Symmetric Chamber Research Articles

Modeling and Analysis of Soft Pneumatic Actuator with Symmetrical Chambers Used for Bionic Robotic Fish.

A theoretical model is built in this study for analyzing and predicting the deformation of a bending-type soft pneumatic actuator used for bionic robotic fish. The actuator is composed of two symmetrically distributed silicone rubber blocks (Ecoflex0030 from Smooth-on Co., Ltd.). Between the two rubber blocks, an ABS plate is fixed to work as a neutral layer. When one side of the actuator is inflated, it consequently bends toward the uninflated side. The deformation of the actuator on the inflated side and the uninflated side, respectively, is analyzed based on principles of elasticity mechanics. The deformation on the inflated side is simplified to planar type and is decomposed into two mutually perpendicular directions to analyze the stress state. A two-step deforming process is proposed to study the stress state on the uninflated side. The two components are combined to determine the relationship between the bending angle of the actuator and the actuating pressure. The proposed model is compared with a finite element analysis model in which the same constraint, load, and materials are used. An experiment under the same conditions was implemented to validate the model. The experiment demonstrates that the accuracy of the theoretical model is adequate to indicate the response of the soft pneumatic actuator to the actuating pressure. A bionic fishtail system based on the soft pneumatic actuator was also established to verify the applicability of the actuator to bionic robotic fish.

Group size and decision making: experimental evidence for minority games in fish behaviour

Animals tend to learn and make decisions inductively, and simple, individual-level behavioural decisions can scale up to yield interesting emergent properties at the population level. The minority game is a theoretical formulation based on the principle of inductive learning, wherein a group of individuals, each facing two equivalent choices, self-organize to achieve maximum coordination. Coordination increases with memory length up to a certain threshold, and thereafter, at very high memory lengths, decisions resemble a random choice game. We invoked and observed minority games in guppies, Poecilia reticulata, by forcing them to choose between two symmetric chambers in a series of repeated trials. At an intermediate timescale, guppies self-organized into a globally efficient state featuring maximum coordination. After a large number of trials, the guppies approached a steady state in which they behaved as if they were randomly choosing between the two chambers. Intriguingly, both the time taken to reach this globally efficient state (i.e. learning time) and the grouping behaviour for decision making depended on the sexual composition of the fish populations. We identified a positive correlation between group size and learning time in the experiments, which we further explored using simulations to uncover the form of decision-making framework at play, testing between a leader-based framework and a consensus-based one. Our simulations supported the presence of a consensus-based decision-making process in the system. This work also provides an unexplored general framework to further investigate and understand simple decision-making dynamics and structure in animal groups.

A Soft Three-Axis Force Sensor Based on Radially Symmetric Pneumatic Chambers

In physical human–machine interaction applications, the accurate measurement of interactive forces between the human and the machine plays a significant role. Sensors for this purpose should not only be accurate and reliable, but also be soft enough to guarantee the safe and compliant interaction. In this aspect, pneumatic sensors with soft air chambers have often been utilized as a soft force sensor system. Although the pneumatic-based force sensor provides a good compliance and softness, however, it measures only a lumped force acting on the chamber, because the pneumatic sensor measures the overall pressure change in the air chamber. In this paper, a three-axis force sensor with three air chambers in a radially symmetric pattern is proposed for the measurement of multi-dimensional interaction forces with high softness and compliance. Each air chamber embeds a pneumatic sensor, and the pressure changes in the three air chambers are measured in order to distinguish the direction of the applied force. By decoupling the sensor signals from the three pneumatic sensors, the three-dimensional force components can be calculated accurately. Consequently, the proposed sensor is able to measure the three-dimensional forces while maintaining the great softness and compliance provided by the soft air chambers. The design, the fabrication method, and the verification of the proposed method are introduced in this paper.

