摘要 :
A novel simulation approach is presented for modeling particle-laden jets using large eddy simulations in an Eulerian-Lagrangian framework based on the spectral element method. Turbulent round jets are simulated under the same con...
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A novel simulation approach is presented for modeling particle-laden jets using large eddy simulations in an Eulerian-Lagrangian framework based on the spectral element method. Turbulent round jets are simulated under the same conditions as experiments in Mostafa et al. (1989), for single-phase and particle-laden cases under different mass loading ratios. Realistic inflow conditions are imposed, where the interaction between gas and solid phase, prior to exiting the inlet pipe, is accounted for. Gas- and solid-phase mean flow statistics are compared against experiments. A parametric study of particle inflow conditions is performed to minimize discrepancies between numerical and experimental data. The effect of particle collisions, particle sub-cycling, hydrodynamic forces and grid resolution on the mean flow is analyzed. Results show how particle injection velocity and location inside the pipe can be varied to match the experimental results with simulations, with particle collisions playing a secondary role in improving the accuracy of simulations and other parameters having negligible effects on the flow.
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摘要 :
A novel simulation approach is presented for modeling particle-laden jets using large eddy simulations in an Eulerian-Lagrangian framework based on the spectral element method. Turbulent round jets are simulated under the same con...
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A novel simulation approach is presented for modeling particle-laden jets using large eddy simulations in an Eulerian-Lagrangian framework based on the spectral element method. Turbulent round jets are simulated under the same conditions as experiments in Mostafa et al. (1989), for single-phase and particle-laden cases under different mass loading ratios. Realistic inflow conditions are imposed, where the interaction between gas and solid phase, prior to exiting the inlet pipe, is accounted for. Gas- and solid-phase mean flow statistics are compared against experiments. A parametric study of particle inflow conditions is performed to minimize discrepancies between numerical and experimental data. The effect of particle collisions, particle sub-cycling, hydrodynamic forces and grid resolution on the mean flow is analyzed. Results show how particle injection velocity and location inside the pipe can be varied to match the experimental results with simulations, with particle collisions playing a secondary role in improving the accuracy of simulations and other parameters having negligible effects on the flow.
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Estimating probability of failure in aerospace systems is a critical requirement for flight certification and qualification. Failure probability estimation (FPE) involves resolving tails of probability distribution and Monte Carlo...
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Estimating probability of failure in aerospace systems is a critical requirement for flight certification and qualification. Failure probability estimation (FPE) involves resolving tails of probability distribution and Monte Carlo (MC) sampling methods are intractable when expensive high-fidelity simulations have to be queried. We propose a method to use models of multiple fidelities, which trade accuracy for computational efficiency. Specifically, we propose the use of multifidelity Gaussian process models to efficiently fuse models at multiple fidelity and thereby offering a cheap surrogate model that emulates the original model at all fidelities. Furthermore, we propose a novel sequential acquisition function based experiment design framework, which can automatically select samples (or batches of samples for parallel evaluation) from appropriate fidelity models to make predictions about quantities of interest in the highest fidelity. We use our proposed approach within a importance sampling setting, and demonstrate our method on the failure level set estimation and FPE on synthetic test functions as well as the reliability analysis of a gas turbine engine blade. We demonstrate that our method predicts the failure boundary and probability more accurately and computationally efficiently while using varying fidelity models compared to using just a single fidelity expensive model.
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摘要 :
Estimating probability of failure in aerospace systems is a critical requirement for flight certification and qualification. Failure probability estimation (FPE) involves resolving tails of probability distribution and Monte Carlo...
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Estimating probability of failure in aerospace systems is a critical requirement for flight certification and qualification. Failure probability estimation (FPE) involves resolving tails of probability distribution and Monte Carlo (MC) sampling methods are intractable when expensive high-fidelity simulations have to be queried. We propose a method to use models of multiple fidelities, which trade accuracy for computational efficiency. Specifically, we propose the use of multifidelity Gaussian process models to efficiently fuse models at multiple fidelity and thereby offering a cheap surrogate model that emulates the original model at all fidelities. Furthermore, we propose a novel sequential acquisition function based experiment design framework, which can automatically select samples (or batches of samples for parallel evaluation) from appropriate fidelity models to make predictions about quantities of interest in the highest fidelity. We use our proposed approach within a importance sampling setting, and demonstrate our method on the failure level set estimation and FPE on synthetic test functions as well as the reliability analysis of a gas turbine engine blade. We demonstrate that our method predicts the failure boundary and probability more accurately and computationally efficiently while using varying fidelity models compared to using just a single fidelity expensive model.
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Applications of liquid jets and sprays in a crossflow can widely range from aerospace combustion to heavy-duty diesel after-treatment systems. While computational fluid dynamics are frequently used for modeling such sprays, additi...
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Applications of liquid jets and sprays in a crossflow can widely range from aerospace combustion to heavy-duty diesel after-treatment systems. While computational fluid dynamics are frequently used for modeling such sprays, additional experimental data is always needed for continued model validation and development. We present time-resolved X-ray radiography and high-speed phase contrast imaging measurements of a pressure-swirl after-treatment injector in a crossflow. The projected density distributions at two different crossflow velocities show an initial transient spray behavior as the injector opens, as well as a steady-state spray structure. Comparisons in the spray density between the two flow velocities are highlighted. The phase contrast images show qualitative spray characteristics as the liquid cone structure sheds ligaments and droplets. The images also provide quantitative metrics on the spray cone structure that can be compared to the radiography data. These measurements also provide quantitative data for spray predictive model development.
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Quantum key distribution allows for a provably secure transmission of cryptographic keys over an optical channel. Encoded polarization states or time-bin degree of freedom have been used for successful demonstrations. However, pho...
