Radial Constraint Research Articles

Obliquity Tides May Drive WASP-12b’s Rapid Orbital Decay

Abstract Recent analyses have revealed a mystery. The orbital period of the highly inflated hot Jupiter, WASP-12b, is decreasing rapidly. The rate of inspiral, however, is too fast to be explained by either eccentricity tides or equilibrium stellar tides. While dynamical stellar tides are possible, they require a subgiant structure for the star, whereas stellar models point toward a main-sequence host. Here, we show that these hitherto irreconcilable observations might be explained by planetary obliquity tides if planet b’s spin vector is trapped in a high-obliquity state maintained by a secular spin–orbit resonance with an unseen exterior perturbing planet. We derive constraints on the obliquity ( ), reduced tidal quality factor ( ), and perturbing planet parameters ( , ) required to generate the observed orbital decay. Direct N-body simulations that include tidal and spin dynamics reinforce the plausibility of the scenario. Furthermore, we show that the resonance could have been captured when planet b’s obliquity was small, making the proposed sequence of events easy to explain. The hypothetical perturbing planet is within the limits of current radial velocity constraints on the system, yet it is also detectable. If it exists, it could provide evidence in favor of the in situ formation hypothesis for hot Jupiters.

Radial constraints and the polarity mechanism of plasma plume

Plasma plumes have found a wide range of applications over the recent decade, stimulating studies of characteristics of plasma plumes generated under different conditions. Regardless of whether they propagate within a dielectric tube or different shielding gases, the behavior of these plumes will be affected by the boundary condition of the plume. Yet, at present, little is known about the behavior of plasma plumes of different polarities, especially negative plasma plumes, when propagating under different boundary conditions. To bridge this gap, in this paper, the characteristics of positive and negative plasma plumes propagating within a quartz tube, ambient Ar, and air are studied. The results reveal that the behavior of the positive plasma plume is similar under three different boundary conditions. However, this is not the case for the negative plasma plume, the behavior of which differs significantly between the three cases. Numerical simulation suggests that electron loss due to the drift in the radial direction impacts significantly the characteristics of the negative plasma plume.

Measurement of Unmanned Aerial Vehicle Attitude Angles Based on a Single Captured Image.

The limited load capacity and power resources of small-scale fixed-wing drones mean that it is difficult to employ internal high-precision inertial navigation devices to assist with the landing procedure. As an alternative, this paper proposes an attitude measurement system based on a monocular camera. The attitude angles are obtained from a single captured image containing five coded landmark points using the radial constraint method and three-dimensional coordinate transformations. The landing procedure is simulated for pitch angles from −15 to −40, roll angles from −15 to +15 and yaw angles from −15 to +15. For roll and pitch angles of approximately 0 and −25, respectively, the accuracy of the method reaches 0.01 and 0.04. This UAV attitude measurement system obtains an attitude angle by a single captured image, which has great potential for assisting with the landing of small-scale fixed-wing UAVs.

MUSE observations of M87: radial gradients for the stellar initial-mass function and the abundance of sodium

Based on MUSE integral-field data we present evidence for a radial variation at the low-mass end of the stellar initial-mass function (IMF) in the central regions of the giant early-type galaxy NGC4486 (M87). We used state-of-the-art stellar population models and the observed strength of various IMF-sensitive absorption-line features to solve for the best low-mass tapered "bimodal" form of the IMF, while accounting also for radial variations in stellar metallicity, the overall $\alpha$-elements abundance, and the abundance of individual elements such as Ti, O, Na and Ca. Our analysis reveals a strong IMF gradient in M87, corresponding to an exceeding fraction of low-mass stars compared to the case of the Milky Way toward the center of M87 that drops to nearly Milky-way levels by 0.4 $R_e$. This IMF gradient is found to correlate well with both the radial profile for stellar metallicity and for $\alpha$-elements abundance but not with stellar velocity dispersion. Such IMF variations correspond to over a factor two increase in stellar mass-to-light M/L ratio compared to the case of a Milky-way like IMF, consistent with other investigations into IMF gradients in early-type galaxies, including recent dynamical constraints on M/L radial variations in M87 by Oldham & Auger. In addition to constraining the IMF in M87 we also looked into the abundance of Sodium, which turned up to be super-Solar over the entire radial range of our MUSE observations and to exhibit a considerable negative gradient. These findings suggest an additional role of metallicity in boosting the Na-yields in the central, metal-rich regions of M87 during its early and brief star-formation history. Our work adds the case of M87 to the few objects that as of today have radial constraints on their IMF or [Na/Fe] abundance, while also illustrating the accuracy that MUSE could bring to this kind of investigations.

