Velocity-based Method Research Articles

Deception Velocity-Based Method to Discriminate Physical Targets and Active False Targets in a Multistatic Radar System

Due to the silent operation of the receiver station in a multistatic radar system, it is difficult for the jammer to generate the cooperative active deception target for the multistatic radar system. Making use of the spatial diversity property, a data level fusion method is proposed to counter the active deception jamming in this paper. According to the spatial correlation difference in physical target and active false target motion states, the deception velocity of the physical target, which is obtained by the radial velocity of each receiver, obeys the Gaussian distribution with zero mean, and the one of the active false target obeys the Gaussian distribution with the mean being its true deception velocity. Based on this fact, the active false target and physical target are discriminated by the deception velocity testing. The proposed deception velocity-based (DVB) method can keep a constant misjudgment probability for physical targets and discriminate active false targets effectively, especially in large deception velocity cases. The simulation verifies the feasibility and validity of the proposed discrimination method. Moreover, the proposed method can be combined with the location information association method to enhance the ability to discriminate the range–velocity joint deception of false targets.

Poster Session II: Investigating photoreceptor function in disease-affected retinas using optoretinography.

Assessing the functional response of photoreceptors is vital in understanding retinal disease progression. Traditional subjective methods like visual acuity and visual fields, and objective ones like electroretinography, have limitations. An ideal complement to these techniques is optoretinography (ORG), which images the retina and tests its function at once. ORG utilizes the phase of the optical coherence tomography (OCT) signal to quantify nanometer-scale changes, measuring subtle photoreceptor responses to stimuli. Efforts to observe stimulus-evoked responses in human cone photoreceptors began with adaptive optics (AO) and common path interferometry, enabling the resolution and tracking of individual cells. Advances in OCT systems with cellular resolution through AO or digital aberration correction successfully measured ORG responses from single cones and rods. This method tracks phase differences between outer segment tips (COST or ROST) and the inner-outer segment junction (IS/OS) to assess individual cell responses. A novel velocity-based method recently demonstrated the feasibility of measuring ORG signals with clinical-grade OCT systems. In the present work, we implemented this technique on disease-affected human retinas, revealing lower magnitudes of response compared to healthy retinas, and highlighting its potential clinical applications.

Free-Weight and Machine-Based Training Are Equally Effective on Strength and Hypertrophy: Challenging a Traditional Myth.

This study aimed to compare the effects of free-weight and machine-based resistance training on strength, hypertrophy, and joint discomfort. Thirty-eight resistance-trained men participated in an 8-wk resistance program allocated into free-weight ( n = 19) or machine-based ( n = 19) groups. Training variables were identical for both modalities, so they only differed in the use of barbells or machines to execute the full squat, bench press, prone bench pull, and shoulder press exercises. The velocity-based method was implemented to accurately adjust the intensity throughout the program. Strength changes were evaluated using eight velocity-monitored loading tests (four exercises × two modalities) and included the relative one-repetition maximum (1RM Rel ), as well as the mean propulsive velocity against low (MPV Low ) and high (MPV High ) loads. Ultrasound-derived cross-sectional area of quadriceps (proximal and distal regions), pectoralis major, and rectus abdominis was measured to examine hypertrophy. Complementarily, Western Ontario and McMaster Universities and Disabilities of the Arm, Shoulder and Hand questionnaires were administrated to assess changes in lower- and upper-limb joint discomfort. Outcomes were compared using ANCOVA and percentage of change (∆) statistics. Each group significantly ( P < 0.001) increased 1RM Rel , MPV Low , and MPV High for both modalities tested, but especially in the one they trained. When considering together the eight exercises tested, strength changes for both modalities were similar (∆ differences ≤1.8%, P ≥ 0.216). Likewise, the cross-sectional area of all the muscles evaluated was significantly increased by both modalities, with no significant differences between them (∆ difference ≤2.0%, P ≥ 0.208). No between-group differences ( P ≥ 0.144) were found for changes in stiffness, pain, and functional disability levels, which were reduced by both modalities. Free-weight and machine-based modalities are similarly effective to promote strength and hypertrophy without increasing joint discomfort.

