Horizontal Spacing Research Articles

Bounce behaviors of double droplets simultaneously impact cold superhydrophobic surface

The real physical process of ice formation involves multiple droplets rather than a single isolated one. Clarifying the mechanism of multi-droplet impact-freezing is important for designing functional surfaces for anti-icing. The rebound behavior of double droplets simultaneously impinging on a cold superhydrophobic surface (SHS) was investigated experimentally and numerically, which is a classical simplified case in multi-droplet impingement. We found five impacting-freezing modes, including no-coalescence rebound (NCR), partial-coalescence rebound (PCR), complete-coalescence rebound (CCR), no-coalescence adhesion (NCA) and coalescence adhesion (CA). Moreover, the effects of horizontal spacing, impact velocity and surface temperature on the spreading factor and uprising sheet height during the impacting-freezing process were also analyzed. The contact time of PCR mode is even shorter than that of a single droplet impact at room temperature, which is verified and explained in our results. However, as the surface temperature decrease, the behavior of the coalescing droplet transitions from PCR to CCR and CA mode. The increase in Weber number could cause the adhesion of double droplets. Moreover, the horizontal spacing strongly affects the coalescing process. Multiple droplet impact-freezing will lead to severe icing on the substrate due to multiple droplets interaction involved. This study is beneficial for anti-icing and de-icing technologies.

Evaporation of twin drops: Effect of acoustics and spacing

The study investigates how an acoustic field influences evaporation and internal circulation of twin drops when their in-between horizontal spacing varies. The acoustic source is a simple sine wave (i) with and (ii) without white noise at various frequencies. The circulation and outer flow are visualized. Maximum evaporation rate and circulation are found for the lowest frequency and highest spacing. The rate rises with the spacing for a given frequency up to a critical distance. The evaporation becomes almost identical beyond the critical spacing. A correlation among the spacing, evaporation rate, and outer flow velocity is demonstrated. The rate becomes lowest for a given frequency at the least spacing since the vapors accumulated in the surrounding are not swept out by the acoustic-induced flow. The visualization shows a horizontal outer flow, which becomes vertical with the rise in spacing because the acoustic wave can sweep the vapor out. The horizontal flow for the least spacing transforms itself to vertical when the wave amplitude is raised. The evaporation thus rises because the wave now sweeps the vapors out. We show that the perception that any acoustic wave enhances the evaporation of multiple nearby drops is incorrect. The evaporation and circulation decline faster with the rise in frequency since the surrounding flow becomes weak. Thus, we show how the spacing influences the evaporation when acoustic is incident and how the evaporation can be raised by sweeping the accumulated vapor out using higher amplitude acoustics for the closer drops.

The impact of altering emission data precision on compression efficiency and accuracy of simulations of the community multiscale air quality model

