Nonlinear Surface Research Articles

Two-Level Hierarchical-Interaction-Based Group Formation Control for MAV/UAVs

Cooperative group formation control of manned/unmanned aircraft vehicles (MAV/UAVs) using a hierarchical framework can be more efficient and flexible than centralized control strategies. In this paper, a two-level hierarchical-interaction-based cooperative control strategy is proposed for the MAV/UAVs group formation. At the upper level, combined with the nonlinear disturbance observer (NDO) and dynamic surface control (DSC) algorithm, a trajectory tracking problem with external disturbances for MAV is formulated. At the lower level, the leader-following formation controller is utilized to deal with the sub-formation keeping control problem for UAVs, based on the sliding mode disturbance observer and fast terminal sliding mode control law, and the robust performance and control accuracy are effectively improved. Moreover, the overall stability of the MAV/UAVs system is demonstrated using Lyapunov theory. The proposed approach is evaluated by simulation under the ground penetration combat mission for MAV/UAVs, and the performance is compared with that of other control strategies.

Intelligent Control Techniques for the Detection of Biomedical Ear Infections.

The capacity to carry out one's regular tasks is affected to varying degrees by hearing difficulties. Poorer understanding, slower learning, and an overall reduction in efficiency in academic endeavours are just a few of the negative impacts of hearing impairments on children's performance, which may range from mild to severe. A significant factor in determining whether or not there will be a decrease in performance is the kind and source of impairment. Research has shown that the Artificial Neural Network technique is capable of modelling both linear and nonlinear solution surfaces in a trustworthy way, as demonstrated in previous studies. To improve the precision with which hearing impairment challenges are diagnosed, a neural network backpropagation approach has been developed with the purpose of fine-tuning the diagnostic process. In particular, it highlights the vital role performed by medical informatics in supporting doctors in the identification of diseases as well as the formulation of suitable choices via the use of data management and knowledge discovery. As part of the intelligent control method, it is proposed in this research to construct a Histogram Equalization (HE)-based Adaptive Center-Weighted Median (ACWM) filter, which is then used to segment/detect the OM in tympanic membrane images using different segmentation methods in order to minimise noise and improve the image quality. A tympanic membrane dataset, which is freely accessible, was used in all experiments.

Inspection of hybrid nanoparticles flow across a nonlinear/linear stretching surface when heat sink/source and thermophoresis particle deposition impacts are significant

The aim of this paper is to highlight the impact of thermophoretic particle deposition (TPD) and heat source/sink on the steady two-dimensional laminar motion of Casson hybrid-type nanoliquid through a nonlinear stretched surface. Ordinary differential equations (ODEs) are created by taking a collection of partial differential equations (PDEs) and simplifying them using an appropriate similarity component. The reduced ODEs are then evaluated using the shooting method and Runge–Kutta–Fehlberg’s fourth and fifth orders. Finally, tables and graphs are used to display the numerical data. It is seen that the fluid velocity step-downs when the porous parametric quantity and solid nanoparticle values increase. Heat distribution is enhanced with an enhancement in the heat source/sink constraint. Concentration goes down with an enhancement in thermophoretic constraint. The use of nanoparticles improves heat dispersion but reduces concentration in the linear case while increasing axial velocity in the nonlinear scenario.

Development and Definition of Biquadratic Transformations Using Spheres and Two-Way Hyperboloids

The insufficient use of quadratic transformations in applied geometry is explained by the fact that the methods of quadratic transformations are not developed much, although dozens of works by leading experts in applied geometry are devoted to the study of this problem, the development of graphic models, and their application in applied geometry. The research is devoted to the development of the theory of definition of biquadratic transformations of the plane. The essence of the proposed method for modeling biquadratic transformations of the plane, generated by a binary mapping of two surfaces of the second order, facilitation and solution of complex problems of applied geometries. And also, by means of graphical models of biquadratic transformations of the plane to facilitate the construction of curves of the second and fourfold orders. Considering a combination of non-linear surfaces of the second order, obtain subgroups of biquadratic transformations of the plane. The developed algorithm will make it possible to determine mathematical models of canonical biquadratic transformations of the plane, which is necessary for their practical application.

