Step Height Ratio Research Articles

Evaluating construction parameters of HB and CD methods for super large section tunnel: a case study

The double sidewall guide pit and centre cross diagram (CRD) methods are often used for the construction of large-section tunnels through water-rich fault fracture zones due to their long construction time and high construction cost. To shorten the construction period and save costs, the top heading and benching method (HB) and centre diaphragm (CD) can be chosen for construction. The construction parameters of the step and CD methods are optimized to ensure the surrounding rock stability and tunnel safety. By relying on the Tongzi Tunnel, we simulate the excavation of different step heights in the construction of the top heading and benching method (HB) and CD methods through numerical simulation, the laws of tunnel vault settlement, and changes in the surrounding rock stress, initial support axial force, bending moment and safety factor. The study shows that as the height of the upper step increases, the settlement of the vault and the convergence of the periphery increase, the initial support safety factor decreases, and the plastic zone of the surrounding rock increases at 30 m from the target face. The step height for the top heading and benching method (HB) of construction is optimized as follows. The ratios of the upper, middle and lower step heights are 0.45H, 0.35H and 0.2H, respectively. The CD method construction step height is optimized to the left (right) upper and left (right) lower step height ratios of 0.5H and 0.5H, respectively.

Automated pose estimation reveals walking characteristics associated with lameness in broilers

Walking ability of broilers can be improved by selective breeding, but large-scale phenotypic records are required. Currently, gait of individual broilers is scored by trained experts, however, precision phenotyping tools could offer a more objective and high-throughput alternative. We studied whether specific walking characteristics determined through pose estimation are linked to gait in broilers. We filmed male broilers from behind, walking through a 3 m×0.4 m (length×width) corridor one by one, at 3 time points during their lifetime (at 14, 21, and 33 d of age). We used a deep learning model, developed in DeepLabCut, to detect and track 8 keypoints (head, neck, left and right knees, hocks, and feet) of broilers in the recorded videos. Using the keypoints of the legs, 6 pose features were quantified during the double support phase of walking, and 1 pose feature was quantified during steps, at maximum leg lift. Gait was scored on a scale from 0 to 5 by 4 experts, using the videos recorded on d 33, and the broilers were further classified as having either good gait (mean gait score ≤2) or suboptimal gait (mean gait score >2). The relationship of pose features on d 33 with gait was analyzed using the data of 84 broilers (good gait: 57.1%, suboptimal gait: 42.9%). Birds with suboptimal gait had sharper hock joint lateral angles and lower hock-feet distance ratios during double support on d 33, on average. During steps, relative step height was lower in birds with suboptimal gait. Step height and hock-feet distance ratio showed the largest mean deviations in broilers with suboptimal gait compared to those with good gait. We demonstrate that pose estimation can be used to assess walking characteristics during a large part of the productive life of broilers, and to phenotype and monitor broiler gait. These insights can be used to understand differences in the walking patterns of lame broilers, and to build more sophisticated gait prediction models.

Simulation of high-Mach-number inviscid flows using a third-order Runge-Kutta and fifth-order WENO-based finite-difference lattice Boltzmann method

A discrete-velocity Boltzmann equation(DVBE) with Bhatnagar-Gross-Krook (BGK) approximation is discretized in time and space using a third-order Runge-Kutta (RK3) and fifth-order weighted essentially nonoscillatory (WENO) finite-difference scheme to simulate benchmark inviscid compressible flows. The implementation of the WENO ensures that solutions behave with minimal or no oscillations, narrowing the gap between the exact and the numerical results. Discrete-velocity sets given by Kataoka and Tsutahara [Phys. Rev. E 69, 056702 (2004)10.1103/PhysRevE.69.056702] are used. The additional dissipation terms as well as artificial viscosity are incorporated in the formulation to solve the compressible flows at high Mach number. Further, the flows which are subjected initially to a high density ratio are effectively simulated. In this article, one-dimensional benchmarks are simulated at initial Mach number up to 30 and density ratio up to 1000, whereas, the benchmarks in two dimensions are simulated with a Mach number up to 10. The algorithm is assessed by simulating numerous benchmarks, namely, (i) one-dimensional Riemann problem for various shock waves combinations [namely (a) shock-shock waves in the case of different Mach numbers, (b) rarefaction-shock waves for various density ratios, (c) sudden contact shock discontinuity, and (d) shock-rarefaction waves for density ratio 5], (ii) isentropic vortex convection test, (iii) regular shock reflection (RR) for Mach numbers 2.9 and 10, (iv) double Mach reflection (DMR) for inflow Mach numbers as 6 and 10, and (v) forward-facing step for inflow Mach numbers 2 to 5. Further, the effect of change in Mach numbers and wedge angles on the flow structures in the case of DMR are detailed. In the case of a forward-facing step, the variations of flow structure (e.g., the Mach stem height, triple points location, and shock standoff distance) are detailed with respect to Mach number, step height, and specific-heat ratios. Finally, the numerical stability of the proposed formulation is carried out to assess the behavior of the free parameters.

