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Modeling Spatially Varying Uncertainty in Composite Structures Using Lamination Parameters

AIAA JOURNAL 2017年第11期55卷 3951-3965页

作者： Scarth, C. Adhikari, S. Swansea Univ Coll Engn Swansea SA1 8EN W Glam Wales Swansea Univ Coll Engn Aerosp Engn Swansea SA1 8EN W Glam Wales

An approach is presented for modeling spatially varying uncertainty in the ply orientations of composite structures. Lamination parameters are used with the aim of reducing the required number of random variables. Karhunen-Loeve expansion is employed to decompose the uncertainty in each ply into a sum of random variables and spatially dependent functions. An intrusive polynomial chaos expansion is proposed to approximate the lamination parameters while preserving the separation of the random and spatial dependency. Closed-form expressions are derived for the expansion coefficients in two case studies;an initial example in which uncertainty is modeled using random variables, and a second random field example. The approach is compared against Monte Carlo simulation results for a variety of layups as well as closed-form expressions for the mean and covariance. By summing the polynomial chaos basis functions through the laminate thickness, the separation of the random and spatial dependency may be preserved at a laminate level and the number of random variables reduced for some minimum number of plies. The number of variables increases nonlinearly with the number of Karhunen-Loeve expansion terms, and as such, the approach is only beneficial in low-order expansions using relatively few Karhunen-Loeve expansion terms.

关键词： Composite Structures Karhunen Loeve Expansion Monte Carlo Simulation Finite Element Method Elastic Modulus Composite Laminates Material Properties probability density functions Aeroelastic Stability Free Vibrations

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Construction of Coarse-Grained Models by Reproducing Equilibrium probability density Function

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Communications in Theoretical Physics 2015年第1期63卷 10-18页

作者：吕世靖周昕 Institute of Modern Physics Zhejiang University School of Physics University of Chinese Academy of Sciences

The present work proposes a novel methodology for constructing coarse-grained （CG） models, which aims at minimizing the difference between CG model and the corresponding original system. The difference is defined as a functional of their equilibrium conformationaJ probability densities, then is estimated from equilibrium averages of many independent physical quantities denoted as basis functions. An orthonormalization strategy is adopted to get the independent basis functions from su^ciently preselected interesting physical quantities of the system. Thus the current method is named as probability density matching coarse-graining （PMCG） scheme, which effectively takes into account the overall cha,~acteristics of the original systems to construct CG model, and it is a rtatural improvement of the usual CG scheme wherein some physical quantities are intuitively chosen without considering their correlations. We verify the general PMCG framework in constructing a one-site CG water model from TIP3P model. Both structure of liquids and pressure of the TIP3P water system are found to be well reproduced at the same time in the constructed CG model.

关键词： coarse-graining models probability density functions molecular dynamics simulations

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Cooperative Robot Localization Using Event-Triggered Estimation

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JOURNAL OF AEROSPACE INFORMATION SYSTEMS 2018年第7期15卷 427-449页

作者： Ouimet, Michael Iglesias, David Ahmed, Nisar Martinez, Sonia SPAWAR Syst Ctr Pacific San Diego CA 92152 USA Univ Colorado Boulder Ann & HJ Smead Aerosp Engn Sci Dept Boulder CO 80309 USA Univ Calif San Diego Dept Mech & Aerosp Engn San Diego CA 92093 USA

This paper describes a novel communication-spare cooperative localization algorithm for a team of mobile unmanned robotic vehicles. Exploiting an event-based estimation paradigm, robots only send measurements to neighbors when the expected innovation for state estimation is high. Because agents know the event-triggering condition for measurements to be sent, the lack of a measurement is thus also informative and fused into state estimates. The robots use a covariance intersection mechanism to occasionally synchronize their local estimates of the full network state. In addition, heuristic balancing dynamics on the robots' covariance-intersection-triggering thresholds ensure that, in large-diameter networks, the local error covariances remains below desired bounds across the network. Simulations on both linear and nonlinear dynamics/measurement models show that the event-triggering approach achieves nearly optimal state estimation performance in a wide range of operating conditions, even when using only a fraction of the communication cost required by conventional full data sharing. The robustness of the proposed approach to lossy communications as well as the relationship between network topology and covariance-intersection-based synchronization requirements are also examined.

关键词： Cooperative Robot Aerial Robots Covariance Intersection Nonlinear Dynamics Extended Kalman Filter Communication Channels Data Fusion Onboard Computing probability density functions Gaussian Mixture Models

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Short-Term Collision probability Algorithm for Parallelepiped-Shaped Satellites

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2022年第6期45卷 1093-1107页

作者： Enriquez, Cesar Daniel Garcia-Pelayo, Ricardo Tech Univ Madrid Madrid 28040 Spain Ronda Poniente 19 Tres Cantos 28760 Spain Tech Univ Madrid Escuela Tecn Super Ingn Aeronaut & Espacio Dept Appl Phys Plaza Cardenal Cisneros 3 Madrid 28040 Spain

The probability of collision of two solid satellites, one of which is a parallelepiped and the other is a parallelepiped or a small sphere, is computed under the assumptions of short-term encounter. The probability is given by the integral of the relative position probability density over a region of the collision plane. This region is the Minkowski sum of the projections of the objects' shapes onto the collision plane. The integration is the only step that cannot be done analytically. When the position probability densities are Gaussians, a very fast and accurate algorithm found in the literature can be applied after several transformations have been performed to the integration region. A comparison against several current methods has been included. When a parallelepiped is involved, the presented method is advantageous with respect to the existing ones.