4 DOFs Hollow Soft Pneumatic Actuator–HOSE

This study reports a novel Hollow Soft Pneumatic Actuator (HOSE), which exhibits 4 degrees of freedom (DOFs). The design consists of a central hollow cylinder surrounded by four twisting symmetric chambers. By virtue of their spiral disposition, each chamber produces a diagonal force along the hollow internal cylinder composed of two components: one parallel to the Z axis and the other one to the plane X-Y. Both top and bottom sections of the actuator are reinforced to avoid deformation, essential for optimal function and dexterity of HOSE. Different movements of the actuator are produced by varying the activation combinations of the 4 chambers. They are constructed from thin walled (0.5 mm) Ecoflex 00–30 super soft silicon rubber, enabling HOSE to perform controlled movements with low pressure not exceeding 35 kPa. HOSE exhibits a maximal extension of 230% of its original length, bends up to i) ±900 around X axis, ii) ±1150 around Y axis, and iii) twists around Z axis with a total range of ±350. The paper describes the manufacturing process together with the actuator performance, reporting the range of motion along each DOF related to the internal pressure, volume versus forces and torques produced along each axis.

The impact of a bilateral symmetric discharge structure on the performance of a scroll expander for ORC power generation system

Scroll expander is a good candidate for small-scale ORC systems. Discharge flow has a significant impact on the expander performance. In this study, a novel bilateral symmetric discharge structure for scroll expander was proposed and compared with the unilateral discharge structure using CFD approach. Discharge flow features and the performances of the scroll expander were analyzed. Results show that the pulsation of the discharge mass flow rate in the expander with bilateral discharge structure is related to both the eccentric rotation of the orbiting scroll and the decompression drainage of the second discharge port. The symmetric discharge structure contributes to the pressure reduction and the uniform flow in working chambers. Both pressure distortions and secondary flows are weakened or even eliminated. Special damped pulsation of pressure in discharge chamber is also revealed, which has an important impact on the driving moments of the scroll segments in discharge chambers. The pulsating pressures in discharge chambers vary in an opposite peak-valley pattern. The symmetric discharge structure could balance the pressure pulsation level between discharge chambers and enhance the driving moment by 6.38%. The driving moment increment of the scroll segments between symmetric working chambers plays a positive role in the expander performance.

Three‐Dimensional Failure Patterns Around an Inflating Magmatic Chamber

AbstractBedrock failure around an inflating magma chamber is an important factor that controls the occurrence of volcanic eruptions. Here, we employ 3‐D numerical models of elasto‐plastic shear failure around an inflating crustal reservoir, to study how the induced failure patterns depend on the geometry of the chamber, on the host rock strength and on the gravitational field. Our simulations show that either localized or diffuse plastic failure domains develop in 3 stages. Failure initiates (stage 1) after a critical overpressure is reached, the value of which depends on effective host rock strength. Next, and with increasing applied overpressure, either distributed (for zero friction angle) or localized plastic failure zones (for 30 friction angle) form (stage 2), until they finally connect to the surface (stage 3). Cylindrical chambers develop prismatic shear zones that merge from the surface and chamber walls. For spherical and prolate chambers, diffuse conical zones of failure develop from the chamber's crest, whereas for oblate symmetrical chambers, shear bands initiate at the horizontal tips but bend back above the center of the chamber to reach the surface. In contrast for asymmetrical oblate chambers, shear bands initiate in their cylindrical section and vanish along the elongated direction. Here, magmatic fluids may migrate both through diffuse elastic dilation zones at the tips, and through localized shear zones from the crest. Our results thus suggest how natural observations may be used to constrain the mode of failure occurring underneath a volcano. We discuss several natural examples in this context.

Ionization chamber radial response deconvolution in megavoltage photon beam

The aim of this paper is to study a radial response model as a method, to correct output factor results gathered with ionization chambers of different size and shape in cone collimated RT fields. An enhanced version of a non-parametric super-resolution deconvolution method able to model a radial response function of a small cylinder symmetric ionization chamber is described and demonstrated. The radial response of four ionization chambers with different geometry and radius are estimated using 6 MV photon beam in water at the isocentre plane. Finally the validity of the estimates is tested by applying the response functions to the output factor measurements of 4–20 mm conical collimators. The enhanced method is demonstrated by obtaining the response function characteristics with a spatial uncertainty smaller than 0.1 mm when the distance from chamber axis is larger than 0.5 mm. In all studied ionization chambers, a significant local response maximum is found close to the air cavity boundary. The agreement between the output factor results of different chambers is promising, the largest difference (max—min) in output factor is 4% obtained for the smallest 4 mm cone size.