Uncertainty Estimation for the Brillouin Frequency Shift Measurement Using a Scanning Tandem Fabry-Pérot Interferometer.

The expanded uncertainty of the measured Brillouin scattering shift frequencies is essential in assessing the measurements of parameters of various materials. We describe the general operation principles of a Brillouin light scattering (BLS) spectrometer with a high-power laser and a scanning tandem Fabry-Pérot interferometer (TFPI) for material characterization. Various uncertainty components have been analyzed for the BLS spectrometer following the Guide to the Expression of Uncertainty in Measurement (GUM). The expanded relative uncertainty in the measured Brillouin frequency shift of 15.70 GHz for polymethyl methacrylate (PMMA) was estimated to be 0.26%. The calculated Brillouin frequency shift (based on material properties of PMMA) was determined to be 15.44 GHz with expanded relative uncertainty of 2.13%. It was shown that the measured and calculated Brillouin frequency shifts for PMMA agree within their expanded uncertainties. The TFPI-based BLS spectrometer can be used to measure the longitudinal modulus of materials with an expanded uncertainty of 1.9%, which is smaller than that of the ultrasonic velocity-based method (estimated to be 2.9%).

Adaptations in athletic performance and muscle architecture are not meaningfully conditioned by training free-weight versus machine-based exercises: Challenging a traditional assumption using the velocity-based method.

Although the superior effectiveness of free-weight over machine-based training has been a traditionally widespread assumption, longitudinal studies comparing these training modalities were scarce and heterogeneous. This research used the velocity-based method to compare the effects of free-weight and machine-based resistance training on athletic performance and muscle architecture. Thirty-four resistance-trained men participated in an 8-week resistance training program allocated into free-weight (n = 17) or machine-based (n = 17) groups. Training variables (intensity, intraset fatigue, and recovery) were identical for both groups, so they only differed in the use of a barbell or specific machines to execute the full squat, bench press, prone bench pull, and shoulder press exercises. The velocity-based method was implemented to accurately adjust the planned intensity. Analysis of covariance and effect size (ES) statistics were used to compare both training modalities on a comprehensive set of athletic and muscle architecture parameters. No between-group differences were found for any athletic (p ≥ 0.146) and muscle architecture (p ≥ 0.184) variable. Both training modalities significantly and similarly improved vertical jump (Free-weight: ES ≥ 0.45, p ≤ 0.001; Machine-based: ES ≥ 0.41, p ≤ 0.001) and lower limb anaerobic capacity (Free-weight: ES ≥ 0.39, p ≤ 0.007; Machine-based: ES ≥ 0.31, p ≤ 0.003). Additionally, the machine-based group meaningfully enhanced upper limb anaerobic power (ES = 0.41, p = 0.021), whereas the free-weight group significantly improved the change of direction (ES = -0.54, p = 0.003) and 2/6 balance conditions analyzed (p ≤ 0.012). Changes in sprint capacity (ES ≥ -0.13, p ≥ 0.274), fascicle length, and pennation angle (ES ≤ 0.19, p ≥ 0.129) were not significant for either training modality. Adaptations in athletic performance and muscle architecture would not be meaningfully influenced by the resistance modality trained.

A practical velocity-based method for signal reproduction control in shaking table tests

