Offset Phenomena Research Articles

Experimental validation study on snap through and coiling up of deployable composite shells

AbstractBistable reeled composite shells (BRCS) have been widely used in deployable space structures due to advanced properties of light weight and large volume reduction. A finite element simulation and experimental validation to study the transition of BRCS between their two stable states are performed. In this article, multiscale representative volume element (RVE) modeling is used to compute the equivalent mechanical properties of carbon/epoxy plain woven fabrics that were utilized to construct the deployable composite laminates, followed by experimental verification. The deformation characteristics and strain energy distribution of the deployable composite shell (DCS) during snap through and coiling up are investigated using finite element analysis (FEA) and verified by strain‐gauge and digital image correlation (DIC) tests. The results show that the strain energy distribution in the snap through and coiling up of the carbon/epoxy plain woven BRCS with laminate stacking sequence of [+45/−45] is approximately symmetric. Additionally, an offset phenomena is observed during the coiling up of the BRCS in the finite element modeling. A parametric analysis is complemented to investigate effects of fiber angles on the deformation characteristics and strain energy distribution of the shell structures during snap through and coiling up.Highlights Shell deformation during snap through and coiling up was investigated. DIC test was performed to capture the shell deformation. Strain energy distribution of the deployable composite shell was discussed. Offset phenomena are observed during the coiling up.

Analysis of neural network connections based on memristors and their multiple offset phenomena

The article suggests a construction method of a magnetron memristor connecting a three-dimensional Hopfield neural network and a Rulkov neuron in order to build a more complex and achieve more bio-like neural network properties, which has rarely been proposed before. It is discovered that the dynamical behavior of this high-dimensional neural network system is rich, and that the system exhibits many dynamical behaviors depending on the parameter changes. It is possible to change the attractor’s amplitude and its offset boosting behavior by varying various parameters. Changing the system parameters and modifying the system’s initial value may result in initial offset boosting behavior. Combining nonlinear dynamics research methodologies, such as phase diagram, bifurcation diagram, Lyapunov exponential spectrum, and time series diagram, demonstrates the system’s complex dynamical behavior. By analyzing the system complexity and random sequence test, we found that the system has the characteristics of large complexity and strong pseudo-randomness. Eventually, the hardware realizability is proved by the construction of the DSP platform.

Application of common reflection surface (CRS) to velocity variation with azimuth (VVAz) inversion of the relatively narrow azimuth 3D seismic land data

Abstract The fracture direction and its intensity are critical properties related to hydrocarbon characterization and identification. Both these properties have an essential role in identifying the direction of hydrocarbon migration, determining the sweet spot area, and optimizing the drilling design. The velocity variation with azimuth (VVAz) is a well-known method to estimate the fracture direction and its intensity. This method is of widespread interest because it predicts the properties based on seismic data without any practical constraints. Despite this interest, the technique requires rich azimuth 3D seismic data in our case, which is rare. This study aims to apply regularization and interpolation by including the wave front attributes based on the Common Reflection Surface (CRS) method before the VVAz inversion. The motivation of using the CRS method is to enrich the current azimuth of the 3D seismic data and improve the S/N ratio. The synthetic and the real 3D seismic data are evaluated to examine the interpolation scheme of the proposed CRS method’s performance. Based on the evaluation of the 3D seismic data after regularization, the amplitude versus offset (AVO) phenomena, and the VVAz inversion results are relatively consistent (or matched) with the model. A similar result is found for the case of real 3D seismic data. A significant positive correlation between the fracture intensity of FMI and the real seismic data of about 0.9 is obtained. Therefore, CRS can be used as a regularization and interpolation method before the VVAz inversion of the relatively narrow azimuth 3D seismic data.

Design and implementation of flywheel energy storage system control with the ability to withstand measurement error

In this paper, attempts are made to design an offset and dead zone resistant digitalized vector control system for the flywheel energy storage system (FESS) based on the permanent magnet assisted synchronous reluctance motor (PMa-SynRM). Typically, in the motor drive set, current sensors are used. Current sensors in the industrial application consist of offset and dead zone phenomena and disturb the performance of the control system. Therefore, the effects of these phenomena in FESS designed control system are investigated, and a modified control system with using a proper filter to eliminate these phenomena is proposed. The proposed filter can eliminate these phenomena from the measured current without any decreasing in signal magnitude. The proposed control system eliminates speed ripple caused by the dead zone and offset effects. The performance of FESS is improved under the modified control system. Simulation and experimental results of the modified control system for FESS are presented to verify the performance of the energy storage drive and the theories.

