Instantaneous Motion Research Articles

Image Motion of Remote Sensing Camera With Wide Field of View Over the Antarctic and Arctic

Imaging by the remote sensing camera with a wide field of view (WFV) is of great significance in the issue of polar environment. However, the instability of the image motion velocity poses a huge challenge to the observation task since the direction of the earth's rotation velocity keeps changing in the polar regions. The edge blur of polar image by the camera with the WFV is usually ignored. Therefore, a specific theoretical model that the camera images over the polar region is supposed to describe the instability distinctly. Mathematical expressions of the image motion velocity field are obtained with a novel method of velocity projection and coordinate transformation. The quantitative analysis of simulation reveals that the increasing anisotropy of the instantaneous image motion velocity field gets most significant near the poles. The value of modulation transfer function at the edge of the field of view decreased by 0.33%, which results in a discrepancy of sharpness in an image. The model is capable of explaining the edge blur, of the image from BNU-1, which provides a theoretical basis for the image motion compensation strategy of cameras with the WFV.

A novel experimental method for in situ strain measurement during selective laser melting

ABSTRACT Selective laser Melting (SLM), a powder bed-based additive manufacturing technology, has been developed and applied in multiple industrial fields in the last decade. However, the distortion and swelling in the SLM process resulting from thermal stress cannot be predicted subject to measurement. In this work, an in situ distortion measurement system applied to the SLM process is presented. The distortion behaviour of component under laser scanning can be precisely recorded in real-time by this system. The detailed evolution and driving force of specimen distortion in the SLM process are discussed based on the experimental results. The distortion in single laser scanning presents a strong instantaneous upward motion of the central section during laser heating and a relatively slow downward recovery motion of the central section during cooling. The distortion behaviour of the sample with and without a layer of metal powder are compared, and laser scanning on the bare sample surface leads to a significantly higher residual distortion. The influence of SLM parameter variables (such as scanning speed, laser power, scanning width, layer thickness and scanning times) on SLM distortion is also analysed. At last, the stress distribution of laser melting is verified by the high-resolution EBSD analysis.

Drag on Janus Sphere in a Channel: Effect of Particle Position

Abstract Potential use of Janus spheres in novel engineering applications is being explored actively in recent years. Hydrodynamics around Janus spheres is different from that around homogeneous sticky or slippery spheres. Instantaneous motion of a sphere in channel flow is governed by hydrodynamic force experienced by the sphere, which in turn depends on the particle to channel size ratio, its instantaneous position, hydrophobicity of its surface, and the particle Reynolds number. We investigate numerically the drag experienced by a Janus sphere located at different off-center positions in a square channel. Two orientations of Janus sphere consisting of a sticky and a slippery hemisphere with the boundary between them parallel to the channel midplane are studied: (1) slippery hemisphere facing the channel centerline and (2) sticky hemisphere facing the channel centerline. The flow field around Janus sphere is found to be steady (for Re ≤ 50 investigated in this work) and asymmetric. Based on the data obtained, a correlation for drag coefficient as a function of particle Reynolds number and dimensionless particle position is also proposed.

Evaluation of gas- and particle-phase separation methods for velocity measurements in turbulent multiphase flows

Two previously established and commonly used methods for separating gas and dispersed particle phases in images are evaluated and directly compared for the first time. Median filtering and subtraction (MFS; Kiger and Pan in J Fluids Eng 122:811, 2000) and two-parameter filtering (TPF; Khalitov and Longmire in Exp Fluids 32:252, 2002) are assessed using both synthetic and experimental data over a broad range of operating conditions to identify limitations in the applicability of the phase-separation methods in deriving instantaneous velocity fields, statistics, and derivative quantities such as vorticity. Both methods are applied to synthetic data containing a controlled number of objects (small tracers and large particles) with defined sizes and evaluated to determine how the methods alter the targeted phases in terms of objects lost and the addition of erroneous artifacts. Subsequently, PIV software is used to determine the effects of the phase separation-induced errors on the tracer images in terms of the derived gas-phase velocities. Both methods return results with sub-pixel PIV errors, with MFS slightly more accurate than TPF. The methods also are evaluated with experimental data from a turbulent multiphase jet. Both MFS and TPF reproduce the bulk (mean) gas-phase velocity, but fail to accurately estimate smaller-scale motions, producing mean error in the velocity fields as high as 25–30%. The errors are observed to be largely independent of large particle concentration indicating that the largest source of error is the direct alteration of the tracer images through the phase separation process. Significant errors are noted in instantaneous velocity fields and gradient quantities such as vorticity, with the MFS results being particularly unreliable. While TPF was shown to be more accurate, the processing time for TPF is several thousand times longer than MFS for the experimental images, limiting its applicability. The results indicate that low-order statistics may be recovered using the two phase-separation approaches, but resolving instantaneous turbulent motion of the continuum phase and fluid-particle interactions may not be possible with the phase-separation approaches.

