Total Open Area Research Articles

Effect of natural ventilation on aerosol transmission and infection risk in a minibus

High passenger density, prolonged exposure, and close interpersonal distance create a high infection risk (IR) in minibuses. While improving natural ventilation induced by turbulent airflows is essential for controlling IR in minibuses, comprehensive studies on its effectiveness are lacking. To address this, we conducted computational fluid dynamics simulations studies coupling indoor–outdoor turbulent airflows to examine the impact of window opening locations, window opening sizes, and initial droplet diameters (dp) on the ventilation airflow and dispersion of pathogen-laden droplets. Results show that the surrounding turbulent flow patterns create higher surface pressure at bus rear than bus front, which is a key factor influencing bus ventilation. When all windows are closed, ventilation is primarily provided by skylights at bus rooftops. Ventilation through only two skylights resulted in an air change rate per hour (ACH) of 17.55 h−1, leading to high IR of passengers. In contrast, fully opening front and rear windows increases ACH by 27.28-fold to 478.79 h−1, significantly reducing IR by 1–2 orders of magnitude compared to skylight ventilation. Expanding window opening sizes can effectively enhance ventilation when both front and rear windows open (attributed to the pumping effect), while is ineffective when only front windows open. To reduce IR in minibuses, we recommend opening multiple windows at the bus front and rear. Even if the total opening area of the front and rear windows is only two-thirds of that of the front window, its ACH is 2.8 times more than only opening front windows.

Optimizing ventilated packaging design for strawberries: Assessing the impact on fruit quality from farm to retailer using physics-based modeling

Amongst fruits and vegetables, strawberries (Fragaria × ananassa) are one of the most perishable products. Consequently, it is challenging to maintain their quality until they reach the consumer. Therefore, keeping optimal hygrothermal conditions around the berries from farm to the consumer is crucial to preserving them and avoiding food loss. Using ventilated packaging design is an established way to address this technological, economic, and environmental problem. Until now, strawberry packaging is often designed using a trial-and-error approach, and a multitude of packaging designs exist. Ideally, the packaging should be designed in such a way that it provides the best preservation of the fruit all the way from farm to retailer. This is challenging since the hygrothermal conditions change significantly along the supply chain. In this study, we use physics-based modeling to evaluate new strawberry packaging designs in regard to cooling performance, risk of condensation, mass loss, and respiration-driven shelf life of the fruit and assess their performance along the whole post-harvest export supply chain from Spain to Switzerland. Twelve packaging designs for strawberries with existing and newly-designed vent hole configurations were investigated. Simulations quantified how the berries physiologically and hygrothermally evolve inside these packages along the whole post-harvest supply chain. Implementing appropriate ventilation in open-and top-sealed trays for strawberries can help to minimize losses along the post-harvest supply chain. As commonly known, strawberries cool significantly faster in better-ventilated trays than in unventilated trays, and condensation-based time of wetness could be reduced by 45% by adding additional ventilation holes in a top-sealed tray. The height of the secondary packaging, the total opening area (TOA), the size, and the placement of the vents have a substantial influence on the performance of the packaging. We recommend a TOA between 5.5% and 7% and a diameter of the vents between 5 and 12 mm. Also, they should be evenly distributed. However, there is always a trade-off in packaging design: a reduced risk of condensation comes along with a higher mass loss of the strawberries. Strawberry packaging models enabled a unique insight into the evolution of the fruits along the supply chain and visualized the spatial distribution of condensation and mass loss inside the package.

