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•Noncontact vibration measurement with high-speed camera and laser speckle projector.•This structured light system allows measuring objects without noticeable features.•Protocol ...successfully applied to measure flat and bent plates with varied surfaces.
3D vision methods are a powerful tool for measuring full-field vibration patterns in the most varied types of surfaces. Digital Image Correlation is typically used to track noticeable features on the surface in order to measure local displacements on the tested system. In this work, a novel randomly structured light system based on laser speckle pattern projection and its calibration procedure are proposed for applying computer vision methods to the measurement of vibration in featureless or reflective objects without modifying them. A simple projector is used based on a laser beam affected by a diffuser element. A stereovision set-up with at least one high-speed camera is used to record video sequences from which the initial shape and evolution of the sample displacement are obtained. The vibration mode behavior of different steel plates are obtained using this full-field vibration measuring technique. The pros and cons of the proposed method are discussed and compared to similar stereovision set-ups.
Abstract Lift coefficient has been evaluated for a subcooled pool boiling system with water as continuous phase and vapor (steam) bubble as dispersed phase generated on vertical walls with constant ...heat flux for a specific Rayleigh number (Ra) range (8x10 12 < Ra < 2x10 13 ) for the first time. Experimental investigation has been done with High Speed Camera while two phase CFD simulations have been performed using Volume of Fluid (VOF) method. The Morton number (M) for this system is log 10 M = -10.6 and Eötvös number (Eo) range is 0.2 < Eo < 1.3 while the shear rates have been maintained in the range 2 ≤ Sr ≤ 2.8. Bubble size of the bubbles arising from the sites on vertical surface have been determined by both experiments and simulations. The CFD predictions for bubble size and lift coefficients agree well with experimental measurements with a deviation of less than 10%. Further, empirical expressions from experimental data for the estimation of bubble size and lift coefficients have also been presented. The data for lift coefficients obtained is different from the ones of bubbles generated by single sparger in air-water systems.
To experimentally investigate the stability of underground excavations under high in situ stress conditions, several rock samples with a mini-tunnel were prepared and subjected to monotonic axial and ...coupled static–dynamic loading until failure. Mini-tunnels were generated by drilling circular or cubic cavities in the centre of granite rock blocks. Strain gauges were used to monitor the deformation of the mini-tunnels at different locations, and a high-speed camera system was used to capture the cracking and failure process. We found that the dynamic crack initiation stress, failure mode and dynamic crack velocity of the specimen all depend on the pre-stress level when the sample is under otherwise similar dynamic disturbance conditions. The crack initiation stress threshold first increased slightly and then decreased dramatically with the increase in the pre-stress value. The specimens were mainly fractured by tensile cracks parallel to the compression line under lower pre-stress, while they were severely damaged with additional shear cracks under higher pre-stress. Furthermore, the propagation velocity of the primary crack was significantly larger than that of the subsequent cracks. The effect of applying different amounts of static pre-stresses on the velocity of the primary tensile crack was similar to that observed for the crack initiation stress threshold; however, it did not affect the velocity of the secondary and subsequent tensile cracks.
Lightning discharges between charged clouds and the Earth's surface are responsible for considerable damages and casualties. It is therefore important to develop better protection methods in addition ...to the traditional Franklin rod. Here we present the first demonstration that laser-induced filaments-formed in the sky by short and intense laser pulses-can guide lightning discharges over considerable distances. We believe that this experimental breakthrough will lead to progress in lightning protection and lightning physics. An experimental campaign was conducted on the Säntis mountain in north-eastern Switzerland during the summer of 2021 with a high-repetition-rate terawatt laser. The guiding of an upward negative lightning leader over a distance of 50 m was recorded by two separate high-speed cameras. The guiding of negative lightning leaders by laser filaments was corroborated in three other instances by very-high-frequency interferometric measurements, and the number of X-ray bursts detected during guided lightning events greatly increased. Although this research field has been very active for more than 20 years, this is the first field-result that experimentally demonstrates lightning guided by lasers. This work paves the way for new atmospheric applications of ultrashort lasers and represents an important step forward in the development of a laser based lightning protection for airports, launchpads or large infrastructures.
