Means Of Passive Control Research Articles

Evaluation of effect of micro-vortex generator on dynamic characteristics of unsteady partial cavitating flow over hydrofoil

The unsteady characteristics of cavitation induce a series of destructive effects, such as cavitation erosion, vibration, and noise. Passive control of hydrofoil cavitation involves changing the structure or material of the hydrofoil surface, thereby inhibiting cavitation damage, and vortex generators (VGs) are the most popular means of passive control because of their effectiveness, simplicity, and lower production and installation costs. In this study, a new VG structure that can improve the cavitating flow state of a hydrofoil is proposed. A multiphase volume-of-fluid model is used to capture the interface between different phases, the Schnerr–Sauer model is used to describe the cavitation process, and turbulence is modeled by large-eddy simulation. The evolution characteristics of the cavitating flow field around a National Advisory Committee for Aeronautics (NACA) 0015 hydrofoil are investigated numerically both with and without the VG to illustrate its control effect. It is found that the VG can change the hydrodynamic characteristics of the cavitating flow field around the hydrofoil, such as the cavity morphology, the vortex structures, and the peak and power spectral density of the pressure. Upon using Lagrangian coherent structures, the motion state of the fluid particles and the distance between adjacent fluid particles are found to change dramatically with time under the effect of the VG. Upon using dynamic mode decomposition, the VG is found to decrease the energy in the first three modes, whereas that in mode 4 is larger without the VG, thereby suggesting that the VG might help to reduce flow noise. Finally, it is found that the VG converts laminar flow to turbulence, thereby increasing the turbulence intensity of the wake flow field and decreasing the maximum value of the turbulence integral scale.

Suppression of instabilities of swirled premixed flames with minimal secondary hydrogen injection

The impact of hydrogen addition on the dynamics of a methane-air premixed flame is explored for different injection strategies. The configuration is a swirled injector with a central tube for pilot fuel injection. Keeping the air flow rate and thermal power of the burner constant, it is shown that even for very small flow rates of hydrogen, as low as one percent of the thermal power, flame stabilization and combustor stability are greatly altered when pure hydrogen is injected through the central tube as a pilot jet. It is also shown that fully premixing the same quantity of hydrogen with methane or use of methane for the pilot jet has no significant effects compared to hydrogen pilot injection strategy. The flame response to forced flow perturbations is use to interpret the observed features. It is shown that hydrogen piloting drastically changes the gain of the flame transfer function at low frequencies and its phase lag at high frequencies, while other injection strategies barely change the flame response for these minute flowrates. CO and NOx emissions are finally examined for the different injection strategies. NOx emissions are found to drastically increase with hydrogen piloting compared to other injection strategies. These experiments indicate that pure hydrogen injected in minute fractions may be used as an efficient passive control means to mitigate combustion instabilities, but a compromise needs to be made with emissions.

MHD mixed convection of nanofluid in a three-dimensional vented cavity with surface corrugation and inner rotating cylinder

PurposeThis study aims to numerically examine mixed convection of CuO-water nanofluid in a three-dimensional (3D) vented cavity with inlet and outlet ports under the influence of an inner rotating circular cylinder, homogeneous magnetic field and surface corrugation effects. In practical applications, it is possible to encounter some of the considered configurations in a vented cavity such as magnetic field, rotating cylinder and it is also possible to specially add some of the active and passive control means to control the convection inside the cavity such as adding nanoparticles, corrugating the surfaces. The complicated physics with nanofluid under the effects of magnetic field and inclusion of complex 3D geometry make it possible to use the results of this numerical investigation for the design, control and optimization of many thermal engineering systems as mentioned above.Design/methodology/approachThe bottom surface is corrugated with a rectangular wave shape, and the rotating cylinder surface and cavity bottom surface were kept at constant hot temperatures while the cold fluid enters the inlet port with uniform velocity. The complicated interaction between the forced convection and buoyancy-driven convection coupled with corrugated and rotating surfaces in 3D configuration with magnetic field, which covers a wide range of thermal engineering applications, are numerically simulated with finite element method. Effects of various pertinent parameters such as Richardson number (between 0.01 and 100), Hartmann number (between 0 and 1,000), angular rotational speed of the cylinder (between −30 and 30), solid nanoparticle volume fraction (between 0 and 0.04), corrugation height (between 0 and 0.18H) and number (between 1 and 20) on the convective heat transfer performance are numerically analyzed.FindingsIt was observed that the magnetic field suppresses the recirculation zone obtained in the lower part of the inlet port and enhances the average heat transfer rate, which is 10.77 per cent for water and 6.86 per cent for nanofluid at the highest strength. Due to the thermal and electrical conductivity enhancement of nanofluid, there is 5 per cent discrepancy in the Nusselt number augmentation with the nanoadditive inclusion in the absence and presence of magnetic field. The average heat transfer rate of the corrugated surface enhances by about 9.5 per cent for counter-clockwise rotation at angular rotational speed of 30 rad/s as compared to motionless cylinder case. Convective heat transfer characteristics are influenced by introducing the corrugation waves. As compared to number of waves, the height of the corrugation has a slight effect on the heat transfer variation. When the number of rectangular waves increases from N = 1 to N = 20, approximately 59 per cent of the average heat transfer reduction is achieved.Originality/valueIn this study, mixed convection of CuO-water nanofluid in a 3D vented cavity with inlet and outlet ports is numerically examined under the influence of an inner rotating circular cylinder, homogeneous magnetic field and surface corrugation effects. To the best of authors knowledge such a study has never been performed. In practical applications, it is possible to encounter some of the considered configurations in a vented cavity such as magnetic field, rotating cylinder and it is also possible to specially add some of the active and passive control means to control the convection inside the cavity such as adding nanoparticles, corrugating the surfaces. The complicated physics with nanofluid under the effects of magnetic field and inclusion of complex 3D geometry make it possible to use the results of this numerical investigation for the design, control and optimization of many thermal engineering systems as mentioned above.

