DDGS HIGH SPEED CAMERA WITH SOME APPLICATIONS

DDGS high speed camera is an improved version of the multispark system. In this system the time delay and the frame interval can be set arbitrarily from 5 mu s to 10000 mu s, and the intervals may be equal or not. The modified spark gaps can provide point flashes that are small enough in size and strong enough in light for both dynamic caustics and dynamic photo-elasticity. In addition, this system can be changed easily to observe the Bow by schlieren method, Thus, this optical system is suitable to investigate many dynamic problems in the fields of solid and fluid mechanics.

Arc Characteristic and Metal Transfer of Pulse Current Horizontal Flux-Cored Arc Welding

In this work, we utilized high-speed video photography to investigate the arc characteristics, metal transfer behavior, and welding spatter of the pulse-current flux-cored arc welding (P-FCAW) process in the horizontal position. The results indicate the presence of a stable “flux pole” during both the pulse-on and pulse-off periods when the mean current ranged from 140 to 170 A. The existence of this “flux pole” was beneficial for droplet transfer in the “axial droplet transfer” mode. With respect to welding spatter, with an increase in the welding current, we observed three kinds of spatter—explosive spatter, rebounded droplet spatter, and scattering spatter. With an increase in the pulse current from 310.6 to 345.6 A, the deflection of the arc reduced from 30.4° to 16.6°, which positively influenced the arc rigidity, particularly in the horizontal position. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

Effect of Space Charge on the Propagation Path of Air Gap Discharge

The existence of space charge may be addressed as one of the reasons that could cause shielding failure of transmission lines. In order to study the effect of space charge on discharge propagation path, a new experimental system, including mainly DC high voltage generator, impulse voltage generator as well as rod-plane electrode, has been established. The space charge was generated around the rod by means of pre-applying DC high voltage, and the air gap dis- charge experiments were conducted with and without pre-applying DC high voltage, respectively. Meanwhile, high speed cameras worked simultaneously from the front and lateral side to record the discharge propagation path so as to obtain the curvature. After statistical analysis, it is shown that the curvature increases in the middle and lower portions of the propagation path when the effect of space charge is taken into account.

Formation Mechanism and Size Prediction of Bubble in Opposite-Flowing T-Shaped Microchannel

Bubble formation in an opposite-flowing T-shaped microchannel with 40 μm in depth and 120 μm in width was real-time visualized and investigated experimentally by means of a high speed camera. N2 bubbles were generated in glycerol-water mixtures with different concentrations of surfactant sodium dodecyl sulfate (SDS). And the images were captured by the high speed camera linked to a computer. Results indicated that the bubble formation process can be distinguished into three consecutive stages, i.e., expansion, collapse and pinching off. The bubble size decreases with the increase of liquid flow rate and viscosity of liquid phase as well as the decrease of gas flow rate. The surface tension of the liquid phase has no measurable influence on the bubble size. Moreover, a new approach to predicting the size of bubbles formed in the T-shaped microchannel is proposed. And the predicted values agree well with the experimental data.

Center of rotation estimation for rocket nozzle by infrared reflective makers and image sequences

The determination of an accurate center of rotation of rocket motor nozzle or other object to be measured is of great interest across a wide range of applications,such as rocket,missile,robotics,industry,spaceflight,aviation and human motion analysis fields,particularly for clinical gait analysis.A new approach was proposed to estimate the moving objects' instantaneous center of rotation and other motion parameters.The new method assumes that the two segment of object to be measured are rigid body which rotates around a center of rotation between each other relatively.The center of rotation varies with time in the global coordinate system but is fixed in the local coordinate system attached to each segment.The models of rocket motor nozzle and its movement were established.The arbitrary moving object's corresponding to motion equations were deduced,and the least square closed-form solutions of the object's motion parameters were figured out.It is assumed that the two high speed CCD cameras mounted on the 750 nm infrared(IR) filter are synchronized and calibrated in advance.The virtual simulation experiment using 3D coordinates of markers was conducted by synchronized stereo image sequences based on 6-DOF motion platform and the experimental results prove the feasibility of our algorithm.The test results show that the precision of x,y,z component on center of rotation is up to 0.14 mm,0.13 mm,0.15 mm.

