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Hydraulic jumps are commonly employed as energy dissipators to guarantee long-term operation of hydraulic structures. A comprehensive and in-depth understanding of their main features is therefore fundamental. In this context, the current study focused on hydraulic jumps with low Froude numbers, i.e. Fr 1 = 2.1 and 2.4, at relatively high Reynolds number: Re ~2 × 10 5 . Experimental tests employed a combination of dual-tip phase-detection probes and ultra-high-speed video camera to provide a comprehensive characterisation of the main air-water flow properties of the hydraulic jump, including surface flow features, void fraction, bubble count rate and interfacial velocities. The current research also focused on the transverse distributions of air-water flow properties, i.e. across the channel width, with the results revealing lower values of void fraction and bubble count rate next to the sidewalls compared to the channel centreline data. Such a spatial variability in the transverse direction questions whether data near the side walls may be truly representative of the behaviour in the bulk of the flow, raising the issue of sidewall effects in image-based techniques. Overall, these findings provide new information to both researchers and practitioners for a better understanding of the physical processes inside the hydraulic jump with low Froude numbers, leading to an optimised design of hydraulic structures. Article Highlights Experimental investigation of air-water flow properties in hydraulic jumps with low Froude numbers Detailed description of the main air-water surface features on the breaking roller Transversal distribution of the air-water flow properties across the channel width and comparison between centreline and sidewall.

This study investigates the unsteady natural convection and entropy generation under the effects of magnetic field and baffles inside a nanofluid filled E-shaped enclosure. The nanofluid flow is driven by time-varying sidewall temperature and is partitioned by baffles. Multiple factors are discussed, including the enclosure aspect ratio (0.2 ≤ AR ≤ 0.7), nanofluid volume fractions (0 ≤ ϕ ≤ 0.1), Hartmann numbers (0 ≤ Ha ≤ 80), frequency of time-varying side wall temperature (0.01 ≤ ω ≤ 0.1), baffle locations (0 ≤ d ≤ 0.4) and length (0 ≤ l ≤ 0.4). An economic analysis is conducted to show the nanofluid cost of enhancing thermal transfer and reducing entropy generation. The modelling results show that increasing aspect ratio and nanofluid volume fraction enhance the thermal transfer behavior, while the magnetic field suppresses the nanofluid natural convection. Total entropy generation monotonically decreases with the increasing nanofluid volume fraction and Hartmann number. Installing baffles into horizontal walls can boost the thermal transfer behavior and decrease the total entropy generation. The economic analysis shows that increasing the nanofluid volume fraction can effectively improve the thermal economy, and this improvement increases with magnetic intensity.

This work is to demonstrate a low cost and time-conserving technique to create nano-trenches by transferring nano-scale polymeric sidewalls into substrate. The polymeric sidewall is a vertically spreading layer deposited by spin-coating a polymer solution on a vertical template. By varying processing parameters such as the solution concentration or the spin-coating speed, the dimension of the sidewall can be changed, which, after pattern transfer, also changes the nano-trench dimension. In this work, high-resolution trenches of about 15 nm have been achieved after transferring straight line sidewalls into substrate. Other than straight line sidewall patterns, this method also fabricates ring-shaped patterns including circles, squares, and concentric squares. With various shapes of sidewall patterns, this technique has a potential to implement other practical applications such as fabricating high-resolution nanoimprint molds of 15 nm.

The challenging machinability of silicon carbide (SiC) ceramic, due to its hardness and brittleness, has traditionally constrained its machined quality and the creation of functional surfaces. Compared to direct laser machining (DLM), waterjet-assisted laser micromachining (WJALM) is an alternative technique for SiC ceramic that is capable of reducing thermal-induced damages. In this paper, high-aspect-ratio (HAR) microchannels are fabricated on silicon carbide ceramic by WJALM, and its effectiveness is verified through comparative experiments with DLM. The effects of the parametric combination of waterjet and laser parameters on machining responses of geometric structural features and sidewall surface quality are investigated by controlled variable experiments. The results revealed that HAR microchannels with almost no recast layers could be obtained when the SiC workpiece was fabricated by a nanosecond laser under the flowing water medium layer, and higher average laser power of 27 W, lower scanning speed of 600 m/s, and medium waterjet velocity of 12/16 m/s contributed to larger aspect ratio, more ablation area and superior sidewall quality of HAR microchannels.

Square hollow section (SHS) is widely used as a chord member in steel trusses. In one connection type, a brace using I-shape or box section at a T-joint transfers out-of-plane bending moment to these chords through double longitudinal plates. Design codes include rules for different connections to hollow sections, but not specifically for this detail. An experimental program is presented in this paper to verify relevant design rules and apply them to the double-plate connection, considering three key parameters: double-plate spacing, connection offset from the chord centerline, and plate width. The test results are evaluated by discussing the connection capacity and the observed failure modes, in addition to plotting both the load-displacement and moment-rotation curves. Applying relative rules from code is found to be on the conservative side and requires adjustment to apply to the current context. However, the rules for single plates are found to be adequate for some of the eccentric double-plate connections with a plate at the chord face center. Some modifications to the existing design rules are proposed to suit the eccentric connection with a plate not at the center.

