Search Results (66)

Research on helicopter stability is essential for the design of flotation systems and serves as a primary basis for evaluating wind and wave resistance. The drainage volume method and fluid–solid coupling method are commonly used for calculating floating characteristics. However, the drainage volume method ignores the flexibility of airbags and their interaction with the helicopter, while the fluid–solid coupling method is computationally intensive. In contrast, the analysis of a helicopter’s hydrostatic floating characteristics is a static problem. It suffices to obtain relevant results when the helicopter reaches a stationary state, without the need to accurately simulate the dynamic process of achieving that state. Therefore, this paper proposes an equivalent calculation method, in which the hydrostatic effect of water on the helicopter is represented by the hydrostatic pressure applied across the entire flotation system. The finite element method (FEM) is then employed to determine the final static state, and the results are compared with those from the drainage volume method and available experimental data to validate the reliability of the proposed approach. To elucidate the influence mechanism of airbags and flexible connecting straps on the lateral static stability of helicopters, this paper analyzes airbag positions at various heeling angles and examines the impact of different internal airbag pressures. The results indicate that the main factor affecting lateral static stability is the displacement of the airbags. This displacement causes variations in the airbag’s buoyancy and center of buoyancy, thereby reducing the lateral heeling moment. Full article

During the waterflooding recovery process, water is injected into the hydrocarbon reservoirs and displaces a portion of the oil and gas, thereby improving oil and gas recovery rates and extending the production life of the reservoir. The macro benefits of waterflooding technology are widely recognized; however, the micro-scale effects of water on the reservoir’s pore structure and fluid distribution during the injection process remain underexplored. Therefore, this study aims to analyze the micro-distribution characteristics of fluids in the reservoir during the oil–water displacement process. To further investigate the micro-mechanisms of waterflooding recovery and the factors influencing recovery efficiency, the study focuses on the impact of permeability, pressure gradient, injection volume, and reverse displacement on oil recovery efficiency. A combined qualitative and quantitative analysis approach was employed, using techniques such as nuclear magnetic resonance (NMR), CT scanning, and fluid distribution tomography to comprehensively analyze the fluid evolution patterns within the reservoir. The results show the following: (1) The movable fluids in the oilfield are primarily distributed within pores ranging from 0.1 to 40 μm; the remaining oil is mainly distributed within pores of 0.1 to 10 μm, accounting for over 85% of the total distribution, and these pores serve as the main space for extracting remaining oil in later stages. (2) Increasing the injection volume significantly improves the oil recovery efficiency in pores ranging from 0.1 to 10 μm. Increasing the displacement pressure gradient effectively reduces remaining oil in pores of 0.1 to 5 μm. However, for reservoirs with permeability greater than 10 mD, once the injection volume exceeds 1 PV or the displacement pressure gradient exceeds 1.8 MPa/m, the increase in oil recovery efficiency becomes marginal. (3) With increasing water injection multiples, the oil displacement efficiency of cores with varying permeability levels shows an overall upward trend. However, the extent of improvement varies significantly, with low-permeability cores exhibiting a markedly greater enhancement in displacement efficiency compared to high-permeability cores. (4) Reverse displacement can reduce the remaining oil in pores ranging from 0.1 to 10 μm, and the increase in oil recovery efficiency is more significant in cores with lower permeability than in those with higher permeability. Therefore, increased production cannot solely rely on improving the production pressure differential to develop remaining oil. Full article

The architectural facade, including balconies, vertical frames, and sunshades, is widely installed on the surfaces of high-rise buildings, and will affect the wind load and airflow around the buildings. However, current studies mainly focus on local wind pressure, with limited research on aerodynamic forces and a lack of optimization design methods for vertical facades. This paper investigates the aerodynamic effects of different vertical facade layouts on high-rise buildings through wind tunnel experiments. Subsequently, CFD simulations were performed on 120 generated models. By combining neural networks and genetic algorithms, this paper optimized the aerodynamics of the vertical facades on a high-rise building, analyzed the flow field around the building, and provided reference for the aerodynamic optimization design of vertical facades on high-rise building facades. The results show that vertical facades could reduce the base shear forces and overturning moments of tall buildings, and the mean drag coefficient can be reduced by up to 31%, and the RMS value of lateral force coefficient by 57%, through the aerodynamic optimization. Through the analysis of flow fields around tall buildings, the “chamfer” formed by the vertical facades and the building corner is attributed as the main reason for reducing the aerodynamic forces of tall buildings. Furthermore, the negative resistance on vertical facades caused by the adverse pressure gradient is another major factor for reducing the mean value of aerodynamic force. Full article