Potential -flow and CFD investigations of bow-flare slamming on a container ship in regular heading waves

This study numerically and experimentally investigates the ship motions and slamming pressures of a 10,000 TEU container ship in regular heading waves. A modified Stavovy–Chuang model that considers the influence of the wave–ship encounter time and asymmetric rolling motions is proposed as the potential-flow method to solve symmetric and asymmetric flare slamming calculations. Instantaneous ship motions from a nonlinear six degree of freedom unified model are adopted to simulate the pressure. The ship flare–wave encounter time determines the duration of the slamming. The commercial software STAR CCM+ is utilised for computational fluid dynamics (CFD) simulations of the slamming and motions. The modified Stavovy–Chuang model, CFD technology, and segmented model tests are used for the first time to predict asymmetric slamming accompanied by parametric rolling. Empirical formulas for various classification society rules are adopted for the cross-validation of the symmetric impact forces. In conclusion, the occurrence of slamming is dominated by the normal impact velocity and the relative positions of the ship and waves. The duration of the slamming, especially under parametric rolling conditions, mainly depends on the rolling period and encountering wave. Under parametric rolling conditions, the magnitude of the slamming pressure decreases and the impact duration increases as the wavelength increases. In simulations of symmetric slamming, only the duration increases as the wavelength increases, and the American Bureau of Shipping and International Association of Classification Societies results are similar to the test results.

Relative Motion in the Hierarchical Triple System ADS48 on the Basis of Gaia DR2 and 26-Inch Refractor of Pulkovo Observatory Data

Abstract—According to the exact positions and proper motions of the three components of the star ADS48 from Gaia DR2, their parallax and radial velocities for the epoch 2015.5 the instantaneous relative positions and motions of the components were determined. Only from the Gaia DR2 observations, the family of orbits of the AB pair was calculated by the method of apparent motion parameters, from which those that best agree with the Pulkovo data were selected. Comparison with the first observations of the 19th century made it possible to independently estimate the sum of the masses of the components in the range 1.15 < MA + B < 1.4 M⊙. The orbits of the outer pair were calculated: with a minimum period of 79 × 103 years and the most probable one—about 3 × 105 years. It is concluded that the system is stable for the most probable value of the relative− radial velocity ∆Vr = 0.7 km s–1 and may be unstable near the boundaries of the possible velocity difference. A detailed analysis of homogeneous Pulkovo observations revealed a disturbance with a period of 11 years. It is shown that this disturbance is associated not with a star, but with a periodic climatic process that changes the observation conditions. Comparison of instantaneous and average relative motion does not exclude the presence of a planetary mass satellite in one of the components.

