This article provides a brief overview of the teaching and research at the School of Aerospace Engineering(SAE) to celebrate the 80 th anniversary of the establishment of aeronautics as a discipline at Tsinghua Univer...This article provides a brief overview of the teaching and research at the School of Aerospace Engineering(SAE) to celebrate the 80 th anniversary of the establishment of aeronautics as a discipline at Tsinghua University. The evolution of the school, undergraduate/graduate students and faculty members, and research activities and achievements have been described. The research input including research funding and research projects are summarized, showing a diversity of funding sources and a significant growth in either sum total or spending per researcher. The achievements including publications and inter/national academic awards are also introduced. It can be seen that the level of academic publications has been growing over the past decades. In addition,four representative research achievements have been briefly described to show the scientific contributions of the school.展开更多
In the present study,an efficient overset grid method by means of parallel implicit hole-cutting is proposed for the sake of simulating unsteady flows in aerospace engineering involving multiple bodies in relative mov...In the present study,an efficient overset grid method by means of parallel implicit hole-cutting is proposed for the sake of simulating unsteady flows in aerospace engineering involving multiple bodies in relative movement.In view of the degraded computational efficiency and robustness for conventional overset grid assembly,several innovative techniques are developed within the overset grid assembly process,viz.,a bookkeeping alternative digital tree method to speed up the donor-cell searching,a fast parallel advancing front algorithm to accelerate the wall-distance calculation and a message-passing strategy with efficient information communication and lower storage expenditure within distributed computational architecture.The contribution of the developed techniques is evidenced by comparison with the existing alternative ways in terms of computing efficiency.Subsequently,the overset grid method is embedded into an inhouse programed URANS solver to examine its capability in predicting the flow field of complex applications such as helicopter,store separation and component deploying.Results show that the developed overset grid methodology is,in practice,able to resolve the aerodynamic characteristics of complex aerospace engineering with a high-fidelity flow topology and accuracy.展开更多
Efficient bolted joint design is an essential part of designing the minimum weight aerospace structures, since structural failures usually occur at connections and interface. A comprehensive numerical study of three-d...Efficient bolted joint design is an essential part of designing the minimum weight aerospace structures, since structural failures usually occur at connections and interface. A comprehensive numerical study of three-dimensional(3D) stress variations is prohibitively expensive for a large-scale structure where hundreds of bolts can be present. In this work, the hybrid composite-to-metal bolted connections used in the upper stage of European Ariane 5ME rocket are analyzed using the global-local finite element(FE) approach which involves an approximate analysis of the whole structure followed by a detailed analysis of a significantly smaller region of interest. We calculate the Tsai-Wu failure index and the margin of safety using the stresses obtained from ABAQUS. We find that the composite part of a hybrid bolted connection is prone to failure compared to the metal part. We determine the bolt preload based on the clamp-up load calculated using a maximum preload to make the composite part safe. We conclude that the unsuitable bolt preload may cause the failure of the composite part due to the high stress concentration in the vicinity of the bolt. The global-local analysis provides an efficient computational tool for enhancing 3D stress analysis in the highly loaded region.展开更多
A knock-down factor is commonly used to take into account the obvious decline of the buckling load in a cylindrical shell caused by the inevitable imperfections. In 1968, NASA guideline SP-8007 gave knock-down factors...A knock-down factor is commonly used to take into account the obvious decline of the buckling load in a cylindrical shell caused by the inevitable imperfections. In 1968, NASA guideline SP-8007 gave knock-down factors which rely on a lower-bound curve taken from experimental data. Recent research has indicated that the NASA knock-down factors are inclined to produce very conservative estimations for the buckling load of imperfect shells, due to the limitations of the computational power and the experimental skills available five decades ago. A novel knock-down factor is proposed composed of two parts for the metallic stiffened cylinders. A deterministic study is applied to achieve the first part of the knock-down factor considering the measured geometric imperfection, the other types of imperfections are considered in the second part using a stochastic analysis. A smeared model is used to achieve the implementation of the measured geometric imperfection for the stiffened cylinder. This new robust and less conservative design for the stiffened cylinders is validated by using test results.展开更多
Inconel 718 superalloy has extensive applications in a variety of industries such as the moulding,aerospace and medical due to its excellent mechanical features such as poor thermal conductivity,high strength at high ...Inconel 718 superalloy has extensive applications in a variety of industries such as the moulding,aerospace and medical due to its excellent mechanical features such as poor thermal conductivity,high strength at high temperatures and corrosion resistance.However,it is very difficult to process by traditional machining and finishing methods.Abrasive based finishing process is one of non-traditional finishing method applied to complex surfaces.Shot peening process is one of the surface treatment processes mostly applied to improve the surface strength.The superior advantages of these two processes are combined into one process.This newly developed and patented process is called as GOV process.In this study,the effects of GOV process parameters(number of cycles,steel ball size,media concentration)on the surface quality of Inconel 718 already pre-processed by wire electric discharge machining are investigated.The performance parameters are identified as surface roughness,material removal and white layer thickness.Surface finishing with the GOV process improves the surface roughness,Ra value by decreasing from 2.63μm to 0.46μm by removing micro-level chips up to 10.7 mg which is supported by SEM images.White layer formed due to nature of EDM process is completely removed from specimen surface.展开更多
The heterogeneity ofα-Al(Fe,Mn)Si dispersoids andβ″precipitates was tuned to enhance the strength−ductility synergy of air-cooled Al−Mg−Si alloys.Scanning electron microscopy(SEM)and transmission electron microscop...The heterogeneity ofα-Al(Fe,Mn)Si dispersoids andβ″precipitates was tuned to enhance the strength−ductility synergy of air-cooled Al−Mg−Si alloys.Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)were employed to elucidate the microstructural parameters of these two strengthening phases.The results show that the microstructural heterogeneity can be triggered by the absence of homogenization,resulting in the presence of dispersoid-free zones(DFZs)and dispersoid zones(DZs),in conjunction with bimodalβ″precipitates.Further analytical calculations,from the strengthening model,clarify that the strategically dispersedα-Al(Fe,Mn)Si andβ″particles create“soft”and“hard”domains within the alloy,resultantly improving the mechanical properties.展开更多