Splashing of a Newtonian drop impacted onto a solid substrate coated by a thin soft layer

For many industrial applications it is important to control the outcome of drop impact. One of the means of passive control for such processes is in the application of smart, deformable, rheologically complex surfaces. In this experimental work an impact of a viscous Newtonian drop onto a substrate coated by a thin visco-elastic layer is investigated. The elastic and viscous properties of the layer are varied in a wide range. It is shown that the properties of the substrate only slightly influence the spreading of the drop after collision, but significantly influence the rate of the receding.It has been shown that the deposition/splashing threshold for smaller Reynolds numbers, Re, is determined by a critical Weber number, We. This result is in agreement with the existing recent theories for splashing threshold which account for the aerodynamic affects in the spreading wedge near the contact line. However, for higher Reynolds numbers the threshold is described well by a new splashing parameter L = WeRe−2/5, obtained from the balance of the inertial and surface tension forces in the spreading lamella. The critical L number is higher on the deformable surfaces than on dry solid substrates, which is caused by dumping of some part of the kinetic energy of impact by the deformable layer. It is interesting that the critical L number does not depend on the rheological properties of the deformable layer.

Control of Vibration Using Compliant Actuators

This work proposes a method for controlling vibration using compliant-based actuators. The compliant actuator combines a conventional actuator with elastic elements in a series configuration. The benefits of compliant actuators for vibration control applications, demonstrated in this work, are twofold: (i) vibration reduction over a wide frequency bandwidth by passive control means and (ii) improvement of vibration control performance when active control is applied using the compliant actuator. The vibration control performance is compared with the control performance achieved using the well-known vibration absorber and conventional rigid actuator systems. The performance comparison showed that the compliant actuator provided a better flexibility in achieving vibration control over a certain frequency bandwidth. The passive and active control characteristics of the compliant actuator are investigated, which shows that the control performance is highly dependent on the compliant stiffness parameter. The active control characteristics are analyzed by using the proportional-derivative (PD) control strategy which demonstrated the capability of effectively changing the respective effective stiffness and damping of the system. These attractive dual passive–active control characteristics are therefore advantageous for achieving an effective vibration control system, particularly for controlling the vibration over a specific wide frequency bandwidth.

The study of frictional damper with various control algorithms

Frictional dampers are used in structural engineering as means of passive control. Meanwhile, frictional damper shave a disadvantage compared to viscous rivals since the slippage force must be exceeded to activate the device, and cannot be ideal full range of possible events. The concept of semi-active control is utilized to overcome this shortcoming. In this paper, a new semi-active frictional damper called Smart Adjustable Frictional (SAF) damper is introduced. SAF damper consists of hydraulic, electronic units and sensors which are all linked with an active control discipline. SAF acts as a smart damper which can adapt its slippage threshold during a dynamic excitation by measuring and controlling the structural response. The novelty of this damper is, while it controls the response of the structure in real time with acceptable time delay. The paper also reports on the results of a series of experiments which have been performed on SAF dampers to obtain their prescribed hysteretic behavior for various control algorithms. The results show that SAF can produce the desired slippage load of various algorithms in real time. Numerical models incorporating control simulations are also made to obtain the hysteretic response of the system which agrees closely with test results.

