Experimental Simulation Research Articles

Image privacy protection scheme based on high-quality reconstruction DCT compression and nonlinear dynamics

The protection of digital image privacy in Big Data environment is a hot issue of increasing concern. To address the contradiction between efficiency and security for privacy protection, this paper proposes a high-quality restored image privacy protection scheme based on Discrete Cosine Transform (DCT) frequency domain compression and nonlinear dynamics. First, the RGB space of the color image is converted to YCbCr domain with 4:2:0 sampling. Then, the image is divided into sub-blocks in the spatial domain, followed by block-wise DCT and quantization into frequency domain information. Next, both Alternating Current (AC) and Direct Current (DC) coefficients of all sub-blocks are individually extracted and subjected to compression encoding. Finally, a Rubik’s Cube permutation and filtering diffusion encryption algorithm based on a nonlinear dynamical chaotic system is designed. Moreover, a mechanism for generating dynamic chaotic sequences associated with plaintext is introduced to effectively counter cryptographic attacks. The combined approach of compression and encryption significantly reduces computational complexity while improving encryption efficiency. Through experimental simulation results, the compression encryption scheme demonstrates high compression ratios as well as excellent image recovery quality while providing enhanced security against common cryptographic attacks. The work in this paper provides a preferred joint compression and encryption technical solution for digital image privacy protection in Big Data network.

Updating the Loth Drag Model to Include Nonspherical Particle Effects

Sophisticated drag models have been developed over the past few decades that are based on ballistic range and other experimental data. These drag models are applicable over a wide range of particle-flow environments and include compressibility and rarefaction effects. One drawback of these sophisticated drag models is that they assume spherical particles. However, Martian dust particles and materials used in ground-based dusty-flow experiments such as Al2O3 or BN are known to be nonspherical. It is well known that nonspherical particles, in general, will experience higher drag forces compared to spherical particles. There has also been a considerable amount of research developing drag models that account for nonspherical particle shapes, but most of these models are restricted to incompressible, continuum particle-flow conditions. This paper presents a simple way to include nonspherical particle effects into the widely used Loth particle drag model. This updated drag model is used to simulate dust-laden flow experiments performed in the German Aerospace Center the multiple phase flow facility (GBK) experimental facility and in the shock layer of a Martian-entry spacecraft to assess the effectiveness and range of applicability of this new drag model. In the GBK experiment simulations, the modified Loth drag model, which includes both compressibility and nonspherical particle effects, showed improved comparison to the experimental data.

Transient Plasma Wind Tunnel Testing Under Thermomechanical Loads for Reentry Break-Up Analysis

This paper introduces a novel approach for transient plasma wind tunnel testing in an arcjet facility, enabling the experimental simulation of the aerothermal loads along reentry trajectory segments. Such experiments newly allow for the investigation of the causes of break-up events. The trajectory segment is simulated by duplicating the time-resolved profiles of the characteristic flow parameters, namely, heat flux and stagnation pressure as well as the mechanical load, which represents the aerodynamic forces. In arcjet facilities, the parameters that govern the plasma condition are split into variable and constant parameters, which define the available altitude range that can be replicated. The variable conditions arc current and ambient pressure were determined with steady-state trajectory points and traces determined between these conditions resulting in a full trajectory segment. The test time then relates directly to an altitude on the trajectory segment, which allows for an experimental determination of the main break-up altitude. The methodology is applied to a trajectory segment of the transport vehicle CYGNUS OA6, covering an altitude range from 85 to 70 km. A transient break-up experiment on an aluminum bar yielded a failure at an altitude corresponding to 77.6 km, showing a thermomechanical characteristic. These results align well with the observed break-up altitude of CYGNUS OA6, showing the potential of the proposed method.

