Radial Constraint Research Articles

Locomotion via Active Suction in a Sea Star-Inspired Soft Robot

Some marine animals, such as sea stars, have developed versatile adhesive appendages that can be used for a variety of behaviors including sticking to surfaces, manipulating objects, and locomoting. These appendages couple reversible adhesion capabilities with muscular structures that can do work on the world while still being soft enough to conform to various surfaces and to squeeze through tight spaces. We took inspiration from the hydraulic tube feet of sea star to create modules consisting of soft active suction discs and soft pneumatic linear actuators. Tube feet convert fluid motion into linear actuation using soft tubes that are constrained radially. In this work, we study the tradeoff between the stiffness of such radial constraints, and the ability of the linear actuators to apply axial forces. The adhesive force of the suction disc is dependent on both the pressure differential between the suction cavity and the environment and the deformation within the body of the disc while it is being loaded. We show that the tube foot modules are capable of creating locomotion over flat surfaces, up small steps, and in a confined space due to the redundancy caused by an array of actuators. We also show that active suction not only enables the use of softer tube foot actuators, but that sensing this active suction line provides feedback to increase the efficiency of locomotion over obstacles.

Flow characteristics and formation optimization of vortex ring air supply.

The vortex rings ventilation (VRV) is a new type of air supply system comprising vortex rings. Compared with an air supply jet, a vortex ring reduces the loss of fresh air during transportation because of its stable structure. However, during the formation of the vortex ring, it entrains the ambient air and reduces the fresh air in the vortex ring. In this study, a vortex ring generator with a fresh air cavity is proposed to form confined vortex rings. This improved the fresh air ratio of the VRV. Based on previous experiments, a piston-orifice axisymmetric model with a dynamic grid was developed to form an air vortex ring. The flow characteristics of free and confined vortex rings during the generation stage were studied. First, the evolution of free vortex rings with different stroke lengths was studied, and the optimal piston stroke length and radial constraint size were determined. Subsequently, the mixing ratios of the free and confined vortex rings were compared and analyzed. The results showed that the mixing ratio of the confined vortex ring formed by the fresh air cavity in the formation stage was zero. Moving to the location of 4.9 times the orifice diameter ( ), reduced the mixing ratio of the confined vortex ring by 77.78% compared with that of the free vortex ring. In addition, the influence of three inner diameters and four outlet diameters of fresh air cavities on the vortex rings was studied to optimize the size of the vortex ring generator. The results showed that the inner diameter of the fresh air cavity was greater than and that an outlet diameter greater than had little influence on the vortex rings.

Mechanical characteristics and microstructure study of saline soil stabilized by quicklime after curing and freeze-thaw cycle

Quicklime is widely utilized in stabilizing special soils, and the curing condition, as well as freeze-thaw cycles (FTCs), can significantly affect the engineering properties of lime-stabilized soil. In this study, quicklime is adopted to stabilize the saline soil in cold regions. The effects of curing time, numbers of freeze-thaw cycles, and constraint conditions (three-dimensional constraint, radial constraint, and no constraint) on mechanical and microstructure characteristics are investigated by performing a series of unconfined compression tests (UCT), X-ray diffraction (XRD) and scanning electron microscope (SEM) tests. The UCT results indicate that specimens obtain the highest unconfined compression strength (UCS) under three-dimensional constraint and the lowest UCSs under no constraint. XRD and SEM tests reveal that pozzolanic reaction and carbonation play an important role during curing. UCSs of specimens cured for 7 days increase with the increase of FTCs while those of specimens cured for 28 days decrease in the early stage of FTCs but increase after 10 FTCs. FTCs destroy the original structure of stabilized soil and break the aggregates. Small particles of free quicklime and broken aggregates fill the pores. In addition, cementitious materials bond these particles together which resulted in a denser microstructure and an increase of UCS after 10 FTCs.