Unsteady Leakage Flow Through Axial Clearance of an ORC Scroll Expander

As the scroll-type expander (STE) becomes an attractive expansion device for small-scale organic Rankine systems, performance enhancement of STE could achieve a further improvement of the energy efficiency of ORC system. The gas leakages through the axial and radial clearances have a great effect on the overall performance of STE. The present work proposed a three-dimensional numerical technique available for modeling the radial leakage flows through the axial clearances at the tip and root of scroll wrap. The radial leakage flow patterns of both axial clearances are investigated. Asymmetrical distribution of the radial leakage flow through the axial clearances at both sides of working chambers are revealed. Leakage flow difference between the top and bottom axial leakage clearances is comparatively discussed. The effects of radial leakage on the flow fields in the working chambers are also analyzed. The results show the radial leakage flows occur at the axial clearances of both the scroll segments between asymmetrical working chambers and those between symmetrical working chambers. Radial leakage flows through the top and bottom axial clearances are approximately symmetrical about the meshing line. Pressure distribution in the axial clearance passage is uneven along the scroll involute direction, especially in the axial clearance passages between asymmetric chambers. Pressure distortion occurs in the downstream of the axial clearance passage between asymmetric working chambers nearby the mesh point of the scroll wraps. Radial leakage flow leads to the secondary vortex flows and non-uniform pressure distributions in the working chambers.

Numerical analysis of the transient flow in a scroll refrigeration compressor

In the present paper, the CFD technology is adopted to simulate the working process of a scroll refrigeration compressor with R22 as working fluid. The structural grids in the scroll compressor were updated continually during the solving process to cope with the movement boundaries of the fluid domain. The radial meshing clearance was 0.008 mm which was the same with that in the real prototype. The pressure, velocity and temperature distribution in chambers of compressor were computed. Also, the transient mass flux diagrams were calculated out. The results indicated that the pressure was asymmetrical in the two symmetrical suction chambers, because the suction port and passage were not absolutely symmetrical. The gradient of temperature was great in each working chamber due to leakage flow. Velocity vector distribution was asymmetrical in each pair of working chamber owing to the movement of orbiting scroll; the flow was complicated in the central working chamber. The movement of the orbiting scroll had different influence on the vortexes formation in each pair of compression chamber. The inlet and outlet mass flux fluctuated with the crank angle obviously. Because of the ‘cut-off’ of the refrigeration fluid in the suction chamber when the crank angle was larger than 220°, the inlet mass flux decreased remarkably. Finally, some useful advices were given to improve the performance of the scroll refrigeration compressor.

The swirl ratio influence on combustion process and heat transfer in the opposed piston compression-ignition engine

In order to maximise engine heat efficiency an engines charge flow must be properly designed -especially its swirl and tumble ratio. A two-stroke compression-ignition opposed piston engine reacts to engine swirl differently compared to a standard automotive engine with axially symmetric combustion chamber. In order to facilitate direct fuel injection, high-pressure injectors must be positioned from the side of combustion chamber. Depending on the combustion chamber geometry the swirling gases impact greatly how the injection stream is formed. If the deformation is too high the high temperature combustion gases can hit the piston surface or get into gaps between the pistons. This greatly affects the heat lost to the pistons and raises their local temperature. More atomised injection stream is more prone to swirling gas flow due to its reduced droplet size and momentum. The paper presents simulation results and analyses for different intake process induced swirl ratios and different types of combustion chambers in an experimental aviation opposed piston engine.

