Forward Mode Research Articles

Modelling and attitude control of novel multi-ducted-fan aerial vehicle in forward flight

Multi-ducted-fan aerial vehicle (MDFAV) is a novel platform for future transportation with promising prospects, which presents brand new challenges to the modelling and control approaches. In this paper, a comprehensive flight dynamical model of MDFAV is established utilising the aerodynamics principles and classical rigid body dynamics theory aiming to balance the complexity and covering necessary important dynamical behaviour of MDFAV, which is converted into state space by linearisation at the specific speed in forward flight mode in the following step. Subsequently a dual closed loop PID controller is put forward to keep flight fast and stable with the key coefficients tuned by non-smooth parameters optimisation method. The software and hardware of flight controller are designed for flight test of MDFAV systematically. Experiment results demonstrate excellent tracking performance and robustness, and at the same time, environment disturbances are suppressed effectively.

Modelling and attitude control of novel multi-ducted-fan aerial vehicle in forward flight

Multi-ducted-fan aerial vehicle (MDFAV) is a novel platform for future transportation with promising prospects, which presents brand new challenges to the modelling and control approaches. In this paper, a comprehensive flight dynamical model of MDFAV is established utilising the aerodynamics principles and classical rigid body dynamics theory aiming to balance the complexity and covering necessary important dynamical behaviour of MDFAV, which is converted into state space by linearisation at the specific speed in forward flight mode in the following step. Subsequently a dual closed loop PID controller is put forward to keep flight fast and stable with the key coefficients tuned by non-smooth parameters optimisation method. The software and hardware of flight controller are designed for flight test of MDFAV systematically. Experiment results demonstrate excellent tracking performance and robustness, and at the same time, environment disturbances are suppressed effectively.

Perturbation confusion in forward automatic differentiation of higher-order functions

AbstractAutomatic differentiation (AD) is a technique for augmenting computer programs to compute derivatives. The essence of AD in its forward accumulation mode is to attach perturbations to each number, and propagate these through the computation by overloading the arithmetic operators. When derivatives are nested, the distinct derivative calculations, and their associated perturbations, must be distinguished. This is typically accomplished by creating a unique tag for each derivative calculation and tagging the perturbations. We exhibit a subtle bug, present in fielded implementations which support derivatives of higher-order functions, in which perturbations are confuseddespitethe tagging machinery, leading to incorrect results. The essence of the bug is as follows: a unique tag is needed for each derivative calculation, but in existing implementations unique tags are created when taking the derivative of a function at a point. When taking derivatives of higher-order functions, these need not correspond! We exhibit a simple example: a higher-order functionfwhose derivative at a pointx, namelyf′(x), is itself a function which calculates a derivative. This situation arises naturally when taking derivatives of curried functions. Two potential solutions are presented, and their deficiencies discussed. One uses eta expansion to delay the creation of fresh tags in order to put them into one-to-one correspondence with derivative calculations. The other wraps outputs of derivative operators with tag substitution machinery. Both solutions seem very difficult to implement without violating the desirable complexity guarantees of forward AD.

Risk characterization of bisphenol-A in the Slovenian population starting from human biomonitoring data

The current study aims to characterize exposure and risk associated to bisphenol-A (BPA) exposure in Slovenia, starting from biomonitoring data. Based on the urinary data, daily intake for the individuals was back-calculated using a physiology based biokinetic (PBBK) model properly parameterized for BPA, coupled with an exposure reconstruction algorithm. Re-running the PBBK model in forward mode allowed the estimation of biologically effective dose (free plasma BPA) and the respective daily area under the curve (AUC). Finally, risk characterization ratio was derived using both external and internal dose metrics. The urinary BPA levels were found low, with GM of 0.79, 1.51 and 0.20 μg/g creatinine for mothers, children and fathers respectively, similar to the levels of other European countries. Based on the above and accounting for the dynamics of exposure and biokinetics, daily intake was estimated, median exposure levels have been estimated equal to 0.019, 0.035 and 0.005 μg/kg_bw/d for mothers, fathers and children respectively. The highest estimated intake level was found in a child, equal to 0.87 μg/kg_bw/d, while the maximum intake for mothers and fathers were 0.7 and 0.8 μg/kg_bw/d respectively. The respective RCR levels using the EFSA t-TDI of 4 μg/kg_bw/d were 2 magnitudes of order lower below 1, independently of the selected method. It has to be noted that had daily intake been estimated solely based on the urinary concentrations mass balance, the estimated intake would be lower, as a result of the oversimplification on exposure and elimination time dynamics. This highlights the importance for using PBBK modelling based exposure reconstruction schemes for rapidly metabolized and excreted compounds such as BPA, as well as the study design of efficient sampling for rapidly metabolized compounds.

