Geometry Parameters Research Articles

The geometry, purity, and grain orientation database of the Cu stabilizer layer and the effect on the electrical and thermal properties of commercial REBCO tapes

Abstract Building upon our previous database of the thermal, electrical, and mechanical properties of commercial REBCO tape, we have constructed a subsequent database focusing on the Cu layer of such tapes from eight distinct manufacturers. This database encompasses information pertaining to the geometry, purity, and grain orientation of the Cu layer. The primary objective of this database is to not only elucidate the material science of the Cu layer across various commercial tapes but also to establish correlations between the thermal, electrical, and mechanical properties and the aforementioned geometry, purity, and grain orientation parameters. After analysis, three significant findings have been validated. Firstly, the non-uniformity of geometry plays a critical role in the electrical resistivity in the radial direction, primarily through altering the actual contact surface area. Secondly, it has been observed that the total grain boundary length per micrometer thickness exhibits a nearly linear correlation with the thermal conductivity in the circumferential direction. Thirdly, the purity of the Cu layer in all the commercial REBCO tapes is lower than anticipated. It is our aspiration that this database will facilitate enhanced comprehension of the Cu layer in REBCO tapes among a broader spectrum of researchers.

Study on resistance performance of hexagonal hull form with variation of angle of attack, deadrise, and stern for flat-sided catamaran vessel

Abstract The flat-sided hull vessel was designed with the purpose of simplifying hull production by eliminating the requirement for fairing, bending, and assembly of curved panel lines. Nevertheless, implementing the flat hull concept may marginally increase the hull resistance. The objective of the study is to investigate the impact of the hexagonal hull concept on resistance characteristics when altering the deadrise angle, angle of attack, and stern angle. Additionally, the resistance performances of the proposed hexagonal hulls were compared to evaluate the influence of the hull design geometry parameter. The contribution of this work is to identify the configuration of the design parameters to achieve an ideal level of resistance in a hexagonal catamaran hull design. The findings indicate that a greater angle of attack could potentially enhance wave generation and increase the resistance. Despite the increase in the wave resistance coefficient caused by the increment in deadrise angle, the overall resistance was reduced due to the significant reduction in wetted surface area resulting from the greater deadrise angle. As a result, the decrease in friction resistance was more pronounced than the increase in wave resistance. At last, the stern angle can cause a substantial oscillation in the curved line, resulting in a large increase in wave generation and overall resistance, particularly at high speeds.

Prediction of bearing capacity of geogrid-reinforced sand over stone columns in soft clay

It is a challenge to estimate the ultimate bearing capacity (qrs) of a geogrid-reinforced sandy bed on vertical stone columns in soft clay due to their complex geometry and uncertain parameters. Predicting qrs can be costly and challenging, so creating an accurate prediction model is important for real-world applications. The research aims to use ensemble techniques like K Nearest Neighbors (KNN), Random Forest (RF), and Extreme Gradient Boosting (XGBoost) to develop a model for estimating the bearing capacity of geogrid-reinforced stone columns (GRBS) on a sandy bed with vertical stone columns in soft clay. A dataset of 245 experimental observations is used to train the models. The present study highlights the potential use of the XGBoost model as a useful tool that can assist in predicting the bearing capacity. The results of the study reveal that this model has performed well in predicting the bearing capacity with high correlation coefficients of 0.9947. Furthermore; a SHAP dependency analysis was conducted to ascertain the significance of each parameter.