Scientific balloons provide an inexpensive and reliable platform for near-space scientific experiments. The analysis of the balloon geometry and forces has always been a major concern for balloon designers. Most previous studies have focused solely on the fully inflated shapes and forces of balloons, analyzing only the membrane structure and simplifying the effects of internal and external gases into a gradient pressure difference. This approach lacks consideration of the fluid–structure interaction (FSI) of scientific balloons. This paper utilizes the Coupled Eulerian–Lagrangian (CEL) method in the Abaqus/Explicit simulation environment to analyze the FSI effects of scientific balloons under the influence of internal helium and external air. Three typical working conditions of scientific balloons are selected for simulation analysis. First, a three-dimensional spherical balloon is simulated during the ascent process to verify the correctness of the CEL simulation framework. This also demonstrates the membrane folding characteristics during balloon ascent, which could not be calculated in previous two-dimensional axisymmetric simulations. Next, the study explores balloon shapes that deviate from quasi-static pressure distributions due to the motion of internal helium. These include the “mushroom” shape observed during the dynamic launching of the balloon on the ground and the “sail” shape caused by lateral airflow. The mushroom shape arises from the sudden loss of the bottom constraint, causing the internal helium to move upward while being resisted by the air at the balloon’s top. The simulation successfully replicates the rapid waist transition and the downward concavity at the top due to air resistance, while also providing the corresponding force distribution. For the sail-shaped condition, the simulation analyzes the balloon’s tilt angle and the characteristic upturn of its windward surface. By a comparison with no-wind conditions, this study quantifies the impact of wind on the forces acting on the balloon, offering practical guidance for balloon launching. The CEL simulation framework established in this study not only provides a new tool for the FSI analysis of scientific balloons but also enriches the mechanical analysis results of these balloons. Full article

Horizontal resistance can be significantly different for gravelly soil slope sites with different gradients. The impact of slope gradient on the horizontal resistance of soil based on a three-dimensional physical simulation test has been investigated, and the displacement of the pile top and soil pressure for four piles under various gradients (slope gradient 0–45°) was analyzed. The research reveals that ① The soil resistance exhibits a linear increase stage, non-linear steep increase stage, and gradually stabilizing stage with the increase in load. ② The ultimate soil resistance is significantly affected by depth and displacement, and hyperbolic variation characteristics related to the displacement stage. It has a slope weakening effect, and the steeper the slope gradient, the lower the ultimate soil resistance of the pile sides, which effect is negligible when the depth exceeds 0.6–0.7 times that of the pile buried depth. ③ Based on the characteristics of horizontal ultimate resistance-displacement-depth variation in soil, a gradient factor, which is only related to the slope gradient, was used to describe the impact of gradient on the soil resistance modulus (k_ini) and ultimate resistance (p_u). k_ini is reduced close to the ground surface and gradually increases with depth until it becomes equal to the value of level ground. The ratio between p_u in slope ground and level ground was determined for slope angles. The above horizontal resistance parameters were expressed as a function based on the test data to calculate the lateral ultimate bearing capacity of gravelly soil considering the slope gradient factor. The research results developed the theory of foundation design for building structures, promoting the reliability evaluation of pile soil systems towards a more scientific and rigorous direction. Full article

Chiral particles have attracted considerable attention due to their distinctive interactions with light, which enable a variety of cutting-edge applications. This review presents a comprehensive analysis of the optical forces acting on chiral particles, categorizing them into gradient force, radiation pressure, optical lateral force, pulling force, and optical force on coupled chiral particles. We thoroughly overview the fundamental physical mechanisms underlying these forces, supported by theoretical models and experimental evidence. Additionally, we discuss the practical implications of these optical forces, highlighting their potential applications in optical manipulation, particle sorting, chiral sensing, and detection. This review aims to offer a thorough understanding of the intricate interplay between chiral particles and optical forces, laying the groundwork for future advancements in nanotechnology and photonics. Full article

In this paper, the dataset is collected from the fluidic muscle datasheet. This dataset is then used to train models predicting the pressure, force, and contraction length of the fluidic muscle, as three separate outputs. This modeling is performed with four algorithms—extreme gradient boosted trees (XGB), ElasticNet (ENet), support vector regressor (SVR), and multilayer perceptron (MLP) artificial neural network. Each of the four models of fluidic muscles (5-100N, 10-100N, 20-200N, 40-400N) is modeled separately: First, for a later comparison. Then, the combined dataset consisting of data from all the listed datasets is used for training. The results show that it is possible to achieve quality regression performance with the listed algorithms, especially with the general model, which performs better than individual models. Still, room for improvement exists, due to the high variance of the results across validation sets, possibly caused by non-normal data distributions. Full article

