Low Velocity Region Research Articles

Nature of mantle discontinuities beneath the Ontong Java Plateau

We determined the depths of the mantle discontinuities with a receiver function method using broadband data recorded on the seafloor and islands of the Ontong Java Plateau (OJP) and its vicinity. The 410-km discontinuity is broadly elevated by 10–20 km beneath the OJP. The elevation is observed in the low-velocity region above a stagnant paleo-Pacific slab that had been subducted until 25 Ma. The elevated 410-km discontinuity and the slow anomalies may be caused by partial melting induced by hydration with water released from the paleo-Pacific slab. The 660-km discontinuity is close to the global average beneath the OJP, suggesting that the stagnant Pacific slab is bottoming in the mantle transition zone. The 410-km discontinuity is depressed by 10–20 km beneath the Caroline volcanic chain, where a low-velocity sheet has been observed by tomographic studies, implying that a sheet-like upwelling occurs at least from the top of the mantle transition zone. The 660-km discontinuity is also depressed by 10–30 km beneath the Caroline volcanic chain, which may be attributed to the majorite-bridgmanite phase change in a high-temperature environment and/or an underestimated velocity correction in the moveout correction of receiver functions. It is thus unclear whether the sheet-like mantle upwelling has its roots in the lower mantle.

Cavitation flow and broadband noise source characteristics of NACA66 hydrofoil with a V groove on the suction surface

In the present work, a V groove on the suction surface is proposed to investigate the cavitation flow and noise sources of a NACA66 hydrofoil. The SST k-ω turbulence model and broadband noise source model is employed to analyze the flow pattern and noise distribution. Proper orthogonal decomposition (POD) is then used to investigate the coherent structure of cavitation flow around the hydrofoil. The results show that, under cloud cavitation conditions, the groove improves the energy characteristics of the hydrofoil and increases the lift-to-drag ratio by 2.95%. During the sheet cavitation growth phase, the groove can suppress the development of low-pressure, low-velocity regions on the hydrofoil surface, thus suppressing cavitation near the leading edge of the hydrofoil. During the cavitation collapse stage, the groove reduces the pressure impact of cavitation collapse on the hydrofoil. The groove extends a cavitation cycle and reduces the average cavitation volume during a cavitation cycle by 17.46%. Results indicate that during a cavitation cycle, the groove reduces the average dipole noise on the hydrofoil surface by 5.07% and the average quadrupole noise on the middle longitudinal section by 6.86%. POD results show that the first five orders of the modes capture more than 90% of the energy of the flow field. The primary frequency of the modal coefficients of Mode 1 and Mode 2 is the cavitation frequency, and the other frequencies are multiples of the cavitation frequency. The groove significantly affects Mode 2, which represents a change in velocity distribution in the flow field characteristics.

A Novel Low-Velocity Impact Region Identification Method for Cantilever Beams Using a Support Vector Machine

Damage induced by a low-velocity impact can reduce the stability and reliability of structures. In this study, a novel low-velocity impact region identification method based on the spectral peak frequency (SPF) and support vector machine (SVM) is proposed to identify the low-velocity impact regions on a steel cantilever beam. A low-velocity impact region identification system of the cantilever beam is established by applying fiber Bragg grating (FBG) sensors, and only 2 sensors are used in this system. The power spectral density functions of the impact response signal are smoothed using the linear weighting method to remove pseudospectral peak frequencies, and then, SPFs are extracted as the features. For 25 low-velocity impact regions with dimensions of 30 mm × 10 mm, the results show that the recognition rate obtained by the proposed method is 100% and the feature vector consisting of the first two SPFs with the largest amplitude has the highest recognition rate. Through the comparative study, it is found that the recognition rate of SVM is higher than that of the probabilistic neural network (PNN) and extreme learning machine (ELM) for low-velocity impact area recognition of cantilever beams. As a result, the low-velocity impact region identification method of this paper can be applied to the real-time health monitoring of cantilever beam structures.

