Rod Speed Research Articles

Multi-Physical Field, Coupled, Mixed Lubrication Analysis of Hydraulic Reciprocating Vacuum Lip Seal

Engineering practice has demonstrated that seal failure can result in severe leakage and wear, reducing the efficiency of hydraulic systems and even leading to major safety risks. Currently, analyses of the thermal aspect of seal interfaces are relatively limited, with most studies focusing on mechanical analysis. However, in actual applications, temperature has a significant impact on sealing performance. In this paper, nonlinear elastomechanics, viscous fluid mechanics, micro-contact mechanics, micro-deformation theory, and thermodynamics are coupled to establish a mixed lubrication model considering the thermal effect. The reliability of the mixed lubrication model is verified through experiments, and the temperature distribution of the oil film in the sealing area and the temperature distribution of the seal ring are simulated. Finally, the effects of the reciprocating speed, root mean square roughness, fluid medium pressure, and seal pre-compression on seal friction force and leakage are investigated. The results show that the heat generated in the sealing area accumulates at the bottom of the V-ring. Under the same conditions, compared with the instroke, the temperature-rise area of the outstroke is biased to the left and the increase in temperature is greater. In addition, the piston rod speed and the preliminary compression of the seal ring have a greater impact on the overall seal friction force and leakage. Under a lower seal pre-compression, the RMS roughness has a great influence on the leakage and friction in the outstroke, while the impact of the internal stroke is limited.

Thermoelastohydrodynamic Mixed Lubrication of Combined Rod Seals Operating at High Pressures and Speeds: Mathematical Modeling and Numerical Analysis

Abstract Thermoelastohydrodynamic (TEHD) mixed lubrication characteristics of a step-combined rod seal under high-pressure and high-speed conditions are analyzed in this article. A novel TEHD mixed lubrication model for combined rod seals is innovatively established from the perspective of “seal-film-rod” system for the first time. Parameterized studies are conducted to evaluate the thermal effect on seal behavior with the comparison of isothermal elastohydrodynamic (EHD) lubrication analysis. Numerical results show that the interface friction heat is quite remarkable and mainly concentrated on the sealing lip, especially in high pressure and speed cases. With the increasing sealed pressure or rod speed, the temperature rise becomes more obvious and has a more significant impact on the sealing performance. The excessively rising temperature will even exceed the melting point of the sealing material, causing thermal damage.

Study on The Rotational Steady-state Dynamics of Viscous Thin Film Fluids

The study of viscous thin film fluid rotation can be applied to a variety of fields, including rotational coating, rotational casting, rotational molding, and the paper industry. In this paper, the parameters affecting the viscous thin film fluid on a rotating rod and the trend of these parameters on the fluid motion and steady state are investigated. The analytical solution of the tangential velocity Uh at steady state of the thin film fluid is solved based on the Nusselt tilted plate thin film fluid model, and the conditions for the fluid attached to the rotating rod to maintain steady state are obtained. The steady state of the fluid at different rotational speeds is simulated using COMSOL and compared with experiments to verify the accuracy of the theoretical model. Then the effects of rotating rod speed, rotating rod diameter and rotating rod friction factor on the steady state, time and attachment of the thin film fluid were investigated experimentally, and the influence trends of each parameter were summarized by three-sample interpolation.

Design and Development of Neutronics and Thermal Hydraulics Modeling Code for ACP1000 Nuclear Reactor Dynamics in LabVIEW

