Velocity Zone Research Articles

Occupant’s thermal comfort in a radiant ceiling cooling room with hot wall surface

A radiant ceiling cooling (CC) system integrated with a mechanical ventilation system was extensively applied in a modern office in a glass curtain wall building. Thermal comfort in a radiant ceiling cooling room with mixing ventilation (MV) or underfloor air distribution (UFAD) was investigated by objective measurements and subjective questionnaires. The external wall surface temperature and mean radiant temperature were 33.9–34.6°C and 27.2–27.4°C, respectively, with a heat transfer of 41.5 W/m2 from the external wall and 37.8–38.6°C and 27.4–28.2°C with a heat transfer of 69.5 W/m2 from the external wall. The indoor air velocity in the occupied zone was 0.17–0.23 m/s in the room with CC+MV and 0.09–0.16 m/s in the room with CC + UFAD. There was a considerable difference between occupants’ thermal perceptions with different distances away from the external wall. Both the ventilation system type and hot wall surface temperature did not influence occupants’ overall thermal perceptions, but their local thermal sensation and skin temperature. The results suggest that the impacts of ventilation system type and hot wall surface temperature on occupants’ local thermal response should be considered during the design of a radiant ceiling cooling system combined with a mechanical ventilation system.

Defining Earth's elusive thermal budget in the presence of a hidden reservoir

A hidden geochemical reservoir has long been a popular concept in the solid Earth sciences, often invoked to explain geochemical paradoxes. Easily overlooked, however, is that such a hidden reservoir invalidates traditional estimates of bulk silicate Earth (BSE) composition, including BSE heat production. Unconstrained BSE heat production threatens our ability to model Earth's thermal evolution. We present a novel method for estimating BSE heat production in the presence of a basal magma ocean—a putative hidden reservoir that has been linked to deep mantle seismic anomalies known as ultralow velocity zones. Our model tracks the thermal evolution of a fully coupled mantle, basal magma ocean, and core. Monte Carlo sampling, together with constraints on upper mantle cooling history and a physical bound on the degree of fractional crystallization, quantifies the major characteristics of Earth's thermal evolution. Chief among these constraints is the previously undefined present-day BSE heat production, which we estimate to be 19±3 TW. Our approach resolves the fundamental difficulty of self-consistent thermal modeling in the presence of a hidden geochemical reservoir, while simultaneously exploring the relevant parameter space. The mantle budget of non-heat-producing elements may require substantial revisions.

Optimization schemes to significantly improve the upstream migration of fish: A case study in the lower Yangtze River basin

The construction of fish passage facilities is a promising approach to balance fish conservation and water resource development by improving river connectivity. To be successful, a fishway must efficiently attract fish to its entrance and have an interior flow field that meets the needs of migrating fish. In this paper, methods were explored to improve the efficiency of fishway passages by optimizing the flow field near the fishway entrance and the flow field inside the fishway in a case study at the Niuling Reservoir in the lower Yangtze River basin. The original engineering design was modified by designing a unique retaining wall with a notch to shape the appropriate flow pattern near the fishway entrance. The new wall optimized the flow field near the fish entrance to meet the hydraulic demands of target fishes under three operating scenarios, and the area of the suitable velocity zone increased by 48.79%, 12.71%, and 4.06% in scenarios 1 through 3, respectively. The original vertical slot fishway was modified with a sill to optimize the flow field inside the fishway. The optimized fishway design scheme reduced the main flow velocity inside the fishway to a large extent, and the maximum flow velocity in the upstream and downstream sections of the fishway decreased by 0.10 m/s and 0.09 m/s on average, respectively. The results of this study provide an important reference for the construction and optimization of fish passage facilities and have great significance for fish migration and biological diversity.