Junction conditions for one-dimensional network hemodynamic model for total cavopulmonary connection using physically informed deep learning technique

Abstract This paper presents a novel methodology utilizing physics-informed neural network (PINN) as a junction condition for a 1D network model of blood flow in total cavopulmonary connection generated by the Fontan procedure. The technique integrates a 3D mesh generation process based on the parameterization of the junction geometry, along with a sophisticated physically regularized neural network architecture. Synthetic datasets are produced using 3D steady Stokes simulations within fixed boundaries. We use a physically informed feedforward neural network that utilizes a physically regularized loss function, which incorporates the principle of mass conservation. Our PINN achieves a tolerance of 6% on the test set. We develop a 1D-PINN multiscale model based on a previously developed method for multiscale 1D–3D simulations. Comparison with 1D–3D Stokes based model and 3D Navier–Stokes based model verifies the 1D-PINN model. In the first and second comparison, the maximum deviations of the averaged pressures and flows do not exceed 1.48% and 12.26%, respectively.

Inverse problems in hydrodynamics lubrication: Parameter identification in the Reynold equation by using physics-informed neural networks

In this work, the inverse problems for hydrodynamic lubrication were solved by using the physics informed neural networks (PINNs) method. Both the conditions without and with the cavitation effects are studied. For the journal bearings without considering the cavitation effects, the eccentricity values can be accurately inverted using only 10 data points with a maximum error of less than 6%. For the problems with the mass-conserving cavitation, the geometry parameters for 1D conditions were estimated and accurate results can be obtained by also using 10 data points. While for the journal bearings with incompressible lubricants, the error was less than 3% with only 50 data points. For the ones with compressible lubricants, the eccentricity ratios can be estimated with 50 data points again, and the maximum error is less than 10%. In addition, the experimental oil pressure data were used to predict the journal bearing eccentricity, and the results were acceptable with only 9 oil pressure data points. The PINNs method presented two significant strengths: its ability to operate effectively with very sparse data points and its precision in delivering results, and it can provide a promising method for identifying unknown parameters in hydrodynamics lubrication with small data.

Predictive factors for recurrent tricuspid regurgitation after tricuspid annuloplasty: 3D echocardiography study

Abstract Introduction There is growing concern about the recurrence of tricuspid regurgitation (TR) after tricuspid annuloplasty (TA) in individuals with functional tricuspid regurgitation (FTR). While TA is effective in treating FTR, a comprehensive understanding of the echocardiographic factors influencing TR recurrence is crucial. Aim This study aims to employ multivariate regression analysis to investigate the prognostic significance of tricuspid valve (TV) geometry and echocardiographic parameters associated with both RV geometry and function. The focus is on comprehending these relationships in the context of recurrent TR subsequent to TA. Methods This prospective observational cohort study aimed to explore factors contributing to recurrent tricuspid regurgitation (TR) after tricuspid annuloplasty (TA). The focus was on patients with moderate or severe functional TR due to left heart valvular disease, particularly severe mitral regurgitation, excluding those with ischemic heart disease. The cohort included 66 individuals undergoing preoperative assessments with 2D and 3D echocardiography, quantifying RV and right atrial (RA) geometry, functional, and tricuspid valve (TV) parameters. TR severity followed ESC guidelines. Patients were categorized into effective TA (50 patients) and recurrent TR (16 patients) groups, defined by mild-moderate TR and significant moderate-severe TR one year post-surgery, respectively. SPSS software facilitated statistical analysis, with adjusted logistic regression considering parameters such as age and gender. Results Among the patients (54% male, mean age 68±9 years), no significant differences were found in gender, left ventricular and atrial parameters, or preoperative TV orifice area between groups (recurrent TR vs. effective TA: 38 [33] mm2 vs. 29 [15] mm2, p=0.117). Univariate logistic regression analysis identified Septal-Lateral Systolic TA Diameter (OR 1.62), Septal-Lateral Diastolic TA Diameter (OR 1.99), and Major Axis Diastolic TA Diameter (OR 1.59) as key predictors. For diagnostic efficacy, ROC analysis revealed Major Axis Diastolic TA Diameter (AUC 0.848; cut-off 52.5 mm), TV Leaflet Tenting Volume (AUC 0.778; cut-off 5.1 ml), and RV Basal Diameter (AUC 0.763; cut-off 47.5 mm) as the most predictive parameters. The combined use of predefined RV basal diameter and Major Axis Diastolic TA Diameter showed the highest odds ratio for recurrent TR. Conclusion Key predictors, including Septal-Lateral Systolic and Diastolic TA Diameters, and Major Axis Diastolic TA Diameter, were identified, emphasizing their significance in understanding TR recurrence after tricuspid annuloplasty. The combination of predefined RV basal diameter and Major Axis Diastolic TA Diameter showed the highest odds ratio for recurrent TR, offering valuable insights for clinical assessment and preventive strategies.

