Fluid-Structure Interaction in Problems of Patient Specific Transcatheter Aortic Valve Implantation with and Without Paravalvular Leakage Complication

Paravalvular Leakage(PVL)has been recognized as one of the most dangerous complications in relation to Transcathether Aortic Valve Implantation(TAVI)activities.However,data available in the literature about Fluid Structure Interaction(FSI)for this specific problem are relatively limited.In the present study,the fluid and structure responses of the hemodynamics along the patient aorta model and the aortic wall deformation are studied with the aid of numerical simulation taking into account PVL and 100%TAVI valve opening.In particular,the aorta without valve(AWoV)is assumed as the normal condition,whereas an aorta with TAVI 26 mm for 100%Geometrical Orifice Area(GOA)is considered as the patient aorta with PVL complication.A 3D patient-specific aorta model is elaborated using the MIMICS software.Implantation of the identical TAVI valve of Edward SAPIEN XT 26(Edwards Lifes ciences,Irvine,California)is considered.An undersized 26 mm TAVI valve with 100%valve opening is selected to mimic the presence of PVL at the aortic annulus.The present research indicates that the existence of PVL can increase the blood velocity,pressure drop and WSS in comparison to normal conditions,thereby paving the way to the development of recirculation flow,thrombus formation,aorta wall collapse,aortic rupture and damage of endothelium.

PILOT LEAKAGE'S INFLUENCES ON THE PERFORMANCES OF EXTRA HIGH PRESSURE PROPORTIONAL PNEUMATIC VALVE

A mathematic model is built up to analyze the influences of a pilot valve'sleakage on the performances of pneumatic pressure proportional valve, and the performances aresimulated by using MATLAB. The results indicate that using slide pilot valve in the valve system isfeasible, but the leakage's influences can not be neglected, especially it may induce instability ina low output pressure situation. A pilot valve using too large throttle window will cause the valveoscillate. To improve the working condition of pilot valve, a method adopting different widths oftwo throttle window is proposed. According to our simulation, this method balances the pressure dropbetween the two stage throttle ports, and reduces the influences of pilot valve's leakage.

A novel adaptive backstepping design of turbine main steam valve control

The problem of transient stability for a single machine infinite bus system with turbine main steam valve control is addressed by means of a novel adaptive backstepping method in this paper.The recursive design procedure of the proposed controller is much simpler than that of the existing controller based on conventional adaptive backstepping method.In the system,the damping coefficient is measured inaccurately,and the reactance of transmission line also contains a few uncertainties.A nonlinear robust controller and parameter updating laws are obtained simultaneously.The system does not need to be linearized,and the closed-loop error system is guaranteed to be asymptotically stable.The design procedure and simulation results demonstrate the effectiveness of the proposed design.

Adaptive H-infinity control of synchronous generators with steam valve via Hamiltonian function method

Based on Hamiltonian formulation, this paper proposes a design approach to nonlinear feedback excitation control of synchronous generators with steam valve control, disturbances and unknown parameters. It is shown that the dynamics of the synchronous generators can be expressed as a dissipative Hamiltonian system, based on which an adaptive H-infinity controller is then designed for the systems by using the structure properties of dissipative Hamiltonian systems. Simulations show that the controller obtained in this paper is very effective.

Study on Valve Management of DEH for Steam Turbine

Valve management is one of the major functions of DEH for steam turbine. It has an important practical significance for the security and economy of the steam turbine. This paper starts from the valve configuration figure of the domestic-type 300 MW steam turbine, and then makes a simple comparison between the two types of valve governing modes. In order to realize the valve control, the structure of control system has been established, in which the roles of the mathematical functions are discussed. On the basis of the experiment of valve flow characteristic, this article carries out a quantitative study on the functions of the valve management and the parameter tuning method. Through a serious corrections, the sequence valve flow characteristic curve is obtained, which can provide significant guidance on the research of valve management of the similar steam turbines.