Abstract. The Community Multiscale Air Quality (CMAQ) model has been a vital tool for air quality research and management at the United States Environmental Protection Agency (US EPA) and at government environmental agencies and academic institutions worldwide. The CMAQ model requires a significant amount of disk space to store and archive input and output files. For example, an annual simulation over the contiguous United States (CONUS) with horizontal grid-cell spacing of 12 km requires 2–3 TB of input data and can produce anywhere from 7–45 TB of output data, depending on modeling configuration and desired post-processing of the output (e.g., for evaluations or graphics). After a simulation is complete, model data are archived for several years, or even decades, to ensure the replicability of conducted research. As a result, careful disk space management is essential to optimize resources and ensure the uninterrupted progress of ongoing research and applications requiring large-scale, air quality modeling. Proper disk-space management may include applying optimal data-compression techniques that are executed on input and output files for all CMAQ simulations. There are several (not limited to) such utilities that compress files using lossless compression, such as GNU Gzip (gzip) and Basic Leucine Zipper Domain (bzip2). A new approach is proposed in this study that reduces the precision of the emission input for air quality modeling to reduce storage requirements (after a lossless compression utility is applied) and accelerate runtime. The new approach is tested using CMAQ simulations and post-processed CMAQ output to examine the impact on the performance of the air quality model. In total, four simulations were conducted, and nine cases were post-processed from direct simulation output to determine disk-space efficiency, runtime efficiency, and model (predictive) accuracy. Three simulations were run with emission input containing only five, four, or three significant digits. To enhance the analysis of disk-space efficiency, the output from the altered precision emission CMAQ simulations were additionally post-processed to contain five, four, or three significant digits. The fourth, and final, simulation was run using the full precision emission files with no alteration. Thus, in total, 13 gridded products (4 simulations and 9 altered precision output cases) were analyzed in this study. Results demonstrate that the altered precision emission files reduced the disk-space footprint by 6 %, 25 %, and 48 % compared to the unaltered emission files when using the bzip2 compression utility for files containing five, four, or three significant digits, respectively. Similarly, the altered output files reduced the required disk space by 19 %, 47 %, and 69 % compared to the unaltered CMAQ output files when using the bzip2 compression utility for files containing five, four, or three significant digits, respectively. For both compressed datasets, bzip2 performed better than gzip, in terms of compression size, by 5 %–27 % for emission data and 15 %–28 % for CMAQ output for files containing five, four, or three significant digits. Additionally, CMAQ runtime was reduced by 2 %–7 % for simulations using emission files with reduced precision data in a non-dedicated environment. Finally, the model-estimated pollutant concentrations from the four simulations were compared to observed data from the US EPA Air Quality System (AQS) and the Ammonia Monitoring Network (AMoN). Model performance statistics were impacted negligibly. In summary, by reducing the precision of CMAQ emission data to five, four, or three significant digits, the simulation runtime in a non-dedicated environment was slightly reduced, disk-space usage was substantially reduced, and model accuracy remained relatively unchanged compared to the base CMAQ simulation, which suggests that the precision of the emission data could be reduced to more efficiently use computing resources while minimizing the impact on CMAQ simulations.

An Air Traffic Control Wind Compression Forecasting Tool for the TRACON Environment

Strong wind in the lower levels of the atmosphere near major airports can impact normal air traffic control (ATC) operations with respect to the horizontal spacing of aircraft. This is known in the ATC community as wind compression. Wind compression occurs when a strong wind from a specific direction and speed (at critical altitudes) impact normal ATC operations. The impact of wind compression becomes most noticeable when the spacing between aircraft decreases near or below minimal acceptable limits. Previous attempts to forecast wind compression have been unsuccessful. Wind shear calculations, time, height wind forecasts, and maximum winds below a certain altitude, such as 3050 m (10 000 ft), do not adequately convey the impact of wind compression. These methods are insufficient because they do not account for the flight profile of the numerous arrival routes that aircraft must travel to land at major airports. The Terminal Radar Approach Control (TRACON) Wind Compression Tool assists aviation forecasters in determining which arrival routes are impacted and the specific layers of the approach that are susceptible to wind compression. This program (1) diagnoses five different layers on an arrival route that may have potential wind compression impacts and (2) forecasts the onset and end of a compression event, the altitudes impacted, and the relative strength of the wind compression. Key information using the wind forecast from three National Weather Service models is condensed for each model hour and is placed into a timeline forecast.

Simultaneous double droplet impact on a molten phase change material pool: An experimental investigation

Although momentous in numerous authentic applications, multiple droplet impacts on the liquid pool are overlooked in most studies. Hence, the impingement of simultaneous double ethanol droplets on the molten phase change material (PCM) pool, instigating the evaporation of droplets and the solidification of PCM, is comprehensively scrutinized for the first time. Experiments were carried out through high-speed imaging for various Weber numbers ranging from 179 to 464, pool temperatures from 70 to 95 °C, and several horizontal impact spacing. By altering impact parameters, five distinct regimes were observed in the case of double droplets. Based on observations, regime maps were also established for conducted experiments. Furthermore, the influences of the impact parameters on the central uprising sheet, formed between two impinging droplets, crater width, crater depth, jet height, and solidified PCM area, created after the impact was investigated. Additionally, the time evolution of crater width and depth was compared with the existing theoretical predictions. It was ascertained that boosting either the Weber number or the impact spacing intensifies the droplets' spreading areas, leading to a larger solidified PCM area, whereas temperature inversely affects this parameter. Moreover, increasing the impact spacing diminishes the central uprising sheet height and retards its formation, while raising the Weber number monotonously strengthens the central uprising sheet. The research, whose results have an immediate application in novel energy storage devices containing droplet–PCM interaction, fills the gap between droplet impact and energy storage.