Accurate reproduction of ground motion time histories with different frequency characteristics is one of the core issues in shaking table tests. Acceleration-based signal reproduction control method (Acceleration-based SRCM), which adopts the acceleration as the primary reference signal for reproducing ground motion time histories, is now widely applied in various shaking table tests. However, due to the performance limitations of the electro-hydraulic system and the low sensitivity of the acceleration signal in the low-frequency band, taking the acceleration as the reference signal may lead to poor reproduction accuracy of ground motions with rich low-frequency components and containing velocity pulses, thus resulting in inaccurate response results of test model systems. To improve the accuracy of the reproduced ground motion in the low-frequency band, a new reproduction control method, Velocity-based SRCM, which adopts the velocity as the reference signal, is explored in this paper, which avoids the high-pass filtering in the acceleration-velocity integration process of the three-variable signal generator. Velocity-based SRCM is tested and compared with Acceleration-based SRCM by the multifunctional shaking table system at Tongji University. The results demonstrated that Velocity-based SRCM improved the accuracy of the low-frequency components below 1.0 Hz in the reproduced signals. Finally, based on the test results, the ground motion intensity and the ratio Tm/Tc are suggested as the identification basis, and a general recommendation for selecting the reproduction method is given.

Velocity-Based Method in Free-Weight and Machine-Based Training Modalities: The Degree of Freedom Matters.

Hernández-Belmonte, A, Buendía-Romero, Á, Pallares, JG, and Martínez-Cava, A. Velocity-based method in free-weight and machine-based training modalities: the degree of freedom matters. J Strength Cond Res 37(9): e500-e509, 2023-This study aimed to analyze and compare the load-velocity relationships of free-weight and machine-based modalities of 4 resistance exercises. Moreover, we examined the influence of the subject's strength level on these load-velocity relationships. Fifty men completed a loading test in the free-weight and machine-based modalities of the bench press, full squat, shoulder press, and prone bench pull exercises. General and individual relationships between relative intensity (%1RM) and velocity variables were studied through the coefficient of determination ( R2 ) and standard error of the estimate ( SEE ). Moreover, the velocity attained to each %1RM was compared between both modalities. Subjects were divided into stronger and weaker to study whether the subject's strength level influences the mean test (mean propulsive velocity [MPV Test ]) and 1RM (MPV 1RM ) velocities. For both modalities, very close relationships ( R2 ≥ 0.95) and reduced estimation errors were found when velocity was analyzed as a dependent ( SEE ≤ 0.086 m·s -1 ) and independent ( SEE ≤ 5.7% 1RM) variable concerning the %1RM. Fits were found to be higher ( R2 ≥ 0.995) for individual load-velocity relationships. Concerning the between-modality comparison, the velocity attained at each intensity (from 30 to 100% 1RM) was significantly faster for the free-weight variant. Finally, nonsignificant differences were found when comparing MPV Test (differences ≤ 0.02 m·s -1 ) and MPV 1RM (differences ≤ 0.01 m·s -1 ) between stronger and weaker subjects. These findings prove the accuracy and stability of the velocity-based method in the free-weight and machine-based variants but highlight the need to use the load-velocity relationship (preferably the individual one) specific to each training modality.

Flow-based method demonstrates improved accuracy for calculating wall shear stress in arterial flows from 4D flow MRI data

Four-dimensional flow magnetic resonance imaging (i.e., 4D flow MRI) has become a valuable tool for the in vivo assessment of blood flow within large vessels and cardiac chambers. As wall shear stress (WSS) has been correlated with the development and progression of cardiovascular disease, focus has been directed at developing techniques to quantify WSS directly from 4D flow MRI data. The goal of this study was to compare the accuracy of two such techniques – termed the velocity and flow-based methods – in the setting of simplified and complex flow scenarios. Synthetic MR data were created from exact solutions to the Navier-Stokes equations for the steady and pulsatile flow of an incompressible, Newtonian fluid through a rigid cylinder. In addition, synthetic MR data were created from the predicted velocity fields derived from a fluid–structure interaction (FSI) model of pulsatile flow through a thick-walled, multi-layered model of the carotid bifurcation. Compared to the analytical solutions for steady and pulsatile flow, the flow-based method demonstrated greater accuracy than the velocity-based method in calculating WSS across all changes in fluid velocity/flow rate, tube radius, and image signal-to-noise (p < 0.001). Furthermore, the velocity-based method was more sensitive to boundary segmentation than the flow-based method. When compared to results from the FSI model, the flow-based method demonstrated greater accuracy than the velocity-based method with average differences in time-averaged WSS of 0.31 ± 1.03 Pa and 0.45 ± 1.03 Pa, respectively (p <0.005). These results have implications on the utility, accuracy, and clinical translational of methods to determine WSS from 4D flow MRI.