A new adaptive backstepping method for nonlinear control of turbine main steam valve

A new approach for nonlinear adaptive control of turbine main steam valve is developed. In comparison with the existing controller based on ＂classical＂ adaptive backstepping, this method does not follow the classical certaintyequivalence principle in the design of adaptive control law. We introduce this approach, for the first time, to power systems and present a novel parameter estimator and dynamic feedback controller for a single machine infinite bus （SMIB） system with steam valve control. This system contains unknown parameters such as reactance of transmission lines. Besides preserving useful nonlinearities and the real-time estimation of uncertain parameters, the proposed approach possesses better performances with respect to the response of the system and the speed of adaptation. The simulation results demonstrate that the proposed approach is better than the design based on ＂classical＂ adaptive backstepping in terms of properties of stability and parameter estimation, and recovers the performance of the ＂full-information＂ controller. Hence, the proposed method provides an alternative for engineers in applications.

Research on gas leakage through suction valves of reciprocating compressor under varying load conditions

A research concerning the coupling conditions of gas leakage through suction valves and capacity regulation is performed in an industrial reciprocating compressor.Both internal flow and thermodynamic characteristic are discussed in detail.The results show that the capacity of compressor can be regulated steplessly by controlling suction valve closure moment.And then the quantitative relationship between the capacity load and the closing angle of suction valve is revealed.The capacity load and valve leakage rate show obvious different features in P-V diagrams,which makes it easier to define appropriate features for detecting cracked or broken reciprocating compressor valves under varying load conditions.A set of curves of compression work and discharge gas mass are obtained and a method for rating thermal performance of a compressor is presented using these curves.

Nonlinear Steam Valve Adaptive Controller Design for the Power Systems

Considering generator rotor and valve by external disturbances for turbine regulating system, the nonlinear large disturbance attenuation controller and parameter updating law of turbine speed governor system are designed using backstepping method. The controller not only considers transmission line parameter uncer-tainty, and has attenuated the influences of large external disturbances on system output. The nonlinear con-troller does not have the sensitivity to the influences of external disturbances, but also has strong robustness for system parameters variation, which is because of the transmission line uncertainty being considered in internal disturbances. The simulation results show that the control effect of the large disturbance attenuation controller more advantages by comparing with the control performance of conventional nonlinear robust controller.

Optimization of the Open Degree of Key Valves Based on Relative Entropy and Pipeline Leakage

Based on information entropy theory, the definition of relative entropy, and the relative entropy minimum principle, this study establishes a multi-objective optimization model for a key valve opening of an urban water distribution network(WDN). Each node pressure is taken as the main research object to reduce pipeline leakage. Moreover, genetic algorithm is applied in the proposed model to solve the key valve opening of the actual WDN in a city in southern China. Using the proposed model, the relevant decision variables of a WDN can be optimized to provide a new manner of network dispatching.

Numerical Simulation and Experimental Study of Heat-fluid-solid Coupling of Double Flapper-nozzle Servo Valve

The double flapper-nozzle servo valve is widely used to launch and guide the equipment. Due to the large instantaneous flow rate of servo valve working under specific operating conditions, the temperature of servo valve would reach 120℃ and the valve core and valve sleeve deform in a short amount of time. So the control precision of servo valve significantly decreases and the clamping stagnation phenomenon of valve core appears. In order to solve the problem of degraded control accuracy and clamping stagnation of servo valve under large temperature difference circumstance, the numerical simulation of heat-fluid-solid coupling by using finite element method is done. The simulation result shows that zero position leakage of servo valve is basically impacted by oil temperature and change of fit clearance. The clamping stagnation is caused by warpage-deformation and fit clearance reduction of the valve core and valve sleeve. The distribution roles of the temperature and thermal-deformation of shell, valve core and valve sleeve and the pressure, velocity and temperature field of flow channel are also analyzed. Zero position leakage and electromagnet＇s current when valve core moves in full-stroke are tested using Electro-hydraulic Servo-valve Characteristic Test-bed of an aerospace sciences and technology corporation. The experimental results show that the change law of experimental current at different oil temperatures is roughly identical to simulation current. The current curve of the electromagnet is smooth when oil temperature is below 80℃, but the amplitude of current significantly increases and the hairy appears when oil temperature is above 80℃. The current becomes smooth again after the warped valve core and valve sleeve are reground. It indicates that clamping stagnation is caused by warpage-deformation and fit clearance reduction of valve core and valve sleeve. This paper simulates and tests the heat-fluid-solid coupling of double flapper-nozzle servo valve, and the obtained results provide the reference value for the design of double flapper-nozzle force feedback servo valve.