To investigate the catastrophic instability mechanisms of roadway roof and sidewall rock masses under deep-hole roof blasting in coal mines, this study establishes potential energy functions and instability criteria models for layered roof and sidewall strata based on cusp catastrophe theory. First, the layered roof is idealized as a simply supported beam. Considering the coupling effects of deep-hole blasting loads, rock mechanical properties, and support resistance, a total potential energy equation for the system is derived, and the cusp catastrophe equation along with sufficient and necessary conditions for instability are obtained. Second, for the roadway sidewall, a tensile-shear coupled sliding failure mechanical model is proposed to analyze the influence of blasting loads on sidewall stability, and a corresponding catastrophe instability criterion is developed. Through theoretical derivation, the critical maximum explosive charge for both the layered roof and sidewall rock masses is formulated, along with a mechanical criterion for instability judgment. Finally, taking the lower roadway of the 2205 working face in Songshan Coal Mine as the engineering background, theoretical calculations indicate that the maximum critical explosive charge for the roadway is 93.3 kg. Field monitoring shows that, within 1 day after blasting, the roof subsidence increased by 5 mm and the convergence of the two sidewalls increased by 11 mm, indicating that the roadway was only slightly affected by roof deep-hole blasting.This work provides a theoretical basis and engineering guidance for the prediction and control of roadway rock instability under deep-hole roof blasting conditions.

The caisson method is typically employed in foundation pit projects characterized by complex surrounding structures and challenging engineering geological conditions. The sinking process involves complex soil-structure interactions, particularly the sidewall friction between the caisson and the surrounding soil strata. This friction is a critical factor, as it not only determines the feasibility and safety of the sinking operation but also influences the pattern and magnitude of surrounding ground subsidence. This study aims to explore the mechanism of sidewall friction between the caisson and strata and its direct impact on controlling the sinking process and mitigating surrounding subsidence. The analysis is based on the large caisson engineering of Zhuchong Pump Station, located in Xinyang City behind the Chushandian reservoir. By conducting a numerical simulation of the sinking process and analyzing measured data from on-site subsidence monitoring points, this research reveals that the caisson induces a parabolic-shaped subsidence curve in the surrounding ground surface. The magnitude and extent of ground subsidence around the caisson increase with greater sinking depth and with proximity decreasing distance from the sidewall. The study further demonstrates that sidewall friction significantly influences ground subsidence. Specifically, lower friction in the initial sinking phase results in noticeable ground uplift due to reduced constraint on soil displacement. Conversely, higher friction leads to increased ground subsidence as the sinking depth progresses. The study reveals that the influence pattern of friction between the caisson sidewall and the surrounding soil on ground surface subsidence, and lower friction would result in pronounced ground uplift due to reduced constraint on surface displacement during the initial sinking phase, and higher friction would increase ground subsidence as the caisson sinking depth increases. The findings of this research may help provide a technical reference for subsidence control in similar large-scale caisson projects.

Single-cell manipulation in microfluidic channels at the micrometer scale has recently become common. However, the current mainstream method using a syringe pump and a piezoelectric actuator is not suitable for long-term experiments. Some methods incorporate a pump mechanism into a microfluidic channel, but they are not suitable for mass production owing to their complex structures. Here, we propose a sidewall-driven micropump integrated into a microfluidic device as well as a method for reducing the pulsation of flow. This sidewall-driven micropump consists of small chambers lined up on both sides along the main flow path, with a wall separating the flow path and each chamber being deformed by air pressure. The chambers are pressurized to make the peristaltic motion of the wall possible, which generates flow in the main flow path. This pump can be created in a single layer, which allows a simplified structure to be achieved, although pulsation can occur when the pump is used alone. We created two types of chips with two micropumps placed in the flow path and attempted to reduce pulsation by driving them in different phases. The proposed dually driven micropump reduced pulsation when compared with the single pump. This device enables precise particle control and is expected to contribute to less costly and easier cell manipulation experiments.

As metasurfaces are in the spotlight, research is being conducted to incorporate them into transmitarray (TA) antennas. Among these, as an attempt to create a low-profile design, a patch antenna classified as low-gain can be utilized as an appropriate source antenna. However, for high efficiency of the TA, the gain of the source antenna must be fundamentally improved. For this, a simple side metal structure was applied to a metallic cross-type slot transmitarray. This acts as a resonant element and reflector by utilizing the electromagnetic wave radiated from the source antenna. The changes in the center frequency and gain due to the application of the side metal structure to the source antenna were analyzed. The gain of the source antenna was improved by a total of 4.63 dB. This is expected to be applied to create various source waves and to conduct future research on improving the gain in transmitarray antennas.

The paper critically reviews the current state of the art in flow inside sidewall gaps of hydraulic pumps and turbines. It describes the consequences of the presence of this type of flow in turbomachinery and then relates it to other physical phenomena that determine the behavior, operating characteristics, and overall performance of the machine. Despite the small dimensions of the rotor-stator spaces, the flow in these regions can significantly affect the overall flow field and, consequently, efficiency. The circulation of the fluid inside the gaps and secondary flow that is caused by rotating elements influences the disk friction losses, which is of great importance, especially in the case of low specific speed pumps and turbines. The flow pattern affects the pressure distribution inside a machine and, thus, generates axial thrust. The presence of secondary flow also significantly changes the rotordynamics and can bring about undesirable vibrations and acoustics issues. This article aims to review and summarize the studies that were conducted on the mentioned phenomena. Experimental and numerical studies are both taken into consideration. It proposes some requirements for prospective research in order to fill current gaps in the literature and reveals the upcoming challenges in the design of hydraulic machines.