Numerical study on turbulent dispersion of diesel sprays under ultrahigh injection pressure using large eddy simulation

ABSTRACT The modern diesel engines equipped with an advanced fuel injection system up to ultrahigh injection pressure of 300 MPa are under development at present. The impact of injection pressure on fuel spray characteristics such as spray penetration and spray cone angle has been widely concerned in previous studies. However, it is still lack of the detailed investigation on the turbulent dispersion of small droplets produced by a high-pressure injector due to the limited capability of optical diagnostic techniques to simultaneously measure the two phases. Droplet dispersion due to turbulence plays a major role in high-velocity fuel spray mixing and combustion processes involving group evaporation of droplets. Thus, the effect of different injection pressures on droplet dispersion in nonevaporating diesel sprays was investigated using the Euler-Lagrange framework with large eddy simulation (LES) implemented in an open-source code OpenFOAM. Size-dependent instantaneous radial motion and dispersion characteristics of droplets dominated by large-scale turbulent structures within a polydisperse downstream spray were analyzed in detail. Results show that increasing injection pressure can modestly promote the radial dispersion of most droplets with diameter of 2 ~ 12 µm further downstream at the late stage of injection. This could be the result of the increasing interaction time of droplets with larger turbulent structures due to the increase of spray penetration with increasing injection pressure. However, increasing injection pressure has no significant impact on the strength of droplet-turbulence interaction in terms of slip velocity between droplet and gas phases and this could be quantitatively explained by the droplet Stokes number (St) estimated in this study. The most droplets with 0.1 < St < 10 tend to move and concentrate further radially outward, leading to droplet clustering. Thus, the effect of injection pressure on droplet-turbulence interaction is much less than its influence on droplet size for high-velocity fuel sprays, indicating that the ultrahigh injection pressure has much less important impact on the spatial inhomogeneity of droplet distribution than its influence on the evaporation rate of individual droplets.

In the Eye of the Storm: Echocardiographic Particle Image Velocimetry Analysis in a Patient with Takotsubo Syndrome.

Echo particle imaging velocimetry (Echo PIV) is a contrast-echo-based technique, used to evaluate the instantaneous vortical blood motion into the left ventricle (LV). Here, we report, for the first time, echo-PIV findings in a patient with Takotsubo syndrome (TTS). Vortex behavior suggested that TTS might present with peculiar PIV characteristics, including relatively preserved intra-ventricular pressure gradient and energy dissipation. Further studies are needed to elucidate whether the preservation of a more physiological vortex behavior could be related to the structural and functional recovery observed in TTS.

Action representation and recognition through temporal co-occurrence of flow fields and convolutional neural networks

Many applications require action recognition skills, from human-machine interaction to intelligent video surveillance. Action recognition in video sequences cannot be based on simply processing raw color images or optical flow fields. Color images provide appearance information of moving objects, but lack motion features. They are also very sensitive to variations due to clothing and camera pose that badly affect the action recognition accuracy. In turn, raw optical flow measures instantaneous motion, not the overall dynamics of actions, and is sensitive to noise. More robust and meaningful motion features and classifiers are thus required for action recognition to be reliable. This paper proposes a new action recognition technique based on a deep convolutional neural network (CNN) fed with Histograms of Optical Flow Co-Occurrence (HOF-CO) motion features. HOF-CO is a robust motion representation previously proposed by the authors to encode the relative frequency of pairs of optical flow directions computed at each image pixel. Experimental results show that this approach outperforms state-of-the-art action recognition methods on three different public datasets KTH, UCF-11 Youtube and HOLLYWOOD2.

Numerical Prediction of the Vertical Responses of Planing Hulls in Regular Head Waves

The evaluation of the hydrodynamic performance of planing vessels has always been one of the most attractive study fields in the maritime agenda. Resistance and self-propulsion studies have been performed using experimental and numerical methods by researchers for a long time. As opposed to this, the seakeeping performance of planing hulls is assessed with 2D approximation methods, but limitedly, while the experimental campaign is not cost-effective for several reasons. With this motivation, pitch and heave transfer functions and accelerations were obtained for a monohedral hull and a warped hull using a state of art commercial Reynolds-averaged Navier–Stokes (RANS) solver, in this study. Moreover, 2-DOF (degree of freedom) dynamic fluid–body interaction (DFBI) equations were solved in a coupled manner with an overset mesh algorithm, to find the instantaneous motion of the body. After verification, obtained numerical results at three different Froude numbers and a sufficiently large wave frequency range were compared with the experiments. The results showed that the employed RANS method offers a very accurate prediction of vertical motions and accelerations for planing hulls.