Numerical investigation of hydraulic fracture deflection in large-angle oblique horizontal wells with staged multi-cluster fracturing

The oblique horizontal well with a large-angle deviated from the direction of the minimum horizontal stress is an essential pilot for stimulating the middle unstimulated area between well pads. It is important to understand the complex deflection behavior of staged multi-cluster hydraulic fractures in oblique horizontal wells. In this study, we develop a fully coupled model of multistage hydraulic fracturing for oblique horizontal wells based on the discrete lattice method, in which synthetic microseismic events are calculated. We quantitatively investigate the effects of horizontal stress difference, injection rate, cluster spacing, and horizontal wellbore azimuth on fracture morphology and fracture deflection, including deflection angle and deflection distance. Simulation results and field microseismic monitoring show that fracturing the oblique horizontal well can stimulate the middle unstimulated area between well pads. Landing the horizontal wellbore in an area with low horizontal stress difference can help improve the stimulation efficiency. Injection rate and cluster spacing have a limited effect on the deflection angle and deflection distance of hydraulic fractures. The horizontal wellbore azimuth, however, significantly affects the fracture morphology and the fracture deflection behavior. Our research results provide theoretical guidance for the optimization and design of efficient fracturing for large-angle oblique horizontal wells.

Phonon interference effects in graphene nanomesh

Graphene nanomesh (GNM) is a single-layer graphene material that has a periodic distribution of nanoscale pores. GNM shows great potential applications in various fields such as thermoelectric energy conversion, energy storage, and field-effect transistors. In this study we utilize non-equilibrium molecular dynamics and lattice dynamics method to investigate the thermal transport mechanism of GNM. The thermal conductivity of GNM is mainly affected by the number of nanoscale pores and their horizontal and vertical spacing. Our study finds that as the number of nanoscale pores increases, the thermal conductivity of GNM decreases significantly. Additionally, the increase of the number of nanoscale pores causes phonon branch to be folded and confined, which results in a flatter dispersion curve, wider bandgap, and slower phonon group velocity. Moreover, the horizontal and vertical spacing of the nanoscale pores jointly affect the thermal transport process of GNM. When the horizontal spacing is small, the thermal conductivity of GNM decreases monotonically with the increase of vertical spacing, and increases monotonically with an increase of horizontal spacing. However, as the horizontal spacing increases, the interference effect caused jointly by phonon reflection and superposition leads to significant fluctuations in thermal conductivity. The analysis of the spectral heat flow, density of states, participation rate, and group velocity of GNM indicate that the variation in vertical spacing leads to different phonon contributions to heat flow, resulting in fluctuations in the thermal conductivity of GNM. These findings could serve as a reference for controlling the thermal transport of graphene nanomesh, and are of great significance in regulating the thermal conductivity and designing nanoscale pores in GNM.

Study on the hydrodynamics of a twin floating breakwater by using SPH method

Numerical and experimental studies are performed on the hydrodynamics including wave-attenuation performances measured by the transmission and reflection coefficients and dynamic responses of a twin floating breakwater. In the present work, the twin floating breakwater consists of two identical single pontoon-type floating breakwaters with independent identical mooring systems. Numerical simulations are performed with the δ -SPH, a Smoothed Particle Hydrodynamics model, after introducing a mooring line computation based on the catenary theory. The experimental tests are carried out in a wave flume at the Ocean University of China. The displacements of the twin floating breakwater and the water surface elevation are recorded in the experiment. Comparison of the numerical and experimental results demonstrates the reasonable accuracy of the present numerical model. Based on the numerical results, the wave-attenuation performances of the twin floating breakwater and a single pontoon floating breakwater are compared. Furthermore, the effects of the wave period and the horizontal spacing between the two pontoons on the hydrodynamics of the twin floating breakwater are studied, and in this process, Bragg resonance reflection of water waves by the twin floating breakwater is discussed. The results reveal that the twin floating breakwater is superior to the single pontoon floating breakwater on wave-attenuation performances. Moreover, comparing with the horizontal spacing between two pontoons, the wave period has a more significant effect on the hydrodynamics of the twin floating breakwater. Furthermore, there could be Bragg resonance reflection between waves and the twin floating breakwater. However, this phenomenon can be significantly weakened by the movement of the twin floating breakwater. • The hydrodynamics of a twin floating breakwater are numerically studied using δ -SPH method after introducing a mooring line computation based on the catenary theory. • Comparison of the numerical and experimental results demonstrates the reasonable accuracy of the present numerical model. • The hydrodynamic performance of the twin floating breakwater is studied numerically. Moreover, Bragg resonant reflection is discussed.