On-board Dynamic Measuring of Long-wave Track Irregularity based on Visual Inertial Fusion

This paper studies an inspection method to measure the long-wave track irregularities using the signals of IMU (Inertial Measurement Unit) and Laser & Camera installed on a bogie, which is implemented in comprehensive inspection trains. To reduce the influence of random noise and vehicle vibration, the mechanical structure is optimized; the spatial-dependent change of the "two-point chord" on the track is observed by high-precision FOC (Fiber Optic Gyroscope) and laser camera components; the angular velocity measurement method is deduced. To eliminate high-frequency attenuation of the signal, a sensor fusion algorithm based on the concept of complementary filters is presented. The angular velocity-based method is also used to measure low spatial frequencies, while the acceleration-based method is used to measure high spatial frequencies. The measurement accuracy of the system is evaluated from two aspects: internal and external coincidence accuracy. The test shows that the repeatability accuracy of the system to alignment and profile of the wavelength of 200 m is 0.5 mm and 0.8 mm, respectively, and the trend item and the line design value maintain good consistency.

Strength and Athletic Adaptations Produced by 4 Programming Models: A Velocity-Based Intervention Using a Real-Context Routine.

To compare the strength and athletic adaptations induced by 4 programming models. Fifty-two men were allocated into 1 of the following models: linear programming (intensity increased while intraset volume decreased), undulating programming (intensity and intraset volume were varied in each session or set of sessions), reverse programming (intensity decreased while intraset volume increased), or constant programming (intensity and intraset volume kept constant throughout the training plan). All groups completed a 10-week resistance-training program made up of the free-weight bench press, squat, deadlift, prone bench pull, and shoulder press exercises. The 4 models used the same frequency (2 sessions per week), number of sets (3 per exercise), interset recoveries (4min), and average intensity throughout the intervention (77.5%). The velocity-based method was used to accurately adjust the planned intensity for each model. The 4 programming models exhibited significant pre-post changes in most strength variables analyzed. When considering the effect sizes for the 5 exercises trained, we observed that the undulating programming (mean effect size = 0.88-2.92) and constant programming (mean effect size = 0.61-1.65) models induced the highest and lowest strength enhancements, respectively. Moreover, the 4 programming models were found to be effective to improve performance during shorter (jump and sprint tests) and longer (upper- and lower-limb Wingate test) anaerobic tasks, with no significant differences between them. The linear, undulating, reverse, and constant programming models are similarly effective to improve strength and athletic performance when they are implemented in a real-context routine.

Velocity-based detumbling strategy for a post-capture tethered net system

Tether-net is known as a popular method to actively remove space debris. After successfully capturing a space debris object by a net, a tethered system consisting of a chaser satellite, a main tether and a target is formed. Since the most urgent and important task after capture is to avoid collision between the chaser and the tumbling target, detumbling of the target via the force by the main tether has to be performed. In this paper, we propose a novel and simple detumbling strategy to effectively stabilize the tethered system by controlling the motion of the chaser. Comparing to a previously proposed tension-based detumbling strategy, this newly proposed velocity-based method is simpler and more practical. Moreover, the fuel consumption of the proposed method is only 1% that of the tension-based method for investigated scenarios. With the proposed detumbling strategy, we not only analyze the influence of the system configuration on the detumbling effectiveness, but also analyze the detumbling capability of the method, concluding that the velocity-based detumbling strategy is able to detumble a spinning target up to 1.5 rad/s under a specific configuration. In addition, the proposed method is found to be suitable for both light and massive target detumbling.