Investigation on fine particle agglomeration and separation promoted by different bluff bodies

Using particle agglomeration to help separate fine particles receives increasing attention in air purification processes. Recent studies suggested that enhanced turbulence using bluff bodies can significantly improve the agglomeration of fine particles. However, since micron-sized particles are difficult to measure, the current exploration of flow fields and particles is mainly based on simulations and lacks experimental validation. This paper innovatively used a phase doppler particle analyzer to measure the flow field in terms of velocity, streamline and turbulence intensity, as well as particle size and number concentration in an agglomeration chamber with a bluff body located at the center. Different shaped bluff bodies were also considered. It was found that low-velocity recirculation region with different shapes appeared in the wake, and vortex flow with special structures were observed. From the perspective of particles, the development of the flow field generated by a single bluff body effectively caused an increase in particle size and a decrease in particle number, which is because that the flow field promotes collisional agglomeration. More specifically, for V-structure bluff body, the particle size improved from 6 μm to a maximum of 13 μm and the particle number concentration decreased by 8 times. The agglomeration efficiency for PM2.5 and PM10 reached 89.06% and 87.38% respectively. Furthermore, by analyzing the velocity of different sized particles, it was reasonable to assume that different sized particles appeared to have velocity differences due to recirculating vortex flow, while the overlapping trajectories of positive and negative moving particles was mainly responsible for the collision probability enhancement. This paper presents new insights into particle agglomeration separation for this environment-friendly and low-cost technology.

Research on the Jet Characteristics and Dephosphorization Efficiency of Converter Oxygen Lance Blowing CO2-O2 Mixed Gas

Utilization of CO2 in steelmaking process has attracted extensive attention in recent years, not only because of its social benefits, but also its better metallurgical performance. Mixing CO2 with O2 blown by converter oxygen lance is gradually being adopted by steelmaking plants, due to its potential of reducing consumption and improving steel quality. In the present research, effect of mixing CO2 on the jet characteristics of a four-nozzle oxygen lance was studied in detail by numerical simulation, taking the combustion behavior between supersonic jets and ambient atmosphere into consideration innovatively. The simulated results showed that the combustion flame is mainly distributed in the region between multiple jets, and the high temperature flame has a noticeable influence on the low-velocity region of the jet. Due to the dilution effect of CO2, mixing CO2 into the oxygen jets will reduce the maximum temperature of the flame and slow down the combustion rate. With the increase of CO2 mixing ratio, the high-temperature zone of combustion flame moves away from the lance tip significantly. At the same distance from the nozzle, although mixing CO2 can hardly increase the velocity magnitude of the jet, but it can achieve higher dynamic pressure, indicating stronger impacting power. Then the industrial experiment of top blowing O2-CO2 was carried out in a 120-ton converter. During the blowing time of 120~300 s, the mixing ratio of CO2 was 15 vol.% for better dephosphorization, and no CO2 was mixed in the rest time of blowing. Due to the stronger stirring and better thermodynamics, the average [P] content in the final molten steel was decreased from 0.0155 wt.% to 0.0129 wt.%, achieving higher dephosphorization efficiency.

Аналіз впливу способу подачі гарячих газів пристрою запалювача на запуск камери згоряння за допомогою тривимірного комп'ютерного моделювання

This paper presents the results of a numerical simulation of the gas flow in the flame tube of an annular combustion chamber of a gas turbine engine. Numerical simulation was performed in the ANSYS Fluent 2022 R1 computational complex, in which the numerical solution of the Reynolds-averaged Navier-Stokes equations (RANS) was implemented, the dissipation rates were determined using the Enhanced Wall Treatment near-wall function. For numerical simulation problems, a computational polyhedral mesh was built. The purpose of the calculations was to evaluate the effect of the method for supplying igniter hot gases to the start of the combustion chamber. The article does not address the operation of the igniter itself (its ignition, combustion, and the flow in it), but only its main task is the generation of a flame (gas) with a given temperature. All calculations were carried out for two gas temperatures, 800 and 1200 °C, at the outlet of the igniter nozzle, and a temperature of minus 20 °C at the inlet to the combustion chamber. In the calculation model, at the inlet to the igniter nozzle, the gas flow rate was set with a temperature taken from the experiment. When the chamber operates in the region of low temperatures, low velocities and pressures at the inlet, the degree of fuel evaporation and the mixing of its vapors with air have a significant effect. Therefore, with an increase in air flow through the chamber, the limits of flame blow-off expand. With a further increase in air flow, the processes of fuel evaporation and its burnout in the reverse current zone are completed, and flameout is mainly determined only by the temperature in the reverse current zone, and the boundaries of stable combustion narrow with increasing flow rate, which is typical for combusting a homogeneous mixture. The calculations found that the penetration and spread of heat when using igniter nozzles with a large diameter (12 mm) in the outlet section are higher than those in holes with a smaller diameter (8 mm). In the variants where the supply of hot gases is in the plane of the nozzle, a better distribution of heat in the zone of reverse currents is shown than where the supply of hot gases is carried out between the nozzles. Also, to analyze the results of the calculation, a criterion was proposed that shows the optimal conditions for the ignition of the mixture.

