Step Wall Research Articles

Enhancing impact resilience of thermal battery through honeycomb-structured aluminum buffering devices: Insights from large-scale gas-gun tests and simulations

Modern warfare relies heavily on electronic equipment, necessitating reliable energy sources like thermal batteries. Assessing their impact resilience, a study employed honeycomb-structured Al plates as buffering devices in a large-scale gas gun simulating artillery fire. Comparison between peak curves from gas-gun tests and simulations with varying honeycomb wall thicknesses revealed unique patterns, attributed to the buffering device's deformation-restoration process. Different honeycomb wall thicknesses led to varying deformation behavior and impact deceleration, complicating effective energy absorption assessment. Stepped honeycomb wall designs aimed to balance compression, extending energy absorption and reducing deceleration peaks. Prototype honeycomb buffering devices showed improved energy absorption and reduced deceleration during gas-gun tests. Gas-gun tests highlighted complexities in energy absorption assessment, with designs proposing improved energy absorption and reduced deceleration. The actual gas-gun test launched a projectile equipped with a thermal battery and buffering device, resulting in slight casing deformation, while battery cells remained intact, exceeding the standard discharge time (1 h).

Computational study of shock diffraction over convex edges

Numerical analysis of normal shock diffraction over various step corners is presented using an implicit second-order upwind least squares cell-based method. Slipstream angle calculation for various corner angles and Mach numbers, variation of pressure load and specific heat flux with incident shock Mach numbers and different step corners along the step wall, separation point movement, and reattachment of the streamlines are some of the key features of the present study. Detailed studies have been conducted about the perturbed region enclosed within the diffracted shock wave and the last running expansion wave with the increase in the incident shock Mach numbers. The finite Volume Method is used to solve the governing equations numerically for the simulation of the moving shock. Various flow characteristics such as secondary shock, contact surface, expansion wave, slipstream, vortex, etc are well captured. Apart from isopycnics; Mach contours, isobars, and isotherms are plotted as well. The reattachment region formed after the flow separation near the step edge is mentioned and corresponding lengths over various steps are presented. Separation point movement along the step wall is highlighted and a relevant increase in reattachment length is reported. The slipstream angles get increased with incident shock Mach numbers and with corner angles. However, the rate of increment of slipstream angle decreases gradually. The core of the vortices generated and the reattachment of the separated streamlines are indicated by the two downfalls in the heat flux values.

Mechanically Stabilized Earth (MSE) retaining wall at hotel in Bariloche City

In the city of Bariloche, Argentina after heavy rains, among other things, a slope failure occurred. At the top of it there were gabions, which, due to the loss of stability, together with a large mass of soil and trees, collided tragically against the facilities of the Hotel. This article describes the use of geosynthetics for the construction of a 20m high MSE (Mechanically Stabilized Earth) retaining wall in order to contain the slope soil. At the same time, the consequent drainages for water runoff and the release of hydrostatic pressures needed to be considered. Instead of gabions, a wall made of prefabricated concrete blocks was proposed, along with PVA geogrids for slope stabilization and soil reinforcement. Due to the large size of the slope, a stepped wall with six terraces was proposed, which would later be naturally vegetated. Each wall was locally dimensioned for a specified height, and then a global stability verification of the structure was carried out.The inclusion of geosynthetic reinforcements in the soil for the construction of a reinforced wall results in a material with better mechanical characteristics. This solution offers significant technical and economic advantages, increasing the shear strength of the system (ensuring stability), reducing the deformability of the structure (both in static and seismic conditions), and saving construction time and material. Thanks to their excellent interaction properties, reinforcement geosynthetics (flexible elements with stiffness and tensile strength) work together with the soil, connecting the potentially "unstable" region (active zone) with the "stable" region (passive zone) for a given failure surface. Furthermore, the system flexibility and adaptability allowed the structure to be adapted in an aesthetic way, respecting the site architecture and environment.