Acceleration-based FIR filters for trajectory interpolation with different kinematic constraints and target velocities for NC systems

Motion planning is a critical issue in CAD/CAM manufacturing systems. Many interpolation algorithms based on velocity-based finite-impulse-response (FIR) filters have been proposed to interpolate fast and smooth trajectories, in which the reference trajectories are usually composed of a series of linear segments. Those methods, however, possess two main limitations: first, they can only interpolate trajectories that maintain the same target velocity, i.e., the corner error equations will fail if the target velocities are different around different corners. Second, many systems have different kinematic constraints around different corners, but all of the methods can only process fixed and conservative kinematic constraints. In order to overcome these two limitations, an interpolation algorithm based on acceleration-based FIR filters is proposed. By applying FIR filters to the acceleration base, the motion planning process will comprise several individual convolution processes. The filters and constraints in each convolution process can be designed differently. Therefore, the interpolation algorithm can generate trajectories with different target velocities and kinematic constraints because the taps and types of FIR filters can be changed accordingly during the interpolation process. The experiment results show that, by applying the proposed method to a non-linear kinematic system, more than 10% of motion time is saved when compared to a velocity-based method, the performance of the system can be fully utilized, and efficiency can be markedly improved.

Overestimation and adjustment of Antarctic ice flow velocity fields reconstructed from historical satellite imagery

Abstract. Antarctic ice velocity maps describe the ice flow dynamics of the ice sheet and are one of the primary components used to estimate the Antarctic mass balance and contribution to global sea level changes. In comparison to velocity maps derived from recent satellite images of monthly to weekly time spans, historical maps, from before the 1990s, generally cover longer time spans, e.g., over 10 years, due to the scarce spatial and temporal coverage of earlier satellite image data. We found velocity overestimations (OEs) in such long-span maps that can be mainly attributed to velocity gradients and time span of the images used. In general, they are less significant in slow-flowing grounded regions with low spatial accelerations. Instead, they take effect in places of high ice dynamics, for example, near grounding lines and often in ice shelf fronts. Velocities in these areas are important for estimating ice sheet mass balance and analyzing ice shelf instability. We propose an innovative Lagrangian velocity-based method for OE correction without the use of field observations or additional image data. The method is validated by using a set of ground truth velocity maps for the Totten Glacier and Pine Island Glacier which are produced from high-quality Landsat 8 images from 2013 to 2020. Subsequently, the validated method is applied to a historical velocity map of the David Glacier region from images from 1972–1989 acquired during Landsat 1, 4, and 5 satellite missions. It is demonstrated that velocity overestimations of up to 39 m a−1 for David Glacier and 195 m a−1 for Pine Island Glacier can be effectively corrected. Furthermore, temporal acceleration information, e.g., on basal melting and calving activities, is preserved in the corrected velocity maps and can be used for long-term ice flow dynamics analysis. Our experiment results in the Pine Island Glacier (PIG) show that OEs of a 15-year span can reach up to 1300 m a−1 along the grounding line and cause an overestimated grounding line (GL) flux of 11.5 Gt a−1 if not corrected. The magnitudes of the OEs contained in both velocity and mass balance estimates are significant. When used alongside recent velocity maps of 1990s–2010s, they may lead to underestimated long-term changes for assessment and forecast modeling of the global climate change impact on the Antarctic ice sheet. Therefore, the OEs in the long-span historical maps must be seriously examined and corrected. We recommend that overestimations of more than the velocity mapping uncertainty (1σ) be corrected. This velocity overestimation correction method can be applied to the production of regional and ice-sheet-wide historical velocity maps from long-term satellite images.

