Static Configuration Research Articles

Stationary plasma configurations in a toroidal trap with D-shaped cross section in the two-fluid MHD approximation (Morozov–Soloviev equations)

In 1974, A.I. Morozov and L.S. Soloviev derived a general set of hydrodynamic equations for two-component ideal plasma under the stationary flow conditions, as applied to the plasma acceleration problems. Under the conditions of axial symmetry, the authors managed to reduce this very complex system to a more simple form by introducing three functions of the flux (the magnetic field flux, electron flux and ion flux). This situation is reminiscent of the one that develops when obtaining the Grad–Shafranov equation: the problem of static plasma equilibrium is reduced to solving one second-order equation for the magnetic field flux function. The rest condition for the two-component plasma is usually interpreted as the condition of vanishing the mass-average plasma velocity. This condition coincides with the condition of ion immobility up to a value of the order of the electron to ion mass ratio. In this work, the Morozov–Soloviev equations will be used for the first time to study the stationary plasma configurations in the toroidal magnetic trap with the D-shaped cross section. The geometric parameters of the trap correspond to those of the two currently operating tokamaks: the JET and the JT60U.

Discharges with Reduced-Volume Plasma Filament in T-15 Upgrade Tokamak

The formation in the T-15 Upgrade tokamak of plasma filaments with a smaller volume than in the base discharge scenario, keeping the total plasma current constant, has been studied by numerical simulation. The purpose of such operating regimes is to raise the specific power of additional plasma heating. These regimes are of interest for attaining highest possible temperatures under limited additional heating power, e.g., for attaining AT (Advanced Tokamak) regimes. Additionally, these operating regimes can be investigated in the early stage of the T-15 Upgrade experiments when the total available heating power is low. Calculations with the Tokameq code have produced stationary equilibrium configurations for reduced plasma volume regimes. Three variants of plasma-volume reduction have been considered: displacing the plasma filament to the strong magnetic field region near the inner chamber wall while maintaining the filament center in the equatorial plane, and also displacing the plasma filament up or down. Numerical calculations have shown that such regimes may reduce the plasma-filament volume by a factor of 2 to 5, thus significantly raising the specific power of additional heating.

An Optimization Principle for Computing Stationary MHD Equilibria with Solar Wind Flow

In this work we describe a numerical optimization method for computing stationary MHD equilibria. The newly developed code is based on a nonlinear force-free optimization principle. We apply our code to model the solar corona using synoptic vector magnetograms as boundary condition. Below about two solar radii the plasma beta and Alfvén Mach number M_{A} are small and the magnetic field configuration of stationary MHD is basically identical to a nonlinear force-free field, whereas higher up in the corona (where beta and M_{A} are above unity) plasma and flow effects become important and stationary MHD and force-free configuration deviate significantly. The new method allows for the reconstruction of the coronal magnetic field further outwards than with potential field, nonlinear force-free or magnetostatic models. This way the model might help to provide the magnetic connectivity for joint observations of remote sensing and in-situ instruments on Solar Orbiter and Parker Solar Probe.

Thin shells in F(R) gravity with non-constant scalar curvature

We introduce two classes of spherically symmetric spacetimes having a thin shell of matter, in non-quadratic F(R) theories of gravity with non-constant scalar curvature R. In the first, the thin shell joins an inner region with an outer one, while in the second it corresponds to the throat of a wormhole. In both scenarios, we analyze the stability of the static configurations under radial perturbations. As particular examples in spacetimes with a cosmological constant, we present charged thin shells surrounding a non-charged black hole and charged thin-shell wormholes. We show that in both cases stable solutions are possible for suitable values of the parameters.

Static equilibrium configuration and nonlinear dynamics of slightly curved cantilevered pipe conveying fluid