Semi-analytical solution for bottomhole pressure transient analysis of a hydraulically fractured horizontal well in a fracture-cavity reservoir

This paper study the role of hydraulic fracture properties on the transient bottomhole pressure (BHP) behavior of a horizontal well producing from a tight fracture-cavity reservoir. A combination of point source function, Laplace transformation and Perturbation transformation are used to obtain BHP step by step. Through literature comparison and numerical simulation, the results of BHP have a good consistency, which indicates the proposed method is scientific and reasonable. We divide the fluid flow into five stages, namely the wellbore storage stage, the karst cave fluid flows to the fracture stage, the radial flow stage of karst cave and fracture system, the matrix fluid flows to the fracture stage and the quasi-steady state stage. We come to the conclusion that the number of fractures and fracture direction mainly affect radial flow stage. In contrast, the length of horizontal subsection and skin factor mainly affect the karst cave fluid flows to the fracture stage. The matrix fluid flows to the fracture stage is more obvious when the fracture half-length and the horizontal segment spacing of the horizontal well are small. The study believes special attention should be paid to reforming the formations at both ends of the horizontal well. The advantage of this method is to incorporate well geometry (skin factor) and hydraulic fracturing design (fracture parameters), which is useful for well test interpretation through generating a new set of type curves. What’s more, this new method has the characteristics of easy calculation. The findings of this study can help for better understanding of well test analysis in fracture-cavity reservoir. However, the limitation of this study is that it is only suitable for this situation the horizontal well does not encounter karst caves and the karst caves in the reservoir are connected to the wellbore through fractures.

Stability Charts for Limiting Horizontal Normal Pressure on Cohesive-frictional Backfill for Deep Contiguous Piled Walls

Background: This study presents a numerical solution for determining the limiting uniform normal pressure acting horizontally behind cohesive-frictional backfill material in a deep contiguous piled wall. At this limiting pressure, the soil tends to flow out in gaps between a series of vertical piles placed at a certain uniform horizontal spacing. Methods: The lower and upper bound plane strain finite element limit analysis (FELA) has been carried out for this purpose. The Mohr-Coulomb failure criterion, using an associated flow rule, was employed to impose the yield condition in the soil mass. Results: A parametric study was carried out to obtain the magnitude of the non-dimensional limiting lateral resistance (F/cD) as a function of normalized pile spacing (S/D), the friction angle of soils (ϕ), and the adhesion factor (δ) at the soil-pile interface; here, F refers to the lateral normal resistance (force) per unit length offered by the pile, S forms the clear spacing between piles, D is the diameter of the pile and c is soil cohesion. The impact of the different parameters on the failure mechanisms has been examined comprehensively. Conclusion: The lateral resistance (F/cD) offered by the piles increases generally with a decrease in the spacing between the piles. The magnitude of F/cD increases further with an increase in the values of ϕ and δ.

