Search Results (14)

To improve the convective heat transfer in internal cooling channels of heavy-duty gas turbine blades, this study experimentally and numerically investigates the thermal performance of rectangular channels with hybrid pin-fins and micro V-ribs turbulators. The transient thermochromic liquid crystal (TLC) technique and ANSYS 2019 R3 (ICEM CFD 2019 R3, Fluent 2019 R3, CFD-Post 2019 R3) were employed under Reynolds numbers ranging from 10,000 to 50,000, with the numerical model rigorously validated against experimental data (the maximum RMSE is 2.5%). It is found that hybrid pin-fins and continuous V-ribs configuration exhibits the maximum heat transfer enhancement of 27.6%, with an average friction factor increase of 13.3% and 21.9% improvement in thermal performance factor (TPF) compared to the baseline pin-fin channel. In addition, compared to the baseline pin-fin channel, hybrid pin-fins and broken V-ribs configuration exhibits average heat transfer enhancement (Nu/Nu0) of 24.4%, an average friction factor increase of 7.2% and 22.5% improvement across the investigated Reynolds number range (10,000~50,000) based on computational results. The synergistic effects of hybrid pin-fin and micro V-rib structures demonstrate superior coolant flow control, offering a promising solution for next-generation turbine blade cooling designs. This work provides actionable insights for high-efficiency gas turbine thermal management. Full article

In recent years, the excellent mechanical properties and lightweight characteristics of multi-layer hollow components have led to a surge in research focused on their forming processes. This growing interest has greatly advanced technological progress in aerospace and other related fields. In this paper, the metal flow behavior of TA15 titanium alloy at different temperatures from 840 °C to 940 °C and different strain rates from 0.001 s⁻¹ to 0.1 s⁻¹ was studied. Utilizing the finite element method, this study examined the local stress concentration, total strain distribution, thickness thinning characteristics, and pressure loading control during the superplastic forming process of the component. The integrated solid/hollow four-layer grid lightweight structural parts were successfully fabricated using the superplastic forming/diffusion bonding (SPF/DB) process. The quality of the components was evaluated using X-ray and ultrasonic C-scan detection methods. The results show that the maximum elongation of the alloy is 1340% at 900 °C/0.001 s⁻¹. When the temperature is too high, the grain size increases remarkably, and the elongation decreases. Based on the finite element simulation results, 900 °C is the best superplastic forming temperature. Under this temperature parameter, the maximum thinning rate of the core sheet is 39.7%, the SPF time is 10,000 s, the maximum thinning rate of the face sheet is 9.8%, and the SPF time is 2400 s. In addition, the solid block has a minimal effect on the thinning of the core sheet. The grid exhibits obvious stress concentration and thinning at its rounded corners, while the thickness distribution in other areas remains relatively uniform. The nondestructive testing results confirmed that the ribs of the component are fully formed, with no missing or broken ribs. The grid exhibits good geometry and high-quality diffusion bonding. The average thickness at key positions of the component is 1.84 mm, with the minimum thickness being 1.7 mm. As the size of the grid cavity decreases, the thickness of the component tends to increase gradually. The maximum error between the simulated and measured values is 4.47%, indicating good accuracy in the simulation. Additionally, the thickness distribution of the component is relatively uniform. Full article

Severe extrusion floor heave is the most common type of failure of floors in deep roadways, and it is also a major problem restricting the safe and efficient mining of deep coal resources. In deep roadways, reducing floor stress is an effective means to control floor heave. In this study, the method of creating directional stress-relief zones by constructing stress-relief boreholes is applied; while the stress is released, the path of stress from the ribs transferred to the floor and to the extrusion failure path is cut off, and floor heave control is achieved. Therefore, based on the stress-boundary and rock-mass parameters of the roadway, the control effects of the borehole angle, length, diameter, and row spacing on the extrusion floor heave were studied, and the reasonable thresholds of borehole parameters were shown to ensure the stress-relief effect on the roadway. In addition, the bolt-grouting technology was used to strengthen the floor of the roadway, the broken surrounding rock was modified via grouting consolidation, the support strength of the floor was increased using high-tension bolts (cable), and there was a good floor heave control effect in the field application. On the basis of traditional floor reinforcement, the control effect of stress regulation on floor heave is fully considered in this study, and stress-relief–anchor-grouting, a collaborative control technology for floor heave in deep roadways, is developed. Based on the three factors affecting the stability of deep roadways (stress, lithology, and support), the collaborative prevention and control of severe extrusion floor heave were realized, which provides a new method for deep roadway floor heave control and has good application value. Full article