The polarization reverse of diode-like conical nanopore under pH gradient

In the past decade, with the improvement of nanofabrication technology, silica nanopores and nanochannels have been widely used in the fields of ion pumps, energy conversion, ion channels, metal ion detection, and biosensors. Although both potential and pH gradient can significantly change the performance of ion current rectification in nanoscale, the potential mechanism is still not fully understood. In this study, the ion current rectification, surface charge distribution and ion selectivity of silica nanopore under different background salt concentration and pH gradient were discussed by an analytical model, which takes into account the effects of electroosmotic flow, multiple ionic species, and the acid base neutralization. The results show that the polarity of nanopore rectifier can be changed by changing the acidity and alkalinity at both ends of the nanopore. For the first time, we find that the rectification polarity of silica conical nanopore exhibits different performances under high and low electric field intensity. One case in this study shows the rectification ratio curve of the nanopore will have a maximum or minimum value and the extreme point is near the zero of the ion current. With the increase of the concentration of background salt solution, the voltage at the zero point of ion current approaches the zero point, and then the maximum or minimum point moves to the left. The extreme point offset and polarity reversal phenomena may have potential application value in nanopore-based sensing devices.

Orbital hybridization-induced band offset phenomena in NixCd1-xO thin films.

Herein, we present the cationic impurity-assisted band offset phenomena in NixCd1-xO (x = 0, 0.02, 0.05, 0.1, 0.2, 0.4, 0.8, and 1) thin films and further discuss them based on orbital hybridization modification. The compositional and structural studies revealed that the cationic substitution of Cd2+ by Ni2+ ions leads to a monotonic shift in the (220) diffraction peak, indicating the suppression of lattice distortion, while the evolution of local strain with an increase in Ni concentration is mainly associated with the mismatch in the electronegativity of the Cd2+ and Ni2+ ions. In fact, Fermi level pinning towards the conduction band minimum takes place with an increase in the Ni concentration at the cost of electronically compensated oxygen vacancies, resulting in the modification of the distribution of carrier concentration, which eventually affects the band edge effective mass of the conduction band electrons and further endorses band gap renormalization. Besides, the appearance of a longitudinal optical (LO) mode at 477 cm-1, as manifested by Raman spectroscopy, also indicates the active involvement of electron-phonon scattering, whereas modification in the local coordination environment, particularly anti-crossing interaction in conjunction with the presence of satellite features and shake-up states with Ni doping, was confirmed by X-ray absorption near-edge and X-ray photoelectron spectroscopy studies. These results manifest the gradual reduction of orbital hybridization upon the incorporation of Ni, leading to a decrement in the band edge effective electron mass. Finally, the molecular dynamics simulation reflected a 13% reduction in the lattice parameter for the NiO thin film compared to the undoped film, while the projected density of states calculation further supports the experimental observation of reduced orbital hybridization with an increase in Ni concentration.

Switched sliding mode approach for motion control systems with friction

The chattering and offset phenomena, which may lead to acceleration disturbances and deteriorate control performance, are the main deficiencies caused by switching signal and mismatched uncertainties when the sliding mode control method is used for motion control systems with friction. The need is highlighted for simultaneous chattering suppression and mismatched uncertainties attenuation of sliding mode control. In this article, a switched sliding mode control method is proposed which uses three sliding surfaces to divide the error state space into three subspaces. Using different sliding mode controllers when error system state is located in different subspaces, the asymptotically stable of motion control system is guaranteed under friction and uncertainties (including matched and mismatched). In addition, through designing proper switching gain for each sliding mode controller, the control law of switched sliding mode control can be continuous. This means that the chattering phenomenon caused by switch...

Enhancement of condensation on a vertical plate (2nd report, prediction of condensation on a dispersed finned surface)

AbstractIn this study, a prediction model for condensation heat transfer on a vertical dispersed finned surface was proposed, utilizing the Adamek‐Webb model for condensation heat transfer outside a horizontal finned tube. The prediction model was based on two main experimental observation results. One is the phenomena of the condensate retention at the bottom of each row of the dispersed fin. Another is the offset phenomena of the condensate flow between each row of the dispersed fin. Given the results by the present model, it is predicted that the dependence of the condensation heat transfer coefficient for the dispersed finned surface on the fin pitch is controlled mainly by the dispersed fin length, not the total fin length. On the contrary, for a different fin pitch, the effect to the condensation heat transfer by dispersing the fin is different. From comparison with the experiment results, it is confirmed that the present model was able to predict the condensation with extremely good precision when the fin pitch was larger. Further, when the fin pitch was smaller, the predicted values were higher than the experimental values, but the tendency of the condensation heat transfer with dispersing the fin was nearly predicted. In addition, this condensing model can predict the experimental values with an error of 25% at the maximum in a range of fin pitch 0.6 mm to 1 mm. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20288