Objectives: To analyze Heart Team decisions and outcomes following failure of surgical aortic valve replacement (SAVR) prostheses. Methods: Patients undergoing re-operations following index SAVR (Redo-SAVR) and those undergoing valve-in-valve transcatheter aortic valve replacement (ViV-TAVR) following SAVR were included in this study. Patients who underwent index SAVR and/or Redo-SAVR for endocarditis were excluded. Data are presented as medians and 25th–75th percentiles, or absolute numbers and percentages. Outcomes were analyzed in accordance to the VARC-3 criteria. Results: Between 01/2015 and 03/2021, 53 patients underwent Redo-SAVR, 103 patients ViV-TAVR. Mean EuroSCORE II was 5.7% (3.5–8.5) in the Redo-SAVR group and 9.2% (5.4–13.6) in the ViV group. In the Redo-SAVR group, 12 patients received aortic root enlargement (22.6%). Length of hospital and ICU stay was longer in the Redo-SAVR group (p < 0.001; p < 0.001), PGmax and PGmean were lower in the Redo-SAVR group as compared to the ViV-TAVR group (18 mmHg (10–30) vs. 26 mmHg (19–38), p < 0.001) (9 mmHg (6–15) vs. 15 mmHg (9–21), p < 0.001). A higher rate of paravalvular leakage was seen in the ViV-TAVR group (p = 0.013). VARC-3 Early Safety were comparable between the two populations (p = 0.343). Survival at 1 year and 5 years was 82% and 36% in the ViV-TAVR cohort and 84% and 77% in the Redo-SAVR cohort. The variables were patient age (OR 1.061; [95% CI 1.020–1.104], p = 0.004), coronary heart disease (OR 2.648; [95% CI 1.160–6.048], p = 0.021), and chronic renal insufficiency (OR 2.711; [95% CI 1.160–6.048], p = 0.021) showed a significant correlation to ViV-TAVR. Conclusions: Heart Team decisions are crucial in the treatment of patients with degenerated aortic bioprostheses and lead to a low mortality in both treatment paths thanks to patient-specific therapy planning. ViV-TAVR offers a treatment for elderly or intermediate-risk profile patients with comparable short-term mortality. However, this therapy is associated with increased pressure gradients and a high prevalence of paravalvular leakage. Redo-SAVR enables the surgical treatment of concomitant cardiac pathologies and allows anticipation for later VIV-TAVR by implanting the largest possible valve prostheses. Full article

The unique composite gradient structure of bamboo has made it widely recognized as an extremely efficient natural structure and material, endowing it with exceptional flexibility and resilience. This enabled bamboo to withstand the forces of wind and snow without fracturing. In this paper, the inherent structural characteristics of bamboo were examined in order to extract its biological advantages through experimental methods. Then, the structural characteristics of bamboo in its vertical and radial directions served as the respective inspiration for two bionic applications, which were further analyzed and optimized using finite element analysis to accurately evaluate their bearing capacities. It can be found that the density of vascular bundles increased proportionally with the height of the bamboo stem, while the circumference exhibited a linear decrease. The wall thickness of the bamboo decreased and stabilized after reaching a height of 10 m. The distribution of nodes exhibited a nearly symmetrical pattern from the base to the top of the bamboo stem. The tapering of the bamboo culm exhibited a non-linear pattern with height, characterized by an initial decrease followed by a slight increase ranging from 0.004 to 0.010. The vascular bundles in bamboo exhibited a functional gradient distribution, which had a 6:3:2 distribution ratio of vascular bundles in the wall’s dense, transition, and sparse areas, respectively. The bionic cantilever beam incorporated characteristics of a hollow structure, a non-uniform distribution of nodes, and a certain amount of tapering, which effectively enhanced its flexural performance compared to the traditional ones. The thin-wall tube, featuring a “dendritic” partial pressure structure, demonstrated exceptional lateral compressive performance in transverse compression, particularly when the tube incorporated a gradient distribution of partition numbers and layer spacing. Full article

