Search Results (800)

This study assesses the wind resistance and vortex-induced vibration (VIV) risks of the Dongzhou River Bridge in China reconstruction during critical construction stages. Computational Fluid Dynamics (CFD) simulations analyzed wind effects when the twin main girders were maximally separated, revealing asymmetric vortex shedding patterns influenced by upstream–downstream aerodynamic interactions. The upstream girder’s wake generated complex flow fields, increasing turbulence on the downstream girder and indicating elevated VIV susceptibility. A 1:50 scale aeroelastic model validated these findings through wind tunnel tests, confirming that CFD-predicted critical VIV wind speeds aligned with experimental observations. Tests identified a distinct “jump-like” vibration mode at specific wind speeds (35–40 m/s full-scale equivalent), characterized by abrupt amplitude escalation rather than gradual growth—a signature of unstable VIV resonance. However, measured amplitudes remained below the 61.5 mm full-scale equivalent safety threshold, confirming that vibrations posed no critical risk. While aerodynamic coupling between girders requires monitoring during cantilever construction, the study concludes that existing control measures ensure safe construction and operation without structural modifications. These results provide actionable guidelines for wind risk mitigation through construction sequencing and real-time wind speed restrictions. Full article

Significant vibrations of the traction wire rope can impact the efficiency and accuracy of static testing in wind turbine blade assessments. This study focuses on the vibration characteristics of the wire rope under static loading conditions. A simulation model for single-point static tests of wind turbine blades was developed using Adams software and validated through wire rope tension and longitudinal acceleration measurements during static tests on a full-scale 71.5-m blade. The validated model was used to analyze the effects of wire rope span and pulley position on vibration amplitude and tension in single-point loading scenarios. The results show that increasing the wire rope span and the distance between the pulley and blade fixture significantly amplifies vibration. Adjusting the span of the wire rope and the pulley position causes the primary vibration frequency to approach the natural frequency, leading to a substantial increase in vibration near the resonance frequency. To avoid resonance and reduce vibration, it is recommended to use two misaligned ground tracks, ensuring the wire rope span does not exceed 30 m and the distance between the pulley and blade fixture does not exceed 7 m. Specific resonance combinations of wire rope span and pulley position should be avoided to improve the precision and reliability of the testing system. Full article

Cross-laminated timber (CLT) presents significant potential for sustainable construction but requires further investigation under seismic conditions. This study develops a numerical model to evaluate the seismic design requirements of CLT buildings according to European (Eurocode 8) and Brazilian (NBR 15421) standards. Experimental data from a full-scale CLT building were used to validate the model. The model was then applied to assess seismic design according to standard requirements across different geographic locations, and a parametric investigation was conducted to evaluate the impact of the connector design on structural performance. The results indicate that the tested CLT building was overdesigned for all evaluated regions, and a significant reduction in displacements—up to 33%—is achieved by adjusting the quantity of the connectors. Additionally, the analysis shows limitations in NBR 15421, as it resulted in higher average lateral displacements due to insufficient consideration of energy dissipation. These findings underscore the importance of optimising connector configurations to enhance the seismic performance of CLT buildings while reducing overdesign. Additionally, properly considering energy dissipation in design standards is crucial. In particular, the Brazilian standard would benefit from a comprehensive review to better address energy dissipation, ensuring safer and more efficient seismic designs. Full article

The SARS-CoV-2 pandemic has led to an urgent need for effective and rapid diagnostic tools. In the present study, we have evaluated the predictive diagnostic potential of nasal microbiota by analyzing microbial community structures at different taxonomic level resolutions—species, genus, family, order, class and phylum—using Random Forest modelling. A total of 179 nasal swabs from COVID-19-positive (n = 85) and COVID-19-negative (n = 94) individuals were sequenced using a full-length 16S rRNA sequencing (Oxford Nanopore) approach. During each iteration of the Random Forest model, the dataset was randomly split into a training set (70%) and a testing set (30%). Model performance improved with finer taxonomic resolution, achieving the highest accuracy at the Species level (AUROC = 0.821 ± 0.059) and a sensitivity of 55.6% at a specificity threshold of 90%. A progressive decline in AUROC and sensitivity was observed at broader taxonomic levels. Furthermore, Beta diversity analysis supported that microbial community structures are more distinct between COVID-19-positive and COVID-19-negative groups at finer taxonomic levels. These findings highlight the potential role of nasal microbiota profiling as a secondary diagnostic tool for COVID-19, particularly at species- and genus-level classification, and underscore the importance of high taxonomic resolution in microbiome-based diagnostics. However, limited by an uneven sample distribution and the lack of medical evaluations, further large-scale studies are needed before the nasal microbiota can be implemented in the clinical diagnostics of COVID-19. Full article