A dynamic target tracking model for uavs based on the fusion of twin networks and deep learning

Abstract In this paper, a deep learning model incorporating twin networks is proposed to address the challenge of dynamic target tracking by UAVs in complex environments. By exploring the combination of twin networks and convolutional neural networks (CNNs) in detail, this study aims to develop an efficient algorithm capable of accurately tracking dynamic targets under various environmental conditions. The design of the model focuses on utilizing the strong feature-matching capability of twin networks and the advantages of CNNs in image processing in order to improve tracking accuracy and response speed. Experimental simulations show that the model in this paper exhibits better accuracy and response time than the existing popular algorithm YOLOv3 in dynamic target tracking tasks at different difficulty levels. In particular, the present model demonstrates higher robustness and adaptability under different conditions. In addition, the practical application potential of the model is discussed in this paper, pointing out its wide application prospects in the fields of unmanned aerial surveillance and environment sensing of self-driving vehicles.

Tensor Ring Decomposition Guided Dictionary Learning for OCT Image Denoising.

Optical coherence tomography (OCT) is a non-invasive and effective tool for the imaging of retinal tissue. However, the heavy speckle noise, resulting from multiple scattering of the light waves, obscures important morphological structures and impairs the clinical diagnosis of ocular diseases. In this paper, we propose a novel and powerful model known as tensor ring decomposition-guided dictionary learning (TRGDL) for OCT image denoising, which can simultaneously utilize two useful complementary priors, i.e., three-dimensional low-rank and sparsity priors, under a unified framework. Specifically, to effectively use the strong correlation between nearby OCT frames, we construct the OCT group tensors by extracting cubic patches from OCT images and clustering similar patches. Then, since each created OCT group tensor has a low-rank structure, to exploit spatial, non-local, and its temporal correlations in a balanced way, we enforce the TR decomposition model on each OCT group tensor. Next, to use the beneficial three-dimensional inter-group sparsity, we learn shared dictionaries in both spatial and temporal dimensions from all of the stacked OCT group tensors. Furthermore, we develop an effective algorithm to solve the resulting optimization problem by using two efficient optimization approaches, including proximal alternating minimization and the alternative direction method of multipliers. Finally, extensive experiments on OCT datasets from various imaging devices are conducted to prove the generality and usefulness of the proposed TRGDL model. Experimental simulation results show that the suggested TRGDL model outperforms state-of-the-art approaches for OCT image denoising both qualitatively and quantitatively.

Research on laser communication ranging Integration and VLC nonlinear compensation technology

Abstract Visible light communication (VLC) is a new spectrum communication technology that provides a new direction to solve spectrum resource problems. The nonlinearity problem in VLC will lead to a significant reduction in the performance of the communication system. To solve this problem, this paper studies the integration of laser communication ranging and VLC nonlinear compensation technology based on analyzing the principles of ranging methods and factors affecting ranging performance. Aiming at the problem that the complexity of the Random Fourier Features Kernel adaptive filter (RFF-KAF) method will increase significantly as the dimension of the mapping space increases, we introduce some second-order Volterra series square terms into the input vector of RFF-KAF and propose an improved prediction method. Experimental simulation results show that the method proposed in this article can greatly improve the performance of the RFF-KAF method while maintaining the same mapping space dimension. Compared with obtaining similar performance by increasing the mapping space dimension, the cost of this method is greatly reduced.

Intertemporal consumption and lifecycle in a pandemic context: an experimental approximation

The Covid-19 pandemic generated uncertainty among consumers, a slowdown in consumption and an increase of the added saving at world level, the microeconomic evidence showed a tendency towards dissaving and growing consumption. These variations activate questioning about the consequences of confinement in intertemporal consumption, at the same time they allow to provide new empirical evidence about life-cycle models in their standard or neoclassical and behavioral versions. The purpose of this work was to experimentally evaluate the intertemporal consumption patterns from the postulates of both life cycle models. To this end, an experimental simulation exercise of online purchases of commodities was carried out with the participation of 210 consumers who were subjected to treatments that included a baseline, income increase scenarios and no-income withdrawal scenarios. The results verified the existence of consistent responses with the behavioral model in 85% of the cases and with the standard model for the remaining 15%; that is, the tendencies to smooth consumption and increase savings were in the minority in the group evaluated and the confinement context did not translate into more self-controlled intertemporal consumption behaviors.

Manoeuvre Target Tracking in Wireless Sensor Networks Using Convolutional Bi-Directional Long Short-Term Memory Neural Networks and Extended Kalman Filtering.

