Critical Height Research Articles

Continuous successive cycles of biosorption and desorption of acid red 27 dye using water hyacinth leaves as an effective, economic, and ecofriendly biosorbent

We investigated the capacity of water hyacinth leaves (LEC) to biosorb 75 mg/L acid red 27 (AR27) in a continuous system comprising 30 successive biosorption/desorption cycles in a packed-bed column at pH 2.0 and 56.5 L/m2·h volumetric flux. Using 0.025 M NaHCO3 eluent at 113 L/m2·h volumetric flux, all the dye was desorbed (100% desorption efficiency) from the loaded LEC biomass within 5–6 h. The same biosorbent was used for 147.5 consecutive days. The AR27 biosorption capacity, breakthrough time, and exhaustion time decreased from 69.4 to 34.5 mg/g, 74.81 to 14.1 h, and 101.1 to 34.1 h, respectively, and the critical bed height increased from 1.04 to 2.35 cm, as the number of biosorption/desorption cycles increased from 1 to 30. LEC life factor based on biosorption capacity predicted that the packed bed would be exhausted after 51.95 cycles. LEC is a promising biosorbent for bioremediation of AR27-laden wastewaters.

The theoretical model and verification of electric-field-driven jet 3D printing for large-height and conformal micro/nano-scale parts

ABSTRACT Electrohydrodynamic (EHD) jet printing, as one of the most popular micro/nano-scale additive manufacturing methods, is still facing challenges in large-height printing and conformal printing due to poor electric field stability. The newly proposed electric field-driven (EFD) jet 3D printing has claimed better electric field stability. To reveal changing behaviour and generation mechanism of the electric field in 3D printing, an electric field model for EFD jet 3D printing was built and further validated by simulation and experiments (line width and critical voltage vs. printing height). Then, the advantage of the EFD method over EHD was confirmed by a case application of conformal printing with a height difference of larger than 9 mm and a multi-layer structure with a height of 5 mm and a line width of 20 μm. Therefore, the EFD jet 3D printing offers the possibility of achieving 3D printing in a larger height range with better electric field stability.

Risk Assessment for Critical Flood Height of Pedestrian Escape in Subway Station

The escape of pedestrians in the subway station is hampered by floods created by heavy rain. In order to explore the critical flood level in a subway station so that pedestrians can escape safely, the case study of the Mingxiu Road subway station in Nanning, China, was conducted using numerical simulation techniques. In total, 30 groups of sample pedestrians with different walking speeds and numbers were randomly generated by the Monte Carlo method, and 3D simulation software was used for escape simulation. The simulated escape data were put into the SVM model, and the maximum pedestrian capacity and minimum speed of pedestrians were solved successfully with different conditions of the Mingxiu Road subway station. Then, a 1:1 contour model of the pedestrian was constructed to simulate the flood resistance of the pedestrian escaping at the minimum speed. The flood resistance and the friction force between the pedestrian and the ground were compared to calculate the critical escape flood level height, and the critical escape flood level height of an adult, child, and elder was 87.4 cm,75.5 cm, and 83.0 cm, respectively.

Optimizing Design of Vortex Suppression Utilizing Static Electromagnetic Field during Steel Teeming from Ladle

Vortex slag entrapment during ladle teeming process causes liquid steel pollution, nozzle clogging, etc. Tangential velocity of molten steel is directly related to the vortex. Herein, the tangential velocity is reduced by the electromagnetic force generated by the interaction between a static electromagnetic field and the molten steel. Through the multiphysical field simulation, influences of the electromagnetic parameter, coil structure, coil position, and ladle structure on the vortex are investigated. Results demonstrate that magnetic induction intensity is proportional to the coil ampere‐turns, thereby affecting the vortex suppression. The action region of the static electromagnetic field expands when the coil diameter increases from 180 to 360 mm; it is beneficial to reduce the vortex critical height by 37.9%. The reduction of the distance between the coil and the molten steel also promotes the vortex suppression. The coil misalignment is beneficial to fully utilize the electromagnetic field; the critical height is reduced by 15%. The tangential velocity is changed when the nozzle diameter and eccentricity are optimized, and the vortex suppression will be amplified by using the electromagnetic field. This study provides the theoretical guidance for the optimizing design of the vortex suppression utilizing the static electromagnetic field.

