Control Cylinder Research Articles

Effect of different surface treatments and adhesives on repair bond strength of resin composites after one and 12 months of storage using an improved microtensile test method.

To evaluate the effect of surface treatments and bonding systems on the repair bond strength between composite materials after one and 12 months of storage, using an improved microtensile test method. A total of 72 composite cylinders (Tetric Evo Ceram, Ivoclar) were fabricated, stored in distilled water for two weeks followed by thermal cycling (5000 times between 5°C and 55°C), and served as substrate. The cylinders were mechanically roughened using 320-grit silicon carbide sandpaper, etched with 37% phosphoric acid gel, rinsed with water, and divided equally into three experimental groups: group 1, unchanged surface; group 2, sandblasting of the surface (CoJet tribochemical silica sand, 3M ESPE; Microetcher II, Danville Engineering Inc); and group 3, surface silane coating (Bis-Silane, BISCO Inc). Eight control cylinders were prepared and underwent similar aging as the substrate. Each experimental group was divided into subgroups that received the following bonding systems: one-step self-etching adhesive (AdheSE One, Ivoclar Vivadent), two-step self-etching adhesive (Clearfil SE, Kuraray America), and three-step etch-and-rinse adhesive (Adper Scotchbond Multi-Purpose, 3M ESPE). Fresh composite (Tetric Evo Ceram, Ivoclar) was placed and cured on top of the prepared substrate cylinders. The specimens were placed in distilled water for a week and thermocycled the same way as before. Eight composite control cylinders were also stored and thermocycled for the same period of time. Half of the cylinders in each test group were tested at one month and the second half at 12 months. The cylinders were serially sectioned in an automatic cutting machine, producing 10 to 20 1.1 × 1.1-mm test specimen beam from each cylinder. Specimens were prepared for microtensile testing and the tensile strength calculated based on the force at fracture and specimen dimension. The fracture surfaces were examined under a stereomicroscope and the type of fracture noted. The mean tensile strength of composite control was 54.5 ± 6.0 MPa at one month and 49.6 ± 5.1 MPa at 12 months. The mean tensile strength for the repaired groups ranged from 26.4 ± 6.8 MPa to 49.9 ± 10.4 MPa at one month and 21.2 ± 9.9 to 41.3 ± 7.5 at 12 months. There was a statistical difference between all groups (p<0.05) at one month. This difference was less pronounced at 12 months. The highest repair strength was obtained in the group having a silane-coated surface and Clearfil, the two-step self-etching adhesive. Clearfil also had the highest repair strength within each surface treatment group. There was a tendency for lower tensile strength at 12 months compared with one month. Most fractures were of the adhesive type; the highest number of cohesive fractures, 16% at one month and 12% at 12 months, were in groups with the highest tensile strength. The best repair bond strength was achieved by using freshly mixed silane solution on the substrate in addition to an adhesive, rendering a thin bonding layer.

A Feed-Forward Approach for the Real-Time Estimation and Control of MFB50 and SOI In Diesel Engines

Feed-forward low-throughput models have been developed to predict MFB50 and to control SOI in order to achieve a specific MFB50 target for diesel engines. The models have been assessed on a GMPT-E Euro 5 diesel engine, installed at the dynamic test bench at ICEAL-PT (Internal Combustion Engine Advanced Laboratory at the Politecnico di Torino) and applied to both steady state and transient engine operating conditions. MFB50 indicates the crank angle at which 50% of the fuel mass fraction has burned, and is currently used extensively in control algorithms to optimize combustion phasing in diesel engines in real-time. MFB50 is generally used in closed-loop combustion control applications, where it is calculated by the engine control unit, cycle-by-cycle and cylinder by-cylinder, on the basis of the measured in-cylinder pressure trace, and is adjusted in order to reduce the fuel consumption, combustion noise and engine-out emissions. A feed-forward approach has been developed in this paper. This approach is capable of predicting MFB50 on the basis of several parameters, such as, the in-chamber thermodynamic conditions, the injected fuel quantities and timings, the injection pressure, the oxygen concentration and the engine speed and load. The approach has also been inverted in order to predict the start of injection required to achieve a specific MFB50 target in real time. This method can be used in model-based real-time control algorithms to adjust the engine parameters in order to prevent the occurrence of nonoptimal combustion cycles.