In engineering applications, fluid-conveying pipes usually have geometric imperfections or initially curved configurations. Unlike the initially curved pipe supported at both ends, a slightly curved cantilevered pipe is capable of displaying some interesting behavior because it is a nonconservative system of fluid-structure interactions. In the present study, nonlinear static and dynamic behaviors of cantilevered pipes conveying fluid are explored, with four different initial shapes being considered. To this end, the strongly nonlinear governing equation is derived by employing the extended Lagrange equations written for dynamical systems containing non-material volumes. The static (steady) equilibrium configurations, stability, and nonlinear dynamics of the slightly curved cantilevered pipes are obtained with the aid of absolute nodal coordinate formulation (ANCF). Based on extensive numerical calculations, some interesting and sometimes unexpected results are displayed. The first unexpected feature in this dynamical system is that the flow-induced static deformation of the pipe can be extremely large even if the initial geometric imperfection of the pipe is quite small. The second unexpected result is that the critical flow velocity for flutter instability of the slightly curved pipe conveying fluid may be either lower or higher than that of a straight pipe, mainly depending on the static equilibrium configuration when the critical flow velocity is just reached. Moreover, it is demonstrated that the slightly curved pipe oscillates about the static equilibrium position instead of the initially curved centerline, and the preferred form of post-instability behavior is periodic motion within a wide range of system parameters considered.

Asymptotically optimal consensus-based distributed filtering of continuous-time linear systems

We describe a consensus-based distributed filtering algorithm for linear systems with a parametrized gain and show that when the parameter becomes large the error covariance at each node becomes arbitrarily close to the error covariance of the optimal centralized Kalman filter. The result concerns distributed estimation over a connected un-directed or directed graph and for static configurations it only requires to exchange the estimates among adjacent nodes. A comparison with related approaches confirms the theoretical results and shows that the method can be applied to a wide range of distributed estimation problems.

Observations on the general nonlocal theory applied to axially loaded nanobeams

Static and dynamic analyses for the pre- and post-buckling behavior of an axially loaded nanobeam modeled with a general form of Eringen’s nonlocal theory are conducted and discussed. The general nonlocal theory is a modified form of Eringen’s nonlocal elasticity theory that, contrary to Eringen’s, considers separate attenuation functions to account for the long-range interactions for the two different material moduli and thus introduces an additional nonlocal parameter. The nanobeam is modeled considering Euler–Bernoulli beam theory and the von Karman geometric nonlinearity for midplane stretching in end-constrained beams. Three sets of boundary conditions are studied, namely clamped–clamped, clamped-hinged, and hinged–hinged. The governing equations are derived by virtue of the Hamilton’s principle. Introducing the general nonlocal theory into a beam system increases the order of the resultant transverse equation of motion from fourth to sixth, thus requiring two additional higher-order boundary conditions. These higher-order boundary conditions are derived using a weighted residual approach and are thus variationally consistent. Through this effort, a focus is placed on the effects that these higher-order boundary conditions have on the static and dynamic responses of the system. Specifically, the nonlocal parameters, Poisson ratio, boundary conditions, and axial load are varied. The static critical buckling loads, bifurcation diagrams, and static post-buckling configurations are examined and presented. Additionally, through a linear eigenvalue analysis, the natural frequencies and mode shapes in the pre- and post-buckling regimes are examined. It is shown that the system is very sensitive to the selected nonlocal parameters and higher-order boundary conditions for both the static and dynamic responses. It is the hope that this expanded model can be used by other researchers to accurately model nanobeams composed of materials outside the limits of applicability of Eringen’s nonlocal theory.

Performance Improvement by Mitigating the Effects of Moving Cloud Conditions

Partial shading is an important subject for the research community to improve the issues in the field of solar array utilization. Shading decreases the life of photovoltaic array, its output power yield, and also generates several peaks in its P-V characteristic curves. Physical relocation of panels can be used as a practical solution to prevent such problems by altering the location of panels but not its electrical circuit. In this article, a reconfiguration technique for all conventional configurations like, series-parallel, bridge-link, honey comb, and total cross tied connections are proposed to reduce current difference between the rows and to improve the irradiance equalization by dispersing the shade. This article proposes a mathematical Tom-Tom puzzle pattern for 5× 5 array to enhance the output parameters. The performance of all configurations is evaluated with artificially generated shading to resemble moving clouds which are incremented progressively in row-wise and diagonal manner. From the extensive analysis of results, it has been found that the proposed reconfigurations show better performance than its respective static configurations. The proposed configuration is also tested in terms of income generated and a comparison with the existing state-of-art methods to show the supremacy of the proposed approach.