Institutional veto players and cabinet formation: The veto control hypothesis reconsidered

AbstractAre potential cabinets more likely to form when they control institutional veto players such as symmetric second chambers or minority vetoes? Existing evidence for a causal effect of veto control has been weak. This article presents evidence for this effect on the basis of conditional and mixed logit analyses of government formations in 21 parliamentary and semi‐presidential democracies between 1955 and 2012. It also shows that the size of the effect varies systematically across political‐institutional contexts. The estimated causal effect was greater in countries that eventually abolished the relevant veto institutions. It is suggested that the incidence of constitutional reform is a proxy for context‐specific factors that increased the incentives for veto control and simultaneously provided a stimulus for the weakening of institutional veto power.

Weakly nonlinear analysis of thermoacoustic instabilities in annular combustors

Rotationally symmetric annular combustors are of practical importance because they generically resemble combustion chambers in gas turbines, in which thermoacoustically driven oscillations are a major concern. We focus on azimuthal thermoacoustic oscillations and model the fluctuating heat release rate as being dependent only on the local pressure in the combustion chamber. We study the dynamics of the annular combustor with a finite number of compact flames equispaced around the annulus, and characterize the flames’ response with a describing function. We discuss the existence, amplitude and the stability of standing and spinning waves, as a function of: (i) the number of the burners; (ii) the acoustic damping in the chamber; (iii) the flame response. We present the implications for industrial applications and the future direction of investigations. We then present as an example the first theoretical study of thermoacoustic triggering in annular combustors, which shows that rotationally symmetric annular chambers that are thermoacoustically unstable do not experience only stable spinning solutions, but can also experience stable standing solutions. We finally test the theory on one experiment with good agreement.

Pore-Scale Investigations on the Dynamics of Gravity-Driven Steam-Displacement Process for Heavy-Oil Recovery and Development of Residual Oil Saturation: A 2D Visual Analysis

Summary The dynamics of a gravity-driven injection process for heavy-oil recovery at the pore scale and the mechanisms leading to the formation of residual oil saturation (ROS) were investigated. The 10 × 15-cm and 5 × 5-cm 2D visual sandpack models (a single layer of sintered microscale glass beads) were prepared and placed into a transparent vacuum chamber to prevent heat loss. The processes were recorded with a high-speed camera to obtain visual data at the pore scale. This process represents the lateral spreading of the steam chamber (half symmetric chamber growth) during steam-assisted gravity drainage (SAGD) for heavy-oil recovery. Oil-trapping mechanisms yielding to the formation of ROS were described and analyzed because of (1) lateral expansion, (2) simultaneous vertical and lateral expansion, (3) pore and particle size, (4) heterogeneities (pore- and particle-size distribution), and (5) wettability. Attention was also given to the ceiling region of the steam chamber and its interaction with the mobilized region at the lateral boundaries of the chamber.

The effect of baffles on self-excited azimuthal modes in an annular combustor

In this paper the effect of inserting baffles on the self-excited azimuthal modes and unsteady heat release rate in an annular combustor are investigated experimentally. Particular attention is given to their effect on the time-varying behaviour of azimuthal modes observed in recent experiments and Large Eddy Simulations (LES) in azimuthally symmetric annular chambers. This time-varying behaviour causes the azimuthal modes to switch back and forth between spinning and standing wave modes. With the addition of a single baffle, the azimuthal symmetry of the chamber was broken leading to a coupling between the clockwise (CW) and anticlockwise (ACW) azimuthal acoustic waves. This eliminated the time-varying behaviour and promoted standing wave modes. It was found that three or more baffles were required to achieve significant damping of the modes. Since almost perfect standing wave modes occurred with the addition of a single baffle, high-speed chemiluminescence measurements were obtained to characterise the unsteady heat release rate at the pressure node and anti-node. Previous studies have shown that maximum and minimum heat release rate is produced at the anti-nodes and nodes respectively. As found previously, peak fluctuations at the anti-nodes result from axisymmetric fluctuations in heat release rate caused by pressure fluctuations driving axial mass flow fluctuations at the burner inlet. However, at the pressure nodes, an anti-symmetric structure was observed producing negligible heat release rate via the mechanism of cancellation. This latter result suggests that transverse velocity fluctuations play an important mechanistic role in ensuring that negligible heat release rate is produced at the node.