Aiming at the problem that traditional wireless sensor networks produce errors in the positioning and tracking of motorised targets due to noise interference, this paper proposes a motorised target tracking method with a convolutional bi-directional long and short-term memory neural network and extended Kalman filtering, which is trained by using the simulated RSSI value and the actual target value of motorised targets collected from the convolutional bi-directional neural network to the sensor anchor node, so as to obtain a more accurate initial value of the manoeuvre target, and at the same time, the extended Kalman filtering method is used to accurately locate and track the real-time target, so as to obtain the accurate positioning and tracking information of the real-time target. Through experimental simulation, it can be seen that the algorithm proposed in this paper has good tracking effect in both linear manoeuvre target tracking scenarios and non-linear manoeuvre target tracking scenarios.

Performance investigation of a supergravity CO2 refrigeration cycle under off-design conditions

The transcritical CO2 refrigeration cycle is a research hotspot in CO2 refrigeration technology, but it suffers from significant throttling, compression, and gas cooling losses. The recently proposed supergravity CO2 refrigeration cycle, which utilizes centrifugal potential energy-pressure energy conversion in the rotating heat exchanger, provides a new approach to address these issues. However, the flow efficiency of the serpentine rotating channels requires further validation, and the operating characteristics of the system under off-design conditions need exploration. To this end, we first conducted a study on the pressure drop characteristics of a serpentine rotating channel using experimental and numerical simulation methods. We found a strong linear relationship between the friction factor and the rotation number, with the flow efficiency approaching 1.0 beyond a certain threshold, providing critical support for the cycle. Additionally, we established a distributed parameter model for the cycle and theoretically analyzed its operational performance. The results show that the COP of this cycle reaches 6.91 under air conditioning conditions. This is primarily because the local isentropic compression/expansion efficiency of CO2 in the rotating channel exceeds 99 %. Additionally, the temperature slip during the gas cooling process is only 1.2 °C, demonstrating the feasibility of achieving nearly isothermal compression through the rotating heat exchanger. Furthermore, the results showed that changes in boundary conditions resulted in minimal changes in system pressure differential, not exceeding 2 %. However, increases in CO2 charge and rotational speed led to substantial changes in system pressure differential, increasing by 39 % and 51 %, respectively. These trends reflect the effect of the centrifugal potential energy-pressure energy conversion on the operating characteristics of the system. In addition, there exists a maximum charge limit to prevent the cycle from entering the two-phase region. There is also an optimal combination of rotating heat exchanger and compressor speeds that ensures maximum COP while guaranteeing the cooling capacity. The main novelty of this paper lies in elucidating the coupling mechanism between operational parameters and the thermodynamic parameters of the supergravity CO2 refrigeration cycle.

Natural polymers and electrolytes enhanced coal dust suppression and explosion prevention: New insight from experimental and molecular dynamic simulations

This paper expressed a new insight including experimental and molecular dynamic simulations to illuminate multi-scale mechanisms of coal dust suppression and explosion prevention when applying natural polymers and electrolyte. Results reveals that the addition of natural polymers and electrolyte achieve a maximum 11.85% improvement on dedusting rate and 36.36% improvement on suppression speed when compares with the individual application of SDBS, the MIE and MITC also receives a maximum 1.5 times and 23.58% improvement as well. This achievement is jointly affected by the wetting and agglomerating behaviour between suppressant and coal particles. The chain-like ionic structure and two benzene rings offer LS-Na exhibits good planarity in space and can vertically embed into the surface of coal particles. The lower diffusion coefficient and larger wetting area brings LS-Na stronger ability to help SDBS adsorbing on the coal particles and therefore exhibit better wettability. However, higher electrostatic potential difference endows CMC-Na stronger ability to absorb H2O molecules to form more viscous liquid environment. More hydrogen bond and higher bond energy of CMC-Na could promote the agglomeration of coal particles. The kinetic analysis reveals that the activation energy of coal particles treated by ternary suppressant is higher than that of binary ones. With the help of neutralization reactions between Na· and Cl· generated by molten NaCl and H· and OH· generated by the combustion, the reactivity of coal particles has been diminished and the combustion chain has been interrupted.

