Search Results (30)

This paper investigates the pressure fluctuation characteristics induced by cavitation in the blade-tip region of an axial flow pump through experimental and numerical methods. Compared with previous studies, this research not only analyzes the development of cavitation bubbles under varying flow rates but also explores the transient pressure fluctuation features caused by cavitation. It is found that partial-loading conditions tend to exacerbate cavitation, leading to more pronounced transient flow characteristics. The primary frequency of pressure fluctuations consistently corresponds to the impeller’s rotational frequency and its harmonics, with the magnitude inversely related to flow rate. At the same cavitation stage, lower flow rates exhibit larger amplitudes and more significant fluctuations in high-frequency components. This indicates stronger entrainment disturbance between the cavitation morphology and the mainstream in the blade-tip region at lower flow rates, resulting in more complex flow structures. This study provides a theoretical basis for understanding the mechanisms of pressure fluctuations induced by cavitation in the blade-tip region of axial flow pumps. Full article

Enhancing the operational flexibility and environmental performance of coal-fired boilers under wide-load conditions presents a critical challenge in China’s low-carbon transition, particularly for low-quality coals (LQCs) with abundant reserves, poor combustibility, and high NO_x emissions. To overcome the intrinsically low reactivity of LQC, peak-shaving performance and combustion behavior were systematically investigated on an MW-grade pilot-scale test platform employing the fuel modification strategy in this study. Stable fuel modification was achieved without any auxiliary energy for LQCs and Shenmu bituminous coal (SBC) across a load range of 20~83% and 26~88%, respectively, demonstrating the excellent fuel reactivity and strengthened release control of volatile and nitrogenous species. The modified LQC exhibited ignition, combustion, and burnout characteristics comparable to Shouyang lean coal (SLC), enabling a “dimensionality-reduction utilization” strategy. The double-side fuel modification device (FMD) operation maintained axially symmetric temperatures (<1250 °C) in horizontal combustion chambers, while single-side operation caused thermal asymmetry, with peak temperatures skewed toward the FMD side (<1200 °C). Original NO_x emissions were effectively suppressed, remaining below 106.89 mg/m³ (@6%O₂) for LQC and 122.76 mg/m³ (@6%O₂) for SBC over broad load ranges, and even achieved ultra-low original NO_x emissions (<50 mg/m³). Distinct load-dependent advantages were observed for each coal type: SBC favored high-load thermal uniformity and low-load NO_x abatement, whereas LQC exhibited the inverse trend. These findings underscore the importance of a load-adaptive coal selection and FMD operation mode. This study provides both theoretical insights and engineering guidance for retrofitting coal-fired power units toward flexible, low-emission operation under deep peak-shaving scenarios. Full article

Three all-steel buckling-restrained brace (ABRB) specimens without unbonded materials were designed and manufactured. Through low-cycle reciprocating load tests, the seismic performance of these buckling-restrained braces was investigated, and the influence of the absence of an unbonded layer on failure modes, energy dissipation capacity, and low-cycle fatigue life was examined. The research findings suggest that in all-steel buckling-restrained braces lacking an unbonded layer, the excessive friction between the energy dissipation unit and the restraining unit can, to a certain degree, increase local compressive stress. This makes the braces more susceptible to local buckling at the ends. The frictional effect causes the axial force of the ABRB to follow a distribution pattern where it is greater at the ends and smaller in the middle. Correspondingly, the buckling wavelength of the energy dissipation unit shows a pattern of being shorter at the ends and longer in the middle, which also results in a significant cyclic hardening phenomenon in the ABRB. The fatigue performance of the ABRB is inversely related to the amplitude of local buckling in the energy dissipation unit. Full article

During deep mining engineering, coal bodies are subjected to complex geological stresses such as periodic roof pressure and blasting impacts, which may induce mechanical property deterioration and trigger severe rock burst accidents. This study systematically investigated the mechanical characteristics and failure mechanisms of coal under strain rates on two orders of magnitude through quasi-static cyclic loading–unloading experiments and split Hopkinson pressure bar (SHPB) tests, combined with acoustic emission (AE) localization and crack characteristic stress analysis. The research focused on the differential mechanical responses of coal-rock masses under distinct stress environments in deep mining. The results demonstrated that under quasi-static loading, the stress–strain curve exhibited four characteristic stages: compaction (I), linear elasticity (II), nonlinear crack propagation (III), and post-peak softening (IV). The peak strain displayed linear growth with increasing cycle, accompanied by a failure mode characterized by oblique shear failure that induced a transition from gradual to abrupt increases in the AE counts. In contrast, under the dynamic loading conditions, there was a bifurcated post-peak phase consisting of two unloading stages due to elastic rebound effects, with nonlinear growth of the peak strain and an interlaced failure pattern combining lateral tensile cracks and axial compressive fractures. The two loading conditions exhibited similar evolutionary trends in crack damage stress, though a slight reduction in stress occurred during the final dynamic loading phase due to accumulated damage. Notably, the crack closure stress under quasi-static loading followed a decrease–increase pattern with cycle progression, whereas the dynamic loading conditions presented the inverse increase–decrease tendency. These findings provide theoretical foundations for stability control in underground engineering and prevention of dynamic hazards. Full article