Prognostic preoperative factors for recurrence of tricuspid regurgitation following annuloplasty: examining the influence of 3d echocardiography

Abstract Introduction The increasing worry revolves around the reappearance of tricuspid regurgitation (TR) following tricuspid annuloplasty (TA) among individuals dealing with functional tricuspid regurgitation (FTR). Despite TA's efficacy as a treatment, a complete understanding of the echocardiographic elements influencing the recurrence of TR is pivotal. This knowledge holds the potential to guide the development of more robust preventive strategies, aiming to ease the incidence of recurrent TR after TA. Aim The aim of this study was to examine the prognostic value of tricuspid valve (TV) and echocardiographic parameters related to both right ventricular (RV) geometry and function. Specifically, our focus is on understanding these relationships in the context of recurrent TR following TA. Methods This prospective observational cohort study aimed to investigate determinants of recurrent TR post-surgical TV repair. The focus was on patients with moderate or severe functional TR related to left heart valvular disease, primarily severe mitral regurgitation, excluding those with ischemic heart disease. The study involved 66 participants, assessed preoperatively with 2D and 3D echocardiography, examining RV and right atrial (RA) geometry, functional, and TV parameters. TR severity followed ESC guidelines. Two groups were formed: effective TA group (50 patients) and recurrent TR group (16 patients), defined by mild to moderate TR and significant moderate-severe TR one year post-surgery, respectively. Statistical analysis employed SPSS software, with adjusted univariate logistic regression considering age and gender. Results Of the patients, 54% were male, with a mean age of 68±9 years. Echocardiography parameters in Table 1 showed no significant differences in gender, left ventricular, atrial geometrical, functional parameters, or preoperative effective regurgitant TV orifice area between groups (recurrent TR vs. effective TA: 38 [33] mm2 vs. 29 [15] mm2, p=0.117). Univariate logistic regression analysis highlighted RV and RA geometry, along with TV diameter, as predictors for recurrent TR. Notably, 3D TV geometrical parameters had prognostic significance, as confirmed by univariate adjusted logistic regression analysis. Functional RV parameters did not exhibit statistical significance in this analysis. Conclusion In conclusion, the recurrence of moderate-severe functional tricuspid regurgitation following tricuspid annuloplasty is linked to the tricuspid annulus size, as well as the geometry of the right atrium and right ventricle before surgery. Notably, no correlation was identified between the recurrence of TR and alterations in RV function.

Prognostic impact of mitral valve geometry in patients with secondary mitral regurgitation: a secondary analysis of the MITRA-FR trial