Nucleation mechanism of the 2021 Mw 7.4 Maduo earthquake, NE Tibetan Plateau: Insights from seismic tomography and numerical modeling

The 2021 Mw 7.4 Maduo earthquake ruptured the Jiangcuo fault, a secondary fault within the Bayan Har block, NE Tibetan Plateau, which attests that large earthquakes can occur on faults with very low slip rates. In this study, we use data from local seismic stations to explore the 3D velocity structure beneath the source region of the Maduo earthquake. Our results indicate that there is a distinct low-velocity anomaly in the mid-lower crust, and the thickness of this low-velocity zone decreases sharply to the east. The Maduo earthquake occurred in the transition zone between the high- and low-velocity regions. Based on our local velocity model and our knowledge of the regional crustal structures, we constructed numerical models to investigate the stress and strain energy distributions in our study area. As indicated by the stress concentration, strain energy accumulation, and low strain rate in the shallow upper crust around the source region, we conclude that the seismic velocity heterogeneity and the weak ductile mid-lower crust provide a unique tectonic environment that facilitated the nucleation of the Maduo earthquake. This study helps to understand the mechanisms of the Maduo earthquake, and more importantly reconciles the seeming contradiction between large earthquakes and low slip and strain rates.

Active Flow Control of a Flame-Holder Wake Using Nanosecond-Pulsed Surface-Dielectric-Barrier Discharge in a Low-Pressure Environment

Flame holders are widely used in ramjet combustors. We propose using surface nanosecond-pulsed surface-dielectric-barrier-discharge (NS-DBD) to manipulate the flame-holder flow field experimentally. The electrical characteristics, induced flow performance, and temperature distribution of NS-DBD were investigated via the electrical and optical measurement system. In the filamentary discharge mode, the discharge energy rose with decrease of the ambient pressure. The discharge pattern of NS-DBD changed from filamentous to uniform around 5 kPa. Starting-vortex intensity and jet-flow angle relative to the wall increased at low pressure. The recirculation zone was asymmetrical at pressures above 60 kPa. The recirculation zone’s area and length were smaller at lower pressures, but when the actuator was operating, the recirculation zone was nearly 11.8% longer. The vorticity increased with pressure. When the pulse width was 300 ns, the actuator had the greatest effect, and the low velocity region (LVR) area and the fuel–air-mixture residence time (FMRT) could be increased by 31.8% and 20.5%, respectively. The actuator had a smaller widening effect on the LVR area at lower pressure. Rising-edge time should increase with pressure to optimize LVR increase; it should be above 300 ns to optimize FMRT increase. We conclude that NS-DBD is a viable method of controlling flame-holder airflow at low pressure.

