Bias Angle Research Articles

Development of scheme to evaluate the performance of parachute canopy fabrics under tensile impact

The present research is an extension of the earlier work wherein a wider scheme of small-scale tensile impact testing is proposed, to characterise the whole parachute canopy instead of full-scale wind tunnel testing. The drop height for equivalent tensile impact on the rectangular stitched specimens is chosen as 300 mm, and accordingly, the dimension (Length × Width) has been decided (300 mm × 100 mm). To evaluate the performance of stitched specimen (at 45° bias angle), ungripped width of 20 mm on both sides of the specimen has been worked out. In the work, the actual payload responsible for parachute inflation has been addressed for the calculation of the exact opening shock force. Subsequently, to apply impact load on the specimen, dead weights are predicted based on the different levels of opening shock forces of the C-9 parachute canopy under different aerodynamic conditions. Considering a specific case, the behaviour of the ripstop and plain-woven fabric sample in terms of load versus extension curve and work done at the time of impact have been analysed under different loads using a high-speed digital camera. This study revealed that the plain-woven fabric is to be preferred for human dropping because it has a higher extension and higher impact duration than ripstop fabric. As a result, the plain-woven fabric will produce a lower impact or shock force in the parachute canopy which is to be transferred to the skydiver. On the other hand, ripstop fabric possesses higher strength, therefore can be preferred for materials dropping.

Numerical Simulation on the Effect of Burner Bias Angles on the Performance of a Two-Stage Entrained-Flow Gasifier.

A 2000 t/day HNCERI (Huaneng Clean Energy Research Institute) entrained-flow pulverized coal gasifier suffers from the problem of a high ash–slag ratio. An appropriate bias angle of the burners is the key to solve this issue for the gasifier with a specific structure. A random pore model considering bulk and pore diffusion effects was extended by user-defined function to describe the gasification reactions. The simulation of the gas flow and char gasification characteristics under different bias angles (0, 1.5, 2.5, 3.5, and 4.5°) of the four burners in the first stage was conducted. The simulation results showed favorable agreement with the industrial data. The evaporation, devolatilization, and char oxidation mainly occurred in the first-stage jet zone, and the upflow and downflow zones are dominated by the gasification reactions. The bias angles of the burners mainly affect the scale of gasification reaction zones. As the bias angles increased from 0 to 4.5°, the gas temperature at the slag tap hole decreased from 1880 to 1500 K. The carbon conversion efficiency of the first stage decreases and that of the second stage increases with the bias angle increasing. An optimal bias angle of 2.5° is recommended for the HNCERI gasifier with a total carbon conversion efficiency of 98.16%.

Characterizing the macroscopic response and local deformation mechanisms of a unidirectional non-crimp fabric

The macroscopic response and local deformation mechanisms of a warp stitched heavy-tow unidirectional non-crimp fabric (UD-NCF) was characterized. Quasi-static uniaxial tests captured the fabric in-plane longitudinal, transverse, and shear deformation response where digital image correlation was employed. The fabric bending response was captured through modified cantilever tests. Off-axis extension tests conducted along 30°, 45° and 60° bias directions revealed that extension and contraction of the polyester stitching web and resulting transverse compression of the carbon fiber tows and inter-tow sliding were the dominant local deformation mechanisms. At a bias angle of 30°, the extent of inter-tow sliding increased when compared to a bias angle of 45° leading to earlier onset of fabric shear locking, while at a bias angle of 60° shear locking also occurred sooner. Shear angle maps and strain profiles at different bias angles further revealed the notable inter-dependency between the fabric shear, longitudinal and transverse deformations, which was governed by the interactions between the stitching and carbon fiber tows. The distinct out-of-plane bending behavior of the fabric reinforcement along longitudinal and transverse directions was also captured and quantified. The study provided a comprehensive characterization of the UD-NCF, which is critical for the development of constitutive models.

