High Velocity Range Research Articles

Modelling for a new mechanical passive damper and its mathematical analysis

To improve ride comfort, an oil damper should restrain its damping force in a high-velocity range. A lot of dampers with such properties were developed. For example, the one controlling the flux of oil by a leaf valve is widely adapted and reasonable. However, it is difficult to represent its dynamics with a simple mathematical model, and the cost of a computational fluid dynamics is too expensive. To overcome the disadvantages, the first author in [15] developed the other mechanical oil damper with sub-pistons instead of the leaf valve, which enabled us to propose a simple mathematical model with linear ordinary differential equations, thanks to the simple mechanism to control the oil flow. In this article, we give a more detailed mathematical model for the damper taking the dynamic pressure resistance into account, which is represented by nonlinear ordinary differential equations. In addition, a numerical scheme for the model is also proposed and its mathematical analysis such as the validity of the numerical solutions is shown.

Marine fishes experiencing high-velocity range shifts may not be climate change winners.

Climate change is driving the global redistribution of species. A common assumption is that rapid range shifts occur in tandem with overall stable or positive abundance trends throughout the range and thus these species may be considered as climate change 'winners'. However, although establishing the link between range shift velocities and population trends is crucial for predicting climate change impacts it has not been empirically tested. Using 2,572 estimates of changes in marine fish abundance spread across the world's oceans, we show that poleward range shifts are not necessarily associated with positive population trends. Species experiencing high-velocity range shifts seem to experience local population declines irrespective of the position throughout the species range. High range shift velocities of 17 km yr-1 are associated with a 50% decrease in population sizes over a period of 10 yr, which is dramatic compared to the overall stable population trends in non-shifting species. This pattern, however, mostly occurs in populations located in the poleward, colder, portion of the species range. The lack of a positive association between poleward range shift velocities and population trends at the coldest portion of the range contrasts with the view that rapid range shifts safeguard against local population declines. Instead, our work suggests that marine fishes experiencing rapid range shifts could be more vulnerable to climatic change and therefore should be carefully assessed for conservation status.

Experimental study of the behavioral response of fish to changes in hydrodynamic indicators in a near-natural environment

The large-scale construction of hydropower projects has significantly altered the ecohydrological conditions of fish habitats, and habitat, migration and other behavior of fish have been affected to varying degrees. Although the behavioral characteristics of fish under different hydrodynamic conditions have been investigated in a number of indoor experiments, it is still difficult to apply the results of hydrodynamic indicators directly to the practice of ecological restoration. In order to investigate the response relationship between fish behavior and hydrodynamic indicators under near-natural conditions, and to clarify the structural linkage of multiple influences between the external ecological environment, external behavior and internal changes of fish, the study relies on a large ecological test site in which the flow rate of the rivers can be changed. A low-frequency radio identification device was used in several monitoring sections in the test river to monitor the behavioral trajectories of fish in real time. The study shows that the method of fish behavior tracking based on passive integrated transponder (PIT) tags is feasible in small near-natural rivers. The test fish were more active under a low flow rate and changed their upstream trajectory in response to flow changes. When the flow velocity reached 1.6–1.8 m/s, the fish upstream gradually shifted from along the mainstream direction to along the shoreline. There was no significant difference in the activity of the test fish between day and night, with fish preferring to inhabit areas of low flow velocity and low turbulent kinetic energy. There was a range of high flow velocities (1.6–1.8 m/s) and high turbulent kinetic energy (0.1–0.15 m2/s2) that stimulated the swimming behavior of the fish. In addition, the physical indicators and physiological and biochemical indicators of fish were also included in the research scope. The test fish with high activity were slender after long-term swimming training, and their hemoglobin concentration and red blood cell number were higher than those of inactive fish and cultured fish. The research results will be used to optimize river restoration projects, promote the recovery of fish resources and population size, and reduce the negative impact of hydropower projects on the ecological environment.