Mega‐Depressions on the Cocos Ridge: Links Between Volcanism, Faults, Hydrothermal Circulation, and Dissolution

AbstractHigh‐resolution bathymetry and three‐dimensional seismic data along the Cocos Ridge reveal a 245 km2 field of ∼1–4 km in diameter seafloor depressions. The seafloor depressions are part of a two‐tiered honeycomb pattern. The lower‐tier depressions have steep faults that truncate strata with chaotic internal reflections consistent with sediment collapse into the depression. These extend into a lens shaped interval just above igneous basement. Overlying these depressions is a second broader set with rough seafloor morphology with gently dipping boundaries defined by pinch‐out stratigraphic patterns. Drilling results indicate that the lens‐shaped zones that host the deeper depressions represent anomalous regions of high porosity, low velocity, and low density within calcareous rich sediment. Analysis of nannofossils from IODP Site U1414 suggests the collapse structures formed during the late Miocene, whereas the younger shallower depressions likely formed between the early Pliocene and the Pliocene‐Pleistocene boundary. Geochemical and petrological analysis at Site U1414 suggests that hydrothermal circulation during the late Miocene led to carbonate dissolution and collapse. Following collapse, focused fluid‐flow and bottom current scouring resulted in formation of the overlying set of depressions and a honeycomb seafloor morphology. Similar sets of depressions along the Carnegie Ridge to the south support the hypothesis that two‐tiered depressions formed in response to processes that occurred broadly across the Panama Basin between the late Miocene and the Pliocene‐Pleistocene transition. Geochemical results at Site U1414, combined with geophysical data, suggest this two‐tiered system of depressions currently guides ongoing fluid outflow.

Micro-particle image velocimetry study on hydrodynamic characteristics of in-line and staggered micro pin fin arrays

Detailed hydrodynamics in microchannels with in-line and staggered circular micro pin fin structures over Reynolds number ranging from 50 to 700 are experimentally studied with micro-particle image velocimetry. The velocity field, vortex structure and vorticity distribution is obtained and analyzed, and differences in flow behavior in the two arrangements are examined. The result indicates a delay in the onset of vortex shedding in micro pin fin arrays as compared to their macro scale counterpart due to the confinement effect of channel walls. Flow pattern in the in-line arrangement is featured by the microchannel-like main stream between the pin rows and the double vortex wake flow behind the pins, while flow in the staggered arrangement is characterized by the wavy main stream and a pair of accelerated flow streams on two sides of the pins. Vorticity bands along the sides of the wake region intensify with the Reynolds number, diffuse further downstream, but narrow in width. Visualization and data extraction results reveal that flow behavior in the staggered arrangement differs from that in the in-line arrangement in terms of a smaller area occupied by the low-velocity wake region and a more sufficient mixing of fluid.

CFD Study of a Tunnel-Ventilated Compost-Bedded Pack Barn Integrating an Evaporative Pad Cooling System.

Simple SummaryIt is known that improving the welfare of cows increases dairy productivity. A compost-bedded pack barn equipped with evaporative cooling pads to regulate the inside environmental conditions of dairy seems to be a synergic combination to improve substantial the welfare in dairy facilities. However, there is a lack of information about both techniques working together. A computational model of a tunnel-ventilated compost-bedded pack barn with an evaporative pad cooling system was developed to know the spatial distribution of temperature, relative humidity and velocity of the air inside the barn. These variables allowed us to compute a thermal stress index for dairy cattle to identify the geometric characteristics and operative conditions of the evaporative pad cooling that provide the best environmental conditions inside the barn according to the outside environmental conditions.Evaporative cooling is one of the most efficient techniques to reduce heat stress in cows in agricultural facilities. Additionally, compost-bedded pack barn has been shown to improve the welfare and production of cows. Two techniques were combined and analysed by developing a computational fluid dynamics (CFD) model of a tunnel-ventilated compost-bedded packed barn that integrated the heat and airflow dynamics of an evaporative pad cooling system. This allowed us to study the distribution of dry-bulb temperature, relative humidity and airflow velocity inside the barn based on the external environmental conditions, thickness of the pad, water temperature and specific manufacturer characteristics of the pad, providing optimal cooling pad location, size and operating conditions in the barn. Employing experimental data the CFD model was validated showing good agreement. The Equivalent Temperature Index for dairy Cattle (ETIC) was used to determine the level of stress of the cows considering the airflow velocity. It was found a moderate stress due to high relative humidity and low airflow velocity. From the predicted results, it was recommended to increase the airflow velocity above 3 m s when simultaneously the external dry-bulb temperature and relative humidity exceed 30 °C and 55%, respectively, simultaneously. Additionally, installation of baffles at the pad outlet to drive the airflow to the floor was suggested to improve the drying of the compost-bedded closed to the pads, where a low airflow velocity region was established.