Direction of arrival estimation for a non-ideal acoustic vector hydrophone array

In this article, to address the direction-of-arrival (DOA) estimation problem via a non-ideal acoustic vector hydrophone (AVH) array, a sparse alternating iterative minimization (SAIM) method is proposed. First, a non-ideal AVH array model is established by introducing the axial angle bias parameter into the signal model. Then, to provide accurate DOA estimation, a new cost function is formulated based on a regularized weighted least squares to recovery the sparse signal and the axial angle bias matrix. In particular, to obtain the closed-form solutions of signal and axial angle bias matrix, the Majorization-minimization algorithm is employed to turn the penalty term with a user parameter optimization problem into the weighted Frobenius norm one. In each iteration, to achieve more accurate DOA estimation, the desired axial angle bias matrix is reconstructed based on the distribution characteristics of axial angle bias parameter in the matrix. Extensive numerical simulation and experimental results show that the DOA estimation performance of the proposed method is superior to several well-known methods for a non-ideal AVH array.

State Estimation With a Destination Constraint Imposed by Proportional Navigation Guidance Law

Proportional navigation (PN) guidance laws have been commonly applied to homing missile systems guiding the missile to its target. When the target is stationary and its location is known a priori, the state of the missile is subjected to a destination constraint, which contains extra information on missile state that can help increase tracking performance. This article concerns with the constraint modeling and the state estimation with a destination constraint imposed by PN guidance law in 3-D space. Constraint models corresponding to three representative PN guidance laws: pure PN, true PN, and generalized PN, are presented using the state augmentation method, which stacks the states at the previous and current time steps in one state vector to express the constraint relationships. For cases where the destination information is noisy and the parameters of the guidance law, i.e., the navigation constant and the bias angle, are not known a priori, the unknown parameters are estimated along with the missile state in the state vector in an augmentation way. Based on the formulations of constraint models, the construction of pseudomeasurements is carried out. A constrained state estimation method is proposed by incorporating the pseudomeasurements into the nonlinear filtering process. In this method, a sequential process framework is employed and the cubature Kalman filter is used to handle the high-dimensional filtering problem and the strong nonlinearity involved in pseudomeasurements. Numerical experiments in three scenarios are performed to demonstrate the validity of the proposed models along with the estimation method.

Twist-Stabilized, Coiled Carbon Nanotube Yarns with Enhanced Capacitance.

Coil-structured carbon nanotube (CNT) yarns have recently attracted considerable attention. However, structural instability due to heavy twist insertion, and inherent hydrophobicity restrict its wider application. We report a twist-stable and hydrophilic coiled CNT yarn produced by the facile electrochemical oxidation (ECO) method. The ECO-treated coiled CNT yarn is prepared by applying low potentiostatic voltages (3.0-4.5 V vs Ag/AgCl) between the coiled CNT yarn and a counter electrode immersed in an electrolyte for 10-30 s. Notably, a large volume expansion of the coiled CNT yarns prepared by electrochemical charge injection produces morphological changes, such as surface microbuckling and large reductions in the yarn bias angle and diameter, resulting in the twist-stability of the dried ECO-treated coiled CNT yarns with increased yarn density. The resulting yarns are well functionalized with oxygen-containing groups; they exhibit extrinsic hydrophilicity and significantly improved capacitance (approximately 17-fold). We quantitatively explain the origin of the capacitance improvement using theoretical simulations and experimental observations. Stretchable supercapacitors fabricated with the ECO-treated coiled CNT yarns show high capacitance (12.48 mF/cm and 172.93 mF/cm2, respectively) and great stretchability (80%). Moreover, the ECO-treated coiled CNT yarns are strong enough to be woven into a mask as wearable supercapacitors.

Estimating the VIIRS Thermal Emissive Band Response Versus Scan (RVS) and Calibration Offsets Using On-Orbit Pitch Maneuver Data

