Changes In Average Velocity Research Articles

Magnetorheological semi-active shock mitigation control. Part I: numerical analysis and preliminary tests

Minimizing shock loads transmitted to sensitive structures or equipment is the objective of shock mitigation control. The core of shock mitigation control using magnetorheological (MR) energy absorber (EA) to minimize impact load is to make full use of the piston stroke of MREA so as to achieve “soft-landing.” The key lies in the precise description of the hysteresis of MREA and the shock mitigation control method. In this part, a single-degree-of-freedom (SDOF) shock mitigation control system using MREA is established, and the corresponding dynamic model and drop-induced shock mitigation test system are established. Based on the optimal Bi number control method and constant force control theory, feedforward controllers featuring resistor-capacitor (RC) operator-based hysteresis model and Bingham model are established to realize “soft-landing” in sequence. Specific performance evaluation indexes for shock mitigation control systems, that is, average velocity change rate (AVCR) and velocity-acceleration conversion ratio (V-ACR), are proposed. The effectiveness of shock mitigation control methods with different models on the MREA-based shock mitigation control system in profiles of simulation and tests are compared and analyzed.

Basic data visualization in vintage seismic profiles: Indications for the interpretation of the ViDEPI database (offshore Puglia, southern Italy)

The Visibility of Petroleum Exploration Data in Italy (ViDEPI) project represents a freely accessible valuable resource for the research community. However, seismic profiles available from this project present several limitations because information such as the basic shape of the seismic wavelets and the seismic polarity are not available. In this study, using subsurface (i.e., 2D seismic profiles) data related to the Marine Zones B, D and F (offshore Puglia) a review of the basic pulse shape and polarity of seismic wavelets, as well as the shape and polarity of principal reflectors has been addressed. Moreover, borehole data (i.e., lithology and sonic logs) have been used to identify abrupt average velocity changes linked to different lithostratigraphic successions recorded as dominant high-amplitude reflectors.

Magnetorheological semi-active shock mitigation control: Part II: System extension and application analysis

In Part I of this work, the dynamic model of drop-induced shock mitigation based on magnetorheological (MR) energy absorber (EA) was deduced. The shock mitigation control effectiveness of constant force control method and optimal Bi number control method were compared based on Bingham model and resistor-capacitor (RC) operator-based hysteresis model. In this part, to further explore the possibility of the application of MREA in the shock mitigation control system, a single-degree-of-freedom (SDOF) shock mitigation control system is built with MREA connected in parallel with a coil spring, which is then connected in series with a vehicle tire to build a one-fourth vehicle suspension shock mitigation control system. Next, the constant force control method and optimal Bi number control method are extended to the SDOF shock mitigation control system. Based on the concept of the optimal Bi number, a two-degree-of-freedom (2DOF) optimal Bi number control method applied to the one-fourth vehicle suspension system is proposed by decoupling and recoupling the damping and stiffness of the vehicle suspension system. Using the control methods conducted in Part I, the motion state of the drop-induced shock mitigation process is simulated and analyzed. The control performances of the control methods in the SDOF shock mitigation control system are compared. Besides, the average velocity change rate (AVCR) and velocity-acceleration conversion ratio (V-ACR) are used to evaluate the effectiveness and stability of the control methods. Finally, the conclusion that the 2DOF optimal Bi number control method can effectively realize the shock mitigation control of a one-fourth vehicle suspension system is verified.

