventually analyses the rate of fuel consumption in the gas turbines as the main driver. The case study shows serial arrangement between MPC-1 and GLC with same gas turbine shaft power as individual configuration can reduce fuel consumption up to 47 kg/hr. It saves as much as USD 7,569.96 per day at low demand and USD 7,569.96 at high-demand cases.

Quantitative assessment of the central versus peripheral effect of intravenous clonidine using baroreflex equilibrium diagrams

Clonidine is a first-generation central antihypertensive that reduces sympathetic nerve activity (SNA). Although clonidine also exerts peripheral vasoconstriction, the extent to which this vasoconstriction offsets the centrally mediated arterial pressure (AP)-lowering effect remains unknown. In anesthetized rats (n = 8), we examined SNA and AP responses to stepwise changes in carotid sinus pressure under control conditions and after intravenous low-dose (2 μg/kg) and high-dose clonidine (5 μg/kg). In the baroreflex equilibrium diagram analysis, the operating-point AP under the control condition was 115.2 (108.5–127.7) mmHg [median (25th–75th percentile range)]. While the operating-point AP after low-dose clonidine was not significantly different with or without the peripheral effect, the operating-point AP after high-dose clonidine was higher with the peripheral effect than without [81.3 (76.2–98.2) mmHg vs. 70.7 (57.7–96.9), P < 0.05]. The vasoconstrictive effect of clonidine partly offset the centrally mediated AP-lowering effect after high-dose administration.

Використання візуальних метрик для аналізу стиснення з втратами зашумлених зображень

The subject of the article is to analyze the effectiveness of lossy image compression using a BPG encoder using visual metrics as a quality criterion. The aim is to confirm the existence of an operating point for images of varying complexity for visual quality metrics. The objectives of the paper are the following: to analyze for a set of images of varying complexity, where images are distorted by additive white Gaussian noise with different variance values, build and analyze dependencies for visual image quality metrics, provide recommendations on the choice of parameters for compression in the vicinity of the operating point. The methods used are the following: methods of mathematical statistics; methods of digital image processing. The following results were obtained. Dependencies of visual quality metrics for images of various degrees of complexity affected by noise with variance equal to 64, 100, and 196. It can be seen from the constructed dependence that a working point is present for images of medium and low complexity for both the PSNR-HVS-M and MS-SSIM metrics. Recommendations are given for choosing a parameter for compression based on the obtained dependencies. Conclusions. Scientific novelty of the obtained results is the following: for a new compression method using Better Portable Graphics (BPG), research has been conducted and the existence of an operating point for visual quality metrics has been proven, previously such studies were conducted only for the PSNR metric.The test images were distorted by additive white Gaussian noise and then compressed using the methods implemented in the BPG encoder. The images were compressed with different values of the Q parameter, which made it possible to estimate the image compression quality at different values of compression ratio. The resulting data made it possible to visualize the dependence of the visual image quality metric on the Q parameter. Based on the obtained dependencies, it can be concluded that the operating point is present both for the PSNR-HVS-M metric and for the MS-SSIM for images of medium and low complexity, it is also worth noting that, especially clearly, the operating point is noticeable at large noise variance values. As a recommendation, a formula is presented for calculating the value of the compression control parameter (for the case with the BPG encoder, it is the Q parameter) for images distorted by noise with variance varying within a wide range, on the assumption that the noise variance is a priori known or estimated with high accuracy.

Reduction of DC-drift in LiNbO3-based Electro-optical Modulator

This work involves results of research on short-term and long-term DC-drifts in electro-optical modulators based on annealed proton exchange waveguides in LiNbO3 crystals after wafer pre-annealing. The relaxation time of the DC-drift of the operating point for a short-term drift is minutes, and for a long-term drift, hours and days. DC-drift was measured by applying bias voltage and changing crystal temperature. Obtained results shows significant impact on stability of operating point in EO-modulators after treatment of defective structure of the near-surface layer of a LiNbO3 crystal. Treatment of the disturbed near-surface layer of a LiNbO3 crystal results in twice reduction of short-term DC-drift and increase of operation stability of electro-optical modulators during long-term measurement of temperature by activation energy calculation.