Predictive autonomic transmission for low-cost low-margin metro optical networks

Low-cost low-margin implementation plays an essential role in upgrading optical metro networks required for future 5G ecosystem. In this regard, low-resolution analog-to-digital converters can be used in coherent optical transponders to reduce cost and power consumption. However, the resulting transmission systems become more sensitive to physical layer fluctuations like the events caused by fiber stressing. Such fluctuations might have a strong impact on the quality of transmission (QoT) of the signals. To guarantee robust operation, soft decision forward error correction (FEC) techniques are required to guarantee zero post-FEC bit error rate (BER) transmission, which could increase the power consumption of the receiver and thus operational expenses. In this paper, we aim at minimizing power consumption while keeping zero post-FEC errors by means of a predictive autonomic transmission agent (ATA) based on machine learning. We present a sophisticated ATA model that, taking advantage of real-time monitoring of state of polarization traces and the corresponding pre-FEC BER, predicts the right FEC configuration for short-term operation, thus requiring minimum power consumption. In addition, we propose a complementary long-term prediction of excessive pre-FEC BER to enable remote reconfiguration at the transmitter side through the network controller. A set of experimental measurements is used to train and validate the proposed ATA system. Exhaustive numerical analysis allows concluding that ATA based on artificial neural network predictors achieves the maximum QoT robustness with 80% power consumption reductions compared to static FEC configuration.

Axisymmetric deformations of neutron stars and gravitational-wave astronomy

Einstein's theory of general relativity predicts that the only stationary configuration of an isolated black hole is the Kerr spacetime, which has a unique multipolar structure and a spherical shape when non-spinning. This is in striking contrast to the case of other self-gravitating objects, which instead can in principle have arbitrary deformations even in the static case. Here we develop a general perturbative framework to construct stationary stars with small axisymmetric deformations, and study explicitly compact stars with an intrinsic quadrupole moment. The latter can be sustained, for instance, by crust stresses or strong magnetic fields. While our framework is general, we focus on quadrupolar deformations of neutron stars induced by an anisotropic crust, which continuously connect to spherical neutron stars in the isotropic limit. Deformed neutron stars might provide a more accurate description for stellar remnants formed in supernovae and in binary mergers, and can be used to improve constraints on the neutron-star equation of state through gravitational-wave detections and through the observation of low-mass X-ray binaries. We argue that, if the (dimensionless) intrinsic quadrupole moment is of a few percent or higher, the effect of the deformation is stronger than that of tidal interactions in coalescing neutron-star binaries, and might also significantly affect the electromagnetic signal from accreting neutron stars.

Effect of the dynamic slip boundary condition on the near-wall turbulent boundary layer

Abstract

Electromagnetic Actuation System for Focused Capturing of Magnetic Particles With a Half of Static Saddle Potential Energy Configuration

Targeted drug delivery using magnetic particles (MPs) and external magnets for focusing them at the diseased regions, called magnetic drug targeting (MDT), is a next-generation therapeutic method that is being continually improved. However, most existing magnetic systems cannot focus MPs in the targeted region due to there not being enough magnetic capturing force and absence of schemes to generate localized high magnetic field at the wall of the target region. This paper suggests a novel scheme to utilize half of a static saddle potential energy configuration generated using four electromagnets that not only enhances the pushing magnetic forces but also simultaneously generates pushing and attracting forces in the desired direction to help focus spherical MPs on the wall of the target region. Furthermore, by changing amplitudes or directions of the currents, the focal point in the target region can be changed. Through extensive simulations and in vitro experiments, we demonstrate that half of a static saddle magnetic potential energy configuration can be successfully utilized to attract and focus MPs at the wall of a target region.

Daylight autonomy improvement in buildings at high latitudes using horizontal light pipes and light-deflecting panels

Horizontal light pipes (HLP) have shown the potential to convey daylight deeper into buildings. The wide variation in incident angles of sunlight rays and the resulting numerous interreflections of light rays within the pipe are the main reasons for the limited light transmittance of such light pipes during certain daylight periods. This paper presents a research study on different configurations of acrylic laser-cut panels (LCP) applied at the entrance of horizontal pipes as light collectors to increase the transmittance of HLPs and improve daylight autonomy in spaces equipped with HLPs. This study required the development of a suitable methodology. The study begins with an experimental laboratory test of a HLP scale model to determine the light transmittance efficiency (standard daylight guide characteristic) of HLPs with several LCP configurations. The results from the laboratory test are combined with the statistical data for both the direct and diffuse illuminance on the vertical south-oriented surface (Satel-Light database) for the location selected for the analyses (Oslo, Norway). The analyses are discussed via the application of a theoretical model of an office space equipped with a HPL as well as through the concept of daylight autonomy (DA) in an indoor space. The paper shows that a certain static LCP configuration has the potential to increase DA100 and DA300 to 10% and 19%, respectively, at a 2.1 m distance from the façade, and 8.75% and 16%, respectively, at a 4.5 m distance. This paper also contributes to lighting science with its data on the light transmittance efficiency of each LCP configuration, which can be applicable in further research.