An advanced neutronics and thermal hydraulics nuclear code, called GNTHACP code, is designed and developed in LabVIEW as Graphical Neutronics and Thermal Hydraulics toolkit for 1100 MWe Advanced Chinese PWR (ACP-1000) nuclear power plant. The reactor neutronics model is developed using a nonlinear point reactor kinetics model, while, the reactor thermal hydraulics model is developed based on nonlinear fuel and coolant temperature dynamics. The heart of the GNTHACP code is the control rod reactivity model. Control rod reactivity banks are comprised of four power compensation banks G1, G2, N1, N2 and one temperature compensation bank R. The reactivity control configuration of these banks is highly nonlinear, complex and challenging in nature. The control rod reactivity model as a function of G1, G2, N1, N2 and R banks is optimized using two distinct techniques. The control rod reactivity model is optimized using Simplex Linear Programming (SLP) technique under constraints of reactor power as safety limit and control rod speed as maximum speed limit in LabVIEW. The control rod reactivity model is also optimized and investigated using nonlinear Sequential Quadratic Programming (SQP) technique under same constraints in LabVIEW. All the models are integrated and the state-of-the-art virtual instruments (VIs) are designed for cost function optimization, configuring models and calibration of model parameters in LabVIEW. The integrated model as graphical coupled neutronics and thermal hydraulics modeling code is optimized and validated against the Final Safety Analysis Report (FSAR) and different parameters of interest are investigated and proved within design limits as reported with CORCA and CORTH benchmark nuclear codes. The proposed code is stable, highly efficient and accurate as compared to other nuclear codes.

Определение конструктивных параметров интенсификатора и условия выталкивания клубня из зазора между прутками сепарирующих элеваторов

Machine potato harvesting is ineff ective on waterlogged soils at a moisture content of more than 24% as rod gaps are clogged with rocks and tubers. The potato harvester design can be improved with an intensifi er in the form of a clamping conveyor with fl at blades set at an angle. The authors analyzed the conditions for ejecting tubers from the rod gaps of the separating elevators and determined the design parameters of the intensifi er: the distance between the bars of 30 mm, the diameter of the bars of 11 mm; the inclination angle of the intensifi er blade to the plane of the conveyor belt of more than 82°. Provision is made that when the tubers are pushed out, the gap between the rod and the tuber should be less than 5 mm. Based on the goal of increasing the completeness of soil separation and excluding damage to potato tubers, theoretical studies have established the kinematic parameters of the intensifi er: a conveyor speed of 0.8 m/s to 1.4 m/s, an elevator rod speed of 1.0 m/s to 1.8 m/s. To prevent tuber damage, the impact velocity of potato tubers with the blades must be less than 2.2 m/s. The blade pitch should equal 210 mm. Agrotechnical assessment of fi eld tests of the KPK-2-01 potato harvester with a separating elevator intensifi er carried out on the premises of the “V.D. Bykov’s Raduga Farm” located in Kamyshi, Kursk district, Kursk region, showed an increase in the completeness of soil separation by 8.3%

Numerical and Experimental Study of Reciprocating Seals in Seawater Hydraulic Variable Ballast Components for 11000m Operation

Seawater hydraulic variable ballast system (SHVBS) is critical equipment for underwater operations. Reciprocating seals play a vital role in the efficiency and safety of seawater hydraulic components working in SHVBS. However, the sealing performance and friction behavior of reciprocating seals remain unknown under high isostatic and water lubricating conditions. In this work, an innovative mixed lubrication model for reciprocating water hydraulic rod seals is developed based on the elastohydrodynamic lubrication (EHL) theory. An elastic deformation method is introduced to update the film thickness rapidly. The characteristics of the reciprocating seal are studied in a full-ocean-depth pressure range. With the rod speed of 500 mm/s, for sealed pressure of 0.1 MPa and 120 MPa, the maximum friction force increases tenfold from about 30 N to 300 N. A test rig is designed to measure friction force under high pressure. The numerical and experimental results have the same variation pattern, and the relative error is less than 15%.

Pneumatic cylinder speed and force control using controlled pulsating flow

An application for accurate and low-cost force and velocity control of a pneumatic actuator, which can be used in any pneumatic circuit, is described in this paper. Control of a pneumatic cylinder is proposed via a pulsating flow technique. The technique uses on/off solenoid coils in the direction control valves in lieu of expensive servo controllers, such as proportional directional control valves. Pulsating air frequencies of 1.5, 3, and 4.5 Hz are applied by the designed circuit to investigate inlet constant pressures ranging from 1.72 to 5.17 × 105 Pa. The speed and force of a pneumatic cylinder rod are controlled using the generated pulsating flow and the results show success of idea of ​​controlling the speed and force of the pneumatic cylinder rod using the pulse flow technique. Empirical correlations suitable for later use in automatic control circuits are derived and are shown to exhibit an accuracy of up to ∼ 90–95.5% in predicting output force and velocity. It is also used to select the required frequency to obtain the speed and force required for the cylinder. To validate the pneumatic cylinder speed and force control using pulse flow technique, simulations are carried out using the Automation Studio program. The results show an improvement in control of the pneumatic cylinder mechanical performance and demonstrate that improvements are a function of the frequency of compressed air source pulses and pressure. An empirical correlation is also derived for predicting the cylinder rod speed and force at any source pressure and pulse frequency.