Machine learning methods are widely used to predict the bearing capacity of concrete-filled steel tubular (CFST) columns. However, in addition to this task, the engineer often faces the inverse problem: to determine what cross-section dimensions of the CFST column are required for given loads. This paper is devoted to the development of machine learning models for predicting the geometric parameters of a circular cross-section for concrete-filled steel tubular (CFST) columns under the combined action of bending moments and compressive axial forces. This problem has not been solved by machine learning methods before. The main focus is on automating the design process of CFST columns using the CatBoost algorithm and artificial neural networks. Three machine learning models were developed to solve the problem. The first and second models are based on the CatBoost algorithm. They predict the column diameter at minimum and maximum wall thicknesses, respectively. The third model is an artificial neural network, which is designed to determine the wall thickness of a CFST column. The models were trained on synthetic data generated in accordance with Russian design codes. The first and second models demonstrated high accuracy in predicting the column diameter (RMSE = 3.86 mm and 4.12 mm, respectively). The third model showed high efficiency over the entire range of wall thicknesses (correlation coefficient R = 0.99974). Feature importance analysis using SHAP values confirmed the key role of bending moment and axial force in predicting geometric parameters. Full article

In order to investigate the lateral working performance of large-scale steel casing-reinforced concrete pile composite members, this paper sets up large-scale steel casing-reinforced concrete pile composite members with different slenderness ratios λ, compressive axial force ratios N, and foundation strengths. It conducts quasi-static loading tests to investigate the effects of these factors on the hysteretic performance, bearing capacity, ductile performance, strength degradation, and stiffness degradation of the members. The results show that the hysteresis curves of the members all have a typical inverse S-shape, which is affected by slip and has a poor degree of fullness. The members with larger slenderness ratios exhibit better ductility performance, deformation performance, and energy dissipation performance, but their poorer bearing capacity and effect on stiffness degradation are limited. While members with smaller slenderness ratios exhibit better bearing capacity, their ductile performance is poor. As the compressive axial force ratio increases, the lateral bearing capacity and ductility of the members slightly improve. However, the bearing capacity rapidly decreases when the compressive axial force ratio reaches a critical value. As the strength of the foundation increased, the lateral bearing capacity of the structures continued to improve, but its improvement effect began to decay after reaching a certain value. This paper investigates the lateral working properties of large-scale steel casing-reinforced concrete pile composite members designed for overhead vertical wharves that are subjected to significant water level differences in inland rivers, aiming to provide a reference for their application in practical engineering. Full article

This study utilizes the inverse finite element method (iFEM) to investigate the strain field reconstruction of ship stiffened plates under multiple loading conditions. The aim is to enhance the monitoring, safety, and reliability of ship structures through multi-condition strain field reconstruction. By applying iFEM, this research addresses the challenge of reconstructing strain fields from discrete strain measurements using a least-squares variational equation derived from elastic mechanics principles. The performance of iFEM was evaluated under five loading conditions: axial compression, non-uniform loading, torsion, combined axial compression with non-uniform loading, and combined axial compression with symmetric uniform loading. To mitigate boundary effects, an extended stiffened plate design was implemented. The results show significant improvements in reconstruction accuracy: under two specific loading conditions, the precision improved by 38.82% and 11.25%, respectively, compared to the original plate. This study underscores the potential of iFEM in improving the monitoring and safety of marine structures. Future work could explore the applicability of iFEM to other marine structures and scenarios, ensuring broader practical applications. Full article