Numerical Investigation on Higher-Order Harmonic Waves Induced by a Submerged Inclined Plate

In this paper, a two-dimensional time-domain numerical flume has been established to model and investigate nonlinear interactions between nonlinear surface waves and a submerged inclined thin plate. The model solves the Laplace equation and the fully nonlinear free surface boundary conditions within the framework of potential flow theory based on the high-order boundary element method. The mixed Euler–Lagrangian method is applied to update the water surface at each time step, and the fourth-order Runge–Kutta method for time stepping. A so-called four-point method was employed to separate the second-order harmonic free and bounded wave that has the same wave frequency but different wave celerity in front of and behind the submerged plate. It is found that the amplitude of the second-order harmonic free wave increases with the inclination angle of the submerged plate, and the level/amount of the increase is larger for a larger wave steepness. In addition, the amplitudes of both the second-order reflected and transmitted waves are found to increase with the wave steepness, and their empirical relationships are derived for potential use in practical engineering.

The Dynamic Sea Clutter Simulation of Shore-Based Radar Based on Stokes Waves

The sea clutter model based on the physical sea surface can simulate radar echo at different times and positions and is more suitable for describing dynamic sea clutter than the traditional models based on statistical significance. However, when applying the physical surface model to shore-based radar, the effects of wave nonlinearity, breaking wave, shadow, and radar footprint size must be considered. In this paper, a dynamic sea clutter simulation scheme based on a nonlinear wave is proposed that uses random Stokes waves instead of linear superposition waves to simulate the nonlinear dynamic sea surface and then calculates echo in the form of scattering cells. In this process, the relationship between wind speed and the nonlinear factor of the Stokes wave is derived, a simple model of shadow modulation is provided, and a method for appending the sea clutter spikes formed by breaking waves is developed. The experimental results show that the simulated sea clutter and the real measured clutter have good consistency in intensity, amplitude statistical distribution, Doppler spectrum, and spatiotemporal correlation. The proposed scheme is suitable for the sea clutter simulation of shore-based radar and can also adjust the relevant parameters to extend to other types of sea clutter simulation.

Intermittency of gravity wave turbulence on the surface of an infinitely deep fluid: Numerical experiment

The intermittency of gravity wave turbulence on the surface of an infinitely deep fluid has been studied numerically. We estimated the scaling exponent of surface elevation structure-functions directly from the equations of motion, e.g., by numerical solution of the underlying equations of motion, without any additional closure assumptions (e.g., phase randomisation) and reduction to the kinetic equations as in the conventional framework of wave turbulence theory. With our high-resolution numerical methods for accurately modelling the nonlinear water surface, we were able to evaluate the scaling exponents of the structure-function up to relatively high orders (p=15), which has not been previously reported. We investigated the effect of wave steepness and forcing on intermittency and compared our results with other analytical and numerical studies, including results on the intermittency of wave turbulence of a different nature (turbulence of bending waves on a plate and magnetohydrodynamic turbulence). Our results support the conjecture of universality for intermittency phenomena in wave turbulence.

Nonlinear surface EMG analysis to detect the neuroprotective effect of citicoline in rat sciatic nerve crush injury.

Surface electromyography (sEMG) is a method involving physiological signals with a complex behavior. The aim is to analyze the sEMG signals by nonlinear techniques for investigating the possible neuroprotective effect of citicoline for early period of administration in rat sciatic nerve crush injury. Thirty-two Wistar rats were randomized into four groups: the sham-operated group with the intact sciatic nerve and the sciatic nerve crush groups, which received crush on the left sciatic nerve and administrated i.p. citicoline (50 and 250mg/kg/day, 7day) or saline (control group). Function assessment analysis was performed and sEMG signals were recorded and analyzed with nonlinear methods. Citicoline administration improved functional recovery in comparison with control group. Largest Lyapunov exponent and correlation dimension parameters were decreased due to the crush injury and increased related with the healing of sciatic nerve. Results of nonlinear analysis of sEMG are in line with the results of functional recovery and electrophysiological assessments. These results suggest that administration of citicoline protects the sciatic nerve from the crush injury which may be attributed to its antioxidative properties. Nonlinear analysis of sEMG is a promising supporting method for determining the nerve regeneration process during the treatment of peripheral nerve injuries.

Nonlinear Bragg scattering of surface waves over a two-dimensional periodic structure

Bragg scattering of nonlinear surface waves over a wavy bottom is studied using two-dimensional fully nonlinear numerical wave tanks (NWTs). In particular, we consider cases of high nonlinearity which lead to complex wave generation and transformations, hence possible multiple Bragg resonances. The performance of the NWTs is well verified by benchmarking experiments. Classic Bragg resonances associated with second-order triad interactions among two surface (linear incident and reflected waves) and one bottom wave components (class I), and third-order quartet interactions among three surface (linear incident and reflected waves, and second-order reflected/transmitted waves) and one bottom wave components (class III) are observed. In addition, class I Bragg resonance occurring for the second-order (rather than linear) transmitted waves, and Bragg resonance arising from quintet interactions among three surface and two bottom wave components, are newly captured. The latter is denoted class IV Bragg resonance which magnifies bottom nonlinearity. It is also found that wave reflection and transmission at class III Bragg resonance have a quadratic rather than a linear relation with the bottom slope if the bottom size increases to a certain level. The surface wave and bottom nonlinearities are found to play opposite roles in shifting the Bragg resonance conditions. Finally, the results indicate that Bragg resonances are responsible for the phenomena of beating and parasitic beating, leading to a significantly large local free surface motion in front of the depth transition.