Parametric design and static behavior analysis of single-layer hemi-ellipsoida latticed shell

The parametric design macro programs of two basic types of single-layer hemi-ellipsoidal latticed shell are developed by using APDL (Ansys Parametric Design Language) parameterized design language. The parametric design of single-layer hemi-ellipsoidal latticed shell structures can be built under the condition of giving the macroscopic geometric parameters such as specifical parameter t, parameter k, span S1, span S2, rise f, valley number Kn, radial node number Nx etc. Ansys software is applied to study comparison of characteristics of the Kewitte type net shell structure of different vector height f, radial node number Nx and boundary constraints. The results show that modeling design of hemi-ellipsoidal latticed shell can be built conveniently and quickly by the application of parametric design of macro program. The three-way grid type is more reasonable force performance, and it’s mechanical performance is better when the span ratio is 1/2. Thus it is suggested to give priority in the project.

The numerical simulation of entire sucker rod string buckling with couplings in vertical wells

A new model is built to study the buckling of a rod string with couplings in the vertical well considering two important loads: the axial distribution load along the rod and the concentrated load at the bottom. Firstly, the calculation method for the axial distribution load of the sucker rod string is established based on a wave equation of longitudinal vibration. And, the simulation results show that the axial distribution load of sucker rod string has an obvious non-uniform distribution characteristic. The friction force between the plunger and the pump barrel (FFPPB), which is an important part of the concentrated load at the bottom, is improved based on both the Newtonian fluid (NF) and the non-Newtonian power law fluid (NNPLF) by using the Flunent software. In view of the above improvement of the computational method, a simulation model of the entire rod string buckling with couplings is established. Under the assumption that the coupling is taken as a radial constraint boundary, the two-point boundary value problem (BVP) algorithm is used to solve the differential equation, and the least square method is used to establish the continuity conditions on the supporting point of coupling. The simulation results show that the eccentric state of the plunger (eccentricity ratio $$\upvarepsilon =0\sim 1$$) has a significant influence on the eccentric wear area between the rod-tubings, which should be taken into account in the practical calculation. And compared without couplings, the contact pressure between the sucker rod string and the tubing is transferred to the couplings, which fits the engineering reality. Further, the simulation result implies the centralizers should be installed firstly near the couplings in order to protect the couplings better. The new method lays the theoretical foundation for the further studying the rod wear life and the design of the eccentric wear prevention.

Investigation of flow between deformed disks in hydro-viscous drive

Abstract In order to investigate the dynamic behavior of oil film between deformed disks in hydro-viscous drive, revised mathematical models based on steady-state and axisymmetric flow conditions are developed. The models consist of two forms of thermal deformation that are caused by the combined effect of frictional heat and radial constraint. An approximate solution to the theoretical model is obtained assuming that the fluid viscosity remains constant. And the model considering the effect of variable viscosity is solved by means of computation fluid dynamics code FLUENT. Then the analytical and numerical solution profiles are compared. The results show that peak velocity at the outlet, pressure gap and temperature rise between the inlet and outlet of the film increase with increasing axial deformation size. The effect of radial deformation on the increase of friction area of the disks leads to the increase of the flow rate. The friction pairs should be kept in reasonable deformation size in case of turbulent flow. It is also found that both axial deformation and radial deformation significantly contribute to the increase of viscous torque on condition that the deformation size is controllable. Based on the comparison with the experimental results, the performance of the theoretical model is found satisfactory.