Forecasting Piston Rod Seal Failure Based on Acoustic Emission Features in ARIMA Model

Fluid leakage due to piston rod seal failure in hydraulic cylinders results in unscheduled maintenance, machine downtime and loss of productivity. Therefore, it is vital to understand the piston rod seal failure at initial stages. In literature, very few attempts have been made to implement forecasting techniques for piston rod seal failure in hydraulic cylinders using acoustic emission (AE) features. Therefore, in this study, we aim to forecast piston rod seal failure using AE features in the auto regressive integrated moving average (ARIMA) model. AE features like root mean square (RMS) and mean absolute percentage error (MAPE) were collected from run-to-failure (RTF) tests that were conducted on a hydraulic test rig. The hydraulic test rig replicates the piston rod movement and fluid leakage conditions similar to what is normally observed in hydraulic cylinders. To assess reliability of our study, two RTF tests were conducted at 15 mm/s and 25 mm/s rod speed each. The process of seal wear from unworn to worn state in the hydraulic test rig was accelerated by creating longitudinal scratches on the piston rod. An ARIMA model was developed based on the RMS features that were calculated from four RTF tests. The ARIMA model can forecast the RMS values ahead in time as long as the original series does not experience any large shifts in variance or deviates heavily from the normal increasing trend. The ARIMA model provided good accuracy in forecasting the seal failure in at least two of four RTF tests that were conducted. The ARIMA model that was fitted with 15 pre-samples was used to forecast 10 out of sequence samples, and it showed a maximum moving absolute percentage error (MAPE value) of 28.99 % and a minimum of 4.950 %. The forecasting technique based on ARIMA model and AE features proposed in this study lays a strong basis to be used in industries to schedule the seal change in hydraulic cylinders.

Theoretical and experimental research on damping characteristics of CDC shock absorber

CDC (Continuous Damping Control) shock absorber is the typical representative of the stepless valve-controlled type, which has the advantages of low cost and stable performance. Based on the throttling characteristics of the CDC valve, the damping force mathematical model of the CDC shock absorber is established. Through simulation analysis, the indicator characteristics and speed characteristics of the CDC shock absorber under different input currents and speeds are obtained. A CDC shock absorber testbed is built to study damping characteristics, and the results are compared with the simulation results. The results show that the indicator diagram obtained by simulation and experiment is smooth without distortion, and the speed characteristic diagram is smooth without a large mutation point. The experimental values of damping force are slightly larger than the simulation values. The relative error between the simulation data and the experimental data is basically less than 10% and the model has high accuracy. When the input current is the same, the damping force increases with the increase of piston rod speed. When the speed of the piston rod is the same, the damping force of the rebound and compression stroke decreases with the increase of input current.

Dynamic modeling and intelligent hybrid control of pressurized water reactor NPP power transient operation

The pressurized water reactor (PWR) is a combined system of several interdependent subsystems that face uncertainties and consist of critical parameters that initiate potential accidents. Therefore, a PWR needs to be controlled continuously for safe operation over its lifetime. To this end, a particle swarm optimization algorithm (PSO) optimized radial basis function neural network (RBF) proportional integral derivative (PID) control approach (PSO-RBF-PID) is proposed to regulate the PWR power at the desired level. The controller computes the control rod speed to optimize the output power to track the reference value. The performance, sensitivity, and stability of the controller are evaluated. The simulation results verified that the control strategy monitors the PWR power successfully and smoothly under different power levels as compared to the PSO-PID method. This study gives the benefit to apply the PSO-RBF-PID control technique for control applications in other nuclear engineering fields.