Fluid-solid coupling numerical simulation of charge process in variable-mass thermodynamic system

A joint solution model of variable-mass flow in two-phase region and fluid-solid coupling heat transfer,concerned about the charge process of variable-mass thermodynamic system,is built up and calculated by the finite element method(FEM).The results are basically consistent with relative experimental data.The calculated average heat transfer coefficient reaches 1.7×105 W/(m2·K).When the equal percentage valve is used,the system needs the minimum requirements of valve control,but brings the highest construction cost.With the decrease of initial steam pressure,the heat transfer intensity also weakens but the steam flow increases.With the initial water filling coefficient increasing or the temperature of steam supply decreasing,the amount of accumulative steam flow increases with the growth of steam pressure.When the pressure of steam supply drops,the steam flow gradient increases during the maximum opening period of control valve,and causes the maximum steam flow to increase.

Numerical Study on Flow-induced Noise for a Steam Stop-valve Using Large Eddy Simulation

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Nonlinear variable structure excitation and steam valving controllers for power system stability

A set of novel nonlinear variable structure excitation and steam-valving controllers are proposed in this paper. On the basis of the classical dynamic equations of a generator, excitation control and steam valving control are simultaneously considered. Design of these controllers combines the differential geometry theory with the variable structure controlling theory. The mathematical model in the form of ＂an affine nonlinear system＂ is set up for the control design of a large-scale power plant. The dynamic performance of the nonlinear variable structure controllers proposed for a single machine connected to an infinite bus power system is simulated. Simulation results show that the nonlinear variable structure excitation and steam-valving controllers give satisfactory dynamic performance and good robustness.

Experimental Verification of Fault Predictions in High Pressure Hydraulic Systems

In this paper a model of a high pressure hydraulic system was developed to simulate the effect of increased internal leakages inside the hydraulic cylinder and the 4/2 way directional control valve and to calculate the main parameters of the hydraulic system under various loads through the use of leakage-simulating throttle valves. After the completion of modeling, the throttle valves that simulate the internal leakages were calibrated and a number of test runs were performed for the cases of normal operation and the operation with increased internal leakages. The theoretical predictions were compared against the experimental results from an actual hydraulic test platform installed in the laboratory. In all cases, modeling and experimental data curves correlate very well in form, magnitude and response times for all the system’s main parameters. This proves that the present modeling can be used to accurately predict various faults in hydraulic systems, and can thus be used for proactive fault finding in many cases, especially when the defective component is not easily detected and obvious at first sight.

Energy Saving Technology for Lowering Air Leakage of Sintering Pallets and Dust Collectors in Sinter Plant

The hot-wire type anemometers were used for measuring the velocity of effective air flowing through sinter bed in this study.Meanwhile,microphones were installed beside the pathway and close to the outer sidewall of travelling pallets for monitoring sound pressure generated by an abnormal air leakage.For identifying the passing pallet,a thermal-resistant type RFID technology was adopted.Based on the measured data via anemometers,the air leakage rate of sintering machine was calculated with the mass balance method,and pallets with the abnormal leakage can be detected and ranked in the severity of leakage from the measured sound pressure with the relevant criteria.In addition,for examining the leakage situation,this study set up a capillary type of differential pressure gauge to double cone valve(DCV)below the electrostatic precipitator(EP)in sintering plant for collecting the larger dust.The criteria of determining leaked DCV and the patterns for replacing the DCV were proposed to develop a detecting and predicting system on the air leakage into dust collectors of sinter machine.It offered field staff a basis of maintaining or renewing DCV via a warning reminding and reducing air leakage to increase EP efficiency for avoiding the dust emission from the stack.These technologies had been implemented in the sintering plants of China Steel Corporation,and they can effectively reduce the air leakage rate by5%at least and further decrease the electricity consumption of the suction fan and coke rate,increase the production for the sintering machine.