Effects of Nonlinearity on Velocity, Acceleration and Pressure Gradient in Free-Stream Zone of Solitary Wave over Horizontal Bed—An Experimental Study

For solitary waves on a horizontal bed, the study deals experimentally with the high ratio of wave height (H0) to still water depth (h0) that amplifies the wave nonlinearity. The value of H0/h0 tested in a wave flume ranges from 0.050 to 0.550, indicating the shift from a quasi-linear solitary wave to a highly nonlinear one. A high-speed particle image velocimetry (HSPIV) and a flow visualization technique of particle-trajectory tracking method are utilized to measure velocity fields and identify near-bed flow structures. The unsteady free-stream velocities with equal magnitude take place in a free-stream zone, FSZ). The FSZ underlies the internal flow zone, over which the external free surface of solitary wave exists and is situated beyond the boundary layer. The spatio-temporal variation of free-stream velocity, moving in phase with the free surface elevation, characterizes the pattern of pressure gradient in the FSZ and thus dominates the behavior of boundary layer flow. Accordingly, nonlinear effects on the time series as well as the maximum values of horizontal velocity, particle acceleration, and pressure gradient in the FSZs of solitary waves are presented. Before, at, and after the wave crest’s intersection with a given measurement location, favorable, zero, and adverse pressure gradients occur in the FSZ, respectively. For H0/h0 = 0.179, 0.363, and 0.550, the values of the dimensionless maximum free-stream velocity are about 3.10, 5.32, and 6.20 times that (= 0.0473) for H0/h0 = 0.050; and the corresponding values of the dimensionless maximum adverse pressure gradient are about 5.74, 14.54 and 19.84 times that (= 0.0061) for H0/h0 = 0.050. This evidence highlights the nonlinear effect on the kinematic and hydrodynamic features of solitary waves. Finally, the effect of nonlinearity on the relationship between the dimensionless time for the maximum adverse pressure gradient in the FSZ and that for the incipient flow reversal in the bottom boundary layer is explored for the first time. It is found that the incipient flow reversal takes place immediately after the maximum adverse pressure gradient, together with a decrease in the dimensionless time for flow reversal if H0/h0 increases. The fact accentuates the nonlinear effect on the incipient flow reversal right above the bed.

Marangoni flow patterns of molten pools in multi-pass laser cladding with added nano-CeO2

Adding rare-earth elements has been proven to modify the microstructure and enhance the mechanical properties of the laser cladding layer. However, the effect of such elements on the flow pattern in molten pools has not been extensively determined, especially for multi-pass laser cladding. The surface tension of T15 high speed steel and nano-CeO 2 mixed powders is measured using the sessile drop method. Comparing the results from the high-speed photography of the molten pool flow and the multicomponent multiphase flow model, various Marangoni flows driven by surface tension are elucidated, and the cross-section of the multi-pass cladding is further analyzed. The surface tension increases with increasing CeO 2 content. When CeO 2 is less than 0.6 wt%, the surface tension monotonically increases with increasing temperature, and the molten pool flows inward. When CeO 2 is greater than 0.6 wt%, the surface tension decreases at high temperatures, and the molten pool exhibits double flows. In multi-pass laser cladding, the inclination of the molten pool increases on adding CeO 2 . Consequently, the inclined angle of the cladding pass interface increases, and the fusion line on the substrate tends to be straightened. At 0.9 wt% CeO 2 , the added powders remain at the center of the molten pool because of a low velocity, creating a low-temperature zone. The temperature coefficient of surface tension demonstrates a positive–negative–positive distribution from the center to the surrounding pool surface, thus forming an outflow. The solidus point of the cladding alloys is lower than that of the substrate, resulting in a small indentation at the remelted region between passes, which increases the interfacial zone. • Flow in multi-pass molten pool changes from inward to outward with CeO 2 addition. • Surface tension curve drops at high temperature with CeO 2 composition above 0.6 wt%. • A low velocity and temperature zone forms in the center of molten pool at 0.9 wt% CeO 2 . • Fusion interface matching with experiments is dominated by flow and solidus point.

Lithospheric heterogeneities of northeast India and Indo-Burma region: Geodynamic implications