Numerical Investigation on Strengthening of Steel Beams for Corrosion Damage or Web Openings Using Carbon Fiber Reinforced Polymer Sheets

Fiber-reinforced polymers (FRPs) have been widely used to strengthen steel structures, which could suffer from corrosion or the introduction of web openings, for utilities such as ductwork, plumbing, electrical conduits, and HVAC systems. The present numerical study involves the application of unidirectional carbon FRP (CFRP) sheets to steel I-beams, damaged due to corrosion or web openings, to regain their lost load-carrying capacity. Finite element analysis (FEA) was utilized to develop and validate three beam models against existing experimentally tested specimens. Subsequently, a parametric study was conducted investigating the effect of various corrosion levels and the number of circular web openings on the yield and ultimate load capacities of the beams. The optimum number of CFRP layers needed to strengthen corroded beams was determined and six CFRP strengthening scenarios were adopted to determine the best configurations to retrofit steel beams with openings (SBWOs). The results revealed that corrosion, introduced by thinning the bottom flange, reduced both yield and ultimate load capacities, with a nearly perfect linear reduction in ultimate load for each 2.5% thickness loss. The optimum number of CFRP layers depended on the level of corrosion damage. Furthermore, while maintaining a constant total opening area, beams with a greater number of smaller circular web openings demonstrated higher yield and ultimate load capacities than those with fewer larger openings. Out of the six adopted CFRP strengthening scenarios, three configurations that involved applying CFRP sheets to both flanges and the web effectively restored the strength of SBWOs, when adequate CFRP layers were used.

Air change rates and infection risk in school environments: Monitoring naturally ventilated classrooms in a northern Italian urban context

The importance of building ventilation in avoiding long-distance airborne transmission has been highlighted with the advent of the COVID-19 pandemics. Among others, school environments, in particular classrooms, present criticalities in the implementation of ventilation strategies and their impact on indoor air quality and risk of contagion. In this work, three naturally ventilated school buildings located in northern Italy have undergone monitoring at the end of the heating season. Environmental parameters, such as CO2 concentration and indoor/outdoor air temperature, have been recorded together with the window opening configurations to develop a two-fold analysis: i) the estimation of real air change rates through the transient mass balance equation method, and ii) the individual infection risk via the Wells-Riley equation. A strong statistical correlation has been found between the air change rates and the windows opening configuration by means of a window-to-volume ratio between the total opening area and the volume of the classroom, which has been used to estimate the individual infection risk. Results show that the European Standard recommendation for air renewal could be achieved by a window opening area of at least 1.5 m2, in the most prevailing Italian classrooms. Furthermore, scenarios in which the infector agent is a teacher show higher individual infection risk than those in which the infector is a student. In addition, the outcomes serve school staff as a reference to ensure adequate ventilation in classrooms and keep the risk of infection under control based on the number of the students and the volume of the classroom.

Performance of Reinforced Concrete Gable Beam with Quadrilateral Openings of Different Side Inclinations

The existence of openings in a gable beam would have numerous advantages, the most important of which would be a reduction in the overall weight. These advantages include geometric flexibility, ease of handling when erected, and more. This study aims to investigate the flexural behavior of reinforced concrete gable beams with quadrilateral openings of different side inclinations; this goal has been specified with beam stiffness, the maximum load-carrying capacity, and strains of the beams. Beams are identical in their dimensions and reinforcement. The experimental program involved casting and testing four simply supported beams: a solid beam (reference beam) and others with quadrilateral openings. They were 3000mm long, 100mm wide, and 400 mm deep in the middle, tapering to 250 mm on both ends, concentrically loaded. The results demonstrate the load-carrying capacity is reduced by 6.1–12.9%, and the mid-span deflection is increased by 13–52% when openings exist compared to the solid gable beam. Enhancement represented by increases in strength and decreases in deflection was observed when the inclination of the quadrilateral side opening decreased from 90 to 60 and then 45o, respectively. In contrast, the total opening area was maintained. The creation of openings in concrete gable beams can reduce their weight by about 12.5%.

