Passive Control Elements Research Articles

Flow in a channel with obstacles of different scales: A detached rib and a forward-facing step

A numerical study of the flow in a channel with a forward- facing step was carried out. A single disconnected rib 3 mm high served as a passive control element in the range of Reynolds numbers from 2700 to 16400. The rib was installed at a distance to the ledge from 1.6 to 0.8 calibers at a height of 0.2 to 1 caliber. The introduction of an edge transforms the flow in front of the step. A tear-off area is created behind the rib. In cases of a high-lying rib, the separation area behind the shoulder becomes larger than the unregulated case, which leads to a loss of total pressure and an increase in the hydraulic resistance of the channel. Thermal-hydraulic efficiency was assessed; installing the fin at a close distance from the wall showed the best result

On the regulation of municipal indebtedness

The indebtedness of the Hungarian domestic municipal lending market was an area of intense research prior to the consolidation of municipal debt. Research analysed the possible causes and explanations of the rise in indebtedness and attempted to identify a model of indebtedness in the domestic municipal system, drawing on the experience of international models and examples. In parallel with the debt consolidation process, which was carried out in several steps between 2011 and 2014, a number of active and passive control elements were introduced in Hungary, which can be grouped in several ways. The introduced control elements have lived up to expectations. At the same time, the increase in the stock of other liabilities in the sector points to a shift in the sector's indebtedness from being indebted to bank financiers to being indebted to other counterparties.

Novel assessment of the variation in cervical inter-vertebral motor control in a healthy pain-free population

Spinal control at intervertebral levels is dependent on interactions between the active, passive and neural control elements. However, this has never been quantifiable, and has therefore been outside the reach of clinical assessments and research. This study used fluoroscopy during repeated unconstrained flexion and return neck movements to calculate intersegmental motor control (MC), defined as the difference and variation in repeated continuous angular motion from its average path. The study aimed to determine control values for MC at individual levels and its variability. Twenty male volunteers aged 19–29 received fluoroscopic screening of their cervical spines during 4 repetitions of neutral to full flexion and return motion. Moving vertebral images from C0–C1 to C6–C7 were tracked using cross-correlation codes written in Matlab. MC for each level was defined as the mean of the absolute differences between each repetition’s angular path and their mean and its variability as represented by the SD. 1-way ANOVA and Tukey multiple comparisons were used to identify significant contrasts between levels. The mean MC differences and SDs were highest at C1-2, suggesting that this level has the least control and the most variability. Results at this level alone were highly significant (F-ratio 10.88 and 9.79 P < 0.0001). Significant contrasts were only found between C1-C2 and all other levels. The mean MC difference for summed C1-6 levels was 3.4° (0.7–6.1). This study is the first to quantify intervertebral MC in the cervical spine in asymptomatic people. Studies of neck pain patients are now merited.

An experimentally validated multifidelity hybrid model for analyzing the pressure variation of a relief system

In a relief system, the pressure variation in the system is often caused by the operations of the pressure control elements such as the pressure relief valve and ball valve, in addition to the pressure fluctuations in the pressure resources. This pressure variation couples with the acoustics or the motion of passive pressure control elements, which may result in system malfunction. To investigate the principles of the pressure variation in a relief system including a reservoir, a pipeline and a spring-loaded pressure relief valve, a multifidelity hybrid model combining the method of characteristics (MOC) and computational fluid dynamics (CFD) method is proposed. In the multifidelity hybrid model, the characteristics of the pressure resources are modeled using their performance curves, the compressible gas transmitted in the pipe is calculated by one-dimensional MOC, and the air flow in the valve as well as the valve motion is simulated by a two-dimensional CFD model. To validate the model, analyses are conducted with a 1:1 scale test rig and a full CFD model. The comparison of the results shows that both the multifidelity hybrid model and the full CFD model can accurately capture the pressure fluctuations in straight pipelines induced by valve closure and predict the forms of valve motion, but the calculation speed of the multifidelity hybrid model is four times faster than that of the full CFD model.