Traversable wormhole on the brane with non-exotic matter: a broader view

In this article, the possibility of construction of a traversable wormhole on the Randall–Sundrum braneworld with non-exotic matter employing the Kuchowicz potential has been studied. We have obtained the solution for the shape function of the wormhole and studied its properties along with validity of null energy condition. The junction conditions at the surface of the wormhole are used to evaluate the model parameters. We also evaluate the surface density and surface pressure for the wormhole. We study the geometrical nature of the wormhole and consider the radial and tangential tidal constraints on a traveller trying to traverse the wormhole. Besides, a linearized stability analysis is performed to obtain the region of stability for the wormhole. Our analysis, besides giving an estimate for the bulk equation of state (EoS) parameter, imposes restrictions on the brane tension, which is a very essential parameter in braneworld physics, and very interestingly the restrictions imposed by our physically plausible and traversable wormhole model are in conformity with those imposed by other braneworld geometries which are not associated with a wormhole solution. Besides, it is important to study such constraints imposed by geometrical objects such as wormholes on any gravity theory operating at high-energy scales like braneworld, as wormholes are believed to have been formed from massive compact objects of high energy densities. Also, we go on to justify that the possible detection of a wormhole may well indicate that we live on a three-brane universe.

Reliability Evaluation Method of AC/DC Hybrid Distribution Network Considering Voltage Source Converter Restoration Capability and Network Reconfiguration

In the AC/DC hybrid distribution network, non-faulty areas can maintain uninterrupted power supply by adjusting the control mode of the voltage source converter (VSC) after a fault. In addition, the non-faulty areas can also be restored through network reconfiguration. To account for the impact of these two restoration methods on reliability accurately, this article proposed a reliability evaluation method for the AC/DC hybrid distribution network considering VSC restoration capability and network reconfiguration. First, a restoration optimization model of the AC/DC hybrid distribution network considering network reconfiguration and control modes of VSC is established, which can give full play to these two restoration methods while ensuring the radial constraints of the network. Then, the failure mode and effects analysis (FMEA) method is introduced and combined with the restoration optimization model to analyze the impact caused by faults on the network. Among them, the FMEA method is utilized to determine the network topology after fault isolation, and on this basis, the restoration optimization model is solved to obtain the outage time of loads in the network. Finally, the aforementioned work is combined with the sequential Monte Carlo method to evaluate the reliability of the AC/DC hybrid distribution network to adequately simulate the fluctuation characteristics of distributed generation (DG) and load. The case study shows that the proposed method can accurately evaluate the reliability of the AC/DC hybrid distribution network.

Performance Improvement of a Mixed Flow Turbine Using 3D Blading

Abstract Mixed flow turbines have reached a level of maturity where iterative performance improvements are very small, with real performance benefits coming from better matching to a given application as opposed to improvements in technology. One ubiquitous design feature of mixed flow turbines used to control stress within the wheel is the radial fiber constraint, wherein blade material is stacked radially outward along the entirety of the blade. While this constraint yields a mechanical benefit, it constrains the aerodynamic design significantly, with the blade shape defined by one camberline. One potential means of realizing a performance improvement is the use of 3D blading, where the blade is not constrained to a radially fibered structure. In such a design, the blade shape could be freely modified to better control blade loading and secondary flows. This study investigated the viability of such 3D blading through optimization of a state of the art mixed flow turbine. An equivalent design was ensured by maintaining the meridional shape and operating conditions of the baseline (BL) wheel, thus facilitating a fair comparison between the radial and 3D wheels. The paper details the optimization including an innovative constraint-driven geometry modification tool, experimental validation of performance predictions, and an investigation into why 3D blading facilitated a performance improvement. The optimization process identified a performance improvement across the entire turbocharger operating line. With performance improvements facilitated through a reduction in tip leakage loss and improved pressure recovery within the conical diffuser. Importantly, the optimized design met targets for mass flow, maximum stress levels, and modal behavior, through the use of the novel geometry modification process.

A new approach for optimal photovoltaic resources in distribution networks with reconfiguration based on L_∞