Changes in Nesting Habitat Availability for Piping Plovers at the John E. Williams Preserve, North Dakota, 1992–2021

Habitat loss is a major threat to the conservation of endangered species. We measured changes in piping plover (Charadrius melodus) nesting habitat at five alkali wetlands in The Nature Conservancy's John E. Williams Preserve, McLean county, North Dakota, from 1992 to 2021. This site has supported nesting by federally threatened piping plovers for decades. We measured the amount of non-vegetated (open) shoreline, required nesting habitat for plovers, from photo plots at 34 sites historically occupied by plovers distributed across the five wetlands. Twenty-six of 34 plots had significant negative trends (95% credible intervals not including zero) in nesting area availability. Nesting habitat increased significantly at one plot. Seven other plots had no detectable trends (i.e., the 95% credible intervals included zero). Mean percent annual change was –1.2% (±0.17 SE) and estimated total loss of nesting habitat within plots was ∼42%. To assess whether plover nesting habitat might have been created at areas outside of our plots, we compared total open shoreline habitat over all five wetlands in 1992 to that in 2017. We detected a ∼42% decline in total open shoreline area. Although measurement methods differed between 1992 and 2017, we found no evidence that nesting habitat was created at non–photo plot areas. In the absence of habitat restoration and management the decline in piping plover nesting habitat is likely to continue. Climate change projections for North Dakota indicate increased annual rainfall, higher CO2 levels, and longer growing seasons, all factors likely to promote vegetative growth at alkali wetlands like those we studied.

Influence of air-assisted atomizer structure on ignition and flame propagation in a trapped-vortex cavity

This study explores the application of a partially-premixed and pre-evaporated air-assisted fuel supply device used in a trapped-vortex cavity. The lean-ignition fuel-air ratio (FAR) was measured under different device structures, total pressures, and incoming Mach numbers. The spanwise flame propagation process was captured by a high-speed camera. Results show that the fuel supply device has outstanding ignition performance, which can realize stable ignition under the total pressure of 0.05 MPa; the lean-ignition FAR never exceeds 0.0044 during the tests. With the increase of the total pressure, the ignition FAR decreases significantly; the rise in inlet Mach number will make the ignition FAR show a decrease-increase trend. Increasing the evaporation pipe's orifice diameter and number will reduce this ignition FAR, which can be attributed to the change in the internal flow field and fuel distribution caused by the rise of the orifice's total opening area. In addition, the flame propagation in the cavity is also affected by the structure of the fuel supply device: a larger opening area will increase the time required for flame spreading in the spanwise direction.

Analysis of different ventilation strategies and CO2 distribution in a naturally ventilated classroom

CO2 monitoring has proven to be an effective and affordable way of controlling air ventilation rates, a paramount task for minimizing airborne contagions in indoor shared spaces. In this work, the CO2 distribution in a naturally-ventilated classroom has been thoroughly characterized, gaining information not only on the effectiveness of diverse ventilation strategies but also on the expected differences between CO2 values when varying the sampling location within the room. The results confirm that an adequate renewal of the air in the room requires the use of cross-ventilation, with openings in different walls. Furthermore, it was found that ventilation is optimized, for a given total opening area, when the openings are distributed as much as possible among different windows. For most of the studied conditions, a global windows opening area of 1.24 m2 with an open door was typically enough to yield CO2 concentrations below 700 ppm. The CO2 readings displayed a noticeable and consistent dependency on the sampling height, with below-average values at 0.75 m, the highest concentrations at 1.5 m, and levels close to the average when sampling at a height of 2.2 m. For a given height, the influence of the sampling location within the room was weaker, and more dependent on the specific ventilation strategy applied. However, the tests consistently showed CO2 records significantly lower for sensors installed on the walls. Besides a detailed spatial and temporal characterization of the ventilation process under different ventilation strategies, these results are thought to provide useful and novel information for a judicious placement of CO2 monitoring systems.