Analysis of factors influencing recovery of low permeability and strong heterogeneous gas reservoirs and establishment of prediction model

Jialingjiang Formation is a typical low permeability carbonate reservoir in Sichuan Basin, which is characterized by strong heterogeneity, low matrix permeability and high-water saturation. Based on seven influencing factors, such as permeability, reservoir thickness and reservoir porosity, this paper evaluates and predicts the oil recovery of Jialingjiang Formation gas reservoir by using two neural network models of multilayer perceptor and radial basis function and nonlinear surface fitting method. The results show that: 1) In the neural network prediction model, the correlation coefficient between the prediction result curve of multilayer perceptron and the original recovery curve reaches 0.88, which is higher than the radial basis function (0.81), indicating that the use of multilayer perceptron can better predict the recovery of gas reservoirs. 2) In the nonlinear curved surface fitting prediction model, the two influencing factors with the greatest linear correlation with the recovery factor, reservoir thickness and gas recovery rate, are selected to fit the prediction model, and the prediction model is obtained. According to the prediction model, the recovery factor is positively correlated with the reservoir thickness and gas recovery rate on the whole. The model can be used to estimate gas recovery from two factors: reservoir thickness and gas recovery rate.

Wideband Series Harmonic Voltage Compensator for Enhancing Stability of Microgrids

A wideband series harmonicvoltage compensator (WSHVC) for mitigating the adverse effect of unknown grid impedance and load condition on the stability of microgrids with multiple grid-connected inverters (GCIs) is presented. The concept is based on extending the concept of series active power filter. A wideband series voltage source inverter is used to compensate for the high-frequency harmonic voltage caused by the impedance at the point of common coupling, thereby creating a virtually zero high-frequency impedance at the output of the GCIs. The system stability is then assured under any operating condition. The bandwidth of the WSHVC ranges from the second harmonic of the grid frequency to 8 kHz, which is sufficiently higher than the cut-off frequency of typical GCIs. Such fast dynamic behavior is realized by a novel fixed-frequency predictive control scheme with nonlinear switching surfaces. Since the WSHVC handles harmonic power only, its volt-ampere rating is lower than that of the entire system. A 500 VA prototype for a 6.5 kVA testbed with three commercial GCIs, nonlinear load, and adjustable grid impedance has been evaluated. The power dissipation of the WSHVC is less than 1% of the VA rating of the testbed. The effectiveness of the WSHVC on improving system stability is studied.

Structural, vibrational spectroscopy, molecular docking, DFT studies and antibacterial activity of (E)-N1-(3-chlorobenzylidene)benzene-1,4-diamine

In this work, (E)-N1-(3-chlorobenzylidene)benzene-1,4-diamine (CBD) compound was synthesized with good yield. The spectral studies were recorded by FT-IR, FT-Raman, NMR and UV-Vis to determine structural parameters. The geometrical parameters were optimized using DFT calculations at 6-311++G(d,p) basis set. The calculated structural parameters of the molecule were in line with the experimental data. The molecular orbitals of the compound were investigated through highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) analysis. The hyper conjugative interaction energy E(2) along with donor, acceptor electron densities (EDs) were determined by natural bond orbital (NBO) analysis. The molecular electrostatic potential (MEP), mulliken atomic charges, non-linear optical (NLO) properties and potential energy surface (PES) scan were also calculated. The 1H and 13C NMR chemical shifts calculated using Gauge invariant atomic orbital (GIAO) method were compared with the experimental NMR chemical shifts. Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC) were carried out to characterise the thermal behaviour and stability of CBD molecule. In addition, PreADMET tool was also used to estimate ADME and Toxicity of CBD compound. The compound screened against four pathogens two gram positive and two gram negative had shown good anti-bacterial behaviour. The molecular docking studies executed against anti-bacterial target topoisomerase DNA gyrase enzyme (2XCT) emphasized good binding behaviour over the standard drug. Communicated by Ramaswamy H. Sarma