Three-dimensional motion parameters estimation from stereo image sequences based on infrared reflective markers

In this paper,an innovative 3D motion parameters estimation method from stereo image sequences based on infrared(IR) reflective markers is presented.It was assumed that two high speed CCD cameras had been calibrated previously.The method consists of the following steps:1) the coordinate of several markers and depth map for each stereo pair was determined from the sequences of stereo images by relations of markers' coordinate the correspondence between markers was established,2) the 3D motion parameters of the target was computed based upon the matched markers' coordinate,and 3) translated 3D motion parameters estimation into the problem of least square according to the movement model of the object to be measured.Without using line,curve or corner correspondence,this method can calculate the depth of these markers feature easily and quickly in contrast to traditional approaches.The two CCD cameras work on 200 f/s,and each processing cost time is about 3 ms.It was found that,by using several markers and a large number of stereo images,this method can improve the computational speed,robustness and numerical accuracy of the motion parameters in comparison with traditional methods.The virtual simulation experiment was conducted using synthesized stereo image sequences based on 6-DOF motion platform and the experimental results proved the validity of our approach and showed that the translation and rotation precision is up to 0.1 mm and 0.1°.

Simulation and Calibration of Hydro-Debris 2D Model （HD2DM） to Predict the Particle Segregation Processes in Debris Flow

The principal aim of a vertical two-dimensional numerical model development is for estimating the particle tracing and mechanism of 10 mm and 2.5 mm debris. The particle tracing movement can be visually analyzed by using a high speed video camera （HSVC）. A numerical model was developed using the Marker and Cell Method, which involves a Subgrid-Scale （SGS） model and the Particle Source in Cell （PSI-Cell） Method. The transportation processes of debris and air bubble were simulated in lagrangian form by introducing air bubbles and debris markers. Air bubble movement characteristics were simulated by this numerical model. Bigger particles flow at the upper part, while smaller particles attach near to the bottom. This phenomenon is similar to what we observed in the experimental studies. As a conclusion, the calibration processes for velocity was successful. The value of virtual mass （CM） was found to be one of the most important criteria that should be considered in the calibration process, as this parameter dominates fundamental characteristics of sediment particle movement in the lagrangian numerical scheme. The best fitted CM in this study was 0.35. The mean average velocity value ranging from 1.2% to 22.61% is obtained from the velocity results of numerical studies compared to the experimental studies.

An approach for ergonomic design of mouse wheel

A new method for ergonomic design of a computer mouse is proposed in this paper. In the method, the movements of joints and tip of the forefinger during operating a mouse was captured by a high-speed video camera. The captured videos were ana- lyzed and an algorithm was developed to decide the size and location of the mouse wheel according to ergonomic principles. The al- gorithm was then coded in a software package with Visual C＋＋ and OpenGL languages. Results of the calculation and simulation agreed well with those of the experiments. The software can also be used for shape design of mouse body, buttons and their layouts.

Close-range optical measurement of aircraft's 3D attitude and accuracy evaluation

A new screen-spot imaging method based on optical measurement is proposed, which is applicable to the close-range measurement of aircraft＇s three-dimensional （3D） attitude parameters. Laser tracker is used to finish the global calibrations of the high-speed cameras and the fixed screens on test site, as well as to establish media-coordinate-frames among various coordinate systems. The laser cooperation object mounted on the aircraft surface projects laser beams on the screens and the high-speed cameras synchronously record the light-spots＇ position changing with aircraft attitude. The recorded image sequences are used to compute the aircraft attitude parameters. Based on the matrix analysis, the error sources of the measurement accuracy are analyzed, and the maximum relative error of this mathematical model is estimated. The experimental result shows that this method effectively makes the change of aircraft position distinguishable, and the error of this method is no more than 3′ while the rotation angles of three axes are within a certain range.