Development of a solar reflector coating on AA6061 alloy by plasma electrolytic oxidation

A spacecraft consists of various components which will function with maximum efficiency only when their operating temperature is maintained within certain specified ranges. Passive thermal control elements play an important role in maintaining the temperature of spacecraft components within the specified ranges by suitable selection of thermo-optical properties of the surfaces namely absorptance and emittance. Plasma electrolytic oxidation of AA 6061 is studied as a method to develop a solar reflector coating for space applications. The coatings are developed by making use of a silicate-based electrolyte. The influence of electrolyte composition, average current density, processing time, positive on-time and pulse frequency on the thermo-optical behaviour of the coating is studied. The thickness of the PEO coating is optimized so as to attain thermo-optical properties similar or better than conventional sulphuric acid anodizing. The optimized coating is subjected to adhesion and humidity tests as well as various space simulation tests such as thermal cycling and thermo-vacuum performance tests to evaluate the suitability of the coating as a thermal control surface for space application. Coatings obtained by PEO process and conventional sulphuric acid anodizing are further characterized using SEM, EDX, XPS, XRD and nanoprofilometry to have a comparative study of their morphology, microstructure and composition.

Control of flow structures around a cylinder in deep water employing a passive control element

This study aimed to experimentally investigate the swirling flow characteristic in the periphery of a cylinder located vertically in a deep water channel using a particle image velocity measurement method (PIV). In addition to the PIV method, paint visualization experiments were performed to observe the structures of vortical flow qualitatively. Based on the cylinder diameter, Reynolds numbers were changed incrementally as 2.5 × 103, 5 × 103, and 7.5 × 103, while the length of the control element, L = 180 mm was kept constant. The flexible splitter plate made of a plastic material was easily deformed under the influence of vortical flow. In the horizontal plane, taken from the middleheight of the cylinder, instantaneous flow data was measured first. Along these measurements, the distributions and magnitude of the velocity vectors, 〈V〉, vorticity concentrations, 〈ω〉, patterns of streamlines, 〈ψ〉, root mean square of velocity component such as 〈urms〉 and 〈vrms〉, correlations of shear stresses, 〈u′u′〉, 〈v′v′〉 and 〈u′v′〉, turbulent kinetic energy, TKE, and spectral analysis is conducted to define the frequency, f of vortex formations. The presence of a flexible flow control element located along the central axis line of the cylinder significantly affects the vortex formations. The existence of the flexible flow control element can significantly influence the wake flow region. Furthermore, many of the value of flow characteristics decreased as mentioned with respect to the bare case.

RF transparent vanadium oxide based single and bi-layer thin films as passive thermal control element for satellite antenna application

Germanium coated black polyimide (GBP) is often used as passive thermal control element for sunshield membrane of satellite antenna. However, GBP degrades fast while there is no protective coating applied. The present work is aimed towards the development of protective films which could hinder the degradation of GBP. At the same time, the basic characteristic of GBP membrane that is RF transparency should not be trade off. Here, RF transparent and protective vanadium oxide (VO) and vanadium oxide/silicon dioxide (VO/SO) thin films are developed by RF magnetron sputtering technique on GBP at a constant 400 W. Field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS) techniques are utilized to investigate microstructural and oxide characteristics, respectively. Thermo-optical properties such as, solar absorptance (αs) and IR emittance (εir) are also evaluated. Introduction of SiO2 layer over vanadium oxide layer leads to decrease in αs to about 12%. RF losses e.g. insertion loss and return loss are measured in Ka band (27–39 GHz) and they found to be RF transparent characteristic. Thermal stability of the oxide films are also studied by differential scanning calorimetry (DSC) technique.

Evaluations of Silica Aerogel-Based Flexible Blanket as Passive Thermal Control Element for Spacecraft Applications

The feasibility of utilizing commercially available silica aerogel-based flexible composite blankets as passive thermal control element in applications such as extraterrestrial environments is investigated. Differential scanning calorimetry showed that aerogel blanket was thermally stable over – 150 to 126 °C. The outgassing behavior, e.g., total mass loss, collected volatile condensable materials, water vapor regained and recovered mass loss, was within acceptable range recommended for the space applications. ASTM tension and tear tests confirmed the material’s mechanical integrity. The thermo-optical properties remained nearly unaltered in simulated space environmental tests such as relative humidity, thermal cycling and thermo-vacuum tests and confirmed the space worthiness of the aerogel. Aluminized Kapton stitched or anchored to the blanket could be used to control the optical transparency of the aerogel. These outcomes highlight the potential of commercial aerogel composite blankets as passive thermal control element in spacecraft. Structural and chemical characterization of the material was also done using scanning electron microscopy, Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy.