• Intercontinental subduction, Cenozoic volcanism and ductile sediments imaged. • Subducting Indian slab is imaged as high-Vp whilst volcanic front by low-Vp. • Dehydration of the slab, serpentinization of the forearc mantle imaged by low-Vp. • Very less seismicity due to ductility of the sediments. • Provides valuable information for intercontinental regions of analogous tectonics. In order to understand the geodynamical implications of intercontinental subduction, Cenozoic volcanism and ductile sediments in the northeast India and Indo-Burma region, a detailed 3-D P-wave tomography has been conducted using high-quality P-wave phase data recorded by local seismographic network ascribed to different agencies of India. This approach of using local earthquake data recorded by the portable seismographs installed for limited duration also provide an opportunity to adjudge the efficacy of local seismic network, which in turn enrich our understanding of intricate issues of Seismogenesis. P-wave tomographic imaging of lithospheric structure using arrival time data from local earthquakes recorded for the northeast India and Indo-Burma region revealed strong velocity heterogeneities beneath the region. The eastward subduction of the Indian slab beneath the Burmese arc with a dipping plane of intermediate-depth earthquakes has been imaged as high velocity (high-V) zones. Under the Cenozoic volcanic front in Burma, low velocity (low-V) anomalies are imaged. The low-V at shallow crustal layers may correspond to surface geological features, sedimentary materials or the faults associated with trapped fluids or loose pelgic sediments due to episodic tectonic upheavals, dehydration of the subducting Indian slab and serpentinization of the forearc mantle beneath the region, while high-V anomalies in the same depth range possibly indicate the presence of dense crystalline rocks under compressional stress that cause seismicity in the region. The distribution of seismicity is associated with major faults and lineaments associated with the distinct structural heterogeneities. The Bengal basin and the Central Burma Molasse basin exhibit low-V anomalies with very less seismicity due to ductility of the sediments. The low-V associated with the thick piles of sediments in the Bengal (>20 km) and Central Burma Molasse (≤12 km) Basin supported by the conspicuous distribution of low-Bouger gravity anomaly, which may have contributed significantly to major load along with an overthrust load of westward moving Indo-Burma ranges over the Indian lithosphere, which may amplify the stresses already acting on the Indian Plate due to load of the Himalaya, and making the region seismically more vulnerable. The present study is found to be in a good unison to the recent studies conducted in the region using different seismo-geophysical tools to different data set. The study provides valuable information on the lithospheric structures associated with seismogenesis and volcanic activity for the intercontinental regions, elsewhere in the world for our better understanding of geodynamical processes.

Crescent-Shaped Low-Temperature Distribution along the Convex Topography in the Southeastern Edge of Taiwan Bank in Summer

Abstract Various physical mechanisms of ocean upwelling usually occur near or along coastal regions worldwide. Five upwelling zones of unequal intensity are found around the Taiwan Strait, and the Taiwan Bank (TB) upwelling zone has the most prominent characteristics of low temperature. In this study, satellite images, shipboard ADCPs (acoustic Doppler current profilers), and CTDs (conductivity–temperature–depth measures) were analyzed to investigate the processes of cold water upwelling around the TB shoaling zone. In addition, the MITgcm numerical model and the flexible cubic spline technique were also employed, allowing us to better understand those processes. The model results suggested that a combination of Ekman transport and the centrifugal force, driven by the geostrophic South China Sea Warm Current (SCSWC), constitutes a physical mechanism to contribute the vigorous upwelling in the TB shoal zone. The upwelling is largely driven by Ekman transport. However, the centrifugal force may explain why the upwelling with a crescent-shaped distribution of low temperatures along the convex topography of the southeastern edge of the TB shoaling zone is more prominent than expected, as it tends toward the so-called gradient wind balance. Sudden relaxation of the friction force occurred because of the very sharp shelf break (20–60 m) and steep slope topography; a discontinuous velocity zone around the shelf break could also lead to vigorous cold water upwelling. Significance Statement Extensive data concerning the Taiwan Bank (TB) shoaling zone have been collected in the past decade in an attempt to improve understanding of the process of cold water upwelling in the area. Because the Kuroshio invades the South China Sea from the east, and the South China Sea Warm Current flows northeastward around the southeastern edge of the TB, water circulation in and around the sandbar is very complicated. Thus, we expanded our model range from small to large scale to avoid the open boundary settings of small-scale model (including the temperature and salinity fields, wind stress, and the model driving forces), which were not easy to set up. Thus, we used a large-scale, high-resolution circulation model to study a small-scale ocean region. Physical processes of this upwelling can finally be verified in the small-scale region. To compensate for the insufficient resolution of the large-scale numerical model, our strategy was to utilize the flexible cubic spline technique to resolve the curvature of the markedly meandering currents. In light of scale analysis, the results showed that in addition to the critical contribution of Ekman transport to the upwelling, the effects of centrifugal forces on upwelling in the TB shoal zone need to be considered.