Taking Haixin Bridge as an example, the structural response of a new type arch bridge composed of an inclined arch and a curved beam under cable breaking is analyzed numerically. The cable breaking at different positions, different numbers of broken cables and different ways of breaking are modeled and calculated, and the remaining cables’ internal force and main girder’s deflection are selected as research indexes to evaluate the degree of impact effect of broken cables on the bridge. The numerical results show that (1) duration time of cable breaking is an important factor affecting the impact effect of the bridge, when the cable breaking time is less than 1% of the first order natural vibration period of the structure, the dynamic response caused by cable breaking no longer variates with time; (2) for the cables adjacent to the breaking cable at equal distances, the cable with a shorter length will carry more released force of breaking cable than the longer, and the impact effect is more significant; (3) the dynamic response of displacement and cable force caused by cables at different locations are different, a cable located in the L/4 arch rib area suddenly breaking shows the largest dynamic response; (4) it is feasible to take the dynamic amplification factor (DAF) of cable force and the main girder’s deflection as 2, but it is unsafe to take the DAF of the arch rib’s deflection as 2; (5) the dynamic response of multiple cables breaking at the same time cannot be simplified as a linear superposition of single cable breaks one by one, and the amplification effect becomes more significant with the increase of the number of broken cables. These conclusions can provide guidance for structural safety assessment of similar arch bridges after cable breakage. Full article

Trapezoidal roadways in large inclination coal seams show asymmetrical tectonic characteristics, while there is still a lack of theoretical results on stress, deformation, and efficient and effective supporting methods on high walls. In this paper, based on the geological characteristics of a large, inclined coal seam roadway, a mechanical model for stress–deformation analysis of trapezoidal section roadway was established. Complex analysis and a comfort map were employed to investigate the stress and deformation distribution on the roadway surface, and a novel yielding prop with high load capacity and constant working resistance was employed to support a high wall side based on analytical results. The results are as follows: (1) The deformation of the high wall is larger than that of the low wall, and the deformation of the roof is larger than that of the floor. The overall deformation of the surrounding rock shows that the rib closure is larger than the roof-to-floor closure. (2) The stress of the surrounding rock shows that both horizontal and vertical stresses are highest in the upper corner, indicating that the broken zone is most likely to occur at this location. (3) A new support employed with a high-yielding prop and a high-strength cable in a large, inclined angle roadway is proposed. On-site experiments were conducted in a large 5-1081 roadway of a coal mine in Shanxi, China. Under the influence of mining disturbance, the deformations at the top corner decreased by 40% compared with before. The test results show that the new support scheme can effectively control the development of roadway deformation and damage during the mining process. The new support also shows friendly environmental support and fast installation. Full article

This retrospective study aimed to predict the injury time of rib fractures in distinguishing fresh (30 days) or old (90 days) rib fractures. We enrolled 111 patients with chest trauma who had been scanned for rib fractures at our hospital between January 2018 and December 2018 using gemstone spectral imaging (GSI). The volume of interest of each broken end of the rib fractures was segmented using calcium-based material decomposition images derived from the GSI scans. The training and testing sets were randomly assigned in a 7:3 ratio. All cases were divided into groups distinguishing the injury time at 30 and 90 days. We constructed radiomics-based models to predict the injury time of rib fractures. The model performance was assessed by the area under the curve (AUC) obtained by the receiver operating characteristic analysis. We included 54 patients with 259 rib fracture segmentations (34 men; mean age, 52 years ± 12.02; and range, 19–72 years). Nine features were excluded by the least absolute shrinkage and selection operator logistic regression to build the radiomics signature. For distinguishing the injury time at 30 days, the Support Vector Machine (SVM) model and human–model collaboration resulted in an accuracy and AUC of 0.85 and 0.871 and 0.91 and 0.912, respectively, and 0.81 and 0.804 and 0.83 and 0.85, respectively, at 90 days in the testing set. The radiomics-based model displayed good accuracy in differentiating between the injury time of rib fractures at 30 and 90 days, and the human–model collaboration generated more accurate outcomes, which may help to add value to clinical practice and distinguish artificial injury in forensic medicine. Full article

The interaction between reinforcement and soil is a key problem in the application of geosynthetics as reinforcement in geotechnical engineering. In this study, tensile and pull-out tests on a uniaxial geogrid were carried out using self-designed tensile and pull-out test equipment. The tensile test evaluated the tensile load–strain characteristics of a geogrid. Under the condition of lateral confinement, the tensile force and secant tensile stiffness of the geogrid increased with an increase in the normal stress when the strain was constant, and the secant tensile stiffness decreased with a decrease in the tensile rate. The stiffness coefficient was used to quantitatively describe the change in the stiffness of the reinforcement. Using the pull-out test, the variation laws of the pull-out force of the geogrid under different normal stresses and different longitudinal rib percentages were obtained. When the geogrid was broken, the pull-out force of the same type of geogrid was not significantly different under different normal stresses. With an increase in the longitudinal rib percentage, the pull-out force of the geogrid under the same normal stress gradually increased, and the apparent friction coefficient was obtained by analysis. The results of the apparent friction coefficient obtained by the analytical method in accordance with French specifications (NF P94-270-2020) are relatively safe compared to the experimental values. Full article