Investigation on seismic behavior of RC shear walls with multiple post-construction openings based on experiment and simulation

The quasi-static tests and finite element simulations of one shear wall without openings and three shear walls with the same total area but different arrangement of post-construction openings were carried out. The failure modes, ultimate loading capacities, skeleton curves, energy dissipation capacities, shear deformations and strain distribution of the shear wall specimens were obtained and analyzed. The results showed that the layout of post-openings has different effects on the failure mode of shear wall. The failure modes of shear wall without openings and the wall with two post-openings arranged vertically in the middle are flexural shear failure with damage at the wall base, while that of the shear wall with one post-openings in the middle or two post-opening arranged horizontally in the middle is shear failure which occurred on the wall limbs on both sides of the openings. The opening generates redistribution of strains in the wall, revealing that the largest strain does not occur at the bottom of the wall, but at the upper corner and bottom corner of the openings, which leads to the vertical reinforcement near the opening to bear greater stress, so it reaches the yield earlier than that in the wall without opening. Compared with the shear wall without openings, the wall with two openings in the horizontal direction has the minimum residual bearing capacity, ductility and energy dissipation capacity, while the wall with two openings in the vertical direction had the maximum residual bearing capacity, ductility and energy dissipation capacity. The energy dissipation capacity, the shear deformation as well as the contribution of shear deformation to the total deformation were all significantly reduced by post-openings.

Analysis of the geometric and natural properties of courtyards in historical houses of Isfahan (Iran)

ABSTRACT Courtyard” is one of the ancient domestic identity patterns of Iranian architecture in most of the traditional houses in hot and dry climate. The aim of this study is to identify the geometric and natural characteristics of courtyards in historical houses of Isfahan city in hot-arid climate. In this research, thirty historical courtyard houses were selected and analyzed as the case studies. The results show that the average ratios of length/width, height/length and height/width of the courtyards are 1.3, 0.3 and 0.4, respectively. The courtyard area averagely covers 31% of total area of houses and about 29% of the courtyard area is allocated to natural elements: 7% to water surface and 22% to plant coverage. The average ratio of the total area of openings to courtyard walls is 35%. As final results, the linear equations and correlation coefficients between the geometric and natural properties of courtyard houses are presented. The results of this research could be used as design guides for contemporary courtyards in hot-arid climate especially in Isfahan city.

Boundary layer wind tunnel modeling experiments on pumping ventilation through a three-story reduce-scaled building with two openings

Pumping ventilation is a special single-sided wind driven building ventilation induced by periodic vortex shedding at the building wake. This work aimed to investigate the oscillating frequency at the building façade opening and ventilation rate of pumping ventilation. The effects of opening separations on different floors of a three-story reduce-scaled building with two openings were considered using boundary-layer wind tunnel experiments. The wind velocity of the surrounding flow field and the center of the opening were measured. The ventilation rate was obtained by tracer gas method with constant and continuous injection rate. The results showed that the oscillating frequency was independent of the opening separation except on the third floor probably because of the disturbance of the rooftop shedding frequency. The oscillating frequency on the first floor was the lowest due to the resistance of the ground to the vortex shedding. Pumping ventilation indicated that its ventilation rate is greater than that of general ventilation across the single opening with the same total opening area. The promotion of ventilation rate was up to about 123% on the first floor, about 65% on the second floor and about 44% on the third floor. Expansion of opening separations could boost the ventilation rate. Meanwhile, the fluctuation of opening center wind velocity and indoor species concentration were not positively correlated with the ventilation rate of pumping ventilation. Conclusions of this research could provide some useful reference to the design of natural ventilation for buildings.