The Effects of Pin Profile on HDPE Thermomechanical Phenomena during FSW.

Friction stir welding (FSW) of polymeric materials has recently attracted significant attention. Herein, we present the effect of the tool pin profile on the FSW of high-density polyethylene (HDPE) joints through joint experimental analysis and thermomechanical simulations. For analysis of pin profile effects on the thermomechanical properties of HDPE joints, frustum (FPT), cubic (CPT), and triangular (TPT) pin shapes were selected in this study. This research investigated the heat generation of the parts of the different tools as well as heat flux (internal and surface). The results revealed that the heat generation in pins with more edges (cubic (96 °C) and triangular (94 °C)) was greater than in pins with a smooth shape (frustum (91 °C)). The higher heat generation caused the heat flux on the surface of the HDPE from the cubic pin profile to be greater than for other joints. Due to the properties of HDPE, higher heat generation caused higher material velocity in the stirring zone, where the velocity of the materials in TPT, CPT, and FPT pins were 0.41 m/s, 0.42 m/s, and 0.4 m/s, respectively. The simulation results show sharp-edged pins, such as triangular and cubic, lead to over-stirring action and internal voids formed along the joint line. Furthermore, the simulation results indicated that the size of the stirred zones (SZs) of the FPT, TPT, and CPT samples were 17 mm2, 19 mm2, and 21 mm2, respectively, which is around three times the corresponding values in the HAZ.

Numerical Method to Generate and Evaluate Environmental Wind Over Hills: Comparison of Pedestrian Winds Over Hills and Plains

It is well known that the wind profile at altitudes below 10m from mean sea level (MSL) depends on the geometry of terrain, due to the boundary layer phenomenon. Hence, the profile of wind changes for hilly terrains and mountainous regions when compared with the plain regions. This phenomenon has become important to study due to the large-scale urbanisation taking place over hilly regions. The changing wind profile presents a challenge to evaluate the pedestrian winds, as depending on the aspect of the terrain an additional vertical velocity component is experienced due to the upwind climb of the winds. This creates a wind profile that is twisted in form. While wind tunnel studies have attempted to recreate this twisted wind profile (TWP), due to the inherent deficiency of wind tunnels to simultaneously map velocity and flow conditions, a lack of three-dimensional flow profile hinders pedestrian comfort evaluation. In the wind tunnel studies, it was also observed that small vertical eddies and wakes behind the interfering building were not identified which are an important factor to determine the pollution load dispersion. The authors have developed a numerical model to generate the twisted wind profile. The specialty of the numerical model lies in it’s unique boundary conditions that enable the visualization and quantification of the complete 3D wind profile, when the wind over a hilly terrain interacts with urban infrastructures. The developed model was validated with the wind tunnel experiments done previously by Tse and colleagues. The specialty of the model is that it ensures horizontal homogeneity while creating vertical heterogeneity. From the 3D flow profile hence generated the authors were able to deduce that the impact of twisted wind profile depends on the yaw angle of wind interacting with the structure and not on the wind attack angle. Also, the more the twist of the wind, more is the clockwise shifting of the far wakes behind the building. It was also seen that there are more low velocity zones in the pedestrian winds over a hill in comparison to that over the plains. The vertical eddies that aid in convective removal of pollutants were also missing in case of pedestrian winds over hilly terrains, which raises the risk of pollutant accumulation. The same was also observed in Hong-Kong during COVID 19, where due to the twisted nature of wind flow, the virus load increased and natural ventilation was inadequate in the removal of the viral load in the air near urban areas.

The root to the Galápagos mantle plume on the core-mantle boundary


 Ultra-low velocity zones (ULVZs) are thin anomalous patches on the boundary between the Earth's core and mantle, revealed by their effects on the seismic waves that propagate through them. Here we map a broad ULVZ near the Galápagos hotspot using shear-diffracted waves. Forward modelling assuming a cylindrical shape shows the patch is ~600 km wide, ~20 km high, and its shear velocities are ~25% reduced. The ULVZ is comparable to other broad ULVZs mapped on the core-mantle boundary near Hawaii, Iceland, and Samoa. Strikingly, all four hotspots where the mantle plume appears rooted by these ‘mega-ULVZs’, show similar anomalous isotopic signatures in He, Ne, and W in their ocean island basalts. This correlation suggests mega-ULVZs might be primordial or caused by interaction with the core, and some material from ULVZs is entrained within the plume. For the Galápagos, the connection implies the plume is offset to the west towards the base of the mantle. 