Hydrodynamical instability of newtonian flow of downstream on axisymmetric sudden contraction

Measures to reduce energy losses in pipeline transport systems must be implemented already at the design stage. In particular, this also applies to local resistances of pipelines. In the paper, the separation length and separation height downstream of the contraction plane of axisymmetric sudden contraction of the circular pipe of a single-phase Newtonian flow have been investigated. Area ratios 0.250 and 0.321 were considered. After all, measures to reduce energy losses on the axisymmetric sudden contraction must be effective at values of the area ratio not less than 0.250. The separation length and separation height have the extreme dependence with a maximum at the transition of the laminar flow into a turbulent flow one. When the values of the Reynolds number at the laminar flow increase, these sizes increase, and they decrease at the turbulent flow. In the first case, the separation point is shifted downstream from the plane of contraction. The separation length and separation height are proportional to the Reynolds number. This is similar to changing the separation length and separation height of upstream from the plane of contraction. A transition zone be located between 9650 and 40000 and 1200 and 5000 if the Reynolds number is based on smaller pipe diameter and step height correspondingly. The separation length of downstream of the contraction plane are decreased if these sizes are length - smaller pipe diameter ratio, and increase if these sizes are length - step height ratio. The changing of separation height is similar. But the change of the separation length is greater than the change of separation height. There is enough good agreement between the experimental results and the results described in the literature. For taking measures providing decrease in energy losses, the investigation of the separation length and separation height downstream of the contraction plane at different values of area ratio being more than 0.250 is proposed.

Flame Stability And Fuel Efficiency Of Gas Diffusion Flame On The Backward Facing Step

Propane and butane injection into the recirculation zone in the fuel area with backward-facing step has a significant effect to the diffusion flame with the characteristic stability which depends on the velocity of the free air stream, the injection position from the step and the injection position to step height ratio. The test result shows that there are two main stable diffusion flames: a stabilized flame in the recirculation zone and a stabilized flame in the shear layer region. There is a decrease of the fuel efficiency due to the effect of the greater ratio of the injection position to the step height and the farther injection position from the steps. The effect of the free air stream velocity is much more significant the injection location near the steps.

Erosional Cyclic Steps Governed by Plunge Pool Erosion: A Parametric Study Based on Field, Laboratory, and Model Data

AbstractFor upland ephemeral gullies, gully erosion is strongly related to the formation and migration of cyclic steps. It is necessary to provide insight into the process of cyclic step development to accurately predict the pace of landscape evolution and soil loss. Information on the geometry of cyclic steps in subaerial environments is limited, and, to our knowledge, no model of cyclic step development considers plunge pool erosion. In this study, we analyze the geometric features and controlling factors of erosional cyclic steps through meta‐analysis of measured data including new measurements in the Loess Plateau, China. We focus on cyclic step dynamics of fluvial beds controlled by bed shear stress and local plunge pool erosion. We develop a new theory to incorporate plunge pool erosion through adapting existing cyclic step and plunge pool models. Our method agrees with measured data, showing that a larger flow rate leads to larger step length Ld and height Hd and increasing erodibility increases step aspect ratio Ld/Hd. The method is also able to predict how the step length, height, and aspect ratio change with the average channel slope. Our results indicate that plunge pool erosion is an important mechanism of cyclic step evolution. However, plunge pool development alone is not sufficient to explain the wide range of Ld/Hd in the measured data. The posed theory relates to equilibrium conditions and thus cannot consider temporal adjustments in step geometry.