Control of natural convection via inclined plate of CNT-water nanofluid in an open sided cubical enclosure under magnetic field

A computational analysis has been performed in this work to solve three-dimensional magnetohydrodynamic natural convection in an open cubical enclosure filled with CNT-water nanofluid. The cavity is heated from left vertical wall and an inclined plate is attached inside the cavity with finite length. The study is solved for different governing parameters as Rayleigh number (103≤Ra≤105), nanoparticle volume fraction (0%≤φ≤5%), Hartmann number (0≤Ha≤100) and inclination angle of the fin (0°≤θ≤360°). It is observed that all of these parameters can be used as passive control element for heat and fluid flow and the maximum heat transfer is formed when θ=180° but minimal value of average Nusselt number is changed according to nanoparticle addition into base fluid.

Efficient optimal design and design‐under‐uncertainty of passive control devices with application to a cable‐stayed bridge

Summary Structures today may be equipped with passive structural control devices to achieve some performance criteria. The optimal design of these passive control devices, whether via a formal optimization algorithm or a response surface parameter study, requires multiple solutions of the dynamic response of that structure, incurring a significant computational cost for complex structures. These passive control elements are typically point-located, introducing a local change (possibly nonlinear, possibly uncertain) that affects the global behavior of the rest of the structure. When the structure, other than these localized devices, is linear and deterministic, conventional solvers (e.g., Runge–Kutta, MATLAB's ode45, etc.) ignore the localized nature of the passive control elements. The methodology applied in this paper exploits the locality of the uncertain and/or nonlinear passive control element(s) by exactly converting the form of the dynamics of the high-order structural model to a low-dimensional Volterra integral equation. Design optimization for parameters and placement of linear and nonlinear passive dampers, tuned mass dampers, and their combination, as well as their design-under-uncertainty for a benchmark cable-stayed bridge, is performed using this approach. For the examples considered herein, the proposed method achieves a two-orders-of-magnitude gain in computational efficiency compared with a conventional method of comparable accuracy. Copyright © 2016 John Wiley & Sons, Ltd.

Hybrid vibration absorber with detached design for global vibration control

A new hybrid vibration absorber, with detached passive and active parts, is designed, analyzed and tested. This is an alternative approach in case the traditional bundled hybrid vibration absorber with collocated active and passive control elements cannot be applied. In fixed-free structures like buildings and towers, a passive dynamic vibration absorber is very popular for vibration control at or near the free ends. Active control may be introduced to improve performance, but space or weight may be limited in some applications. It may not be practical to attach an actuator near the passive part. The new approach provides more flexibility to retrofit a passive dynamic vibration absorber into a high performance hybrid vibration absorber by installing the actuator at a more suitable location than collocated with the passive part. The proposed hybrid vibration absorber is based on the pole-placement control strategy. Its controller is able to deal with a possible nonminimum-phase secondary path caused by noncollocated actuator sensors. This feature does not exist in a bundled hybrid vibration absorber with collocated actuator sensors. The performance of the new hybrid vibration absorber is analyzed in this study. Experimental and simulation results are used to verify the theoretical results and demonstrate the excellent performance of the new hybrid vibration absorber for vibration control at multiple points. A bundled hybrid vibration absorber with collocated passive and active elements is compared with the proposed hybrid vibration absorber with detached control elements, using experimental and simulation results. It was found that the vibration attenuation performance of the proposed hybrid vibration absorber can be better than the traditional bundled hybrid vibration absorber. The optimal actuator location, which is not necessarily the coupling point of the passive resonator, can be selected numerically by a proposed procedure. One could miss a better solution for vibration control if he/she only uses the bundled hybrid vibration absorber without considering the detached hybrid vibration absorber as a possible alternative.

