Symmetric Valve Research Articles

Гидравлическое сопротивление системы управления движением инспекционного снаряда с клапаном обтекаемой формы в газопроводе низкого давления

The main problem while developing inspection shells for low-pressure gas pipelines is mainte-nance of their uniform motion under the action of the pumped gas. In the present work, we propose a solution to this problem based on changing the cross-section of the central flow channel of the smart pig by moving an axially symmetric valve along the axis of the channel. Two types of valves with a drop-shaped and a cone-shaped front part were considered. The choice of the valve shape and size can be made by calculating the forces acting on the smart pig during gas flow. The prob-lem was solved by the methods of computational fluid dynamics under the assumption of axial flow symmetry. The gas was considered to be compressible. The calculations showed that the total force acting on the valve and walls of the flow channel does not depend on its shape and, depending on the valve position, can change by more than two times. The optimum length of a drop-shaped valve is nearly half that of a conical valve. Although the drop-shaped valve produces a more inhomoge-neous velocity field than the conical valve, the former is more acceptable for regulating gas flow through the central channel of the inspection smart pig.

Autologous repair of "very asymmetric" bicuspid aortic valves using geometric ring annuloplasty.

Repair of regurgitant bicuspid aortic valves (BAVs) can yield good long-term results and achieve excellent long-term survival.1-3 Favorable results stem from in-depth understanding of BAV anatomy and function. A repair-oriented anatomical classification of BAV has been presented: type A—symmetrical valve with commissural orientation of 180° to 160°; type B—asymmetrical BAV with commissural orientation of 159° to 140°; and type C—“very asymmetrical” BAV with commissural orientation of 139° to 120°.

Analysis and Verification on Energy Consumption of the Quadruped Robot with Passive Compliant Hydraulic Servo Actuator

The hydraulic servo actuator with passive compliance (HPCA) is designed for hydraulically-driven quadruped robots. It is characterized by an accumulator that connects to the piston chamber of the hydraulic cylinder to buffer impact forces between a robot’s feet and the ground. This paper studies the energy efficiency of this actuator in the dynamic locomotion of a quadruped robot. Different from the traditional methods of storing potentially recyclable energy using accumulators, the energy-saving principle of HPCA is to utilize the pressure-transition characteristics of the asymmetric hydraulic cylinder with control of the symmetrical valve. The accumulator can store and release oil during the switching of the transition point in each gait cycle of the robot, thereby improving the energy efficiency of the actuator. The influence of the initial inflation pressure and working volume of the accumulator on the energy efficiency of the HPCA is studied by simulation and physical experiments. The results show that the HPCA has a higher energy efficiency that is independent of the physical parameters of the accumulator.

Repair of bicuspid aortic valve: Simple and effective achievement of symmetric valve orientation

Repair of bicuspid aortic valve: Simple and effective achievement of symmetric valve orientation

Symmetrical valve controlled asymmetrical cylinder based on wavelet neural network

PurposeThe symmetrical valve is usually used in the hydraulic servo control system to control the asymmetrical cylinder, but this system’s structure involves asymmetry, and so its dynamic characteristics are asymmetrical, which causes issues in the control system of symmetric response. The purpose of this paper is to achieve the aim of symmetric control.Design/methodology/approachIn this paper, the authors proposed a method that combined wavelet neural network (WNN) and model reference adaptive control. The reference model determined the dynamic response that the system was expected to achieve, and the WNN adaptive control made the system follow the reference model to achieve the purpose of symmetric control.FindingsThe experimental results show that the method can achieve a more accurate symmetric control and position control compared with the solutions via the classical PID control.Originality/valueThe proposed combination of the WNN and the reference model can effectively compensate for the asymmetry of dynamic response of the asymmetric cylinder in forward and return directions, which can be extended to deal with other classes of applications.