Nonlinear Surface Conductivity Characteristics of Epoxy Resin-Based Micro-Nano Structured Composites

Nonlinear composite materials serve to homogenize electric fields and can effectively improve the local concentration of the electric field in power systems. In order to study the nonlinear surface conductivity properties of micro-nano epoxy composites, two types of epoxy micro-nano composite specimens were prepared in the laboratory using the co-blending method. The surface conductivity of the composites was tested under different conditions using a high-voltage DC surface conductivity test system. The results show that the surface conductivity of micro-nano structured composites increases and then decreases with the rise of nanofiller doping concentration. The nonlinear coefficient was 1.781 at 4 wt% of doped nanostructured SiC, which was the most significant nonlinear coefficient compared to other doping contents. For the same doping concentration, the micro-nano structured composites doped with nanostructured SiC have more significant surface conductivity at the same test temperature with a nonlinear coefficient of 1.635. As the temperature increases, the surface conductivity of the micro-nano structured composite increases significantly, and the threshold field strength moves towards the high electric field. Along with the increase in temperature, the nonlinear coefficients of micro-nano composites after doping with nanostructured SiC showed a gradually decreasing trend. The temperature has little effect on the nonlinear coefficients of the micro-nano structured composites after doping with O-MMT.

Hyperbolic relaxation models for thin films down an inclined plane

We present a family of relaxation models for thin films flows where both viscosity and surface tension effects are inherent. In a first step, a first-order hyperbolic approximation to the dissipationless part of the system is presented. The method is based on an augmented Lagrangian approach, where a classical penalty method is used and high-order derivatives in the Lagrangian are promoted to new independent variables, for which hyperbolic closure equations are sought. Then, we show that the viscous terms can be treated either by plugging them directly to the obtained system, making it of the hyperbolic-parabolic type or by casting them into an approximate algebraic source term that is asymptotically equivalent to the former formulation. Finally, the extension of the method to a classical nonlinear surface tension model is also presented. Numerical results, for all the proposed models are shown and compared with experimental results and reference solutions.

Experimental study on the water entry of a 3D bow-flared model with various inclination angles

Oblique water entry of the ship bow has both the complexity of structure shape and the water entry attitude, which involves strong nonlinear free surface effect and thus, complexes the prediction of slamming loads. This paper conducted the drop experimental investigation on the impact hydrodynamics of a 3D bow-flare model with inclination angles to help clarify the impact characteristics. The experimental uncertainty was discussed based on repeatable and oscillation analysis showing good stability. Characteristics of bow-flared model in oblique impact including water entry depth, acceleration, pressure and impact force were analyzed. Differing to simple 3D bodies like cones and cylinders, multiple pressure peaks appear at some positions, which should be paid attention. The influence of inclination angles on pressure was further discussed, showing the pressure at the bottom and leeward side (right side) decreases while it increases on the windward side with inclination angle. These findings offer evidence for a complex interplay between geometric parameters and inclination angles, which could ultimately serve the ship design.

MHD flow and heat transfer of a hybrid nanofluid past a nonlinear surface stretching/shrinking with effects of thermal radiation and suction

The essence of this study is to explore the nonlinearly stretching/shrinking hybrid nanofluid in terms of its steady flow and heat transfer with the effects of magnetohydrodynamics (MHD), thermal radiation, and suction. The governing partial differential equations are modified by similarity solution into nonlinear ordinary differential equations and solved numerically by bvp4c. The effects of profile on both velocity and temperature, the skin friction coefficient, and the Nusselt number were examined. It was discovered that dual solutions were present, and water has superior heat transfer performance compared to nanofluids and hybrid nanofluids. The thermal boundary layer thickness increases as magnetic and suction parameters increase. According to the stability analysis, first solution is steady, and second solution is unsteady.

Quantitative measurement of corrosion at the nanoscale by in situ spectral modulation interferometry