Experimental investigation on mechanical, acoustic, and fracture behaviors and the energy evolution of sandstone containing non-penetrating horizontal fissures

Flaws are the weakest part of rock mass, which directly determine the stability of underground engineering. Existing investigations on the mechanical behaviors of flawed rock mainly emphasize on the geometric parameters of the fissure, such as inclination, width, and length, but few works have been conducted on the effect of fissure location on rock properties. This study explores the influences of two fissure layouts (distance between horizontal single fissure and specimen end, and horizontal double fissures spacing) on the sandstone properties under uniaxial compression. The properties studied include strength and deformation, failure mode, acoustic emission (AE) characteristics, and energy evolution. The findings indicated that pre-existing fissures significantly reduced the rock's strength, elastic modulus, and peak strain, and the rock's mechanical properties decreased as the distance between the horizontal single fissure and the specimen end decreased and as the double fissures spacing increased. Furthermore, it was observed that intact specimens mainly underwent shear failure and the flawed rocks under uniaxial compression experienced splitting failure or both. The flawed specimens presented multiple higher AE counts before the peak stress, corresponding to crack initiation, propagation and coalescence, which were distinctly distinct from the intact specimen. The energy evolution characteristics of the fissured sandstone reflected their damage process. The findings are promising to improve the understanding of mechanical mechanisms and energy evolution of flawed rock engineering.

Study on axial compression bearing capacity of in-sulated sandwich concrete wall with embedded columns

An insulated sandwich concrete wall with embedded columns (ISCW-EC) is proposed by introducing horizontal reinforcements and cold formed steel embedded columns to the traditional insulated sandwich concrete wall. Axial compression load tests were performed on two full-scale specimens with different horizontal reinforcement spacings to investigate the failure mode of ISCW-EC. The failure patterns of both specimens are the same: splitting cracks present at the bottom of specimen and local buckling occurs at the bottom of the embedded column. The test results show that the specimen with smaller horizontal reinforcement spacing has smaller cracking load, lower secant stiffness, lower ductility and higher compression bearing capacity. Based on the test results, refined finite element models were established to perform a multi-parameter analysis in which the influences of horizontal reinforcement spacing, embedded column spacing, concrete strength and steel wire diameter are studied. The multi-parameter analysis results show that the increase of concrete strength and wire diameter improve the axial compression bearing capacity while the increase of the horizontal reinforcement spacing and embedded column spacing reduce it. Finally, the calculation formula of axial compression capacity of ISCW-EC is put forward based on both test and finite element analysis results.

Evaluation of the Fitch Wind-Farm Wake Parameterization with Large-Eddy Simulations of Wakes Using the Weather Research and Forecasting Model

Abstract Wind-farm parameterizations in weather models can be used to predict both the power output and farm effects on the flow; however, their correctness has not been thoroughly assessed. We evaluate the wind-farm parameterization of the Weather Research and Forecasting Model with large-eddy simulations (LES) of the wake performed with the same model. We study the impact on the velocity and turbulence kinetic energy (TKE) of inflow velocity, roughness, resolution, number of turbines (one or two), and inversion height and strength. We compare the mesoscale with the LES by spatially averaging the LES within areas correspondent to the mesoscale horizontal spacing: one covering the turbine area and two downwind. We find an excellent agreement of the velocity within the turbine area between the two types of simulations. However, within the same area, we find the largest TKE discrepancies because in mesoscale simulations, the turbine-added TKE has to be highest at the turbine position to be advected downwind. Within the downwind areas, differences between velocities increase as the wake recovers faster in the LES, whereas for the TKE both types of simulations show similar levels. From the various configurations, the impact of inversion height and strength is small for these heights and inversion levels. The highest impact for the one-turbine simulations appears under the low-speed case due to the higher thrust, whereas the impact of resolution is low for the large-eddy simulations but high for the mesoscale simulations. Our findings demonstrate that higher-fidelity simulations are needed to validate wind-farm parameterizations.

The Optimization Study for Electromagnetic Radiation With Ultrahigh Voltage Transmission Lines

Several factors affect the electromagnetic environment changes generated underneath high-voltage transmission lines. This article carries out a study on the impact of the electromagnetic environment on high-voltage transmission lines based on different tower structures, voltage levels, conductor layouts, conductor parameters, and other full range of engineering factors. First, the model of wire three-phase phase sequence, ground height, horizontal phase spacing, wire splitting number, split spacing, and model values are built. By continuously adjusting and optimizing the parameters, the electromagnetic environment distribution curve at 1.8 m above the horizontal plane is obtained. Then, according to the characteristic analysis of the distribution law after optimization, the simulation results under some typical factors are compared with the standard limits. Simultaneously, the effect of this optimization is verified by comparison with relevant literature. Finally, some suggestions on the optimization of the pole tower structure, transmission line parameters, and the influence of electromagnetic radiation in transmission line corridors are proposed in high-voltage transmission line projects, which may potentially have constructive contributions and value.

