最新刊期
期 19 ， 2023
- 摘要：To measure the velocity distribution of a complex flow， a femtosecond laser electronic excitation tagging （FLEET） system was established based on the principle of molecular tagging velocimetry. The velocity distribution of a supersonic mixing layer flow， which was generated from a primary stream of Mach number 3.0 and secondary streams of Mach numbers 2， 2.5， and 2.9， were obtained. In addition， the flow structure of the mixing layer was obtained through large-eddy simulation and a schlieren experiment. The uncertainty of FLEET velocity measurement is better than 5 m/s by calculating the displacement difference between the fluorescence baseline and the 10-μs-delay fluorescence filament. In the main stream， the velocity results measured by FLEET were essentially consistent with the calculation results. In the mixing layer， the obvious gradient velocity distribution was obtained， and the thickness of the mixed layer was essentially consistent with the schlieren experimental result. Therefore， the FLEET system can be used for complex velocity distribution measurements， such as supersonic mixing layer flow.关键词：femtosecond laser;molecular tagging;velocity measurement;supersonic mixing layer
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发布时间：2023-10-12 - 摘要：Shock waves represent a primary form of damage from explosions， and explosive-driven shock tubes can simulate high overpressure shock wave scenarios. It is essential to determine test parameters， including the separation among the shock wave， explosion products， wave-front shape. Traditional pressure measurements， grounded in electrical principles， are insufficient for current flow field characterization research. Leveraging the reflection schlieren principle， a diagnostic system is developed for the shock tube nozzle's flow field. This system utilizes a laser source and sequence of optical elements. By integrating visual observations of flow phenomena with conventional pressure data， the method for analyzing flow field characteristics is enhanced. The findings indicate that the schlieren system captures high-resolution images of the shock wave and product flow field at the exit of the shock tube. Synchronized schlieren images， aligned with the pressure tests of the shock tube and ignition timings， offer insights into data oscillation， pressure anomalies， and the drift observed in piezoelectric pressure sensors. They also highlight the vibration effects in the nozzle and surrounding air， resulting from stress waves post-explosion within the tube. Through image analysis， the spatial decay patterns of the velocity and pressure of the shock wave at the explosive outlet of the shock tube can be obtained. These results furnish a novel diagnostic technique and analytical foundation， enhancing our comprehension of the formation and evolution of shock wave pressure in the explosive-driven shock tube.关键词：optical measurement;shock tube;explosion flow field;Schlieren method;shock wave
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发布时间：2023-10-12 - 摘要：The influence of non-uniform distributions of thermochemical parameters on the sooting flame measurements was comprehensively studied via the line-of-sight （LOS） dual-color laser absorption spectroscopy （LAS） in flame thermometry. Six representative absorption line pairs of water vapor （H2O） within the wavelength range of 1.3-3.0 μm were selected as optimal for the investigations. High-fidelity spectral simulations were performed to investigate the influence of the non-uniform temperature and concentration distributions on sooting flames with nitrogen and air co-flows. The non-uniformity conditions for sooting flames with nitrogen co-flow and sooting flames with air co-flow were abtained. For sooting flames with nitrogen co-flow， the maximum temperature deviations of the spectral line pairs （4 029.52 cm-1/4 030.73 cm-1 and 5 553.86 cm-1/5 554.18 cm-1） were observed to be the smallest （i.e.， 4.72%） and largest （i.e.， 12.40%）， respectively. For sooting flames with air co-flow， the temperature deviations exhibited positive and negative values， with the maximum positive and negative values observed under the non-uniformity condition of δ/L=80%. In particular， the maximum positive and negative temperature deviations were 14.43% and -2.51% for the line pair 5 553.86 cm-1/5 554.18 cm-1， and 3.22% and -13.21% for the spectral line pair 4 029.52 cm-1/4 030.73 cm-1. The numerical simulation results were subsequently compared with experimental measurements using the line pair near 4 029.52 cm-1/4 030.73 cm-1. The experimental results indicated that， in two typical sooting flames， the line pair 4 029.52 cm-1/4 030.73 cm-1 can effectively mitigate the influence of non-uniform distributions of thermochemical parameters on the temperature measurement.关键词：laser absorption spectroscopy;non-uniform distribution of thermochemical parameters;sooting flame;temperature measurement
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发布时间：2023-10-12
Laser Spectroscopy Technology and Equipment for Flow-field Diagnosis