Artificial roughness on the absorber of the solar air heater (SAH) is considered to be the best passive technology for performance improvement. The roughened SAHs perform better in comparison to conventional SAHs under the same operational conditions, with some penalty of higher pumping power requirements. Thermo-hydraulic performance, based on effective efficiency, is much more appropriate to design roughened SAH, as it considers both the requirement of pumping power and useful heat gain. The shape, size, and arrangement of artificial roughness are the most important factors for the performance optimization of SAHs. The parameters of artificial roughness and operating parameters, such as the Reynolds number (Re), temperature rise parameter (ΔT/I) and insolation (I) show a combined effect on the performance of SAH. In this case study, various performance parameters of SAH have been evaluated to show the effect of distinct artificial roughness, investigated previously. Therefore, thermal efficiency, thermal efficiency improvement factor (TEIF) and the effective efficiency of various roughened absorbers of SAH have been predicted. As a result, thermal and effective efficiencies strongly depend on the roughness parameter, Re and ΔT/I. Staggered, broken arc hybrid-rib roughness shows a higher value of TEIF, thermal and effective efficiencies consistently among all other distinct roughness geometries for the ascending values of ΔT/I. This roughness shows the maximum value of effective efficiency equals 74.63% at a ΔT/I = 0.01 K·m²/W. The unique combination of parameters p/e = 10, e/D_h = 0.043 and α = 60° are observed for best performance at a ΔT/I higher than 0.00789 K·m²/W. Full article

Background: In polytrauma (PT) patients, osseous thoracic injuries are commonly observed. One of the most severe injuries is the flail chest where the rib cage is broken in such a way that leads to a partial functional detachment of the thoracic wall. Especially in PT patients, the integrity of the respiratory system and especially, of the respiratory muscles is essential to prevent respiratory failure. Besides conservative treatment options, flail chest injuries may be surgically stabilized. However, this treatment option is rarely carried out and evidence on the outcome of surgically treated flail chest patients is rare. Objective: This study intends to investigate the clinical outcome of PT patients with the diagnosis of a flail chest who received an osteosynthetic stabilization for that compared to the same group of patients without an operative treatment. The between-groups outcome was compared regarding the duration of the total hospital and the intensive care unit (ICU) stay, the total of the invasive ventilation days, the incidence of pneumonia, and the dosage of the pain medication at the hospital discharge. Methods: A retrospective analysis was conducted including all PT patients who received an osteosynthetic stabilization of a flail chest. Furthermore, another cohort of PT patients and the diagnosis of a flail chest but without operative treatment was determined. Both groups were case-control matched for the Injury Severity Score (ISS) and age. Further statistical analysis was performed using the Wilcoxon signed-rank test and the McNemar’s test. Results: Out of eleven operatively and 59 conservatively treated patients, eleven patients per group were matched. Further analysis revealed no significant differences in the normal ward treatment duration (5.64 ± 6.62 and 6.20 ± 5.85 days), the invasive ventilation duration (was 6.25 ± 7.17 and 7.10 ± 6.14 days), the morphine equivalent dosage of the oral analgesia (61.36 ± 67.23 mg and 39.67 ± 65.65 mg), and the pneumonia incidence (36.4 and 54.5%) when conservatively and operatively treated patients were compared, respectively. However, surgically treated patients had a longer ICU (25.18 ± 14.48 and 15.27 ± 12.10 days, Z = −2.308, p = 0.021) and a longer total hospital treatment duration (30.10 ± 13.01 and 20.91 ± 10.34 days, Z = −2.807, p = 0.005) when compared to conservatively treated patients. Conclusion: In the present study cohort, there was no outcome difference between conservatively and operatively treated patients with the diagnosis of a flail chest regarding the normal ward treatment duration, the invasive ventilation duration, the morphine equivalent dosage of the oral analgesia, and the pneumonia incidence while ICU treatment duration and hospital treatment duration was longer in operatively treated patients. Full article

