An Enhanced GAN for Image Generation

Generative adversarial networks(GANs)with gaming abilities have been widely applied in image generation.However,gamistic generators and discriminators may reduce the robustness of the obtained GANs in image generation under varying scenes.Enhancing the relation of hierarchical information in a generation network and enlarging differences of different network architectures can facilitate more structural information to improve the generation effect for image generation.In this paper,we propose an enhanced GAN via improving a generator for image generation(EIGGAN).EIGGAN applies a spatial attention to a generator to extract salient information to enhance the truthfulness of the generated images.Taking into relation the context account,parallel residual operations are fused into a generation network to extract more structural information from the different layers.Finally,a mixed loss function in a GAN is exploited to make a tradeoff between speed and accuracy to generate more realistic images.Experimental results show that the proposed method is superior to popular methods,i.e.,Wasserstein GAN with gradient penalty(WGAN-GP)in terms of many indexes,i.e.,Frechet Inception Distance,Learned Perceptual Image Patch Similarity,Multi-Scale Structural Similarity Index Measure,Kernel Inception Distance,Number of Statistically-Different Bins,Inception Score and some visual images for image generation.

Data augmentation method for insulators based on Cycle-GAN

Data augmentation is an important task of using existing data to expand data sets.Using generative countermeasure network technology to realize data augmentation has the advantages of high-quality generated samples,simple training,and fewer restrictions on the number of generated samples.However,in the field of transmission line insulator images,the freely synthesized samples are prone to produce fuzzy backgrounds and disordered samples of the main insulator features.To solve the above problems,this paper uses the cycle generative adversarial network(Cycle-GAN)used for domain conversion in the generation countermeasure network as the initial framework and uses the self-attention mechanism and channel attention mechanism to assist the conversion to realize the mutual conversion of different insulator samples.The attention module with prior knowledge is used to build the generation countermeasure network,and the generative adversarial network(GAN)model with local controllable generation is built to realize the directional generation of insulator belt defect samples.The experimental results show that the samples obtained by this method are improved in a number of quality indicators,and the quality effect of the samples obtained is excellent,which has a reference value for the data expansion of insulator images.

Synthesis and microwave absorption performance of heat-treated RF/SiO_(2)aerogels

The well-designed composite with satisfactory electromagnetic microwave absorption at high temperatures remains a serious challenge.Herein,we fabricated a resorcinol-formaldehyde/silica dioxide composite aerogel(RF/SiO_(2))with a three-dimensional network structure using sol-gel,atmospheric pressure drying technique as well as heat-treated processes to achieve enhanced microwave absorption capabilities in the low frequency range.The pristine RF/SiO_(2)aerogel presented a typical micropores structure with a surface area,porous volume,and density of 146.82 m^(2)/g,62.40%,and 0.28 cm^(3)/g,respectively.Remarkably,the RF/SiO_(2)aerogel showed an effective absorption bandwidth of 3.56 GHz and a minimum reflection loss value of-46.10 d B at 2.25 mm after being heat-treated at 1500°C,while the maximum effective absorption bandwidth was 3.60 GHz at 2.30 mm.The intricate three-dimensional networks possessed remarkable impedance matching,multiple attenuation mechanisms,interfacial polarization,and dielectric loss,which were attributed to the exceptional ability to absorb electromagnetic microwaves.It offered a fresh approach to creating adaptable and effective microwave absorption materials in military defense.

A robust deformed convolutional neural network(CNN)for image denoising

Due to strong learning ability,convolutional neural networks(CNNs)have been developed in image denoising.However,convolutional operations may change original distributions of noise in corrupted images,which may increase training difficulty in image denoising.Using relations of surrounding pixels can effectively resolve this problem.Inspired by that,we propose a robust deformed denoising CNN(RDDCNN)in this paper.The proposed RDDCNN contains three blocks:a deformable block(DB),an enhanced block(EB)and a residual block(RB).The DB can extract more representative noise features via a deformable learnable kernel and stacked convolutional architecture,according to relations of surrounding pixels.The EB can facilitate contextual interaction through a dilated convolution and a novel combination of convolutional layers,batch normalisation(BN)and ReLU,which can enhance the learning ability of the proposed RDDCNN.To address long-term dependency problem,the RB is used to enhance the memory ability of shallow layer on deep layers and construct a clean image.Besides,we implement a blind denoising model.Experimental results demonstrate that our denoising model outperforms popular denoising methods in terms of qualitative and quantitative analysis.Codes can be obtained at https://github.com/hellloxiaotian/RDDCNN.