Aeroacoustic and aerodynamic interaction effects between electric vertical takeoff and landing rotors

Electric vertical take-off and landing (eVTOL) aircraft are characterized by their unconventional wing and electric rotor configurations, which involve both side-by-side and tandem rotor configurations. These configurations create unique aerodynamic and acoustic flow-fields. We numerically investigate the interaction effects between rotor pairs as well as their individual and combined acoustic radiation. We examine horizontal and vertical spacing, rotor tilt angles, and forward flight effects. Performance is characterized by thrust coefficient, blade passage frequency (BPF) sound pressure level (SPL), and overall sound pressure level (OASPL). This study is performed with a mid-fidelity aerodynamic solver, Dust, which is used to predict the aerodynamic flow-field. The tonal acoustic pressure at observer positions is predicted via the Farassat F-1A solution of the Ffowcs Williams and Hawkings equation utilizing the aerodynamic flow-field. The configurations studied show strong aerodynamic interaction effects in thrust, as well as out-of-plane acoustic radiation from the aft rotor. Base predictions of thrust and noise are validated via experimental measurement. As rotor separation decreases, we observe that aft rotor thrust decreases and BPF SPL increases. The most forward rotor, however, is marginally impacted by the interactions. [This research is supported by Archer Aviation Inc.]

Ka-Band Single-Layer High-Efficiency Circular Aperture Microstrip Array Antenna

Based on microstrip antenna technology, a compact single-layer circular aperture array is proposed in this paper. The proposed method is suitable for designing large-scale and high-efficiency patch array in Ka band. By using the high-impedance characteristic of the coupled microstrip line, a novel multi-stage feeding network that can realize large power division ratio is proposed, and its structure is center-symmetrical and is fed through a coaxial probe at the center. The parallel branch of the multi-stage divider is connected to the row array, and the array elements can obtain uniform excitation through the design of the division ratio of each stage. A 256-element patch array operating at 35 GHz is proposed, the length and width of the antenna unit are 2.74 mm and 3 mm, respectively, the horizontal spacing between the array elements is 0.742λ0, the vertical spacing varies from 0.677λ0 to 0.737λ0, and the radius of the proposed array is 60 mm (7λ0 at 35 GHz). At the end, a prototype is fabricated and measured, the measured results show that the maximum gain is 29.5 dBi at 35 GHz, which correspond to the radiation efficiency and aperture efficiency of 61.66% and 46.07%, respectively, and the results show that the proposed antenna achieves high efficiency in Ka band, which verifies the correctness of the design. The proposed array antenna is compact in structure and only needs single-layer design, which can achieve high efficiency and low in manufacture cost, which is an excellent candidate for millimeter-wave large-scale array application.

Statistical post-processing of reanalysis wind speeds at hub heights using a diagnostic wind model and neural networks

Abstract. The correct representation of wind speeds at hub height (e.g., 100 m above ground) is becoming more and more important with respect to the expansion of renewable energy. In this study, a post-processing of the wind speed of the regional reanalysis COSMO-REA6 in Central Europe is performed based on a combined physical and statistical approach. The physical basis is provided by downscaling wind speeds with the help of a diagnostic wind model, which reduces the horizontal grid point spacing by a factor of 8 compared to COSMO-REA6 and considers different vertical atmospheric stabilities. In the second step, a statistical correction is performed using a neural network, as well as a generalized linear model based on different variables of the reanalysis. Although only a few measurements by masts or lidars are available at hub height, an improvement of the wind speed in the root-mean-squared error of almost 30 % can be achieved. A final comparison with radiosonde observations confirms the added value of combining the physical and statistical approaches in post-processing the wind speed.