The extensive applications of cubic silicon in flexible transistors and infrared detectors are greatly hindered by its intrinsic properties.Metastable silicon phases,such as Si-Ⅲ,Ⅳ,andⅫ,prepared using extreme press...The extensive applications of cubic silicon in flexible transistors and infrared detectors are greatly hindered by its intrinsic properties.Metastable silicon phases,such as Si-Ⅲ,Ⅳ,andⅫ,prepared using extreme pressure methods,provide a unique“genetic bank”with diverse structures and exotic characteristics.However,exploration of their inherent physical properties remains underdeveloped.Herein,we demonstrate the phase engineering strategy to modulate the thermal conductivity and mechanical properties of metastable silicon.The thermal conductivity,obtained via the Raman optothermal approach,exhibits broad tunability across various Si-Ⅰ,Ⅲ,Ⅻ,andⅣphases.The hardness and Young's modulus of Si-Ⅳare significantly greater than those of the Si-Ⅲ/Ⅻmixture,as confirmed by the nanoindentation technique.Moreover,it was found that pressure-induced structural defects can substantially degrade the thermal and mechanical properties of silicon.This systematic investigation offers a feasible route for designing novel semiconductors and further advancing their desirable applications in advanced nanodevices and mechanical transducers.展开更多
We present a numerical framework for simulating viscous compressible flows in the presence of solid particles with large size ratios.The volume-filtered Navier-Stokes equations are discretized using a class of high-or...We present a numerical framework for simulating viscous compressible flows in the presence of solid particles with large size ratios.The volume-filtered Navier-Stokes equations are discretized using a class of high-order low-dissipative finite difference operators with energy-preserving properties.No-slip,adiabatic boundary conditions are enforced at the surface of large particles(with diameters significantly larger than the local grid spacing)using a ghost-point immersed boundary method.Two-way coupling between the gas phase and small particles(with diameters proportional to the grid spacing)is accounted for through volumetric source terms for interphase momentum and energy exchange.A simple and efficient approach for collision detection between small and large particles is proposed.The framework is applied to simulations of planar shocks interacting with bidisperse distributions of particles with size ratios of approximately thirty.Particle dispersion and size segregation are reported and a simple analytical model for size segregation is proposed.展开更多
Noncohesive particle clusters are identified and tracked in turbulent flows to determine the breakdown and time evolution of cluster statistics and their implications for interscale mass transfer,which has connections...Noncohesive particle clusters are identified and tracked in turbulent flows to determine the breakdown and time evolution of cluster statistics and their implications for interscale mass transfer,which has connections to the classical turbulent energy cascade and its mass cascade counterpart running in parallel.In particular,the formation and dynamics of sediment and larvae clusters are of interest to coral larvae settlement in coastal regions and particularly the resilience of green-gray coastal protection solutions.Analogous cluster behavior is relevant to cloud microphysics and precipitation initiation,radiation transport and light transmission through colloids and suspensions,heat and mass transfer in particle-laden flows,and viral and pollutant transmission.Following a comparison between various clustering techniques,we adopt a density-based cluster identification algorithm based on its simplicity and efficiency,where particles are clustered based on the number of neighboring particles in their individual spheres of influence.We establish parallels with lattice-based percolation theory,as evident in the power-law scaling of the cluster size distribution near the percolation threshold.The degree of discontinuity of the phase transition associated with this percolation threshold is observed to broaden with larger Stokes numbers and thereby large-scale clustering.The sensitivity of our findings to the employed clustering algorithm is discussed.A novel cluster tracking algorithm is deployed to determine the interscale transfer rate along the particle-number phase-space dimension via accounting of cluster breakup and merger events,extending previous work on the bubble breakup cascade beneath surface breaking waves.Our findings shed light on the interaction between particle clusters and their carrier turbulent flows,with an eye toward transport models incorporating cluster characteristics and dynamics.展开更多
Good distribution of samples and weights can improve the computational accuracy and efficiency in the stochastic response analyses of aerospace problems with uncertain parameters.This work proposes a new Generalized L...Good distribution of samples and weights can improve the computational accuracy and efficiency in the stochastic response analyses of aerospace problems with uncertain parameters.This work proposes a new Generalized L2 Discrepancy based on a General Point(GL2D-GP)for generating samples and their corresponding weights.The proposed GL2D-GP is an extension of the existing discrepancy by introducing the non-same weights and a smaller box to measure probability errors.Minimizing the GL2D-GP can yield a weight optimization formula that generates a set of optimal non-identical weights for a given sample set.Through minimizing the GL2D-GP assigned to the set of optimal non-same weights,a new sample and weight generation method is developed.In the proposed method,the samples can be easily generated in terms of the generalized Halton formula with a series of optimal permutation vectors which are found by the intelligent evolutionary algorithm.Once the sample set is obtained,the optimal weights can be generated in terms of the weight optimization formula.Five numerical examples are presented to verify the high accuracy,efficiency,and strong robustness of the proposed sample generation method based on GL2D-GP.展开更多
An unsteady numerical simulation is conducted to examine the dynamic runback characteristics of a water film flow driven by a boundary layer airflow over a solid surface pertinent to the dynamic glaze ice accretion pr...An unsteady numerical simulation is conducted to examine the dynamic runback characteristics of a water film flow driven by a boundary layer airflow over a solid surface pertinent to the dynamic glaze ice accretion process over aircraft wing surfaces.The multiphase flow simulation results of the wind-driven water runback(WDWR)flow are compared quantitatively with the experimental results in terms of the time-dependent variations of the water film thickness profiles and evolution of the front contact point of the runback water film flow.The underlying mechanism of the intermittent water runback behavior is elucidated by analyzing the time evolution of the airflow velocity and vorticity fields above the runback water film flow over the solid surface.To the best knowledge of the authors,the work presented here is the first successful attempt to numerically examine the transient runback characteristics of WDWR flows.It serves as an excellent benchmark case for the development of best practices to model the important micro-physical processes responsible for the transient water transport over aircraft wing surfaces.展开更多