Interactions of Solitary Wave with a Submerged Step: Experiments and Simulations

A series of experiments exploring the propagation of a solitary wave over a submerged step were performed using a flow-field visualization measurement system, an image-connection technique as well as model simulations. The experimental data were used to validate a one-layer finite-element non-hydrostatic model and a multi-layer finite-difference non-hydrostatic σ model for various submerged step configurations and wave conditions—combinations of step height ratios d/h, width ratios B/h and solitary wave height ratios H/h, where d denotes the step height, B the step width, H the solitary wave height, and h the still water depth. The main differences between the numerical results and the experimental data are highlighted. The effect of the height and width of the submerged step as well as the wave height of the solitary wave are quantified in terms of reflection (R), transmission (T), and energy dissipation (D). Through a series of numerical experiments, an optimal combination of the height ratio d/h, width ratio B/h, and solitary wave height ratio H/h for breakwater design for coastal protection is suggested.

Laminar Flow Control and Drag Reduction using Biomimetically Inspired Forward Facing Steps

This paper explores the use of shark-skin inspired two-dimensional forward facing steps to attain laminar flow control, delay boundary layer transition and to reduce drag. Computation Fluid Dynamics (CFD) simulations are carried out on strategically placed forward facing steps within the laminar boundary layer using the Transition SST model in FLUENT after comprehensive benchmarking and validation of the simulation setup. Results presented in this paper indicate that the boundary layer thickness to step height ratio (d/h), as well as the location of the step within the laminar boundary layer (x/L), greatly influence transition onset. The presence of a strategically placed forward facing step within the laminar boundary layer might damp disturbances within the laminar boundary layer, reduce wall shear stress and energize the boundary layer leading to transition onset delay and drag reduction as compared to a conventional flat plate. Results presented in this paper indicate that a transition delay of 20% and a drag reduction of 6% is achievable, thereby demonstrating the veracity of biomimicry as a potential avenue to attain improved aerodynamic performance.

The effect of rotatory inertia on natural frequency of cracked and stepped nanobeam

Nanobeams are extensively used in the arena of modern science and technology. The dynamic model of nanobeam with steps and cracks is formed by the combination of classical beam theory and nonlocal theory of elasticity. Homotopy perturbation method is employed to solve the governing equations for two steps nanobeam. The results of this approximation method are compared with the results of exact solution technique. Our vital concern is to analyse the effect of rotatory inertia on the dynamic behaviour of nanobeam. The effect of crack severity, crack and step position, step height ratio, axial load on the vibration of nanobeam are also studied. The results show that the effect of rotatory inertia is very significant in the nanobeam and its influence increases with the increase of mode of frequency.

Free vibration analysis of adhesively bonded lap joints through layerwise finite element

An investigation of vibration characteristics on adhesively bonded lap joints which considers the damping property of the adhesive layer is presented. For this purpose, a layer-wise plate finite element method is proposed and extended to model the lap joint. By imposing some additional virtual boundary conditions on the joint structure, the lap joint can be treated as a special sandwich plate, which can be hence modeled by the present method. The applicability of the present modeling method is verified through comparison with the numerical data obtained by traditional solid finite element for a functionally graded single lap joint and a two-step lap joint. Finally, a parametric study following the proposed method is also conducted to evaluate the effect of the adhesive loss factor, the overlap area, the adhesive thickness, the step height ratio and step number on the modal frequency and its corresponding modal loss factor.

INCREASE IN CONVECTIVE HEAT TRANSFER OVER A BACKWARD-FACING STEP IMMERSED IN A WATER-BASED TiO2 NANOFLUID

Investigation of flow separation and reattachment of 0.2% water-based TiO2 nanofluid in an annular suddenly expanding pipe is presented in this paper. Such flows occur in various engineering and heat transfer applications. A computational fluid dynamics package (FLUENT) is used to study turbulent nanofluid flow in this research. Only a quarter of an annular pipe was investigated and simulated because of its symmetrical geometry. Standard k–e second-order implicit, pressure based-solver equations are applied. Reynolds numbers between 17,050 and 44,545, step height ratio of 1.82, and a constant heat flux of 49,050 W/m2 were utilized in simulation. The numerical simulation results show that increase in the Reynolds number leads to an increase of the heat transfer coefficient and of the Nusselt number. Moreover, the surface temperature dropped to its lowest value after the expansion and then gradually increased along the pipe. Finally, the chaotic movement and high thermal conductivity of the TiO2 nanoparticles have contributed to the overall heat transfer enhancement of the nanofluid.