Finite Element Analysis of Precast Concrete Deck-Steel Beam-Connection Concrete (PCSC) Connectors Using Ultra-High Performance Concrete (UHPC) for the Composite Beam

A precast concrete deck-steel beam-connection concrete (PCSC) connector using ultra-high-performance concrete (UHPC) as post-cast concrete has been proposed to enable rapid on-site construction of assembled composite bridges. This paper aims to optimize the structure of PCSC connectors using the finite element (FE) model to maximize material utilization and economic efficiency. A refined FE model comprising the bond degradation at the steel–UHPC interface was developed based on the push-out experimental results of PCSC connectors. The shear mechanism of the PCSC connectors was analyzed. Subsequently, parametric analyses were performed to investigate the effects of stud diameter, height, spacing, and concrete strength on the mechanical properties of PCSC connectors. The results indicate that the bond at the steel–connection concrete interface positively affects the shear bearing capacity and stiffness of the PCSC connectors. When UHPC was used as connection concrete, it improved the bearing capacity by about 20% and the shear stiffness of the stud by about 16% compared with normal concrete, but the ductility was 38% lower. It was also found that increasing the compressive strength of the connection concrete increased the shear strength of specimens. However, when the compressive strength of UHPC exceeded 130 MPa, the additional UHPC strength did not significantly enhance the shear performance of specimens. In order to ensure the effective restraint of the connection concrete to studs, it is recommended that the minimum width and height of the connection concrete (UHPC) be determined based on the minimum horizontal spacing and height of the studs. Specifically, the length-to-diameter ratio of studs is greater than or equal to 3.18, the horizontal spacing of studs can be at least 2.82 d, and the clear distance between the outer stud shank and the edge of the UHPC cannot be less than 30 mm. The results are expected to provide a reference for the engineering design of PCSC connectors and a reference for conventional stud connectors with UHPC.

Deformation Characteristics of the Foundation Pit of the Underpass Viaduct and Grey Relational Analysis of the Maximum Horizontal Deflection of the Retaining Wall

With the rapid development of rail transit, the excavation of new foundation pits will inevitably approach or pass through existing structures. Therefore, choosing a reasonable support scheme can effectively control the deformation of the foundation pit and ensure the safety of existing structures. This paper investigates the excavation of a typical foundation pit in Guangdong that underpasses a viaduct as the research object. This study uses field monitoring and numerical simulations to analyze the deformation characteristics of the supporting structure and introduces grey relational analysis (GRA) to investigate the key factors that influence the maximum horizontal deflection of the retaining wall. The results indicate that all monitored values are substantially less than the warning value specified in the code. Moreover, the horizontal deflection of the retaining wall and the horizontal displacement of the top of the wall at the measuring points near the existing bridge piles are smaller than at other measuring points. This support system has a high safety factor and a large space for optimization. The main factors affecting the maximum horizontal deflection of the retaining wall are as follows: second strut horizontal spacing > first strut horizontal spacing > layered excavation thickness > retaining wall thickness > retaining wall stiffness. The results of this study will provide technical guidance for the design of similar projects and optimization of their construction.

Numerical Simulation of Ventilation Performance in Mushroom Solar Greenhouse Design

Numerical simulation is an effective tool for the thermal management of propulsion systems. Moreover, it contributes to the design and performance assessment of solar greenhouses for mushroom ventilation. Because the planning and design of the clustered solar greenhouse are still undiscovered, this study has developed a 3-D mathematical model suitable for a large-scale park of mushroom solar greenhouses based on computational fluid dynamics (CFD) theory. The effects of the orientation arrangement, horizontal spacing, vertical spacing of the cultivation racks, and the building distance between adjacent greenhouses on the ventilation performance were analyzed. The numerical simulation showed good agreement with the experimental measurement. The CFD results indicated that the reasonable layout of cultivation racks in mushroom solar greenhouses is a north-south arrangement. The horizontal spacing of cultivation racks has a significant influence on the wind speed and cooling rate, and the optimal spacing is 0.8 m. The overall height of the cultivation racks has little effect on the ventilation performance. Nevertheless, the vertical spacing between cultivation rack layers has a remarkable effect, and the optimal vertical spacing is 0.29 m. Reducing the building distance between the two adjacent greenhouses within a certain range helps increase the ventilation efficiency, leading to an increase in land utilization in the greenhouse park. The optimal building distance between the adjacent greenhouses is 10 m. The research results can provide theoretical guidance for improving the production quality and land utilization of mushroom facilities.