Energy recovery from shock absorbers through a novel compact electro-hydraulic system architecture

Riding a road vehicle involves only 10-16% of the fuel energy to overcome the resistance from friction and air drag, while the rest contributes to a massive ecological and economic damage. From an energy balance point of view, a great amount of energy is dissipated as vibrations at the shock absorbers level. In this paper, a hydraulic regenerative shock absorber, able to recover and convert the vibration energy caused by road profiles is designed and manufactured by exploiting off-the-shelf components to reduce R&D costs, and its overall maximum efficiency is measured. The prototype is composed of a twin tube electronically controlled shock absorber and of an electro-hydraulic unit (also called regenerative valve) rigidly connected to it. The main relations ruling the dynamics of a regenerative damper are discussed and the main features of the regenerative valve are designed to comply with size, performance, and safety requirements. Parametric relations are illustrated and properly managed to justify the choice of a dedicated electric motor. Performances are assessed through simulations and experimental tests, while reliability is confirmed through a thermal analysis that reveals no thermal issues. The prototype reaches a maximum overall harvesting efficiency of 11.7% for an intermediate value of the external electric load at a 500mm/s rod speed and a maximum electric power in output of 75W for a high external electric load at 1000mm/s rod speed. Efficiency is strongly hindered at low values of rod speed because of predominant friction effects. It is also demonstrated the possibility to modify the damping curve by varying the electrical characteristics of the circuit connected to the electric machine. The compact design of the RSA, with a mass of only 5.8kg, allows its installation into the suspension of a B-class SUV with a minimum impact on the current damper structure.

Remarks on Modeling the Oil Film Generation of Rod Seals

The oil film generation of a U-cup rod seal and the oil film thickness on the rod after outstroke were analyzed analytically, numerically, and experimentally. The analyzed sealing system consists of an unmodified, commercially available U-cup, a polished rod, and mineral oil. The inverse theory of hydrodynamic lubrication (IHL) and an elastohydrodynamic lubrication (EHL) model—both based on the Reynolds equation for thin lubricating films—were utilized to simulate the oil film generation. In the EHL analysis, physical parameters and numerical EHL parameters were varied. Both the analytical and numerical results for the varied parameters show that the film thickness follows a square-root function (i.e., with a function exponent of 0.5) with respect to the product of dynamic viscosity and rod speed, also referred to as the duty parameter. In comparison to the analytical and numerical results, the film thickness obtained via ellipsometry measurements is a function of the duty parameter with an exponent of approximately 0.85. Possible causes for the discrepancy between theory and experiments are discussed. A potential remedy for the modeling gap is proposed.

Disturbance observer-based robust backstepping load-following control for MHTGRs with actuator saturation and disturbances

This paper presents a disturbance observer-based robust backstepping load-following control (DO-RBLFC) scheme for modular high-temperature gas-cooled reactors (MHTGRs) in the presence of actuator saturation and disturbances. Based on reactor kinetics and temperature reactivity feedback, the mathematical model of the MHTGR is first established. After that, a DO is constructed to estimate the unknown compound disturbances including model uncertainties, external disturbances, and unmeasured states. Besides, the actuator saturation is compensated by employing an auxiliary function in this paper. With the help of the DO, a robust load-following controller is developed via the backstepping technique to improve the load-following performance of the MHTGR subject to disturbances. At last, simulation and comparison results verify that the proposed DO-RBLFC scheme offers higher load-following accuracy, better disturbances rejection capability, and lower control rod speed than a PID controller, a conventional backstepping controller, and a disturbance observer-based adaptive sliding mode controller.

A multipronged core power control strategy for Reaktor TRIGA PUSPATI

At present, the power tracking performance of nuclear Reaktor TRIGA PUSPATI (RTP) is considered unsatisfactory performance due to relatively long settling time during transient and a chattering noise during steady-state power output. Application of the conventional Feedback Control Algorithm (FCA) as a power control technique is proven to be inadequate to keep the core power output stable and within tight multiple parameter constraints for the safety demand of the RTP. Hence, the present study proposed a multipronged core power control strategy improvement through manipulation of the current Control Rod Selection Algorithm (CRSA), Control Rod Speed Design (CRSD), and Power Change Rate Constraint (PCRC) which are part of the core power control design. In this paper, the profiling and analysis of the multipronged core power control strategy are presented. The model for core power control consists of mathematical models of the reactor core, FCA controller, and a series of multipronged models. The mathematical models of the reactor core are based on the point kinetics model, thermal-hydraulic model, and reactivity model. The reactor model is integrated with the FCA controller and a combination of CRSA-CRSD-PCRC models. The power tracking performance of the proposed control strategy and conventional FCA is compared via computer simulation. Overall, the results show the multipronged FCA offers a wider options for optimum operation of the TRIGA reactor.