Swelling Pressure of Double‐Expansive Material and Its Active Support Effect for Coal Seam Gas Drainage Borehole

To improve coal seam gas drainage performance, we developed a double‐expansive (DE) material to seal the borehole. The swelling process of this material includes an initial swelling stage and a secondary swelling stage. We studied the swelling pressure properties of the DE material under four constraint conditions using a self‐made swelling test device. Further, the active support effect of the DE material on the borehole was analyzed by simulating borehole stability with COMSOL Multiphysics software. The results exhibit the following: (1) The swelling pressure of the DE material exhibits time‐dependent behavior, and the mathematical relationship between the swelling pressure and time can be obtained by nonlinear fitting. (2) The radial swelling potential is principally formed during the secondary swelling stage, providing the main active support on the radial constraint. (3) The active support imposed on the hole wall can prevent the extension of plastic and damage regions around the borehole, for improved stability of the gas drainage borehole. Finally, field tests demonstrate improved gas drainage performance of the borehole sealed by the DE material compared to a conventional sealing material.

Global dynamics below excited solitons for the nonlinear Schrödinger equation with a potential

Consider the nonlinear Schrödinger equation (NLS) with a potential with a single negative eigenvalue. It has solitons with negative small energy, which are asymptotically stable, and, if the nonlinearity is focusing, then also solitons with positive large energy, which are unstable. In this paper we classify the global dynamics below the second lowest energy of solitons under small mass and radial symmetry constraints.

An experimentally constrained MHD model for a collisional, rotating plasma column

A steady-state single fluid MHD model which describes the equilibrium of plasma parameters in a collisional, rotating plasma column with temperature gradients and a non-uniform externally applied magnetic field is developed. Two novel methods of simplifying the governing equations are introduced. Specifically, a ‘radial transport constraint’ and an ordering argument are applied. The reduced system is subsequently solved to yield the equilibrium of macroscopic plasma parameters in the bulk region of the plasma. The model is benchmarked by comparing these solutions to experimental measurements of axial velocity and density for a hydrogen plasma in the converging-field experiment MAGPIE and overall a good agreement is observed. The plasma equilibrium is determined by the interaction of a density gradient, due to a temperature gradient, with an electric field. The magnetic field and temperature gradient are identified as key parameters in determining the flow profile, which may be important considerations in other applications.

A High Precision Approach to Calibrate a Structured Light Vision Sensor in a Robot-Based Three-Dimensional Measurement System.

A robot-based three-dimensional (3D) measurement system is presented. In the presented system, a structured light vision sensor is mounted on the arm of an industrial robot. Measurement accuracy is one of the most important aspects of any 3D measurement system. To improve the measuring accuracy of the structured light vision sensor, a novel sensor calibration approach is proposed to improve the calibration accuracy. The approach is based on a number of fixed concentric circles manufactured in a calibration target. The concentric circle is employed to determine the real projected centres of the circles. Then, a calibration point generation procedure is used with the help of the calibrated robot. When enough calibration points are ready, the radial alignment constraint (RAC) method is adopted to calibrate the camera model. A multilayer perceptron neural network (MLPNN) is then employed to identify the calibration residuals after the application of the RAC method. Therefore, the hybrid pinhole model and the MLPNN are used to represent the real camera model. Using a standard ball to validate the effectiveness of the presented technique, the experimental results demonstrate that the proposed novel calibration approach can achieve a highly accurate model of the structured light vision sensor.

Compressive behaviour of unconstrained and constrained integral-skin closed-cell aluminium foam

The aim of this paper is to evaluate the quasi-static and dynamic compressive crush performance of integral-skin closed-cell aluminium alloy foam with and without radial constraints. The foam specimens were prepared by the powder compact foaming method. The behaviour under different loading conditions (loading velocity and radial constraints) has been determined by an extensive experimental program. The results show a significant increase in the collapse stress of the integral-skin closed-cell aluminium foam under quasi-static loading when radial constraints are applied. The radial constraint induces a significant strain hardening of the foam, where the densification occurs at lower strains, consequently enhancing the energy absorption per unit volume of the deformed foam. The strain hardening is also sensitive to the foam density, increasing with the density.

Master equation as a radial constraint

We revisit the problem of perturbations of Schwarzschild-AdS$_4$ black holes by using a combination of the Martel-Poisson formalism for perturbations of four-dimensional spherically symmetric spacetimes and the Kodama-Ishibashi formalism. We clarify the relationship between both formalisms and express the Brown-York-Balasubramanian-Krauss boundary stress-energy tensor, $\bar{T}_{\mu\nu}$, on a finite-$r$ surface purely in terms of the even and odd master functions. Then, on these surfaces we find that the spacelike components of the conservation equation $\bar{\mathcal{D}}^\mu \bar{T}_{\mu\nu} =0$ are equivalent to the wave equations for the master functions. The renormalized stress-energy tensor at the boundary $\displaystyle \frac{r}{L} \lim_{r \rightarrow \infty} \bar{T}_{\mu\nu}$ is calculated directly in terms of the master functions.