3D-ambient noise surface wave tomography of Fogo volcano, Cape Verde

Fogo volcano belongs to the Cape Verde Archipelago, and it is one of the most active volcanoes in the Atlantic Ocean, which most recent eruption occurred from November 2014 to February 2015. We analyzed ambient seismic noise recordings of three different networks deployed in the island, totalizing 14 seismic stations, to derive a crustal 3D shear-wave crustal velocity model of the volcano. Through the phase cross-correlation technique followed by a time-domain phase weighted stack, we were able to measure Rayleigh wave group-velocity dispersion measurements in the period range from 1.0 to 10 s. These dispersion measurements were used to invert for 2D group velocity maps at selected periods, and then inverted to produce a 3D shear-wave velocity model of the island. The tomographic model shows three velocity domains. First, an asymmetric upper layer, above 5–6 km of depth, with lower velocities concentrated in the northeastern sector of the island and a clear higher-velocity horizontal body at 3–4 km of depth in the southwestern sector of the island; the spatial correlation between these two velocity zones and the Galinheiros normal fault suggests a genetic link between the high velocities and long-term surface deformation, which we related to sill intrusions between 3 and 4.5 km depth, beneath the southwestern sector of the island. Second, a marked higher-velocity horizontal layer in between 5 and 6 km and 8–9 km, interpreted as the seismic expression of pervasive sill and laccolith intrusions, now cooled, beneath the volcanic edifice and within the underlying oceanic crust. Third, a lower velocity layer below 8–9 km of depth, more pronounced beneath the northeastern sector, which could be explained by a hotter and possibly melt-rich zone beneath the volcano or a significantly altered/serpentinized crust. Finally, our study also confirms that Fogo lacks any sizable magma chambers (ancient or recent) within the volcanic edifice, in agreement with other geophysical and petrological studies. These observations demonstrate that 3D-ambient noise Rayleigh wave tomography is a powerful tool to image the crustal and upper mantle structure beneath volcanic islands, as shown here for Fogo volcano.

Combining different 3-D global and regional seismic wave propagation solvers towards box tomography in the deep Earth

SUMMARY In previous publications, we presented a general framework, which we called ‘box tomography’, that allows the coupling of any two different numerical seismic wave propagation solvers, respectively outside and inside a target region, or ‘box’. The goal of such hybrid wavefield computations is to reduce the cost of computations in the context of full-waveform inversion for structure within the target region, when sources and/or receivers are located at large distances from the box. Previously, we had demonstrated this approach with sources and receivers outside the target region in a 2-D acoustic spherical earth model, and demonstrated and applied this methodology in the 3-D spherical elastic Earth in a continental scale inversion in which all stations were inside the target region. Here we extend the implementation of the approach to the case of a 3-D global elastic earth model in the case where both sources and stations are outside the box. We couple a global 3-D solver, SPECFEM3D_GLOBE, for the computation of the wavefield and Green’s functions in a reference 3-D model, with a regional 3-D solver, RegSEM, for the computation of the wavefield within the box, by means of time-reversal mirrors. We briefly review key theoretical aspects, showing in particular how only the displacement is needed to be stored at the boundary of the box. We provide details of the practical implementation, including the geometrical design of the mirrors, how we deal with different sizes of meshes in the two solvers, and how we address memory-saving through the use of B-spline compression of the recorded wavefield on the mirror. The proposed approach is numerically efficient but also versatile, since adapting it to other solvers is straightforward and does not require any changes in the solver codes themselves, as long as the displacement can be recovered at any point in time and space. We present benchmarks of the hybrid computations against direct computations of the wavefield between a source and an array of stations in a realistic geometry centred in the Yellowstone region, with and without a hypothetical plume within the ‘box’, and with a 1-D or a 3-D background model, down to a period of 20 s. The ultimate goal of this development is for applications in the context of imaging of remote target regions in the deep mantle, such as, for example, Ultra Low Velocity Zones.