USING A NONUNIFORM MAGNETIC FIELD TO ENHANCE HEAT TRANSFER BEFORE A SUDDEN COMPRESSION IN A 2D MILLI-CHANNEL

The advancement of electronic devices has made heat dissipation challenging, but heat convection shows promise as a solution. However, obstacles like resistors in the way of a straight channel can slow the flow and weaken heat transfer, particularly where the horizontal and vertical walls meet at sudden compression. This study examines numerically using nonuniform magnetic fields to enhance thermal energy transfer in the mentioned critical regions in a sudden compression inside a two dimensional milli-channel. The study includes placing single or multiple dipoles either beneath the lower heated wall (where the compression occurs) or over the upper wall. The effects of number, the longitudinal and vertical locations of dipoles, and the inlet flow Reynolds number are examined. The ferrofluid used in this study is EMG-805. The findings of this study demonstrate that heat transfer improves when single or multiple dipoles are positioned downstream of the step wall on the heated wall. The location of dipoles is critical. For example, the best minimum local Nusselt number (70.7% increase with respect to the base case) is achieved when the single dipole is at <i>a</i> = 49 mm (from the inlet). Increasing the number of dipoles in the thermally weak region improves heat transfer. For instance, by having three dipoles of equal strength in that area, the minimum local Nusselt number is enhanced by 90.1%, resulting in a Nusselt number before the step that surpasses the Nusselt number immediately after the step. Furthermore, as the Reynolds number increases, the effects of the magnetic field disappear.

The design of circular tubes with stepped varying thicknesses and their synergistic multi-tube combination

A stepped wall circular tube with varying thickness (STVT) and its multi-tube synergistic combination energy absorption structure were developed to address the shortcomings of the high initial peak force of thin-walled metal tubes and the significant load fluctuation of conventional multi-tube combination structures. The STVT was designed with different thickness variations, and its crashworthiness was evaluated numerically and experimentally. An analysis was done on the influences of various characteristics, such as the number of steps and thickness variation, on the crashworthiness of STVTs. Research shows that the STVT with three and four steps has improved crashworthiness. The phase of the curve is significantly influenced by the initial thickness, and for each 0.6 mm difference in step thickness, the peak phase shifts by about 5.5%. In comparison to the combination of four equal-thickness tubes of the same mass, the optimal combination structure optimizes smoothness by 10.67%, energy absorption by 19.52%, crushing force efficiency by 15.30%, and initial crushing force by 20.70%.

Modelling of bubble dynamics on vertical rough wall with conjugate heat transfer

The wall temperature distribution and wettability greatly influence the bubble dynamics and heat transfer process. In this work, lattice Boltzmann (LB) method is implemented to investigate the bubble dynamics on the vertical rough heating wall, where the conjugate heat transfer process is taken into consideration. The interaction between bubble dynamics and boiling heat transfer characteristics is revealed. The results reveal that the bubble motion and the gas–liquid interface are dependent on the wall thermal conductivity. A high wall thermal conductivity will cause the gas film to cover the wall surface and hinder the heat transfer process. Moreover, the influence of the wall mixed wettability on the conjugate heat transfer behaviors is also analyzed. The findings demonstrate that the step wall wettability can promote the nucleation efficiency so as to achieve the enhancement of the wall heat transfer.

Backward-facing step heat transfer enhancement: a systematic study using porous baffles with different shapes and locations and corrugating after step wall

Backward-facing step heat transfer enhancement: a systematic study using porous baffles with different shapes and locations and corrugating after step wall

Effects of Chute Block Geometry on the Performance of the USBR II Stilling Basin

Stilling basins are designed to reduce the high kinetic energy of supercritical flow in a downstream spillway. The USBR II stilling basin is distinguished by chute blocks fixed at the upstream end and a dented sill at the downstream end, allowing for the effective dissipation of excess energy. This research investigates the effect of chute-block geometry on the hydraulic performance of the USBR II stilling basin. Six modified chute-blocks with identical dimensions and spacings as standard blocks were constructed and evaluated for six incoming Froude-number values. The results indicate that chute blocks containing stepped side walls are more effective than standard blocks, increasing energy dissipation by 1.47% and decreasing the sequent depth ratio by 3.91%. Blocks with gradually increased spacings lose 0.7% more energy than standard blocks and reduce the sequential depth ratio by 1.91%. However, blocks with prismatic spacings and top surface angles of 152 degrees, relative to the downstream slope of the spillway, are less effective than standard blocks with energy dissipation reduced by 2.73% and the depth ratio increased by 7.24%.

Numerical Investigation of Fluid Flow and Heat Transfer Characteristics over Double Backward-Facing Step with Obstacles

Many engineering device, including nuclear reactors, heat exchangers, and electronic circuit boards, exhibit flow separation and reattachment. To reduce thermal stress impacts, the components of these devices, which resemble stepped channel designs and are susceptible to high heat flux, must be properly cooled. The present work numerically investigates the fluid flow and heat transfer characteristics through a double backward-facing step with elliptic obstacles located after each step. For this purpose, equations governing fluid flow and heat transfer are solved in a Cartesian framework using an in-house code based on streamline upwind/Petrov-Galerkin finite element method. The effect of various parameters (axis ratios (0.25, 0.5, 0.75, 1), vertical location of obstacles (0.38, 0.577, 0.769), Reynolds number (300, 500, 800, 1000)) on fluid flow and heat transfer characteristics in the channel with and without obstacles are compared and quantified. The recirculation region length of the double backward-facing stepped channel with obstacles decreases after the first and second steps when compared with no obstacles. The local Nusselt number distribution along the corner regions of the stepped wall is enhanced due to obstacles. The axis ratio of obstacles has less influence on the convective heat transfer enhancement than the vertical location of the obstacles.