Experimental study of voiding effects with thorium based MOX fuel cluster in Critical Facility

An Advanced Heavy Water Reactor (AHWR) based on thorium fuel is being designed and developed in India. The design has many inherent safety features; the most important among them is its negative coolant void coefficient. An experimental facility, named AHWR Critical Facility, has been built to validate the physics design parameters. Coolant void worth which is an important safety parameter was measured using differential critical height in a thoria based experimental MOX fuel assembly placed in the center of the core. The voiding effects were experimentally determined with both water and high density polyethylene (HDP) coolant. Different fractional voids were obtained using combinations of HDP block of compatible shape and sizes.The aim of the experiment was to validate the code systems used in physics design and in particular, to assess their capability of modeling the voiding conditions in thorium based fuel cluster. The validation exercise was performed with both deterministic and stochastic methods. The theoretical estimates of the void worth were found in very good agreement with that of the measurement. The results have enhanced the confidence in the code system used for AHWR physics design.

Observation of water droplet motion in a shear flow

Although numerous studies have investigated droplets in shear flows, the features of these droplets are incompletely understood. This paper reports our experimental visualization results of sessile droplets in fully developed turbulent shear flows and the onset of their movement. The visualization was performed from the side and bottom views. Furthermore, the droplet height is much smaller than the boundary-layer thickness, and the droplet motions are strongly affected by turbulent velocity fluctuation. The droplets were deformed toward the front and spread in a spanwise direction. The front and rear-side contact angles recover the balance position, that changes symmetrically over time and are not clearly related to sessile droplet oscillation. The droplet oscillation frequencies were well predicted by the model based on the resonant vibrations of the standing waves except for the lowest mode. Based on the critical air velocity and droplet height, the motion onset was adequately approximated by a simple empirical relation between the Weber and Reynolds numbers.

Flame Acceleration and DDT in a Channel with Continuous Triangular Obstacles: Effect of Blockage Ratio

ABSTRACT Experiments were conducted in a stoichiometric hydrogen-oxygen mixture at initial pressure of 1 atm to study the flame acceleration and deflagration-to-detonation transition (DDT) in a 20 mm high channel equipped with continuous triangular obstacles. Effect of blockage ratio (br) was explored by considering different obstacle heights of 0, 1 mm, 3 mm, 5 mm, and 7 mm, corresponding to br = 0, 0.1, 0.3, 0.5, and 0.7, respectively. High-speed schlieren photography and OH* chemiluminescence recording were used to visualize the processes. Results show that blockage ratio has a significant effect on the scales and velocities of the vortices generated in the gaps between neighboring obstacles and consequently on the subsequent flame-vortex interactions. Higher br leads to faster flame acceleration via stronger flame-vortex interactions. The intricate shock-flame interactions cause successive local explosions in the br = 0.3, 0.5, and 0.7 cases, creating conditions for DDT. An eventual choking regime occurs in the br = 0.7 case due to energy losses by continuous diffractions at the obstacle vertices. It was found that the onset of DDT is triggered when the critical height of the unobstructed passage is approximately greater than three detonation cell sizes. The mechanism of DDT changes as the br decreases. One important feature observed is that the br = 0.1 case has the shortest DDT distance. In addition, the final flame speed (~740 m/s, 1.4 times unburned sound speed) before DDT for br = 0.1 is significantly smaller than those (~1300 m/s, 2.4 times unburned sound speed) for br ≥ 0.3. The reason is that the low obstacles retain the characteristics of the obstacle, while mimicking the wall roughness, resulting in both shock compression of unburned gas and viscous heating in the boundary layer ahead of the flame front. The combined effects promote the occurrence of DDT for the case with br = 0.1.