Prelaunch rolling of maritime rockets threatens the reliability of launch in rough sea conditions.In order to suppress the prelaunch rolling,this study introduces advanced smart prediction designed especially for mari...Prelaunch rolling of maritime rockets threatens the reliability of launch in rough sea conditions.In order to suppress the prelaunch rolling,this study introduces advanced smart prediction designed especially for maritime rockets.The suggested approach introduces a hybrid model that combines random forest(RF)and Adaptive boosting(Ada Boost)methods to describe the coupling mechanism of factors affecting rocket rolling and to suppress the rolling.This combination improves forecast accuracy.Thereafter,the dimensionality reduced response surfaces are used to visually present the coupling between rocket rolling and influencing factors,which reveals the prelaunch rolling mechanism.When angle between the launch device and the ship's bow is within 80°-100°,the dynamic friction coefficient between adapters and guideways is 0.4,and the dynamic friction coefficient between the rocket and launchpad is within 0-0.15 or0.5-0.7,the prelaunch rolling of rocket during one motion cycle of the ship is less than 0.065°,originally 0.27°,reduced by 75.93%,effectively suppressing the prelaunch rolling.This study improves the prelaunch stability of maritime rockets in rough sea conditions and establishes a mapping relationship between the factors affecting rocket rolling and the structure of the sea launch system,guiding the optimization of future sea launch systems.展开更多
Traditional dynamic analysis of mechanical structures,often limited to individual beams or plates,fails to fully capture their dynamic behaviors.In systems where space and mass are constrained,such as the battery supp...Traditional dynamic analysis of mechanical structures,often limited to individual beams or plates,fails to fully capture their dynamic behaviors.In systems where space and mass are constrained,such as the battery support structures in electric aircraft,conventional absorbers and isolators are insufficient for effective vibration control.This study simplifies the battery support structure of electric aircraft as an integrated composite beam consisting of three interconnected beams,and investigated its structural dynamics properties and nonlinear vibration control under thermal conditions caused by battery heat.The nonlinear vibration control is performed using the Nitinol steel wire ropes(Ni Ti-ST),with nonlinear damping properties.The natural frequencies of system are determined using the Rayleigh-Ritz technique.Theoretical results are validated through both Finite Element Method(FEM)and hammer tests.Moreover,the dynamic equations are derived using the Lagrange method and discretized via the Galerkin Truncation Method(GTM).The Harmonic Balance Method(HBM)is used to evaluate the vibration responses of the integrated model,with further verification through the Runge-Kutta Method(RKM).The experiments are conducted to corroborate the theoretical analysis.The results show that the system frequency changes in stages with the increase of the stiffness of the integrated composite beam connection.Especially in the case of varying environments,as the temperature increases,the frequency of system will first increase to a certain maximum value and then gradually decrease.Furthermore,the NiTi-ST effectively reduces vibration in the integrated composite beam,particularly under varying temperatures and external excitations.展开更多
This study investigates the performance boundaries of ramjet and scramjet engines fueled by boronbased propellant through full-scale engine modeling and three-dimensional computational fluid dynamics simulations.Resul...This study investigates the performance boundaries of ramjet and scramjet engines fueled by boronbased propellant through full-scale engine modeling and three-dimensional computational fluid dynamics simulations.Results show that the performance boundary between ramjets and scramjets occurs near Mach 7.Specifically,at Mach 6,the ramjet exhibits a 1290 m/s higher specific impulse than the scramjet;however,at Mach 7,their performance becomes comparable.The ramjet's higher static temperature promotes boron particle vaporization and B_(2)O_(2) dissociation,limiting the total temperature increase,unlike in scramjets.The boron vapor mass fraction significantly impacts this temperature difference,with ramjets exhibiting values 8.5 and 3.9 times higher than scramjets at Mach 6 and Mach 7,respectively.Despite lower total temperatures,ramjets achieve more efficient boron combustion due to the combined effects of higher pressures and longer particle residence times.These findings offer valuable insights for engine designers in selecting ramjet or scramjet configurations for boron-fueled propulsion systems.展开更多
Quasi-periodic solutions with multiple base frequencies exhibit the feature of 2π-periodicity with respect to each of the hyper-time variables.However,it remains a challenge work,due to the lack of effective solution...Quasi-periodic solutions with multiple base frequencies exhibit the feature of 2π-periodicity with respect to each of the hyper-time variables.However,it remains a challenge work,due to the lack of effective solution methods,to solve and track the quasi-periodic solutions with multiple base frequencies until now.In this work,a multi-steps variable-coefficient formulation is proposed,which provides a unified framework to enable either harmonic balance method or collocation method or finite difference method to solve quasi-periodic solutions with multiple base frequencies.For this purpose,a method of alternating U and S domain is also developed to efficiently evaluate the nonlinear force terms.Furthermore,a new robust phase condition is presented for all of the three methods to make them track the quasi-periodic solutions with prior unknown multiple base frequencies,while the stability of the quasi-periodic solutions is assessed by mean of Lyapunov exponents.The feasibility of the constructed methods under the above framework is verified by application to three nonlinear systems.展开更多
The performance of deep recommendation models degrades significantly under data poisoning attacks.While adversarial training methods such as Vulnerability-Aware Training(VAT)enhance robustness by injecting perturbatio...The performance of deep recommendation models degrades significantly under data poisoning attacks.While adversarial training methods such as Vulnerability-Aware Training(VAT)enhance robustness by injecting perturbations into embeddings,they remain limited by coarse-grained noise and a static defense strategy,leaving models susceptible to adaptive attacks.This study proposes a novel framework,Self-Purification Data Sanitization(SPD),which integrates vulnerability-aware adversarial training with dynamic label correction.Specifically,SPD first identifies high-risk users through a fragility scoring mechanism,then applies self-purification by replacing suspicious interactions with model-predicted high-confidence labels during training.This closed-loop process continuously sanitizes the training data and breaks the protection ceiling of conventional adversarial training.Experiments demonstrate that SPD significantly improves the robustness of both Matrix Factorization(MF)and LightGCN models against various poisoning attacks.We show that SPD effectively suppresses malicious gradient propagation and maintains recommendation accuracy.Evaluations on Gowalla and Yelp2018 confirmthat SPD-trainedmodels withstandmultiple attack strategies—including Random,Bandwagon,DP,and Rev attacks—while preserving performance.展开更多