Wind loading on a stepped roof building: Comparison of field measurements, wind tunnel data, and standard provisions

This study investigates wind loads on stepped roof buildings measured in the field and in an atmospheric boundary layer wind tunnel to verify the suitability of the North American codes and standards for the design of stepped roofs. Good agreement has been generally found between field and wind tunnel results. The field measurements and wind tunnel results were compared with the NBCC 2020 and ASCE/SEI 7–22 (2022) provisions. It was found that the Edge provisions of NBCC 2020 are currently underestimated and need to be increased. The study suggests merging the Corner and Edge zones into a single “Perimeter” zone in NBCC 2020 as this would resolve the current underestimation of the NBCC Edge wind loads and add simplicity to the Code provisions. Peaks of ASCE/SEI 7–22 (2022) were found conservative, except for the zone near the step wall on the lower roof; ASCE/SEI 7–22 (2022) positive peaks seem to be underestimated.

Model for the current plateau observed on the (310) plane of a room temperature W field electron source

An unexpected pause is observed in the usual exponential current decay when residual gas adsorption occurs on the (310) plane of a room temperature W field emitter (CFE). For most ultrahigh vacuum environments currently achievable, the primary residual gas is H2. High index crystal planes are known to consist of terraces separated by step walls. For a (310) orientation, the bcc crystal terraces and step walls consist of (100) and (110) orientations, respectively. Evidence is presented that the step wall adsorption sites are the preferential sites for initial H2 adsorption causing the work function (ϕ) to decrease. According to Fowler–Nordheim (FN) theory, which relates the CFE emission current and ϕ, the current should increase. Instead, the decrease in ϕ is accompanied by a concomitant decrease in the FN equation pre-exponential factor, which leads to a relatively constant value of the CFE current until these step-wall sites are saturated, after which the ϕ increases with further H2 adsorption. The latter leads to an exponential decrease in the emission current. This fortuitous balance between the ϕ and FN equation pre-exponential factor upon initial H2 adsorption appears to be unique to the (310) crystal plane of a W CFE.

Finite element analysis of heat assisted incremental sheet forming process

ABSTRACT Incremental sheet forming is a flexible method to produce 3D sculptured sheet metal parts without expensive and dedicated tools. The present work studies the behaviour of sheets with low ductility undergoing forming under warm conditions. The material selected is Ti6Al4 V titanium alloy which is very hard to deform at room temperature. The temperature of around 500 - 700°C, i.e. below the recrystallisation temperature, is provided to the sheet. In this numerical simulation, a predefined temperature of 500°C is provided initially to the sheet in the predefined field using ABAQUS® software to carry out the test runs. With the increase in temperature, the ductility of the material increases, and the sheet becomes easy to form. The analysis is carried out at a temperature range of 500 - 700°C with different process parameters, viz. step depth, wall angle, and constant tool diameter. Von-Mises stresses, forming depth, and thickness distribution at various input process parameters were studied in the present work. The results obtained show that the fracture depth and thickness distribution increase with a decrease in the mesh size and step depth, whereas they decrease with the decrease in the temperature and increase in the wall angle.

Turbulent Fluid Flow and Heat Transfer Enhancement Using Novel Vortex Generator

One of several effective methods for improving heat transfer in heat exchangers is the use of vortex generators in channels. The flow of fluid through a channel with a vortex generator is disrupted by the development of recirculation zones on the step wall, which improves fluid mixing and heat transmission. The current work investigates the flow and heat transfer of turbulent fluid flow through channels with various vortex generator designs mathematically (triangular, half-circle, and quarter circle). The finite volume method (FVM) is used to discretize and solve the continuity, momentum, and energy equations. The SIMPLE algorithm approach is used to connect the pressure and velocity fields within the domain. The effect of geometrical factors such as step height (2, 3, 4, 5, and 6 mm) on the flow and heat fields is demonstrated and analyzed, as is the effect of Reynolds number. As the step height increases, so do the surface Nusselt number and skin friction coefficient, which peak at 4 mm. According to the findings, as Re increases, so does the average Nusselt number. The quarter circle vortex generator has the best thermal-hydraulic performance at a 4 mm amplitude height, followed by the triangle vortex generator. The simulation results are consistent with those found in the literature.