The aim of this study was to employ artificial intelligence (AI)-based magnetic resonance imaging (MRI) brain volumetry to potentially distinguish between idiopathic normal pressure hydrocephalus (iNPH), Alzheimer’s disease (AD), and age- and sex-matched healthy controls (CG) by evaluating cortical, subcortical, and ventricular volumes. Additionally, correlations between the measured brain and ventricle volumes and two established semi-quantitative radiologic markers for iNPH were examined. An IRB-approved retrospective analysis was conducted on 123 age- and sex-matched subjects (41 iNPH, 41 AD, and 41 controls), with all of the iNPH patients undergoing routine clinical brain MRI prior to ventriculoperitoneal shunt implantation. Automated AI-based determination of different cortical and subcortical brain and ventricular volumes in mL, as well as calculation of population-based normalized percentiles according to an embedded database, was performed; the CE-certified software mdbrain v4.4.1 or above was used with a standardized T1-weighted 3D magnetization-prepared rapid gradient echo (MPRAGE) sequence. Measured brain volumes and percentiles were analyzed for between-group differences and correlated with semi-quantitative measurements of the Evans’ index and corpus callosal angle: iNPH patients exhibited ventricular enlargement and changes in gray and white matter compared to AD patients and controls, with the most significant differences observed in total ventricular volume (+67%) and the lateral (+68%), third (+38%), and fourth (+31%) ventricles compared to controls. Global ventriculomegaly and marked white matter reduction with concomitant preservation of gray matter compared to AD and CG were characteristic of iNPH, whereas global and frontoparietally accentuated gray matter reductions were characteristic of AD. Evans’ index and corpus callosal angle differed significantly between the three groups and moderately correlated with the lateral ventricular volumes in iNPH patients [Evans’ index (r > 0.83, p ≤ 0.001), corpus callosal angle (r < −0.74, p ≤ 0.001)]. AI-based MRI volumetry in iNPH patients revealed global ventricular enlargement and focal brain atrophy, which, in contrast to healthy controls and AD patients, primarily involved the supratentorial white matter and was marked temporomesially and in the midbrain, while largely preserving gray matter. Integrating AI volumetry in conjunction with traditional radiologic measures could enhance iNPH identification and differentiation, potentially improving patient management and therapy response assessment. Full article

Utilizing the discrete fracture model (DFM), a transient flow model is established for fractured horizontal wells in tight oil reservoirs, accounting for threshold pressure gradient (TPG), stress sensitivity effect, hydraulic fracture parameters, and fracture distribution pattern. This model is solved using the finite-volume method (FVM), and an important sensitivity analysis is conducted. The findings reveal that the models incorporated by the threshold pressure gradient result in an upward trend in the pressure-derivative curve. As the threshold pressure gradient increases, this upward trend becomes more pronounced, rendering the distinction between flow regimes more challenging. The stress sensitivity effect predominantly impacts the pressure-derivative curve during the later flow period. Additionally, as the fracture half-length increases, the pressure performance of both fracture radial flow and formation radial flow becomes more difficult. Fracture conductivity has a significant influence during the early flow period, facilitating the identification of flow regimes with the trend of increasing fracture conductivity. Full article

The time-periodic plane Poiseuille flow of electrically conducting incompressible generalized Burgers fluids through a porous medium is analytically and numerically investigated in the presence of a transverse uniform magnetic field. The main purpose is to provide analytical expressions for the dimensionless steady-state fluid velocity, non-trivial shear stress and Darcy’s resistance, which can be used to bring to light important characteristics concerning fluid behavior. Similar solutions corresponding to the Poiseuille flow of the same fluids induced by a constant pressure gradient are obtained as limiting cases of previous results. The present results reduce to known solutions from the literature when magnetic and porous effects are neglected, and their validation is graphically proved. The needed time to reach a steady state has been graphically determined. It was found that the steady state is later obtained in the absence of a magnetic field and porous medium. The impact of a magnetic field and porous medium on the fluid velocity, shear stress and flow resistance has been systematically examined and elucidated through graphical representations. The findings reveal that the presence of a magnetic field or porous medium results in a reduction in the fluid velocity, accompanied by an increase in the flow resistance. Full article