PurposeIn the vast majority of published papers, the optimal allocation of photovoltaic distributed generation (PVDG) units and reconfiguration problems are proposed along with the number of PVDG used in the simulation. However, optimisation without selecting the number of PVDG units installed in the distribution grid is insufficient to achieve a better operational performance of power systems. Moreover, multi-objective installation of PVDG units and reconfiguration aims to simultaneously relieve congestion problems, improve voltage profile and minimise the active and reactive power losses. Therefore, this paper aims to propose a new modified camel algorithm (NMCA) to solve multi-objective problems considering radial distribution system to achieve secure and stable operation of electric power system with good performance.Design/methodology/approachIn this paper, the decision variables include the location and size of PVDG units with specific rang to determine the number of PVDG units needed to install and open network lines determined using NMCA based on the L_∞ technique. This also satisfies the operating and radial constraints. Furthermore, a benchmark comparison with different well known optimisation algorithms has been made to confirm the solutions. Finally, an analysis of the findings was conducted, and the feasibility of solutions was fully verified and discussed.FindingsTwo test systems – the institute of electrical and electronics engineers (IEEE) 33-bus and IEEE 69-bus, were used to examine the accuracy and effectiveness of the proposed algorithm. The findings obtained amply proved the efficiency and superiority of the NMCA algorithm over the other different optimisation algorithms.Originality/valueThe proposed approach is applied to solve the installation PVDG unit’s problem and reconfiguration problem in the radial distribution system, satisfying the operating and radial constraints. Also, it minimises active and reactive power losses and improves voltage profile.

Lithium orthosilicate as nuclear fusion breeder material: Optimization of the drip casting production technology

The production of nuclear fusion energy, in the future DEMOnstration power plant (DEMO), is based on tritium self-sufficiency, achievable exploiting neutron-lithium reaction occurring in the breeding blanket modules. To fulfil the plant design conditions ceramic materials containing lithium are suggested. A lot of research efforts focused on the past years on the investigation and selection of the most suitable breeding material.In this study, the lithium orthosilicate, in pebble form, produced at room temperature at the University of Pisa was investigated and characterized from a thermo-mechanical point of view. The pebbles were produced by a drip casting forming technique, starting from an aqueous suspension of a Li4SiO4 precursor obtained by hydrolytic sol–gel method, and dropping it into a calcium chloride/lithium acetate solution. A high temperature thermal treatment was applied to green pebbles to synthesize Li4SiO4 and densify the structure. Thermal analysis and static uniaxial compression tests, without radial constraints, were carried out on different types of pebbles produced varying the composition of the precursor suspension by means of cellulose fiber additions. Results show the influence of the cellulose content on morphological and physical properties of the obtained pebbles. Li4SiO4 pebbles with a density of 88 % and a crush load of about 30 N were obtained when the suspension was modified by adding 15 wt% of cellulose fibers to the sol–gel precursor powders.

Reconfiguration Strategy for DC Distribution Network Fault Recovery Based on Hybrid Particle Swarm Optimization

DC distribution network faults seriously affect the reliability of system power supply. Therefore, this paper proposes a fault recovery reconfiguration strategy for DC distribution networks, based on hybrid particle swarm optimization. The original particle swarm algorithm is improved by simplifying the distribution network structure, introducing Lévy Flight, and designing an adaptive coding strategy. First, the distribution network structure is equivalently simplified to reduce the problem dimensionality. Further, the generated branch groups are ensured to satisfy the radial constraints based on the adaptive solution strategy. Subsequently, Lévy flight is introduced to achieve intra-group optimality search for each branch group. The method is simulated in several distribution systems and analyzed in comparison with the particle swarm algorithm, genetic algorithm, and cuckoo algorithm. Finally, the results validate the accuracy and efficiency of the proposed method.

CCREM: New Reference Earth Model From the Global Coda‐Correlation Wavefield

AbstractThe existing reference Earth models have provided an excellent one‐dimensional representation of Earth's properties as a function of its radius and explained many seismic observations in a broad frequency band. However, some discrepancies still exist among these models near the first‐order discontinuities (e.g., the core‐mantle and the inner‐core boundaries) due to different data sets and approaches. As a new paradigm in global seismology, the analysis of coda‐correlation wavefield is fundamentally different from interpreting direct observations of seismic phases or free oscillations of the Earth. The correlation features exist in global correlograms due to the similarity of body waves reverberating through the Earth's interior. As such, there is a great potential to utilize the information stored in the coda‐correlation wavefield in constraining the Earth's internal structure. Here, we deploy the global earthquake‐coda correlation wavefield as an independent data source in the 15–50 s period interval to increase the Earth's radial structure constraints. We assemble a data set of multiple pronounced correlation features and fit both their travel times and waveforms by computing synthetic correlograms through a series of candidate models. Misfit measurements for correlation features are then computed to search for the best‐fitting model. The model that provides an optimal representation of the correlation features in the coda‐correlation wavefield is CCREM. It displays differences in radial seismic velocities, especially near the first‐order discontinuities, relative to previously proposed Earth‐reference models. This is the first application of the earthquake‐coda correlation wavefield in constraining the whole Earth's radial velocity structure.