Evolution of the critical torus instability height and coronal mass ejection likelihood in solar active regions

Aims. Working towards improved space weather predictions, we aim to quantify how the critical height at which the torus instability drives coronal mass ejections (CMEs) varies over time in a sample of solar active regions. Methods. We model the coronal magnetic fields of 42 active regions and quantify the critical height at their central polarity inversion lines throughout their observed lifetimes. We then compare these heights to the changing magnetic flux at the photospheric boundary and identify CMEs in these regions. Results. In our sample, the rates of CMEs per unit time are twice as high during phases when magnetic flux is increasing than when it is decreasing, and during those phases of increasing flux, the rate of CMEs is 63% higher when the critical height is rising than when it is falling. Furthermore, we support and extend the results of previous studies by demonstrating that the critical height in active regions is generally proportional to the separation of their magnetic polarities through time. When the separation of magnetic polarities in an active region increases, for example during the continuous emergence and expansion of a magnetic bipole, the critical height also tends to increase. Conversely, when the polarity separation decreases, for example due to the emergence of a new, compact bipole at the central inversion line of an existing active region or into a quiet-Sun environment, the critical height tends to decrease.

Assessing the Stability of Dip Slopes Based on Analyzing the Stress at a Key Point on the Sliding Surface

Dip slopes are often encountered in deep-cut canyons and engineering projects. Such slopes, when they become unstable, commonly undergo bi-planar failure, and this mode of failure tends to produce the widest-ranging effects. In this work, a novel method is proposed for assessing the potential of a slope to undergo bi-planar failure based on a stress analysis at a key point on the sliding surface, namely, the point at which the two sections of the sliding surface are connected. Discrete-element simulations are first carried out to capture the essence of the penetration process of the bi-planar sliding surface based on displacement results, plastic failure, and principal stress development. Then, the key point on the sliding surface is skillfully selected according to the sliding surface penetration process, and the characteristics of the stress changes leading to slope failure are investigated using the stress analysis method. Subsequently, considering the stress states of this key point both in the overlying rock strata and in the intact rock at the toe of the slope, a novel method is proposed for assessing the stability of the dip slope and predicting the bi-planar failure surface formed. The stability of dip slopes was subsequently analyzed using both numerical and theoretical methods. The results obtained are highly consistent, confirming the feasibility and accuracy of the proposed method. The results also show that the bi-planar failure process is progressive and that the range of the failure is mainly located in the stress reduction zone. Moreover, the critical height of the dip slope remains approximately unchanged as the stratum thickness is changed. However, it decreases as the slope angle increases and increases linearly if the strength of either the rock or joints is increased. Additionally, if the joint strength is low, the dip slope undergoes buckling failure—increasing the joint strength, however, increases the likelihood of the occurrence of bi-planar failure. The proposed method offers a novel approach to assessing and designing dip slopes.

Influence of Spray Control Parameters on the Performance of an Air-Blast Sprayer

Orchard plant protection machinery in China still has a low application efficiency. Air-blast sprayers represent the primary development direction of pesticide applications in orchards. The spray control parameters have to be matched to the tree canopy status to achieve precise results. In this study, a vertical patternator was used to determine the accuracy of spraying fruit trees. The influences of three control parameters (blower speed, spray angle, and spray distance) on the spray performance of the air-blast sprayer were analyzed, and the volume of the spray was measured in collection plates at different heights. The quantitative relationship between the overall collection volume and the critical height collection volume was obtained for different parameter values, and the combined effects of any two control parameters on the collection performance and the position of the optimum collection area were obtained. The regression model describing the relationship between the collection volume in the critical height range and the three factors was established, and the main effects of the control parameters were determined. The results showed that if one parameter remained constant, the correlation between the other two parameters was non-significant. The collection volume in the critical height range increased initially and then decreased as the spray distance increased. The maximum collection volume was obtained at a spray distance of 1.762 m. The regression model can be used to obtain the optimum values of the parameters.