The S38C railway axle undergoes induction hardening,resulting in a gradient-distributed microstructure and mechanical properties.The accurate identification of gradient-distributed plastic parameters for the S38C axle...The S38C railway axle undergoes induction hardening,resulting in a gradient-distributed microstructure and mechanical properties.The accurate identification of gradient-distributed plastic parameters for the S38C axle remains a challenging task.To tackle this challenge,the present study proposes a novel approach for identifying the gradient-distributed plastic parameters for the S38C axle by integrating nano-indentation techniques with the machine learning method.Firstly,nano-indentation tests are conducted along the radial direction of the S38C axle to obtain the gradient-distributed load-displacement curves,nano-hardness,and elastic modulus.Subsequently,the dimensionless analysis is performed to obtain the representative stress,strain,and yield stress from load-displacement curves.These parameters are then incorporated into the machine learning method as physical information to identify the gradient-distributed plastic parameters of the S38C axle.The results indicate that the proposed method based on the physics-informed neural network and multi-fidelity neural network successfully identifies the gradient-distributed plastic parameters of the S38C axles and demonstrates superior prediction accuracy and generalization compared with the purely data-driven machine learning method.展开更多
Porous ionic liquid electrospray thrusters are the ideal propulsion technology for CubeSats because of their structural simplicity,high thrust accuracy and plume self-neutralization.The electrowetting technology can r...Porous ionic liquid electrospray thrusters are the ideal propulsion technology for CubeSats because of their structural simplicity,high thrust accuracy and plume self-neutralization.The electrowetting technology can replenish the propellant for the emitter online,thus prolonging the lifetime of the thruster.In order to gain a deeper understanding of its operating characteristics,the changes in thruster performance before and after propellant replenishment deserve to be scrutinized.In this study,the performance changes of a porous electrowetting ionic liquid electrospray thruster are tested by voltage-current test and time-of-flight mass spectrometry over a long operating time.The experimental results show that asymmetric operation with a negative current less than positive current for a long period of time causes anions to compensate for the emission after accumulation at the emitter,resulting in a phenomenon that the negative current is much larger than positive current.The reason for the difference in emission characteristics between the positive and negative modes is that the plume in the positive mode is quite ionized while the plume in the negative mode contains liquid droplets.This study provides a reference for the selection of operating conditions for ionic liquid electrospray thrusters.展开更多
With the increasing complexity of industrial automation,planetary gearboxes play a vital role in largescale equipment transmission systems,directly impacting operational efficiency and safety.Traditional maintenance s...With the increasing complexity of industrial automation,planetary gearboxes play a vital role in largescale equipment transmission systems,directly impacting operational efficiency and safety.Traditional maintenance strategies often struggle to accurately predict the degradation process of equipment,leading to excessive maintenance costs or potential failure risks.However,existing prediction methods based on statistical models are difficult to adapt to nonlinear degradation processes.To address these challenges,this study proposes a novel condition-based maintenance framework for planetary gearboxes.A comprehensive full-lifecycle degradation experiment was conducted to collect raw vibration signals,which were then processed using a temporal convolutional network autoencoder with multi-scale perception capability to extract deep temporal degradation features,enabling the collaborative extraction of longperiod meshing frequencies and short-term impact features from the vibration signals.Kernel principal component analysis was employed to fuse and normalize these features,enhancing the characterization of degradation progression.A nonlinear Wiener process was used to model the degradation trajectory,with a threshold decay function introduced to dynamically adjust maintenance strategies,and model parameters optimized through maximum likelihood estimation.Meanwhile,the maintenance strategy was optimized to minimize costs per unit time,determining the optimal maintenance timing and preventive maintenance threshold.The comprehensive indicator of degradation trends extracted by this method reaches 0.756,which is 41.2%higher than that of traditional time-domain features;the dynamic threshold strategy reduces the maintenance cost per unit time to 55.56,which is 8.9%better than that of the static threshold optimization.Experimental results demonstrate significant reductions in maintenance costs while enhancing system reliability and safety.This study realizes the organic integration of deep learning and reliability theory in the maintenance of planetary gearboxes,provides an interpretable solution for the predictive maintenance of complex mechanical systems,and promotes the development of condition-based maintenance strategies for planetary gearboxes.展开更多
Introducing Ti_(2)AlC particles into TiAl alloys can effectively improve their strength,but this can also lead to stress concentration at the interface,resulting in the reduction of ductility.Therefore,Mn is adopted t...Introducing Ti_(2)AlC particles into TiAl alloys can effectively improve their strength,but this can also lead to stress concentration at the interface,resulting in the reduction of ductility.Therefore,Mn is adopted to synergistically improve the strength and ductility of the Ti_(2)AlC/TiAl composite through solid solution and interface manipulation.The first-principles calculation shows the Ti-Mn bonds are formed at the Ti_(2)AlC/TiAl interface after Mn doping,characterized primarily by metallic bonds with some covalent bonding.This combination preserves strength while enhancing ductility.Then,Ti_(2)AlC/TiAl-Mn composite is prepared.The Ti_(2)AlC,with an average size of 1.6μm,is uniformly distributed within the TiAl matrix.Mn doping reduces the lamellar colony size and lamellar thickness by 25.1%and 27.4%,respectively.A small quantity of Mn accumulates at the boundaries of the lamellar colonies.The Mn content must be controlled to avoid segregation,which may negatively impact performance.The yield stress,ultimate compressive stress,fracture strain,and product of strength and plasticity of the Ti_(2)AlC/TiAl-Mn composite have been increased by 5.5%,11.5%,10.4%,and 23.0%,respectively,compared to those of the Ti_(2)AlC/TiAl composite.The enhancement in strength is due to the combined effects of grain refinement,solid solution of Mn,and twining strengthening.Grain refinement and twin strengthening also can reduce stress concentration and improve ductility.In addition,at the electronic level,the Ti-Mn bond formed at the interface is contributed to the improvement of ductility.展开更多
文摘This article provides a brief overview of the teaching and research at the School of Aerospace Engineering(SAE) to celebrate the 80 th anniversary of the establishment of aeronautics as a discipline at Tsinghua University. The evolution of the school, undergraduate/graduate students and faculty members, and research activities and achievements have been described. The research input including research funding and research projects are summarized, showing a diversity of funding sources and a significant growth in either sum total or spending per researcher. The achievements including publications and inter/national academic awards are also introduced. It can be seen that the level of academic publications has been growing over the past decades. In addition,four representative research achievements have been briefly described to show the scientific contributions of the school.