Failure Mechanism and Optimization of Throttle Valve Based on Computational Fluid Dynamics

Throttle valve is an important device in well control manifold. In the process of field use, the valve seat and plug of the valve often have corrosion failure, which brings serious potential safety hazards to the well control work. Using the three-dimensional flow field analysis software of computational fluid dynamics (CFD), it is found that the velocity on the left wall is greater than that on the right. The field failure investigation also proved that the erosion damage mainly occurred on the left wall of the throttle valve, which verified the failure causes of the throttle valve core and valve seat. In addition, the flow field of the erosion resistance device is numerically simulated. The results show that under the given boundary conditions, when the fluid passes through the inlet and outlet of the erosion resistance device, the average velocity changes little. It is known from the velocity curve that under a certain flow rate, the smaller the overflow area is, the greater the velocity is, which is consistent with the hydrodynamic control equation. From the velocity curve data on the alloy head, it is found that the velocity changes little and tends to be horizontal, and the surface velocity of the alloy head is relatively flat, which shows that the fluid velocity on the wall can be effectively reduced after adding the stab prevention short section, so as to reduce the erosion on the wall.

Detailed space–time variations of the seismic response of the shallow crust to small earthquakes from analysis of dense array data

SUMMARYWe compute high-resolution space–time variations of subsurface seismic properties from autocorrelation functions (ACF’s) of noise and local earthquakes, recorded by the Sage Brush Flat dense array deployed around the Clark branch of the San Jacinto fault. The resolved temporal changes are referred to as apparent velocity changes because they reflect both nonlinear response and variations of material properties such as cracking and damage. Apparent velocity changes are estimated at four frequency bands (10–15, 10–20, 15–30 and 20–40 Hz) for two local earthquake data sets. In one analysis, ACF’s from P- and S-wave windows of 31 small events with magnitudes below 3.1 are used to compute the apparent velocity variations with respect to the mean ACF of each phase, and we also use the mean ACF of noise data as reference to estimate the changes. In a further analysis, the temporal evolution of properties is computed using moving time windows in continuous waveform over one-hour long data with noise and earthquake signals. The apparent velocity changes and recovery times are frequency dependent and present a strong spatial variability across the array. The resolved changes are larger and recovery time shorter with data associated with higher frequencies. At frequencies larger than 15 Hz, and using the mean ACF of noise data as a reference, the apparent average velocity changes across the array during the passage of the P and S waves from the small local events are 2.5 per cent and 6 per cent, respectively. The apparent velocity changes decrease by one order of magnitude when the earthquake data are used as a reference. The relatively large changes in response to very low ground motion have important implications on nonlinear processes involving degradation and healing of the subsurface material during common earthquake shaking.

Experimental study of change of average velocity in a drop on crystalization

The behavior of convection dynamics during high-temperature heating inside a drop of an aqueous solution of LiBr salt at the moment of crystalline-hydrated crust movement was studied experimentally. To measure the instantaneous velocity fields in the horizontal section of a sedentary drop, the optical PIV method was used. The measurement of convection velocity in a drop through a thick crust of crystalline hydrates did not affect the accuracy of measurements. The maximum average velocity UAv is equal to 0.39-0.42 mm/s was realized at the initial time. Over 30-35 s the temperature gradient decreases due to heating of the solution by 3.5 times which led to a decrease in UAv by 3-4 times. After 32 s heat transfer and evaporation enter quasi-stationary mode.

Numerical Simulation of Velocity Field around Two Columns of Tandem Piers of the Longitudinal Bridge

This research explores the effects of different spans of two columns of tandem piers on the characteristics of x-velocity near the river bed based on computational fluid dynamics (CFD) simulations. With a span shorter than 27.5D (D is the diameter of piers), the shape and the lateral range of the x-velocity increases with the increase of distance downwards the x-direction. For the area between the tandem piers and the wall, the VRi/VR1 (the ratio of the x-velocity at the i-th row to the x-velocity of the first row in each model) near the wall increases up to 1.26. For the area between the two columns of tandem piers, the profile of VRi/VR1 changes from a “∩-shape” to an “M-shape” in each model. RAVC (average velocity change ratio) of different spans increases gradually and tends to be stable with the increases of the span. The largest RAVC is about −17.66% with a span of 0.52 m. The RMV (the ratio of the maximum x-velocity among piers in each row in different models to the maximum x-velocity of the two piers arranged side by side) of piers in the first row of different models is around 0.95. The RMV becomes 0.82 at the second pier in each model when the span is shorter than 27.5D, and increases to 0.91 if the span is longer than 27.5D. If the span is longer than 27.5D, the RMV of different piers are close to each other from the 2nd pier to the last one.