Radial constraints on the initial mass function from TiO features and Wing–Ford band in early-type galaxies

At present, the main challenge to the interpretation of variations in gravity-sensitive line strengths as driven by a non-universal initial mass function (IMF), lies in understanding the effect of other parameters describing unresolved stellar populations, such as elemental abundance ratios. We combine various TiO-based, IMF-sensitive indicators in the optical and NIR spectral windows, along with the FeH-based Wing-Ford band to break this degeneracy. We obtain a significant radial trend of the IMF slope in XSG1, a massive early-type galaxy (ETG), with velocity dispersion sigma~300km/s, observed with the VLT/X-SHOOTER instrument. In addition, we constrain both the shape and normalization of the IMF based only on a stellar population analysis. We robustly rule out a single power-law to describe the IMF, whereas a power law tapered off to a constant value at low masses (defined as a bimodal IMF) is consistent with all the observational spectroscopic data and with the stellar M/L constraints based on the Jeans Anisotropic Modelling method. The IMF in XSG1 is bottom-heavy in the central regions (corresponding to a bimodal IMF slope Gb~3, or a mass normalization mismatch parameter alpha~2), changing towards a standard Milky-Way like IMF (Gb~1.3; alpha~1) around half of the effective radius. This result, combined with previous observations of local IMF variations in massive ETGs, reflects the varying processes underlying the formation of this type of galaxies, between the central core and the outer regions.

Dispersion curve veering of longitudinal guided waves propagating inside prestressed seven-wire strands

Elastic guided waves are of interest for the non-destructive evaluation of cables. Such structures are usually helical, multiwired and highly prestressed, which greatly complicates the understanding of wave propagation from a theoretical point of view. A remarkable feature is the occurrence of a missing frequency band in experimental time–frequency diagrams, sometimes referred to as notch frequency in the literature. The central frequency of this band increases under tensile loads. Recently, a numerical model has been proposed to compute the dispersion curves of prestressed helical seven-wire waveguides. Results have shown that the notch frequency indeed corresponds to a curve veering phenomenon between two longitudinal-like modes and that the increase of the notch under tensile loads is mainly due to interwire contact mechanisms. The main goal of this paper is to highlight the origin of this curve veering phenomenon, which is still unexplained up to the author׳s knowledge. This paper also provides further results which allow us to clarify the accuracy of numerical solutions as well as the influence of contact assumptions. First, the static part of the model, necessary to compute the prestress state including contact effects, is checked from reference analytical solutions. Owing to the importance of contact, the accuracy of results is discussed both in statics and in dynamics. The influence of slip contact conditions is outlined. Then, some numerical tests are conducted by varying the Poisson coefficient and the helix lay angle. These tests allows us to find out that the radial displacement constraint imposed on peripheral wires by the central one in the contact regions constitutes the main source of curve veering. More precisely, it is shown that a similar curve veering does occur for an uncoupled single peripheral wire when constrained by a radially blocked motion localized in its contact zone. Indeed, such a localized boundary condition completely breaks the circular symmetry of the wire cross-section, yielding coupling between longitudinal, flexural and torsional motion together with curve veering phenomena.

A novel method based on adaptive cuckoo search for optimal network reconfiguration and distributed generation allocation in distribution network

Abstract This paper proposes a new methodology to optimize network topology and placement of distributed generation (DG) in distribution network with an objective of reduction real power loss and voltage stability enhancement. A meta-heuristic cuckoo search algorithm (CSA) inspired from the obligate brood parasitism of some cuckoo species which lay their eggs in the nests of other birds of other species for solving optimization problems is adapted to simultaneously reconfigure and identify the optimal location and size of DG units in a distribution network. The graph theory is used to determine the search space which reduces infeasible network configurations of reconfiguration process and check the radial constraint of each configuration of distribution network. The effectiveness of the proposed method has been validated on three different distribution network systems at seven different scenarios. The obtained results show well the effectiveness and performance of the proposed method in distribution network reconfiguration with optimal location and size of DG problems.