Impact of baffle on forced convection heat transfer of CuO/water nanofluid in a micro-scale backward facing step channel

Numerical simulations have been carried out to investigate the thermal-hydraulic characteristics using water-based CuO nanofluid with volume fraction (ϕ) = 0 - 5% and fixed nanoparticle size (dp) = 20 nm at Reynolds numbers (Re) = 100 - 389 in a micro-scale backward facing step channel with and without a baffle using finite volume method. The flow is steady, laminar, and incompressible. The channel has an expansion ratio (ER) = 1.9423with a fixed step height (S) of 490 μm. To study the effect of the baffle, different geometrical configurations have been developed by varying its height and location. The height of the baffle is varied as Hb = 160 - 640 μm. The baffle is stationed on the upper wall of the channel at a dimensionless distance (D)= 1, 2, 3 and 4. The upstream, step and upper walls are thermally insulated while the lower wall downstream of the step is under a constant heat flux (qs") = 20000 W/m2. The parameters of interest for analysis are Nusselt number, skin friction coefficient and velocity distribution under different flow conditions. Results indicate that the rise in volume fraction and Reynolds number enhances the Nusselt number, indicating improved heat transfer. However, the skin friction coefficient decreases with the increment in Reynolds number. The increase in baffle height causes the Nusselt number and skin friction coefficient to rise. As the baffle is moved away from the step, the Nusselt number tends to decrease. In comparison to water, the heat transfer improved by about 164% using CuO nanofluid at Re = 389 with ϕ = 5% in the presence of the baffle with Hb = 640 μm and D = 1. However, the heat transfer enhancement has been achieved at the cost of higher pumping power requirements.

Design of cylindrical steel liquid tanks with stepped walls using One-foot method

Cylindrical steel tanks are used in most countries to store bulk volumes of both solid and liquid products such as water, oil, gasoline and grain. Such steel tanks are prone to buckling when subjected to external pressure either due to vacuum or due to wind. These types of shell structures are generally controlled by elastic buckling failure because of the thin wall thickness. Cylindrical shells are commonly constructed with stepwise variable wall thickness due to economic reasons. The thickness of the tank shell wall is designed to increase from top to bottom because the stress resultants on the tank wall gradually increase towards the base of the tank. For open-top tanks, a primary stiffening ring is required at or near the top to maintain roundness under all loads. Stress resultants in a primary stiffening ring were previously identified by the Author for uniform wall thick tanks. In this new study, the applicability of this hand calculation method in stepped wall tanks has been investigated. Pursuant to this goal, a specified tank shell was designed considering One-foot method. Then, the stepped wall tank was transformed into an equivalent 1-course tank for hand calculation. Using the previously developed hand calculation method by Author, a test for the in-plane bending moment in the ring was conducted to achieve an acceptable value for stepped wall tanks. The analysis results show that the previously proposed method for uniform wall thick tanks may also be used for stepped wall tanks considering an equivalent thickness. On the other hand, using Linear Buckling Analysis (LBA), the buckling mode was obtained for two different stepped wall tanks in the study.

Effects of a Labyrinth Weir with Outlet Ramps on Downstream Steep-Stepped Chute Sidewall Height Requirements

Labyrinth weirs are commonly used to increase spillway discharge capacity. Stepped chutes represent a common spillway element used to help dissipate kinetic energy, thus reducing the size requirement and often the cost of the downstream energy dissipation basin. When combined, the complex, highly turbulent, aerated flow patterns generated by the labyrinth weir create different aeration inception point behaviors relative to traditional stepped chute applications (e.g., linear weir upstream). To reduce the risk of erosion and other damage near the spillway, stepped chute sidewalls are typically designed with sufficient height to contain the majority, if not all, of the bulked air-water spillway flow and surface waves. This study evaluated some of the hydraulic impacts of coupling a labyrinth weir with a relatively steep-stepped chute (08H:1V) at the laboratory scale in an effort to provide some useful guidance related to the sizing stepped chute wall heights. Test results showed that required chute wall heights for bulked flow containments were higher at the chute entrance than the traditional stepped chute (i.e., no labyrinth weir) design predictions. Placing ramped floors in the labyrinth weir downstream cycles facilitates the transition from the labyrinth outlet cycles to the steep chute and, in some cases, reduced maximum chute water levels. To better understand this phenomenon and provide guidance toward the use of ramped floors to reduce chute wall height requirements, the hydraulic behavior of various ramped floor configurations was systematically evaluated. The results for the geometries tested ranged from no effect to a 15% reduction in maximum chute flow depth.