A bending-active twisted-arch plywood structure: computational design and fabrication of the FlexMaps Pavilion

Bending-active structures are able to efficiently produce complex curved shapes from flat panels. The desired deformation of the panels derives from the proper selection of their elastic properties. Optimized panels, called FlexMaps, are designed such that, once they are bent and assembled, the resulting static equilibrium configuration matches a desired input 3D shape. The FlexMaps elastic properties are controlled by locally varying spiraling geometric mesostructures, which are optimized in size and shape to match specific bending requests, namely the global curvature of the target shape. The design pipeline starts from a quad mesh representing the input 3D shape, which defines the edge size and the total amount of spirals: every quad will embed one spiral. Then, an optimization algorithm tunes the geometry of the spirals by using a simplified pre-computed rod model. This rod model is derived from a non-linear regression algorithm which approximates the non-linear behavior of solid FEM spiral models subject to hundreds of load combinations. This innovative pipeline has been applied to the project of a lightweight plywood pavilion named FlexMaps Pavilion, which is a single-layer piecewise twisted arch that fits a bounding box of 3.90x3.96x3.25 meters. This case study serves to test the applicability of this methodology at the architectural scale. The structure is validated via FE analyses and the fabrication of the full scale prototype.

Ring-like vortices in a logarithmic generalized Maxwell theory

We investigate the presence of vortex structures in a Maxwell model with a logarithmic generalization. This generalization becomes important because it generates stationary field solutions in models that describe the dynamics of a scalar field. In this work, we will choose to investigate the dynamics of the complex scalar field with the gauge field governed by the Maxwell term. For this, we will investigate the Bogomol'nyi equations to describe the static field configurations. Then, we show numerically that the complex scalar field solutions that generate minimum energy configurations have internal structures. Finally, assuming a planar vision, the magnetic field and the density energy show the interesting feature of the ring-like vortex.

Improving reproducibility of data science pipelines through transparent provenance capture

Data science has become prevalent in a large variety of domains. Inherent in its practice is an exploratory, probing, and fact finding journey, which consists of the assembly, adaptation, and execution of complex data science pipelines. The trustworthiness of the results of such pipelines rests entirely on their ability to be reproduced with fidelity, which is difficult if pipelines are not documented or recorded minutely and consistently. This difficulty has led to a reproducibility crisis and presents a major obstacle to the safe adoption of the pipeline results in production environments. The crisis can be resolved if the provenance for each data science pipeline is captured transparently as pipelines are executed. However, due to the complexity of modern data science pipelines, transparently capturing sufficient provenance to allow for reproducibility is challenging. As a result, most existing systems require users to augment their code or use specific tools to capture provenance, which hinders productivity and results in a lack of adoption. In this paper, we present Ursprung, 1 a transparent provenance collection system designed for data science environments. 2 The Ursprung philosophy is to capture provenance and build lineage by integrating with the execution environment to automatically track static and runtime configuration parameters of data science pipelines. Rather than requiring data scientists to make changes to their code, Ursprung records basic provenance information from system-level sources and combines it with provenance from application-level sources (e.g., log files, stdout), which can be accessed and recorded through a domain-specific language. In our evaluation, we show that Ursprung is able to capture sufficient provenance for a variety of use cases and only adds an overhead of up to 4%.

Thermodynamics of two aligned Kerr black holes

We investigate the first law of thermodynamics in the stationary axisymmetric configurations composed of two Kerr black holes separated by a massless strut. Our analysis employs the recent results obtained for the extended double-Kerr solution and for thermodynamics of the static single and binary black holes. We show that, similar to the electrostatic case, in the stationary binary systems the thermodynamic length $\ell$ is defined by the formula $\ell=L\exp(\gamma_0)$, where $L$ is the coordinate length of the strut, and $\gamma_0$ is the value of the metric function $\gamma$ on the strut.