Surface profile and milling force prediction for milling thin-walled workpiece based on equivalent 3D undeformed chip thickness model

With the development of the aviation manufacturing industry, the application range of thin-walled parts is rapidly increasing. Accurate machining process and surface topography prediction are the keys to ensuring machining quality. This article is based on the relative geometric relationship between the real motion trajectory of the milling cutter and the workpiece; the undeformed chip thickness equation and the two-dimensional surface contour feature algorithm are established. By introducing the parameters of milling cutter critical height, milling cutter helix angle, and lag angle parameters, the three-dimensional surface profile prediction model and the equivalent three-dimensional model considering the chip formation process are derived. And the calculation equations of the instantaneous chip cross-sectional area and the blade-workpiece contact length of the three phases of chip formation are established, respectively. The multiple linear regression method was used to fit the orthogonal test results of titanium alloy Ti-6Al-4 V, so as to complete the dynamic milling force identification, and finally establish the milling force prediction model. The accuracy of the prediction model was verified by the single factor method, and the influence of different parameters on the milling process of thin-walled parts was observed. The results show that the established model has high accuracy in predicting the surface profile and milling force of thin-walled parts. This study provides guidance for efficient prediction of the milling process of thin-walled parts.

3D concrete printing: Lattice modeling of structural failure considering damage and deformed geometry

This research studies the impact of localized damage and deformed printing geometry on the structural failure of plastic collapse for 3D concrete printing (3DCP) using the lattice model. Two different approaches are utilized for buildability quantification: the (previously developed) load-unload method, which updates and relaxes the printing system after each analysis step and repeatedly applies the gravitational loading to the undeformed structure; and the incremental method, which keeps the load after each analysis step and applies the incremental loading to the deformed printing system. The former can consider the material yielding but cannot capture accurately the structural deformation during printing process. Compared to the load-unload method, the incremental method can not only consider deformed printing geometry but can also simulate the non-proportional loading conditions and disequilibrium force occurring during 3D printing. In this study, computational uniaxial compression tests are first conducted to compare two algorithms. The numerical results indicate the consideration of nonequilibrium force and deformed geometry affects the peak load and crack information for fracture analysis. Subsequently, the incremental method is incorporated into the lattice model to quantify buildability of 3DCP. The predictions are compared with previously published numerical results obtained using the load-unload method. The lattice model based on incremental method reproduces correct failure mode; better quantitative agreement about critical printing height also can be obtained. These numerical analyses demonstrate that the incremental solution is an approximate method for buildability quantification since it can account for the nonequilibrium force induced by the deformed printing geometry and localized damage.

Time-dependent fresh properties characterization of 3D printing engineered cementitious composites (3DP-ECC): On the evaluation of buildability

Failure of the structure due to poor buildability is a major concern in 3D printing of cementitious materials. Evaluation of buildability based on fresh material properties and print parameters is of significance. In this paper, the buildability of printable engineered cementitious composites was investigated and quantified at the material and the structural scale. Fresh ECC material showed excellent load capacity and deformation resistance at the material scale, therefore preventing material failure of the bottom layers, as confirmed by constant shear rate tests and incremental loading tests. To predict vertical deformation of a 3DP structure, a time-dependent strain-stress model of printable ECC was proposed and validated based on the green strength evolution of the material and the buildup rate of the designed structure. At the structural scale, the approach of predicting critical height at self-buckling failure based on stiffness evolution was validated by printing a straight wall and a cylinder structure.

Numerical simulation of elastic buckling in 3D concrete printing using the lattice model with geometric nonlinearity

This paper explores buildability quantification of randomly meshed 3D printed concrete objects by considering structural failure by elastic buckling. The newly proposed model considers the most relevant printing parameters, including time-dependent material behaviors, printing velocity, localized damage and influence of sequential printing process. The computational uniaxial compression tests were first conducted to calibrate age-dependent elastic modulus and yield stress. Subsequently, analyses of the 3D printing process of a free wall structure and a square layout were performed. The model can reproduce the asymmetry of buckling failure accurately and the predicted critical printing height is in excellent agreement with experimental data from the literature. It can be concluded the combined effect of material variability and non-uniform gravitational loading due to sequential printing process resulted in structural failure during 3D concrete printing. Using this model, printing parameters can be optimized and a suitable printing scheme can be devised to improve structure buildability.