Pulse frequency modulation and unilateral dual‐phase‐shift hybrid control strategy for bidirectional full‐bridge LLC resonant converter

Bidirectional LLC resonant converter has been popular in applications such as electric vehicle, energy storage system and uninterruptible power supply for its good soft-switching characteristics. A novel control strategy combined pulse frequency modulation (PFM) with unilateral dual-phase-shift (DPS) control is proposed in this work. By controlling the switches in the converter, the forward buck mode operation can be realised under PFM control, as well as the backward boost mode operation can be realised under unilateral DPS control; therefore, the bidirectional power flow and zero-voltage-switching of all switches can be realised; thus, the efficiency of the converter is improved. The detailed operation principle, control strategies, voltage gain expression, soft-switching characteristics and design of parameters are analysed. The feasibility of PFM-DPS control is finally verified by PSIM simulation and prototype experimental results.

The Development of Athlete Performance Capabilities Index (APCI) Model for Male U12 Player Selection using Multivariate Analysis

This study develops an Athlete Performance Capabilities Index (APCI) model using multivariate analysis for selecting the best player of under twelve (U12). Measurement of anthropometrics and physical fitness were evaluated among 178 male players aged 12±0.52 years. Factor score derived by Principal Component Analysis were used to obtain a model for APCI and Discriminant Analysis (DA) were conducted to validate the correctness of group classification by APCI. Result was found two factors with eigenvalues greater than 1 were extracted which accounted for 62.00% of the variations present in the original variables. The two factors were used to obtain the factor score coefficients explained by 35.72% and 26.67% of the variations in athlete performance respectively. Factor 1 revealed high factor loading on fitness compared to Factor 2 as it was significantly related to anthropometrics. A model was obtained using standardized coefficient of factor 1. Three clusters of performance were shaped in view by categorizing APCI ≥ 75%, 25% ≤ APCI < 75% and APCI < 25% as high, moderate and low performance group respectively. Three discriminated variables out of thirteen variables were obtained using Forward and Backward stepwise mode of DA, which were weight, standing broad jump, and 40 meters’ speed. Such variables were established as essential indicator for selecting the best player among male U12.

Flow field research on electrochemical machining with gas film insulation

Electrochemical machining (ECM) is an efficient method for fabricating crucial components of aircraft engines, such as integral blisks and diffusers. This paper proposes a new method for decreasing the stray corrosion in trepanning ECM, in which air is supplied around the machined workpiece to remove stray electrolyte. Specifically, compressed air was blown into the cathode and through the workpiece in a forward flow mode, thereby forming a gas film on the machined surface. Simulations were performed using the ANSYS software to determine the distributions of compressed air and electrolyte in the machined area. The simulation results demonstrated a uniform air–electrolyte distribution and a stable flow field under the optimal parameters. Experiments were conducted to verify these results, and the gas film was found to exert an obvious influence on reducing the taper angle and improving the surface quality of the workpiece. Severe corrosion of the workpiece occurred in the absence of air flow, whereas the stray corrosion was significantly reduced when air was supplied through the cathode. Upon increasing the feed rate from 0.5 to 1.5 mm/min, the taper angle decreased from −0.012° to −0.003° and the surface roughness decreased from Ra 0.841 μm to Ra 0.266 μm, whereas the optimal values for the samples obtained without the gas film were 0.096° and Ra 0.993 μm at the feed rate limit of 1.0 mm/min.

Gate Conduction Mechanisms and Lifetime Modeling of p-Gate AlGaN/GaN High-Electron-Mobility Transistors

The gate conduction mechanisms in p-gallium nitride (GaN)/AlGaN/GaN enhancement mode transistors are investigated using temperature-dependent dc gate current measurements. In each of the different gate voltage regions, a physical model is proposed and compared to experiment. At negative gate bias, Poole–Frenkel emission (PFE) occurs within the passivation dielectric from gate to source. At positive gate bias, the p-GaN/AlGaN/GaN “p-i-n” diode is in forward operation mode, and the gate current is limited by hole supply at the Schottky contact. At low gate voltages, the current is governed by thermionic emission with Schottky barrier lowering in dislocation lines. Increasing the gate voltage and temperature results in thermally assisted tunneling (TAT) across the same barrier. An improved gate process reduces the gate current in the positive gate bias region and eliminates the onset of TAT. However, at high positive gate bias, a sharp increase in current is observed originating from PFE at the metal/ p-GaN interface. Using the extracted conduction mechanisms for both devices, accurate lifetime models are constructed. The device fabricated with the novel gate process exhibits a maximum gate voltage of 7.2 V at ${t}_{\textsf {1}\%}=\textsf {10}$ years.