Effect of elastic support on the linear buckling response of quasi-isotropic cylindrical shells under axial compression

Cylindrical shells under compressive loading are highly sensitive to boundary conditions. Considering that these structures are connected by surrounding structural components with finite stiffness, an accurate evaluation of the effects of their boundary stiffness is crucial in their design. As such, this work investigates the effect of elastic boundary conditions on the linear buckling behaviour of cylindrical shells under compressive loading. To achieve this goal, a virtual testing investigation on the effect of translational and rotational constraints to the linear buckling response of a quasi-isotropic cylinder subjected to axial compression is performed. Subsequently, the effect of many kinds of constraints on linear buckling behaviour is discussed and interesting insights regarding a significant coupling effect between the radial and tangential translational constraints are given. Results obtained from virtual testing show that seven recurrent buckling mode shapes occur with seven corresponding similar linear buckling loads. Therefore, based on these similarities, seven groups of classical boundary conditions are introduced to classify all possible linear buckling behaviours exhibited by the cylinder under consideration. Finally, these findings can support the development of theoretical models for cascade, or flange, designs of multiple connecting cylinders.

E-H mode transitions and high-energy electron characteristics of helical antenna coupled plasma

Metastable and high-energy electron characteristics obtained from optical emission spectroscopy are used to analyze the dependence of the H mode on the magnetic field strength and discharge pressure. The results show that the H-mode characteristics gradually appears as the magnetic field strength is increased, the reason being that electrons undergo multiple acceleration-collision cycles at high magnetic field strength, thereby the metastable ionization will be increased. This improves energy utilization and making the H mode appearing. The variation in the density of metastable states and the Langmuir probe data shows that the electron energy distribution function evolves from non-Maxwellian to Maxwellian. The radial constraint of the magnetic field to the electrons and thus reduces the electron heating efficiency. Moreover, the increase in electric field strength with magnetic field leads to an increase in energy obtained by the electrons per unit distance. The competition between the two makes the number of high-energy electrons decrease rapidly first, and then increase slowly with magnetic field strength increasing. The turning point increases with the increase of discharge pressure and radio-frequency (RF) power. And the higher the pressure the lower the high-energy electron. For fields between 105.5 G and 212.7 G. In the H-mode regime, and with increasing RF power, the number of high-energy electrons will be sudden rise after experiencing a steady increase. The sudden rise RF power increase with magnetic field and decrease with discharge pressure increase. However, at high magnetic fields (>265 G) and high power (>450 W), the high-energy electron density decreases with power increasing.

Constraints on the Upper Mantle Structure Beneath the Pacific From 3‐D Anisotropic Waveform Modeling

AbstractSeismic radial anisotropy is a crucial tool to help constrain flow in the Earth's mantle. However, Earth structure beneath the oceans imaged by current 3‐D radially anisotropic mantle models shows large discrepancies. Here, we provide constraints on the radially anisotropic upper mantle structure beneath the Pacific by waveform modeling and subsequent inversion. Specifically, we objectively evaluate three 3‐D tomography mantle models which exhibit varying distributions of radial anisotropy through comparisons of independent real data sets with synthetic seismograms computed with the spectral‐element method. The data require an asymmetry at the East Pacific Rise (EPR) with stronger positive radial anisotropy ξ = = 1.13–1.16 at ∼100 km depth to the west of the EPR than to the east (ξ = 1.11–1.13). This suggests that the anisotropy in this region is due to the lattice‐preferred orientation of anisotropic mantle minerals produced by shear‐driven asthenospheric flow beneath the South Pacific Superswell. Our new radial anisotropy constraints in the Pacific show three distinct positive linear anomalies at ∼100 km depth. These anomalies are possibly related to mantle entrainment at the Nazca‐South America subduction zone, flow at the EPR and from the South Pacific Superswell and shape‐preferred orientation (SPO) of melt beneath Hawaii. Radial anisotropy reduces with lithospheric age to ξ < 1.05 in the west at ∼100 km depth, which possibly reflects a deviation from horizontal flow as the mantle is entrained with subducting slabs, a change in temperature or water content that could alter the anisotropic olivine fabric or the SPO of melt.