Oil film characteristics and flow field analysis of asymmetrical hydrostatic support structure with full hydraulic fixed-length shear servo cylinder

The heavy-duty servo cylinder is the main actuator of the full-hydraulic fixed-length shear. The cylinder requires horizontal articulated mounting for accurate curve forces. The output of the curvilinear force causes the piston rod to be subjected to a dynamic bias load, and the presence of the bias load adversely affects the servo cylinder seal structure. In this paper, an asymmetric hydrostatic support structure is designed in the guide sleeve for the bias load problem of the servo cylinder, and the anti-offset capacity of the structure is theoretically studied. The oil film characteristics and oil film stiffness of the structure are deduced and analyzed. Fluent software is used to simulate, and then analyze the influence of inlet pressure, piston rod speed, eccentricity and partial load on the performance of asymmetric static pressure bearing oil film. Asymmetrical hydrostatic support structure servo hydraulic cylinder test bench is built for anti-bias load performance and friction performance experiments. The research results show that the new asymmetric hydrostatic support structure has a good effect on balancing the dynamic partial load, effectively reducing the friction of the servo cylinder and making the automatic alignment of the piston rod and the guide sleeve, which proves that the technology can be effective, increase the service life of the servo hydraulic cylinder and then improve the overall efficiency of the full hydraulic dividing shear, while broaden the application field of the heavy duty servo cylinder.

A Numerical Wear Simulation Method of Reciprocating Seals with a Textured Rod.

Reciprocating rod seals are widely used in the hydraulic actuator to prevent the leakage of fluid. The sealing lip profile changes with the seal wear, resulting in an increase in the leakage. A texturing rod changes the lubrication characteristics of the seal, so it affects the wear and leakage of the seal. A numerical simulation method is proposed to investigate the wear of the hydraulic reciprocating seal with textured rods. Several kinds of macro-cavity textures on the rod surface, including circle, square and triangle shapes, have been simulated and discussed. The effects of three shape parameters including area ratio, depth, and ratio of the axial length to the circumferential length on the seal wear are analyzed in detail. The texturing rod slightly increases the seal wear, but decreases the seal leakage. When the rod speed is increasing, the wear time rates of the seal increase, while the wear distance rates decrease, regardless of the texture shapes. When the texture area ratio is increasing, the wear of the reciprocating seal increases. Seal wear decreases with an increasing texture depth during the outstroke, however, it increases during the instroke. The ratio of the axial length of the macro-cavity to the circumferential length has no effect on the seal wear.

Toll Plaza Lane Choice and Lane Configuration Strategy for Autonomous Vehicles in Mixed Traffic

Toll plazas are one kind of highway node that pose a challenge to the flow of autonomous vehicles (AVs). Some toll roads have open road tolling (ORT), which makes it easier and more efficient for AVs, but most toll plazas do not have ORT. The authors developed a decision model to assist AVs in choosing the right lane that involves two main indicators, the rod speed (SRi) and the decision-making value (DSRi). The decision model was applied to a six-lane toll plaza with manual toll collection (MTC), electronic toll collection (ETC), and electronic toll collection for AVs toll types. The suitable lane configurations for the varying percentages of AVs in traffic were as follows: at 10% AV, the optimal lane configuration was 4 MTC and 2 ETC/AV (4M2EA), at 30% AV it was 3M3EA, at 40%–60% AV it was 3M2EA1A, and at 70% AV it was 2M2EA2A. Thus AVs should share toll lanes with ETC manned vehicles before the population of AVs reaches 30%; after that dedicated lanes may be introduced. It was also concluded that a 10% increase in AVs reduces delays by 9% if the populations of ETC and MTC vehicles are equal.