A Comparison of Electron, Proton and Gamma Irradiation Effects on the I-V Characteristics of 200 GHz SiGe HBTs

Total ionizing dose effects induced by 1 MeV electron and 5 MeV proton on the dc electrical characteristics of 200 GHz silicon germanium heterojunction bipolar transistors (SiGe HBTs) were investigated. These results were compared with 60Co gamma irradiation results to understand the linear energy transfer effects on the electrical characteristics of SiGe HBTs. The different electrical parameters like forward and inverse mode Gummel characteristics, excess base current ( ${\boldsymbol \Delta } I_{\mathbf {B}}$ ), current gain ( $\boldsymbol {h}_{\mathbf {FE}}$ ), and output characteristics ( $\boldsymbol {I}_{\mathbf {C}}$ - $\boldsymbol {V}_{\mathbf {CE}}$ ) were systematically studied before and after irradiation. The electrical characteristics of irradiated SiGe HBTs degrade with an increase in total dose. The more degradation in device parameters was observed in case of 5 MeV proton irradiated HBTs when compared to other radiations. The irradiated devices were also subjected to isochronal annealing to analyze the recovery of electrical parameters.

Bioinspired polarization imager with high dynamic range

Polarization is one of the three fundamental properties of light, along with color and intensity, yet most vertebrate species, including humans, are blind with respect to this light modality. In contrast, many invertebrates, including insects, spiders, cephalopods, and stomatopods, have evolved to detect polarization information with high-dynamic-range photosensitive cells and utilize this information in visually guided behavior. In this paper, we present a high-dynamic-range polarization imaging sensor inspired by the visual system of the mantis shrimp. Our bioinspired imager achieves 140 dB dynamic range and 61 dB maximum signal-to-noise ratio across 384×288 pixels equipped with logarithmic photodiodes. Contrary to state-of-the-art active pixel sensors, where photodiodes in individual pixels operate in reverse bias mode and yield up to ∼60 dB dynamic range, our pixel has a logarithmic response by operating individual photodiodes in forward bias mode. This novel pixel circuitry is monolithically integrated with pixelated polarization filters composed of 250-nm-tall × 75-nm-wide aluminum nanowires to enable snapshot polarization imaging at 30 frames per second. This sensor can enable many automotive and remote sensing applications, where high-dynamic-range imaging augmented with polarization information can provide critical information during hazy or rainy conditions.

Modal switching of bubbly Taylor–Couette flow investigated by particle tracking velocimetry

Injection of bubbles into Taylor–Couette flow creates new flow modes which have not been experienced in single-phase flow conditions. An array of spiral vortices array is one such mode departing from the original toroidal Taylor vortices. The aim of the present study is to explore the mode transition of the two-phase flow using particle tracking velocimetry. Vertical-axis concentric cylinder with a rotating inner cylinder was used to measure the motion of both phases in the range 600 < Re < 4500. From time–space mapping of the experimentally measured stream functions, we found that bubble injection intensified the axial displacement of the wavy Taylor vortices in the toroidal array, and there was a smooth switching to a spiral array when the azimuthal traveling velocities coincided between two phases. During this vortical reconnection, the two counter-rotating vortices were attenuated asymmetrically. After the two phases co-organized a spiral array, the spiral-maintaining mechanism was weakened to restore the toroidal vortices. These forward and backward mode transitions occurred periodically as bubble injection flow rates increased. We, therefore, concluded that modal switching was an evidence of two-way bubble–vortex interaction for a maximized state, causing the largest drag reduction reported in this regime.

L’intelligence économique en faveur de la dynamique entrepreneuriale par les pôles économique intelligents Étude exploratoire a l’entreprise sonatrach aval

In a difficult economic context caused by Low oil prices. The Algerian government hasadopted a new economic approach centered on local development. Thus, by putting forward anew mode of participative management allowing triggering an entrepreneurial dynamic throughthe creation of economic poles. The results we have achieved show that economic intelligencerepresents a promising alternative for the Algerian government, to instil the momentum ofproductive investment, by stimulating entrepreneurial actions, through an interconnectionbetween all actors economies in the domain of enterprises creation and support.