Determining the appropriate position of a positive pressure ventilator, where it exhibits the highest efficiency (measured by the achieved volumetric flow rate), can influence the success of rescue operations conducted by fire protection units. The aim of this article is to evaluate the possibility of using LES (Large Eddy Simulation) analyses to verify the positioning parameters of positive pressure ventilators in numerical simulation conditions, without the need for time-consuming experiments. The article presents a comparative analysis of full-scale experimental studies (conducted on a test setup to assess the velocity profile of the air jet in open flow) and CFD numerical analyses. The analysis confirmed the convergence of the flow rate parameter entering the surface of the door opening model installed on the test setup. Depending on the distance of the ventilator position (1–7 m), a convergence degree ranging from 1.6% to 3.8% was achieved for the volumetric flow rate. This publication demonstrates that the LES model is a suitable tool for effectively determining the working positions of positive pressure ventilators, as defined in real working conditions (open flow). The analysis may serve as a helpful tool for manufacturers of mobile ventilators, who can use the method for the technological testing of their units without conducting time-consuming experiments. Full article

Steel-lattice transmission towers require efficient and reliable connection designs to ensure structural safety and cost-effectiveness. While traditional gusset plate connections increase their complexity and structural weight, direct bolted connections offer a simpler and lighter alternative. However, the adoption of staggered bolt arrangements, necessitated by the geometric constraints of chord angle members, challenges the applicability of existing design standards—particularly regarding block shear and net section failure modes. This study explores the structural behavior of staggered two-bolt angle connections through a combination of experimental testing and numerical modeling. Twelve full-scale specimens were subjected to axial tension to investigate the effects of key geometric parameters, including end distance, edge distance, and bolt stagger. Finite element analyses, which incorporate material nonlinearity and fracture criteria, delve deeper into the stress distribution and failure mechanisms. The results demonstrate significant deviations in failure modes compared with conventional parallel bolt arrangements, underscoring the limitations of current design standards (DL/T 5486, ASCE 10-15, and EN 1993-1-8) in accurately predicting the capacity of staggered connections. Based on the identified failure modes of staggered two-bolt connections, this study proposes an enhanced design methodology for member fracture capacity, incorporating block shear calculation models from the three aforementioned standards. Comparative analysis demonstrates that the ASCE standard provides superior predictive accuracy, with experimental validation exceeding 95% agreement. The study culminates in specific design recommendations for staggered two-bolt connections, offering critical insights into stress redistribution mechanisms, material behavior, and deformation-induced failure patterns. These findings contribute to the development of more accurate and safer design guidelines for bolted connections in steel transmission towers. Full article

The ability of computer simulations to model airflows in a tunnel can significantly contribute to the effectiveness of fire safety precautions. This study examines two ways of modelling the Polana tunnel (Slovakia) and its influence on the airflow created via longitudinal ventilation using a fire dynamics simulator. The first class of studied models is based on the assumption that the airflow in the tunnel is influenced to a large extent by the supporting structures and other installations under the tunnel ceiling. Due to the resolution of the computational grid, the constructions are modelled using a system of cuboids distributed along the tunnel at regular distances. The second class of models combines this approach with the previous one, in which tunnel drag is modelled by increased roughness of the tunnel walls. Unlike the previous model, the roughness values are not constant but reflect the curvature of the tunnel walls. The simulations results are compared against on-site measurements during a full-scale ventilation test conducted in 2017 by a grid of five anemometers, as well as with the results of the previous model. The results agree well with the experimental data with relative errors below 2% for bulk velocities and with mean absolute percentage deviations of 3, 6, and 10% for velocities measured using individual grid anemometers for three ventilation modes. The new models achieve several improvements in accuracy compared to the previous one. Full article

