查看更多>>摘要：Configuration stability is essential for a space-based Gravitational-Wave(GW)observa-tory,which can be impacted by orbit insertion uncertainties.Configuration uncertainty propagation is vital for investigating the influences of uncertainties on configuration stability and can be poten-tially useful in the navigation and control of GW observatories.Current methods suffer from draw-backs related to high computational burden.To this end,a Radial-Tangential-Ddirectional State Transition Tensor(RT-DSTT)-based configuration uncertainty propagation method is proposed.First,two sensitive directions are found by capturing the dominant secular terms.Considering the orbit insertion errors along the two sensitive directions only,a reduced-order RT-DSTT model is developed for orbital uncertainty propagation.Then,the relationship between the uncertainties in the orbital states and the uncertainties in the configuration stability indexes is mapped using high-order derivatives.The result is a semi-analytical solution that can predict the deviations in the con-figuration stability indexes given orbit insertion errors.The potential application of the proposed RT-DSTT-based method in calculating the feasible domain is presented.The performance of the proposed method is validated on the Laser Interferometer Space Antenna(LISA)project.Simula-tions show that the proposed method can provide similar results to the STT-based method but requires only half of the computational time.
查看更多>>摘要：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 gen-erating 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 for-mula 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.
查看更多>>摘要：Estimating the failure probability of highly reliable structures in practice engineering,such as aeronautical components,is challenging because of the strong-coupling and the small failure probability traits.In this paper,an Expanded Learning Intelligent Back Propagation(EL-IBP)neu-ral network approach is developed:firstly,to accurately characterize the engineering response cou-pling relationships,a high-fidelity Intelligent-optimized Back Propagation(IBP)neural network metamodel is developed;furthermore,to elevate the analysis efficacy for small failure assessment,a novel expanded learning strategy for adaptive IBP metamodeling is proposed.Three numerical examples and one typical practice engineering case are analyzed,to validate the effectiveness and engineering application value of the proposed method.Methods comparison shows that the EL-IBP method holds significant efficiency and accuracy superiorities in engineering issues.The current study may shed a light on pushing the adaptive metamodeling technique deeply toward complex engineering reliability analysis.
查看更多>>摘要：Full lifecycle high fidelity digital twin is a complex model set contains multiple functions with high dimensions and multiple variables.Quantifying uncertainty for such complex models often encounters time-consuming challenges,as the number of calculated terms increases exponen-tially with the dimensionality of the input.This paper based on the multi-stage model and high time consumption problem of digital twins,proposed a sparse polynomial chaos expansions method to generate the digital twin dynamic-polymorphic uncertainty surrogate model,striving to strike a bal-ance between the accuracy and time consumption of models used for digital twin uncertainty quan-tification.Firstly,an analysis and clarification were conducted on the dynamic-polymorphic uncertainty of the full lifetime running digital twins.Secondly,a sparse polynomial chaos expan-sions model response was developed based on partial least squares technology with the effectively quantified and selected basis polynomials which sorted by significant influence.In the end,the accu-racy of the proxy model is evaluated by leave-one-out cross-validation.The effectiveness of this method was verified through examples,and the results showed that it achieved a balance between maintaining model accuracy and complexity.
查看更多>>摘要：This paper introduces techniques in Gaussian process regression model for spatio-temporal data collected from complex systems.This study focuses on extracting local structures and then constructing surrogate models based on Gaussian process assumptions.The proposed Dynamic Gaussian Process Regression(DGPR)consists of a sequence of local surrogate models related to each other.In DGPR,the time-based spatial clustering is carried out to divide the systems into sub-spatio-temporal parts whose interior has similar variation patterns,where the temporal information is used as the prior information for training the spatial-surrogate model.The DGPR is robust and especially suitable for the loosely coupled model structure,also allowing for parallel computation.The numerical results of the test function show the effectiveness of DGPR.Further-more,the shock tube problem is successfully approximated under different phenomenon complexity.
查看更多>>摘要：Assessment of imprecise time-variant reliability in engineering is a critical task when accounting for both the variability of structural properties and loads over time and the presence of uncertainties involved in the ambiguity of parameters simultaneously.To estimate the Imprecise Time-variant Failure Probability Function(ITFPF)and derive the imprecise reliability results as a byproduct,Adaptive Combination Augmented Line Sampling(ACALS)is proposed.It consists of three integrated features:Augmented Line Sampling(ALS),adaptive strategy,and the optimal combination.ALS is adopted as an efficient analysis tool to obtain the failure probability function w.r.t.imprecise parameters.Then,the adaptive strategy iteratively applies ALS while considering both imprecise parameters and time simultaneously.Finally,the optimal combination algorithm collects all result components in an optimal manner to minimize the Coefficient of Variance(C.o.V.)of the ITFPF estimate.Overall,the proposed ACALS method outperforms the original ALS method by efficiently estimating the ITFPF while guaranteeing a minimal C.o.V.Thus,the proposed approach can serve as an effective tool for imprecise time-variant reliability analysis in real engineering applications.Several examples are presented to demonstrate the superiority of the proposed approach in addressing the challenges of estimating the ITFPF.