Experimental Study of the Gas Triggered Switch's Breakdown by Optical Measurement

In this paper the main technical data of the high speed camera(HSFC-PRO),components of gas triggered switch and the primary experimental results of the breakdown of gas triggered switch using high speed camera are introduced.Four photographs totaling in 24 nanoseconds in single trigger mode manifest that the breakdown consists of two phases,which are the breakdowns of the trigger electrode with positive and negative electrode successively. This phenomenon is consist with the electric field distribution simulation result with the help of the software ANSYS. Eight photographs in double trigger mode prove that the breakdown time of the gas triggered switch is above 10.5 microseconds.The elementary results show that high speed camera is a very efficient apparatus to study the discharge characteristics.This optical measuring technique is helpful to profoundly study the breakdown of high voltage switch. More studies and experiments would be continued in future.

Cavitation bubbles collapse characteristics behind a convex body

Cavitation bubbles behind a convex body were experimentally studied by a high speed camera and a hydrophone synchronously. The experiments were conducted in a circulating water tunnel with five various contraction ratios： β = 0.497, β= 0.6, β= 0.697, β= 0.751, and β= 0.799. The distributions of the cavitation bubble collapse positions behind the five different convex bodies were obtained by combining the images taken by the high speed camera. According to the collapse positions, it was found that no cavitation bubble was collapsed in the region near the wall until the ratio of the water head loss over the convex body height was larger than 20, which can be used to predict if the cavitation damage would occur in the tunnel with orifice energy dissipaters.

Flow structures and hydrodynamics of unsteady cavitating flows around hydrofoil at various angles of attack

This paper investigates the unsteady structures and the hydrodynamics of cavitating flows. Experimental results are presented for a Clark-Y hydrofoil fixed at ？= 0？, 5？ and 8？, for various cavitation numbers, from subcavitating flow to supercavitation. The high-speed video camera and the particle image velocimetry（PIV） are applied to observe the transient flow structures. Statistics of the cavity lengths, the velocity and vorticity distributions, as well as the turbulent intensities are presented to quantify the unsteady process. Meanwhile, the dynamic measurement system is used to record the dynamic characteristics. The experimental results show that the flow structures and the hydrodynamics of the cavitation vary considerably with various combinations of angles of attack and cavitation numbers. Under various conditions, the cavitation can be generally grouped as the inception cavitation, the sheet cavitation, the cloud cavitation and the supercavitation. The cloud cavitation exhibits noticeable unsteady characteristics. Experimental evidence indicates that the hydrodynamics are clearly affected by the cavitating flow structures, the amplitude of the load fluctuation is much higher in the cloud cavitating cases.

Experiment and analysis of potato-soil separation based on impact recording technology

In order to discover the damage mechanism and improve separation performance in the separation process of potato-soil mixture,the experiment was conducted on an in-house test-bed.The impact recording device and high-speed camera technology were employed in order to obtain the instantaneous dynamics of the potato-soil mixture for detail data analysis.Five vibration intensities were defined according to the vibration frequency and amplitude.It was found that the mean number of impacts and maximum impact acceleration increased significantly as the level of vibration intensity rose.As a result,the separation performance increased significantly,however,the bruising rate also increased to a certain extent.The mathematical relationship between the maximum impact acceleration and the factors of interest,including vibration amplitude,the vibration frequency and the operating speed of the separation sieves was established through the response surface experiment.It was demonstrated that the presented model was capable to reflect the degree of the factors on influencing bruising rate and separation performance.According to the significance on the maximum impact acceleration,the factors of interest were given in a descending order with vibration frequency,vibration amplitude,running speed of the separation sieve.A set of the optimum operating parameters were found to achieve a desired separation performance as follows,the vibration amplitude was 34.1 mm,the vibration frequency was 5.24 Hz,the running speed of the separation sieve was 2.05 m/s;where the maximum impact acceleration was 98.62 g,the relative error was 3.23%,the bruising rate was 1.81%and the separation performance was 98.5%.The presented model can potentially provide a technical reference for further investigation of the separation mechanism and development of measures for reducing the loss of separation.