In this paper, the low-cycle reciprocating load test was carried out on four-limb concrete-filled steel tubular (CFST) lattice columns with different slenderness ratios and axial compression ratios, and the seismic performance was studied. Two performance indicators, namely damage and hysteretic energy dissipation, were defined as the objective functions, and the axial compression ratio was used as an optimization variable to perform the multi-objective optimization analysis of four-limb CFST lattice columns. Optimization using the max–min problem approach aims to optimize the axial compression ratio to minimize damage and maximize the dissipation of hysteresis energy. The seismic performances before and after optimization were determined using a restoring force model and were evaluated by the finite element method under different axial compression ratios. The results show that, under low-cycle reciprocating loads, the load–displacement hysteresis curve is a bow shape (Members 1 and 2), inverse S-shape (Member 3), and approximate shuttle shape (Member 4). Through multi-objective optimization, the optimized axial compression ratio is 0.25 and the finite element analysis indicates that the optimal seismic performance is at an axial compression ratio of 0.25. Through the optimized design, the maximum horizontal load of lattice columns, the elastic stiffness, the dissipation capacity, and the seismic performance are all improved, under the premise of satisfying the structural safety. Full article

Anchor rock bolts are among the essential support components employed in coal mine support engineering. Measuring the axial load of the supporting anchor bolts constitutes an important foundation for evaluating the support effect and the mechanical state of the surrounding rock. The existing methods for measuring the axial load of rock bolts have difficulty meeting the actual demands in terms of accuracy and means. Therefore, we propose a novel inverse method for determining the axial load of rock bolts. On the basis of the dynamic relationship between the axial load of the anchor bolt and the strain of the plate, a calculation model for the inverse analysis of the axial load from the plate strain is presented, and it is verified and corrected through finite element analysis and indoor physical experiments. By combining the calculation model with the digital image correlation method, a low costinversion of the axial load of the anchor bolt in actual support engineering is achieved. The experimental results demonstrate that the average errors of the load inversion of anchor bolts in three different states via the theory and method proposed in this paper are less than 8.8% (4 kN), 3.6% (3.2 kN), and 14.7% (5.5 kN), respectively, and the average error of the axial load of the rock bolts in the proposed method is only 4.23 kN. It possesses relatively high accuracy and can be effectively applied in the actual production processes of mines. Full article

In order to determine the adhesive anchors’ capacity under tensile loading, two test methods (confined and unconfined) are suggested in the guideline. Improvements for one of the two configurations are proposed and tested in this paper. The alternative setup currently being evaluated is a modified version of the one proposed by the RILEM technical recommendation, which is used to determine the bond properties of reinforced concrete elements. Finding a better and more consistent definition of the bonded length, removing the concrete surface contribution from the determined bond resistance, and testing the stability improvements were considered during the proposed setup development. In order to describe the adhesive anchor system’s behaviour, a stress-slip relation (law), which relates the local axial bond stress to the local axial slippage, can be used. Analytical and numerical procedures have been proposed in the literature in order to determine such a law. Here, an inverse calibration method based on Sequentially Linear Analysis (SLA) is applied in order to identify the stress-slip law of pull-out tests. Full article

The measurement of musculoskeletal tissue properties and loading patterns during physical activity is important for understanding the adaptation mechanisms of tissues such as bone, tendon, and muscle tissues, particularly with injury and repair. Although the properties and loading of these connective tissues have been quantified using direct measurement techniques, these methods are highly invasive and often prevent or interfere with normal activity patterns. Indirect biomechanical methods, such as estimates based on electromyography, ultrasound, and inverse dynamics, are used more widely but are known to yield different parameter values than direct measurements. Through a series of literature searches of electronic databases, including Pubmed, Embase, Web of Science, and IEEE Explore, this paper reviews current methods used for the in vivo measurement of human musculoskeletal tissue and describes the operating principals, application, and emerging research findings gained from the use of quantitative transmission-mode ultrasound measurement techniques to non-invasively characterize human bone, tendon, and muscle properties at rest and during activities of daily living. In contrast to standard ultrasound imaging approaches, these techniques assess the interaction between ultrasound compression waves and connective tissues to provide quantifiable parameters associated with the structure, instantaneous elastic modulus, and density of tissues. By taking advantage of the physical relationship between the axial velocity of ultrasound compression waves and the instantaneous modulus of the propagation material, these techniques can also be used to estimate the in vivo loading environment of relatively superficial soft connective tissues during sports and activities of daily living. This paper highlights key findings from clinical studies in which quantitative transmission-mode ultrasound has been used to measure the properties and loading of bone, tendon, and muscle tissue during common physical activities in healthy and pathological populations. Full article

In order to precisely ascertain the temperature at the hot spot within the intermediate joint of a three-core cable, this study focused on a 10 kV three-core cable joint as its primary subject. A three-dimensional finite element model of the cable joint was constructed, enabling the calculation of both the steady-state hot spot temperature field distribution and the transient temperature rise curve of the joint. Employing a one-dimensional transient thermal path model for the cable body, a radial inversion model for the cable core temperature was established. Through simulating the transient temperature field of the cable joint under varying currents, a fitting relationship was determined for the axial temperature points of the cable core. Subsequently, an inversion perception model was devised to calculate the hot spot temperature of the cable joint based on temperature measurements at specific points on the outer surface of the cable. Under both continuous and periodic loads, the inversion results revealed a consistent trend in the temperature at the joint crimping point with the finite element calculation outcomes, demonstrating a maximum error of within 3 degrees Celsius. This verification underscores the precision of the temperature combination inversion method when applied to three-core cable joints. Full article