查看更多>>摘要：The study presents an experimental exploration into the mode transition of an over-under TBCC(Turbine-Based Combined Cycle)inlet,with a specific emphasis on the flow charac-teristics at off-design transition Mach number.A systematic investigation was undertaken into the mode transition characteristics in both unthrottled and throttled conditions within a high-speed duct,employing high speed Schlieren and dynamic pressure acquisition systems.The results show that the high-speed duct faced flow oscillations primarily dictated by the separation bubble near the duct entrance during the downward rotation of splitter,leading to the duct's unstart under the unthrottled condition.During the splitter's reverse rotation,a notable hysteresis of unstart/restart of the high-speed duct was observed.Conversely,hysteresis vanishes when the initial flow-field nears the critical state owing to downstream throttling.Moreover,the oscillatory diversity,a distinctive characteristic of the high-speed duct,was firstly observed during the mode transition induced by throttling.The flow evolution was divided into four stages:an initial instability stage characterized by low-frequency oscillations below 255 Hz induced by shock train self-excitation oscillation and high-frequency oscillations around 1367 Hz caused by the movement of separation bubble.This stage is succeeded by the"big buzz"phase,comprised of pressure accumulation/re-lease within the overflow-free duct and shock motion outside the duct to retain dynamic flow bal-ance.The dominant frequency escalated with the increase of the internal contraction ratio in the range of 280 Hz to 400 Hz.This was followed by a high-frequency oscillation stage around 453 Hz dominated by a large internal contraction ratio with low pulsating energy,accompanied by a continuous supersonic overflow.Lastly,as the splitter gradually intersected the boundary layer of the first-stage compression surface,the capture area and the turbulence intensity of the incoming flow underwent a sudden shift,leading to a more diverse flow oscillation within the duct,manifested as various forms of mixed buzz.
查看更多>>摘要：The high-efficiency Shock Vectoring Control Serpentine Nozzle(SVCSN)takes into account both thrust vectoring and infrared stealth,and significantly improves the comprehensive performance of the aero-engines through an additional auxiliary duct.In this paper,the schlieren photographs at the exit of the high-efficiency SVCSN and the wall static pressure distributions were obtained by experiments,and the numerical results were used to enrich the thrust vectoring char-acteristics.The effects of the auxiliary injection were analyzed first to reveal the advantages of the high-efficiency SVCSN compared to the conventional SVCSN.Then,the aerodynamic param-eters and the structural parameters of the high-efficiency SVCSN were investigated,including the Nozzle Pressure Ratio(NPR),the Secondary flow Pressure Ratio(SPR),the secondary flow relative area and the secondary flow injection angle.Finally,the coupling performance of the high-efficiency SVCSN is studied by using the approximate modeling technology.Results show that the auxiliary injection increases the range between the two shock legs of the"λ"shock wave induced by the sec-ondary flow,then causes the separation zone and high-pressure boss of the down wall to expand upstream,and finally results in a prominent increase in the thrust vectoring performance.The thrust vectoring angle and Vectoring Efficiency(VE)of the high-efficiency SVCSN are about 61.6％and 75.7％,respectively,higher than those of the conventional SVCSN at NPR=6.The effects of the NPR and the SPR on the thrust vectoring performance of the high-efficiency SVCSN are coupled with each other.A larger NPR matched with a smaller SPR shows better thrust vectoring perfor-mance.The maximum fluctuations in thrust vectoring angle and VE caused by the NPR and SPR are about 22％and 64％.The VE decreases monotonously with the increase of the secondary flow relative area.Smaller secondary flow injection angle shows better thrust vector performance,and the thrust vectoring angle and VE of the secondary flow injection angle of 90° are about 20％higher than those of the secondary flow injection angle of 110° at NPR=6.Therefore,the secondary flow relative area of 0.06 and the secondary flow injection angle of 90° are recommended.
查看更多>>摘要：Current transient analysis predominantly relies on zero-dimensional/one-dimensional tools,proficient at capturing aerothermodynamic variations across critical engine stations but insuf-ficient for analyzing the internal flow field evolution during transients.Addressing this gap,the study presents an enhanced quasi-three dimensional(quasi-3D)transient simulation technique that integrates component volume effects,offering a significant leap from the preceding quasi-3D tran-sient simulation method based on quasi-steady assumption.By embedding the component volume effects on density,momentum,and energy within the physical temporal dimension of the Navier-Stokes equations,the refined quasi-3D transient model achieves a closer representation of physical phenomena.Validation against a single-shaft turbofan engine's experimental data confirms the model's accuracy.Average errors for key performance indicators,including shaft speed,thrust,mass flow rate,and critical component exit temperature and pressure,remain below 0.41％,5.69％,2.55％,3.18％and 0.67％,respectively.Crucially,the model exposes a discernible temporal lag in the compressor outlet pressure and temperature response due to volume effects—previously unquantified in quasi-3D transient simulations.And further exploration of the meridional flow field emphasizes the consequential role of volumes in transient flow field evolution.Incorporating vol-ume effects within quasi-3D transient simulations enhances engine modeling and is pivotal for pre-cise transient analysis in engine design and optimization.
查看更多>>摘要：In modern aero-engine,the turbine rim seals whose purpose is to reduce the ingress are located in a complex flow region between the mainstream and secondary air flows.The sealing air discharged from the compressor of engine is used to purge turbine cavity.In order to examine the effects of ingress through four distinct rim seals,a one-stage test rig was used in the experiments presented in this work.At a Reynolds number of 5.16 × 105 in the mainstream and(0.85-2.13)× 106 in the rotational,the radial pressure distribution on the stator was determined.To assess flow characteristics and sealing efficacy,measurements of the swirl ratio and CO2 concentration were made.The reliability of turbine rim-seals is determined by the locations of the hook and teeth,as well as their effect on hot gas ingestion.To evaluate the performance of four types of seals:a datum double-rim seal and three derivatives with different clearances,the data are employed.Due to the inlet air position,the swirl ratio exhibited a pronounced inflection for all the rim seals.The sealing efficiency can be decreased by putting the hook closer to the rim or by taking the teeth out.Static pressure measurements in the turbine cavity indicate that the seal position has a signif-icant impact.The analysis results revealed that the existence of slot vortex is beneficial to improving efficiency.
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