Memory synchronisation of delayed neural networks via variable sampling control

This paper tackles the challenge of memory synchronisation of delayed neural networks by implementing a variable sampling control approach. On the one hand, in the light of constructing novel Lyapunov functionals, the conservativeness of the criteria obtained for delayed neural networks is significantly reduced. On the other hand, in light of memory sampling method, the transmission delay is introduced in sampling control scheme, and the information can be fully utilised. The constructed Lyapunov functionals have an advantage, i.e. it is not necessary to be positive on sampling intervals, and also to be continuous at the sampling instants. Finally, to demonstrate the effectiveness and advantages of the proposed methods, two experimental simulations are conducted for delayed neural networks. Two simulations provide empirical evidence supporting the validity of the techniques developed in this study, highlighting their potential for practical application in delayed neural network systems.

Dynamic synergies in cable-driven exosuits for gait assistance

Exosuits for the lower limb have developed rapidly as an affordable, light, and more cost-effective alternative to the bulkier, traditional exoskeletons. The synergy-based approach aims at further emphasizing such advantages, providing even lighter and cheaper solutions, thanks to its reduction in actuators and the subsequent simplification of the actuation unit. In this paper, a design approach based on dynamic synergies is proposed to reduce the number of required actuators, thus decreasing the price and weight of walking-assistance exosuits. Also, in this work, we propose a methodology to calculate motor torque output and cable forces during assisted gait. Mechanical designs for the actuation unit are proposed along with experimental and computer-based testing and simulation. Lastly, actuation units with one and two motors are studied and compared, regarding control, mechanical complexity, and metabolic cost reduction. The results show that dynamic synergies can indeed contribute to the design of these assistive devices, with its own set of advantages and disadvantages when compared to the previously proposed postural synergies: while the latter led to a higher cumulative variance of the first principal component and the transmission system is simpler, control may be more unpredictable and forces upon the system, harder to estimate. With dynamic synergies, more related to muscle synergies, metabolic benefit on users may be more significant.

A new insight to investigate the strain distribution, evolution, and crack development of cement-stabilized coral aggregate

Cement-stabilized coral aggregate (CSCA) can be used as a base material for roads and airports in island engineering. In this study, four-point bending (FPB) tests were conducted on CSCA with different prefabricated crack depths, and distributed fiber optic sensor (DFOS) was used. The testing process of the CSCA beams was simulated using an improved bond-based peridynamic (BBPD) model that combines the bilinear damage principle and fracture parameters random field. The results indicate that DFOS has the potential to monitor strain evolution and detect crack in CSCA. The strain distribution in the spanwise direction of the beam during the plastic phase presents a single peak, which can be described by a Pearson-VII function. The fracture location can be predicted from the positions of the tensile strain peaks. The neutral axis begins to move gradually toward the compressed part of the specimen after the external load greater than 0.6 Pmax. The compression modulus of the CSCA material peaks is 4500 MPa, that is three times larger than its tensile modulus and can satisfy the requirement of semi-rigid base layer construction of island roads. The improved BBPD model is able to effectively simulate the strain-softening behavior of CSCA materials with consideration of the effect of material inhomogeneity on the actual fracture path. The peak load prediction error was less than 7 %. The R2 between the numerically predicted load-displacement curves and the test results were bigger than 0.95. The improved BBPD method can predict the actual fracture location of the specimen with a horizontal position deviation of less than 2 cm. The bending fracture process of CSCA are further explored from both experimental and numerical simulations by this study.

Numerical method for predicting the nucleation and propagation of multiple cracks based on the modified extended finite element method

In practical engineering, structures will inevitably suffer from multiple cracks and require accurate numerical methods to calculate the structural behavior. Regarding the multi-crack problems, the nucleation of new cracks and the development of existing cracks will affect the subsequent structural responses. Therefore, the criterion for calculating crack nucleation and development is a critical factor influencing the numerical results. This paper presents a modified Extended Finite Element Method (XFEM) to predict the nucleation and development of multiple cracks in plane members focusing on the interaction of multiple cracks. In the proposed method, the crack competition criterion is based on the minimum total energy principle, which can ensure that the nucleation and development of cracks can achieve a maximum energy dissipation per unit length. The effectiveness and robustness of the presented method are verified by comparing the numerical results with experimental and/or other numerical simulations. The result shows that the proposed competition criterion can accurately judge the sequence of new-crack nucleation and existing-crack propagation.