Hydrodynamic pressure sensors offer an auxiliary approach for ocean exploration by unmanned underwater vehicles (UUVs). However, existing hydrodynamic pressure sensors often lack the ability to monitor subtle hydrodynamic stimuli in deep-sea environments. In this study, we present the development of a deep-sea hydrodynamic pressure sensor (DSHPS) capable of operating over a wide range of water depths while maintaining exceptional hydrodynamic sensing performance. The DSHPS device was systematically optimized by considering factors such as piezoelectric polyvinylidene fluoride–trifluoroethylene/barium titanate [P(VDF-TrFE)/BTO] nanofibers, electrode configurations, sensing element dimensions, integrated circuits, and packaging strategies. The optimized DSHPS exhibited a remarkable pressure gradient response, achieving a minimum pressure difference detection capability of approximately 0.11 Pa. Additionally, the DSHPS demonstrated outstanding performance in the spatial positioning of dipole sources, which was elucidated through theoretical charge modeling and fluid–structure interaction (FSI) simulations. Furthermore, the integration of a high Young’s modulus packaging strategy inspired by fish skull morphology ensured reliable sensing capabilities of the DSHPS even at depths of 1000 m in the deep sea. The DSHPS also exhibited consistent and reproducible positioning performance for subtle hydrodynamic stimulus sources across this wide range of water depths. We envision that the development of the DSHPS not only enhances our understanding of the evolutionary aspects of deep-sea canal lateral lines but also paves the way for the advancement of artificial hydrodynamic pressure sensors. Full article

Long-span bridges are susceptible to damage, aging, and deformation in harsh environments for a long time. Therefore, structural health monitoring (SHM) systems need to be used for reasonable monitoring and maintenance. Among various indicators, bridge displacement is a crucial parameter reflecting the bridge’s health condition. Due to the simultaneous bearing of multiple environmental loads on suspension bridges, determining the impact of different loads on displacement is beneficial for the better understanding of the health conditions of the bridges. Considering the fact that extreme gradient boosting (XGBoost) has higher prediction performance and robustness, the authors of this paper have developed a data-driven approach based on the XGBoost model to quantify the impact between different environmental loads and the displacement of a suspension bridge. Simultaneously, this study combined wavelet threshold (WT) denoising and the variational mode decomposition (VMD) method to conduct a modal decomposition of three-dimensional (3D) displacement, further investigating the interrelationships between different loads and bridge displacements. This model links wind speed, temperature, air pressure, and humidity with the 3D displacement response of the span using the bridge monitoring data provided by the GNSS and Earth Observation for Structural Health Monitoring (GeoSHM) system of the Forth Road Bridge (FRB) in the United Kingdom (UK), thus eliminating the temperature time-lag effect on displacement data. The effects of the different loads on the displacement are quantified individually with partial dependence plots (PDPs). Employing testing, it was found that the XGBoost model has a high predictive effect on the target variable of displacement. The analysis of quantification and correlation reveals that lateral displacement is primarily affected by same-direction wind, showing a clear positive correlation, and vertical displacement is mainly influenced by temperature and exhibits a negative correlation. Longitudinal displacement is jointly influenced by various environmental loads, showing a positive correlation with atmospheric pressure, temperature, and vertical wind and a negative correlation with longitudinal wind, lateral wind, and humidity. The results can guide bridge structural health monitoring in extreme weather to avoid accidents. Full article

Introduction: High-resolution ano-rectal manometry (HRAM), part of the investigative process to diagnose disorders of recto-anal co-ordination, is currently performed in the left-lateral position (LLP). This may seem unnatural for patients and recent data suggest that the seated, squatted position (SP) may improve rectal drive and recto-anal pressure gradients, raising the question as to whether defaecatory dyssenergia (DD) is over-diagnosed when the test is carried out in the LLP. Aim/method: A single centre study was carried out in patients with faecal incontinence and/or constipation to evaluate the effect of SP versus LLP on HRAM analysis and resultant manometric diagnosis of DD. Positioning was consecutive and the order was randomised for each patient. The HRAM protocol was carried out in accordance with the manufacturer’s guidelines (Manoscan). Data analysis and interpretation were blinded with a consensus reached for each test position. Data (mean ± SEM) were analysed using an unpaired t-test and Chi-square test. Results: In total, 40 patients completed the study, including 33 females with a median age of 56 (IQR 48–63). The mean rectal drive was significantly higher in the SP vs. LLP (82.6 ± 5.3 mmHg vs. 44.1 ± 3.9 mmHg, respectively, p < 0.0001). No difference in the anal sphincter relaxation pressure (66.7 ± 5.7 mmHg vs. 70.9 ± 5.5 mmHg, p = 0.9535) was detected. The manometric diagnoses of abnormal ano-rectal co-ordination were significantly higher in the LLP, when p = 0.013. Patients reported a significant preference for the seated position, when p = 0.0001. Conclusion: These data show that HRAM in the seated position improves rectal drive, which reduces manometric diagnoses of abnormal ano-rectal coordination. These findings may have important implications for practice and may inform future guidelines. Full article