机匣-动叶的相对运动对高负荷涡轮叶顶气热性能的影响

Base on the standard k-ωturbulent model,numerical method for solving three dimensional Reynolds Averaged Navier-Stokes(RANS)was adopted to study the aerothermal characteristics of the turbine blade with casing relative motion.Experimental data were used to verify the effectiveness of the numerical method and turbulent model.The effect of blade tip clearance,geometry and relative motion on blade tip aerothermal characteristics were analyzed.The numerical results show that for the flat tip,relative motion can effectively suppress tip leakage and reduce leakage vortex size at rotating blade-static casing(BRCS)and static bladerotating casing(BSCR)conditions.A high level of heat transfer region can be observed near the leading edge at the conditions of rotating bladerotating casing(BRCS)and static bladestatic casing(BSCR).The blade tip heat transfer coefficient expands with the increase of tip clearance at different relative motion modes.At the brcs and bscs,the axial average heat transfer trend is the closest when the tip clearance is 1.5%H.The scraping vortex generated by relative motion at brcr and bscs inhib-its the development of leakage flow for squealer tip because of its sealing effect.High level of heat transfer region is also concentrated in the leading edge at brcr and bscs.The size of scraping vortex weakens with the increase of cavity depth.The distribution trend of the average heat transfer coefficient is similar in the two cases of relative static and relative motion,except for the case of 2.5%H cavity depth.

The aging behavior,microstructure and mechanical properties of AlN/AZ91 composite

Microstructure evolution and mechanical properties of the aging treated AlN/AZ91 composites were systematically investigated by optical microscopy(OM),high resolution scanning electron microscopy(HRSEM)with an energy dispersive spectrum(EDS),and high-angle annular dark field scanning transmission electron microscopy(HAADF-STEM).The results show that the higher fracture elongation(14±1%)and ultimate tensile strength(275±6 MPa)were simultaneously obtained in the peak-aged AlN/AZ91 composites.Comparied with AZ91 matrix alloy,the strength was increased by about 44%and the elongation was approximately five times higher,which mainly attributed to the precipitation of nano-sizedγ-Mg_(17)Al_(12)phase and the activation of non-basal slip systems induced by in-situ AlN particles at room temperature.However,the in-situ formation of AlN reinforcements consumed part of Al element in the matrix alloy,which resulted into the volume fraction decreasing ofγ-Mg_(17)Al_(12)precipitates,and then the age hardening and strengthening efficiency were reduced in the AlN/AZ91 composites.On the other hand,the mismatch of thermal expansion coefficient between AlN particles and AZ91 matrix generated high density dislocations around AlN particles,which promoted the precipitation ofγ-Mg_(17)Al_(12)phase,and then the peak aging time and temperature were decreased.

Progress of Chinese“Dove”and Future Studies on Flight Mechanism of Birds and Application System

This paper introduces the Chinese"Dove"——A practical application system of bird-mimetic air vehicles developed for more than a decade by the Institute of Flight Vehicle Innovation of Northwest Polytechnic University(NWPU)in China.Firstly,the main components,flight capability and flight verification of the Chinese"Dove"are presented.Then,the methods for the aerodynamic simulation and wind tunnel experiments are put forward.Secondly,the design of high-lift and high-thrust flexible flapping wings,a series of flapping mechanisms,gust-resistance layout and micro flight control/navigation system are presented.Some future studies on the application system of bionic micro air vehicles are given,including observation of natural flight creatures,aerodynamics in flight,mechanical and new material driving systems,structural mechanics,flight mechanics,and the information perception and intelligent decision-making control,which are related to research of flight bioinformatic perception and brain science.Finally,some application examples of complex flapping movements,active/passive deformation of bird wings,new low-energy motion-driven system,bionic intelligent decision-making and control/navigation are discussed.