High-resolution wide-field OCT angiography with a self-navigation method to correct microsaccades and blinks.

In this study, we demonstrate a novel self-navigated motion correction method that suppresses eye motion and blinking artifacts on wide-field optical coherence tomographic angiography (OCTA) without requiring any hardware modification. Highly efficient GPU-based, real-time OCTA image acquisition and processing software was developed to detect eye motion artifacts. The algorithm includes an instantaneous motion index that evaluates the strength of motion artifact on en face OCTA images. Areas with suprathreshold motion and eye blinking artifacts are automatically rescanned in real-time. Both healthy eyes and eyes with diabetic retinopathy were imaged, and the self-navigated motion correction performance was demonstrated.

Portland Cement-TiO2 triboelectric nanogenerator for robust large-scale mechanical energy harvesting and instantaneous motion sensor applications

Abstract The cement-based triboelectric nanogenerator (TENG) was developed for the first time to harvest mechanical energy. With the use of TiO2 nanoparticles as a filler material at 0.2%wt in Portland cement, the cement-TiO2 nanocomposite can generate high electrical output under a vertical contact-separation mode, which was three times higher than the pristine cement TENG. The maximum power density of 265 mW/m2 can be achieved. In addition, the fabricated TENG can detect a motion force as small as 0.6 N under finger touching. The high performance of the fabricated TENG is due to the enhanced dielectric property of cement-TiO2 nanocomposite. The TiO2 nanoparticles are also found to improve the mechanical strength of cement by increasing compressive strength approximately 1.3 times of that of ordinary Portland cement. Moreover, the cement-TiO2 TENG prepared by mechanical mixing resulted in superior energy conversion efficiency compared to those prepared by ball milling technique. The cement with a small amount of TiO2 nanomaterials with improved energy harvesting performance and mechanical property can be used directly as a base for construction material. Together with the ease of fabrication, the developed cement-based TENGs are thus a good potential for upscaling to a robust large-scale mechanical energy harvesting and a motion sensor application.

Dynamics and bifurcation of passive tracers advected by a ring of point vortices on a sphere

We consider the dynamics of a passive tracer, advected by the presence of a latitudinal ring of identical point vortices. The corresponding instantaneous motion is modeled by a one degree of freedom Hamiltonian system. Such a dynamics presents a rich variety of behaviors with respect to the number of vortices, N, and the ring’s co-latitude, θo—or, equivalently, its vertical position qo = cos θo. We carry out a complete description of the global phase portrait for the cases N = 2, 3, 4 by determining equilibrium points, their stability, and bifurcations with respect to the parameter θo, and by characterizing the separatrix skeleton. Moreover, for N ≥ 5, we prove the existence of a value of bifurcation θoN such that when θo = θoN (θo = π − θoN, respectively) the south (north, respectively) pole becomes a N-bifurcation point, i.e., a symmetric web of N centers and N saddles bifurcates from the corresponding pole.

Predicting Protein Functional Motions: an Old Recipe with a New Twist

Large macromolecules, including proteins and their complexes, very often adopt multiple conformations. Some of them can be seen experimentally, for example with x-ray crystallography or cryo-electron microscopy. This structural heterogeneity is not occasional and is frequently linked with specific biological function. Thus, the accurate description of macromolecular conformational transitions is crucial for understanding fundamental mechanisms of life’s machinery. We report on a real-time method to predict such transitions by extrapolating from instantaneous eigen motions, computed using the normal mode analysis, to a series of twists. We demonstrate the applicability of our approach to the prediction of a wide range of motions, including large collective opening-closing transitions and conformational changes induced by partner binding. We also highlight particularly difficult cases of very small transitions between crystal and solution structures. Our method guarantees preservation of the protein structure during the transition and allows accessing conformations that are unreachable with classical normal mode analysis. We provide practical solutions to describe localized motions with a few low-frequency modes and to relax some geometrical constraints along the predicted transitions. This work opens the way to the systematic description of protein motions, whatever their degree of collectivity. Our method is freely available as a part of the NOn-Linear rigid Block (NOLB) package.