Profiling and analysis of control rod speed design on core power control for TRIGA reactor

In nuclear reactor TRIGA PUSPATI (RTP) operation, conventional Control Rod Speed Design (cCRSD) uses hard saturation to control rod insertion step as a function of the reactivity insertion rate in the reactor core to ensure the power output will not exceed the limit for the operational safety. The cCRSD which is part of the core power control system produces relatively long settling time during transient and a chattering noise signal during steady-state. Therefore, the current study proposed a new CRSD based on different saturation types such as soft and sigmoid function saturation and changes in the maximum control rod speed limiter value. In this paper, the new CRSD (nCRSD) is designed, profiled, and analyzed based on simulation of an actual Control Rod Drive Mechanism (CRDM) model, common types of saturation models, and reactivity rod worth curve experimental data to predict the best reactivity insertion rate response for operations. The model for core power control is based on mathematical models of the reactor core, the FCA controller, and the CRSD model. The mathematical models of the reactor core are based on a point kinetics model, thermal-hydraulic models, and reactivity models. The nCRSD model is integrated with the Proportional-Integral (PI) type controller and the model of the reactor core. The performance of the nCRSD and cCRSD is compared via computer simulation and experiments. Overall, the results show that the response from the nCRSD offers better results than the cCRSD, which reduces the rise time by up to 52%, the settling time by up to 26%, and the chattering error by up to 25% of the nominal value.

Application of fuzzy logic for power change rate constraint in core power control at Reaktor TRIGA PUSPATI

The 1MWth Reaktor TRIGA PUSPATI (RTP) in Malaysia Nuclear Agency has been in operation more than 37 years. The existing core power control uses a conventional controller known as Feedback Control Algorithm (FCA). It is technically challenging to keep the core power output stable and operate within the acceptable error bands for the safety demand of the RTP. At present, the power tracking performance of the system could be considered unsatisfactory where constant gains of power change rate constraint and control rod speed constraint are used. Hence, a study of a new power change rate constraint design to achieve safe control rod speed range is conducted to improve the current performance. In this paper, a new power change rate constraint (PCRC) method using fuzzy logic is proposed to control the core power. The Takagi-Sugeno (T-S) type Fuzzy model is chosen due to its capability to work well with linear controller and making the computational control algorithm efficient. The model for core power control consists of mathematical models of the reactor core, FCA, and control rods selection algorithm. The mathematical models of the reactor core are based on point kinetics model, thermal-hydraulic models and reactivity models. The performance of power tracking and actuation signal for control rod drive input are compared between the conventional PCRC (cPCRC) and Fuzzy PCRC using MATLAB. In conclusion, the proposed Fuzzy PCRC has satisfactory performance in core power tracking for controlling the nuclear reactor with high reliability and safety.

A multiscale wear model for reciprocating rod stepseal under mixed lubricating conditions based on linear elasticity

The macroscale simulation methods are commonly used to study the wear of reciprocating seals to analyze macroscopic effects on the seal wear. There is a lack of numerical method for analyzing the wear of reciprocating seal under mixed lubricating conditions. According to experimental studies, some microscopic factors, including lubrication characteristics and surface roughness, are important for wear of reciprocating seal. Hence, in the presented research, a numerical model is proposed to analyze the effects of microscopic factors on reciprocating rod stepseal wear. O-ring of the stepseal is considered to be hyper elastic, while Turcon ring of the stepseal, which directly contacts with rod surface, is assumed to be linear elastic. The effects of microscopic aspects, including lubrication characteristics, are highlighted and analyzed. Furthermore, the seal wears under different operating conditions are analyzed and discussed. The simulation results show that the seal wears during outstroke and instroke are different. With the rod speed increasing, the wear distance rate increases during outstroke, while decreases during instroke. The seal wear increases with the sealed pressure increasing and/or compression rate increasing. With the increase in the fluid viscosity, the wear of the seal increases during outstroke and decreases during instroke. With the increase in the seal surface roughness, the seal wear decreases during outstroke and increases during instroke.