Dynamic affine formation control of networked under-actuated quad-rotor UAVs with three-dimensional patterns

This paper focuses on the solution to the dynamic affine formation control problem for multiple networked underactuated quad-rotor unmanned aerial vehicles(UAVs)to achieve a configuration that preserves collinearity and ratios of distances for a target configuration.In particular,it is investigated that the quad-rotor UAVs are steered to track a reference linear velocity while maintaining a desired three-dimensional target formation.Firstly,by integrating the properties of the affine transformation and the stress matrix,the design of the target formation is convenient and applicable for various three-dimensional geometric patterns.Secondly,a distributed control method is proposed under a hierarchical framework.By introducing an intermediary control input for each quad-rotor UAV in the position loop,the necessary thrust input and the desired attitude are extracted.In the attitude loop,the desired attitude represented by the unit quaternion is tracked by the designed torque input.Both conditions of linear velocity unavailability and mutual collision avoidance are also tackled.In terms of Lyapunov theory,it is prooved that the overall closed-loop error system is asymptotically stable.Finally,two illustrative examples are simulated to validate the effectiveness of the proposed theoretical results.

Development and Analysis of a New Cylindrical Lithium-Ion Battery Thermal Management System

With the development of modern technology and economy,environmental protection and sustainable development have become the focus of global attention.The promotion and development of electric vehicles(EVs)have bright prospects.However,many challenges need to be faced seriously.Under diferent operating conditions,various safety problems of electric vehicles emerge one after another,especially the hidden danger of battery overheating which threatens the performance of electric vehicles.This paper aims to design and optimize a new indirect liquid cooling system for cylindrical lithium-ion batteries.Various design schemes for diferent cooling channel structures and cooling liquid inlet directions are proposed,and the corresponding solid-fuid coupling model is established.COMSOL Multiphysics simulation software is adopted to simulate and analyze the cooling systems.An approximate model is constructed using the Kriging method,which is considered to optimize the battery cooling system and improve the optimization results.Sensitivity parameter analysis and the optimization design of system structure are performed through a set of infuencing factors in the battery thermal management.The results indicate that the method used in this paper can efectively reduce the maximum core temperature and balance the temperature diferences of the battery pack.Compared with the original design,the optimized design,which is based on the non-dominated sorting genetic algorithm(NSGA-II),has an excellent ability in the optimized thermal management system to dissipate thermal energy and keep the overall cooling uniformity of the battery and thermal management system.Furthermore,the optimized system can also prevent thermal runaway propagation under thermal abuse conditions.In summary,this research can provide some practical suggestions and ideas for the engineering and production applications and structural optimization design carried by electric vehicles.

A Hybrid CNN for Image Denoising

Deep convolutional neural networks(CNNs)with strong learning abilities have been used in the field of image denoising.However,some CNNs depend on a single deep network to train an image denoising model,which will have poor performance in complex screens.To address this problem,we propose a hybrid denoising CNN(HDCNN).HDCNN is composed of a dilated block(DB),RepVGG block(RVB),feature refinement block(FB),and a single convolution.DB combines a dilated convolution,batch normalization(BN),common convolutions,and activation function of ReLU to obtain more context information.RVB uses parallel combination of convolution,BN,and ReLU to extract complementary width features.FB is used to obtain more accurate information via refining obtained feature from the RVB.A single convolution collaborates a residual learning operation to construct a clean image.These key components make the HDCNN have good performance in image denoising.Experiment shows that the proposed HDCNN enjoys good denoising effect in public data sets.