基金supported by the National Natural Science Foundation of China(Nos.11672133,12002161)Open Foundations of EDL Laboratory,China(No.EDL19092111)+2 种基金supports from National Science Foundation of Shaanxi Province,China(No.2021JQ-078)Fundamental Research Fund of Zhuhai,China(No.ZH22017003210011PWC)Aeronautical Science Foundation of China(No.F2021110)are acknowledged as well。
文摘In the present study,an efficient overset grid method by means of parallel implicit hole-cutting is proposed for the sake of simulating unsteady flows in aerospace engineering involving multiple bodies in relative movement.In view of the degraded computational efficiency and robustness for conventional overset grid assembly,several innovative techniques are developed within the overset grid assembly process,viz.,a bookkeeping alternative digital tree method to speed up the donor-cell searching,a fast parallel advancing front algorithm to accelerate the wall-distance calculation and a message-passing strategy with efficient information communication and lower storage expenditure within distributed computational architecture.The contribution of the developed techniques is evidenced by comparison with the existing alternative ways in terms of computing efficiency.Subsequently,the overset grid method is embedded into an inhouse programed URANS solver to examine its capability in predicting the flow field of complex applications such as helicopter,store separation and component deploying.Results show that the developed overset grid methodology is,in practice,able to resolve the aerodynamic characteristics of complex aerospace engineering with a high-fidelity flow topology and accuracy.
基金Project(282522)supported by the European Union's Research and Innovation Funding Programme
文摘Efficient bolted joint design is an essential part of designing the minimum weight aerospace structures, since structural failures usually occur at connections and interface. A comprehensive numerical study of three-dimensional(3D) stress variations is prohibitively expensive for a large-scale structure where hundreds of bolts can be present. In this work, the hybrid composite-to-metal bolted connections used in the upper stage of European Ariane 5ME rocket are analyzed using the global-local finite element(FE) approach which involves an approximate analysis of the whole structure followed by a detailed analysis of a significantly smaller region of interest. We calculate the Tsai-Wu failure index and the margin of safety using the stresses obtained from ABAQUS. We find that the composite part of a hybrid bolted connection is prone to failure compared to the metal part. We determine the bolt preload based on the clamp-up load calculated using a maximum preload to make the composite part safe. We conclude that the unsuitable bolt preload may cause the failure of the composite part due to the high stress concentration in the vicinity of the bolt. The global-local analysis provides an efficient computational tool for enhancing 3D stress analysis in the highly loaded region.
基金supported by the European Community’s Seventh Framework Programme FP7/2007-2013(Grant No.282522)
文摘A knock-down factor is commonly used to take into account the obvious decline of the buckling load in a cylindrical shell caused by the inevitable imperfections. In 1968, NASA guideline SP-8007 gave knock-down factors which rely on a lower-bound curve taken from experimental data. Recent research has indicated that the NASA knock-down factors are inclined to produce very conservative estimations for the buckling load of imperfect shells, due to the limitations of the computational power and the experimental skills available five decades ago. A novel knock-down factor is proposed composed of two parts for the metallic stiffened cylinders. A deterministic study is applied to achieve the first part of the knock-down factor considering the measured geometric imperfection, the other types of imperfections are considered in the second part using a stochastic analysis. A smeared model is used to achieve the implementation of the measured geometric imperfection for the stiffened cylinder. This new robust and less conservative design for the stiffened cylinders is validated by using test results.
文摘Inconel 718 superalloy has extensive applications in a variety of industries such as the moulding,aerospace and medical due to its excellent mechanical features such as poor thermal conductivity,high strength at high temperatures and corrosion resistance.However,it is very difficult to process by traditional machining and finishing methods.Abrasive based finishing process is one of non-traditional finishing method applied to complex surfaces.Shot peening process is one of the surface treatment processes mostly applied to improve the surface strength.The superior advantages of these two processes are combined into one process.This newly developed and patented process is called as GOV process.In this study,the effects of GOV process parameters(number of cycles,steel ball size,media concentration)on the surface quality of Inconel 718 already pre-processed by wire electric discharge machining are investigated.The performance parameters are identified as surface roughness,material removal and white layer thickness.Surface finishing with the GOV process improves the surface roughness,Ra value by decreasing from 2.63μm to 0.46μm by removing micro-level chips up to 10.7 mg which is supported by SEM images.White layer formed due to nature of EDM process is completely removed from specimen surface.
基金supported by the National Natural Science Foundation of China(Nos.52301025,52371065,52301179)the Fundamental Research Program of Shanxi Province,China(Nos.202203021222039,202203021212124)。
文摘The heterogeneity ofα-Al(Fe,Mn)Si dispersoids andβ″precipitates was tuned to enhance the strength−ductility synergy of air-cooled Al−Mg−Si alloys.Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)were employed to elucidate the microstructural parameters of these two strengthening phases.The results show that the microstructural heterogeneity can be triggered by the absence of homogenization,resulting in the presence of dispersoid-free zones(DFZs)and dispersoid zones(DZs),in conjunction with bimodalβ″precipitates.Further analytical calculations,from the strengthening model,clarify that the strategically dispersedα-Al(Fe,Mn)Si andβ″particles create“soft”and“hard”domains within the alloy,resultantly improving the mechanical properties.