Abstract Background Mitral valve (MV) transcatheter edge-to-edge repair (TEER) has emerged as a second line therapy on top of guidelines-directed medical treatment (GDMT) in heart failure (HF) patients with severe secondary mitral regurgitation (SMR). Following the disparate results of the COAPT and MITRA-FR pivotal trials, echocardiographic markers of LV remodeling and MR severity have been proposed to select patients most likely to benefit from MV-TEER. The characterization of MV geometry arises as a potential tool to stratify risk of outcomes in SMR patients, who underwent classical surgery or MV-TEER intervention. However, it remains unknown whether MV geometry parameters were associated with prognosis in MITRA-FR patients and whether MV-TEER could modulate their impact on outcomes. Purpose To evaluate the association between MV geometry and outcomes of HF patients with SMR in the MITRA-FR trial, as well as the impact of SMR treatment modality. Methods Thirteen MV geometry parameters were assessed from baseline transthoracic echocardiograms in patients from the MITRA-FR trial. The prognostic impact of MV geometry parameters was studied on top of the baseline clinical variables used in the primary analysis of MITRA-FR (i.e. age, atrial fibrillation [AF], ischemic cardiomyopathy, myocardial infarction, left ventricular ejection fraction [LVEF] and effective regurgitant orifice area [EROA]). The primary endpoint was the composite of all-cause mortality or HF hospitalization (HFH) within 2 years. The effect of treatment arms (MV-TEER plus GDMT vs. GDMT alone) on this association was also evaluated. Results Among the 307 patients included in the pivotal trial, 272 were analyzed in the present study (i.e. 135 from the GDMT group and 137 from the GDMT + MV-TEER group). Mean age was 70±10, 74% male. 50% had ischemic cardiomyopathy and 34% AF. LVEF was 33±7% and EROA was 31±11 mm². MV geometry parameters were presented for the whole population and according to the randomization group in the Table. Among these parameters, only MV tenting area remained independently associated with the primary endpoint (Hazard Ratio (HR) = 1.22 per 1 cm², Confidence Interval (CI) = 1.01-1.47; p=0.041) after multivariate analysis (Figure). Tenting height was independently associated with the risk of HFH (HR=1.07 per 1 mm, CI=1.00-1.14, p=0.037), but no MV geometry variable was associated with all-cause death. These findings remained consistent in both treatment arms (p>0.20 for interaction). Conclusion In HF patients with SMR included in the MITRA-FR trial, MV tenting area and MV tenting height were independently associated with the risk of HFH or all-cause mortality and HFH respectively, without any difference according to treatment arms. These data suggest that MV tethering provides an incremental prognostic value beyond classical echocardiographic variables, including EROA, and then should be considered in the risk stratification of patients with HF and SMR.Table of MV geometry parameters featuresMultivariate analysis (Forrest-plots)

3D modelling-based left atrium geometry analysis to predict atrial fibrillation in patients with cryptogenic stroke

Abstract Introduction Atrial fibrillation (AF) is a high prevalence condition associated with high morbidity and mortality. Its early diagnosis allows to initiate several prophylactic treatments that have proved to improve its prognosis. 3D modeling techniques allow to design accurate representations of cardiac cavities from diverse source images. Purpose We evaluated the association between new geometrical measurements obtained by 3D echocardiographic models of the left atrium (LA) and the presence of underlying paroxysmal AF in patients with cryptogenic stroke (CS). Methods 3D LA volumes from a sample of consecutive patients aged ≥60 years old and admitted to our Stroke Unit with the diagnosis of CS from April 2019 to November 2020 were analyzed. 15 days ECG monitoring was performed after discharge to detect underlying paroxysmal AF. All 3D echo volumes were analyzed by a 3D modeling open-source application. From this analysis several LA geometry parameters were obtained: sphericity, elongation, flatness, major axis length, minor axis length, maximum 2D diameter (max2Ddiam) and surface-volume ratio (S/V). Functional atrial parameters (3D left atrial ejection fraction, LAEF) were also determined. Results 36 patients were analyzed. Mean age was 78 ± 7 years old. 19% were diabetic, 58% had high blood pressure and 14% of patients had history of ischemic cardiomyopathy. Mean body-mass index was 26. These baseline characteristics were equally distributed between groups. Baseline proBNP was significantly higher in patients developing atrial fibrillation (949 vs 275 pg/mL; p= 0,014.). Maximum 2D diameter (max2Ddiam) and Surface-volume ratio (S/V) were the best predictors of AF (AUC of ROC curves: 0.69; 0.49 – 0.88 and 0.63; 0.42 – 0.84, respectively). An optimal cut-off point of 39 mm was selected for max2Ddiam and of 0.20 for S/V. These values were included in a multivariate model adjusted by baseline proBNP. A Max2Ddiam <39 mm and a S/V ≥0.20 were both significantly associated with the presence of paroxysmal AF (OR 6.96; p= 0.048 and OR 12.22; p = 0.043, respectively). Conclusions New geometrical atrial parameters can be obtained from echo 3D models and might be able to predict AF in patients with CS. Further analysis and larger samples are required to better understand these findings.TableFigure