- 摘要：To generate high-order and fractional-order vortex beams， a spatial light modulator was used to simulate a forked grating. This was performed to generate and isolate the desired vortex beams with the different orbital angular momentum (OAM) of l, and investigated their characteristics. Measurement of their topological charges via the interference method validated the availability and the accuracy of the experimental method. An optical path for vortex beam generation was designed， and a computer program was developed to create a forked grating hologram. This grating was simulated using a transmissive spatial light modulator and uploaded on the modulator as a hologram. By adjusting the parameters， the holographic grating pattern could be modified to produce integer-order vortex beams with topological charges ranging from 1.00 to 100.0. In addition， fractional-order vortex beams were generated at intervals of 0.1. The first order diffraction was isolated using an aperture diaphragm. Subsequently， its characteristics were analyzed， and its topological charge was measured via interferometry. A consistent relationship was observed between the distributions of integer- and fractional-order light fields and their respective topological charge numbers. Notably， as the topological charge number neared 100， a marked reduction was observed in the beam quality. The topological charge number， determined via interferometry， matched the parameters set in the computer-generated hologram， validating the computer-generated holography method's accuracy. Given its straightforward setup and adjustable parameters， this method could serve as a reference for the creation and application of high-order and fractional-order vortex light.关键词：optical vortex;spatial light modulator;diffraction grating;orbital angular momentum
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发布时间：2023-10-12 - 摘要：An algorithm was designed to assess the fluctuation in the mode control ability of the photonic lantern. This algorithm incorporated a module specifically for extracting the gray matrix from the light field image. To analyze the fluctuations in the photonic lantern's mode control along with the beam power， numerical results were used in place of angular power distribution variance. Initially， the theoretical foundation of the algorithm was established using the power flow equation and adjacent mode coupling theory. Following this， the gray extraction algorithm， detailing its structure and parameters were elaborated. By utilizing the gray matrix， a restored image was derived and compared with the original light field image. The findings confirmed that the algorithm effectively translates the light intensity distribution into a gray value matrix. Finally， the mode control changes of a custom 3×1 photonic lantern was evaluated under varying beam-combining power. During the experiment， the beam combining power was increased from 0 to 270 mW. The experimental outcomes indicate that our analysis accounts for the variations in the slope of the light beam combining loss curve for the 3×1 photonic lantern and the fluctuation in the maximum Gaussian fit degree of the combined beam as the power increases. In summary， this algorithm offers a simple and efficient method for assessing the fluctuation in the mode control ability of the photonic lantern when generating the fundamental mode beam. It exhibits low environmental sensitivity， and its accuracy in extracting light field data exceeds 99%.关键词：Diode laser;mode control;gray matrix;photonic lantern;beam combining
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发布时间：2023-10-12 - 摘要：The direct monitoring of strontium in aerosols is crucial for air pollution prevention and the monitoring of emissions from industrial facilities. Laser-induced plasma spectroscopy （LIPS） offers a promising method for the direct and online monitoring of environmental mediums. Specifically， LIPS requires no sample preparation， allows rapid analysis， and facilitates online detection. This study introduces the direct detection of strontium in aerosols using an LIPS setup. The experimental findings confirm that， through ensemble averaging， the limit of detection （LOD） for strontium aerosols is 809 μg/m3. Conditional analysis enhances the signal-to-noise ratio of the average spectrum eight-fold for low-density aerosols. Furthermore， this study delves into the effects of aerosol statistical characteristics and spectral analysis methods on spectral line intensity. Given that the aerosol particle density has minimal impact on plasma temperature and the spectral intensity is influenced by particle density， the scope of conditional analysis is further explored. Hence， it is proposed that the sensitivity of LIPS can be enhanced nearly three-fold by substituting the average spectrum with the cumulative spectrum over a given measurement period. With this adjustment， the LOD of the setup can approach 1.3 μg/m3， fulfilling the requirements of industrial emission monitoring.关键词：laser-induced plasma spectroscopy;aerosol analysis;Sr;conditional analysis
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发布时间：2023-10-12
Modern Applied Optics
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Magnetic field time-gate displacement sensor based on discrete winding and its error characteristics
摘要：Addressing the challenges in the manufacturing of high-precision displacement sensors， a magnetic-field time-gate displacement sensor based on discrete windings was proposed. Through a specific arrangement of discrete exciting windings and valid shape of the discrete inducing windings， the change law of induced displacement signals was controlled. High-precision displacement was achieved using a combined measurement method. Furthermore， the influence of errors in exciting signals and the installation errors of the sensor on the measurement precision was analyzed via theoretical modeling， simulated analysis， and experimental verification. The experiment results showed that the DC error and 2nd harmonic error were introduced directly within the pitch by the amplitude errors between the two excitation signals and installation errors， with the 2nd harmonic error being the primary contributor to the measurement errors. As installation errors increased， the 2nd harmonic error also increased. The most significant impact on the measurement error was found to be the deflection error along the Z axis， followed by the flip error along the Y axis， and the least impactful was the tilt error along the X axis. After error correction was applied， the peak-to-peak value of the measurement error was found to be 4.5 μm within 144 mm， and the resolution was determined to be 0.15 μm. The primary feature of the method proposed is that discrete exciting windings and inducing windings on a millimeter scale were used to achieve measurement precision on a micrometer scale. This approach was shown to significantly reduce the manufacturing challenges of the displacement sensor， providing academic value and practical value.关键词：Linear displacement;discrete windings;combined measurement;time-gating sensors;error analysis- 3