The Visible Infrared Imaging Radiometer Suite (VIIRS) is onboard the Suomi National Polar-orbiting Partnership (S-NPP) and the National Oceanic and Atmospheric Administration - 20 (NOAA-20) satellites. This study presents a method for estimating VIIRS Thermal Emissive Bands (TEB) Response Versus Scan (RVS) and calibration offsets simultaneously using on-orbit pitch maneuver data (METHOD2021). Raw Earth View (EV) RVS is estimated using an existing method (METHOD2019), with prelaunch RVS and calibration offsets as first guesses. Errors in the calibration offset are derived based on a prelaunch data-based assumption. Moreover, RVS and calibration offsets are optimized iteratively using the updated calibration coefficients until results converge. Compared to the METHOD2019, the METHOD2021 derived RVS is not affected by errors in the calibration offsets. Evaluation results using independent co-located Cross-track Infrared Sounder (CrIS) observations indicate that the METHOD2021 could effectively mitigate NOAA-20 scan angle and scene temperature dependent biases in M15-M16 and I5, as well as the cold bias in S-NPP M15. S-NPP TEB striping at cold scene temperatures can also be significantly reduced. Furthermore, NOAA-20 I5 and M15 measurements become more in family with S-NPP VIIRS and other radiometers at extremely low temperatures. Our analysis indicates that the impacts of the METHOD2021 and METHOD2019 on TEB SDRs are generally comparable. The METHOD2019 is simpler, while the METHOD2021 better explains the root causes of the VIIRS TEB scan angle and scene temperature dependent biases. Both can be used for improving VIIRS TEB on-orbit calibration, especially at cold scenes.

Design and Synthesis of Ferrite Strip-Line Circulator Based on Enhanced Closed Form Solution and Power Handling Analysis

In this article, Y-junction strip-line circulators are designed using an enhanced closed form solution consisting of unified key equations and a flowchart design, which serves as a direct procedure for designing a ferrite circulator. This design methodology is combined with a 3D EM simulation that allows for the calculation of the saturation magnetization, uniform biasing, and ferrite dimensions needed for a circulator to operate in both modes. In addition, the closed form can be used to calculate the Y-junction parameters and allow the matching network to be calculated and the uniform circulator biasing design ended. Our analysis starts with the ferrite calculation to ensure that it is uniformly biased magnetically, and this is followed by strip-line design, Y-junction matching, and biasing circuit design. Using full-wave electromagnetic (EM), HFSS and magnetostatic (MS), Maxwell3D simulations, several key design parameters such as the saturation magnetization, coupling angle, and various external permanent magnetic biases are investigated. To validate the proposed concept, two strip-line circulators are designed and fabricated for operation in wide-bandwidth and narrow-bandwidth applications. Good agreement is found between the simulated and experimental responses for the S-parameters of the circulators. We also present a semi-analytical analysis of the concept of breakdown, which enables calculation of the peak power and total thermal rise in the strip-line structure. The average power handling capability of a strip-line circulator is studied for the first time. The proposed closed form expressions can also be implemented in various ferrite circulators using different guiding technologies for millimeter-wave applications.

Sensitivity of a one-line longshore shoreline change model to the mean wave direction

The sensitivity of a one-line longshore shoreline change model to the incident wave direction is evaluated at Narrabeen Beach (Australia). As previously observed, the application of the one-line model using wave conditions generated along the 10-m depth contour produces a long-term reorientation of the coastline, with an initial transition period and then a new stable equilibrium during the 10-year period from 2005 to 2015. However, this coastline change in shoreline planform shape is not observed in the shoreline position measurements. The source of this error is investigated by assuming that it is caused by biases in the incident wave direction and by using a Monte Carlo approach to search for the optimal set of wave angle bias corrections to apply at each cross-shore transect. The obtained optimal values enable the one-line model to reproduce accurately the shoreline planform, and they are coherent with estimates of the wave breaking angle obtained independently using a nearshore wave propagation model. Then, using the corrected wave angle time series as a reference, a second Monte Carlo analysis is completed to investigate the sensitivity of the model to errors in the mean wave direction drawn from Gaussian distributions with varying standard deviations. The analysis shows the range of expected errors in shoreline position for an estimated range of errors in the mean wave direction at Narrabeen beach. This work highlights the importance of considering the sensitivity of one-line longshore model simulations to errors in the incident wave angle, which can be relatively large given the uncertainties in spectral wave model estimates of wave direction, in wave buoy observations, and in wave propagation methods or input bathymetry used to estimate wave breaking conditions.