Experimental, electrochemical and DFT simulation studies of a novel Schiff base derivative as an efficient mild steel corrosion inhibitor in acidic environments

A newly synthesized Schiff base, consisting 3-methyl-2-{(E)-[(2E)-3-phenylprop-2-en-1-ylidene] amino} butanoic acid, is utilized to prevent mild steel from corroding in acidic environments. FTIR spectra validate the prepared SB. The corrosion rate at various temperatures was measured using electrochemical techniques like as polarization and electrochemical impedance tests. At a higher temperature of 333K, this molecule exhibits about 90% inhibition efficacy with 50 ppm inhibitor. The corrosion inhibition mechanism was measured using thermodynamic and adsorption characteristics. These findings suggest that chemical adsorption causes a surface layer to form on the metal surface. The Langmuir adsorption isotherm is followed. The creation of the adsorption layer on the metal surface is confirmed by SEM and AFM pictures. Quantum chemical calculations were calculated and discussed.

Hydrogen explosion characteristics in the obstructed chamber by changing blockage ratio among adjacent obstacles

Using the experimental and large eddy simulation (LES) methods, the impacts of equivalence ratio and adjacent obstacle blockage ratio on flame propagation, flame moving velocity, and explosion overpressure in a closed obstructed duct are investigated. The results indicate that the developed LES method is able to reproduce the tendency of flame propagation, flame moving velocity, and explosion overpressure of BR = 30%, 50%, 70% and BR = 70%, 50%, 30%. The early flame propagation and flame moving velocity are not affected by the first obstacle. As the explosion flame passes through the three obstacles, the flame acceleration and deceleration occur in sequence due to the decreasing cross-section and vortex-flame interaction, eventually forming three ascending peak flame moving velocity. The higher vorticity magnitude of BR = 70%, 50%, 30% and BR = 30%, 50%, 70% is mainly concentrated in the early stage and later stage of hydrogen explosion, which directly results in the fact that the flame acceleration and rise rate of explosion overpressure of BR = 70%, 50%, 30% is higher than that of BR = 30%, 50%, 70%. Additionally, the maximum value of flame moving velocity and explosion overpressure of BR = 30%, 50%, 70% is higher than that of BR = 70%, 50%, 30%.

The influence of heat treatment process on the dynamic recrystallization evolution mechanism of Inconel 718 during high-speed machining

This study aims to investigate the cutting mechanisms of Inconel 718 alloy under different heat treatment processes and the grain refinement patterns of the transformed layer. By establishing a constitutive model suitable for cutting and importing it into DEFORM-3D for heat treatment processing and single-factor cutting experiment simulation, the effects of heat treatment processes and cutting parameters on cutting force, cutting temperature, and surface grain refinement were studied. The results indicate that the increase in cutting force is maximum, approximately 12 %, after the aging temperature is raised from 668 °C to 718 °C. The cutting force generated after aging heat treatment shows a negative correlation with cutting speed, whereas the cutting force after solution heat treatment rises significantly between 1400 and 1600 mm/s. The maximum cutting temperature occurs in workpieces after solution heat treatment, about 112 % of that of workpieces treated at 718 °C aging heat treatment. At the onset of cutting, the size relationship of the original grain volume is as follows: untreated < solution heat treatment < aging heat treatment; the number of nucleation points for dynamic recrystallization at grain boundaries is as follows: aging heat treatment < solution heat treatment < untreated. The most significant increase in the number of dynamic recrystallizations is observed after aging heat treatment at 621 °C, with the relationship of the number of recrystallizations in different cutting deformation zones being: secondary deformation zone < primary deformation zone < tertiary deformation zone. With the increase in cutting depth, the grain size of the workpiece after solution heat treatment first increases then decreases during the cutting process; the grain size of the workpiece after aging heat treatment first decreases then increases. The grain size of the workpiece during the cutting process after heat treatment is negatively correlated with cutting speed. Specifically, when the cutting speed is 600 mm/s, the grain size after solution heat treatment is the largest, about 1.1 times that of the 718 °C aging heat-treated workpiece.