Experiments on Dissimilar Valve Lift (DVL) for Turbulence Increment on a Bi-Fuel Compressed Natural Gas (CNG) Engine

Current engines are readily available for CNG bi-fuel conversions because it requires only minor engine modifications. However, CNG flame speed is lower than gasoline, therefore reducing the power and range of the vehicle when operating on CNG. This situation can be improved by increasing the flame speed via higher turbulence generated by swirl motion. A computational fluid dynamics (CFD) model was used to analyse the swirl generated by dissimilar valve lift (DVL) profiles on the intake valve. A 3D engine simulation shows differences in swirl motion and turbulence between the original symmetric valve lift profile and the DVL. The swirl before combustion was found to increase almost 25%. The higher swirl number can increase the turbulence kinetic energy (TKE) level which improves better fuel mixing. The 1 mm DVL proved to be the better choice from CFD analysis and later was tested on a K3-VE engine. Pressure analysis shows peak pressure increased by 5.6% and burn rate shows CNG had a slower burning speed on the small engine

Research of Electro-Hydraulic Position Servo System Based on PID with Disturbance Observer

According to the characteristics of the electro-hydraulic position servo system of asymmetric hydraulic cylinder controlled by symmetric valve and its performance requirements, the PID controller based on disturbance observer is introduced. The improved controller can observe the equivalent disturbances and introduce the equivalent compensation to the control system, so it can achieve suppression of disturbance. In the MATLAB Simulink environment, the simulation results show that the controller has the very good quick response, the stronger robustness and the higher tracking precision.

大動脈弁の対象、比対称動作による流れの違い

大動脈弁の対象、比対称動作による流れの違い

Characteristics of transonic moist air flows around butterfly valves with spontaneous condensation

Effects of spontaneous condensation of moist air on the shock wave dynamics around butterfly valves in transonic flows are investigated by experimental and numerical simulations. Two symmetric valve disk shapes namely- a flat rectangular plate and a mid-plane cross-section of a prototype butterfly valve have been studied in the present research. Results showed that in case with spontaneous condensation, the root mean square of pressure oscillation (induced by shock dynamics) is reduced significantly with those without condensation for both shapes of the valves. Moreover, local aerodynamic moments were reduced in case with condensation which is considered to be beneficial in torque requirement in case of on/off applications of valves as flow control devices. However, total pressure loss was increased with spontaneous condensation in both the valves. Furthermore, the disk shape of a prototype butterfly valve showed better aerodynamic performances compared to flat rectangular plate profile in respect of total pressure loss and vortex shedding frequency in the wake region.

Bicuspid aortic valve repair by complete conversion from “raphe'd” (type 1) to “symmetric” (type 0) morphology

An anterior cusp with a median raphe and false commissure is the most common bicuspid aortic valve phenotype. The cusp is typically restricted and its annular attachment malpositioned, often resulting in significant aortic regurgitation. A novel valve repair strategy was designed to create a symmetric valve to improve both function and durability. The technique involves converting the valve into a "symmetric" bicuspid valve by resection of the median raphe, with shortening of the anterior cusp's leading edge; resection of the false commissure with complete anterior annular detachment; enlargement, reinforcement, and translocation of the anterior cusp deeper into the left ventricular outflow tract; and valve-sparing aortic root replacement with concomitant annuloplasty. A total of 32 patients with a bicuspid valve, aortic insufficiency, and aortic dilatation have undergone valve repair with root replacement. No operative deaths or strokes occurred, and no permanent pacemakers were required. Thirteen patients underwent complete conversion from "raphe'd" to "symmetric" morphology; the others underwent less complex repairs without translocation. The postoperative transvalvular gradients remained normal. Freedom from grade >1+ aortic regurgitation and valve-related reoperation was 100%. All 13 symmetric conversion patients have continued to have no or trace aortic regurgitation (grade < 1+) at a mean follow-up of 2.9 years (range, 0.4-7). Repair of the common, "raphe'd" bicuspid phenotype by reconfiguration into "symmetric" morphology is both feasible and desirable, regardless of the degree of preoperative aortic regurgitation. This repair strategy appears durable at the mid-term without evolving signs of deterioration or stenosis, offering a potentially superior option over prosthetic root replacement for younger patients.

Research on an Asymmetric Highspeed Pneumatic Servo Valve

This paper describes an asymmetric electro-pneumatic servo valve and hardware compensation approaches for high speed control of rise time and step-down time. The flow capacity of the downstream control orifice of asymmetric valve is about twice of that of the symmetric valve at the same spool displacement. Experimental results show that the bandwidth is 200Hz and rise time is less than 1 ms. The flow capacity of the downstream control orifice of asymmetric valve (337NL/min) is about twice of that of the symmetric valve (171NL/min).