Quasi-laminar stability and sensitivity analyses for turbulent flows: Prediction of low-frequency unsteadiness and passive control

This article presents a quasi-laminar stability approach to identify in high-Reynolds number flows the dominant low-frequencies and to design passive control means to shift these frequencies. The approach is based on a global linear stability analysis of mean-flows, which correspond to the time-average of the unsteady flows. Contrary to the previous work by Meliga et al. [“Sensitivity of 2-D turbulent flow past a D-shaped cylinder using global stability,” Phys. Fluids 24, 061701 (2012)], we use the linearized Navier-Stokes equations based solely on the molecular viscosity (leaving aside any turbulence model and any eddy viscosity) to extract the least stable direct and adjoint global modes of the flow. Then, we compute the frequency sensitivity maps of these modes, so as to predict before hand where a small control cylinder optimally shifts the frequency of the flow. In the case of the D-shaped cylinder studied by Parezanović and Cadot [J. Fluid Mech. 693, 115 (2012)], we show that the present approach well captures the frequency of the flow and recovers accurately the frequency control maps obtained experimentally. The results are close to those already obtained by Meliga et al., who used a more complex approach in which turbulence models played a central role. The present approach is simpler and may be applied to a broader range of flows since it is tractable as soon as mean-flows — which can be obtained either numerically from simulations (Direct Numerical Simulation (DNS), Large Eddy Simulation (LES), unsteady Reynolds-Averaged-Navier-Stokes (RANS), steady RANS) or from experimental measurements (Particle Image Velocimetry - PIV) — are available. We also discuss how the influence of the control cylinder on the mean-flow may be more accurately predicted by determining an eddy-viscosity from numerical simulations or experimental measurements. From a technical point of view, we finally show how an existing compressible numerical simulation code may be used in a black-box manner to extract the global modes and sensitivity maps.

Vortex Shedding with Fluid Mechanics from Two Cylinders of Different Diameters in a Tandem Arrangement

The vortex shedding from two circular cylinders of different diameters in a tandem arrangement is numerically investigated at a Reynolds number of 100 and 150. The studied Reynolds number based on the diameter of the downstream main cylinder. The diameter of the downstream main cylinder was kept constant, and the diameter ratio between the upstream control cylinder and the downstream one was varied from 0.1 to 1.0. The gap between the control cylinder and the main cylinder ranged from 0.1 to 4.0 times the diameter of the main cylinder. It is concluded that the gap ratio and the diameter ratio between the two cylinders have important effects on vortex shedding from two cylinders of different diameters in a tandem arrangement.

Drag Coefficients Acting on Two Tandem Cylinders of Different Diameters

The flow past two tandem circular cylinders of different diameters is simulated by using a finite volume method. The diameter of the downstream main cylinder is kept constant, and the diameter ratio between the upstream control cylinder and the downstream one is varied from 0.1 to 1.0. The Reynolds number based on the diameter of the downstream main cylinder is 100 and 150. The gap between the control cylinder and the main cylinder ranges from 0.1 to 4.0 times the diameter of the main cylinder. It is concluded that the gap ratio and the diameter ratio between the two cylinders have important effects on the drag coefficients and flow characteristics.

Lift Coefficients and Pressure Distribution Acting on Two Tandem Cylinders of Different Diameters

Flow characteristics of two different diameters cylinders in a tandem arrangement were investigated numerically in a uniform flow. The diameter of the downstream main cylinder was kept constant, and the diameter ratio between the upstream control cylinder and the downstream one was varied from 0.1 to 1.0. The studied Reynolds number based on the diameter of the downstream main cylinder were 100 and 150. The gap between the control cylinder and the main cylinder ranged from 0.1 to 4.0 times the diameter of the main cylinder. It is concluded that the gap ratio and the diameter ratio between the two cylinders have important effects on the lift coefficients and pressure distribution.