基金supported by the National Natural Science Foundation of China(Grant Nos.52472040,52072032,and 12090031)the 173 JCJQ program(Grant No.2021JCJQ-JJ-0159)。
文摘The extensive applications of cubic silicon in flexible transistors and infrared detectors are greatly hindered by its intrinsic properties.Metastable silicon phases,such as Si-Ⅲ,Ⅳ,andⅫ,prepared using extreme pressure methods,provide a unique“genetic bank”with diverse structures and exotic characteristics.However,exploration of their inherent physical properties remains underdeveloped.Herein,we demonstrate the phase engineering strategy to modulate the thermal conductivity and mechanical properties of metastable silicon.The thermal conductivity,obtained via the Raman optothermal approach,exhibits broad tunability across various Si-Ⅰ,Ⅲ,Ⅻ,andⅣphases.The hardness and Young's modulus of Si-Ⅳare significantly greater than those of the Si-Ⅲ/Ⅻmixture,as confirmed by the nanoindentation technique.Moreover,it was found that pressure-induced structural defects can substantially degrade the thermal and mechanical properties of silicon.This systematic investigation offers a feasible route for designing novel semiconductors and further advancing their desirable applications in advanced nanodevices and mechanical transducers.
基金This work used Expanse systems at UCSD through an allocation[PHY240089]from the Advanced Cyberinfrastructure Coordination Ecosystem:Services&Support(ACCESS)programsupported by U.S.National Science Foundation(Grant Nos.2138259,2138286,2138307,2137603 and 2138296).
文摘We present a numerical framework for simulating viscous compressible flows in the presence of solid particles with large size ratios.The volume-filtered Navier-Stokes equations are discretized using a class of high-order low-dissipative finite difference operators with energy-preserving properties.No-slip,adiabatic boundary conditions are enforced at the surface of large particles(with diameters significantly larger than the local grid spacing)using a ghost-point immersed boundary method.Two-way coupling between the gas phase and small particles(with diameters proportional to the grid spacing)is accounted for through volumetric source terms for interphase momentum and energy exchange.A simple and efficient approach for collision detection between small and large particles is proposed.The framework is applied to simulations of planar shocks interacting with bidisperse distributions of particles with size ratios of approximately thirty.Particle dispersion and size segregation are reported and a simple analytical model for size segregation is proposed.
文摘Noncohesive particle clusters are identified and tracked in turbulent flows to determine the breakdown and time evolution of cluster statistics and their implications for interscale mass transfer,which has connections to the classical turbulent energy cascade and its mass cascade counterpart running in parallel.In particular,the formation and dynamics of sediment and larvae clusters are of interest to coral larvae settlement in coastal regions and particularly the resilience of green-gray coastal protection solutions.Analogous cluster behavior is relevant to cloud microphysics and precipitation initiation,radiation transport and light transmission through colloids and suspensions,heat and mass transfer in particle-laden flows,and viral and pollutant transmission.Following a comparison between various clustering techniques,we adopt a density-based cluster identification algorithm based on its simplicity and efficiency,where particles are clustered based on the number of neighboring particles in their individual spheres of influence.We establish parallels with lattice-based percolation theory,as evident in the power-law scaling of the cluster size distribution near the percolation threshold.The degree of discontinuity of the phase transition associated with this percolation threshold is observed to broaden with larger Stokes numbers and thereby large-scale clustering.The sensitivity of our findings to the employed clustering algorithm is discussed.A novel cluster tracking algorithm is deployed to determine the interscale transfer rate along the particle-number phase-space dimension via accounting of cluster breakup and merger events,extending previous work on the bubble breakup cascade beneath surface breaking waves.Our findings shed light on the interaction between particle clusters and their carrier turbulent flows,with an eye toward transport models incorporating cluster characteristics and dynamics.
基金the support of the National Natural Science Foundation of China(Nos.12372190,12272077)the Fundamental Research Funds for the Central Universities,China(Nos.DUT20RC(5)009,DUT20GJ216).
文摘Good distribution of samples and weights can improve the computational accuracy and efficiency in the stochastic response analyses of aerospace problems with uncertain parameters.This work proposes a new Generalized L2 Discrepancy based on a General Point(GL2D-GP)for generating samples and their corresponding weights.The proposed GL2D-GP is an extension of the existing discrepancy by introducing the non-same weights and a smaller box to measure probability errors.Minimizing the GL2D-GP can yield a weight optimization formula that generates a set of optimal non-identical weights for a given sample set.Through minimizing the GL2D-GP assigned to the set of optimal non-same weights,a new sample and weight generation method is developed.In the proposed method,the samples can be easily generated in terms of the generalized Halton formula with a series of optimal permutation vectors which are found by the intelligent evolutionary algorithm.Once the sample set is obtained,the optimal weights can be generated in terms of the weight optimization formula.Five numerical examples are presented to verify the high accuracy,efficiency,and strong robustness of the proposed sample generation method based on GL2D-GP.
基金supported by the National Science Foundation(NSF)of the USA(Grant Nos.TIP-2140489,CBET-2313310,and CBET-2415347).
文摘An unsteady numerical simulation is conducted to examine the dynamic runback characteristics of a water film flow driven by a boundary layer airflow over a solid surface pertinent to the dynamic glaze ice accretion process over aircraft wing surfaces.The multiphase flow simulation results of the wind-driven water runback(WDWR)flow are compared quantitatively with the experimental results in terms of the time-dependent variations of the water film thickness profiles and evolution of the front contact point of the runback water film flow.The underlying mechanism of the intermittent water runback behavior is elucidated by analyzing the time evolution of the airflow velocity and vorticity fields above the runback water film flow over the solid surface.To the best knowledge of the authors,the work presented here is the first successful attempt to numerically examine the transient runback characteristics of WDWR flows.It serves as an excellent benchmark case for the development of best practices to model the important micro-physical processes responsible for the transient water transport over aircraft wing surfaces.