A Prediction Model of Cutting Force about Ball End Milling for Sculptured Surface

Cutting force prediction is very important to optimize machining parameters and monitor machining state. In order to predict cutting force of sculptured surface machining with ball end mill accurately, tool posture, cutting edge, contact state between cutter, and workpiece are studied. Firstly, an instantaneous motion model of ball end mill for sculptured surface is established. The instantaneous milling coordinate system and instantaneous tool coordinate system are defined to describe the position and orientation of tool, and the transformation matrix between coordinate systems is derived. Secondly, by solving three boundaries around engagement of cutter and workpiece, a cutter-workpiece engagement model related to tool posture, milling parameters, and tool path is established. It has good adaptability to the variable tool axis relative to the machining surface. Finally, an algorithm of thickness about an instantaneous undeformed chip is researched, and a prediction model of cutting force is realized with microelement cutting theory. Also, the model is suitable for sculptured surface machining with arbitrary tool posture and feed direction. The accuracy of the proposed prediction model was verified by a series of experiments.

Screw Theory-Based Motion/Force Transmissibility Analysis of High-Speed Parallel Robots With Articulated Platforms

Abstract Motion/force transmissibility is an essential property reflecting the kinematic performance of parallel robots. Research on this performance of the single-platform parallel robots (SPPRs) has long been concerned and studied. In contrast, although many innovations and applications of the high-speed articulated-platform parallel robots (APPRs) have been presented, few studies on their motion/force transmissibility have been reported. This paper deals with the motion/force transmissibility analysis of high-speed parallel robots with articulated platforms. A modified output transmission index (MOTI) for the high-speed parallel robots with articulated platforms is proposed based on a newly defined concept of equivalent transmission wrench screw. Furthermore, by having an insight into the instantaneous relative motion inside the mobile platform, a medial transmission index (MTI) is proposed to evaluate its internal motion/force transmissibility. Based on these foundations, the local transmission index (LTI) is redefined as the minimum value of the input, modified output, and medial transmission indices. Under the framework of the above performance indices, motion/force transmissibility analysis of two typical high-speed articulated-platform parallel robots, i.e., Heli4 and Par4, are presented. The proposed indices are excepted to be applied to the optimal design of high-speed parallel robots with articulated platforms.

Two-phase flow measurement of sub-millimeter sized particles falling in water with grid-generated turbulence

Sediment transport is one key process in sedimentation problems. The dynamics of sediments in rivers will lead to an ecological change of the catchment. Among all complicated processes in sediment transport, the settling dynamics of solid particles in the water contribute to the water quality and geomorphology of a river channel directly. This paper aims at an investigation of the interaction between particle movement and water flow, with application to hydro-environment situations such as transport of fine sand sediment in natural streams. The Stokes number in this type of application is much smaller than unity at which enhancement of particle settling velocity by strong ambient turbulence has been observed in many numerical and laboratory studies. The present laboratory study is conducted to study the settling of sub-millimeter sized heavy particles in water with a relatively weak grid-generated turbulence. The two-phase flow is measured with the whole-field imaging techniques of particle image velocimetry (PIV) and particle tracking velocimetry (PTV). A two-camera PIV/PTV technique is used to obtain the instantaneous settling velocities of the solid particles and the turbulent water velocity field. Phase separation is based on an effective optical distinction of the two light scattering signals with fluorescent tagging on the solid particles. With this technique, it is found that in most cases of grid-generated turbulence the settling velocity of the heavy particles is slightly lower than the still water value. The falling heavy particles are also found to cause additional turbulence in the water with low ambient turbulence intensities. At one particular case of grid turbulence, the particles are found to fall with a depth-averaged settling velocity evidently higher than the still water value. The instantaneous turbulent fluid motions and particle trajectories tend to support the fast tracking effect to be related to the higher particle falling velocities.