关键词： Satellites Computing probability density functions Space Situational Awareness Numerical Integration Numerical Algorithms Monte Carlo Simulation High Aspect Ratio Radar Imaging Space Agencies

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Engineering Design with Digital Thread

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AIAA JOURNAL 2018年第11期56卷 4515-4528页

作者： Singh, Victor Willcox, K. E. MIT Dept Aeronaut & Astronaut Cambridge MA 02139 USA MIT Aeronaut & Astronaut 77 Massachusetts Ave Cambridge MA 02139 USA

Digital Thread is a data-driven architecture that links together information generated from across the product lifecycle. Though Digital Thread is gaining traction as a digital communication framework to streamline design, manufacturing, and operation processes in order to more efficiently design, build, and maintain engineering products, a principled mathematical formulation describing the manner in which Digital Thread can be used for critical design decisions remains absent. The contribution of this paper is to present such a formulation from the context of a data-driven design and decision problem under uncertainty. This formulation accounts for the fact that the design process is highly iterative and not all information is available at once. Output design decisions are made not only on what data to collect but also on the costs and benefits involved in experimentation and sensor instrumentation to collect that data. The mathematical formulation is illustrated through an example design of a structural fiber-steered composite component. In this example, the methodology highlights how different sequencing of small-scale experimentation with manufacturing and deployment lead to different designs and different associated costs.

关键词： Sensors Material Properties Model Based System Engineering probability density functions Structural Failure Multidisciplinary Design Optimization Finite Element Modeling Wingbox Stochastic Optimization Elastic Modulus

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Collision probability with Gaussian Mixture Orbit Uncertainty

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2014年第3期37卷 979-984页

作者： DeMars, Kyle J. Cheng, Yang Jah, Moriba K. Missouri Univ Sci & Technol Dept Mech & Aerosp Engn Rolla MO 65409 USA Mississippi State Univ Dept Aerosp Engn Mississippi State MS 39762 USA US Air Force Res Lab Kirtland AFB NM 87117 USA

No abstract available.

关键词： probability density functions Monte Carlo Simulation Right Ascension Space Surveillance Computing Earth International Space Station Unscented Kalman Filter Orbit Determination Space Debris

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CONCENTRATION IMAGING MEASUREMENTS IN TURBULENT CONCENTRIC-JET FLOWS

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AIAA JOURNAL 1992年第2期30卷 384-394页

作者： NAMAZIAN, M KELLY, J SCHEFER, RW SANDIA NATL LABS COMBUST RES FACILLIVERMORECA 94550

Raman scattering images were used to determine the CH4 concentration in nonreacting concentric-jet flows. The flow consists of a central CH4 jet and a concentric air jet separated by a bluff body. Three jet velocity ratios were studied under isothermal conditions. At high momentum-flux ratios, the CH4 jet penetrates the recirculation zone formed by the airflow behind the bluff body. At low momentum ratios, the jet is stagnated and fuel is dispersed into the recirculation zone. The large-scale instantaneous boundary between the stagnated jet and the air is time varying and creates a sharp peak in the rms CH4 fluctuations in the stagnation region. Two-point spatial correlations were obtained over the flowfield to quantify the scale of the structures in these flows. Based on the limited data presented, it was found that the CH4 concentration field is similar for equal momentum-flux ratios. The CH4 concentration in the recirculation zone has a maximum at a momentum-flux ratio of unity, corresponding to the nearly penetrated case. In the nonpenetrated case, mixing of the central jet with surrounding air is substantially enhanced. Under these conditions, a considerable portion of the flowfield is mixed to conditions where combustion could occur. This enhanced mixing explains why bluff-body flames are more stable than jet flames into still air.