Convective heat transfer in a lid-driven cavity with a heat-conducting solid backward step under the effect of buoyancy force

Mixed convection in a lid-driven cavity filled with an alumina-water nanofluid in the presence of a bottom heat-conducting solid backward step has been studied numerically. Mathematical model includes partial differential equations formulated on the basis of conservation laws for mass, momentum and energy using dimensionless variables such as stream function, vorticity and temperature, and corresponding boundary conditions. The boundary-value problem has been solved by finite difference method of the second order accuracy. The effects of Richardson number (Ri=0.01–10.0), wall step height ratio (0.3⩽h2/L⩽0.7), distance ratio between left wall and wall step (0.3⩽l/L⩽0.7), thermal conductivity ratio (1.0≤K≤10.0), and nanoparticles volume fraction (0≤ϕ≤0.05) on streamlines and isotherms as well as average Nusselt number at moving hot wall and fluid flow rate have been analyzed for Reynolds number (Re=100), Prandtl number (Pr=6.82) and solid wall thickness ratio (h1/L=0.1). It has been found that sizes and thermal conductivity of a backward step can essentially modify the flow and heat transfer patterns with the process intensity.

Loss Mechanisms of Interplatform Steps in a 1.5-Stage Axial Flow Turbine

In this paper, the detailed steady and unsteady numerical investigations of a 1.5-stage axial flow turbine are conducted to determine the specific influence of interplatform steps in the first stator—as caused by deviations in manufacturing or assembly. A basic first stator design and a design consisting of a bow and endwall contours are compared. Apart from step height, the position and geometry of the interplatform border are varied for the basic design. To create the steps, every third stator vane was elevated, together with its platforms at hub and shroud, such that the flow capacity is only little affected. The results show that the effects of steps on the platform borders in front and aft of the first stator can be decoupled from those occurring on the interplatform steps. For the latter, being the main contributor to the additional loss, the intensity of recirculation zones and losses increase substantially when the platform border is located close to the suction side. Using a relative step height of 1.82% span, the entropy production doubles when compared to a position close to the pressure side, which can be explained by differences in local flow velocity level. Regarding a circular-arc-shaped platform, the losses can be more than halved—mainly due to lower included angles between step and endwall flow streamlines. The findings can be explained by a nondimensional relation of the local entropy production using local values for step height and characteristic flow quantities. Furthermore, a reduction in step height leads to an attenuation of the otherwise linear relationship between step height and entropy production, which is mainly due to lower local ratio of step height and boundary layer thickness. In the case of laminar or transitional flow regions on the endwall, typical for turbine rigs with low inlet turbulence and low-pressure turbines under cruise conditions, the steps lead to immediate local flow transition and thus substantially different results.

Effects of fluid inertia forces in ferrofluid lubricated circular stepped squeeze films – Shliomis model

Purpose This paper aims to study the inertia squeeze film characteristics between ferrofluid-lubricated circular stepped disks. Owing to the development of modern machine systems, the application of ferrofluids has received great attention. Because the circular disks are a special situation of circular stepped squeeze films, a further study of fluid inertia force effects on the ferrofluid-lubricated circular stepped squeezing mechanism is motivated. Design/methodology/approach On the basis of the ferrohydrodynamic flow model of Shliomis incorporating the momentum integral method, the effects of fluid inertia forces in ferrofluid-lubricated circular stepped squeeze films in the presence of external magnetic fields are investigated in this study. Analytical solutions of squeeze film performances are derived. Findings The fluid inertia force effects provide an increased load capacity and a longer squeeze film time for the ferrofluid-lubricated circular stepped squeeze film, especially for a larger value of the inertia parameter, the Langevin parameter and the volume concentration and a smaller value of the radius ratio and the step height ratio. Originality/value For engineering applications, numerical tables for squeeze film loads of circular stepped disks are also provided in this paper.