Reproducibility of global electrical heterogeneity measurements on 12-lead ECG: The Multi-Ethnic Study of Atherosclerosis

ObjectiveVectorcardiographic (VCG) global electrical heterogeneity (GEH) metrics showed clinical usefulness. We aimed to assess the reproducibility of GEH metrics. MethodsGEH was measured on two 10-s 12‑lead ECGs recorded on the same day in 4316 participants of the Multi-Ethnic Study of Atherosclerosis (age 69.4 ± 9.4 y; 2317(54%) female, 1728 (40%) white, 1138(26%) African-American, 519(12%) Asian-American, 931(22%) Hispanic-American). GEH was measured on a median beat, comprised of the normal sinus (N), atrial fibrillation/flutter (S), and ventricular-paced (VP) beats. Spatial ventricular gradient's (SVG's) scalar was measured as sum absolute QRST integral (SAIQRST) and vector magnitude QT integral (VMQTi). ResultsTwo N ECGs with heart rate (HR) bias of −0.64 (95% limits of agreement [LOA] -5.68 to 5.21) showed spatial area QRS-T angle (aQRST) bias of −0.12 (95%LOA −14.8 to 14.5). Two S ECGs with HR bias of 0.20 (95%LOA −15.8 to 16.2) showed aQRST bias of 1.37 (95%LOA −33.2 to 35.9). Two VP ECGs with HR bias of 0.25 (95%LOA −3.0 to 3.5) showed aQRST bias of −1.03 (95%LOA −11.9 to 9.9). After excluding premature atrial or ventricular beat and two additional beats (before and after extrasystole), the number of cardiac beats included in a median beat did not affect the GEH reproducibility. Mean-centered log-transformed values of SAIQRST and VMQTi demonstrated perfect agreement (Bias 0; 95%LOA −0.092 to 0.092). ConclusionGEH measurements on N, S, and VP median beats are reproducible. SVG's scalar can be measured as either SAIQRST or VMQTi. SignificanceSatisfactory reproducibility of GEH metrics supports their implementation.

Bio-Inspired Design, Modeling, and Control of Robotic Fish Propelled by a Double-Slider-Crank Mechanism Driven Tail

Abstract This paper presents the design, modeling, and control of a three-joint robotic fish propelled by a double-slider-crank (DSC) driven caudal fin. DSC is a mechanism that can use one direct current motor to achieve oscillating foil propulsion. Its design is guided by a traveling wave equation that mimics a fish's undulatory locomotion. After multiple tests, the robotic fish displayed good performance in mimicking a real fish's swimming motion. DSC mechanism is proven to be an effective propulsion technique for a robotic fish. With the help of another servomotor at the first joint of the fish's tail, the robotic fish can have a two-dimensional free-swimming capability. In experiments, the robotic fish can achieve a swimming speed of 0.35 m/s at 3 Hz, equivalent to 0.98 body length (BL) per second. Its steering rate is proportional to a bias angle. The DSC benefits the control of the robotic fish by independently adjusting its steering and swimming speed. This characteristic is studied in a hydrodynamic model that derives the thrust within a DSC frame. Besides the dynamic model, a semiphysics-based and data-driven linear model is established to connect bias angle to robotic fish's heading angle. The linear model is used for designing an observed-state feedback control control, and the controller has been examined in simulation and experiments.

Emergent spiral vortex of confined biased active particles

Confinement is known to have profound effects on the collective dynamics of many active systems. Here, we investigate a modeled active system in circular confinement consisting of biased active particles, where the direction of active force deviates a biased angle from the principle orientation of the anisotropic interaction. We find that such particles can spontaneously form a spiral vortex with two concentric and counter-rotating regions near the boundary. The emerged vortex can be measured by the vortex order parameter which shows nonmonotonic dependencies on both the biased angle and the strength of the anisotropic interaction. Our work can provide an understanding of such dynamic behaviors and enable different strategies for designing ordered collective behaviors.

Design of Force-to-Rebalanced System With Adaptive Fuzzy-PID Controller for N = 3 MEMS Disk Gyroscope

In this paper, an adaptive fuzzy-PID controller is proposed to make the closed-loop drive system of a MEMS disk gyroscope with a high Q respond faster without overshoot and achieve high stability accuracy. The principle of the MEMS disk gyroscope operating in force-to-rebalanced (FTR) mode is studied. An adaptive fuzzy-PID controller is designed and implemented. The fuzzy controller adjusts the parameters of the PID controller online according to the input error and error change rate. The response time of closed-loop drive of the gyroscope is reduced from 1.09 s to 0.54 s, and the overshoot is reduced from 20% to 0.004%, with no degradation in angle random walk (ARW) and bias instability (BI). The FTR control system is implemented on a field programmable gate array (FPGA) platform. The performance of the $n=3$ MEMS disk gyroscope with natural frequency of 9,536 Hz and a quality factor of ~20000 using the novel FTR control system revealed an ARW of 0.1667 deg/ $\surd $ hr and an in-run BI of 1.177 deg/hr.