Stability of Poiseuille flow in a fluid overlying an anisotropic and inhomogeneous porous layer.

We present the linear stability analysis of horizontal Poiseuille flow in a fluid overlying a porous medium with anisotropic and inhomogeneous permeability. The generalized Darcy model is used to describe the flow in the porous medium with the Beavers-Joseph condition at the interface of the two layers and the eigenvalue problem is solved numerically. The effect of major system parameters on the stability characteristics is addressed in detail. It is shown that the anisotropic and inhomogeneous modulation of the permeability of the underlying porous layer provides an effective means for passive control of the flow stability.

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.

Selective Roughness in the Boundary Layer to Suppress Flow-Induced Motions of Circular Cylinder at 30,000<Re<120,000

A passive control means to suppress flow-induced motions (FIM) of a rigid circular cylinder in the TrSL3, high-lift, flow regime is formulated and tested experimentally. The developed method uses passive turbulence control (PTC) consisting of selectively located roughness on the cylinder surface with thickness about equal to the boundary layer thickness. The map of “PTC-to-FIM,” developed in previous work, revealed robust zones of weak suppression, strong suppression, hard galloping, and soft galloping. PTC has been used successfully to enhance FIM for hydrokinetic energy harnessing using the VIVACE Converter. PTC also revealed the potential to suppress FIM to various levels. The map is flow-direction dependent. In this paper, the “PTC-to-FIM” map is used to guide development of FIM suppression devices that are flow-direction independent and hardly affect cylinder geometry. Experiments are conducted in the Low Turbulence Free Surface Water Channel of the University of Michigan on a rigid, horizontal, circular cylinder, suspended on springs. Amplitude and frequency measurements and broad field-of-view visualization reveal complex flow structures and their relation to suppression. Several PTC designs are tested to understand the effect of PTC roughness, location, coverage, and configuration. Gradual modification of PTC parameters, leads to improved suppression and evolution of a design reducing the VIV synchronization range. Over a wide range of high reduced velocities, VIV is fully suppressed. The maximum amplitude occurring near the system’s natural frequency is reduced by about 63% compared to the maximum amplitude of the smooth cylinder.

Numerical and experimental study of hysteretic behavior of cylindrical friction dampers

Frictional dampers utilize the mechanism of friction for absorbing and dissipating the energy imparted to the dynamic systems. Frictional dampers are widely used in mechanical systems in various industries in order to mitigate the impact and vibration effects. Frictional dampers are also utilized in structures as means of passive control to improve the seismic behavior of structures. In this investigation, an innovative type of frictional damper called cylindrical friction damper (CFD) is proposed. This damper consists of two main parts, the inner shaft and the outer cylinder. Dimensions and properties of the main parts are defined based on seismic demand of structures. These two parts are assembled such that one is shrink fitted inside the other. Upon application of proper axial loading to both ends of the CFD, the shaft will move inside the cylinder by overcoming the friction. This in turn leads to considerable dissipation of mechanical energy. In contrast to other frictional dampers, the CFDs do not use high-strength bolts to induce friction between contact surfaces. This reduces construction costs, simplifies design computations and increases reliability in comparison with other types of frictional dampers. The hysteretic behavior of CFD is studied by experimental and numerical methods. The results show that the proposed damper has great energy absorption by stable hysteretic loops, which significantly improves the performance of structures subjected to earthquake loads. Also, a close agreement between the experimental and numerical results is observed.

A hybrid control approach for pole assignment to second-order asymmetric systems

Structural modification in the form of adding mass and stiffness (and sometime damping) as a means of passive control to assign desirable poles and zeros for symmetric systems has been extensively studied. Pole and zero assignment by means of active control has also attracted much research. Assignment of poles to stabilise second-order damped asymmetric dynamic systems using structural modifications and state-feedback control, respectively, was carried out recently. It was found that the former is often incapable of assigning complex poles with negative real parts for asymmetric systems while the latter is nearly always capable of doing that. However, the gains required to assign poles with negative real parts using active control can be high. This paper presents a two-stage passive (structural modification) and active (state-feedback) combined control approach to assign complex poles with negative real parts to damped asymmetric dynamic systems to suppress flutter instability. This hybrid approach is motivated by possible restriction to gains of actuators and cost of sole active control. Simulated numerical examples show its effectiveness over the individual control strategies of passive control and active control.