Nano-Sized Chemical Release Capsules Enable High Planarization Efficiency CMP Processes

General Engineering & Research, L.L.C. (GE&R) has developed slurries containing nano-sized chemical release capsules (nano-CRC) which provide highly controlled processing and efficient planarization. Instead of the traditional mixture of solid nanoparticles and chemicals, nano-CRC based slurries consist of a core-shell nanoparticle where the mechanical and chemical components are combined into a single entity (Figure 1). When the nanoparticle contacts the wafer surface during CMP, the polymer coating is torn away and the chemical payload is released in an area localized to where it is needed. Various abrasive particles are possible (SiO2, Al2O3, etc.) as well as different chemical payloads. In this research effort, nano-CRC particles made from various sized (20nm – 200nm) porous colloidal silica abrasives were loaded with glycine, and then coated with a polymer to encapsulate the glycine. Slurries containing these nano-CRC particles were tested on the copper CMP process. All wafers were polished in house on a Strasbaugh 6EC CMP tool using IC1000 polishing pad and Kinik Diagrid conditioning stone, with wafer downforce of 3psi, head/platen speed of 60/60 rpm and 150ml/min slurry flowrate. All slurries contained 4wt% silica nanoparticles. The nano-CRC slurry surface removal mechanism consists of a simultaneous mechanical abrasion in combination with a localized release of the chemical payload. These slurries do not require any other stabilizers, surfactants, inhibitors, etc., however, because of this, electrophoretic influences can be significant. The nano-CRC interaction with the surface is influenced by solution chemistry, such as pH and oxidizer concentration, which determines the zeta potential of the capsules and the charge on the wafer surface film. The polymer coating on the nano-CRC is thin enough that the capsules typically retain the colloidal properties of the base particle, i.e. the iso-electric-point (IEP) of the silica based nano-CRC slurries is pH~2. Acidic nano-CRC slurries provide good material removal rates (MRR) of copper films (IEP pH~9), however, alkaline solutions provide little to no removal of the copper surface due to the copper surface and nano-CRC particles being similarly charged and repelling each other. Oxidizer concentration in the slurry also affects copper oxide film formation and may inhibit the copper-glycine complex if used in excess. Figure 2 shows the MRR vs. H2O2 concentration for 40nm silica nanoparticles (no loading or polymer coating) and 40nm nano-CRC (glycine loading and polymer coating) slurries, where the MRR of the nano-CRC slurry is very sensitive to H2O2 concentration. The particle size also influences CMP performance. Figure 3 shows the Cu CMP MRR and planarization efficiency (PE) (ratio of step height removed to thickness removed), for slurries containing bare silica particles and the nano-CRC particles. The PE was calculated using a feature with 50um line spacing and 50um line width. Interestingly, of the bare silica slurries, the 80nm particle size provided the highest MRR, however, no improvement in MRR was observed with the 80nm nano-CRC slurry. The 40nm nano-CRC slurry shows both the highest MRR~200nm/min and PE>90%. Both the porosity and the hardness of the particles, which varies with particle size, may influence the CMP performance. Further optimization, particularly increasing the porosity of the nanoparticles, is expected to provide nano-CRC slurries with even higher MRR and high PE. Figure 1

Ventilated cavity flow over a backward-facing step

Ventilated cavities detaching from a backward facing step (BFS) are investigated for a range of upstream boundary layer thicknesses in a cavitation tunnel. The upstream turbulent boundary layer thickness is varied by artificial thickening of the test section natural boundary layer using an array of transversely injected jets. Momentum thickness Reynolds numbers from 6.6 to 44 x 103 were tested giving boundary layer thickness to step height ratios from 1.25 to 3.8. A range of cavity lengths were obtained by variation of the ventilation flow rate for several freestream Reynolds numbers. Cavity length to step height ratios from 20 to 80 were achieved. Cavity length was found to be linearly dependent on ventilation rate and to decrease with increasing boundary layer thickness and/or Reynolds number. This result may have implications in the practical optimization of these flows which occur in applications such as drag reduction on marine hull forms.