The dynamic equations of many continuum and soft robot designs can be succinctly formulated as a set of partial differential equations (PDEs) based on classical Cosserat rod theory, which includes ...bending, torsion, shear, and extension. In this work we present a numerical approach for forward dynamics simulation of Cosserat-based robot models in real time. The approach implicitly discretizes the time derivatives in the PDEs and then solves the resulting ordinary differential equation (ODE) boundary value problem (BVP) in arc length at each timestep. We show that this strategy can encompass a wide variety of robot models and numerical schemes in both time and space, with minimal symbolic manipulation required. Computational efficiency is gained owing to the stability of implicit methods at large timesteps, and implementation is relatively simple, which we demonstrate by providing a short MATLAB-coded example. We investigate and quantify the tradeoffs associated with several numerical subroutines, and we validate accuracy compared with dynamic rod data gathered with a high-speed camera system. To demonstrate the method’s application to continuum and soft robots, we derive several Cosserat-based dynamic models for robots using various actuation schemes (extensible rods, tendons, and fluidic chambers) and apply our approach to achieve real-time simulation in each case, with additional experimental validation on a tendon robot. Results show that these models capture several important phenomena, such as stability transitions and the effect of a compressible working fluid.
•Quantitative and qualitative description of drop impact onto conifer.•Three types of conifers investigated.•Determination of characteristics of droplets formed after water drop impact.•Influence of ...conifer properties on the measured quantities.
A raindrop may encounter various obstacles on its journey and, as a result of impacts, be broken up into smaller droplets. One such naturally occurring obstacle is the above-ground part of plants. This study presents the impact of a precipitation drop on three selected coniferous shoots that differ in morphology: the eastern hemlock (Tsuga canadensis), the blue spruce (Picea pungens), and the Scots pine (Pinus sylvestris). The falling drops came from a generator and had a diameter of 4.2 mm with a kinetic energy of 0.49 mJ. From the high-speed camera footage, the number and size of droplets formed by the breakdown of an incident drop and the angle at which they travelled were determined. The average number of droplets into which an incident drop broke ranged from 74 to 308, with an average diameter of 0.31 to 0.35 mm, and depended on the species of plant on which the incident drop broke. It was also found that, in the case of the eastern hemlock (Tsuga canadensis), the quantities depended on the location of the drop impact (on the branch or the needles). The size and speed of the droplets after breaking affect the quantity of the throughfall and the rate of water evaporation during falling and from the soil and plant surfaces. The characteristics of the breaking of raindrops into small droplets as a result of hitting branches and leaves can improve our understanding of the role that canopy interception plays in the water cycle.
Abstract
In order to study the arming process of electromechanical fuze security mechanism, a dynamic simulation method using ADAMS software is proposed; The simulation model of the security ...mechanism is established, and the existence of complex factors such as contact and collision between the rotor and adjacent components is considered in the calculation process. The time of the horizontal rotor is simulated, and the flexibility and rapidity of the rotor rotation are verified, as well as the reliability of the locking mechanism; The simulation results are compared with the statistical results of high-speed camera test, and the correctness of ADAMS software simulation results is verified.
In the context of setting up a stereo high-speed camera system for accurate 3D measurements in highly dynamic experiments, the potential of a
stereo system is evaluated by testing different camera ...configurations and motion scenarios. A thorough accuracy analysis is performed using spatial rigid-body transformations and relative measurement analyses of photogrammetrically reconstructed surfaces of nondeformable objects. The effects of camera calibration, exposure time, object velocity, and object surface pattern quality on the quality of adjusted 3D coordinates are taken into consideration. While the exposure time does not significantly influence the quality of the static measurements, the results of dynamic experiments demonstrate that not only an insufficient frame rate but also an increased noise level resulting from short exposure times affects 3D coordinate accuracy. Using appropriate configurations to capture dynamic events, the errors in dynamic experiments do not differ significantly from the errors obtained in static measurements. A spatial mapping error of less than 1 μm is obtained through the experiments, with proper testing configurations for an object surface area of 5×20 mm. These findings are relevant for users of high-speed stereo imaging techniques to perform geometric 3D measurements, deformation, and crack analyses.
In table tennis, developing a precise ball-racket rebound model is crucial for predicting the trajectory and spin of a ball after it hits the racket, which is instrumental in racket design and ...enhancing the capabilities of table tennis robots. To this end, accuracy and computational efficiency are two challenges to overcome, which has not been perfectly handled using existing methods such as finite element and simplified rigid-body models. This paper introduces a new model that calculates ball-racket rebounds in two orthogonal directions. Vertically, the collision dynamics are analyzed with the Kelvin-Voigt model, revealing that the contact duration is independent of the incoming ball's velocity. Horizontally, we establish that the restitution coefficient varies as a function of the incident velocity, based on a continuous contact force model and momentum conservation principles. High-speed camera data corroborate these findings and confirm the model's efficacy across diverse conditions. Compared to an established representative model, our method not only maintains high computational efficiency but also improves the accuracy of predicting the ball's linear and angular velocities by an average of 42.72% and 33.77%, respectively, as evidenced by our experimental data.
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