STUDI WINDOW-TO-WALL RATIO PADA KANTOR PEMERINTAH DI JAKARTA SELATAN

Kantor pemerintah merupakan bangunan yang diharapkan dapat menjadi contoh sebagai bangunan hemat energi yang baik. Banyak usaha yang dapat dilakukan untuk menghemat energi, salah satunya memperhatikan desain fasade. Jendela sebagai bukaan pada fasade dapat diatur sedemikian rupa sehingga panas matahari tidak membuat peningkatan energi untuk mendinginkan ruangan sekaligus mengurangi penggunaan lampu pada siang hari. Salah satu aspek yang dapat digunakan untuk menilai kinerja bukaan jendela adalah Window-to-Wall Ratio (WWR). Rasio diperoleh dengan membagi total luas bukaan pada dinding yang menggunakan kaca dengan luas permukaan keseluruhan bidang selubung bangunan. Tujuan dari penelitian ini adalah mempelajari nilai WWR dari bangunan kantor pemerintahan yang ada di Jakarta Selatan. Penelitian ini menggunakan tampak bangunan dari 20 gedung kantor pemerintahan di Jakarta Selatan sebagai kasus studi. Hasil penelitian berupa nilai rata rata WWR kantor pemerintahan yang nantinya dibandingkan dengan rata-rata WWR kantor sejenis dari literatur lain. Dari hasil penelitian, diperoleh rata rata nilai WWR sama dengan 24.6%, yang mana masih berada di rentang WWR dalam penelitian lain.Kata kunci : Hemat Energi, Selubung Bangunan, Kantor Pemerintah, Window-to-Wall Ratio (WWR)

Carbon dioxide hydrodynamics along a wetland-lake-stream-waterfall continuum (Blue Mountains, Australia).

The small-scale spatial variability in dissolved carbon dioxide (CO2) and water-air CO2 flux dynamics were investigated within first-order catchments of the upper Blue Mountains Plateau (New South Wales, Australia). Water samples were collected at 81 locations during winter and summer over two consecutive years across seven aquatic ecosystem types: wetland, impoundment, lake, tributary stream, mainstem, escarpment complex, and urban-aquatic interface. Dissolved [CO2] ranged from 15 to 880μM (94 to 4760%Sat), and dissolved [O2] from 0 to 350μM (0 to 101%Sat). CO2 supersaturation was typically highest in wetlands and vegetated impoundments of the upper plateau, and decreased downstream approaching atmospheric equilibrium at the escarpment waterfalls. Gas transfer velocities ranged from 0.18m d-1 in lentic waters to 292m d-1 at the bottom of waterfalls due to bubble-mediated transfer. The first- and second-order streams represented only 4.8% of the total open water area yet contributed to 61% of the total water-air CO2 outgassing. The lake, escarpment and mainstem group systems had narrow diel and seasonal CO2 concentration variability, while wetlands and vegetated impoundments had the widest ranges. Our high resolution spatio-temporal sampling was essential to identifying CO2 outgassing hotspots in these geomorphically diverse catchments. Overall, >95% of excess dissolved CO2 traversing the upper Blue Mountains Plateau was outgassed to the atmosphere.

Crab burrow aspect ratio influences particle capture rates on intertidal sandflats

Crabs are ecosystem engineers that dig burrows, which can trap sediment. We used a field experiment to explore how burrow aspect ratio (depth/diameter) affects the trapping efficiency of sediments and organic material. Arrays of burrows mimics were constructed using tubes of similar depths but two different opening diameters: fat tubes (aspect ratio of 3.8) and thin tubes (7.1). Different arrays were tested to examine whether the combination of burrows with two different aspect ratios affects the material capture, while retaining the same total area of openings per array. The results showed that, in general, the fat tubes trapped more organic material, especially large pieces, and more sediment than thin tubes. Furthermore, the silt-clay content of the sediment trapped in the tubes was up to 50% greater than the surrounding surficial sediment. Hence, we conducted 2D numerical simulations of flow around, and into, a single burrow to elucidate the mechanisms behind particle capture. Results showed that the flushing rate and the turbulent kinetic energy were greater in the fat tubes. However, turbulence persisted for a longer distance downstream of the thin tubes than the fat tubes. The enhanced turbulence may increase the flux of sediment into the tubes where particles can settle and, consequently, promote the sediment capture and sedimentation rate. Our results demonstrate that the aspect ratio of burrows significantly affects capture processes of organic material and sediment particles. Moreover, this capture mechanism depends on the flow regime, as faster flows are associated with larger amounts of material in the water column.