Role of mechanical stress localizations on the radiation hardness of AlGaN/GaN high electron mobility transistors

Abstract Multi-material, multi-layered systems such as AlGaN/GaN high electron mobility transistor (HEMTs) contain residual mechanical stresses that arise from sharp contrasts in device geometry and materials parameters. These stresses, which can be either tensile or compressive, are difficult to detect and eliminate because of their highly localized nature. We propose that their high stored internal energy make potential sites for defect nucleation sites under radiation, particularly if their locations coincide with the electrically sensitive regions of a transistor. In this study, we validate this hypothesis with molecular dynamic simulation and experiments exposing both pristine and annealed HEMTS to 2.8 MeV Au+3 irradiation. Our unique annealing process uses mechanical momentum of electrons, also known as the electron wind force (EWF) to mitigate the residual stress at room temperature. High-resolution transmission electron microscopy (TEM) and cathodoluminescence spectra reveal the reduction of point defects and dislocations near the two-dimensional electron gas region of EWF-treated devices compared to pristine devices. The EWF-treated HEMTs showed relatively higher resilience with approximately 10% less degradation of drain saturation current and ON-resistance and 5% less degradation of peak transconductance. Both mobility and carrier concentration of the EWF-treated devices were less impacted compared to the pristine devices. Our results suggest that the lower density of nanoscale stress localization contributed to the improved radiation tolerance of the EWF-treated devices. Intriguingly, the EWF is found to modulate the defect distribution by moving the defects to electrically less sensitive regions in the form of dislocation networks, which act as sinks for the radiation induced defects and this assisted faster dynamic annealing.

Enhancing the Performance of Oxide‐Based Transverse Thermoelectric Generators by Optimized Internal Geometry

AbstractIn transverse thermoelectric generators (TTEGs), comprising an artificially anisotropic material formed by a layered and tilted structure of two materials, the induced thermoelectric voltage is generated perpendicular to the applied temperature gradient. The performance of TTEGs composed of alternate layers of La1.99Sr0.01CuO4 (LSCO) and silver (Ag), tilted at an angle φ, with metal‐to‐ceramic thickness ratio νt, is investigated. Improvement in performance is achieved by optimizing the internal geometry parameters, φ and νt of the tilted layered structure. The transverse power factor PFtr and figure‐of‐merit ZtrT of the artificially tilted material composite are analytically calculated and presented in color contours. Experimentally, a power output Pout of 14.5 mW at ΔT = 140 K is measured for a TTEG with φ = 66°, compared to 2.8 mW and 11 mW for generators with φ of 20° and 45°, respectively. Moreover, TTEGs with different values of νt are prepared. Furthermore, transverse multilayer thermoelectric generators (TMLTEG) with output power of 14.3 mW at ΔT = 225 K are fabricated utilizing the ceramic multilayer technology. It is demonstrated that the transverse thermoelectric effect using an artificial anisotropic material consisting of ceramic and metal can be explored for autonomous thermoelectric energy generation for low‐power applications.