Influence of the multi-burner bias angle on the air/particle flow characteristics in an improved fly ash entrained-flow gasifier

The counter-biased burner arrangement has been confirmed to strengthen mixing between burner jets and reduce the risks of firebrick burning in the fly ash entrained-flow gasifier. The burner centerline angle, which represents the bias angle combination of multiple burners, is a critical factor that requires further experimental investigation to boost the air/particle mixture extent in the improved gasifier. In a 1:8-scale model of the 80,000 Nm3/h fly ash entrained-flow gasifier, air/particle flow characteristics under various burner centerline angles (75°, 72°, and 69°) are obtained by a particle dynamics anemometer. The results show that when the burner centerline angles are 75°, 72°, and 69°, the ratio of total particle volume flux in the near-wall region to the total particle volume flux in the measurement zone is 45.9%, 65.3%, and 57.8%; the ratio of the reflux particle quantity in the mixing zone is 0.88:1.27:1. As the burner centerline angle drops from 75° to 69°, the mixing zone radius decreases from 0.275 to 0.174. Simultaneously, the dimensionless difference of particle volume concentration gradually decreases, indicating that lowering burner centerline angle effectively improves the air-particle mixture extent between the burner jets. An optimal burner centerline angle of 69° is recommended.

Effects of both the drive- and sense-mode circuit phase delay on MEMS gyroscope performance and real-time suppression of the residual fluctuation phase error

This work analyses circuit phase delay for carrier-modulation MEMS capacitive gyroscopes. The temperature-dependent circuit phase delay is a major source of gyroscope output drift, which deteriorates the gyroscope bias instability (BI) and angle random walk (ARW). Effects of both drive-mode and sense-mode circuit phase delay on gyroscope performance when using different signal extraction architectures are analyzed in detail. The online suppression method which combines the so-called modified double sideband (MDSB) extraction architecture in the gyroscope drive mode and closed-loop force-rebalance loop in the sense mode can eliminate the impact of residual fluctuation error of circuit phase delay in real time. When drive-mode circuit phase delay equivalently varies from −20° to 20°, using MDSB decreases the fluctuation of the open-loop zero-rate output (ZRO) by 70% compared to using double sideband (DSB) and by 99.7% with respect to using single sideband (SSB). Meanwhile, improvement for the closed-loop ZRO using MDSB is 92.48% and 94% compared to cases using DSB and SSB, respectively. Furthermore, when the equivalent circuit phase delay of the sense-mode alters from −20° to 20°, ZRO variation for the gyroscope with force rebalanced sense loop and quadrature stiffness nulling loop decreases by 80% in contrast to the case with open loop, which demonstrates the effectiveness of online suppression for circuit phase delay of both the drive-mode and sense-mode. Using the online suppression method, the gyroscope has achieved a BI of 0.16° h−1 and ARW of 0.011° (√h)−1. Furthermore, using the MDSB in the drive mode obtains the best stability compared to using the DSB and SSB as the temperature changes.

Multi-source off-grid DOA estimation using iterative phase offset correction in coarray domain

Direction-of-arrival (DOA) estimation performance degrades when arrival angles of incident signals do not locate exactly on the discretized grid points. Existing off-grid DOA estimation algorithms either suffer from high computational complexity or are restricted to uniform linear arrays (ULAs). In order to overcome these disadvantages, we propose a simple but effective off-grid DOA estimation method, referred to as iterative phase offset correction (IPOC), for non-uniform linear arrays (NLAs) in this work. The proposed IPOC first transforms the received signal into the coarray domain and then iteratively corrects the phase offset between the coarray data and presumed model caused by angle biases according to a closed-form formula. In the case of multiple sources, we separate these sources using generalized inner product and then utilize IPOC to sequentially estimate the off-grid angle of one source in each iteration. The spectral leakage between multiple sources is reduced as well by subtracting cross-correlation terms, thus overcoming the shortage of requiring a large number of training snapshots. We calculate the mean squared error (MSE) of the proposed method theoretically. Simulation results demonstrate the effectiveness and efficacy of the proposed method for off-grid DOA estimation using NLAs with very few snapshots.

