Digital processing of shadowgraph images taking into account the diffraction of light at a shock front

The aim of the study is to determine the shock wave position in experimental shadowgraph images and to evaluate the accuracy by digital image processing. The experimental images were obtained with the shock tube with a rectangular channel. The shadowgraph optical system formed a parallel light beam. It passed through the plane-parallel quartz glasses of the shock tube test section. The process synchronization system at the facility allows registering the shadowgraph images of unsteady flows with shock waves with a high-speed camera or with a single frame camera. The obtained spatial intensity profiles were used to determine the coordinates of gas-dynamic discontinuities at different stages of the flow evolution. shadowgraph patterns were analysed taking into account diffraction at the shock front in case of a laser light source.

Moving computational multi-domain method for modelling the flow interaction of multiple moving objects

This study proposes a method where the flow field variables are communicated between multiple separate moving computational domains and simulates the flow interaction of multiple moving objects. Instead of using the conventional approach with a single fixed computational domain covering the whole flow field, this method advances the moving computational domain (MCD) method in which the computational domain itself moves in line with the motions of an object inside. The computational domains created around each object move independently, and the flow fields of each domain interact where the flows cross. This eliminates the spatial restriction for simulating multiple moving objects. After the results of the shock tube test verify that the interpolation has been achieved between grids, a validation test is conducted in which two spheres are crossed, and the forces exerted on one object due to the other’s crossing at a short distance are calculated. The results verify the reliability of this method and show that it is applicable to the flow interaction of multiple moving objects.

Dynamic Compensation of Piezoresistive Pressure Sensor Based on Sparse Domain

In the process of transient test, due to the insufficient bandwidth of the pressure sensor, the test data is inaccurate. Firstly, based on the projection of the shock tube test signal in the sparse domain, the feature expression of the signal sample is obtained. Secondly, the problem of insufficient bandwidth is solved by inverse modeling of sensor dynamic compensation system based on swarm intelligence algorithm. In this paper, the method is used to compensate the shock tube test signals of the 85XX series pressure sensors made by the Endevco company of the United States, the working bandwidth of the sensor is widened obviously, the rise time of the pressure signal can be compensated to 12.5 μs, and the overshoot can be reduced to 8.96%. The repeatability of dynamic compensation is verified for the actual gun muzzle shock wave test data, the results show that the dynamic compensation can effectively recover the important indexes such as overpressure peak value and positive pressure action time, and the original shock wave signal is recovered from the high resonance data.

Optimization and Experimental Investigation of the Ability of New Material from Aluminum Casting on Pumice Particles to Reduce Shock Wave

Some materials, due to their inherent properties, can be used as shock and wave absorbers. These materials include foam and porous materials, in this study, specimens were made by casting aluminum on porous mineral pumice. Which can replace aluminum foam in some applications with lesser cost, at first, the material is compared with aluminum foam using compression test and quasi-static loading diagram. Which compares the diagrams of these two materials showing the similarity of their behavior in quasi-static loading. Initially, the elastic bending of the walls causes an elastic region in the stress-strain curve of the material. Then, the plastic collapsing of the cells forms a large and relatively smooth region along the elastic and after the plastic collapse of the cells, the area known as foam densification begins where the density of the foam closer to the density of its constituent material causes a sudden increase in the stress level in the specimen. These steps have also been seen in the quasi-static loading of aluminum foam. Then, by using numerical simulations with ANSYS AUTODYN and the shock tube test the ability of these specimens were investigated to reduce the shock wave. The behavior of the material in this case is also very similar to the results of previous studies on aluminum foam.

First Principles Estimation of Shock Tube Tests on Nanoreinforced Composite Materials

Extreme loads events can cause enormous human and infrastructure losses. Computer modeling is the key to reducing the high cost of dynamic monitoring and experimentation. Engineers in various fields have undertaken complicated modeling for structures under abnormal loads. However, an efficient and accurate model is necessary to more rapidly address dangerous shock problems. Composite materials have replaced metals in various applications thanks to their superior shock resistance properties. This investigation particularly relates to their usage on naval ships to achieve improved blast survivability with the additional benefit of lower cost. A relatively simple model is detailed for the approximate centerline response prediction of the specific complex case of composite materials tested in a shock tube. A modal analysis simulation of a beam is performed using gross properties as well as physical geometry and arbitrary shock. Closed form equations have been employed to derive the eigenproblem that generates mode shapes and natural frequencies, and the resulting responses are compared to experimental shock tube test results. The best outcome was generated by the simplest model consisting of a shock pressure pulse averaged in two divisions and applied over the entire beam span. For this case, the simulation and experimental responses had reasonable correlation for fractured E-glass/vinyl-ester composite specimens with both nanoclay and graphite platelet reinforcement. This model is also a conservative estimate for the transient test deflection range for all other specimens.

Experimental Investigation of Two Cylindrical Water Columns Subjected to Planar Shock Wave Loading

Two water columns with identical initial diameters of 4.8 mm were placed 30 mm apart inside a shock tube test section and were loaded by a shock wave of Mach number 1.47 in atmospheric air. The Weber and Reynolds numbers corresponding to these flow conditions are 6900 and 112,000, respectively. Double-exposure holographic interferometry was used to visualize the shock/water columns interaction. The process of the water columns deformation, displacement, and acceleration was well visualized and hence the drag coefficient of shock loaded water columns was evaluated. The front water column behaved virtually the same as a single water column under the same flow conditions. However, the displacement and acceleration of the rear water column was less significant than that of the front one. Hence, its drag coefficient is less. These results show that the front water column has affected the flow field around the rear water column.

Study of Two Cylindrical Water Columns Subjected to Planar Shock Wave Loading

Two water columns with identical initial diameters of 4.8 mm were placed 30 mm apart inside a shock tube test section and loaded by a shock wave of Mach number 1.47 in atmospheric air. The Weber and Reynolds numbers corresponding to these flow conditions are 6,900 and 112,000, respectively. Double exposure holographic interferometry was used to visualize the shock/water columns interaction. The process of the water columns deformation, displacement, acceleration was well visualized and hence the drag coefficient of shock loaded water columns was evaluated. The water column in the front behaved virtually the same as a single water column. However the displacement and acceleration of the rear water column was less significant than that of the front one. Hence its drag coefficient is less. These results show that the frontal water column has affected the flow field around the rear water column.