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发布时间：2023-10-12 - 摘要：To integrate efficient mixing functions inside small chips with variable Reynolds numbers， this study developed a strategy for designing micromixers by increasing the concentration difference through matching contact surfaces based on Fick's law and Einstein's equation for Brownian motion. Subsequently， the Coanda effect was extended by analyzing the flow direction of the fluid over the channel surface and abstracting four functions from specific microchannel modules. These functions were used to predict and modulate the concentration gradient and construct the micromixer. Two three-dimensional structures of passive micromixers were designed using four functional modules to rotate and adjust the fluid interface. A three-dimensional Navier-Stokes system of equations was used for numerical analysis， and a micromixer was constructed via soft lithography for experimental verification. The experimental and simulation results showed that the designed micromixer consistently exhibits a mixing efficiency of 94%-99% at 3.3 mm， which is 22 times the hydraulic diameter length， for Reynolds numbers ranging from 0.1 to 100. This demonstrates a clear advantage over existing methods at an equal hydraulic diameter. Furthermore， the structure is easy to integrate on a chip， indicating the superiority of the modular design.关键词：microfluidics;micromixer;split and recombination;rotation effect;lab on a chip
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发布时间：2023-10-12 - 摘要：Microfeature positioning based on machine vision is a crucial aspect of precision automated assembly. External interference and differences in the parts themselves can easily cause visual guidance errors and the success rate of assembly. Therefore， a composite positioning method consisting of rough positioning and fine positioning was proposed. First， the region of interest was extracted through a target-frame-detection algorithm based on a convolutional neural network to achieve rough positioning. Based on this， precise positioning of parts was achieved through contour geometric feature registration. A dynamic learning mechanism assisted by automatic labeling was also adopted in the algorithm to solve the problem of the high positioning failure rate resulting from the difference between the different batches of parts. The method was tested on assembly equipment developed by the research group. The effects of brightness， defocusing， and posture changes on the robustness of visual positioning algorithms were analyzed. Furthermore， positioning accuracy and small-batch assembly experiments were conducted. The results show that the proposed method has good robustness and repeatability with various forms of interference， with an assembly success rate of 97%. Both the absolute accuracy and repetitive accuracy of visual positioning are<2 μm， and assembly accuracy is<10 μm. Therefore， the research results effectively meet the dual requirements of both accuracy and robustness of the positioning algorithm in precision microassembly.关键词：precision microassembly;machine vision;feature positioning;target detection
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发布时间：2023-10-12 -
Research process on operation performances of parallel type six-axis acceleration sensing mechanisms
摘要：Six-axis acceleration sensing has urgent application demands in the fields of robotics， aerospace， and ultra-precision machining， having become the core technology in the development of cutting-edge high-end equipment. Parallel-type six-axis accelerometers offer the salient advantages of compact structures and high decoupling precisions， and their measurement performance relates to the operation performance of sensing mechanisms. First， from the perspective of working mechanisms， this paper clarifies five differences between parallel-type six-axis acceleration sensing mechanisms， parallel robots， and parallel-type six-axis force sensing mechanisms. From mathematical and mechanical perspectives， it then systematically describes the characterization and optimization methods for operation performance factors， including static stiffness， singularity， fundamental resonance， and fault restoration， and analyzes reasons for the non-adaptive nature of existing methods. Subsequently， the necessity and basic requirements of six-dimensional acceleration calibration platforms are elucidated， and the advantages and disadvantages of four principle schemes are analyzed. Finally， it is concluded that to fully leverage the performance advantages of parallel-type six-axis acceleration sensing mechanisms， it is necessary to further address key technical problems by exploring internal performance relationships， structures， and excitations； reconfiguring geometric and topological structures； and designing and optimizing calibration platforms.关键词：Six-axis accelerometer;parallel mechanism;static stiffness;singularity;fundamental resonance;fault restoration- 2