Resonance mechanism of flapping wing based on fluid structure interaction simulation

Certain insect species have been observed to exploit the resonance mechanism of their wings.In order to achieve resonance and optimize aerodynamic performance,the conventional approach is to set the flapping frequency of flexible wings based on the Traditional Structural Modal(TSM)analysis.However,there exists controversy among researchers regarding the relationship between frequency and aerodynamic performance.Recognizing that the structural response of wings can be influenced by the surrounding air vibrations,an analysis known as Acoustic Structure Interaction Modal(ASIM)is introduced to calculate the resonant frequency.In this study,Fluid Structure Interaction(FSI)simulations are employed to investigate the aerodynamic performance of flapping wings at modal frequencies derived from both TSM and ASIM analyses.The performance is evaluated for various mass ratios and frequency ratios,and the findings indicate that the deformation and changes in vortex structure exhibit similarities at mass ratios that yield the highest aerodynamic performance.Notably,the flapping frequency associated with the maximum time-averaged vertical force coefficient at each mass ratio closely aligns with the ASIM frequency,as does the frequency corresponding to maximum efficiency.Thus,the ASIM analysis can provide an effective means for predicting the optimal flapping frequency for flexible wings.Furthermore,it enables the prediction that flexible wings with varying mass ratios will exhibit similar deformation and vortex structure changes.This paper offers a fresh perspective on the ongoing debate concerning the resonance mechanism of Flexible Flapping Wings(FFWs)and proposes an effective methodology for predicting their aerodynamic performance.

在高应变率拉伸/压缩-扭转载荷下TC17钛合金的屈服和塑性流动行为

金属材料经常暴露在高应变率和复杂的应力条件下.研究这些材料的动态力学行为对工程设计和工业应用至关重要.本文研究了TC17钛合金在压缩/拉伸-扭转作用下的动态塑性流动行为.研究了TC17钛合金在准静态和动态载荷下的初始屈服行为,并采用杨、郭和李提出的动态不对称屈服准则(DAYC)来表征动态初始屈服行为.根据不同应力状态下的硬化特性,提出了一种修正的动态硬化规律(MDHL)来拟合加载面.研究了TC17钛合金在准静态和动态载荷作用下的塑性流动方向.结果表明,塑性势函数基本符合相关联流动法则.总之,本文系统性的研究了TC17钛合金的屈服性能,应变硬化规律和塑性流动规律,并利用DAYC和MDHL对其进行了表征.

Design and Experimental Verification of a Roll Control Strategy for Large Wingspan Flapping-Wing Aerial Vehicle

Most flapping-wing aircraft wings use a single degree of freedom to generate lift and thrust by flapping up and down,while relying on the tail control surfaces to manage attitude.However,these aircraft have certain limitations,such as poor accuracy in attitude control and inadequate roll control capabilities.This paper presents a design for an active torsional mechanism at the wing's trailing edge,which enables differential variations in the pitch angle of the left and right wings during flapping.This simple mechanical form significantly enhances the aircraft's roll control capacity.The experimental verification of this mechanism was conducted in a wind tunnel using the RoboEagle flapping-wing aerial vehicle that we developed.The study investigated the effects of the control strategy on lift,thrust,and roll moment during flapping flight.Additionally,the impact of roll control on roll moment was examined under various wind speeds,flapping frequencies,angles of attack,and wing flexibility.Furthermore,several rolling maneuver flight tests were performed to evaluate the agility of RoboEagle,utilizing both the elevon control strategy and the new roll control strategy.The results demonstrated that the new roll control strategy effectively enhances the roll control capability,thereby improving the attitude control capabilities of the flapping-wing aircraft in complex wind field environments.This conclusion is supported by a comparison of the control time,maximum roll angle,average roll angular velocity,and other relevant parameters between the two control strategies under identical roll control input.