Experimental investigation of hail impacts over a wide range of high velocities

In the presented work, high velocity hail impact tests have been conducted on an instrumented rigid target. The synthetic hails, consisting of ice spheres with a nominal diameter of 48 mm and a mass between 50 and 55 g conditioned to temperatures in the range of -3, -20 and -50 °C were accelerated using a gas gun. The range of impact velocities was 46–314 m/s leading to maximal impact energies between 2000 and 3000 J which had not been investigated so far in the literature. Peak force and time to reach the peak force where extracted from the experimental tests. The obtained results were compared with results from the literature using empirical equations established in another publication from the literature. The obtained results confirm the trend reported in the literature in terms of dimensionless peak force versus dimensionless impact velocity. However, the dimensionless time to reach the peak force during the impact could not be compared successfully with previous results. The role of the target characteristics is estimated to be the reason for this difference.

Three-dimensional Tidal Dynamic Characteristics and Tidal Current Energy Evaluation in the Southern Sea Area of Hainan Island

Tidal current energy is a kind of marine renewable energy. It has broad application prospects. In this paper, a three-dimensional tidal current numerical model was established, and the model was verified by the measured data of the tide level station. Based on the numerical model, the tidal current feature and tidal current energy distribution were accurately simulated and analyzed in the southern sea area of Hainan Island. The results showed that the annual average velocity of the current was evenly distributed among the space in the study area. But the annual cumulative time of typical velocity in different sea areas was different in space. C2 had more accumulative time for the low-velocity range (<0.4m/s) of the surface, while C1 had more accumulative time for the low-velocity range (<0.3m/s) of the water depth of 8.5m. C3 sea area had more accumulative time in the high-velocity range at the surface (0.4~2.0m/s) and water depth of 8.5m (>0.3m/s). And the area with the highest annual average tidal current energy density at the water depth of 8.5m was C3, which is up to 128.40w/m2. C2 sea area had the smallest energy, only 62.63w/m2. Compared with C1 and C2 sea areas, the C3 area should be developed emphatically when developing tidal current energy resources in this sea area.

Numerical Simulation of High-Speed Rotor for Air-cooled Eddy Current Dynamometer

The key feature of air-cooled dynamometer is the geometry of the rotor, which played a vital role in effective heat rejection. Dual application is limited for air cooled eddy current dynamometer due to excessive heat generation when the operating speed is up to a certain range. The aim of this research is to observe the air flow pattern and temperature distribution on the rotor of the air-cooled dynamometer with different geometry designs. In addition, the air flow and heat transfer simulation were carried out by using ANSYS software. Besides, the setting of normal size mesh was proposed in all design cases to reduce the computational time and the mesh files size of the simulation. Furthermore, a total of four configurations of rotating domain were designed and created using SolidWorks software, with each one differentiated with the features of holes and cover. The results of air flow velocity contour were compared with those of without the cover and holes on the rotor design. The optimum design in air motion distributed within all cases of numerical simulation were then observed and compared. To validate the simulation setup, experimental data were used to validate the airflow and heat transfer coupling simulation models. The results revealed that an improvement with more air volume movement can be observed at medium range and high velocity range for all models with cover features over the models without cover. Besides, the results also shows that the influences of hole features on air flow velocity were less significant as compared to the one with cover features. Also, the rotor design with cover and without holes were found to be the best configuration as it allows the as high as 27.7% greater air flow dynamic to achieved lowest steady state temperature as compared with those of baseline design. The Design C also improved in term of temperature as compared to the simple model of plane rotor, with as high as 11.6% reduction in overall temperature. Through the results of this analysis, it was justifiable that the Design C can be suggested as the best-case scenario for further experimental study. These results will serve as a basis for rotor design to improve the performance of the air-cooled eddy current dynamometer.

Independent Component Analysis Filter for Small Vessel Contrast Imaging During Fast Tissue Motion.

Suppressing tissue clutter is an essential step in blood flow estimation and visualization, even when using ultrasound contrast agents. Blind source separation (BSS)-based clutter filter for high-framerate ultrasound imaging has been reported to perform better in tissue clutter suppression than the conventional frequency-based wall filter and nonlinear contrast pulsing schemes. The most notable BSS technique, singular value decomposition (SVD) has shown compelling results in cases of slow tissue motion. However, its performance degrades when the tissue motion is faster than the blood flow speed, conditions that are likely to occur when imaging the small vessels, such as in the myocardium. Independent component analysis (ICA) is another BSS technique that has been implemented as a clutter filter in the spatiotemporal domain. Instead, we propose to implement ICA in the spatial domain where motion should have less impact. In this work, we propose a clutter filter with the combination of SVD and ICA to improve the contrast-to-background ratio (CBR) in cases where tissue velocity is significantly faster than the flow speed. In an in vitro study, the range of fast tissue motion velocity was 5-25 mm/s and the range of flow speed was 1-12 mm/s. Our results show that the combination of ICA and SVD yields 7-10 dB higher CBR than SVD alone, especially in the tissue high-velocity range. The improvement is crucial for cardiac imaging where relatively fast myocardial motions are expected.