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Quantum key distribution allows for a provably secure transmission of cryptographic keys over an optical channel. Encoded polarization states or time-bin degree of freedom have been used for successful demonstrations. However, photon losses in long fibers, slow single photon detectors, and detector dark counts significantly limit, the overall bit rate. Improving key throughput and reducing the overhead of key reconciliation remain as major challenges. Methods which utilize multiple time bins allow for multiple key bits to be encoded in a single photon, thus increasing the fidelity of transmitted keys and decreasing the overhead of key reconciliation in real-world conditions. Previous implementations of these methods required that Alice and Bob share a time reference by sharing a dedicated classical channel used for synchronization. This work presents a technique that allows two parties to exchange time-bin encoded photons without the need for synchronized time references. Our technique uses a framing protocol which allows Alice to encode a time reference along with a key which is determined by Alice before transmission. Security can be achieved by monitoring the visibility of a pair of Franson interferometers, using decoy pulses and measuring the round trip time between Alice and Bob. The bit rate of this technique is limited only by the recovery time of the detector and the speed of the modulation electronics. We experimentally demonstrate a raw bit rate of 5Mb/s over an optical channel with 55dB of loss, which is competitive with current research. We also demonstrate absolute timing synchronization with an accuracy of 20ps.
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摘要 :
Quantum key distribution allows for a provably secure transmission of cryptographic keys over an optical channel. Encoded polarization states or time-bin degree of freedom have been used for successful demonstrations. However, pho...
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Quantum key distribution allows for a provably secure transmission of cryptographic keys over an optical channel. Encoded polarization states or time-bin degree of freedom have been used for successful demonstrations. However, photon losses in long fibers, slow single photon detectors, and detector dark counts significantly limit, the overall bit rate. Improving key throughput and reducing the overhead of key reconciliation remain as major challenges. Methods which utilize multiple time bins allow for multiple key bits to be encoded in a single photon, thus increasing the fidelity of transmitted keys and decreasing the overhead of key reconciliation in real-world conditions. Previous implementations of these methods required that Alice and Bob share a time reference by sharing a dedicated classical channel used for synchronization. This work presents a technique that allows two parties to exchange time-bin encoded photons without the need for synchronized time references. Our technique uses a framing protocol which allows Alice to encode a time reference along with a key which is determined by Alice before transmission. Security can be achieved by monitoring the visibility of a pair of Franson interferometers, using decoy pulses and measuring the round trip time between Alice and Bob. The bit rate of this technique is limited only by the recovery time of the detector and the speed of the modulation electronics. We experimentally demonstrate a raw bit rate of 5Mb/s over an optical channel with 55dB of loss, which is competitive with current research. We also demonstrate absolute timing synchronization with an accuracy of 20ps.
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Solid fuel ramjets (SFRJ) are a promising propulsion system due to its simplicity and long-range potential. Challenges exist understanding the near surface (fuel-air interface) phenomenon due to issues related to optical opacity, ...
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Solid fuel ramjets (SFRJ) are a promising propulsion system due to its simplicity and long-range potential. Challenges exist understanding the near surface (fuel-air interface) phenomenon due to issues related to optical opacity, beam steering, and diffraction. In this work, synchrotron phase contrast imaging is used for the first time on a miniature SFRJ slab burner. Results identify evidence of both a froth and melt layer above the solid fuel. Temporal and spatial dependence on froth layer thickness and regression rate are quantified. Uncertainty caused by the froth layer and 3D effects in the burner are discussed.
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Ultra-small-angle X-ray Scattering (USAXS) has been used previously to measure the atomization behavior in the liquid dense regions of various spraying systems, through collection of projection information. Here, similar projectio...
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Ultra-small-angle X-ray Scattering (USAXS) has been used previously to measure the atomization behavior in the liquid dense regions of various spraying systems, through collection of projection information. Here, similar projections of x-ray scattering measurements have been collected for the spray from a reference simplex atomizer and processed into line-of-sight surface area measurements. Additionally, these x-ray scattering measurements have been collected for a multitude of angular perspectives of the same spray, and computed tomography (CT) processing applied to derive the surface area per unit volume. The standardized simplex atomizer spray allows agreeable comparison to prior studies, specifically phase Doppler interferometry, where the measurements are volumetric. X-ray transmission was also measured for these multiple perspectives near-simultaneously, for matched conditions and spatial registration, and through CT reconstruction, resulted in liquid volume distribution. Combined liquid volume and USAXS-derived surface area provided planar mappings of Sauter mean diameter, which is comparable to PDI measurements. Through the use of a reference simplex injector, this effort continues, and improves upon the library of studies and comparisons that are made between different diagnostic methods.
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Polymer matrix composites are popular in the aerospace industry due to their high strength to weight ratio. While they have become popular, understanding and predicting their specific damage evolution mechanisms remains a challeng...
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Polymer matrix composites are popular in the aerospace industry due to their high strength to weight ratio. While they have become popular, understanding and predicting their specific damage evolution mechanisms remains a challenge especially in designing with damage tolerance criteria. One challenge often faced is the presence of surface damage either induced during manufacturing, machining, or service of a composite part. While many studies have investigated how quasi-static, low-velocity, and ballistic impact results in damage in the material, there remains a need to further understand the reduction in performance that results from such surface damage. In this work, micro-indentation was conducted on a unidirectional IM7/8552 laminate composite specimen to induce quasi-static impact damage that results in surface damage. The specimen was then loaded in tension to 33% of its expected failure load and imaged using synchrotron X-ray micro-computed tomography to qualitatively investigate the progression of surface damage into sub-surface damage. This work shows that at 33% of tensile failure load, surface damage propagates into delamination and fiber breakage of plies directly sub-surface. This work sheds light on the progression of surface damage at loads less than 50% of the ultimate strength of a unidirectional laminate composite.
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