CURRENT PROBLEMS AND PERSPECTIVES OF COMPUTER SIMULATION OF CONTINUOUS STEEL CASTING

Nowadays we can see increase in using of engineering analysis systems in the field of continuous steel casting simulation due to their high accuracy and convergence with industrial experiments results. Such powerful systems as «ANSYS» and «ProCast» allows solving gas-, hydrodynamic and thermal problems, the parallel interaction of which constitutes the essence of most metallurgical processes. Group of authors from the LSTU Chair “Metallurgical technology” have successfully carried out computer experiments in tundish and continuous casting mold processes simulation. The experiments were aimed at first, on studying of further improving in liquid steel flow modifiers (partitions, turbo-stops, thresholds) design, at second, on influence of argon blowing regime on liquid steel flow parameters in the 50-ton tundish workspace, and, at third, on influence of submerged nozzles design on the liquid steel flow in crystallizer, assuming deterministic-dynamic operation mode. The results of calculations are velocity fields of liquid steel flow and flow temperatures fields in tundish and crystallizer, as well as temperature fields in the tundish refractory lining. An equation of primary flow average velocity change on exit from submerged nozzle was also formulated. These preliminary results allow us to assess the velocity changes and direction of the melt flow and formation of volumes with different melt temperatures when using flow modifiers in the ladle, including using of “argon curtain” in the casting chamber. Obtained data on melt flow motion and on location of erosion spots in crystallizing «crust», also on the presence of temperature gradient zones in various regions of crystallizer workspace may be useful to practice engineers engaged in choice of crystallizer submerged nozzle design. Effective control of melt flow in tundish and in crystallizer allows significant improvements in continuous cast slabs and rolled products quality in context of reducing metal products rejection due to defects associated with slag or nonmetallic inclusions presence and due to cracks formed as the result of insufficient thickness of crystallized «crust».

Effects of deceleration-focused exercise strategies on shoulder range of motion and throwing velocity in baseball and softball athletes

ABSTRACT This study examined the effects of deceleration-focused exercises on shoulder range of motion and throwing velocity in both softball and baseball players. Volunteers included 28 Division III William Paterson University baseball and softball athletes (18 females and 10 males), who were evenly distributed across two groups both undertaking 14 sessions of either resistance band or handheld medicine ball exercises (band vs. ball group). A pre-test and post-test measured participants’ best active internal/external shoulder rotation and best throwing velocity at a target 40 ft away. A two-tailed, independent t-test showed no significant differences in velocity, internal rotation or external rotation (p < 0.01) between the band and ball groups. However, the average change in velocity in the ball group was double that of the band group (1.50 ± 2.06 m/s versus 0.73 ± 2.24 m/s). For change in both internal and external rotation the band group (2.86 ± 5.27° and 3.29 ± 3.87°, respectively) was greater than the ball mean (1.93° ± 3.32° and 1.29 ± 6.52°, respectively). These findings suggest that overhead athletes aiming to increase throwing velocity can benefit from performing deceleration training with weighted balls whereas resistance bands appear to improve shoulder rotation.