The role of pre-existing tectonic structures and magma chamber shape on the geometry of resurgent blocks: Analogue models

A set of analogue models has been carried out to understand the role of an asymmetric magma chamber on the resurgence-related deformation of a previously deformed crustal sector. The results are then compared with those of similar experiments, previously performed using a symmetric magma chamber. Two lines of experiments were performed to simulate resurgence in an area with a simple graben-like structure and resurgence in a caldera that collapsed within the previously generated graben-like structure. On the basis of commonly accepted scaling laws, we used dry-quartz sand to simulate the brittle behaviour of the crust and Newtonian silicone to simulate the ductile behaviour of the intruding magma. An asymmetric shape of the magma chamber was simulated by moulding the upper surface of the silicone. The resulting empty space was then filled with sand. The results of the asymmetric-resurgence experiments are similar to those obtained with symmetrically shaped silicone. In the sample with a simple graben-like structure, resurgence occurs through the formation of a discrete number of differentially displaced blocks. The most uplifted portion of the deformed depression floor is affected by newly formed, high-angle, inward-dipping reverse ring-faults. The least uplifted portion of the caldera is affected by normal faults with similar orientation, either newly formed or resulting from reactivation of the pre-existing graben faults. This asymmetric block resurgence is also observed in experiments performed with a previous caldera collapse. In this case, the caldera-collapse-related reverse ring-fault is completely erased along the shortened side, and enhances the effect of the extensional faults on the opposite side, so facilitating the intrusion of the silicone. The most uplifted sector, due to an asymmetrically shaped intrusion, is always in correspondence of the thickest overburden. These results suggest that the stress field induced by resurgence is likely dictated by the geometry of the intruding magma body, and the related deformation is partially controlled by pre-existing tectonic and/or volcano-tectonic structures.

Vortex-aided inertial microfluidic device for continuous particle separation with high size-selectivity, efficiency, and purity

In this paper, we report an inertial microfluidic device with simple geometry for continuous extraction of large particles with high size-selectivity (<2 μm), high efficiency (∼90%), and high purity (>90%). The design takes advantage of a high-aspect-ratio microchannel to inertially equilibrate cells and symmetric chambers for microvortex-aided cell extraction. A side outlet in each chamber continuously siphons larger particles, while the smaller particles or cells exit through the main outlet. The design has several advantages, including simple design, small footprint, ease of paralleling and cascading, one-step operation, and continuous separation with ultra-selectivity, high efficiency and purity. The described approach is applied to manipulating cells and particles for ultra-selective separation, quickly and effectively extracting larger sizes from the main flow, with broad applications in cell separations.

An experimental study of a floating breakwater with asymmetric pneumatic chambers for wave energy extraction

Integrating oscillating-water-column type converters (pneumatic chambers) with slack-moored floating breakwaters can be a viable option for cost-sharing between wave energy capturing devices and shore-protection structures, and thus enhance the cost-effectiveness of wave energy utilization. When designing such integrated systems, it is desirable to have a system that can capture wave energy over a wide range of wave frequency. In this study, a configuration of floating breakwater with asymmetric pneumatic chambers (a narrower chamber on the seaside and a wider chamber on the leeside) is proposed to increase the amplitude of the oscillating air-pressures inside both chambers over a wide range of wave frequency (thus to improve the performance in wave energy extraction). A series of experiments were carried out under regular wave conditions to study the effects of asymmetric pneumatic chambers on the hydrodynamic performance of the floating breakwater and on the oscillating air-pressures inside the two chambers. It was shown that (1) the breakwater with asymmetric chambers performed as good as that with symmetric chambers in terms of wave transmission and motion responses and (2) with asymmetric configuration, it is possible to increase the amplitude of the oscillating air-pressures inside both chambers. The new concept provides a promising way to extend the frequency range over which wave energy can be extracted.