Prediction of cooling efficiency of forced-air precooling systems based on optimized differential evolution and improved BP neural network

This paper proposes an approach to predict the efficiency of forced-air cooling of fresh apples that combines the optimized differential evolution (DE) algorithm and the back-propagation (BP) neural network algorithm. First, to balance population diversity and fast convergence, the individual mutation operation of the basic DE algorithm was optimized by dividing the entire population into two equal parts according to the fitness value of individuals, and DE-best-1 and DE-current-to-rand-1 are used as individual mutation operations for the superior- and inferior-part individuals, respectively. Moreover, the selection operation of basic DE was also changed by using a crowding scheme, which helps maintain population diversity and discover more regions containing the global optima. Second, an optimized DE-BP neural network model was established by using the optimized DE to determine the initial weights and thresholds of the BP neural network to avoid being trapped in local minima, following which the effect of input parameters on the network output was subjected to a comprehensive sensitivity analysis based on the trained neural network. The results show that the optimized DE-BP model accurately predicts the efficiency with which apples are cooled. Furthermore, the airflow velocity and total opening area have a significant negative correlation with the average apple temperature and a positive correlation with the cooling rate of the apples. Finally, the most important factor influencing the cooling efficiency of the pre-cooling system is the total opening area of the ventilated packaging.

Comparison of LiDAR and Digital Aerial Photogrammetry for Characterizing Canopy Openings in the Boreal Forest of Northern Alberta

Forest canopy openings are a key element of forest structure, influencing a host of ecological dynamics. Light detection and ranging (LiDAR) is the de-facto standard for measuring three-dimensional forest structure, but digital aerial photogrammetry (DAP) has emerged as a viable and economical alternative. We compared the performance of LiDAR and DAP data for characterizing canopy openings and no-openings across a 1-km2 expanse of boreal forest in northern Alberta, Canada. Structural openings in canopy cover were delineated using three canopy height model (CHM) alternatives, from (i) LiDAR, (ii) DAP, and (iii) a LiDAR/DAP hybrid. From a point-based detectability perspective, the LiDAR CHM produced the best results (87% overall accuracy), followed by the hybrid and DAP models (47% and 46%, respectively). The hybrid and DAP CHMs experienced large errors of omission (9–53%), particularly with small openings up to 20m2, which are an important element of boreal forest structure. By missing these, DAP and hybrid datasets substantially under-reported the total area of openings across our site (152,470 m2 and 159,848 m2, respectively) compared to LiDAR (245,920 m2). Our results illustrate DAP’s sensitivity to occlusions, mismatched tie points, and other optical challenges inherent to using structure-from-motion workflows in complex forest scenes. These under-documented constraints currently limit the technology’s capacity to fully characterize canopy structure. For now, we recommend that operational use of DAP in forests be limited to mapping large canopy openings, and area-based attributes that are well-documented in the literature.

Aortic valve opening and closure: the clover dynamics.

Systolic aortic root expansion is reported to facilitate valve opening, but the precise dynamics remain unknown. A sonometric study with a high data sampling rate (200 to 800 Hz) was conducted in an acute ovine model to better understand the timing, mechanisms, and shape of aortic valve opening and closure. Eighteen piezoelectric crystals were implanted in 8 sheep at each annular base, commissures, sinus of Valsalva, sinotubular junction, nodulus of Arantius, and ascending aorta (AA). Geometric changes were time related to pressures and flows. The aortic root was hemodynamically divided into left ventricular (LV) and aortic compartments situated, respectively, below and above the leaflets. During isovolumetric contraction (IVC), aortic root expansion started in the LV compartment, most likely due to volume redistribution in the LV outflow tract below the leaflets. This expansion initiated leaflet separation prior to ejection (2.1%±0.5% of total opening area). Aortic compartment expansion was delayed toward the end of IVC, likely related to volume redistribution above the leaflets due to accelerating aortic backflow toward the aortic valve and coronary flow reduction due to myocardial contraction. Maximum valve opening during the first third of ejection acquired a truncated cone shape [leaflet free edge area smaller than annular base area (-41.5%±5.5%)]. The distal orifice became clover shaped because the leaflet free edge area is larger than the commissural area by 16.3%±2.0%. Aortic valve opening is initiated prior to ejection related to delicate balance between LV, aortic root, and coronary dynamics. It is clover shaped at maximum opening in systole. A better understanding of these mechanisms should stimulate more physiological surgical approaches of valve repair and replacement.