Acoustic Emission Characteristics of Fracture and Damage in Coal Samples under Overstress Loading and Unloading Paths

Abstract As coal mining depth is over 1000 m, an overstressed effect is commonly observed around working face which shows a higher stress than the ultimate strength of the coal mass. Aiming at the problem of dynamic disasters induced by overstress loading and loading, a true triaxial AE monitoring unit was designed to systematically investigate the acoustic emission (AE) characteristics of fracture and damage. The AE results show that the ring counts of coal sample under true triaxial loading are influenced by three factors: loading level, individual differences, and loading rates. When under lower true triaxial loads, the coal sample damage represented by ring counts appears largely in loading phase, and the quantity is few. When true triaxial loads increase, the number of ring counts, especially in packing phase, increases significantly, which indicates that the damage process is transferred from loading phase to packing phase. The study on evolution laws of microcracks, wave velocity, and energy indicates that, during the initially true triaxial loads, the primary microcracks and the initial loading on primary dense areas contributes to a small amount of lower and higher velocity regions in the sample. Along with the increase of true triaxial loading, the closure of the primary microcracks and the fracture of the dense area result in a transfer and expansion of higher velocity regions and the formation of velocity anomaly regions. When approaching failure, the macrocracks throughout the sample present a large area of lower velocity band. The formation and closure of cracks, the fast transfer of high velocity region, and the velocity anomaly region indicate the unstable status of the sample. During the packing phase of true triaxial loads, the cracks are compacted, and the inner structures are thoroughly damaged in the sample, which eventually presents a continuous damage in a form of the shrink of the lower velocity region and the increase of integral velocity of the sample.

Advective Trapping in the Flow Through Composite Heterogeneous Porous Media

We study the mechanisms of advective trapping in composite porous media that consist of circular inclusions of distributed hydraulic conductivity embedded in a high conductivity matrix. Advective trapping occurs when solute enters low velocity regions in the media. Transport is analyzed in terms of breakthrough curves measured at the outlet of the system. The curve’s peak behavior depends on the volume fraction occupied by the inclusions, while the tail behavior depends on the distribution of hydraulic conductivity values. In order to quantify the observed behaviors, we derive two equivalent upscaled transport models. First, we derive a Lagrangian trapping model using the continuous-time random walk framework that is parameterized in terms of volume fraction and the distribution of conductivities in the inclusions. Second, we establish a non-local partial differential equation for the mobile solute concentration by volume averaging of the microscale transport equation. We show the equivalence between the two models as well as (first-order) multirate mass transfer models. The upscaled approach parameterized by medium and flow properties captures all features of the observed solute breakthrough curves and sheds new light on the modeling of advective trapping in heterogeneous media.

Machine Learning-Based Earthquake Catalog and Tomography Characterize the Middle-Northern Section of the Xiaojiang Fault Zone

Abstract The left-lateral strike-slip Xiaojiang fault is an important tectonic boundary between Sichuan–Yunnan diamond block and the Yangtze block, which accommodated several M > 7.0 damaging earthquakes in the past ∼500 yr, as well as intense tectonic deformation. However, the seismogenesis of its middle-northern section are not well understood due to the lack of dense stations. In this study, we analyze one year of continuous seismic records from November 2019 to November 2020, which are recorded at a recently deployed dense seismic array. We build a high-precision earthquake catalog for the region using our recently developed machine learning-based earthquake location workflow (LOC-FLOW), which consists of machine learning phase picking, phase association, velocity model updating, and station correction, absolute location, and double-difference relative location. We then adopt a double-difference tomography method (tomoDD) to refine locations of 16,000 events and build a high-resolution 3D velocity model using both machine learning differential times and cross-correlation differential times. The seismicity distribution not only delineates detailed geometry of the main fault system but also characterizes several branch faults, including two echelon subfaults crossing the north–south-striking main fault. The velocity model shows strong lateral heterogeneities and exhibits a clear relationship to the seismicity distribution: the boundary of high- and low-velocity regions or high-velocity regions above low-velocity bodies accommodate the majority of earthquakes. The variation of the constructed 3D velocity model can be well explained by geological and tectonic settings of the region. In addition, we identify two seismic gaps, which accumulate stress and imply the potential of hosting future moderate-to-large earthquakes. Our study demonstrates, with the aid of LOC-FLOW and tomoDD, machine learning-based phase picks lead to promising performance in constraining high-precision earthquake catalogs and constructing high-resolution velocity models. Machine learning-based tools are becoming the next generation of routine earthquake analysis.