Thickness-variation measurement at downstream regions for Li target of fusion neutron sources

In the developing fusion neutron sources (FNS), a liquid lithium (Li) free-surface jet is adopted as a beam target for neutron field generation. Owing to beam irradiation, Li must flow at a high velocity range to remove the heat load. In addition, Li needs to maintain a stable surface to maintain the objective neutron environment and soundness of the target system. In previous studies on the Li target of a fusion neutron source, experiments attempting to clarify the flow characteristics of free-surface Li were conducted using Li loops. Most of these studies focused on the area from the nozzle exit to the beam irradiation area. Then, in this study, in order to confirm the jet condition in the downstream region, where is a candidate region for monitoring in the actual FNS, the thickness variation was measured at a distance of 10 to 490 mm from the nozzle exit in the Li loop at Osaka University. In that region, it is to be expected that the influence of the well-developed bottom-wall boundary layer and wakes from sidewalls would not be negligible. The laser probe (LP) method was used to apply a noncontact-type optical-comb distance meter. The characteristics of surface fluctuation, such as the average thickness and wave heights, were analyzed from the obtained data. As a result, the increase of the jet thickness was observed in the downstream region, and it was also confirmed that wave heights become larger as flowing downstream. Except for the maximum wave height, the increasing tendencies were not simply linear. However, the complex change of surface-fluctuation characteristics was expected to occur at the region further downstream from the candidate monitoring point in the actual Li target system.

A reactive material double-bumper shield for centimeter sized projectile

The hypervelocity impact of space debris will cause fatal damage to spacecraft. At present, most of the protective shield structures can only resist the impact of millimeter sized projectiles, and it is very difficult for the protective structure with the finite area density and overall spacing to be impacted by the projectile with the diameter ≥1cm without failure. In this paper, a PTFE (polytetrafluoroethylene)/Al (aluminum) reactive material double-bumper shield for centimeter sized space debris was presented, and the experiments of projectiles with hypervelocity impact on PTFE/Al reactive material double-bumper shields were carried out by using two-stage light-gas gun. The hypervelocity impact characteristics of Aluminum alloy double-bumper shield and PTFE/Al reactive material double-bumper shield were compared by numerical simulation. The ballistic limit curve of the PTFE/Al reactive material double-bumper shield was obtained by experiments and numerical simulations. The PTFE/Al reactive material double-bumper shield can resist the impact of the projectiles with the diameter ≥1cm at the low velocity range, intermediate velocity range, and the high velocity range. The PTFE/Al reactive material double-bumper shield can stop projectiles with 2∼4 times greater mass than the Aluminum alloy double-bumper shield at these impact conditions, and the PTFE/Al reactive material double-bumper shield can provide better protection than the Aluminum alloy double-bumper shield of equivalent weight. Compared with the Nextel/Kevlar Stuffed-Whipple shield, the impact resistance of PTFE/Al reactive materials is not lower than that of Nextel/Kevlar fiber materials.

Sensitivity Analysis of Schlieren-Particle Image Velocimetry System for Simultaneous Measurement of Flow and Temperature Field of a Free Convective Flow Inside a Cubic Cavity