The construction of large-diameter shield tunnels underwater involves complex variations in water and earth load outside the tunnel segment, as well as intricate mechanical responses. This study analyzes the variation laws of external loads, axial forces, and bending moments acting on the segment ring during the shield assembly and removal from the shield tail. It accomplishes this through the establishment of an on-site monitoring system based on the Internet of Things (IoT) and proposes a Bayesian-genetic algorithm model to estimate the water and earth pressure. The fluctuation section exhibits a peak load twice as high as that in the stable section. These variations are influenced by Jack thrust, shield shell force, and grouting pressure. The peak load observed in the fluctuation section is twice as high as the load observed in the stable section. During the shield tail removal process, the internal forces undergo significant fluctuations due to changes in both load and boundary conditions, and the peak value of the axial force during the fluctuation section is eight times higher than that during the stable section, while the peak value of the bending moment during the fluctuation section is five times higher than that during the stable section. The earth and water pressure calculated using the inversion analysis method, which relies on the measured internal forces, closely matches the actual measured values. The results demonstrate that the accuracy of the water and earth pressure obtained through inversion analysis is twice as high as that obtained using the full coverage pressure method. These results can serve as a valuable reference for similar projects. Full article

Human T-cell leukemia virus type 1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients may have brain white matter (WM) lesions, but the association of these lesions with disease activity is poorly understood. We retrospectively evaluated the brain WM lesions of 22 HAM/TSP patients (male 4: female 18) including 5 rapid progressors, 16 slow progressors, and 1 very slow progressor. The severity of WM brain lesions on axial Fluid Attenuated Inversion Recovery images was evaluated utilizing the Fazekas scale, cerebrospinal fluid biomarkers, and proviral load in peripheral blood mononuclear cells. Imaging and biological data were compared at the first visit and a subsequent visit more than 4 years later. Patients with comorbidities including adult T-cell leukemia–lymphoma and cerebrovascular disease were excluded. The results revealed that brain WM lesions in the rapid progressors group were more pronounced than those in slow progressors. In patients with HAM/TSP, severe and persistent inflammation of the spinal cord may cause brain WM lesions. Full article

Gravity pier is a widely employed pier type in railway bridges worldwide. It is characterized by a solid cross-section with a low longitudinal reinforcement ratio which can be even lower than 0.5%. These low-reinforced gravity piers have been found to be vulnerable under major earthquakes, but their seismic performance has not been fully understood. Improving the seismic safety of these piers and reducing the consumption of reinforcing steels coincide with multiple Sustainable Development Goals (SDG 6, 7, and 9). In this concern, three main objectives are achieved in the present research. Firstly, quasi-static tests were conducted on two gravity piers with low longitudinal reinforcement ratios: 0.3% and 0.4%. The tests found the reinforcement ratio significantly affected the failure mode and seismic capacity. A typical brittle failure was observed in the specimen with the 0.3% reinforcement ratio. Fracture of longitudinal reinforcing steels was heard, and only a few cracks formed within a narrow region at the pier bottom, whereas the structural behavior of the specimen with a 0.4% reinforcement ratio was ductile, and cracks were located within a wider region (800 mm) at the pier bottom. Increasing the reinforcement ratio significantly increased the energy dissipation capacity and the displacement ductility. Secondly, finite element models of two specimens built using ANSYS were validated with test results, and then a series of finite element models were built to further investigate the influences of three important parameters on the seismic capacity. The three parameters are shear span to depth ratio, axial compression ratio, and longitudinal reinforcement ratio. The validations found that the load–displacement hysteretic curves and the distributions of concrete plastic strain from finite element analyses matched well with those from tests. Further finite element analyses found that the shear span to depth ratio was inversely correlated with the peak lateral load, but positively correlated with the displacement ductility. Conversely, increasing the axial compression ratio increased the peak lateral load but decreased the displacement ductility. Thirdly, an analytical equation was proposed to predict the displacement ductility of low-reinforced gravity piers, and the predicted ductilities agreed well with those obtained from finite element analyses. The findings provide a better understanding of the seismic performance of low-reinforced gravity piers, which helps extend the application of these piers. Furthermore, the proposed analytical equation assists in the evaluation and design of these piers. Full article