Combined control of variant clearance and casing aspiration on tip flow field and instability of a transonic compressor

To enhance the transonic compressor performance, the axially non-uniform variant tip clearance schemes and combined schemes with casing aspiration were applied and their effects on the tip flow field and flow instability were studied numerically. The results show that the expanding tip clearance can increase the stall margin and peak efficiency by reducing the tip leakage flow intensity within the first half chord, and cause the interface between the leakage flow and mainstream to move downstream. The effect of the shrinking clearance is on the contrary. The compressor performance can be further improved by the combination of expanding clearance and casing aspiration. When the circumferential suction groove is located at 35% of the axial chord length corresponding to the low-velocity region due to the leakage vortex breakdown, the stability enhancement is the largest, which is about 7.2% higher than that under the uniform clearance scheme. Casing aspiration decreases the blade tip loading and attenuates the tip leakage vortex, tip secondary vortex, and their interaction, which results in the suppression of vortex breakdown and tip flow blockage. Moreover, the oscillations and instability of the flow field are weakened. Therefore, the tip flow field is modified and the compressor performance is improved.

Adaptive force tracking control of electrohydraulic systems with low load using the modified LuGre friction model

The force tracking performance of controllers is seriously degraded by the complex friction behaviors when the electrohydraulic system applies low load. The existing LuGre model is employed in the motion control system with the known trajectory. In this work, a modified LuGre model combined with a zero-velocity crossing window is established to address the lag issue and model oscillation in force control system. Then, the Stribeck curve in the friction model is accurately obtained using a fast measurement method, and the impact of friction parameters on the accuracy of the LuGre model is analyzed. Next, an adaptive friction compensation control scheme is proposed for the electrohydraulic system with low load using the modified LuGre model to compensate for dynamic friction behavior and improve the force tracking performance. The uncertain friction parameters are tuned online to reduce the force error of the low-velocity region via the derived adaptive law and a dual-observer. The disturbance observer is effectively integrated to reduce the negative influence of unconsidered dynamics. Finally, comparative experiments are conducted to verify the effectiveness of the proposed controller in static and dynamic loading modes.

Optical Fiber Thermal Anemometer With Light Source-Heated Fabry–Perot Interferometer

An optical fiber thermal anemometer with a light source-heated Fabry–Perot interferometer (FPI) is proposed. The FPI is fabricated on the tip of a single-mode fiber using an ultraviolet-cured adhesive. A broadband light source acts as a heating light source as well, eliminating the need for a heating resistor or a pump laser which are usually required in optical fiber thermal anemometers. The interference fringe of the FPI shifts with airflow velocity because airflow not only reduces temperature of the FPI but also introduces strain due to wind force. Airflow velocity is therefore measured by detecting wavelength shift of the interference fringe. In the experiment, a high sensitivity up to −3.13 nm/(m·s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) was achieved at the low velocity region, reducing to ∼−0.2 nm/(m·s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) at the high velocity region within the measurement range of 0–7 m/s. The response and recovery time is 250 and 580 ms, respectively. It is worth noting that the anemometer maintains a relatively high sensitivity at the high velocity region due to the contribution of wind force effect that makes it outperform most of the fiber thermal anemometers.