Distributed generator-based distribution system service restoration strategy and model-free control methods

The rapid growth of distributed generator (DG) capacities has introduced additional controllable assets to improve the performance of distribution systems in terms of service restoration. Renewable DGs are of particular interest to utility companies, but the stochastic nature of intermittent renewable DGs could have a negative impact on the electric grid if they are not properly handled. In this study, we investigate distribution system service restoration using DGs as the primary power source, and we develop an effective approach to handle the uncertainty of renewable DGs under extreme conditions. The distribution system service restoration problem can be described as a mixed-integer second-order cone programming model by modifying the radial topology constraints and power flow equations. The uncertainty of renewable DGs will be modeled using a chance-constrained approach. Furthermore, the forecast errors and noises in real-time operation are solved using a novel model-free control algorithm that can automatically track the trajectory of real-time DG output. The proposed service restoration strategy and model-free control algorithm are validated using an IEEE 123-bus test system.

Influence of Rotor Eccentricity Types on the Operating Performance for a 100 KW HTS Maglev Flywheel System

Due to the low radial restoring force stiffness of the radial high-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconducting maglev bearing (SMB) in high-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconducting flywheel energy storage system (SFESS), it is difficult to provide enough radial constraint when the rotation speed is high. The dynamic simulation analysis of the SFESS rotor was carried out based on the testing and analysis of the static force results of the SMB. On the one hand, according to the results of dynamic analysis, the flywheel rotor would be eccentric when it is subjected to an unbalanced force. On the other hand, because of the special operation mechanism of the SFESS, the flywheel rotor would be prone to be eccentric before rotation. These two types of eccentricity will affect the operating performance of SFESS. Therefore, the research on the working condition of SFESS under eccentric state not only can predict the operating performance of SFESS in extreme cases in advance but also judge whether the SFESS has eccentric operation by comparing the real-time speed value with the preset value, which is of great significance to the further research of the SFESS.

Calibration Algorithm for Error Screening Based on Line Structured Light

The 3D measurement system based on line-structured light uses a camera to capture laser stripes due to changing in the shape of an object, and uses the acquired pixel coordinates for 3D reconstruction. System calibration is an important step in 3D measurement. The current camera calibration algorithm research mainly focuses on improving the algorithm itself, and there is less research on the influence of external factors. This paper proposes a coplanar hybrid calibration algorithm based on the error screening model by combining the error screening model, mathematical model and neural network model. It is mainly divided into two steps. The first step is to use the radial array constraint calibration algorithm based on the error screening model to solve the camera’s internal and external parameters. The second step uses the camera internal and external parameters obtained in the first step to convert the pixel coordinates into real three-dimensional coordinates, and compares the calculated three-dimensional coordinates with the actual coordinates. Using machine learning to establish a compensation network, get a compensation function, and use the resulting 3D world coordinates to perform point cloud stitching. Experiments show that compared with the traditional calibration algorithm, the calibration algorithm has a small error and reduces the calibration error by about 6.5%.

The completed SDSS-IV extended baryon oscillation spectroscopic survey: growth rate of structure measurement from anisotropic clustering analysis in configuration space between redshift 0.6 and 1.1 for the emission-line galaxy sample

ABSTRACT We present the anisotropic clustering of emission-line galaxies (ELGs) from the Sloan Digital Sky Survey IV (SDSS-IV) extended Baryon Oscillation Spectroscopic Survey (eBOSS) Data Release 16 (DR16). Our sample is composed of 173 736 ELGs covering an area of 1170 deg2 over the redshift range 0.6 ≤ z ≤ 1.1. We use the convolution Lagrangian perturbation theory in addition to the Gaussian streaming redshift space distortions to model the Legendre multipoles of the anisotropic correlation function. We show that the eBOSS ELG correlation function measurement is affected by the contribution of a radial integral constraint that needs to be modelled to avoid biased results. To mitigate the effect from unknown angular systematics, we adopt a modified correlation function estimator that cancels out the angular modes from the clustering. At the effective redshift, zeff = 0.85, including statistical and systematical uncertainties, we measure the linear growth rate of structure fσ8(zeff) = 0.35 ± 0.10, the Hubble distance $D_ H(z_{\rm eff})/r_{\rm drag} = 19.1^{+1.9}_{-2.1}$, and the comoving angular diameter distance DM(zeff)/rdrag = 19.9 ± 1.0. These results are in agreement with the Fourier space analysis, leading to consensus values of: fσ8(zeff) = 0.315 ± 0.095, $D_H(z_{\rm eff})/r_{\rm drag} = 19.6^{+2.2}_{-2.1}$, and DM(zeff)/rdrag = 19.5 ± 1.0, consistent with ΛCDM model predictions with Planck parameters.