关键词： Unsteady Turbulent Flow Flow Visualization Raman Scattering Vortices Shear Layers Numerical Modeling probability density functions Large Eddy Simulation Mie Scattering Laser Induced Fluorescence

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Reynolds number effects on three-dimensional vorticity in a turbulent wake

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AIAA JOURNAL 2004年第5期42卷 1009-1016页

作者： Yiu, MW Zhou, Y Zhou, T Cheng, L Hong Kong Polytech Univ Dept Mech Engn Kowloon Hong Kong Peoples R China Nanyang Technol Univ Dept Mech Engn Singapore 639798 Singapore

When Reynolds number Re (equivalent to U(infinity)d/v, where U. is the free stream velocity, d is the cylinder diameter, and v is the kinematic viscosity of fluid) varies from 103 to 104, there is a large change in the turbulent near-wake dynamics (e.g., the base pressure coefficient, fluctuating lift coefficient, and vortex formation length) of a circular cylinder, which has previously been connected to the generation of small-scale Kelvin-Helmholtz vortices. This work aims to investigate how this Re variation affects the three components of the vorticity vector and to provide a relatively complete set of three-dimensional vorticity data. All three components of vorticity were simultaneously measured in the intermediate region of a turbulent circular-cylinder wake using a multiwire vorticity probe. It is observed that the root-mean-square values of the three vorticity components increase with Re, especially the streamwise component, which shows a large jump from Re = 5 X 10(3) to Re = 10(4). At Re = 2.5 X 10(3), the maximum phase-averaged spanwise vorticity variance (omega(z)(2))(*), normalized by d and U-infinity, is twice as large as its counterpart for the streamwise component, (omega(x)(2))(*), or the lateral component, (omega(y)(2))(*). However, at Re = 10(4), the maximum (omega(z)(2))(*) is only 55% larger than the maximum (omega(x)(2))(*) or 47% larger than the maximum (omega(y)(2))(*). The observation is consistent with the perception that the three-dimensionality of the flow is enhanced at higher Re due to the occurrence of Kelvin-Helmholtz vortices. The effect of Re on vorticity signals, spectra, and coherent and incoherent vorticity fields is also examined.

关键词： Free Stream Velocity Pressure Coefficient Karman Vortex Street Kinematic Viscosity Lift Coefficient Yaw Normal Stress Particle Image Velocimetry probability density functions Direct Numerical Simulation

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Assessment of Finite-Rate Chemistry Effects in a Turbulent Dilute Ethanol Spray Flame

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JOURNAL OF PROPULSION AND POWER 2022年第4期38卷 607-622页

作者： Yin, Yu Yang, Tianwei Zhou, Hua Ren, Zhuyin Tsinghua Univ Sch Aerosp Engn Beijing 100084 Peoples R China Tsinghua Univ Inst Aero Engine Beijing 100084 Peoples R China

Simulations of a benchmark ethanol dilute spray flame are performed with four combustion models at different levels of closure for turbulence-chemistry interaction (TCI) to provide a head-to-head comparative analysis on the closure effects of TCI. The evaluation is performed in the context of Reynolds-averaged Navier-Stokes simulations taking advantage of the simple jet configuration, together with a Lagrangian discrete phase model for tracking the spray droplets. Two well-validated ethanol mechanisms consisting of 40 and 50 species, respectively, are employed to describe the chemical kinetics and reveal the impact of chemistry. Results are compared against measurement, including gas-phase velocity, temperature, and droplet velocity, demonstrating the improvement with the increasing accuracy in TCI modeling from characteristic time scale model, laminar finite rate model, eddy dissipation concept model, and transported probability density function (PDF) model. Effects of micromixing in PDF simulation are further investigated considering different model formulations and mechanical-to-scalar timescale ratios (C-phi). The Euclidean minimum spanning tree model with C-phi=1.5 yields the best prediction of the mean temperature. The analysis on flame structure suggests that the flame exhibits a mixed mode of combustion, i.e., a stratified premixed flame in the upstream and a typical non-premixed flame in the downstream.

关键词： Flamelet Generated Manifold Gas Phase Chemical Kinetics Reynolds Averaged Navier Stokes probability density functions Large Eddy Simulation Chemical Equilibrium Pilot Velocity Profiles Heat Transfer Modeling Ideal Gas

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density Fluctuations Measurement by Rayleigh Scattering Using a Single Photomultiplier

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AIAA JOURNAL 2018年第4期56卷 1310-1316页

作者： Mercier, Bertrand Castelain, Thomas Jondeau, Emmanuel Bailly, Christophe Cent Sch Lyon CNRS UMR 5509 LMFA F-69134 Ecully France Claude Bernard Univ Lyon 1 LMFA CNRS UMR 5509 F-69134 Ecully France

Rayleigh scattering provides a direct nonintrusive method for density measurement, which is of particular interest in aeroacoustics. However, two major concerns arise linked to the use of photomultipliers. First, the detection of photon flux is corrupted by the presence of dust particles in the flow. An original signal processing is proposed in this study to remove their signatures. Second, the random arrival of photons on a photomultiplier induces shot noise, which can be partly removed by using two photomultipliers. It is shown in this study that a single photomultiplier combined with suitable processing can also be used to remove shot noise. Both approaches are compared for the case of a compressible subsonic jet exhausting in an anechoic wind tunnel.

关键词： Rayleigh Scattering Wind Tunnels Aeroacoustics Signal Processing Jet Exhaust Compressible Flow probability density functions Flow Velocity Doppler Effect Convergent Nozzles

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