Effects of wave-field nonlinearity on motions of ship advancing in irregular waves using HOS method

The effects of incident-wave nonlinearity on motions of ships advancing in irregular waves are investigated here in statistical sense. The study is carried out by exploiting the combination of HOS method (High Order Spectral method) and time-domain Rankine source method incorporated with HOBEM (Higher-order Boundary Element Method). In the proposed model, HOS method is employed to simulate nonlinear irregular wave fields in cubic order and Rankine source method incorporated with HOBEM is applied to compute ship wave potential as well as disturbed potential, the equations of motions of ship advancing with constant forward speed in nonlinear waves are further established. Instead of employing simplified steady flow models such as uniform stream, steady ship wave potential is computed beforehand and applied to solve ship motions. Weakly nonlinear scheme considering nonlinear F–K (Froude-Krylov) and restoring forces is adopted.The proposed model is first validated in the case of linear regular and irregular waves via comparisons to experiment data and then applied to three different irregular sea states defined by spectrum with respective BFIs (Benjamin-Feir index). A series of long-time numerical simulations are carried out for both linear wave cases and nonlinear ones, and the statistical properties of nonlinear incident waves and the induced influence on ship motions are investigated and further analyzed. The analysis reveals that with large BFI, the skewness and kurtosis of wave surface elevation manifest departures from Gaussian values and the probability density function (p.d.f.) of the surface elevation performs departures from Gaussian behavior. In nonlinear cases, p.d.f. of instantaneous motions and motion amplitudes as well as exceedance probability of motion amplitudes are notably different from their linear counterparts. Higher possibilities for large motions occur in nonlinear cases.

STA-CNN: Convolutional Spatial-Temporal Attention Learning for Action Recognition.

Convolutional Neural Networks have achieved excellent successes for object recognition in still images. However, the improvement of Convolutional Neural Networks over the traditional methods for recognizing actions in videos is not so significant, because the raw videos usually have much more redundant or irrelevant information than still images. In this paper, we propose a Spatial-Temporal Attentive Convolutional Neural Network (STA-CNN) which selects the discriminative temporal segments and focuses on the informative spatial regions automatically. The STA-CNN model incorporates a Temporal Attention Mechanism and a Spatial Attention Mechanism into a unified convolutional network to recognize actions in videos. The novel Temporal Attention Mechanism automatically mines the discriminative temporal segments from long and noisy videos. The Spatial Attention Mechanism firstly exploits the instantaneous motion information in optical flow features to locate the motion salient regions and it is then trained by an auxiliary classification loss with a Global Average Pooling layer to focus on the discriminative non-motion regions in the video frame. The STA-CNN model achieves the state-of-the-art performance on two of the most challenging datasets, UCF-101 (95.8%) and HMDB-51 (71.5%).

Experimental study on the cavity dynamics of oblique impact of sphere on a viscous liquid floating on water

Oblique water entry of marine structure involves complex hydrodynamics phenomena including splash formation, asymmetrical cavity and pinch-off that have been observed in previous systematic experiments. However, very few studies focus on such phenomena induced by oblique impact of object in a two-layer liquid system. In this paper, we present an experimental investigation of oblique entry of a sphere into a deep pool of water within a layer of highly viscous dimethicone floating on the water. In the experiment, a high speed digital camera is established to obtain the instantaneous cavity and motion trajectories for both qualitative and quantitative analysis. The results show that the upper-layer viscous liquid introduces a significant change in the splash formation mechanism and the special behaviors are characterized by stratified splash and corresponding asymmetrical shrinkage structures. Meanwhile, it is observed that the difference in splash characteristics caused by different thicknesses of viscous fluid layer is obvious, and the pinch-off depth is independent of the thickness value which studied in our experiments. In addition, it is found that increasing the horizontal impact velocity will cause a delay in the splash closure and the vertical displacement of the sphere during the dimethicone-water enter process is independent of the horizontal impact velocity. Hydrodynamic force model is established to explain the trajectory of the sphere. Furthermore, the splash angle, pinch-off depth, pinch-off time and the water entry depth at pinch-off locations and the corresponding change tendency are obtained qualitatively and quantitatively. These results indicate that the dimethicone layer is critical in determining the cavity dynamics, especially splash formation and pinch-off characteristics.