Efficiency calculation of the nMCP with 10B doping based on mathematical models

The nMCP (Neutron sensitive microchannel plate) combined with advanced readout electronics is widely used in energy selective neutron imaging because of its good spatial and timing resolution. Neutron detection efficiency is a crucial parameter for the nMCP. In this paper, a mathematical model based on the oblique cylindrical channel and elliptical pore was established to calculate the neutron absorption probability, the escape probability of charged particles and overall detection efficiency of nMCP and analyze the effects of neutron incident position, pore diameter, wall thickness and bias angle. It was shown that when the doping concentration of the nMCP was 10 mol%, the thickness of nMCP was 0.6 mm, the detection efficiency could reach maximum value, about 24% for thermal neutrons if the pore diameter was 6 μm, the wall thickness was 2 μm and the bias angle was 3 or 6°. The calculated results are of great significance for evaluating the detection efficiency of the nMCP. In a subsequent companion paper, the mathematical model would be extended to the case of the spatial resolution and detection efficiency optimization of the coating nMCP.

Risk assessment of collapse in mountain tunnels and software development

As most frequent geological hazard, the collapse is a great threat to safe construction of tunnels. The risk assessment method for collapse in mountain tunnels was presented with six evaluation indices, including surrounding rock level I1, rock mass integrity I2, buried depth I3, bias angle I4, groundwater I5, and construction factors I6. According to the non-linear relationship between the collapse and its influencing factors, the synthetic attribute assessment model was improved based on the concept of normal distribution. The weight of each index consisted of two parts: the subjective weight obtained by analytic hierarchy process (AHP) and the objective weight determined by correlation analysis. The Mountain Tunnel Collapse Risk Assessment System (TCAS) was developed based on Visual Studio 2012 and C# programming language. The TCAS was applied to assess the collapse risk of Hongyansi tunnel from Baoyi to Yichang expressway (Xiangyang section). The result was a good agreement with actual excavation situation that a “closed door” collapse happened. Therefore, the software system can not only accurately assess the risk level of collapse but also will play an important role in rapid assessment in the whole process of tunnel construction.

A Brewster incidence method for shocked dynamic metrology of transparent materials and its error evaluation

The shock etalon method with normal incidence is an effective method to extract the shocked dynamic parameters of transparent materials. In order to eliminate the sample surface reflection, additional efforts on the sample preparation are usually introduced, which may limit the application of the method. Here, we proposed a Brewster incidence method to carry out the shock compression experiment on transparent materials. By utilizing the p-polarized light as the probe pulse at Brewster incidence, the sample surface reflection can be directly eliminated, which consequently simplified the experiment preparations. The errors of the proposed method have been evaluated using a set of virtual experiments. The results show that the shocked dynamic parameters can be accurately and robustly retrieved even when the nominal refractive index of the sample deviates 0.01 from its true value, or the incident angle bias 0.33° from the Brewster angle. Finally, a set of shock compression experiments on a polycarbonate film sample are carried out, and shocked dynamic parameters, such as shock velocity, particle velocity, and shocked refractive index, are successfully measured, for demonstration.

Thermal Actuation Analysis of Twisted and Coiled Polymer Actuators

Twisted and coiled polymer actuators (TCPAs), an emerging class of artificial muscles, exhibit the advantages of large stroke, low hysteresis, low cost, etc. The effect of design parameters on thermal actuation is important for the effective design of TCPAs. In this study, a new model has been developed to describe the effect of geometrical parameters on thermal actuation based on Castigliano’s second theorem. In this model, an equivalent modulus based on its radial bias angle has been introduced from the twisted polymer actuator (TPA)’s equivalent model. The proposed model provides a simple and accurate expression to describe the TCPA’s thermal actuation by using its fundamental characteristic. The proposed model was validated with respect to the experimental data from the literature and subsequently used in the parametric analysis of TCPA. The numerical results show that the amplitude of actuation increases linearly with pitch angle and nonlinearly with spring index.