This research study presents a novel application of a quantitative phase microscopy technique, spectral modulation interferometry (SMI), for in situ nanoscale characterization of corrosion of an aluminum alloy in real time. SMI offers high sensitivity, rapid image acquisition, and speckle-free images; thus, real-time quantification of surface topography evolution during corrosion can be obtained accurately to evaluate the temporally- and spatially-dependent corrosion rates. With an innovative additive-manufactured fluid cell, experiments were performed in situ under flowing solution conditions. Electrochemical tests via stepwise polarization and solution chemistry through collected aliquots of outflow solution were also performed alongside the nanoscale SMI experiment to simultaneously provide a corroborating corrosion rate measurement. Based on the quantitative 3D height profiles across the corroded surface, pit formation resulting from rapid local corrosion was predominant, appearing at different times and are heterogeneously distributed across the surface. The computed time-dependent dissolution rates of aluminum also varied as the experiment proceeded, with the combination of linear and nonlinear surface normal distributions. An initial mean linear dissolution rate of [0.40 ± 0.007] μmol m−2 s−1 transitioned to a more rapid mean rate of [1.95 ± 0.035] μmol m−2 s−1, driven by the anodic polarization. Dissolution rates from the three performed methods follow similar trends and there is the visibility of linking the nanoscale in situ SMI data to the electrochemical corrosion measurements and ex situ chemical solution analysis. At the end of the corrosion period, rates of 118 μmol m−2 s−1, 71 μmol m−2 s−1, and 2.45 μmol m−2 s−1 were obtained from electrochemical measurements, ex situ solution analyses, and in situ SMI corrosion measurement, respectively. Finally, these experimental results validate the applicability of SMI for in situ nanoscale characterization of a corroding alloy surface.

Nonlinear surface SH waves in a half-space covered by an irregular layer

Nonlinear surface SH waves in a half-space covered by an irregular layer

Nonlinear Surface Polaritons near the Interface between a Magneto-Optical Substance and a Nonlinear Metamaterial with a Permittivity Close to Zero

Relevance. Considerable attention of researchers is drawn to nonlinear surface optical waves, as they are promising for application in optical information processing systems, ultra-sensitive sensors, and modern telecommunications components. Purpose. To obtain an exact solution of the Maxwell equation system for TM-polarised nonlinear surface polaritons propagating along the interface between an optically linear magnetic medium and an optically nonlinear medium with saturated nonlinearity. Methods. Analysis of the properties of nonlinear surface polaritons (NSP) and mathematical modelling of the dependence of the permittivity of a nonlinear medium on the intensity are used. Results. TM-polarised nanoparticles propagating along the interface of a magneto-optical medium and a nonlinear optical metamaterial with a permittivity close to zero (ENZ-metamaterial) are studied. For NSP in such a structure, an exact solution of the Maxwell equation system is obtained, considering the saturation effect of optical nonlinearity. On this basis, the dependences of constant propagation on the total energy flux of NSP and energy fluxes in contact media in the structure were investigated: magneto-optical ENZ-metamaterial with negative permittivity/nonlinear self-focusing ENZ-metamaterial. Conclusions. The NSP energy flow is positive in a nonlinear medium and negative in a linear one. As the saturation level decreases, the NSP energy fluxes in the contacting media increase modulo, if the value of the NSP propagation constant (NSPPC) is fixed. The lowest NSPPC value for guiding nonlinearity is obtained when the total energy flow of the NSP becomes zero. As the saturation level decreases, the NSP propagation variable (NSPPV) increases. At a fixed NSPPC, with a decrease in the magnetic permeability, the energy fluxes of NSP in the contacting media increase. When the magnetic permeability decreases to zero and the NSP energy flux is positive, the NSPPV change range narrows

Impact of thermal energy on MHD Casson fluid through a Forchheimer porous medium with inclined non-linear surface: A soft computing approach

In this work, the influence of thermal energy in term of heat source, thermal radiation and chemical reaction on magneto hydrodynamic Casson fluid flow model (MHD-CFM) over a nonlinear slanted extending surface with slip velocity in a Forchheimer permeable medium is numerically studied using the Levenberg Marquardt methodology with backpropagated learning mechanism. It is valuable to evaluate the flow of Cason fluids based on materials (such as drilling muds, clay coatings, various suspensions and certain lubricating oils, polymeric melts, and a wide range of colloids) in the occurrence of heat transfer. Using efficient data, PDEs of (MHD-CFM) were converted to ordinary differential equations. These obtained non-linear ODEs are then rectified using the computational power of the Lobatto IIIA approach to obtain a dataset of Levenberg Marquardt algorithm based trained neural networks (LMA-TNN) for six scenarios of this presented model, which were graphically represented using nftool to obtain regression, efficiency, fit curve, error bars, and trained state analysis. The velocity, temperature, and concentration profiles were computed, and the findings were presented. Additionally, the skin friction coefficient, Nusselt number, & local Sherwood number are explored. The graphs show that when values of radiation parameter and the Forchheimer porous media parameter increase, the temperature of the plate drops. In the existence of a chemical process and a high Schmidt number, the concentration drops. The accuracy achieved in terms of relative error demonstrates the validity and significance of the solution process.