Bulbar conjunctival microvascular responses in dry eye

PurposeConjunctival microvascular responses may be a surrogate metric of efferent neural pathway function innervating the ocular surface as changes in blood flow occur within seconds after a stimulus. As somatosensory dysfunction may partially underlie dry eye (DE), in this study we evaluate whether bulbar conjunctival microvascular alterations correlate with various aspects of DE. MethodsFifty-six DE patients were prospectively recruited from a Veterans Affairs ophthalmology clinic over an 11-month period. DE symptoms and ocular pain were assessed along with DE signs. A novel functional slit lamp biomicroscope (FSLB) was used to image the temporal bulbar conjunctiva from the right eye before and after central corneal stimulation with an air puff. Blood flow velocities were measured and noninvasive microvascular perfusion maps (nMPMs) were created. ResultsThe bulbar blood flow velocity was 0.50 ± 0.15 mm/s at baseline and increased to 0.55 ± 0.17 mm/s after stimulation (P < 0.001); the average change in velocity was 0.05 ± 0.09. nMPMs values and venule diameter, on the other hand, did not significantly increase after stimulation (1.64 ± 0.004 at baseline, 1.65 ± 0.04 after stimulation, P = 0.22 and 22.13 ± 1.84 μm at baseline, 22.21 ± 2.04 μm after stimulation, P = 0.73, respectively). Baseline blood flow velocity positively associated with Schirmer scores (r = 0.40, P = 0.002). Those with higher self-rated wind hyperalgesia demonstrated less change in blood flow velocity (r = −0.268, P = 0.046) after air stimulation on the central cornea. ConclusionConjunctival blood flow velocity, but not vessel diameter or complexity, increases after wind stimuli. Baseline flow positively correlated with Schirmer scores while change in flow negatively correlated with self-reported wind hyperalgesia.

Monitoring Velocity Changes Caused By Underground Coal Mining Using Seismic Noise

We use passive seismic interferometry to monitor temporal variations of seismic wave velocities at the area of underground coal mining named Jas-Mos in Poland. Ambient noise data were recorded continuously for 42 days by two three-component broadband seismometers deployed at the ground surface. The sensors are about 2.8 km apart, and we measure the temporal velocity changes between them using cross-correlation techniques. Using causal and acausal parts of nine-component cross-correlation functions (CCFs) with a stretching technique, we obtain seismic velocity changes in the frequency band between 0.6 and 1.2 Hz. The nine-component CCFs are useful to stabilize estimation of velocity changes. We discover correlation between average velocity changes and seismic events induced by mining. Especially after an event occurred between the stations, the velocity decreased about 0.4 %. Based on this study, we conclude that we can monitor the changes of seismic velocities, which are related to stiffness, effective stress, and other mechanical properties at subsurface, caused by mining activities even with a few stations.

Comparison of pregnant and non-pregnant occupant crash and injury characteristics based on national crash data

The objective of this study was to provide specific characteristics of injuries and crash characteristics for pregnant occupants from the National Automotive Sampling System/Crashworthiness Data System (NASS/CDS) database for pregnant women as a group, broken down by trimester, and compared to non-pregnant women. Using all NASS/CDS cases collected between the years 2000 and 2012 with at least one pregnant occupant, the entire pregnant data set included 321,820 vehicles, 324,535 occupants, and 640,804 injuries. The pregnant occupant data were compared to the characteristics of NASS/CDS cases for 14,719,533 non-pregnant females 13–44 years old in vehicle crashes from 2000 to 2012. Sixty five percent of pregnant women were located in the front left seat position and roughly the same percentage of pregnant women was wearing a lap and shoulder belt. The average change in velocity was 11.6mph for pregnant women and over 50% of crashes for pregnant women were frontal collisions. From these collisions, less than seven percent of pregnant women sustained MAIS 2+ injuries. Minor differences between the pregnant and non-pregnant occupants were identified in the body region and source of injuries sustained. However, the data indicated no large differences in injury or crash characteristics based on trimester of pregnancy. Moreover, the risk of an MAIS 2+ level injury for pregnant occupants is similar to the risk of injury for non-pregnant occupants based on the total vehicle change in velocity. Overall this study provides useful data for researchers to focus future efforts in pregnant occupant research. Additionally, this study reinforces that more detailed and complete data on pregnant crashes needs to be collected to understand the risk for pregnant occupants.