Enhanced near-field radiative heat transfer between core-shell nanoparticles through surface modes hybridization

Core-shell nanoparticles(CSNPs)are widely used in energy harvesting,conversion,and thermal management due to the excellent physical properties of different components.Because of the synergistic interaction between the core and the shell,the thermal radiative properties are expected to be further enhanced.In this work,we achieve near-field radiative heat transfer(NFRHT)enhancement between SiC@Drude CSNPs.Numerical results show that the total heat flux between NPs is 1.47 times and 9.98 times higher than homogeneous SiC and Drude NPs at the same radius when the core volume fraction is 0.76.Surface modes hybridization arising from the interfaces of the shell-core and shell-air contributes to the improved thermal radiation.The effect of shift frequency on the NFRHT between SiC@Drude CSNPs is studied,showing that the enhancement ratio of NFRHT between CSNPs can reach 4.34 at a shift frequency of 1×10^(14) rad/s,which is 38.34 times higher than the previous work.This study demonstrates that surface modes hybridization in CSNPs can significantly improve NFRHT and open a novel path for high-efficiency energy transport at the nanoscale.

Unsteady characteristic research on aerodynamic interaction of slotted wingtip in flapping kinematics

The slotted wingtip structure of birds is considered to be the product of improving flight efficiency in the process of evolution. It can change the vortex structure of wingtip and improve aerodynamic efficiency. This paper reports a numerical investigation of slotted wing configuration undergoing bio-inspired flapping kinematics(consisting of plunging and in-line movement)extracted from a free-flying bald eagle wing. The aim is to eluci-date the collective mechanism of the flow generated by slotted tips and the lift contribution of each tip. Specifi-cally, the objective of the study is to determine how changes in the wing spacing affect the resulting aerodynamic interaction between the slotted tips and how that affects the force generation and efficiency. Changes in the phase angle between the flapping motions of slotted tips, as well as the spacings among them,can affect the resulting vortex inter-actions. The rear tips often operates in the wake of the frontal tips and, meanwhile, the vortex generated by the movement of the rear tips promote the frontal tips.The interaction of vortices in time and space leads to wing-wing interference and the flow around slotted tips becomes complicated and unstable. The innovative study of wingtip slot in unsteady state leads us to find that the aerodynamic interaction among slotted tips makes the overall lift characteristic better than that of the unslotted wings. The slotted wing configuration can efficiently convert more energy into lift. As the flapping frequency increases, the collective feature of slotted wing with constantly changing gaps can be more advantageous to enhance lift-generation performance.

A Brief Review on Aerodynamic Performance of Wingtip Slots and Research Prospect

Wingtip slots,where the outer primary feathers of birds split and spread vertically,are regarded as an evolved favorable feature that could effectively improve their aerodynamic performance.They have inspired many to perform experiments and simulations as well as to relate their results to aircraft design.This paper aims to provide guidance for the research on the aerodynamic mechanism of wingtip slots.Following a review of previous wingtip slot research,four imperfections are put forward:vacancies in research content,inconsistencies in research conclusions,limitations of early research methods,and shortage of the aerodynamic mechanism analysis.On this basis,further explorations and expansion of the influence factors for steady state are needed;more attention should be poured into the application of flow field integration method to decompose drag,and evaluation of variation in induced drag seems a more rational choice.Geometric and kinematic parameters of wingtip slot structure in the unsteady state,as well as the flexibility of wingtips,should be taken into account.As for the aerodynamic mechanism of wingtip slots,the emphasis can be placed on the study of the formation,development,and evolution of wingtip vortices on slotted wings.Besides,some research strategies and feasibility analyses are proposed for each part of the research.

Review on ultra-lightweight flapping-wing nano air vehicles:Artificial muscles,flight control mechanism,and biomimetic wings