SIMULATION OF LAMINAR FORCED CONVECTION HEAT TRANSFER AND FLUID FLOW OVER A BACKWARD FACING STEP WITH OBSTACLE USING (SIO ) NANOPARTICLES

Simulation of Heat transfer and laminar Sio2/water and Sio2/oil-engine flow over backward facing step with and without obstacle numerically studied in this paper. The finite volume method adopted to solve continuity,momentum and energy equations in two dimensions. The aspect ratio of triangular obstaclew/e= 0.5 presented.The step height and expansion ratio of channel were 4.8mm and 2 respectively, the range of Reynolds number varied from 100 to 250, constant heat flux subjected on downstream of wall was 2000W/m2.Two types of base fluid used in this simulation the water and oil-engine with constant properties at T = 300K°, The Sio2nanoparticles used with nanoparticles diameter 30nm and volume friction 4%. The average nusselt number noticed increase with increase Reynolds number withobstaclefor two basefluid and also noticed that the nanofluid of Sio2-oil engine has higher nusselt number compared with other nonofluid. The result shows increase of local nusselt numberfor backward facing step with obstacle in compared to those without obstacle. The maximum enhancement of heat transfer observed at obstacle due to increase recirculation flow after the obstacle. Streamline showing the increase of recirculation region with used obstacle in compared without obstacle and highest recirculation region observed at obstacle.

Comparative analysis for estimation of the height of training wall of convergent stepped spillway

For a dam system with inadequate capacity of spillway, provision of (RCC) roller compacted concrete stepped spillways with converging training walls prove to be an appropriate alternative. Sufficient number of guidelines and literature references are available on the design of straight side walled stepped spillways. The need was felt to conduct the experiments on stepped spillways with convergent training walls, as limited literature is available. This paper presents the comparative analysis of an experimentation conducted on flow over convergent stepped spillways having 1:1 chute slope with 45o convergence angle for different step height ratios leading to different step height variations. The findings are presented in the form of expressions for the maximum depth of flow through the training walls required to accommodate the flow rate. The observed maximum depth of flow along the training walls also compared with estimated maximum height of the training wall as per the criteria available within literature and percentage variation is worked out taking into account the step height variation. Outcomes of the experimental findings are expected to be useful for assessment of height of training walls by the hydraulic design engineers involved in rehabilitation of existing dam system and also in design of the modified spillway system that is necessarily associated with convergent training walls and stepped chute.

Combined effects of fluid inertia forces and non-Newtonian rheology in circular stepped squeeze film disks

Based on the Stokes microcontinuum fluid model together with the averaged inertia principle, the combined effects of fluid inertia forces and non-Newtonian rheology on the squeeze film characteristics between circular stepped disks have been presented in this paper. Comparing with the case of a Newtonian lubricant without inertia forces, the influences of convective inertia forces and non-Newtonian couple stresses provide an increase in values of the load-carrying capacity and the approaching time. The improved performances are more pronounced for stepped squeeze films operating with a larger density parameter and couple stress parameter, and a smaller step height ratio and radius ratio.

Numerical simulation of heat transfer to separation tio2/water nanofluids flow in an asymmetric abrupt expansion

Abstract. Flow separation and reattachment of 0.2% TiO2 nanofluid in an asymmetric abrupt expansion is studied in this paper. Such flows occur in various engineering and heat transfer applications. Computational fluid dynamics package (FLUENT) is used to investigate turbulent nanofluid flow in the horizontal double-tube heat exchanger. The meshing of this model consists of 43383 nodes and 74891 elements. Only a quarter of the annular pipe is developed and simulated as it has symmetrical geometry. Standard k-epsilon second order implicit, pressure based-solver equation is applied. Reynolds numbers between 17050 and 44545, step height ratio of 1 and 1.82 and constant heat flux of 49050 W/m2 was utilized in the simulation. Water was used as a working fluid to benchmark the study of the heat transfer enhancement in this case. Numerical simulation results show that the increase in the Reynolds number increases the heat transfer coefficient and Nusselt number of the flowing fluid. Moreover, the surface temperature will drop to its lowest value after the expansion and then gradually increase along the pipe. Finally, the chaotic movement and higher thermal conductivity of the TiO2 nanoparticles have contributed to the overall heat transfer enhancement of the nanofluid compare to the water.