Suppression of Vortex Shedding of Circular Cylinder by a Small Control Rod

The physical phenomena of vortex suppression and flow patterns by deploying a very mall control cylinder in the near wake region of a main cylinder in low Reynolds numbers is studied numerically. The control diameter effect on vortex suppression and three flow patterns has been studied. The results shows the control cylinder can reduce vortex shedding frequency and suppress shedding partially or completely dependent on the diameter of control cylinder and Reynolds number. The results of a cylinder with control and without control agree with experimental and numerical studies.

Pressure Compensator Design for a Swash Plate Axial Piston Pump

An in-line axial-piston swash-plate pump with pressure compensator is widely used for its fast speed of response and power economy. Although several simulation based design approaches exist to minimize issues like fluid-born noises, ample scope exists for more exhaustive design analysis. The most popular pressure compensator for a variable displacement pump with a spool valve actuating the control and bias cylinders has been taken up here. With an existing comprehensive flow dynamics model, an updated model for swiveling dynamics has been coupled. The dynamics also includes the force containment and friction effects on the swash plate. A design optimization has been accomplished for the pressure compensator. The target of the optimal design has been set as minimizing the transient oscillations of the swash plate, the compensator spool, pressures in the bias and control cylinders along with avoidance of both over-pressurization and cavitation in the bias cylinder. It has been found that the orifice diameters in the spring-side and at the metering port of the spool valve and in the backside of the bias cylinder have critical role in arriving at an optimum design. The study has led to a useful design procedure for a pressure compensated variable displacement pump.

Very Large Eddy Simulation of Passive Drag Control for a D-Shaped Cylinder

The numerical study reported here deals with the passive flow control around a two-dimensional D-shaped bluff body at a Reynolds number of Re=3.6×104. A small circular control cylinder located in the near wake behind the main bluff body is employed as a local disturbance of the shear layer and the wake. 3D simulations are carried out using a newly developed very large eddy simulation (VLES) method, based on the standard k − ε turbulence model. The aim of this study is to validate the performance of this method for the complex flow control problem. Numerical results are compared with available experimental data, including global flow parameters and velocity profiles. Good agreements are observed. Numerical results suggest that the bubble recirculation length is increased by about 36% by the local disturbance of the small cylinder, which compares well to the experimental observations in which the length is increased by about 38%. A drag reduction of about 18% is observed in the VLES simulation, which is quite close to the experimental value of 17.5%. It is found that the VLES method is able to predict the flow control problem quite well.

Dynamic high-frequency behaviour of the swash plate in a variable displacement axial piston pump

In variable displacement axial piston pumps and motors, the rotation of the barrel causes a strong vibrating torque load on the variable displacement components, that is, on the swash plate. In most analysis, this vibrating torque is counteracted by a mechanical end stop, thereby forcing a constant swash plate angle. However, in real pump and motor operation, the swash plate is not held mechanically. Instead, the position of the swash plate is defined by a hydraulic control system. The vibrating torque load on the swash block is compensated by the control piston and cylinder, in which the pressure changes dynamically, as a reflection of the dynamic torque load created by the rotating barrel. The variation of the control pressure demands the swash plate to oscillate around the average swash plate position, which is defined by the control system of the pump (or motor). In this study, the vibrating movement of the swash plate is measured in a variable displacement floating cup pump. The floating cup principle features two swash plates, which are operated out of phase. This has given the opportunity to connect the control systems of both swash plates by means of a restriction. The experiments have shown that the swash plate vibration has a significant effect on the displacement of the individual pistons, while commutating in and around the top and bottom dead centres. The study shows that the swash plate vibration needs to be included in the analysis of variable displacement axial piston pumps and motors.

RENOVATION OF NMIJ'S 5 MN HYDRAULIC AMPLIFICATION TYPE FORCE STANDARD MACHINE

The 5 MN hydraulic amplification type force standard machine was renovated by replacing its hydraulic pressure control system, measuring ram and cylinder. For re-evaluation of uncertainty of force amplification factor, diameters of the main and mearsuring rams and cylinders were re-measured. A programmable logic controller with a personal computer is used to control the weight motion and the valve actuation, to monitor various kinds of sensors output, and to record readings of a force transducer under calibration. Fluctuation of calibration force was suppressed by using a quartz-resonance type pressure gauge, and measurement repeatability was improved to some extent. However, there remains room for improvement to further stabilize the calibration force by modifying the measuring ram.