Abstract Fluid flows characterized by density variations have been studied using the schlieren-particle image velocimetry (PIV) system. The knife-edge location plays a crucial role in determining the system’s sensitivity, which significantly affects the accuracy of the measured quantities. Further, the optimum knife-edge position and the correct combination of image recording speed and interrogation window size are desirable for achieving the most accurate and reliable results. The present paper discusses the above issues on the measured quantities, such as temperature field, local Nusselt number distribution along the conducting walls, average Nusselt number, and velocity field. The experiment is performed to investigate laminar and steady natural convective flow in a water-enclosed cubic cavity with a left hot wall and a right cold wall. The analysis is undertaken for various knife-edge positions (0–90%), different image time separation varying (20–200 ms,) and interrogation window size using two passes varying from W1 = 32 pixels, W2 = 16 pixels to W1 = 128 pixels, W2 = 64 pixels. The results are presented for two distinct Rayleigh number, 1 × 108 and 3 × 108. Three-dimensional simulations have been carried out to check the fidelity of the experiment for Ra = 1 × 108. A high dynamic range of temperature is obtained for the range of knife-edge position in 50–65% while a high-velocity range is realized for knife-edge cutoff of 65% and combination of image time separation of Δt = 100 ms and interrogation window size with two passes of W1 = 64 pixels followed by W2 = 32 pixels.

Shake-The-Box particle tracking with variable time-steps in flows with high velocity range (VT-STB)

We present a novel evaluation mode for Lagrangian Particle Tracking methods in general, applied to the Shake-The-Box method specifically. The aim is to attain high levels of accuracy and a removal of false (‘ghost’) tracks in flow situations, where significant amounts of particles show small relative movement with respect to each other in consecutive time-steps. An iterative approach using variable time separations is employed, which starts by tracking particles at high timeseparations, followed by an iterative reduction of time separation, while feeding the particle tracked within the previous iterations. The process allows for applying tracking parameters fine-tuned to the different flow regimes tracked within each iteration. Experimental validation was performed using a dataset on impinging jet flow, created in collaboration with the School of Mechanical Engineering of Pusan National University. Evaluation of this flow with high velocity range shows distinct advantages in reduction of ghost tracks and in tracking accuracy.

Novel strategy for wide-range wind vector measurement using the hybrid CP/CTD heating mode and sequential measuring and correcting

To improve the performance of wind sensors in the high velocity range, this paper proposes a wind measurement strategy for thermal wind velocity sensors that combines the constant power and constant temperature difference driving modes of the heating element. Based on the airflow distribution characteristics from fluid dynamics, sequential measurement and correction is proposed as a method of measuring wind direction. In addition, a wind velocity and direction measurement instrument was developed using the above-mentioned approaches. The test results showed that the proposed instrument can obtain large dynamic wind velocity measurements from 0 to 60 m/s. The wind velocity measurement accuracy was ±0.5 m/s in the common velocity range of 0-20 m/s and ±1 m/s in the high velocity range of 20-60 m/s. The wind direction accuracy was ±3° throughout the 360° range. The proposed approaches and instrument are not only practical but also capable of meeting the requirements of wide-range and large dynamic wind vector measurement applications.

Relationship between Microstructure Evolution and Tensile Properties of AlSi10Mg Alloys with Varying Mg Content and Solidification Cooling Rates

This work explored and contrasted the effect of microstructure on the tensile properties of AlSi10Mg alloys generated by transient directional solidification depending on variations in cooling rate and magnesium (Mg) content (i.e., 0.45 and 1 wt.% Mg), with a focus on understanding the dendritic growth and phases constitution. Optical and scanning electron (SEM) microscopies, CALPHAD, and thermal analysis were used to describe the microstructure, forming phases, and resulting tensile properties. The findings showed that the experimental evolution of the primary dendritic spacing is very similar when both directionally solidified (DS) Al-10 wt.% Si-0.45 wt.% Mg and Al-10 wt.% Si-1 wt.% Mg alloys samples are compared. The secondary dendritic spacing was lower for the alloy with more Mg, especially considering the range of high growth velocities. Moreover, a greater fraction of (Al + Si + Mg2Si) ternary eutectic islands surrounding the α-Al dendritic matrix was noted for the alloy with 1 wt.% Mg. As a result of primary dendritic spacings greater than 180 μm related to lower cooling rates, slightly higher tensile properties were attained for the Al-10 wt.% Si-0.45 wt.% Mg alloy. In contrast, combining dendritic refining (&lt;150 μm) and a larger Mg2Si fraction, fast-solidified DS Al-10 wt.% Si-1 wt.% Mg samples exhibited higher tensile strength and elongation. The control of cooling rate and fineness of the dendritic array provided a new insight related to the addition of Mg in slightly higher levels than conventional ones, capable of achieving a better balance of tensile properties in AlSi10Mg alloys.