Xiong'an Railway Station: A Supersized Railway Station in a High Seismic Intensity Zone

Xiong'an Railway Station is the first super-large elevated railway station located in a high seismic intensity zone. A reinforced concrete frame structural system is adopted for the rail-bearing floor and the lower floors, while a steel structural system is adopted for the large-span roof. H-shaped steel frame beams are adopted for the elevated waiting hall, while double flange H-shaped steel beams are adopted in areas subject to great forces. Plane trusses are arranged bidirectionally between the frame beams to facilitate the laying and maintenance of equipment pipelines. The main span of the elevated waiting hall is 78 m, and variable-height box beams are adopted. The platform canopies are supported by specially shaped steel pipe columns, and the roof frame beams are connected to the tops of columns through spherical bearings. Structural innovations have been carried out in terms of semi-embedded column bases, stepped wall thickness steel pipe columns with special section shapes, large-span stiffened thin-walled box beams, and bidirectional large displacement bearings.

Performance Evaluation of H2/Air Premixed Combustion in a Suddenly Expanded Microcombustor with Wall Fin

Herein, a 2D, axisymmetric microcombustor with a backward‐facing step and triangular wall fin is considered for enhancement of combustor performance. The outer wall temperature, combustor efficiency, and pressure characteristics of the microcombustor are numerically investigated with a detailed chemical kinetic mechanism and conjugate heat transfer. The proposed microcombustors with variable blockage ratios, wall fin shapes, and locations are analyzed with respect to flow and combustion interaction, along with heat flux exchange between the flame and combustor wall. Combustion performance is also evaluated by means of the amount of heat transferred through the combustor wall, conversion ratio of input chemical energy to exploitable heat, and OH mass fraction distributions. Standard k–ε turbulence along with 9 species and the 19‐step combustion reaction scheme is implemented using the eddy dissipation concept (EDC) model in the numerical study. The results indicate that the wall fin blockage ratio alters the reaction zone and improves combustor performance significantly at lower inlet velocities (4–20 m s−1). The fin location and shape are observed to influence the temperature distribution. However, the higher blockage ratio adversely impacts the combustion characteristics at the higher inlet velocity, that is, 48 m s−1.

Study of Friction and Wear Effects in Aluminum Parts Manufactured via Single Point Incremental Forming Process Using Petroleum and Vegetable Oil-Based Lubricants.

This paper focuses on studying how mineral oil, sunflower, soybean, and corn lubricants influence friction and wear effects during the manufacturing of aluminum parts via the single point incremental forming (SPIF) process. To identify how friction, surface roughness, and wear change during the SPIF of aluminum parts, Stribeck curves were plotted as a function of the SPIF process parameters such as vertical step size, wall angle, and tool tip semi-spherical diameter. Furthermore, lubricant effects on the surface of the formed parts are examined by energy dispersive spectroscopy (EDS) and scanning electron microscope (SEM) images, the Alicona optical 3D measurement system, and Fourier-transform infrared spectroscopy (FTIR). Results show that during the SPIF process of the metallic specimens, soybean and corn oils attained the highest friction, along forces, roughness, and wear values. Based on the surface roughness measurements, it can be observed that soybean oil produces the worst surface roughness finish in the direction perpendicular to the tool passes (Ra =1.45 μm) considering a vertical step size of 0.25 mm with a 5 mm tool tip diameter. These findings are confirmed through plotting SPIFed Stribeck curves for the soybean and corn oils that show small hydrodynamic span regime changes for an increasing sample step-size forming process. This article elucidates the effects caused by mineral and vegetable oils on the surface of aluminum parts produced as a function of Single Point Incremental Sheet Forming process parameters.

Optimum flow depths prediction along the convergent stepped spillways side walls

Stepped spillway designs are popularly adopted in dam systems due to their distinct advantage of enhanced energy dissipation of flow. Several references and literature are available for the design of stepped chute with straight side walls. For spillway modification works or due to site-specific situations, spillways may sometimes be provided with convergent training walls. But very few literature references are available on spillways having stepped chute provided with convergent side walls instead of straight side walls. The outcome of comprehensive experimental investigations carried out on spillway experimental set up with 0.7H:1V (i.e. θ = 55°) slope of stepped chute and side walls with 15° convergence on both sides is presented. This paper described expressions for estimation of optimum depth of flow and decide the height of sidewall in spillways having stepped chute required to be provided with symmetrically converging side walls.