Physical modeling of vortical cross-step flow in the American paddlefish, Polyodon spathula.

Vortical cross-step filtration in suspension-feeding fish has been reported recently as a novel mechanism, distinct from other biological and industrial filtration processes. Although crossflow passing over backward-facing steps generates vortices that can suspend, concentrate, and transport particles, the morphological factors affecting this vortical flow have not been identified previously. In our 3D-printed models of the oral cavity for ram suspension-feeding fish, the angle of the backward-facing step with respect to the model’s dorsal midline affected vortex parameters significantly, including rotational, tangential, and axial speed. These vortices were comparable to those quantified downstream of the backward-facing steps that were formed by the branchial arches of preserved American paddlefish in a recirculating flow tank. Our data indicate that vortices in cross-step filtration have the characteristics of forced vortices, as the flow of water inside the oral cavity provides the external torque required to sustain forced vortices. Additionally, we quantified a new variable for ram suspension feeding termed the fluid exit ratio. This is defined as the ratio of the total open pore area for water leaving the oral cavity via spaces between branchial arches that are not blocked by gill rakers, divided by the total area for water entering through the gape during ram suspension feeding. Our experiments demonstrated that the fluid exit ratio in preserved paddlefish was a significant predictor of the flow speeds that were quantified anterior of the rostrum, at the gape, directly dorsal of the first ceratobranchial, and in the forced vortex generated by the first ceratobranchial. Physical modeling of vortical cross-step filtration offers future opportunities to explore the complex interactions between structural features of the oral cavity, vortex parameters, motile particle behavior, and particle morphology that determine the suspension, concentration, and transport of particles within the oral cavity of ram suspension-feeding fish.

Solar Open Flux Migration from Pole to Pole: Magnetic Field Reversal

Coronal holes are solar regions with low soft X-ray or low extreme ultraviolet intensities. The magnetic fields from coronal holes extend far away from the Sun, and thus they are identified as regions with open magnetic field lines. Coronal holes are concentrated in the polar regions during the sunspot minimum phase, and spread to lower latitude during the rising phase of solar activity. In this work, we identify coronal holes with outward and inward open magnetic fluxes being in the opposite poles during solar quiet period. We find that during the sunspot rising phase, the outward and inward open fluxes perform pole-to-pole trans-equatorial migrations in opposite directions. The migration of the open fluxes consists of three parts: open flux areas migrating across the equator, new open flux areas generated in the low latitude and migrating poleward, and new open flux areas locally generated in the polar region. All three components contribute to the reversal of magnetic polarity. The percentage of contribution from each component is different for different solar cycle. Our results also show that the sunspot number is positively correlated with the lower-latitude open magnetic flux area, but negatively correlated with the total open flux area.

Antiflotation design for water tank using pressure relief technique

ABSTRACTA pressure relief technique has been proposed to reduce hydrostatic pressures by opening drainage holes around a water tank. This solution is evaluated by laboratory experiments and numerical parametric investigation. After seepage flow is allowed, the hydraulic head acting on the water tank is reduced due to seepage losses. The drainage holes should be opened on the base slab near the sidewalls, and at a certain height on the sidewalls. Given a fixed total opening area, the number of drainage holes with smaller diameter should be allowed near the edge of the water tank to increase the efficacy of the approach. The properties of the surrounding soil influence the results significantly, where a cushion layer with a higher hydraulic conductivity and a greater thickness is beneficial to the stability of the water tank, and a backfill layer with adequate thickness and hydraulic conductivity should be selected. An illustrative example is given in the end to demonstrate the advantage of the proposed antiflotation design strategy compared to the conventional enhanced self-weight method, and more economic design using less reinforcement and concrete can be achieved.