Wettability of graphite under 2D confinement

The thermodynamics of solid/liquid interfaces under nanoconfinement has tremendous implications for liquid transport properties. Here using molecular dynamics, we investigate graphite nanoslits and study how the water/graphite interfacial tension changes with the degree of confinement. We found that, for nanochannel heights between 0.7 nm and 2.6 nm, graphite becomes more hydrophobic than in bulk, and that the value of the surface tension oscillates before eventually converging towards a constant value for larger slits. The value of the surface tension is correlated with the slip length of the fluid and explained in terms of the effective and interfacial density, hydration pressure and friction coefficient. The study clearly indicates that there is a critical channel height of 0.9 nm (achievable experimentally [1]) at which the surface tension reaches its highest value, but the water diffusion across the channel is at its minimum. The structural analysis shows that for this pore size a transition between a 2D and 3D hydrogen bond network is accompanied by an abrupt increase in configurational entropy. Our results show that the wettability of solid surfaces can change under nanoconfinement and the data can be used to interpret the experimental permeability data.

Flange Wrinkling in Deep-Drawing: Experiments, Simulations and a Reduced-Order Model

Flange wrinkling is often seen in deep-drawing process when the applied blankholding force is too small. This paper investigates the plastic wrinkling of flange under a constant blankholding force. A series of deep-drawing experiments of AA1100-O blanks are conducted with different blankholding forces. The critical cup height and wrinkling wave numbers for each case is established. A reduced-order model of flange wrinkling is developed using the energy method, which is implemented to predict the flange wrinkling of AA1100-O sheet by incrementally updating the flange geometry and material hardening parameters during the drawing process. A deep-drawing finite element model is developed in ABAQUS/standard to simulate the flange wrinkling of AA1100-O blanks under constant blankholding force. The predicted cup height and wave numbers from the finite element model and reduced-order model are compared with the experimental results, which demonstrates the accuracy of the reduced-order model, and its potential application in fast prediction of wrinkling in deep-drawing process.

Tuning Topological Spin Textures in Size-Tailored Chiral Magnet Insulator Particles

Topological spin textures such as skyrmions hold high potential for use as magnetically active elements in diverse near-future applications. While skyrmions in metallic multilayers attract great attention in this context, unleashing the myriad potential of skyrmions for various applications requires the discovery and customization of alternative host system paradigms. Here, we developed and applied a chemical method to synthesize octahedral particles of the chiral insulating skyrmion host Cu2OSeO3 with both narrow size distribution and tailored dimensions approaching the nanoscale. Combining magnetometry and neutron scattering experiments with micromagnetic simulations, we show that the bulk phase diagram of Cu2OSeO3 changes dramatically below octahedral heights of 400 nm. Further, particle size-dependent regimes are identified where various topological spin textures such as skyrmions, merons, and bobbers can stabilize, prior to a lower critical octahedral height of ∼190 nm below which no topological spin texture is found stable. These findings suggest conditions under which sparse topological spin textures confined to chiral magnet nanoparticles can be stable and provide fresh potential for insulator-based application paradigms.

The efficacy of wildlife fences for keeping reindeer outside a chronic wasting disease risk area