Time‐lapse monitoring of velocity changes in Utah

AbstractThe Eastern part of the Basin and Range, extending to the Wasatch fault region, is an actively deforming region characterized by varieties of extensive features and prominent seismicity along the intermountain seismic belt. The present‐day deformation of the intermountain seismic belt and the eastern Basin and Range province motivates an interest in continuous monitoring of the region. In this study we monitor time‐lapse velocity changes within Utah and eastern Nevada using coda waves generated by repeatable explosions. This monitoring characterizes velocity changes within the region from June to September of 2007. We observe, both temporally and spatially, variable velocity changes within the monitored region, with a maximum path average velocity change of 0.2%. This suggests a significant change in the velocity within the region given the short monitoring duration. Correlation of the temporal variation of the average velocity change with strains derived from GPS‐detrended displacements suggests that the velocity change might be driven by the broad deformation within the monitored region.

Monitoring the Effect of Race-Analysis Parameters on Performance in Elite Swimmers

Time trials are commonly used in the lead-up to competition. A method that evaluates the relationship between time trial and competition performance in swimming would be useful for developing performance-enhancement strategies. To use linear mixed modeling to identify key parameters that can be used to relate time-trial and competition performance. Ten swimmers participated in the study. Each swimmer was analyzed during 3 time trials and 1 competition. Race video footage was analyzed to determine several key parameters. Pooling of strokes and distances was achieved by modeling changes in parameters between time trials and competition within each subject as linear predictors of percent change in performance using mixed modeling of log-transformed race times. When parameters were evaluated as the effect of 2 SD on performance time, there were very large effects of start time (2.6%, 90% confidence interval 1.8-3.3%) and average velocity (-2.3%, -2.8% to -1.8%). There was also a small effect for stroke rate (-0.6%, -1.3% to 0.2%). Further analysis revealed an improvement in performance time of 2.4% between time trials and competition, of which 1.8% (large; 1.4-2.1%) was due to a change in average velocity and 0.9% (moderate; 0.6-1.1%) was due to a change in start time; changes in remaining parameters had trivial effects on performance. This study illustrates effective analytical strategies for identifying key parameters that can be the focus of training to improve performance in small squads of elite swimmers and other athletes.

Influnce of the external force on the directed transport of feedback-coupled Brownian ratchet

The directed transport performance of two coupled Brownian particles in the double-well ratchet potential under the external force has been studied in this paper. Langevin equation in the overdamped regime is solved numerically. The influence of the external force, the thermal noise, and the asymmetric parameter of the potential on the transport properties of the coupled Brownian particles including the average velocity, the effective diffusion coefficient Deff , and the Pe number, is discussed in detail. It is found that the average velocity changes periodically under the external force. Meanwhile, there is an optimal value of the intensity of the thermal noise at which the current reaches the maximum. It is worthwhile to point out that the enhancement of the current can be achieved by changing the structure of the ratchet potential.

Flow resistance in alluvial channels

There have been numerous fluvial studies of flow resistance in alluvial channels during the last few decades. Significant progress has been made towards predicting flow resistance (and therefore velocity) for a given discharge. These past applications rely heavily on the characterization of particle sizes and the effects of changing relative submergence on flow resistance estimates. Different types of equations have been shown to provide reasonably good estimates in specific environments. Major difficulties arise from characterizing mobile beds, bed topography and its evolution and how these factors control rates of change of average velocity as discharge rises along a given river reach. Different issues can be recognized as a function of the spatial and temporal scales of investigation. A case can made that more emphasis should be placed upon reach-scale investigations. Detailed studies of bed topography, its maintenance, its evolution (at the reach scale) and its interactions with macroturbulence structure and sediment transport would ultimately provide valuable information and improved knowledge on both flow resistance processes and applications (predictions). Moreover, technological means now allow detailed characterization of bed topography and flow fields of large river systems. Such promising avenues should be further pursued with the goal of providing not only a better understanding of flow-bed-sediment transport interactions in large river systems but also a better understanding of flow stage variations, flood hazards, flow resistance estimates and therefore partitioning of depth and velocity as discharge rises along major river systems.