Limited refugia and high velocity range-shifts predicted for bat communities in drought-risk areas of the Northern Hemisphere

Species occupying semi-arid and dry regions around the globe face an uncertain future due to increases in the frequency and severity of droughts. In this study we modelled the potential effect of climate change on bat communities within two high-drought risk regions of the world and assessed the magnitude and direction of the predicted shifts in climatic suitability, locating climate change refugia and identifying species at greatest risk of population declines. To do this, we compared climate suitability models for 43 species using three global climate models and three emissions scenarios for current (1950–2000) and future (2061–2080) climates within two regions where droughts are predicted to increase, the Western Palaearctic and Western North America. Our models predicted an overall reduction in bat richness with future climates. Areas projected to support high species richness in the current climate coincided with greatest predicted species loss and greatest future drought risk. For species with the potential to extend their range, high velocity range shifts would be required to keep pace with these changes, particularly in the Western Palaearctic, where additional barriers to movement include seas and areas of high human population density. Predicted refugial zones were limited and occurred in similar areas across continents (montane and high latitude with some coastal areas). The area of climate suitability was predicted to contract for around half of study species, with nine identified as species of conservation concern due to low overlap between current and future modelled ranges. The best-case scenario for bat diversity in semi-arid and dry regions in the future is likely to be reduced species richness, with many species facing rapid range expansion over challenging landscapes to access climatically suitable areas. Conservation of bats in high drought risk regions will likely depend on protection of identified refugia and networks of water sources, as well as global measures to protect biodiversity and human wellbeing, such as reduction in global carbon emissions.

ПЕРВАЯ КРАЕВАЯ ЗАДАЧА ДИНАМИКИ АНИЗОТРОПНОГО УПРУГОГО ПОЛУПРОСТРАНСТВА ПРИ ДЕЙСТВИИ ДОЗВУКОВЫХ ТРАНСПОРТНЫХ НАГРУЗОК

The first boundary value problem of the theory of elasticity for an anisotropic elastic half-space is solved when a transport load moves along its surface. The subsonic Raleigh case is considered, when the velocity of motion is less than the velocity of propagation of bulk and surface elastic waves. The Green’s tensor of the transport boundary value problem is constructed and on its basis the solution of boundary value problems for a wide class of distributed traffic loads is given. To solve the problem, the methods of tensor and linear algebra, integral Fourier transform, and operator method for solving systems of differential equations were used. The obtained solution makes it possible to investigate the dynamics of the rock mass for a wide class of transport loads, in a wide range of velocities, both low velocities and high velocities, and to evaluate the strength properties of the rock mass under the influence of road transport. In particular, determine the permissible velocities of its movement and carrying capacity. In addition, a investigation on its basis of the movement of the day surface along the route will make it possible to establish criteria for the seismic resistance of ground structures and the permissible distances of their location from the route.

Wellbore fluid sonic conditions during blowouts

The understanding of high-velocity two-phase flow is critical for predicting worst-case discharge scenarios. During a blowout, the fluid discharge rate can be very high, and its velocity may reach the sonic speed at the surface. Therefore, it is crucial to understand the fluid dynamics and flow characteristics of multiphase flow in the high-velocity range. In this investigation, two-phase (air-water) flow experiments were conducted to study the flow evolution in extreme high-velocities occurring during worst-case discharge. The experiments were performed in a vertical pipe section with a diameter of 83 mm and a length of 5.5 m. A fully transparent viewport was installed on the test section to monitor the flow pattern. The superficial gas velocities were ranging approximately from 8 to 160 m/s. During the test, the pressure gradient was monitored while increasing the gas rate at a constant liquid rate. Under subsonic conditions, the pressure gradient increase with superficial gas velocity indicating the establishment of friction dominated flow regime. However, the pressure-gradient trend changed when shock waves formed in the test section. With increasing the superficial gas velocity at a given liquid rate, the pressure gradient attained its maximum when flow transition occurred and shock waves formed in the test section, which were observed through the viewport. Under sonic conditions, increasing the superficial gas velocity a constant liquid flow rate reduced the pressure-gradient.After examining various two-phase flow sonic velocity models and measurements, a new correlation has been developed to predict sonic conditions during worst-case discharge. Experimental results are compared with predictions of existing wave propagation models and demonstrated reasonable agreement. Subsequently, a computational tool has been developed to estimate fluid flow rates for worst-case discharge scenarios involving sonic flow conditions. The new correlation has been implemented in the computational tool to forecast the establishment of sonic flow conditions in the wellbore. The computational tool shows a reasonable agreement with commercial packages for basic worst-case discharge circumstances. A sensitivity analysis performed using the computational model suggests that the discharge rate varies with the in-situ parameters such as skin factor, pay-zone height, and reservoir permeability.