Comprehensive Geometric Parameterization and Computationally Eficient 3D Shape Matching Optimization of Realistic Stents

Abstract Flexible and compact shape representation schemes are essential for design optimization problems. Current shape representation schemes for coronary stent designs concern predominantly idealized or Independent Ring (IR) designs, which are outdated and only consider a small number of core design variables (such as strut width, height, and thickness) and ignore clinically critical characteristics such as the number of connectors. No reports exist on the geometry parameterization of the latest Helical Stents (HS) that have more complex designs than IR stents. Here, we present two new shape parameterization schemes to fully capture the 3D designs of contemporary IR and double-helix HS stents. We developed a 3D stent geometry builder based on 17 (IR) and 18 (HS) design variables, including strut width, thickness, height, number of connectors and rings, stent length, and strut centerline shape. The shape of the strut centerline was derived via a combination of NURBS, PARSEC, quarter circle, and straight line segments. Shape matching for complex 3D geometries, such as the contemporary stents within limited function evaluations, is not trivial and requires efficient parameterization and optimization algorithms. We used shape matching optimization with a limited function evaluation budget to test the proposed parameterization and two surrogate-assisted optimization algorithms relying on predictor believer and an expected improvement maximization formulation. The performance of these algorithms is objectively compared with a gradient-based optimization method to highlight their strengths. Our work paves the way for more realistic, full-fledged stent design optimization with structural and hemodynamic objectives in the future.

HyG: A hydraulic geometry dataset derived from historical stream gage measurements across the conterminous US

Regional- and continental-scale hydrologic models are increasingly important forecasting tools, yet they rely on highly variable channel parameters (e.g. width, depth, hydraulic resistance) that remain unquantified for millions of stream reaches across the country. Existing hydrologic models utilize over-simplified channel geometries that directly impact the accuracy of streamflow estimates, with cascading effects for water resource and hazard prediction. Here, we present a hydraulic geometry dataset, termed ‘HyG’, derived from discharge field measurements at U.S. Geological Survey (USGS) stream gages across the conterminous United States (CONUS). The HyG dataset includes (1) at-a-station hydraulic geometry parameters, (2) at-a-station hydraulic resistance (Manning’s n) calculated from the Manning equation, (3) daily discharge percentiles, and (4) regionalized downstream hydraulic geometry parameters based on HUC4 (Hydrologic Unit Code 4), derived from a total of 4,051,682 individual measurements from 66,841 total gages. The regionalized HyG dataset can be used directly to improve channel representations in models over CONUS. The original HyG relationships can also be regionalized for finer scales if required.

Modeling CSF circulation and the glymphatic system during infusion using subject specific intracranial pressures and brain geometries

BackgroundInfusion testing is an established method for assessing CSF resistance in patients with idiopathic normal pressure hydrocephalus (iNPH). To what extent the increased resistance is related to the glymphatic system is an open question. Here we introduce a computational model that includes the glymphatic system and enables us to determine the importance of (1) brain geometry, (2) intracranial pressure, and (3) physiological parameters on the outcome of and response to an infusion test.MethodsWe implemented a seven-compartment multiple network porous medium model with subject specific geometries from MR images using the finite element library FEniCS. The model consists of the arterial, capillary and venous blood vessels, their corresponding perivascular spaces, and the extracellular space (ECS). Both subject specific brain geometries and subject specific infusion tests were used in the modeling of both healthy adults and iNPH patients. Furthermore, we performed a systematic study of the effect of variations in model parameters.ResultsBoth the iNPH group and the control group reached a similar steady state solution when subject specific geometries under identical boundary conditions was used in simulation. The difference in terms of average fluid pressure and velocity between the iNPH and control groups, was found to be less than 6% during all stages of infusion in all compartments. With subject specific boundary conditions, the largest computed difference was a 75% greater fluid speed in the arterial perivascular space (PVS) in the iNPH group compared to the control group. Changes to material parameters changed fluid speeds by several orders of magnitude in some scenarios. A considerable amount of the CSF pass through the glymphatic pathway in our models during infusion, i.e., 28% and 38% in the healthy and iNPH patients, respectively.ConclusionsUsing computational models, we have found the relative importance of subject specific geometries to be less important than individual differences in resistance as measured with infusion tests and model parameters such as permeability, in determining the computed pressure and flow during infusion. Model parameters are uncertain, but certain variations have large impact on the simulation results. The computations resulted in a considerable amount of the infused volume passing through the brain either through the perivascular spaces or the extracellular space.