Phase-Space Interpolated Perturbation Theory with Application to Advanced Test Reactor Shim Rotation Automation

A modified form of first-order perturbation theory, called phase-space interpolated perturbation theory (PSIPT), was developed to more accurately model families of perturbations where changes are intermediate to defined reference and bounding configurations. PSIPT can thus be used on any application where the range of change to the system is known a priori but the magnitude of change is not known. PSIPT is demonstrated for several applications, notably the position of the outer shim control cylinders (OSCCs) at the Advanced Test Reactor (ATR). The current method used for calculating the OSCC positions during a cycle startup utilizes a heuristic trial-and-error approach that is impractical with advanced computationally intensive reactor physics tools. PSIPT is implemented into a method to automate shim rotation prediction for startup.

Effect of Post-Heated Concrete Cylinders Repaired with CFRP Reinforcement

This paper presents the experimental results of post-heated concrete cylinders repaired externally using Carbon Fibre Reinforced Polymer (CFRP) fabrics. Eighteen concrete cylinders of size 155mm x 300mm were exposed to different temperatures of 100, 200, and 300°C for 3 hours. Subsequently, the exposed concrete cylinders were naturally cooled down to room temperature and repaired externally using CFRP reinforcement. All these cylinders were tested to failure under axial loading. Results show that the residual strength of post-heated CFRP repaired concrete cylinders was significantly increased between 47 to 51% over the control cylinders. However, the ductility of CFRP repaired concrete cylinders was increased at the elevated temperatures.

Flow past a circular cylinder with momentum injection: optimal control cylinder design

The flow past a circular cylinder in the presence of two counter-rotating control cylinders is analytically investigated. It is shown that vortex formation behind a circular cylinder can be suppressed by introducing two small counter-rotating circular cylinders. However, choosing an appropriate position and optimal circulation strength for the control cylinders is central to achieving optimal control cylinder design. Solving the complete Navier–Stokes (NS) equations can be time consuming if we approach parameterizing the position and circulation strength of the control cylinders. Instead, reduced-order models can be employed to save the computational expenditure associated with solving the complete NS models. To this end, a Föppl model is employed to investigate the influence of position of the control cylinders on the flow separation from the main circular cylinder. Conformal mapping techniques are used to investigate the flow features, from which the optimum value of circulation was found based on pressure distribution and drag forces. Analytical solutions are complemented through finite volume-based viscous flow calculations.

Research on Low Cost Automatic Polishing Machine for Die/Mold Manufacturing

In order to improve die/mold polishing worker’s environment and polishing automation level, we introduce a kind of low cost automatic polishing machine (LCAPM) with compliant actuator. The actuator is composed of a Tripod mechanism driven by pneumatic cylinders. Proportional valve is used to guarantee precision of cylinder’s position, and a 3D force sensor is used to adjust polishing contact force between grind stone tool and workpiece. Structure of LCAPM is described in detail; pneumatic control circuit and cylinder’s position are modeled in succession. Finally, a computing case of cylinder’s position for given workpiece is shown.

Sensitivity of 2-D turbulent flow past a D-shaped cylinder using global stability

We use adjoint-based gradients to analyze the sensitivity of turbulent wake past a D-shaped cylinder at Re = 13000. We assess the ability of a much smaller control cylinder in altering the shedding frequency, as predicted by the eigenfrequency of the most unstable global mode to the mean flow. This allows performing beforehand identification of the sensitive regions, i.e., without computing the actually controlled states. Our results obtained in the frame of 2-D, unsteady Reynolds-averaged Navier–Stokes compare favorably with experimental data reported by Parezanović and Cadot [J. Fluid Mech. 693, 115 (2012)] and suggest that the control cylinder acts primarily through a local modification of the mean flow profiles.