The one that got away: a unique eclipse in the young brown dwarf Roque 12

We report the discovery of a deep, singular eclipse of the bona fide brown dwarf Roque 12, a substellar member of the Pleiades. The eclipse was 0.65mag deep, lasted 1.3h, and was observed with two telescopes simultaneously in October 2002. No further eclipse was recorded, despite continuous monitoring with Kepler/K2 over 70d in 2015. There is tentative (2sigma) evidence for radial velocity variations of 5km/s, over timescales of three months. The best explanation for the eclipse is the presence of a companion on an eccentric orbit. The observations constrain the eccentricity to e>0.5, the period to P>70d, and the mass of the companion to ~0.001-0.04Msol. In principle it is also possible that the eclipse is caused by circum-sub-stellar material. Future data releases by Gaia and later LSST as well as improved radial velocity constraints may be able to unambiguously confirm the presence of the companion. This would turn the system into one of the very few known eclipsing binary brown dwarfs with known age.

Phase transitions of liquid crystal confined in electrospun polymer nanofibres

Phase behaviour as well as phase transitions of $$4'$$ -pentyl-4-biphenylcarbonitrile (5CB) liquid crystal (LC) confined in an amorphous polymer matrix of electrospun nanofibres were investigated. The nanofibres were fabricated from simple monoaxial electrospinning using 5CB/polymer mixtures as well as coaxial electrospinning, where the polymer solution and neat 5CB constituted the shell- and core-forming fluids, respectively. The 5CB was found to be miscible with polystyrene (PS) and poly(4-vinyl pyridine) (P4VP). This was evident from the sharp drop in the glass transition temperature ( $$T_{\mathrm{g}}$$ ) of PS and P4VP in their mixtures with 5CB. Hence, the phase transitions of 5CB were completely suppressed in its mixture with PS and P4VP in electrospun nanofibres as ascertained from DSC and polarized optical microscopy measurements. However, the electrospun nanofibres composed of poly(vinyl pyrrolidone) (PVP) and 5CB showed phase-separated morphology. The phase-separated morphology was unambiguously characterized using SEM and TEM measurements. Furthermore, the phase separation resulted in 5CB exhibiting its liquid crystalline characteristics. However, the radial constraint of the nanofibres led to the formation of small-sized 5CB domains with limited spatial connectivity, which resulted in deviation from the known phase-transition characteristics of 5CB. It was also observed that the inherent orientation of the nanofibres favours the nematic to crystalline transition in the blend nanofibres. The present study gives new insight and understanding about phase behaviour of LC in electrospun polymer fibre and has technological relevance for the design of LC-based flexible fibrous components with tunable optical, thermal and dielectric properties.

Camera calibration method with focus-related intrinsic parameters based on the thin-lens model.

In this paper, a calibration method for a camera with focus-related intrinsic parameters based on the thin-lens model is proposed to realize highly accurate measurement for small objects with extended depth of field (DOF). It mainly solves inaccurate calibration and small DOF problems at high magnification of vision systems. The mathematical camera model, initial camera calibration based on the iterative radial alignment constraint (IRAC) and optimization strategy are presented. The effectiveness, accuracy and practicality of the proposed calibration method are verified by both simulations and experiments. The root mean square errors of measured points in the 3D world coordinates with the proposed calibration method decrease from 22.02 μm to 1.66 μm when the magnification of the vision system increases from 0.12× to 0.66×. With the proposed calibration method based on the thin-lens model, accurate measurement, extended DOF and low calibration workload can be achieved.