Contribution of Moisture from Mediterranean Sea to Extreme Precipitation Events over Danube River Basin

In the most recent decades, central Europe and the Danube River Basin area have been affected by an increase in the frequency and intensity of extreme daily rainfall, which has resulted in the more frequent occurrence of significant flood events. This study characterised the link between moisture from the Mediterranean Sea and extreme precipitation events, with varying lengths that were recorded over the Danube River basin between 1981 and 2015, and ranked the events with respect to the different time scales. The contribution of the Mediterranean Sea to the detected extreme precipitation events was then estimated using the Lagrangian FLEXPART dispersion model. Experiments were modelled in its forward mode, and particles leaving the Mediterranean Sea were tracked for a period of time determined with respect to the length of the extreme event. The top 100 extreme events in the ranking with durations of 1, 3, 5, 7, and 10 days were analysed, and it was revealed that most of these events occurred in the winter. For extreme precipitation, positive anomalies of moisture support from the Mediterranean were found to be in the order of 80% or more, but this support reached 100% in summer and spring. The results show that extreme precipitation events with longer durations are more influenced by the extreme Mediterranean anomalous moisture supply than those with shorter lengths. However, it is during shorter events when the Mediterranean Sea contributes higher amounts of moisture compared with its climatological mean values; for longer events, this contribution decreases progressively (but still doubles the climatological moisture contribution from the Mediterranean Sea). Finally, this analysis provides evidence that the optimum time period for accumulated moisture to be modelled by the Lagrangian model is that for which the extreme event is estimated. In future studies, this fine characterisation could assist in modelling moisture contributions from sources in relation to individual extreme events.

Analysis of single stage steam generating absorption heat transformer

Absorption heat transformer (AHT) has played a role in producing available heat from the low temperature of waste heat sources. This study proposes two operating modes regarding the way to supply heat source to the AHT system, and aims to investigate the operating characteristics of the steam generating AHT system concerning heating source temperature. First, this study describes the thermodynamic cycle of the single stage AHT operating with water-lithium bromide pair, and two operating modes are illuminated: a forward flow mode for heat source input to the evaporator and then to the generator, and a reverse flow mode for heat source input to the generator and then to the evaporator. Second, the first law of theoretical simulation characterizes the effects of the different operating modes on the heat transfer rates of each AHT component, the coefficient of performance (COP), and the steam generation rate. The experimental studies validate the theoretical simulation models; consequently, the results obtained herein lay a foundation of further investigation for the thermodynamic characteristics of the steam generating AHT system to maximize the operating performance.

Combination Parametric Resonance of Nonlinear Unbalanced Rotating Shafts

In this paper, dynamic response of a rotating shaft with geometrical nonlinearity under parametric and external excitations is investigated. Resonances, bifurcations, and stability of the response are analyzed. External excitation is due to shaft unbalance and parametric excitation is due to periodic axial force. For this purpose, combination resonances of parametric excitation and primary resonance of external force are assumed. Indeed, simultaneous effect of nonlinearity, parametric, and external excitations are investigated using analytical method. By applying the method of multiple scales, four ordinary nonlinear differential equations are obtained, which govern the slow evolution of amplitude and phase of forward and backward modes. Eigenvalues of Jacobian matrix are checked to find the stability of solutions. Both periodic and quasi-periodic motion were observed in the range of study. The influence of various parameters on the response of the system is studied. A main contribution is that the parametric excitation in the presence of nonlinearity can be used to suppress the forward synchronous vibration. Indeed, in the presence of combination parametric excitation, the energy is transferred from forward whirling mode to backward one. This property can be applied in control of rotor unbalance vibrations.

Family of isolated bidirectional resonant converters with duty‐cycle control and automatic power flow transition

This study proposes a family of duty-cycle controlled bidirectional resonant converters and its uniform modulation schemes. This family of converters is composed of a current-fed stage, a transformer with LC resonant tank and a voltage-fed stage. Therefore, high-voltage gain and low-current ripple can be achieved. With the proposed uniform modulation schemes, automatic forward and backward mode transition is realised. Furthermore, the voltage gain is only determined by the duty cycle, independent of load and power flow direction, thus simple control can be adopted and voltage can be regulated in a wide range. Zero-voltage switching of all switches can be achieved over a wide load range. The operation principle and analysis of one of the converters are presented as an example. Design considerations are provided. Experimental results are shown to verify the theoretical analysis.