Super-resolution non-parametric deconvolution in modelling the radial response function of a parallel plate ionization chamber

The signal of the dosimetric detector is generally dependent on the shape and size of the sensitive volume of the detector. In order to optimize the performance of the detector and reliability of the output signal the effect of the detector size should be corrected or, at least, taken into account. The response of the detector can be modelled using the convolution theorem that connects the system input (actual dose), output (measured result) and the effect of the detector (response function) by a linear convolution operator. We have developed the super-resolution and non-parametric deconvolution method for determination of the cylinder symmetric ionization chamber radial response function. We have demonstrated that the presented deconvolution method is able to determine the radial response for the Roos parallel plate ionization chamber with a better than 0.5 mm correspondence with the physical measures of the chamber. In addition, the performance of the method was proved by the excellent agreement between the output factors of the stereotactic conical collimators (4–20 mm diameter) measured by the Roos chamber, where the detector size is larger than the measured field, and the reference detector (diode). The presented deconvolution method has a potential in providing reference data for more accurate physical models of the ionization chamber as well as for improving and enhancing the performance of the detectors in specific dosimetric problems.

SU-E-I-107: Suitability of Various Radiation Detectors Used in Radiation Therapy for X-Ray Dosimetry in Computed Tomography.

Assessment of suitability for X-ray dosimetry in computed tomography of various ionization chambers, diodes and two-dimensional detector arrays primarily used in radiation therapy. An Oldelft X-ray simulation unit was used to irradiate PTW 60008, 60012 dosimetry diodes, PTW 23332, 31013, 31010, 31006 axial symmetrical ionization chambers, PTW 23343, 34001 plane parallel ionization chambers and PTW Starcheck and 2D-Array seven29 as well as a prototype Farmer chamber with a copper wall. Peak potential was varied from 50 kV up to 125 kV and beam qualities were quantified through half-value-layer measurements. Energy response was investigated free in air as well as in 2 cm depth in a solid water phantom and refers to a manufacturer calibrated PTW 60004 diode for kV-dosimetry. The thimble ionization chambers PTW 31010, 31013, the uncapsuled diode PTW 60012 and the PTW 2D-Array seven29 exhibit an energy response deviation in the investigated energy region of approximately 10% or lower thus proving good usability in X-ray dosimetry if higher spatial resolution is needed or rotational irradiations occur. It could be shown that in radiation therapy routinely used detectors are usable in a much lower energy region. The rotational symmetry is of advantage in computed tomography dosimetry and enables dose profile as well as point dose measurements in a suitable phantom for estimation of organ doses. Additional the PTW 2D-Array seven29 can give a quick overview of radiation fields in non-rotating tasks.

Biocathode microbial fuel cell for efficient electricity recovery from dairy manure

Microbial fuel cells (MFCs) represent a new biological method for generating electricity directly from biodegradable compounds. Efficiency of MFCs using manure as substrate is generally low. This study proposed a new design by incorporating biocathodes into a three-chamber MFC, which yielded maximum power densities much higher than those reported in literature. The new design placed cylindrical anode chamber for easy stirring and two symmetrical cathodic chambers with reduced anode–cathode distance. The biocathodes were applied to reduce charge transfer resistance. Additionally, biocathode microbial community was cultured to enrich favorable microorganisms. With external loading of 100Ω, the power densities for new biocathode MFC using 2, 4, 6, 8 and 10% total solids diary manure reached 7.85±1.0Wm−3, 7.84±1.20Wm−3, 8.15±0.20Wm−3, 7.60±0.97Wm−3 and 5.63±0.97Wm−3, respectively. The pH drop as a result of manure hydrolysis limited the power output. To provide detailed information of the microbial community in the biocathode MFC, the 454-pyrosequencing technique was adopted. The Firmicutes, γ-, β-, α- and δ-Proteobacteria, Bacteroidetes and Actinobacteria were the major groups on the anode, while γ-, β-, and α-Proteobacteria, Bacteroidetes and Actinobacteria were the predominant groups on the cathode.