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发布时间：2023-10-12
Micro/Nano Technology and Fine Mechanics
- 摘要：The training data of fully supervised video instance segmentation networks are highly dependent on accurate mask annotations under high labor and time costs， owing to which intelligent machines are unable to quickly adapt to new scenes. Therefore， a mask generation， dynamically regulated weakly supervised video instance segmentation （WSVIS） network was proposed. First， to overcome the loss of instance activation features caused by the sudden dimension drop of the initial mask prediction layer channel， a multi-level feature fusion module was used to predict the initial instance features through a step-by-step feature reuse strategy and to generate the initial mask by fusing the relative position information. Second， a dynamic regulation mechanism was introduced to establish mask feature dependencies in the channel and spatial dimensions to strengthen the dynamic interaction between the initial predicted mask and instance-aware information. Finally， the network replaces fine mask labeling with the binary color similarity of images， and the bounding box consistency loss and supervised video instance segmentation mask were replaced with bounding box labeling only. Experimental results reveal that on the BoxSet and YT-VIS datasets， the WSVIS network achieves similar segmentation accuracy and segmentation effect as the fully supervised network and can satisfy real-time reasoning， providing theoretical support and an algorithmic basis for intelligent machines to quickly adapt to new scenes to realize real-time environmental perception and understanding.关键词：intelligent machine;weakly supervised video instance segmentation;multi-level feature fusion;dynamic regulation;binary color similarity
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发布时间：2023-10-12 - 摘要：The perpendicular-orbit circular scanning sensor， a new optical imaging system， can capture images with an ultra-wide swath width （thousand-kilometer level） and high resolution （meter level） that are much larger than those obtained by traditional satellites （with a single image being up to several hundred gigabytes）. A rigorous imaging model was constructed for the perpendicular-orbit circular scanning sensor based on an analysis of its imaging principles. Based on the characteristics of the perpendicular-orbit circular scanning sensor， a terrain-dependent control point layout scheme combined with DEM was developed. In addition， a method to determine the initial iteration interval was proposed using the coordinate of the sub-satellite point to solve the problem of back projection calculation failure under the condition of a wide swath， which could help obtain a solution from the object space coordinate to the image space coordinate within the whole scene range of an arbitrary-width image. In this study， a RFM construction test was conducted by simulating images with different swath width， orbital， and altitudinal data to explore the fitting accuracy of RFM in different object square coordinate systems. When the swath width of the image reaches 3 000 km， the RFM fit error is 3 004.25 and 1 939.04 pixels in different schemes. The RFM fit error constructed by the terrain-dependent scheme is 27.5 and 24.96 pixels when a geocentric rectangular coordinate system was used. Images captured by the perpendicular-orbit circular scanning sensor can have widths of several thousand kilometers； therefore， the accuracy of RPC is significantly affected by the curvature of earth， and the accuracy of RPC solved under the condition of geocentric rectangular coordinate system is better than that of a geodetic coordinate system. The initial exploration of the RFM accuracy of perpendicular-orbit circular scanning sensor images can provide a foundation for the application of the satellite.关键词：perpendicular-orbit circular scanning sensor;rigorous sensor model;rational function model;back project calculation;accuracy assessment
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发布时间：2023-10-12 - 摘要：A point cloud object detection network， Pillar-FFNet， is proposed by introducing a multiscale feature fusion strategy and an attention mechanism to address the ineffectiveness of PointPillar in detecting small sparse objects in point clouds in autonomous driving road scenarios. First， a backbone network based on a residual structure is designed for feature extraction in the network. Second， a simple and effective multiscale feature fusion strategy is designed to address the problem that the feature maps fed into the detection head do not make full use of the semantic information of high-level features and the spatial information of low-level features. Finally， a convolutional attention mechanism is proposed to treat information redundancy in the feature maps extracted using the backbone network. To validate the performance of the proposed algorithm， experiments are conducted on the KITTI and DAIR-V2X-I datasets. The results show that the proposed algorithm achieves maximum average accuracy improvements of 0.84%， 2.13%， and 4.02% for cars， pedestrians， and cyclists， respectively， on the KITTI dataset and maximum average accuracy improvements of 0.33%， 2.09%， and 4.71% for cars， pedestrians， and cyclists， respectively， on the DAIR-V2X-I dataset compared with the PointPillar results. Experimental results demonstrate the effectiveness of the proposed method for the detection of sparse small objects in point clouds.关键词：small object detection;point cloud sparse;PointPillar;residual structure;multi-scale feature fusion;convolutional attention
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发布时间：2023-10-12
Information Sciences
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