Improving the mechanism of smoothing packet traffic type bucket tokeniv

For the implementation of adaptive control mechanism for redistributing bandwidth packet switch between the ports you need to create the structure of the physical mechanism for smoothing the flow of packets, which would be able to sync changes the width of their bands with changes in average velocity smoothed flows. Based on the mechanism of smoothing algorithm was taken «buckets tokeniv»

Students' mathematical modeling of motion

AbstractWe present results of an investigation of university students' development of mathematical models of motion in a physical science course for preservice teachers and graduate students in science and mathematics education. Although some students were familiar with the standard concepts of position, velocity, and acceleration from physics classes, most students had difficulty using these concepts to characterize actual or hypothetical motions. Furthermore, some students developed their own nonstandard method of describing accelerated motion in terms of changes in the average velocity, from the start of the motion up to a given time. This is in contrast to the physics community's use of the acceleration construct, defined in terms of changes in the instantaneous velocity, to describe such motion. Although the change in average velocity is not typically identified as an important construct in traditional physics texts, some students found it intuitively appealing, and were able to use it successfully to describe and predict motion. We conclude that by focusing on standard constructs, and ignoring possible intuitive ways that students might view motion, standard kinematics instruction may miss an opportunity to maximize student understanding. © 2007 Wiley Periodicals, Inc. J. Res. Sci. Teach 45: 153–173, 2008.

Characteristics Of Butterfly Stroking Skill In Elite Swimmers Detected By Means Of A Speed Meter

A speed meter that measures a subject's moving velocity by pulling a fine wire over a generator (Maglischo, 2003) for a distance of 25m was developed for use with competitive swimmers. In our previous study, the authors used the speed meter to check for skill differences between competitive breaststroke swimmers of international achievement and collegiate breaststroke swimmers who had not reached national or international levels. The results showed that this method was useful for identifying differences in skill between the two groups of swimmers. PURPOSE: In this study the authors applied the speed meter to the butterfly stroke in order to study the skills of elite swimmer. METHODS: Subjects were four male competitive butterfly stroke swimmers, i.e., one who had reached international level (ranked 3rd in the world in 2006), and three who had reached the national but not international level. The velocity curves were compared among these swimmers. The wire line of the speed meter was attached to swimmers by means of a belt and their intracyclic velocity changes were recorded precisely for several stroke cycles while swimming at maximum speed. The average velocity changes for one stroke cycle were calculated with data from all successive stroke curves. The average stroke cycles were compared among the four subjects. RESULTS: Four propulsive phases were picked up from each average stroke cycle. They were as follows; 1) first kick phase, 2) insweep phase, 3) upsweep and second kick phase, and 4) wave phase (during the arm recovery). Average velocities during each phase were compared among the four swimmers. In consequence, no significant differences were observed between three national level swimmers for all phases. Additionally, there were no significant differences among four swimmers for first kick phase, insweep phase, and wave phase. However, for upsweep and second kick phase, a significantly higher average velocity was observed for the international level swimmer compared with the other swimmers (Steel-Dwass Test, p<0.05). CONCLUSIONS: It was suggested that improvements in butterfly stroke for elite swimmers were dependent upon improving average velocity during the upsweep and second kick phase.

The Role of Beam Flexibility and Ground Contact Model in the Clattering of Deformable Beams

It has been shown in previous research that, relative to (the usually considered case of) a single impact, multiple impacts (clattering) of rigid casings can greatly enhance the probability of failure of fragile components mounted on or inside them. This paper addresses the important issues of the roles of casing flexibility and contact model in the above situation. A finite element analysis of clattering of a Timoshenko beam is carried out here. Dependence of the maximum change in average velocity due to impact, on the beam stiffness and coefficient of restitution, are studied here.