English

An internal combustion engine produces excessive exhaust noise. A good exhaust system should control and keep the exhaust noise within the passable limit. Passive noise control techniques are employed to control the exhaust noises. Mufflers acts as a passive noise control elements in an exhaust system which attenuates noise by reflecting the sound wave and cancels it by destructive interferences and by absorbing the sound and dissipate into heat using absorptive materials .The muffler using absorptive materials for attenuating noise can cover a wide range of higher frequencies creating less back pressure while a reflection type muffler works well in lower and mid range frequencies but produces higher back pressure. This papers discusses the experimental results and performance evaluation of both absorption and reflective mufflers which are calculated by sound transmission loss (STL) experiment technique .

Dynamics of flow control in an emulated boundary layer-ingesting offset diffuser

Dynamics of flow control comprised of arrays of active (synthetic jets) and passive (vanes) control elements , and its effectiveness for suppression of total-pressure distortion is investigated experimentally in an offset diffuser, in the absence of internal flow separation. The experiments are conducted in a wind tunnel inlet model at speeds up to M = 0.55 using approach flow conditioning that mimics boundary layer ingestion on a Blended-Wing-Body platform. Time-dependent distortion of the dynamic total-pressure field at the ‘engine face’ is measured using an array of forty total-pressure probes, and the control-induced distortion changes are analyzed using triple decomposition and proper orthogonal decomposition (POD). These data indicate that an array of the flow control small-scale synthetic jet vortices merge into two large-scale, counter-rotating streamwise vortices that exert significant changes in the flow distortion. The two most energetic POD modes appear to govern the distortion dynamics in either active or hybrid flow control approaches. Finally, it is shown that the present control approach is sufficiently robust to reduce distortion with different inlet conditions of the baseline flow.

Control of Laminar Pulsating Flow and Heat Transfer in Backward-Facing Step by Using a Square Obstacle

In the present study, laminar pulsating flow over a backward-facing step in the presence of a square obstacle placed behind the step is numerically studied to control the heat transfer and fluid flow. The working fluid is air with a Prandtl number of 0.71 and the Reynolds number is varied from 10 and 200. The study is performed for three different vertical positions of the square obstacle and different forcing frequencies at the inlet position. Navier–Stokes and energy equation for a 2D laminar flow are solved using a finite-volume-based commercial code. It is observed that by properly locating the square obstacle the length and intensity of the recirculation zone behind the step are considerably affected, and hence, it can be used as a passive control element for heat transfer augmentation. Enhancements in the maximum values of the Nusselt number of 228% and 197% are obtained for two different vertical locations of the obstacle. On the other hand, in the pulsating flow case at Reynolds number of 200, two locations of the square obstacle are effective for heat transfer enhancement with pulsation compared to the case without obstacle.

Distortion Management in a Boundary Layer Ingestion Inlet Diffuser Using Hybrid Flow Control

Flow distortion in a 5% scale model of a blended-wing-body, boundary-layer-ingesting offset diffuser is mitigated at high subsonic speeds (up to ) using integrated, hybrid actuators comprised of tandem configurations of passive (vanes) and active (synthetic jets) flow control elements. The inlet flow of the model diffuser is conditioned to simulate the inlet flow of an airborne blended-wing-body offset diffuser by implementation of a novel boundary layer fence. It is shown that flow distortion at the engine face is reduced by each of the passive and active elements, and the reduction is even more significant when both actuation approaches are implemented, concurrently, over the entire range of test Mach numbers. Hybrid actuation yields an overall distortion reduction of 35% at the design flow condition () using a control system that is fail safe and does not require an external air supply.

Track-position and vibration control simulation for strut of the Stewart platform

Vibrations inherently generated by on-board disturbance sources degrade the performance of the instruments in an on-orbit spacecraft, which have stringent accuracy requirements. The Stewart platform enables both track-positioning and vibration control. The strut of the Stewart platform is designed as a piezoelectric (PZT) element in series with a voice coil motor (VCM) element and a viscoelastic element. The track-positioning system uses a VCM as the main positioning control driver and a PZT as the positioning compensator. The vibration control system uses the characteristics of struts including active and passive control elements to attenuate the vibration. Simulation results indicate that the Stewart platform with the designed struts has good performance in tracking and vibration attenuation with different interference waves.