Nitrate transport velocity data in the global unsaturated zones

Nitrate pollution in groundwater, which is an international problem, threatens human health and the environment. It could take decades for nitrate to transport in the groundwater system. When understanding the impacts of this nitrate legacy on water quality, the nitrate transport velocity (vN) in the unsaturated zone (USZ) is of great significance. Although some local USZ vN data measured or simulated are available, there has been no such a dataset at the global scale. Here, we present a Global-scale unsaturated zone Nitrate transport Velocity dataset (GNV) generated from a Nitrate Time Bomb (NTB) model using global permeability and porosity and global average annual groundwater recharge data. To evaluate GNV, a baseline dataset of USZ vN was created using locally measured data and global lithological data. The results show that 94.50% of GNV match the baseline USZ vN dataset. This dataset will largely contribute to research advancement in the nitrate legacy in the groundwater system, provide evidence for managing nitrate water pollution, and promote international and interdisciplinary collaborations.

Flow mechanism and axial force distribution characteristics of multistage pump cavity.

The gap leakage between the impeller ring leads to the change of the pump cavity flow characteristics, resulting in the uneven pressure distribution of shroud, which causes the axial force of the cavity to change. In this paper, the flow in the front and the rear cavity of the multistage centrifugal pump was taken as the research object. Through the numerical method, the radial flow velocity, the leakage flow size and its direction, the core zone rotation factor of the front and the rear cavity of the multistage pump impeller at all stages and the axial force of pump cavity were studied. The results show that the leakage in the front cavity of multistage pump impeller at all stages flows inward along radial direction (i.e. it flows from the inlet of pump cavity to the front ring clearance). The rotation factor in core zone is higher than 0.5, and with the increase of rotation factor, the axial force of the front pump cavity increased. The leakage in the rear pump cavity flows outward along radial direction (i.e. it flows from the rear ring to the inlet of pump cavity). The rotation factor in core zone is less than 0.5, and with the increase of rotation factor, the axial force decreased gradually. Besides, the radial velocity and rotation factor in the front and the rear multistage pump of impellers were obviously along the axial direction at three regions, the regions are pump case boundary layer, core zone and impeller boundary layer. The flow in the core zone is dominated by circumferential circular motion, and the radial velocity in the core zone is 0. It is shown that the direction of the leakage in the pump cavity and the rotation effect of the flow micelle in the mainstream core zone are the main factors affecting the axial force of the pump cavity, and the research results can provide theoretical guidance for the calculation and suppression of axial force of multistage pumps.

The effect of high and low velocity-based training on the throwing performance of collegiate handball players.

BackgroundThe intensity of strength training exercise is generally regarded to be the most essential element in developing muscle strength and power. The exercise intensity of strength training is known as one-repetition maximum (1RM). Velocity-based training (VBT) has been proposed as a different approach for determining training intensity. VBT relies on the use of linear position transducers and inertial measurement units, providing real-time feedback to objectively adjust the exercise intensity based on an athlete’s velocity zone.MethodsThis study investigated the effects of two different training interventions based on individualized load velocity profiles (LVP) on maximal bench press strength (i.e., 1RM), maximum throwing velocity (TV), and skeletal muscle mass (SKMM). Twenty-two university handball players were randomly assigned to Group 1 (low-movement speed training) or Group 2 (high-movement speed training). Group 1 exercised with a bar speed of 0.75–0.96 m/s, which corresponds to a resistance of approximately 60% 1RM, whereas Group 2 trained at 1.03–1.20 m/s, corresponding to a resistance of approximately 40% 1RM. Both groups exercised three times a week for five weeks, with strength and throwing tests performed at baseline and post-intervention.ResultsA two-way repeated measures ANOVA was applied, and the results showed the interaction between group and time was not statistically significant for SKMM (p = 0.537), 1RM (p = 0.883), or TV (p = 0.774). However, both groups significantly improved after the five weeks of training: SKMM (3.1% and 3.5%, p < 0.01), 1RM (15.5% and 15.0%, p < 0.01), and throwing velocity (18.7% and 18.3%, p < 0.01) in Group 1 and 2 respectively. Training at both prescribed velocities in this study elicited similar changes in strength, muscle mass, and throwing velocity.