Abstract Emerging wildlife diseases often comes with negative cultural and economic impact. Limiting disease spread is a recurrent goal and challenge, but the efficacy of various mitigation measures is rarely assessed. Chronic wasting disease (CWD) is a lethal disease among cervids that was discovered among alpine reindeer (Rangifer tarandus) in the Nordfjella mountain range of Norway in 2016. After de‐population, the entire range was fallowed to avoid re‐emergence from environmental pathogen reservoirs. This involved installing perimeter fences in the alpine areas in order to keep reindeer from adjacent populations outside of the CWD risk area, while other cervids (red deer Cervus elaphus, roe deer Capreolus capreolus and moose Alces alces) were likely to enter through the forested areas. We used camera trapping and surveillance reports to assess the efficacy of the perimeter fences. All four species of cervids were documented inside the CWD risk area. For reindeer, only 12.0% of observations were inside the CWD risk area, while this was 28.7% for the other cervids. The higher proportion of observations outside of the fenced area indicate that fences provided a barrier and lowered the number of crossings also of red deer, roe deer and moose. Fences do not provide complete barriers, and we discuss practical solutions for how to avoid ‘intruders’ entering a given area, such as maintenance at critical points (e.g. river and road crossings) and height of fences (e.g. species variation in jumping; deep snow) to uphold their desired effect. We argue that two fence lines with a buffer zone would be required when re‐introduction of reindeer are planned in the CWD risk area after fallowing, similar to what has been suggested for other wildlife diseases.

Numerical Analysis of Seepage Failure Modes of Sandy Soils within a Cylindrical Cofferdam

Soil seepage failure within cofferdams is a dangerous phenomenon that always poses difficulties for designers and builders of excavations in zones with high water levels. When the hydraulic head difference H between the upstream and downstream sides reaches a critical height, the downstream soil seepage failure occurs. Depending on soil properties, soil-wall interface characteristics, and cofferdam design, different seepage failure modes can be observed: heaving, boiling, liquefaction, or failure by reduction of the passive earth pressure. In the literature, there are differences, sometimes very large, in the critical value of the hydraulic head loss Hc/D inducing seepage failure given by several methods proposed for stability verification. Then, complex cases are generally approached using simplifying assumptions and adopting large safety factors to take account of uncertainties. In practice, geotechnical engineers deal with many kinds of excavations and different shapes of cofferdams, such as rectangular, square, or circular, which generate three-dimensional (3D) flow conditions. Axisymmetric seepage flow through the soil in a circular cofferdam is often used to model such 3D seepage flow. In this paper, using the numerical code FLAC, several numerical simulations are carried out in axisymmetric groundwater flow conditions to analyze the seepage failure modes of cohesionless sandy soils within a cylindrical cofferdam. The effects of the cofferdam radius, internal soil friction, soil dilatancy, and interface friction on the Hc/D value and failure mode are studied. The numerically obtained seepage failure modes are presented and discussed in various scenarios. The present results, illustrated in both tables and graphs, show a significant decrease in the value of Hc/Dinducing seepage failure, with a decrease in the cofferdam radius. They also indicate the sensitivity of the seepage failure mode to internal soil friction, soil dilatancy, interface friction, and cofferdam radius. As well, new terms are proposed for the seepage failure mode designations based on the 3D view of the downstream soil deformation. Doi: 10.28991/CEJ-2022-08-07-06 Full Text: PDF

Numerical simulation theory and structural optimization of a flexible AMOLED module subjected to the impact of a falling ball

When the flexible active-matrix organic light-emitting diode (AMOLED) module is subjected to external impact, the key display device is easily damaged, so it is necessary to optimize the module structure to improve the impact resistance of the module. The adhesives in the module make the structural optimization of the module extremely complicated. In this paper, the viscoelastic and hyperelastic constitutive models of adhesives are established, and the method of simplifying the simulation model of the impact test is studied. Through the attenuation of the stress wave in the transmission, the reason why the dead pixels appear in the center of the module impacted by the ball is explained. According to the actual result that the area of dark spots does not expand with time, it is inferred that the AMOLED layer is damaged, and the maximum principal strain of that is extracted for analysis. In order to ensure the impact resistance of the module, the thickness of each layer should be increased to a certain extent. Slightly increasing the modulus of the film on the upper side of the AMOLED layer is likely to reduce the impact resistance of the module, whereas greatly increasing the modulus of that can improve the impact resistance of the module. An experimental method for determining the critical height of the falling ball is proposed, and it proves that the simulation theory and the optimization scheme are reasonable.