RECONFIGURABLE MICROSTRIP PATCH ANTENNA WITH SWITCHABLE POLARIZATION

A new reconfigurable microstrip patch antenna allowing switching between two circular polarizations is proposed. It consists of a square radiating patch and a 3 dB hybrid coupler. Using only a single-polar-double-throw (SPDT) switch,the polarization switching can be achieved. This design of the dc-bias network is extremely simple. From experimental results,the proposed antenna avoids the frequency offset phenomena which often happened to antennas with switchable polarization.

Effects of polarization and permittivity gradients and other parameters on the anomalous vertical shift behavior of graded ferroelectric thin films

We studied theoretically the dependence of the “polarization offset” on various parameters in compositionally graded ferroelectric thin films. Our model adopts the Landau-Khalatnikov equation to describe hysteresis behavior and takes the time-dependent space-charge-limited conductivity into account to investigate the effects of polarization and permittivity gradients, charge mobilities, and thickness in graded ferroelectric thin films. We found that both polarization and permittivity gradients are requisite for the occurrence of offset phenomena. It is also found that larger gradients of remanent polarization and permittivity, a smaller thickness, and a larger charge mobility can generally enhance the effect of vertical offsets. The qualitative agreement between simulation and experiment further supports our previous notion that the asymmetric conduction current arising as a result of the composition gradient is an important factor leading to the polarization offset phenomenon.

Explicit expressions for the dynamic polarization behavior in ferroelectrics with symmetric/asymmetric electrical conductivity

We model the dynamic polarization behavior of ferroelectric films by an analytical approach. Using a parallelogramlike P-E hysteresis model, explicit expressions were obtained for describing the D-E loops of ferroelectric films as would be measured from a Sawyer-Tower circuit. By introducing the consideration of electrical conduction, resistive losses inflate the ferroelectric loop to some extent. In addition, an asymmetric conduction will result in polarization offsets with the magnitude and direction depending on the asymmetric conductivities of the materials. The inflated loop, as well as the offset phenomena, which have been observed experimentally [e.g., L. Zheng, C. Lin, W.-P. Xu, and M. Okuyama, J. Appl. Phys. 79, 8634 (1996)], will be discussed by means of our modeled results. Some simple exact formulas have been derived and the effects of electric, dielectric, and ferroelectric parameters, as well as the applied field on the “apparent” polarization were also examined.

Multistep Model Predictive Control Based on Artificial Neural Networks

This work studies the effect of different models on the performance of multistep model predictive control (MMPC) via simulation examples and bench- and pilot-scale experiments. The models used in the study are two common types of artificial neural networks (ANNs), namely, feedforward networks (FFNs) and external recurrent networks (ERNs). The steady-state offset of MMPC using FFN models is observed throughout simulation cases and experiments in case that prediction horizon is longer than the control horizon. This study further explains the FFN-induced offset phenomena mathematically. In the experimental part of this work, we compare the performances of MMPC using these two ANN models, conventional proportional−integral controllers and linear model predictive control in the dual-temperature control problems, which include a bench-scale ethanol and water distillation column and a pilot-scale i-butane and n-butane distillation column.

Gravity characteristics of the Pan-African Orogen in Ghana, Togo and Benin (west Africa)

In the area of study, 4718 gravity data have been processed. Distribution of the resulting anomalies confirms the continuity towards the south of the three characteristic gravity domains already identified north of the parallel 9 °N. Positive anomaly belts underline the presence of magmatic rocks in the foreland of the chain. The tectonic overload characterizing its external zone is mirrored by a very strong overcompensation. A main gradient zone (the regional gradient) is superimposed on a suture zone of allochtonous basic massifs. The internal zone is characterized by a very important undercompensation connected with heavy deep structures. Numerous gravity discontinuities line the three previous sets (foreland, external and internal zones), revealing the great structural complexity of the region. Nevertheless this complexity is frequently concealed or attenuated by smoothing and offset phenomena which are expressed through more regular anomalies and profiles.The present study strengthens the hypothesis of a continental collision chain for the Dahomeyides and emphasizes the hypotheses of micro-continent aggregation together with a progressive rise of the southern part of the studied sector during the Pan-African tectogenesis.