Experimental investigation of flow pattern over a fully developed bed at a 60° river confluence in large floods

River confluences have a complex flow and sedimentation pattern that have vital influences on the hydraulic and bed morphology of river reach and the surrounding area. Confluences can be observed in waterways with various situations such as live bed conditions. This condition is a hydro-morphological situation with a high densimetric Froude number, i.e., bed load transport is supplied from upstream. According to the literature review, most of the experimental studies investigate the flow pattern on the flatbed and not on the developed riverbed, or/and in the low densimetric Froude number, or/and without supplying the sediment from upstream. Therefore, in the present study for the quantification of the flow pattern under these conditions, each developed bed was fixed with the cement blanket method in the laboratory. Then, the 3D velocity was measured at specific points at the confluence. The current study was designed to understand the flow pattern corresponding to the river bed behavior in the case of large floods. It is expected that the morphological features downstream of the confluence have a different pattern than the ones in the condition described in other literature. Thus, this paper describes briefly what are the different bed features and investigates the corresponding flow pattern. The results of the flow pattern on the developed bed show that all zones at the river confluence can be observed except the point bar due to the approximate equality of the mean longitudinal velocity of the separation zone and the main channel upstream of the confluence. Moreover, results show that by increasing the bedload ratio (sediment discharge to water discharge of the main channel of upstream of the confluence) from 0 to 3 × 10−4, flow deflection to the outer bank of the channel decreased down to 45%, the stagnation equivalent area decreased down to 2.5 times, and bed shear stress decreased down to 40%. Hence, the momentum of lateral flow decreased with increasing bedload. Besides, the recovery zone occurred at a longer distance after the confluence compared to the case without bedload. Hence, the location of the maximum velocity zone, vortices, and secondary flows changed downstream of the confluence, by changing the bed load value.

Crustal structure beneath the Cyclades Metamorphic Core Complex, Aegean Sea, Greece

The velocity structure of the crust and sediments of the Cyclades Metamorphic Core Complex (CMCC), central Aegean Sea, Greece, was obtained from active seismic observations. The CMCC comprises blueschists resulted from subduction during Eocene-Oligocene, and greenschists formed during exhumation and magmatic/volcanic intrusions during Miocene. Crustal thickness below the Myrtoon Sea is 23 km, thinning below Andros Island to 20 km and, gradually thickening towards the Chios Basin to 23 km, resulting to a dome structure. The upper crust is inhomogeneously structured with high Vp-velocity of 6.4 to 6.8 km/s, exposed to surface levels, followed by a velocity inversion of 5.8 to 5.5 km/s. Geometry of the velocity units indicates that, during crustal shortening, delamination of crustal layers involved in the subduction was significant. The high velocity units exposed on the islands correspond to pelagic volcano-sedimentary rocks and ophiolites of the Pindos-Cyclades oceanic domain, overthrusting low velocity units of the External Carbonate Platform of the Hellenides developed above continental crust that followed into the subduction. Internal thrusting and isoclinal folding have produced thickening of the Cycladic blueschists bearing nappes and duplication of the nappe pile with younger thrusting beneath Andros Island, resembling the structure of Northern Attica. Below the Chios Basin, velocity units are associated with the Internal Carbonate Platform of the Hellenides developed above the Pelagonian continental basement. Below the crust/mantle boundary we mapped reflectivity separating low velocity zones (7.5 to 7.9 km/s) up to 65 km depth. This low velocity upper mantle, associated also with low density, contributes to the isostatic equilibrium of the CMCC. Sediments of 2.6 to 3.6 km thickness are observed within post tectonic basins underlain by extensional detachments. The high velocity (4.8 to 5.3 km/s) sediments at the lower part of the surficial basins are most probably klippen of the Internal Carbonate Platform.