Adjoint Optimization of Multistage Axial Compressor Blades with Static Pressure Constraint at Blade Row Interface

AbstractAdjoint method is an important tool for design refinement of multistage compressors. However, the radial static pressure distribution deviates during the optimization procedure and deteriorates the overall performance, producing final designs that are not well suited for realistic engineering applications. In previous development work on multistage turbomachinery blade optimization using adjoint method and thin shear-layer N-S equations, the entropy production is selected as the objective function with given mass flow rate and total pressure ratio as imposed constraints. The radial static pressure distribution at the interfaces between rows is introduced as a new constraint in the present paper. The approach is applied to the redesign of a five-stage axial compressor, and the results obtained with and without the constraint on the radial static pressure distribution at the interfaces between rows are discussed in detail. The results show that the redesign without the radial static pressure distribution constraint (RSPDC) gives an optimal solution that shows deviations on radial static pressure distribution, especially at rotor exit tip region. On the other hand, the redesign with the RSPDC successfully keeps the radial static pressure distribution at the interfaces between rows and make sure that the optimization results are applicable in a practical engineering design.

Crystallization behaviour of poly(ethylene oxide) under confinement in the electrospun nanofibers of polystyrene/poly(ethylene oxide) blends.

We have studied the confined crystallization behaviour of poly(ethylene oxide) (PEO) in the electrospun nanofibers of the phase-separated blends of polystyrene (PS) and PEO, where PS was present as the major component. The size and shape of PEO domains in the nanofibers were considerably different from those in the cast films, presumably because of the nano-dimensions of the nanofibers and the extensional forces experienced by the polymer solution during electrospinning. The phase-separated morphology in turn influenced the crystallization behaviour of PEO in the blend nanofibers. At a PEO weight fraction of ≥0.3, crystallization occurred through a heterogeneous nucleation mechanism similar to that in cast blend films. However, as the PEO weight fraction in the blend nanofibers was reduced from 0.3 to 0.2, an abrupt transformation of the nucleation mechanism from the heterogeneous to predominantly homogenous type was observed. The change in the nucleation mechanism implied a drastic reduction of the spatial continuity of PEO domains in the nanofibers, which was not encountered in the cast film. The melting temperature and crystallinity of the PEO crystallites developed in the nanofibers were also significantly lower than those in the corresponding cast films. The phenomena observed were reconciled by the morphological observation, which revealed that the phase separation under the radial constraint of the nanofibers led to the formation of small-sized fibrillar PEO domains with limited spatial connectivity. The thermal treatment of the PS/PEO blend nanofibers above the glass transition temperature of PS induced an even stronger confinement effect on PEO crystallization.

A Hybrid Heuristic and Evolutionary Algorithm for Distribution Substation Planning

This paper presents an enhanced evolutionary algorithm to solve the static distribution substation planning problem within large distribution networks. It is based on a deterministic heuristic algorithm to find the approximate substation service areas for each substation and an expert selection strategy that increases the convergence chance to a global optimal solution. The introduced algorithm takes different electrical constraints such as voltage drops, power flow, radial flow constraints, and all prevalent cost indices into consideration. In addition, effects of unreliability within network feeders and substations are investigated on the obtained layouts. The developed method is applied to four benchmark test systems and an actual large-scale distribution system with about 140 000 customers, followed by a discussion on results.

Strain-Controlled Cyclic Simple Shear Tests on Sand with Radial Strain Measurements

AbstractStrain-controlled cyclic simple-shear tests were performed on silica sand with radial strain measurements. The specimens were tested under a constant K0 condition and subjected to cyclic loading and postcyclic monotonic loading. Threshold cyclic shear strain, volumetric strain, secant shear modulus, and damping ratio are investigated. Generally, the volumetric strain behavior in this study agreed well with literature findings that were investigated using the conventional cyclic direct simple shear test (without radial constraints). Radial strain during monotonic simple shear (postcyclic loading) was found to be a good parameter in monitoring the onset of flow slide in cohesionless soil. The concept of threshold cyclic shear strain, γt, was adequately applied in assessing the specimen volume change. Dynamic engineering properties, including equivalent shear modulus and damping ratio, were also studied. The damping ratio was found to decrease when the cyclic shear strain amplitude was greater than 2...