Variation Of Airflow Pattern Through Dissimilar Valve Lift In A Spark Ignition Engine

Bi-fuel conversions are a common alternative fuelling option for mono-fuel gasoline SI vehicles because of the minor vehicle modifications required. In Malaysia, most bi-fuel vehicles are fuelled with compressed natural gas (CNG) and gasoline. However, CNG flame speed is lower than gasoline reducing the power and range of the vehicle when operating on CNG. This situation can be improved by increasing the flame speed via higher swirl generation. A Computational fluid dynamics model is used to analyse swirl generated by dissimilar valve lift (DVL) profiles on the intake valve. A three-dimensional engine simulation shows differences in swirl motion and turbulence between the original symmetric valve lift profile and the DVL. The higher swirl number reduces the turbulence kinetic energy level slightly. The best case profile is selected for further experimental testing.

A Dual-Fuzzy Pressure Compensation Based Symmetric Control Scheme of Single-Rod Electro-Hydraulic Actuator

In hydraulic robots, single-rod electro-hydraulic actuator is widely employed for fast response, small size-to-power ratio, large output force and compact size. The differences of open loop gains and other parameters make the dynamic characteristics of two moving directions asymmetric in symmetric valve controlled asymmetric cylinder system. To ensure robots moving smoothly and improve control precision, a novel pressure compensation based symmetric control scheme is proposed. Pressure feedback algorithm is mathematically proved feasible. Therefore, a displacement and pressure signals fused fuzzy PID controller is designed. Simulation results verify the feasibility and validity for compensating the asymmetric problems.

The Application of All-Autologous Three-Sinus Repair for Supravalvular Pulmonary Stenosis

Various surgical techniques have been proposed for the repair of supravalvular pulmonary stenosis (SVPS) in pediatric populations. Whereas growth potential should be promised, excessive expansion under the presence of undiminished high pulmonary arterial pressure should be avoided. The authors applied all-autologous three-sinus repair, the so-called modified Brom or Myers technique, to SVPS and examined the midterm outcomes. Between March 2010 and March 2012, 15 patients (8 boys) with a median age of 12 months who had SVPS underwent all-autologous three-sinus repair. Of the 15 patients, 13 (87 %) had previously undergone pulmonary artery (PA) banding for treatment of high pulmonary vascular resistance. Two patients (13 %) had Noonan syndrome. A follow-up evaluation was completed for all the patients, and the median follow-up period was 13.5 months (range, 1 month to 2.4 years). No mortalities occurred. The diameter of the stenotic part at the main PA increased from 47.0 ± 14.1 % (range 29.1-70.0 %) of the normal PA diameter at the preoperative evaluation to 108.9 ± 25.7 % (range 58.9-148.1 %) at 6 months, and then to 104.7 ± 11.4 % (range 87.7-134.1 %) 1 year after the operation. The estimated mean pressure gradient across the main PA decreased from 76.2 ± 12.2 mmHg (range 57.8-108.2 mmHg) at the preoperative evaluation to 11.3 ± 12.0 mmHg (range 1.4-49.0 mmHg) at 6 months, and then to 6.4 ± 5.5 mmHg (range 2.0-19.4 mmHg) 1 year after the operation. No patients showed moderate or greater pulmonary insufficiency. The midterm outcomes after supravalvular pulmonary stenosis by all-autologous three-sinus repair were acceptable. Although a long-term follow-up evaluation is mandatory, application of this technique may provide a just enough growth of the reconstructed main pulmonary artery with symmetric pulmonary valve geometry.

The analysis of new hydraulic rolling shear servo system dynamic characteristics

The hydraulic rolling shear whose hydraulic system is researched in this article is designed based on the theory of rolling shear. This article builds the transfer function of the unsymmetrical valve controlling unsymmetrical cylinder system and gets the expressions of the flow gain and the flow pressure coefficients and then compares them with the system controlled by symmetric valve. After the theoretical analysis, this article compares the control effects between the unsymmetrical valve and symmetric valve with the simulation software HYVOS. The simulation declares that when the unsymmetrical cylinder is controlled by the unsymmetrical valve, its control voltage is one-third of that controlled by the symmetric valve. Using unsymmetrical valve to control the unsymmetrical cylinder is perfect and meets the demands of the rolling shears as shown by the data collected from the field.