A Novel Method for Streamline-Based Tortuosity Calculation and Investigation of Obstacles Shape Effect on Tortuosity in Porous Media with Random Elliptical Obstacles Using Lattice Boltzmann Method

In this research, the lattice Boltzmann method was used to simulate the fluid flow in the random elliptical porous media. Since the tortuosity is one of the most important parameters of porous media and also, the hydraulic tortuosity is more accurate and more realistic than geometric tortuosity, therefore, the hydraulic tortuosity was discussed thoroughly in this study. Contrary to many studies in which the velocity-based method has been used for calculation of tortuosity, one of the novelties in this paper is the application of streamline-based tortuosity including the detailed description of mathematical method for calculation of streamline-based tortuosity and also, the calculation of it numerically and the comparison with velocity-based tortuosity at different porosities and at various aspect ratios. Furthermore, the deviation percentage of velocity-based tortuosity from streamline-based tortuosity was surveyed and depicted. Also, the behavior of streamline-based tortuosity was illustrated as a function of porosity at different aspect ratios and the results were compared with Comiti–Renaud equation and a new equation was proposed. With the structure factor defined as the ratio of porosity to tortuosity, the variation of this quantity with respect to porosity was displayed at different aspect ratios. Also, the formation factor variation versus porosity was discussed at different aspect ratios, too. Finally, the influence of obstacles shape on the tortuosity by varying aspect ratio was investigated and it was concluded that the orientation of elliptical obstacles (vertically or horizontally) has severe effect on the tortuosity.

A comprehensive analysis of the velocity-based method in the shoulder press exercise: stability of the load-velocity relationship and sticking region parameters.

The purpose of this study was threefold: i) to analyse the load-velocity relationship of the shoulder press (SP) exercise, ii) to investigate the stability (intra-individual variability) of this load-velocity relationship for athletes with different relative strength levels, and after a 10-week velocity-based resistance training (VBT), and iii) to describe the velocity-time pattern of the SP: first peak velocity [Vmax1], minimum velocity [Vmin], and second peak velocity [Vmax2]. This study involves a cross-sectional (T1, n = 48 subjects with low, medium and high strength levels) and longitudinal (T2, n = 24 subjects randomly selected from T1 sample) design. In T1, subjects completed a progressive loading test up to the 1RM in the SP exercise. The barbell mean, peak and mean propulsive velocities (MV, PV and MPV) were monitored. In T2, subjects repeated the loading test after 10 weeks of VBT. There were very close relationships between the %1RM and velocity attained in the three velocity outcomes (T1, R2: MV = 0.970; MPV = 0.969; PV = 0.954), being even stronger at the individual level (T1, R2 = 0.973–0.997). The MPV attained at the 1RM (~0.19 m·s-1) was consistent among different strength levels. Despite the fact that 1RM increased ~17.5% after the VBT programme, average MPV along the load-velocity relationship remained unaltered between T1 and T2 (0.69 ± 0.06 vs. 0.70 ± 0.06 m·s-1). Lastly, the three key parameters of the velocity-time curve were detected from loads > 74.9% 1RM at 14.3% (Vmax1), 46.1% (Vmin), and 88.7% (Vmax2) of the concentric phase. These results may serve as a practical guideline to effectively implement the velocity-based method in the SP exercise.

Reinvestigation into railway wheel-track interaction and suspension damage

Without considering either velocity or acceleration effects, the current conventional method presented in literature applies the vertical deflection of a wheel centre caused by a flat defect to the Hertzian contact theory. This method has been numerically and theoretically proved to be inappropriate and can incorrectly predict a higher wheel-rail impact force for a low speed than a high speed. Therefore, under a hypothesis of no wheel bouncing and sliding, two new methods, the velocity-based and the acceleration-based have been proposed. The former method takes the wheel centre deflection change in each computational increment from the Hertzian contact theory while the latter applies the wheel centre acceleration caused by the flat in revolutions to the wheel as a force in dynamic simulation, which interprets the speed effects on impacts precisely. A sensitivity study proves that the velocity-based method is unreliable as opposed to the acceleration-based method. A beam/rigid FE model has also been developed to inspect the wheel-track interaction by performing dynamic analysis in the time domain. It has been found out that the impact responses predicted by the FE analysis and the velocity method are similar and the FE results heavily depend on the compute increment, which implies the FE modelling in ABAQUS may be unreliable for this issue with current applied increments. Finally, the results calculated using the acceleration method have been employed to study the suspension/damper torsional stress caused by a wheel flat. This indicates that a wheel flat may lead to potential fatigue damage if without proper maintenance management.