Balancing efficiency and accuracy is often challenging in the numerical solution of three-dimensional (3D) point source acoustic wave equations for layered media. To overcome this, an efficient solution method in the spatial-wavenumber domain is proposed, utilizing the Non-Uniform Fast Fourier Transform (NUFFT) to achieve arbitrary non-uniform sampling. By performing a two-dimensional (2D) Fourier transform on the 3D acoustic wave equation in the horizontal direction, the 3D equation is transformed into a one-dimensional (1D) space-wavenumber-domain ordinary differential equation, effectively simplifying significant 3D problems into one-dimensional problems and significantly reducing the demand for memory. The one-dimensional finite-element method is applied to solve the boundary value problem, resulting in a pentadiagonal system of equations. The Thomas algorithm then efficiently solves the system, yielding the layered wavefield distribution in the space-wavenumber domain. Finally, the wavefield distribution in the spatial domain is reconstructed through a 2D inverse Fourier transform. The correctness of the algorithm was verified by comparing it with the finite-element method. The analysis of the half-space model shows that this method can accurately calculate the wavefield distribution in the air layer considering the air layer while exhibiting high efficiency and computational stability in ultra-large-scale models. The three-layer medium model test further verified the adaptability and accuracy of the algorithm in calculating the distribution of acoustic waves in layered media. Through a sensitivity analysis, it is shown that the denser the mesh node partitioning, the higher the medium velocity, and the lower the point source frequency, the higher the accuracy of the algorithm. An algorithm efficiency analysis shows that this method has extremely low memory usage and high computational efficiency and can quickly solve large-scale models even on personal computers. Compared with traditional FEM, the algorithm has much higher advantages in terms of memory usage and efficiency. This method provides a new approach to the numerical solution of partial differential equations. It lays an essential foundation for background field calculation in the scattering seismic numerical simulation and full-waveform inversion of acoustic waves, with strong theoretical significance and practical application value. Full article

Crashworthiness is a critical property that enables aerospace structures to minimise injuries and equipment damage during impact scenarios. This review examines the current state of crashworthiness research, with a focus on regulatory frameworks, experimental testing, and numerical modelling techniques. Stringent safety standards set by the Federal Aviation Administration (FAA) and the European Union Aviation Safety Agency (EASA) guide the design and certification protocols for aeronautical structures. Experimental crash testing, which includes both full-scale and subscale impact tests, provides essential data for validating material behaviour and energy absorption capabilities under both quasi-static and dynamic loading conditions. Advanced numerical modelling tools offer significant insights into crash behaviour, enabling optimisation of structural designs whilst reducing reliance on costly physical testing. This review highlights the integration of regulations, empirical data, and computational tools in advancing crashworthiness research, with an emphasis on developing safer, more efficient, and sustainable aerospace designs. Future directions should prioritise the use of sustainable materials and optimise crashworthy designs through artificial intelligence (AI) and advanced numerical models to enhance structural performance and safety. Full article

Heterogeneity of adsorption pore volume distribution affects desorption and diffusion processes of coal reservoirs. In this paper, N₂ and CO₂ adsorption and desorption experiment tests were used to study the pore structure of middle and high rank coal reservoirs in the study area. The fractal theory of volume and surface area is used to achieve a full-scale fractal study of adsorption pores (pore diameter is less than 100 nm) in the study area. Firstly, adaptability and control factors of volume fractals and surface area fractals within the same aperture scale range are studied. Secondly, fractal characteristics of micro-pores and meso-pores are studied. Thirdly, fractal characteristics within different aperture scales and the influencing factors of fractal characteristics within different scale ranges are studied. The results are as follows. With the increase in coal rank, pore volume and specific surface area of pores less than 0.8 nm increase, and dominant pore size changes from 0.55~0.8 nm (middle coal rank) to 0.5~0.7 nm (high coal rank). As coal rank increases, TPV and average pore diameter (APD) decrease under the BJH model, while SSA changes are not significant under the BET model. Moreover, as the pore diameter decreases, the correlation between the integral dimension of pore volume and degree of coal metamorphism decreases. This result can provide a theoretical basis for the precise characterization of the target coal seam pore and fracture structure and support the optimization of favorable areas for coalbed methane. Full article

The seismic response of confined masonry (CM) walls, built from innovative hollow clay blocks featuring large thermal insulation cavities and bonded with polyurethane glue instead of thin-layer mortar, was investigated. A 3D micro-model was subsequently developed in Abaqus and validated against results from cyclic shear tests on full-scale CM wall specimens. Once validated, the model was utilized in an extensive parametric study to investigate the effects of openings on the walls. This parametric study considered the size of the opening, its position, the aspect ratio of the walls, and different sizes of tie-columns. The results showed that the size and placement of openings substantially and negatively affected seismic response, and that the detrimental effects can be alleviated by placing strong tie-columns next to the openings. Full article

With the growing demand for drug products requiring lyophilization, it is essential to either expand aseptic drying capacity or improve the efficiency of existing capacity through process intensification, ensuring that resources are utilized to their full potential. In this regard, mathematical models are highly recommended to assist professionals in process optimization. To effectively utilise these models, it is also essential to develop robust techniques for determining key parameters, including the product resistance to vapour flow. Traditional experimental methods for evaluating this coefficient are time-intensive and/or require the insertion of probes into the product, which is not feasible at a manufacturing scale. This study addresses these challenges by introducing a novel deep learning framework designed to predict the mass transfer coefficient directly from Field Emission Scanning Electron Microscope images. This approach significantly streamlines the evaluation process, leveraging the high-resolution capabilities of Field Emission Scanning Electron Microscope for detailed analysis. In this work, we focus on advanced Field Emission Scanning Electron Microscope image processing, choice of strategic convolutional neural network configuration, and thorough model performance evaluation to predict the mass transfer coefficient. Given the frequent scarcity of datasets in this field, we have employed data augmentation techniques to enhance the robustness of our model. The results demonstrate good predictive accuracy (error on the interpolation test data lower than 5%), highlighting the potential of this framework to facilitate the assessment of mass transfer coefficients in freeze-dried products. Full article