Precision Ventilation for an Open-Plan Office: A Study of Variable Jet Interaction between Two Active Chilled Beams

Precision ventilation is developed to achieve thermal comfort for occupants in an office by creating micro-climate zones. The present study aims to achieve individual thermal comfort for occupants with different metabolic rates by using higher airspeeds for enhancing heat transfer. The variable jet interaction between two ACBs with JetCone adjustments cause higher velocity jets to reach different regions of the occupied zone. The colliding jets from the center of a thermal isolated room were moved towards different zones in an office configuration with a constant room temperature of 23 °C. This study was conducted for five different cases in a room divided into four zones according to occupants’ metabolic rates. The experimental and CFD results show that occupants facing symmetrical airflow distribution and with a constant 1.2 metabolic rate (Case 1) had a similar predicted mean vote (PMV) index. The zones with higher-metabolic-rate occupants, i.e., 1.4 met and 1.6 met in cases 2 and 3 were exposed to air velocities up to 0.4 and 0.5 m/s, respectively. In case 4, the air velocity in the single zone with 1.6 met occupants was raised to 0.6 m/s by targeted airflow distribution achieved by adjusting JetCones. These occupants with higher metabolic rates were kept thermally neutral, in the −0.5 to +0.5 PMV range, by pushing the high velocity colliding jets from the center towards them. In case 5, the results showed that precision ventilation can maintain the individual thermal comfort of up to three different zones (in the same office space) by exposing the occupants with metabolic rates of 1.2, 1.4, and 1.6 met to airspeeds of 0.15, 0.45, and 0.55 m/s, respectively.

Numerical study of post-combustion characteristic in a smelting reduction furnace

Abstract For a smelting reduction furnace, the main role of the post-combustion operation in the upper space is to supply the energy required by the endothermic reduction reaction of iron oxide occurring in the melt bath, and thus the post-combustion behavior is important in the respect of reducing the coal consumption. In this paper, based on a developed 3D model composed of the Realizable k–ε model and DO radiation model, the post-combustion characteristics in a smelting reduction furnace was studied by numerical simulation, and the effects of top lance height, top-blown hot air flowrate and nozzle inclination angle of top lance on the flow and temperature fields, CO content distribution in the upper space were investigated. The results show that with the increase of top lance height, the length and temperature of combustion flame in the upper space increase, which is beneficial to expanding the post-combustion zone and improving the post-combustion of CO gas. And as the top-blown hot air flowrate increases, the position of the maximum temperature in the upper space gradually moves down and the CO content in gas mixtures decreases, which is conducive to the heat transport back to the melt bath. In addition, a proper velocity and temperature distribution in the upper space and distribution of CO content is obtained under the nozzle inclination angle range from 10° to 15°, but a larger nozzle inclination angle reduces the velocity and temperature in the central zone.

A model developed for predicting thermal comfort during sleep in response to appropriate air velocity in warm environments

Using air movement to improve sleeping environments is widely practiced in summer; while research into how to evaluate thermal comfort and sleep quality under such non-uniform environments is lacking, due to the greatly reduced ability of occupants to adjust to the immediate environments during sleep. This study conducted climate chamber sleeping experiments under a combination of conditions of temperature (28 / 30 / 32 °C), relative humidity (50% / 80%), and air velocity (0.39 / 0.69 / 1.17 m / s). The results showed that the appropriate air velocities alleviated the thermal discomfort caused by higher temperature and humidity; however, when the temperature was higher than 32 °C and coupled with high humidity, the cooling efficiency of air velocity was reduced significantly. The subjective evaluations of sleep quality were consistent with the measured sleep indicators - Total Sleep Time (TST), Sleep Onset Latency (SOL), and Slow Wave Sleep (SWS) - indicating that recall-based sleeping evaluations after waking up could reflect the actual sleep quality to some degree. A developed PMVs model was proposed considering three aspects of the body heat exchanges: the parts in contact with the mattress (e.g. back, buttocks), the parts covered by the quilts or clothes (e.g. abdomen, chest), and the parts directly exposed to the air (e.g. head, arms, legs). The upper temperature and humidity limits, appropriate air velocity zones, and different bedding thermal insulation levels were thus obtained. The work can guide the application of local ventilation devices in sleeping environments in summer and contribute to reducing the use of air conditioners and achieving energy savings in residential buildings. • Explore sleep thermal comfort in warm-humid environments with air movement. • Increased airflows improve the sleeping thermal comfort except for hot-humid condition. • Subjective evaluations are consistent with measured sleep indicators such as Total Sleep Time (TST). • Develop a PMVs model including three heat exchange aspects with/without body coverings. • Appropriate temperature, humidity and air velocity designs are obtained by PMVs model.