Nonlinear Free Vibration of Spinning Viscoelastic Pipes Conveying Fluid

Drill strings are one of the most significant rotor components employed in oil and gas exploitation. In this paper, an improved dynamical model of drill-string-like pipes conveying fluid is developed by taking into account the axial spin, fluid–structure interaction (FSI), damping as well as curvature and inertia nonlinearities. The partial differential equations of motion are derived by two sequential Euler angles and the Hamilton principle and then directly handled by the multiple scales method. The nonlinear amplitudes, frequencies and whirling mode shapes are all investigated towards various system parameters to display the nonlinear dynamical characteristics of such a special rotor system coupled with FSI. It is revealed that the nonlinear amplitudes and frequencies are explicitly dependent on the spinning speed, while the flowing fluid mainly contributes to the linear frequencies, and consequently influences the nonlinear amplitudes and frequencies. The FSI effect and axial spin can both improve the forward procession mode and suppress the backward one, while both procession modes will be suppressed by the viscoelastic damping. The pipe will ultimately present a forward as well as decayed whirling motion for the fundamental mode.

Spatial and Temporal Assessment of Titiwangsa Lake Water Quality Using Chemometrics Analysis

Titiwangsa Lake is a renowned recreational lake in Kuala Lumpur, Malaysia. The present study was purposely to define the current status of Titiwangsa Lake water quality and propose a water quality monitoring program to conserve and sustain the health of this lake. Samples were collected in January 2017 during the day and night-time periods. Spatial classification using hierarchical agglomerative cluster analysis (HACA) has clustered the sampling stations into low, medium and high contaminated areas. Temporal classification of discriminant analysis (DA) forward stepwise mode has highlighted DO, chlorophyll-a and E-coli are the significant variables. They showed a lower range of data during the day-time period compared to night-time period. DA backward stepwise model showed significant variables of total suspended solid (TSS) and total phosphate (TP) were higher in concentration during the day-time period as compared to night-time period. The significant of varimax factors (VFs) in the principal component analysis (PCA) might contribute by the landscaping, small-scale domestic wastewater, urban stormwater and land erosion. In a nutshell, based on HACA classification, samples can be collected at only three stations represent each cluster during the next water quality monitoring activities as this could reduce the time and cost of sampling and sample analysis.

Nonlinear dynamic analysis using the complex nonlinear modes for a rotor system with an additional constraint due to rub-impact

Abstract A rub-impact can bring the impact load and friction force onto the rotor, and in the meantime, it can also produce the additional effect of changing the stiffness of the rotor system. Past analysis and numerical simulation work related to rub-impact problems primarily focus on the complicated nonlinear vibration responses caused by the rubbing force. However, the influence of the additional effect on the rotor’s modal characteristics is rarely studied. The present study investigates the modal characteristic of the rotor system with the additional constraint and how it affects the rotor’s responses. The governing equation for a modified Jeffcott rotor system with a rub-impact is established first. Next, the complex nonlinear modes concept is introduced, and the corresponding solution method is derived. Finally, the modal characteristics are analyzed in detail, such as the modal frequency, the modal damping, the stability and the interaction between the nonlinear mode motion and rotor’s responses. The results show that the rubbing rotor system possesses both forward whirl mode motion and backward whirl mode motion. The magnitudes of the modal frequencies for both the forward whirl and backward whirl increase with an increase in the amplitude of the mode motion (modal amplitude). Nevertheless, the magnitudes are limited to an interval range, which can be approximately determined through the linear rotor without rub-impact and the coupled linear rotor/stator system. Differing from the forward whirl mode motion, the backward whirl mode motion can be unstable, since its modal damping may be less than zero in certain cases. Moreover, the instability of the backward whirl mode motion is only the primary physical mechanism for the partial rub transmitting into dry whip.

Circular-to-linear polarization converter based on composite via-coupled patch frequency selective surfaces

In this paper, we present a design of circular-to-linear polarization converter operating in C-band based on a composite frequency selective surface which consists of two types of via-coupled patch modules. The building unit cell is built with four modules, and each one is a truncated patch pair printed on the double-layer substrate and vertically connected by a metal via-hole. A perforated common ground plane is sandwiched between the double layers to support transverse electric and magnetic mode coupling between the front and back patches. The front diagonally truncated patch array responds to the incident right-handed circularly polarized wave, and it is identically converted into general right- and left-handed elliptically or circularly polarized waves with same phase shifts, amplitudes and axial ratio, thus a resultant linear polarized wave is generated in forward transmission mode.