Adjacent existing box girder bridges should be spliced in the long-span bridge expansion project. A type of integral splicing composite structure for connecting the adjacent flange plates is designed herein. The mechanical characteristic of the integral splicing composite structure is tested using a local full-scale model, and a refined simulation model is also proposed for the optimization of the integral splicing composite structure. The loop bar in the joint connection segment and the application of Ultra-High-Performance Concrete (UHPC) material can guarantee the effective connection between the existing flange plate and the splicing structure. The embedded angled bar can delay the interface debonding failure and interface slip. The UHPC composite segment below the flange plate (segment CF) can bend together with the existing flange plate. In this study, an innovative integral splicing composite structure for a long-span bridge extension project is proposed and verified using both a local full-scale model test and finite element simulation. The adaptation of UHPC material and loop bar joint connection form can meet the cracking loading requirements of the splicing box girder structure. By proposing a refined simulation model and comparing the calculation result with the test result, it is found that the flexural performance of the integral splicing composite structure depends on the size of the composite segment below the flange plate (segment CF). Increasing the width of segment CF is beneficial to delay the interface debonding failure, and increasing its thickness can effectively delay the cracking load of the flange plate. Finally, the scheme of segment CF with one side width of 200 cm and a minimum thickness of 15 cm can improve the flexural resistance of the spliced structure and avoid the shear effect caused by the lane layout scheme and the location of the segment CF end. Through the research in this paper, the reasonable splicing form of a long-span old bridge is innovated and verified, which can be used as a reference for other long-span bridge splicing projects. Full article

Hydropower is a vital strategic component of China’s clean energy development. Its construction and optimized water resource allocation are crucial for addressing global energy challenges, promoting socio-economic development, and achieving sustainable development. However, the optimization scheduling of cascade hydropower stations is a large-scale, multi-constrained, and nonlinear problem. Traditional optimization methods suffer from low computational efficiency, while conventional intelligent algorithms still face issues like premature convergence and local optima, which severely hinder the full utilization of water resources. This study proposed an improved whale optimization algorithm, the Black-winged Differential-variant Whale Optimization Algorithm (BDWOA), which enhanced population diversity through a Logistic-Sine-Cosine combination chaotic map, improved algorithm flexibility with an adaptive adjustment strategy, and introduced the migration mechanism of the black-winged kite algorithm along with a differential mutation strategy to enhance the global search ability and convergence capacity. The BDWOA algorithm was tested using test functions with randomly generated simulated data, with its performance compared against five related optimization algorithms. Results indicate that the BDWOA achieved the optimal value with the fewest iterations, effectively overcoming the limitations of the original whale optimization algorithm. Further validation using actual runoff data for the cascade hydropower station optimization scheduling model showed that the BDWOA effectively enhanced power generation efficiency. In high-flow years, the average power generation increased by 8.3%, 6.5%, 6.8%, 4.1%, and 8.2% compared to the five algorithms while achieving the shortest computation time. Significant improvements in power generation were also observed in normal-flow and low-flow years. The scheduling solutions generated by the BDWOA can adapt to varying inflow conditions, offering an innovative approach to solving complex hydropower station optimization scheduling problems. This contributes to the sustainable utilization of water resources and supports the long-term development of renewable energy. Full article

This study focuses on the manoeuvring characteristics of model- and full-scale ships. Various methods, including free-running model tests (FRMTs), computational fluid dynamics (CFD), and theoretical approaches, were employed to estimate ship manoeuvring performance. However, these methods are typically simulated at model-scale, which introduces discrepancies in the Reynolds number due to Froude scaling laws. Although numerous studies have investigated scale effects, most have concentrated on ship resistance, with limited research on manoeuvring performance. To address this gap, this study developed a free-running CFD simulation model for both a model-scale and full-scale ONRT. The study involved a detailed analysis of manoeuvring trajectories, forces, and moments. This analysis aimed to highlight differences in manoeuvring performance caused by Reynolds number discrepancies between model- and full-scale ships, providing a quantitative assessment of performance variations across scales and contributing to a more accurate understanding of manoeuvring characteristics at full scale. Full article