Influence of non‐Newtonian behavior of lubricant on performance of hole‐entry hybrid journal bearings employing constant flow valve restrictors

Purpose – This paper aims to describe the theoretical study concerning the effect of non‐linear behavior of the lubricant on the performance of symmetric constant flow valve compensated hole‐entry hybrid journal bearing. The bearing performance characteristics have been computed for various values of non‐linearity factor, land width ratio, aspect ratio and external load.Design/methodology/approach – The analysis considers the generalized Reynolds equation governing the flow of lubricant having variable viscosity in the clearance space and equation of flow of lubricant through constant flow valve restrictor. The non‐Newtonian lubricant is assumed to follow the cubic shear stress law.Findings – The study indicates that for generation of accurate bearing characteristics data, the inclusion of non‐linear effects of lubricant in the analysis is essential.Originality/value – The performance characteristics in terms of minimum fluid‐film thickness, fluid‐film stiffness and damping coefficients, critical mass and...

Numerical simulation on a throttle governing system with hydraulic butterfly valves in a marine environment

Hydraulic butterfly valves have been widely applied in marine engineering because of their large switching torque, low pressure loss and suitability for large and medium diameter pipelines. Due to control problems resulting from switching angular speeds of the hydraulic butterfly valve, a throttle-governing control mode has been widely adopted, and detailed analysis has been carried out worldwide on the structural principle concerning speed-regulation and the load torque on the shaft while opening or closing a hydraulic butterfly valve. However relevant reports have yet been published on the change law, the error and the influencing factors of the rotational angular velocity of the hydraulic butterfly valve while opening and closing. In this article, research was based on some common specifications of a hydraulic butterfly valve with a symmetrical valve flap existing in a marine environment. The throttle governing system supplied by the accumulator to achieve the switching of the hydraulic control valve was adopted, and the mathematical models of the system were established in the actual conditions while the numerical simulations took place. The simulation results and analysis show that the rotational angular velocity and the error of the hydraulic butterfly valve while switching is influenced greatly by the drainage amount of the accumulator, resulting in pressure loss in the pipeline, the temperature of hydraulic medium and the load of the hydraulic butterfly valve. The simulation results and analysis provide a theoretical basis for the choice of the total capacity of the accumulator and pipeline diameters in a throttle governing system with a hydraulic butterfly valve. It also determines the type and specification of the hydraulic butterfly valve and the design of motion parameters of the transported fluid.

Analysis of Asymmetric Valve Control Asymmetric Cylinder System of Hydraulic Leveler

Symmetric valve controlled asymmetric cylinder which is applied to force down system of hydraulic leveler. In this case, the flow metering-in is not equal with metering-out universally in proportional or servo control hydraulic system, "pressure jump" will appear at the time of symmetric valve changing direction[1,2]. To deal with this disadvantage well and improve the system, the disadvantage of symmetric valve controlled asymmetric cylinder is altered by the solution that asymmetric valve controlled asymmetric cylinder. In this paper, the mathematic model of the solution has been worked out actually and the transfer function has been constructed. Finally using simulink software of MATLAB to simulate the system and analyze the stability of closed-loop.

Adaptive controller and its application in force system of asymmetric cylinder controlled by symmetric valve

Partial pressure,system vibration and asymmetric system dynamic performance exit in asymmetric cylinder controller by symmetric valve hydraulic system.To solve this problem in the force control system,model reference adaptive controller is designed using equilibrium point stability theory and output error equation polynomial.The reference model is selected in such a way that it meets the system dynamic performance.Hardware configuration of asymmetric cylinder controlled by asymmetric valve hydraulic system is replaced by intelligent control algorithm,thus the cost is low- ered and easy to application.Simulation results demonstrate that the proposed adaptive control sheme has good adaptive ability and well solves asymmetric dynamic performance problem.The designed adaptive controller is fairly robust to load disturbance and system parameter variation.

APPLICATION OF ERROR POLYNOMIAL THEORY BASED MODEL REFERENCE ADAPTIVE CONTROL IN THE SYSTEM OF ASYMMETRIC CYLINDER CONTROLLED BY SYMMETRIC VALVE

The main idea of adaptive control design theory based on the error polynomial algebra is to make the adaptive control error incline to zero as time passed. It can make the adaptive control system be steady on the basis of the theory of LIAPUNOV A M. An adaptive control method adapted to the asymmetric cylinder hydraulic servo system controlled by symmetric valve is presented to make the output of the system follow the output of the reference model progressively, so that the problems of dynamic performance asymmetry, low accuracy, low stability, narrow bandwidth and big delay are resolved.