Modeling of Catalyst Degradation in Polymer Electrolyte Membrane Fuel Cells Applied to Three‐Dimensional Computational Fluid Dynamics Simulation

ABSTRACTIn a polymer electrolyte membrane (PEM) fuel cell, the following degradation mechanisms are associated with the catalyst particles and their support: carbon support corrosion triggered by carbon and platinum oxidation, platinum dissolution with redeposition, and particle detachment with agglomeration. In this work, an electrochemical model for those degradation effects is presented as well as its coupling with a three‐dimensional computational fluid dynamics PEM fuel cell performance model. The overall model is used to calculate polarization curves and current density distributions of a PEM fuel cell in a fresh and aged state as well as the degradation process during an accelerated stress test with 30 000 voltage cycles. The obtained simulation results are compared to measurements on a three‐serpentine channel PEM fuel cell with an active area of 25 cm2 under various temperatures and humidities. The experimental data are obtained with a segmented test cell using respective degradation protocols and test conditions proposed by the United States Department of Energy. In addition to the temperature and humidity changes, the influence of geometry and material parameters on the degree of degradation and the resulting fuel cell performance is explored in detail.

Design of piezoelectric quasi— zero—stiffness metastructures for improved low—frequency vibration isolation

Abstract In this paper, a novel type of piezoelectric quasi–zero stiffness (QZS) metastructure is proposed and the improved vibration isolation performance is investigated. A piezoelectric QZS metastructure is composed of curved beams covered with piezoelectric macro–fiber composite patches, to which digital circuits are connected. Based on the principle of minimum potential energy and the mode superposition method, the constrain on the geometry and material parameters of the piezo–curved beams to achieve QZS is given. According to this design criterion, 1D, 2D and 3D piezoelectric QZS metastructures are designed, and their improved low–frequency vibration isolation characteristics are comprehensively analyzed through theoretical, numerical and experimental studies. It is demonstrated that by optimizing the parameters of the resonant transfer functions implemented in the digital circuits, high–level damping localized near the first resonant peak can be introduced into the curved beams. As a result, the resonant peaks of the metastructures can be reduced without compromising the isolation performance beyond those peaks.

Cross-crack group interaction and initiation mechanism under hydraulic-mechanical coupling

Based on the distributed dislocation function, the complex function of arbitrary position and branch cross-crack group under hydraulic-mechanical in the infinite plate is derived and the maximum Mode I and Mode II stress intensity factors (SIFs) of cross-crack group are obtained. The influence of cross-crack group geometry parameters on the maximum SIFs is analyzed and the multiple cross-cracks dangerous zone is obtained. Using the maximum shear and tensile SIF ratio criterion as a basis, the initiation process of double cross-cracks is predicted and verified by red sandstone double cross-cracks uniaxial compression test. Results show that for the double cross-crack in an infinite plate, h/a should be greater than 8 and the value of α2 should not range from 75° to 90° to avoid possible cracking. For the triple cross-crack in an infinite plate, when the water pressure is low (less than 5 MPa), the influence of the stress field exceeds the influence of water pressure. For red sandstone samples with double cross-cracks under uniaxial compression, the inner tips of cross-cracks always connected and penetrated and the inner and outer tips of cross-cracks often eventually joined together. The multiple cross-crack initiation criterion was validated by the good agreement between the test results and the prediction results of red sandstone with double cross-cracks. All the initiation mechanisms are Mode I fracture.