Soft robots with self-powered configurational sensing

Abstract In recent years, soft robots have been evolved at a rapid pace. Soft robots possess infinite degrees of freedom because of the stretchability, which also poses a great challenge for sensing and controlling. Triboelectric nanogenerator (TENG) holds a promising potential as a self-powered sensor for soft robots due to its high sensitivity, flexibility and simplicity. In this work, a sensorized pneumatic soft actuator (PSA) is designed by integrating TENG based self-powered sensors inside the chambers. The sensors give feedback on the dynamic and static configurations of the PSA. The output voltage of a TENG has a good linear relationship with the local bending angle. In addition, the voltage output of all TENGs connected in parallel is linearly related to the total bending angle of the PSA. Applications of the sensorized PSA in a universal soft gripper and humanoid fingers are demonstrated. The self-powered sensors can give corresponding feedback when the soft gripper catches cups with different sizes/weights or when the humanoid fingers make different gestures. The sensorized PSA pave the way for precise control and safely interaction.

Parametric resonances of Timoshenko pipes conveying pulsating high-speed fluids

Parametric resonances of pipes caused by pulsating fluids have received much attention. However, the main concern is the pulsation of subcritical flow. Moreover, it is usually based on the Euler-Bernoulli pipe model. This paper focuses on revealing the characteristics of parametric resonances of the Timoshenko pipe with pulsation of supercritical high-speed fluids. Supercritical flow causes the linear instability of the pipe. The coupled partial differential equations with varying parameters are derived for governing the vibration of the pipe around the non-trivial static equilibrium configuration. A direct multi-scale method is developed to analytically obtain parametric resonance responses from coupled partial differential equations with varying parameters. For the first time, the nonlinear parametric response of the Timoshenko pipe is verified by using the finite difference method (FDM). Some interesting phenomena are demonstrated. For example, unlike parametric resonance at subcritical speeds, the steady-state response of velocity pulsation excitations at supercritical speeds is not monotonic with changes in some physical parameters. For another example, when pulsation occurs at supercritical speeds, the smaller steady-state response and the instability region can be obtained through the Timoshenko pipe model. In addition, the relationship between the instability threshold of the velocity pulsation amplitude and the slenderness ratio is non-monotonic, suggesting that the Euler-Bernoulli pipe model may simplify some vibration characteristics. Due to these different phenomena, the necessity of studying the velocity pulsation in the supercritical high-speed range and the necessity of the Timoshenko model are demonstrated.

Vibration and dynamic behavior of electrostatic size-dependent micro-plates

The recent trend of using thin micro-plate structures in severe operational conditions caused the classical theory (CT) to be no longer suited in analyzing the dynamic characteristics of them. For this study, the modified version of the couple stress theory (MCST) is adopted. Then, using Hamilton’s principle and Kirchhoff plate theory, the dynamic form of the size-dependent equation of motion for micro-plates stimulated by electrostatic dynamic excitation is acquired. The mixed extended Kantorovich and differential transformation methods on partial differential equations are applied to obtain the mode shapes and natural frequencies. The mode shapes from the linear free vibration solution are used as the mode shapes of the assumed multi-mode displacement field. The displacement field is required to solve the dynamical equation of motion. The equations are subsequently solved by the fourth-order Runge–Kutta method. Some universal graphs are also presented using the MCST to predict the effects of the size effect, tensile and compressive residual stresses, and aspect ratio of micro-plate on the free vibration and dynamic behaviors of micro-plates around their static configuration. It is found that the non-dimensional natural frequency parameter varies linearly versus the other non-dimensional parameters of the micro-plate. Various interesting phenomena are observed from the current simulations of the dynamic response of micro-plates to both DC and AC excitation, as well as the boundary of the frequency behavior conversion. A comparison is drawn between the responses of the micro-plate based on the modified couple stress and CT taking the size dependency into account. To facilitate understanding of the physical phenomena observed in the results, a simple physical analog to the micro-plates is suggested. This physical analog, which describes the boundary of frequency behavior conversion, is the linear relationship between the non-dimensional parameters of the system. The study of this model can help to realize some of the complex responses of the micro-plates.