Slip-discreteness-corrected strain gradient crystal plasticity (SDC-SGCP) theory

Strain gradient plasticity theory addresses the plastic strain gradient induced hardening by considering the internal stress and Taylor hardening associated with the geometrically necessary dislocations (GNDs). However, the continuum description of internal stress associated with GNDs is inaccurate due to the coarsening of discrete dislocations. Corrections are thus derived as the difference between the stresses produced by the continuous configuration and the discrete configuration. We further demonstrate the capability of this correction in effectively capturing the internal stress induced strengthening effect associated with GNDs, and elucidate that its role in strengthening is to homogenize the deformation and extend the influence of grain boundaries into the interior of grains within polycrystals. This capability to capture intragranular slip distribution is validated through the simulation of a polycrystalline tensile experiment. This work explains the limitations of classical crystal plasticity theory under high strain gradients and offers a straightforward yet robust slip discreteness correction to crystal plasticity with transparent input from dislocation theory, opening a new perspective for the connections between continuum crystal plasticity theory and dislocation theory.

Haze factor of silver nanowires in variable refractive index environment: experimental and simulation approaches

While silver nanowires (Ag NWs) have been demonstrated as a highly efficient transparent conducting material, they suffer from strong light scattering, which is quantified by a large haze factor (HF) in the optical spectrum. Here we investigate the influence of the dielectric environment on the light scattering of Ag NWs by comparing experimental measurements and simulations. In air, two peaks on the HF spectra are observed experimentally at the wavelength of λ I = 350 nm and λ II = 380 nm and are attributed by simulations to the influence of the Ag NWs pentagonal shape on the localized surface plasmon resonance. The relative intensity between the two peaks is found to be dependent on whether the Ag NWs are in contact with the glass substrate or not. The HF behaviour in the near IR region seems to be dominated by Rayleigh scattering following simulations results. Dielectric environments of Ag NWs with various refractive indexes were obtained experimentally by the conformal deposition of different metal oxide coatings using atomic layer deposition, including Al-doped zinc oxide, Al2O3 and SiO2 coatings. The HF is found to be correlated with the refractive index environment in terms of HF peaks position, intensity and broadening. This trend of HF peaks is supported by a theoretical model to understand the optical mechanism behind this phenomenon.

Achieving low hot tearing susceptibility in high-strength cast Al–Li alloys: Experimental investigation and simulation assessment

Due to the exceptional low density and high stiffness, cast Al–Li alloys are deemed suitable for structural applications. However, their economic benefits are limited by intolerable hot tearing susceptibility (HTS) during casting. This work aims to optimize alloy compositions that compromise low HTS and good mechanical properties. Six alloys (Alloys 1–6) with potentially high hot tearing resistance were selected by regulating Li, Cu and Mg additions based on the Kou's criterion and ProCAST simulation. Experimental results indicated that in contrast to Alloys 1–4, Alloys 5 & 6 containing higher solute contents show anomalously high HTS, significantly deviating from the predictions. It was further revealed that this phenomenon originates from a variety of Li-rich inclusions formed at interdendritic channels, which lead to strain localization and hinder residual liquid refilling. Then, Alloys 1–4 with low HTS were subjected to a tailored subsequent heat treatment to achieve optimal mechanical properties. Among the tested alloys, Alloys 3 & 4 exhibit comparatively lower ductility attributed to strain accumulation at the interface between coalesced Sʹ-Al2CuMg phases and Al matrix. In comparison, a good combination of strength and ductility (YS = 371 ± 14 MPa, UTS = 456 ± 19 MPa, EL = 2.5 ± 0.1 %) was successfully achieved in Al-2.5Li–2Cu–1Mg-0.15Zr alloy (Alloy 2) due to the synergistic reinforcement of δʹ-Al3Li and T1-Al2CuLi precipitates. Compared to other available cast Al–Li alloys, Alloy 2 possesses better hot tearing resistance while being highly competitive in strength. Our results are anticipated to contribute scientific guidance for developing high-performance cast Al–Li alloys with low HTS.