Oscillatory sensitivity patterns for global modes in wakes

AbstractGlobally unstable wakes with co-flow at intermediate Reynolds numbers are studied, to quantify important spatial regions for the development and control of the global instability. One region of high structural sensitivity is found close to the inlet for all wakes, in agreement with previous findings for cylinder wakes. A second, elongated region of high structural sensitivity is seen downstream of the first one for unconfined wakes at $\mathit{Re}= 400$. When base-flow modifications are considered, a spatially oscillating sensitivity pattern is found inside the downstream high-structural-sensitivity region. This implies that the same change in the base flow can either destabilize or stabilize the flow, depending on the exact position where it is applied. It is shown that the sensitivity pattern remains unchanged for different choices of streamwise boundary conditions and numerical resolution. The actual base-flow is modified in selected configurations, and the linear global modes recomputed. It is confirmed that the linear global eigenvalues move according to the predicted sensitivity pattern for small-amplitude base-flow modifications, for which the theory applies. We also look at the implications of a small control cylinder for the flow. Only the upstream high-sensitivity region proves to be robust in terms of control, but one should be careful not to disturb the flow in the downstream high-sensitivity region, in order to achieve control. The findings can have direct implications for the numerical resolution requirements for wakes at higher Reynolds numbers. Furthermore, they provide one more possible explanation for why confined wakes have a more narrow frequency spectrum than unconfined wakes.

On experimental sensitivity analysis of the turbulent wake from an axisymmetric blunt trailing edge

The sensitivity to steady local disturbances of the turbulent wake over a 3D blunt body with an axisymmetric trailing edge is investigated at Re = 2.1 × 104. The flow presents a favored m = 2 azimuthal periodicity due to the mounting of the body. It is proved that two asymmetric flows cohabit and generate a statistically symmetric natural flow. Topology shifts are random but are visible after a large number of global mode periods. The statistical symmetry is highly sensitive to any steady antisymmetric disturbance. As a consequence, depending on its position, a small control cylinder (considered as a disturbance with m = 1 azimuthal periodicity) in the close wake fixes the flow to one asymmetric topology affecting shedding activity as well as drag. On the contrary, a thin control ring (i.e., m = 0 disturbance) preserves the mean flow symmetry and has a greater impact on global mode frequency and drag. Whatever the disturbance, the sensitivity of the wake to control devices is concentrated into the mixing layers; the observed effects seem to depend more upon their local turbulent characteristics than on the global inviscid dynamics of vorticity.

Experimental sensitivity analysis of the global properties of a two-dimensional turbulent wake

AbstractThe sensitivity of the global properties of a two-dimensional turbulent wake produced by the separated flow of a ‘D’-shaped cylinder at$\mathit{Re}= 13\hspace{0.167em} 000$is investigated experimentally using a small circular control cylinder as a local disturbance. The height of the main cylinder is$D= 25~\mathrm{mm} $and control cylinders are of diameters$d= 0. 04D$and$d= 0. 12D$, the former being smaller than the shear layer thickness detaching from the main cylinder, while the latter is larger. In both cases, the control cylinder is able to modify the global frequency, base pressure and spanwise velocity correlation. The results are presented as sensitivity maps. Reynolds stresses spatial structure and the recirculation bubble length are examined in detail when the control cylinder is displaced vertically across the wake at a fixed downstream location. It is found that the increase of the recirculation bubble length is accompanied by a damping of Reynolds stresses with a downstream shift of their spatial structures together with the base pressure increase. The global frequency can be either decreased or increased independently of the bubble length modification. The sensitivity of these global properties is interpreted on the basis of the ability of the control cylinder to change the size of the formation region of the Kármán vortex street by interacting with the primary detached shear layers. The corresponding physical mechanisms are discussed. The impact of a two-dimensional control cylinder on the three-dimensional properties of the wake is examined through spanwise correlation. This is found to be improved whenever the control cylinder is placed inside the recirculation region of the main cylinder wake.

Research on trajectory tracking control for wet clutch engagement based on SMC

To improve tracking control quality of the clutch actuator during the wet clutch engagement, models of the clutch actuator were established firstly, including the control cylinder model, flow equilibrium equation and pressure control model. Secondly, taking the clutch output speed as tracking target, the state space equation of the tracking control system was set up and the sliding mode controller (SMC) was designed. Finally, a simulation test was performed. The results show that a higher tracking accuracy as well as a better performance to resist disturbance can be achieved with the proposed sliding control method, compared to PI control. It was also shown that the exponent approaching sliding mode control can produce smaller chattering compared with the constant rate approaching sliding mode control.