High speed ghost imaging based on a heuristic algorithm and deep learning

We report an overlapping sampling scheme to accelerate computational ghost imaging for imaging moving targets,based on reordering a set of Hadamard modulation matrices by means of a heuristic algorithm. The new condensed overlapped matrices are then designed to shorten and optimize encoding of the overlapped patterns, which are shown to be much superior to the random matrices. In addition, we apply deep learning to image the target, and use the signal acquired by the bucket detector and corresponding real image to train the neural network. Detailed comparisons show that our new method can improve the imaging speed by as much as an order of magnitude, and improve the image quality as well.

Digital image correlation based high-speed crack tip locatingmethod and its application

Based on a digital image correlation（DIC）method with the measurements of a high speed crack＇s displacement and strain fields,a technique to accurately and automatically locate its crack tip has been developed.The crack tip is identified by finding the abrupt jump on the opening（or dislocation）curve of a point on the trace of the crack propagation,while the opening is measured through a virtual extensometer technique and the abrupt jump is identified by finding the peak on the curve.The method was verified using a specially designed experiment and applied to measure the critical crack tip opening angle of a rock sample.Because the involvement of analytical models has been avoided and then the good performance could be ensured for low resolution speckle images,this technique is expected to be very useful in the quantitative study of high speed cracks in experiments using high speed cameras.

Experimental Investigation of Flame Dynamics Based on High-Speed Images in Swirl Combustion Systems

The interaction mechanism of internally-staged-swirling stratified flame is complex,and the pilot flame has a manifest influence on flame stability.To study this,a series of experimental investigations for the pilot flame has been carried out in a model swirl combustor by only supplying the pilot fuel.The CH*chemiluminescence images of the pilot flame are acquired by a high-speed camera with a CH*bandpass filter,whose dynamic characteristics are identified by image statistical analysis and proper orthogonal decomposition(POD)analysis.And the fast algorithm based on matrix theory proposed in this paper increases the operation efficiency and operability of POD.With the pilot equivalence ratioΦincrease,the pilot flame gradually shows an unstable state,whose POD energy distribution is significantly different.In the unstable state,the flame dynamics include three modes—spiral motion mode,flame shedding mode,and axial oscillation mode,whose formation reasons have also been further analyzed in combination with the experimental characteristics.And the fast Fourier transform(FFT)analysis of the time coefficients for the first four POD modes indicates all the dominant frequency is 280 Hz,which means the model combustor is in resonance.In addition,a sensitivity analysis based on the different image resolutions further reveals the robustness of the POD method and its optimization direction.These results emphasize the important influence of the pilot fuel flow rate on the stability of the pilot flame.

Optimizationof Design Concept of Construction for Railway Passenger Stations in New Era

The concept of building up a“well-connected fully-integrated,enviomentfriendly,passenger-oriented,economic-efficient,culturally-rich,intelligent and A convenient”station has been being applied to practice in recent years.China State Railway Group Co.Ltd .(hereinafier referred to as CHINA RAILWAY)and the Academyof Arts&Design,Tsinghua University have jointly initiated a series of study projects around the topic of“cultural and artistic expression”aiming to optimize design concepts and explore the design aesthetics of China's railway passenger stations in practice.These projects have achieved some positive results and this paper aims to provide a better analysis of the design concept of railway passenger stations in the new era through ananalysis of those stations' design aesthetic.

Combustion instability of pilot flame in a pilot bluff body stabilized combustor

Combustion instability of pilot flame has been investigated in a model pilot bluff body stabilized combustor by running the pilot flame only. The primary objectives are to investigate the pilot flame dynamics and to provide bases for the study of the interaction mechanisms between the pilot flame and the main flame. Dynamic pressures are measured by dynamic pressure transduc- ers. A high speed camera with CH＊ bandpass filter is used to capture the pilot flame dynamics. The proper orthogonal decomposition （POD） is used to further analyze the high speed images. With the increase of the pilot fuel mass flow rate, the pilot flame changes from stable to unstable state grad- ually. The combustion instability frequency is 136 Hz when the pilot flame is unstable. Numerical simulation results show that the equivalence ratios in both the shear layer and the recirculation zone increase as the pilot fuel mass flow rate increases. The mechanism of the instability of the pilot flame can be attributed to the coupling between the second order acoustic mode and the unsteady heat release due to symmetric vortex shedding. These results illustrate that the pilot fuel mass flow rate has significant influences on the dynamic stability of the pilot flame.

Effect of pressure on the performance of plasma synthetic jet actuator

The effects of the ambient air pressure level on the performance of plasma synthetic jet actuator have been investigated through electrical and optical diagnostics.Pressures from 1 atm down to 0.1 atm were tested with a 10 Hz excitation.The discharge measurement demonstrates that there is a voltage range to make the actuator work reliably.Higher pressure level needs a higher breakdown voltage,and a higher discharge current and energy deposition are produced.But when the actuator works with the maximum breakdown voltage,the fraction of the initial capacitor energy delivered to the arc is almost invariable.This preliminary study also confirms the effectiveness of the plasma synthetic jet at low pressure.Indeed,the maximum velocities of the precursor shock and the plasma jet induced by the actuator with maximum breakdown voltage are independent of the ambient pressure level;reach about 530 and 460 m/s respectively.The mass flux of the plasma jet increases with ambient pressure increasing,but the strength of the precursor shock presents a local maximum at 0.6 atm.