An experimental study on flowrate and stability for 600MW supercritical steam-turbine control valve

An experimental study on flowrate and stability of a type of control valve of 600MW supercritical steam-turbine was presented by measuring instruments of static, dynamic pressure and vibration in self-designed test rig. The investigation shows that flow coefficient is 30% up more than that of the control valve of GX-1 type used widely in domestic power plants now, as small-medium lifts. If the relative lift (h/D) is less than 20%, the valve can always work steadily in all the pressure ratios. When the h/D is between 20% to 24%, big vibration of valve stem occurs if the pressure ratio is between 0.7 to 0.8. When h/D is more than 25%, relatively great vibration happens in a wide range of pressure ratios of 0.4 to 0.85.

水汽系统积盐问题分析及处理

尿素水解制氨技术已广泛应用于火电机组脱硝还原剂的制备。然而,若出现尿素质量不合格,尿素水解器发生泄漏以及水解器疏水回用至凝汽器的情况,会对热力系统造成巨大危害。对某燃煤机组尿素水解器泄漏致水汽系统严重积盐及过热器爆管进行了分析,并提出了补充处理方案。实施后机组各项水汽指标均达到《火力发电机组及蒸汽动力设备水汽质量》(GB/T 12145—2016)要求,为水汽系统积盐的原因分析及处理提供了解决方案。

绥中880MW汽轮机阀门进汽方式优化

绥中880MW机组虽进行过现代化通流改造,但调节阀、进汽机构及控制形式并未改造,仍沿用原单阀运行模式,对机组效率影响较大。通过优化阀门开启顺序、优化流量曲线重叠度并进行大量轴承载荷理论计算,对阀门不同进汽方式进行优化研究,推荐合理运行方式,解决单阀一直无法切换问题,达到了预期效果,提高了经济性,在同类机组中具有较高的应用推广价值。

拖拉机多路阀节流槽动态特性研究与试验

为优化部分拖拉机多路阀流量特性、减小压差等问题,设计一种具有U-半圆形节流槽结构的拖拉机多路阀,通过仿真试验研究U-半圆形节流槽拖拉机多路阀的动态特性。结果表明:U-半圆形节流槽出口流量呈现先小后大再小的特点。多路阀出口稳态流量为113 L/min,流量变化稳定无冲击,控制特性好。制定U-半圆形节流槽拖拉机多路阀试验方案,通过试验得出阀口压差随着阀芯位移的增大而减小,阀口最小压差为1.2 MPa;测得多路阀最大泄漏量为10.5 mL/min,满足泄漏指标。从而验证U-半圆形节流槽多路阀流量变化稳定,内泄漏量小。

核电主蒸汽阀站中电磁先导阀的动态响应仿真研究

针对核电主蒸汽阀站中关键部件之一——大气释放阀前置隔离阀在实际工况中常出现响应超时的问题,采用数值仿真软件Fluent中的动网格以及用户自定义函数技术,对控制其启闭过程的电磁先导阀动态响应过程进行了研究。首先,研究了电磁先导阀中先导结构的动态响应过程以及阀杆的受力情况;然后,研究了电磁先导阀中主阀的动态响应过程以及主阀泄压时阀内的压力和速度分布情况;最后,综合两个动态过程,分析了电磁先导阀整阀的运动时间。研究结果表明,电磁先导阀的运动时间为8.5 ms,其中先导结构的运动时间占比较小,85%的时间集中在电磁先导阀主阀动作过程。该研究结果可对前置隔离阀响应时间的优化提供参考。