Flying insects are capable of flapping their wings to provide the required power and control forces for flight.A coordinated organizational system including muscles,wings,and control architecture plays a significant role,which provides the sources of inspiration for designing flapping-wing vehicles.In recent years,due to the development of micro-and meso-scale manufacturing technologies,advances in components technologies have directly led to a progress of smaller Flapping-Wing Nano Air Vehicles(FWNAVs)around gram and sub-gram scales,and these air vehicles have gradually acquired insect-like locomotive strategies and capabilities.This paper will present a selective review of components technologies for ultra-lightweight flapping-wing nano air vehicles under 3 g,which covers the novel propulsion methods such as artificial muscles,flight control mechanisms,and the design paradigms of the insect-inspired wings,with a special focus on the development of the driving technologies based on artificial muscles and the progress of the biomimetic wings.The challenges involved in constructing such small flapping-wing air vehicles and recommendations for several possible future directions in terms of component technology enhancements and overall vehicle performance are also discussed in this paper.This review will provide the essential guidelines and the insights for designing a flapping-wing nano air vehicle with higher performance.

Numerical Investigation on Flow and Cooling Characteristics of a Micro-Ribbed Vane Endwall

The secondary flow originated from the inherent pressure gradient inside the vane cascade has a strong impact on the endwall cooling performance as the crossflow sweeps the upstream coolant jet towards the suction side,resulting in intensifying thermal load near the pressure side endwall.Hence a novel ribbed-endwall is introduced to suppress passage crossflow.The effects of the mass flow ratio and the rib layout were examined using numerical simulations by solving the three-dimensional Reynolds-averaged Navier-Stokes(RANS)equations with the shear stress transport(SST)k-ωturbulence model.The results indicate that the ribs effectively prevent the coolant migrating from the pressure side to the suction side,helping the coolant jet to spread along the lateral orientation.Therefore,the endwall adiabatic film cooling effectiveness is substantially improved.The maximum cooling effectiveness is achieved for the case with three-ribs when the height of the rib equals one hole diameter among all cases.The area-averaged adiabatic cooling effectiveness is enhanced by 31.6%relative to the flat endwall when the mass flow ratio of coolant to mainstream equals to 0.52%.More importantly,the ribbed-endwall obtains a relatively lower level of aerodynamic loss owing to the reduced lateral migration inside the vane cascade.

Nanoporous Metals Based on Metallic Glasses:Synthesis,Structure and Functional Applications

Nanoporous metals have emerged as a new class of functional materials with unique structures and properties.Compared to conventional metals and alloys,nanoporous metals possess a high surface area,unique pore size distribution and enhanced catalytic activity,making them highly desirable for a wide range of applications,such as photonics,sensing,supercapacitors and catalysis.In this review paper,we aim to summarize recent advances in the fabrication,structural regulation and functional applications of nanoporous metals and their composites via the dealloying of metallic glasses.Particularly,we will discuss the factors that affect the nanoporous structure,including precursor composition,dealloying conditions and post-treatment methods.We will also cover topics such as the preparation of immiscible nanoporous metals and the control of hierarchical nanoporous structures.Finally,we will provide a brief overview of the current situation and discuss the current challenges and potential research directions in the field.

Experimental Study on the Overall Cooling Effectiveness of Effusion-Cooling Ceramic Matrix Composite Platform

Ceramic matrix composite(CMC),with higher thermal limit and lower density relative to the superalloy,is regarded as the most important structural material for modern gas turbine engines.However,the anisotropic thermal conductivities caused by the weave patterns totally change the thermal conduction performance inside the solid domain.Therefore,the present study aims to use the infrared thermographic to measure the SiC/SiC composite platform with staggered effusion holes along with the superalloy platform.CMC platform is prepared by 2-D plain weave braid structure with chemical vapor infiltration(CVI)process.The temperature of mainstream is 900 K to match the real mainstream to coolant temperature ratio(T_(g)/T_(c)=1.5,2.1).The experimental was conducted with seven mass flow ratios(MFR=1.5%-4.5%).The results indicate that the thermal conductivity along the thickness direction is of great importance for the CMC platform.The superalloy platform obtains higher level of overall cooling effectiveness than CMC at T_(g)/T_(c)=1.5.However,the CMC platform achieves greater overall cooling effectiveness relative to superalloy at T_(g)/T_(c)=2.1.In addition,CMC platform presents enhanced uniformity of overall cooling effectiveness due to the larger in-plane thermal conductivity.