Hemodynamic study of the effect of the geometric height of leaflets on the performance of the aortic valve under aortic valve reconstruction

BackgroundAlthough aortic valve reconstruction has become an alternative treatment for aortic valve disease, the design of the geometric parameters of the reconstructed leaflet still mainly depends on the experience of doctors. The present study investigates the effects of the height of the leaflets on the performance and biomechanical states of the reconstructed aortic valve.MethodsThis numerical study was carried out using the finite element approach and the lattice Boltzmann method. The dynamic and biomechanical characteristics of the leaflets were evaluated by using the finite element approach, while the blood flow in the aortic sinus was evaluated by applying the lattice Boltzmann method. Three types of leaflets with different heights were designed. Then the dynamic characteristics, stress distribution, and effective orifice area (EOA) of the aortic valve and flow pattern were calculated as the indicators.ResultsThe results demonstrated that the height of the leaflets could indeed regulate the performance and the biomechanical states of the aortic valve. The rapid valve opening times of the 3 types of leaflets gradually reduced along with the decrease of the height ratio (HR_0.8: 120 ms vs. HR_1.0: 68 ms vs. HR_1.2: 31 ms), while the rapid valve closing times (RVCTs) of the 3 types of leaflets were similar to each other (approximately 75 ms). Moreover, the radial displacement of the leaflet at the fully open time increased along with the decrease of the HR of the leaflets (HR_0.8: 8 mm vs. HR_1.0: 6 mm vs. HR_1.2: 4 mm). In addition, the stress level of the leaflets also increased with the increase of the height of the leaflets (max stress, HR_0.8: 0.5 MPa, vs. HR_1.0: 1.1 MPa, vs. HR_1.2: 1.8 MPa). Similarly, the low velocity region near the ascending aortic wall and the wall shear stress (WSS) level on the ventricular side of the leaflets also increased along with the increase of the HR of the leaflets.ConclusionsIn short, the height of the leaflets mainly affects the opening performance of the reconstructed aortic leaflets. The HR of the reconstructed leaflets for adults should be less than 1.0 to balance the opening and closing performance of aortic leaflets.

The channel‐source hypothesis: Empirical evidence for in‐channel sourcing of dissolved organic carbon to explain hysteresis in a headwater mountain stream

AbstractCatchment hydrologists have long puzzled over the question: How can catchments rapidly generate storm flows and pulses of solutes in response to storm events? Conceptual models viewing catchments as composed of discrete source areas generating flow at unique time scales and with unique chemical characteristics have been used to explain the observed changes in flow and water chemistry. Surprisingly, those conceptual models usually do not treat the stream channel as one of the potential source areas. Here, we propose the channel‐source hypothesis in which the stream itself should be considered as a potential source with the same rigour as other contributing areas. We pose this in the spirit of the scientific use of the word: a hypothesis is not a proven idea but rather a provisional supposition serving as the basis for further study. We suggest that the channel should be considered as a potential source for dissolved organic carbon (DOC). Channels store substantial amounts of organic matter, and stream ecologists have long studied stream carbon cycling. From those studies, we know that leaching and decomposition can generate DOC from particulate organic carbon (POC). Further, POC is stored in channel ‘dead‐zones’—regions of low flow velocity ‐ that can be activated as flow velocity increases, thus releasing accumulated DOC during storms. All catchments are different; there is no reason to assume that channel sources are always important, in every catchment, in every storm. Thus, the channel‐source hypothesis does not replace existing conceptual models. Instead, it adds another potential mechanism that may explain DOC dynamics observed in streams. The channel‐source hypothesis has substantial implications for catchment studies examining sources of DOC in stream water or using DOC as a tracer to determine the locations of, and proportional contributions of, different source areas for streamflow generation.

Particle movement in the spheronizer – Experimental investigations with respect to the toroidal and poloidal direction

Oberservation of particle movement during wet granulation is crucial for identifying granulation mechanisms, process optimizations and troubleshooting. An example of such a process is spheronization, which is commonly used as a wet granulation technique to produce spherical, pharmaceutical pellets. Due to the dense particle bed, measurements of poloidal pellet velocities remain a challenge and have not been yet been reported in literature.In this work, a modelling approach was used in combination with particle image velocimetry (PIV) and mixing progress as a surrogate parameter to obtain information about the movement inside the pellet bed, including those parts not visible from outside the pellet bed.A good agreement between the experiment and the simulation was found. Regions of low poloidal velocities were found in both experiments and simulations. The initial pellet shape was not identified as a significant influence on the mixing progress.