文摘Prelaunch rolling of maritime rockets threatens the reliability of launch in rough sea conditions.In order to suppress the prelaunch rolling,this study introduces advanced smart prediction designed especially for maritime rockets.The suggested approach introduces a hybrid model that combines random forest(RF)and Adaptive boosting(Ada Boost)methods to describe the coupling mechanism of factors affecting rocket rolling and to suppress the rolling.This combination improves forecast accuracy.Thereafter,the dimensionality reduced response surfaces are used to visually present the coupling between rocket rolling and influencing factors,which reveals the prelaunch rolling mechanism.When angle between the launch device and the ship's bow is within 80°-100°,the dynamic friction coefficient between adapters and guideways is 0.4,and the dynamic friction coefficient between the rocket and launchpad is within 0-0.15 or0.5-0.7,the prelaunch rolling of rocket during one motion cycle of the ship is less than 0.065°,originally 0.27°,reduced by 75.93%,effectively suppressing the prelaunch rolling.This study improves the prelaunch stability of maritime rockets in rough sea conditions and establishes a mapping relationship between the factors affecting rocket rolling and the structure of the sea launch system,guiding the optimization of future sea launch systems.
基金supported by the National Natural Science Foundation of China(No.12272240)the Liaoning Revitalization Talents Program,China(No.XLYC2203197)。
文摘Traditional dynamic analysis of mechanical structures,often limited to individual beams or plates,fails to fully capture their dynamic behaviors.In systems where space and mass are constrained,such as the battery support structures in electric aircraft,conventional absorbers and isolators are insufficient for effective vibration control.This study simplifies the battery support structure of electric aircraft as an integrated composite beam consisting of three interconnected beams,and investigated its structural dynamics properties and nonlinear vibration control under thermal conditions caused by battery heat.The nonlinear vibration control is performed using the Nitinol steel wire ropes(Ni Ti-ST),with nonlinear damping properties.The natural frequencies of system are determined using the Rayleigh-Ritz technique.Theoretical results are validated through both Finite Element Method(FEM)and hammer tests.Moreover,the dynamic equations are derived using the Lagrange method and discretized via the Galerkin Truncation Method(GTM).The Harmonic Balance Method(HBM)is used to evaluate the vibration responses of the integrated model,with further verification through the Runge-Kutta Method(RKM).The experiments are conducted to corroborate the theoretical analysis.The results show that the system frequency changes in stages with the increase of the stiffness of the integrated composite beam connection.Especially in the case of varying environments,as the temperature increases,the frequency of system will first increase to a certain maximum value and then gradually decrease.Furthermore,the NiTi-ST effectively reduces vibration in the integrated composite beam,particularly under varying temperatures and external excitations.
基金funded by the National Natural Science Foundation of China(Grant No.U21B2086)。
文摘This study investigates the performance boundaries of ramjet and scramjet engines fueled by boronbased propellant through full-scale engine modeling and three-dimensional computational fluid dynamics simulations.Results show that the performance boundary between ramjets and scramjets occurs near Mach 7.Specifically,at Mach 6,the ramjet exhibits a 1290 m/s higher specific impulse than the scramjet;however,at Mach 7,their performance becomes comparable.The ramjet's higher static temperature promotes boron particle vaporization and B_(2)O_(2) dissociation,limiting the total temperature increase,unlike in scramjets.The boron vapor mass fraction significantly impacts this temperature difference,with ramjets exhibiting values 8.5 and 3.9 times higher than scramjets at Mach 6 and Mach 7,respectively.Despite lower total temperatures,ramjets achieve more efficient boron combustion due to the combined effects of higher pressures and longer particle residence times.These findings offer valuable insights for engine designers in selecting ramjet or scramjet configurations for boron-fueled propulsion systems.
基金supported by the National Natural Science Foundation of China(Grant Nos.12172267 and 12302014).
文摘Quasi-periodic solutions with multiple base frequencies exhibit the feature of 2π-periodicity with respect to each of the hyper-time variables.However,it remains a challenge work,due to the lack of effective solution methods,to solve and track the quasi-periodic solutions with multiple base frequencies until now.In this work,a multi-steps variable-coefficient formulation is proposed,which provides a unified framework to enable either harmonic balance method or collocation method or finite difference method to solve quasi-periodic solutions with multiple base frequencies.For this purpose,a method of alternating U and S domain is also developed to efficiently evaluate the nonlinear force terms.Furthermore,a new robust phase condition is presented for all of the three methods to make them track the quasi-periodic solutions with prior unknown multiple base frequencies,while the stability of the quasi-periodic solutions is assessed by mean of Lyapunov exponents.The feasibility of the constructed methods under the above framework is verified by application to three nonlinear systems.
文摘The performance of deep recommendation models degrades significantly under data poisoning attacks.While adversarial training methods such as Vulnerability-Aware Training(VAT)enhance robustness by injecting perturbations into embeddings,they remain limited by coarse-grained noise and a static defense strategy,leaving models susceptible to adaptive attacks.This study proposes a novel framework,Self-Purification Data Sanitization(SPD),which integrates vulnerability-aware adversarial training with dynamic label correction.Specifically,SPD first identifies high-risk users through a fragility scoring mechanism,then applies self-purification by replacing suspicious interactions with model-predicted high-confidence labels during training.This closed-loop process continuously sanitizes the training data and breaks the protection ceiling of conventional adversarial training.Experiments demonstrate that SPD significantly improves the robustness of both Matrix Factorization(MF)and LightGCN models against various poisoning attacks.We show that SPD effectively suppresses malicious gradient propagation and maintains recommendation accuracy.Evaluations on Gowalla and Yelp2018 confirmthat SPD-trainedmodels withstandmultiple attack strategies—including Random,Bandwagon,DP,and Rev attacks—while preserving performance.
基金supported by the National Key Research and Development Plan(Grant No.2022YFB3401901)the National Natural Science Foundation of China(Grant Nos.12192210,12192214,12072295,and 12222209)+1 种基金Independent Project of State Key Laboratory of Rail Transit Vehicle System(Grant No.2023TPL-T03)Fundamental Research Funds for the Central Universities(Grant No.2682023CG004).