Fire and smoke transport dynamics in a dead-end tunnel under heavy rainfall

Fire is one of the most common major accidents during tunnel construction and operation. This work conducted scale-model experiments to investigate the pool burning progress and flame characteristics in a dead-end tunnel with one end closed and the other open under heavy rainfall. The results show that, compared to opening both ends, the global burning time of fires is significantly decreased, and the quasi-stable burning phase is advanced under the combined effects of the closed end and heavy rainfall. The reason is that the increase in ceiling temperature, resulting from the accumulation of hot smoke, leads to an increase in radiative feedback of the fuel from the environment and an acceleration in the pool's burning rate. A coefficient (denoted by γ) is defined to evaluate the increase in the burning rate resulting from the dead-end. The enhancement ratio is found to be related to rainfall intensity, raindrop size, and pool size, and a correlation has been established based on the experimental results. The fire has an increased flame height and a reduced tilt angle under the impact of the dead-end. The changes in flame geometry parameters are mainly influenced by thermal buoyancy and the restriction of the dead-end. Prediction formulas for flame height and tilt angle under the combined effects of the dead-end and heavy rainfall have been proposed based on theoretical analysis. Under these combined effects, the tunnel space becomes eroded by dirty air.

Multi-Feature-Filtering-Based Road Curb Extraction from Unordered Point Clouds

Road curb extraction is a critical component of road environment perception, being essential for calculating road geometry parameters and ensuring the safe navigation of autonomous vehicles. The existing research primarily focuses on extracting curbs from ordered point clouds, which are constrained by their structure of point cloud organization, making it difficult to apply them to unordered point cloud data and making them susceptible to interference from obstacles. To overcome these limitations, a multi-feature-filtering-based method for curb extraction from unordered point clouds is proposed. This method integrates several techniques, including the grid height difference, normal vectors, clustering, an alpha-shape algorithm based on point cloud density, and the MSAC (M-Estimate Sample Consensus) algorithm for multi-frame fitting. The multi-frame fitting approach addresses the limitations of traditional single-frame methods by fitting the curb contour every five frames, ensuring more accurate contour extraction while preserving local curb features. Based on our self-developed dataset and the Toronto dataset, these methods are integrated to create a robust filter capable of accurately identifying curbs in various complex scenarios. Optimal threshold values were determined through sensitivity analysis and applied to enhance curb extraction performance under diverse conditions. Experimental results demonstrate that the proposed method accurately and comprehensively extracts curb points in different road environments, proving its effectiveness and robustness. Specifically, the average curb segmentation precision, recall, and F1 score values across scenarios A, B (intersections), C (straight road), and scenarios D and E (curved roads and ghosting) are 0.9365, 0.782, and 0.8523, respectively.

A Non‐Iterative Wheel‐Rail Contact Geometry Determination Algorithm and Its Application

AbstractTo ensure a more accurate simulation of the wheel‐rail contact state in vehicle‐track interaction, a non‐iterative contact geometry determination algorithm is proposed. This algorithm decouples lateral movement and roll, independently calculates the minimum wheel‐rail gap on both sides, and overcomes the limitation of simultaneous wheel‐rail contact on both sides. It can be applied to single‐side and two‐side wheel‐rail separation problems. Additionally, by converting track irregularity and rail deformation into the reverse displacement of the wheel, it avoids real‐time calculation of the wheel‐rail spatial position, thereby improving calculation efficiency. The effectiveness of the algorithm is verified through Universal Mechanism software and field measurements. Subsequently, the influence of the measured wheel‐rail profile, rail cant, and rail gauge on the wheel‐rail contact characteristics is analyzed. Finally, vehicle shaking caused by track irregularity and wheel‐rail contact is examined from the perspective of wheel‐rail matching. The study demonstrates that the non‐iterative algorithm is suitable for online simulation by pre‐processing the contact geometry parameters. When the track gauge and rail cant increase, the distribution of wheel‐rail contact points becomes more concentrated. Furthermore, when the excitation frequency of wheel‐rail matching is close to the track irregularity excitation frequency, it causes vibration amplification, resulting in lateral vehicle shaking.