Shaping of Tip End-Plate to Control Leakage Vortex Swirl in Axial Flow Fans

This paper reports on quantitative tests of passive techniques for rotor-tip noise control in low-speed axial flow fans, based on blade-tip modifications involving the addition of antivortex appendages as end-plates. The end-plate thickness chordwise distribution is determined to control the chordwise evolution of the leakage vortex rotation number. The results confirm that the new end-plate configurations provide a mechanism by which leakage vortex bursting can be avoided. As such, the modified rotors represent an effective means of passive control of vortex breakdown.

Recent Advances in Liquid Sloshing Dynamics

A liquid free surface in partially filled containers can experience a wide spectrum of motions such as planar, non-planar, rotational, quasi-periodic, chaotic, and disintegration. Civil engineers and seismologists have been studying liquid sloshing effects on large dams, oil tanks and elevated water towers under ground motion. Since the early 1960’s, the problem of liquid sloshing dynamics has been of major concern to aerospace engineers studying the influence of liquid propellant sloshing on the flight performance of jet vehicles. Since then, new areas of research activities have emerged. The modern theory of nonlinear dynamics has indeed promoted further studies and uncovered complex nonlinear phenomena. These include rotary sloshing, Faraday waves, nonlinear liquid sloshing interaction with elastic structures, internal resonance effects, stochastic sloshing dynamics, hydrodynamic sloshing impact dynamics, g-jitter under microgravity field, cross-waves, and spatial resonance. The dynamic stability of liquid gas tankers and ship cargo tankers, and liquid hydrodynamic impact loading are problems of current interest to the designers of such systems. This article will address the means of passive control of liquid sloshing and the use of liquid sloshing forces to control vibratory structures. Other important contributions include the development of digital computer codes to solve complex problems that were difficult to handle in the past. The purpose of this article is to review the research work developed in different applications. It will highlight the major achievements and results reported in the literature. Some early work will be cited very briefly in order to provide an updated bibliography of liquid sloshing dynamics. This review article contains 1,319 references.

A simple approach to the seismic design of friction damped braced medium-rise frames

This paper is concerned with the seismic design of steel frames using friction damped slotted bolted connections (SBCs) in the diagonal braces as a means for passive control. A dynamic model that uses bilinear hysteretic behavior for the damper describes the response of a single degree of freedom (SDOF) steel frame and constitutes the basis for the design. A design procedure that attains the stiffness of the individual braces and their elongation at the threshold of activation is then applied to 10-story and 3-story steel frames. This design procedure is a two-phase iterative scheme of the analysis/redesign type, the analysis of which is modal. Finally, a full nonlinear dynamic analysis that uses a generalized version for MDOF's of the bilinear hysteretic SDOF model assesses the design.

Design guidelines for a glazing with a seasonally dependent solar transmittance

The basic design guidelines for a window and facade glass which rejects direct solar radiation during the summer period and which transmits direct solar radiation during the remainder of the year are derived. The design employs purely passive control means and is based on the seasonal change of the incident angle of solar rays and on the capability of glass prisms to refract and totally reflect or transmit solar rays dependent on the relevant incident angle. Two new design elements essentially extend the applicability of the glass in accordance with window orientation and season of direct solar light rejection.

Experimental investigation of friction-base isolation

Structural vibration control is one of the main goals of civil engineers involved in the structural safety and reliability of buildings situated in regions susceptible to earthquakes. Friction-base isolators have been adopted as a means of passive control. The purpose of this experimental investigation is to measure the response statistics in the presence of base friction and other friction sources. The experimental model emulates a single-floor building supported on four leaf springs, subjected to band limited random excitation. Two different types of model base are considered, a friction base and a frictionless base. In both cases, friction can also be applied at two sides of the models main mass against the direction of its motion. Excitation and response transducer signals are processed to estimate excitation and response statistics in the presence and in the absence of top mass friction. Measured statistics include mean squares, autocorrelation functions, power spectra, and probability density functions. The dependence of the mean square response on the excitation level in the presence of friction reveals linear and nonlinear regimes, as well as a drift in the response due to dry friction. Above a certain excitation level the response-excitation relationship displays nonlinearity. A transition from narrow band to wide band response spectra is observed when friction is applied to the systems top mass. Analytical and Monte Carlo simulation results are compared with those measured experimentally based on a constant friction force.