Realistic Multi-Agent Formation Using Discretionary Group Behavior (DGB)

Simulating groups and their behaviors have been one of the important topics recently. This paper proposes a novel velocity-based method to simulate the realistic behavior of groups moving in a specific formation in a virtual environment including other groups and obstacles. The proposed algorithm, we called “DGB—Discretionary Group Behavior”, takes advantage of ORCA (Optimal Reciprocal Collision Avoidance) half-planes for both grouping and collision avoidance strategy. By considering new half-planes for each agent, we can have more reasonable and intelligent behavior in front of challenging obstacles and other agents. Unlike recent similar works, independent members in a group do not have predefined connections to each other even though they can keep the group’s formation while moving and trying to follow their best neighbors discretionarily in critical situations. Through experiments, we found that the proposed algorithm can yield more human-like group behavior in a crowd of agents.

Longitudinal and transverse dispersion coefficients of 2D contaminant transport model for mixing analysis in open channels

In this study, longitudinal and transverse dispersion coefficients of the two-dimensional advection-dispersion model were calculated using both the velocity and concentration data obtained through tracer tests in large-scale meandering channels. The velocity-based dispersion coefficients calculated by applying the theoretical equations to the velocity data were compared with concentration-based dispersion coefficients that were calculated by applying the routing procedure to the measured concentration curves. The results showed that the cross-sectional averaged values of the dimensionless longitudinal dispersion coefficient, DL/HU∗, calculated from the velocity profile data ranged 4.1–6.5, which corresponded to the theoretical value, whereas DL/HU∗ by concentration data ranged 14.7–35.5, which was 4–6 times larger than the velocity-based coefficient. The cross-sectional maximum values of the dimensionless transverse dispersion coefficient, DT/HU∗, by the velocity-based method ranged 0.1–3.3, whereas DT/HU∗ by concentration-based method was 0.9–2.9. These results revealed that the velocity-based longitudinal dispersion coefficient is a fractional value of the concentration-based result, which contained mixing caused by channel irregularities throughout the reach, in addition to shear dispersion by vertical velocity variations, while transverse dispersion coefficients by both methods represented the same dispersion mechanism which was dominated by the secondary currents developed in highly sinuous channels.

Feasibility of Velocity-Based Method for Transverse Mixing Coefficients in River Mixing Analysis

AbstractThe feasibility of using the velocity-based method for calculating the transverse mixing coefficient of the two-dimensional contaminant transport model was studied to substitute the concent...

Dynamic crushing of cellular materials: a particle velocity-based analytical method and its application

Cellular material under high-velocity impact exhibits a typical feature of layerwise collapse. A cell-based finite element model is employed herein to simulate the direct impact of a closed-cell foam, and one-dimensional velocity field distributions are obtained to characterize the crushing band propagating through a cellular material. An explicit expression for the continuous velocity distribution is derived based on the features of the velocity gradient distribution. The velocity distribution function is adopted to determine the dynamic stress–strain states of cellular materials under dynamic loading. The local stress–strain history distribution reveals that sectional cells experience a process from the precursor elastic behavior to the shock stress state, passing through the dynamic initial crushing state. A power-law relation between the dynamic initial crushing stress and the strain rate is established, which confirms the strain rate effect of cellular materials. By extracting the critical points immediately before the unloading stage in the local dynamic stress–strain history curves, the dynamic stress–strain states of cellular materials are determined. They exhibit loading rate dependence but are independent of the initial impact velocity. Furthermore, with increase of the relative density, the dynamic hardening behavior of the cellular specimen is enhanced and the crushing process event is advanced. The particle velocity-based analytical method is applied to analyze the dynamic responses of cellular materials. This method is better than continuum-based shock models, since it does not require a preassumed constitutive relation. Therefore, the particle velocity-based analytical method proposed herein may provide new ideas to carry out dynamic experimental measurements, which is especially applicable to inhomogeneous materials.