Sensitivity analysis of a time-delayed thermo-acoustic system via an adjoint-based approach

AbstractWe apply adjoint-based sensitivity analysis to a time-delayed thermo-acoustic system: a Rijke tube containing a hot wire. We calculate how the growth rate and frequency of small oscillations about a base state are affected either by a generic passive control element in the system (the structural sensitivity analysis) or by a generic change to its base state (the base-state sensitivity analysis). We illustrate the structural sensitivity by calculating the effect of a second hot wire with a small heat-release parameter. In a single calculation, this shows how the second hot wire changes the growth rate and frequency of the small oscillations, as a function of its position in the tube. We then examine the components of the structural sensitivity in order to determine the passive control mechanism that has the strongest influence on the growth rate. We find that a force applied to the acoustic momentum equation in the opposite direction to the instantaneous velocity is the most stabilizing feedback mechanism. We also find that its effect is maximized when it is placed at the downstream end of the tube. This feedback mechanism could be supplied, for example, by an adiabatic mesh. We illustrate the base-state sensitivity by calculating the effects of small variations in the damping factor, the heat-release time-delay coefficient, the heat-release parameter, and the hot-wire location. The successful application of sensitivity analysis to thermo-acoustics opens up new possibilities for the passive control of thermo-acoustic oscillations by providing gradient information that can be combined with constrained optimization algorithms in order to reduce linear growth rates.

A Control Approach for Actuated Dynamic Walking in Biped Robots

This paper presents an approach for the closed-loop control of a fully actuated biped robot that leverages its natural dynamics when walking. Rather than prescribing kinematic trajectories, the approach proposes a set of state-dependent torques, each of which can be constructed from a combination of low-gain spring-damper couples. Accordingly, the limb motion is determined by interaction of the passive control elements and the natural dynamics of the biped, rather than being dictated by a reference trajectory. In order to implement the proposed approach, the authors develop a model-based transformation from the control torques that are defined in a mixed reference frame to the actuator joint torques. The proposed approach is implemented in simulation on an anthropomorphic biped. The simulated biped is shown to converge to a stable, natural-looking walk from a variety of initial configurations. Based on these simulations, the mechanical cost of transport is computed and shown to be significantly lower than that of trajectory-tracking approaches to biped control, thus validating the ability of the proposed idea to provide efficient dynamic walking. Simulations further demonstrate walking at varying speeds and on varying ground slopes. Finally, controller robustness is demonstrated with respect to forward and backward push-type disturbances and with respect to uncertainty in model parameters.

Integrated Design of Controlled Linear Structural Systems

This paper addresses the integrated design of civil engineering structures with control systems. Simultaneous optimization of such controlled structures is considered, showing that new alternative solutions can be achieved through integrated design. A procedure for design of controlled structural systems is developed using a two-stage approach: (1) a design of an optimal control system using a linear quadratic regulator algorithm; and (2) a redesign using an optimization procedure to match the performance of the controlled system obtained in (1). A linear single degree of freedom steel portal frame and a linear nine degree of freedom shear-type structure are used as examples to illustrate the feasibility of the proposed approach that reduces the structural weight of buildings by incorporating active or passive control elements while preserving the performance objectives.

Transient simulations of the electrophoretic motion of a cylindrical particle through a 90° corner

The trajectory of a cylindrical particle driven by electrophoresis was transiently simulated as the particle moves through a 90° corner. A variety of system parameters were tested to determine their impact on the particle motion. The zeta potential, channel width, and particle aspect ratio were shown to have a minimal effect on the particle motion. Conversely, the initial vertical position of the particle and initial angle with respect to the horizontal had a significant impact on the particle motion. The presence of the 90° corner acts to reduce the initial distribution of angles to the vertical of 90° to less than 30°, demonstrating the possibility of using a corner as a passive control element as part of a larger microfluidic system. However, the reduction in angle is limited to the area near the corner posing a limitation on this means of control.