文摘The S38C railway axle undergoes induction hardening,resulting in a gradient-distributed microstructure and mechanical properties.The accurate identification of gradient-distributed plastic parameters for the S38C axle remains a challenging task.To tackle this challenge,the present study proposes a novel approach for identifying the gradient-distributed plastic parameters for the S38C axle by integrating nano-indentation techniques with the machine learning method.Firstly,nano-indentation tests are conducted along the radial direction of the S38C axle to obtain the gradient-distributed load-displacement curves,nano-hardness,and elastic modulus.Subsequently,the dimensionless analysis is performed to obtain the representative stress,strain,and yield stress from load-displacement curves.These parameters are then incorporated into the machine learning method as physical information to identify the gradient-distributed plastic parameters of the S38C axle.The results indicate that the proposed method based on the physics-informed neural network and multi-fidelity neural network successfully identifies the gradient-distributed plastic parameters of the S38C axles and demonstrates superior prediction accuracy and generalization compared with the purely data-driven machine learning method.
基金co-supported by the National Key R&D Program of China(Nos.2020YFC2201103 and 2022YFB4601300)the National Natural Science Foundation of China(No.U22B20120)+1 种基金the Program of Beijing Engineering Research Center of Efficient and Green Aerospace Propulsion Technology,China(No.Lab ASP-2024-09)the Beijing Institute of Technology Research Fund Program for Young Scholars,China。
文摘Porous ionic liquid electrospray thrusters are the ideal propulsion technology for CubeSats because of their structural simplicity,high thrust accuracy and plume self-neutralization.The electrowetting technology can replenish the propellant for the emitter online,thus prolonging the lifetime of the thruster.In order to gain a deeper understanding of its operating characteristics,the changes in thruster performance before and after propellant replenishment deserve to be scrutinized.In this study,the performance changes of a porous electrowetting ionic liquid electrospray thruster are tested by voltage-current test and time-of-flight mass spectrometry over a long operating time.The experimental results show that asymmetric operation with a negative current less than positive current for a long period of time causes anions to compensate for the emission after accumulation at the emitter,resulting in a phenomenon that the negative current is much larger than positive current.The reason for the difference in emission characteristics between the positive and negative modes is that the plume in the positive mode is quite ionized while the plume in the negative mode contains liquid droplets.This study provides a reference for the selection of operating conditions for ionic liquid electrospray thrusters.
基金funded by scientific research projects under Grant JY2024B011.
文摘With the increasing complexity of industrial automation,planetary gearboxes play a vital role in largescale equipment transmission systems,directly impacting operational efficiency and safety.Traditional maintenance strategies often struggle to accurately predict the degradation process of equipment,leading to excessive maintenance costs or potential failure risks.However,existing prediction methods based on statistical models are difficult to adapt to nonlinear degradation processes.To address these challenges,this study proposes a novel condition-based maintenance framework for planetary gearboxes.A comprehensive full-lifecycle degradation experiment was conducted to collect raw vibration signals,which were then processed using a temporal convolutional network autoencoder with multi-scale perception capability to extract deep temporal degradation features,enabling the collaborative extraction of longperiod meshing frequencies and short-term impact features from the vibration signals.Kernel principal component analysis was employed to fuse and normalize these features,enhancing the characterization of degradation progression.A nonlinear Wiener process was used to model the degradation trajectory,with a threshold decay function introduced to dynamically adjust maintenance strategies,and model parameters optimized through maximum likelihood estimation.Meanwhile,the maintenance strategy was optimized to minimize costs per unit time,determining the optimal maintenance timing and preventive maintenance threshold.The comprehensive indicator of degradation trends extracted by this method reaches 0.756,which is 41.2%higher than that of traditional time-domain features;the dynamic threshold strategy reduces the maintenance cost per unit time to 55.56,which is 8.9%better than that of the static threshold optimization.Experimental results demonstrate significant reductions in maintenance costs while enhancing system reliability and safety.This study realizes the organic integration of deep learning and reliability theory in the maintenance of planetary gearboxes,provides an interpretable solution for the predictive maintenance of complex mechanical systems,and promotes the development of condition-based maintenance strategies for planetary gearboxes.
基金supported by the National Natural Science Foundation of China(Nos.52371031 and 52574435)the Science and Technology Development Program of Jilin Province,China(No.20250102103JC)+2 种基金the Science and Technology Development Program of Changchun City,China(No.23JQ03)Changbaishan Laboratory,China(No.CBS2025004-03)the Undergraduate Innovation Fund of Jilin University,China(No.S202410183310).
文摘Introducing Ti_(2)AlC particles into TiAl alloys can effectively improve their strength,but this can also lead to stress concentration at the interface,resulting in the reduction of ductility.Therefore,Mn is adopted to synergistically improve the strength and ductility of the Ti_(2)AlC/TiAl composite through solid solution and interface manipulation.The first-principles calculation shows the Ti-Mn bonds are formed at the Ti_(2)AlC/TiAl interface after Mn doping,characterized primarily by metallic bonds with some covalent bonding.This combination preserves strength while enhancing ductility.Then,Ti_(2)AlC/TiAl-Mn composite is prepared.The Ti_(2)AlC,with an average size of 1.6μm,is uniformly distributed within the TiAl matrix.Mn doping reduces the lamellar colony size and lamellar thickness by 25.1%and 27.4%,respectively.A small quantity of Mn accumulates at the boundaries of the lamellar colonies.The Mn content must be controlled to avoid segregation,which may negatively impact performance.The yield stress,ultimate compressive stress,fracture strain,and product of strength and plasticity of the Ti_(2)AlC/TiAl-Mn composite have been increased by 5.5%,11.5%,10.4%,and 23.0%,respectively,compared to those of the Ti_(2)AlC/TiAl composite.The enhancement in strength is due to the combined effects of grain refinement,solid solution of Mn,and twining strengthening.Grain refinement and twin strengthening also can reduce stress concentration and improve ductility.In addition,at the electronic level,the Ti-Mn bond formed at the interface is contributed to the improvement of ductility.