Review of experimental techniques for impact property of adhesive bonds

Assessing the impact property of the adhesives and the joints requires specific suitable experimental methods. Especially the most of the adhesives are sensitive to the strain rate that they must have to meet when a load is applied abruptly on the adhesive and adhesively bonded joints. In general, the impact tests of adhesive joints are usually divided into three ranges including low, medium and high velocity. Sometimes a body in hypervelocity collides with another one is faster than the sound velocity. This document aims to review the experimental methods that have been previously undertaken in this field. Discussed research topics include the impact test methods for the adhesive joints under low, medium, high and hypervelocity. The standard impact tests for adhesive joints (involving both bonded blocks and strips) are typically test methods with low-velocity and they are discussed. In the medium-velocity range, the applications of drop weight, inertia wheel, wedge falling, servohydraulic and pneumatic test methods are presented. In the high-velocity range, the advance of Split-Hopkinson bar as a special apparatus conceived to test materials is reported. The final section describes two practical applications of adhesive joints impacted under hypervelocity.

High dynamic range particle image velocimetry analysis of viscous inhalant flows

High dynamic velocity range (DVR) flows are challenging to measure with traditional double-pulse particle image velocimetry (PIV) since no single correlation time scale optimally resolves particle displacements over the entire DVR of interest. Inhalant flows are ubiquitous in engineering and biology and feature a high DVR as they draw viscous fluid through an orifice from a surrounding reservoir since large interior tube velocities rapidly attenuate with exterior distance from the inhalant orifice. We conducted a high-DVR PIV study of viscous inhalant flow hydrodynamics by developing and applying a multi-time-lag type processing scheme to construct DVR-enhanced flowfields. The algorithm adapts existing multi-time-lag type schemes into one that is well suited for slowly evolving flows with a persistent spatiotemporal structure. Correlation analyses between image pairs across two optimized time scales produce a pair of correlation maps well suited for resolution of targeted high and low measurement velocities. An evaluation map based on the best statistical relative strength of the local correlation peak amplitude and peak ratio is then used to spatially reconstruct a single DVR-enhanced velocity field with a DVR on the order of 1000:1. Numerical simulations show close agreement with measured flows everywhere following DVR enhancement, and the high-DVR PIV results reveal marked differences in the exterior flow kinematics and dynamics due to varying viscous and boundary interaction effects. The inlet velocity profiles at the tube orifice are highly sensitive to the Reynolds number within this range (1–100) and show notable departures from classically assumed uniform pipe entry profiles, impacting flow development lengths downstream.

Modified Sediment Pick-Up Function

AbstractThis paper addresses the sediment pick-up process in the high-velocity range of 2–6 m/s. An existing sediment pick-up function was recalibrated and modified using data of new experiments i...

MIMO-OFDM Radar Using a Linear Frequency Modulated Carrier to Reduce Sampling Requirements

The requirement of fast analog-to-digital (AD) and digital-to-analog (DA) converters is a challenge for high-resolution orthogonal frequency division multiplexing (OFDM) radars. This paper introduces a method to increase the modulation bandwidth of an OFDM signal by using an additional frequency modulated continuous wave carrier to reduce the requirements for the AD/DA converters while maintaining a high unambiguous velocity range. Multiplexing of transmit antennas with OFDM is still possible with the combined modulation. The presented approach is verified by simulations and measurements. A reduction of AD/DA converter bandwidth by factor eight is achieved.