Aiming at the large deformation instability problem caused by the excavation unloading of a coal roadway in deep-buried slowly inclined jointed rock mass, the geomechanical parameters and deformation failure characteristics of an engineering geomechanical model were investigated. The in-situ stress state of the model was measured with the stress relief method. The geological and mechanical properties of roadway surrounding rock were described. The surrounding rock structure was revealed with the electron microscopy scanning method, micro-fractures and randomly distributed joints highly developed in roadway surrounding rock. Field investigation and monitoring indicated the cross-section of roadway surrounding rock shrank continuously and the deformation distribution was obviously asymmetric. Shotcrete spalling and cable broken failures frequently occurred in the middle and ride side of roof and right rib. Based on the geomechanical conditions of the coal roadway, a discrete element numerical model of coal roadway in gently inclined jointed rock mass was established. The parameters of rock mass in the numerical model were calibrated. The model ran in unsupported condition to restore the evolution process of stress, crack propagation and deformation in roadway surrounding rock due to gradual deviatoric stress release caused by excavation. On this basis, the space-time evolution characteristics and law of stress, crack propagation and deformation were obtained and then the asymmetric large fragmentation and dilatation deformation failure mechanism of roadway surrounding rock in deep-buried slowly inclined jointed rock mass was revealed. The failure reasons of the support structure were analyzed, and the relevant support principles were proposed. The research results can provide scientific references for the stability control of roadways excavated in jointed rock mass. Full article

Techniques to analyze damage to a human body provide an important foundation to investigate the human body’s dynamics during accidents. However, the systematic investigation and analysis of accidents’ causes are limited due to a lack of suitable technology, personnel, and equipment. Recently, 3-D technologies and engineering verification through the finite element method have become widespread in forensics to investigate accidents’ causes and dynamic environments. Bone fracture analyses can provide important information on how victims may have died and injured. In this study, 3-D images obtained from multi-detector computed tomography of personal injuries and closed-circuit television, as well as image analyses based on forensic investigations, are used in a finite element program to analyze how ribs are broken during an accident and the possibility of further body damage. Technologies that deduce stress states and mechanisms are also developed in this study using FE analyses of the reconstructed model. Full article

The large mining height (LMH) in shallow coal seam has been widely applied in the Shenfu coalfield, China. The dynamic load is obvious, and the rib spalling is serious when the LMH working face concerns roof weighting. The advanced breaking position of the roof affects the strength of the ground pressure when the roof is broken. Firstly, based on a large number of actual measurements and physical simulation experiments, the rock formation in the fall zone, where the articulated structure cannot be articulated between the coal seam and the main roof, is called the equivalent immediate roof (EIR). When the mining height increases, the thickness of the EIR increases non-linearly. Next, based on the theory of “elastic foundation beam”, a mechanical model for the advanced breaking of the roof is established in shallow coal seam, and the calculation equation for the advanced breaking position of the roof is given; then, designed and carry out boreholes of the no. 22201 working face in the Zhangjiamao Coal Mine. The theoretical calculation of key strata results (5.6–6.9 m) are in the range of field measurement results (5–8 m). According to the field measurement results, the roof movement of the LMH working face is ahead of the roof weighting. Finally, we define the thickness of EIR and the mining height ratio as the immediate mining ratio k_i, which affects the degree of filling of the goaf and determines the structural form of the main roof. When the k_i is small, the goaf is fully filled; when the k_i is large, the goaf is fully filled. Under the same conditions, different filling rate conditions will form different roof structures. Results of this research can be helpful to control roof weighting and provide early warning of possible safety problems related to the LMH working face in shallow coal seam. Full article

Enhancements in heat transfer, and consequently the thermohydraulic performance of solar air heaters (SAHs), are necessary to widen and optimize their use in many applications such as solar drying or heating buildings. In this investigation, two techniques were used. A novel solar selective coating combined with broken arc ribs roughness was employed with a SAH and the evaluation of the energetic and exergetic performance was applied under four airflow working conditions compared to a smooth absorber SAH coated with the same coating. The results revealed that the Nusselt number of roughened SAH with the new coating exhibited a notable improvement compared to a smooth absorber SAH and a roughened SAH without a coating. Furthermore, the thermal efficiency increased with the increase in the air flow rate and the maximum rise was 18.8% compared to a smooth SAH. The highest increase in exergy was 51.6% with minimum values of exergy destruction and improvement potentials. In brief, the roughened SAH with 4% CNTs/CuO-black paint under the airflow rate of 0.0244 m³/s (condition C) exhibited the best energetic and exergetic performance. Full article

Substantial heat transfer enhancement can be achieved by cooling with air/water mist flow because of droplet impingement and liquid film/fragment evaporation on the heated surface, which leads to a high heat-removal rate. An experimental investigation was conducted in a square channel with continuous and broken V-shaped ribs. To generate a mist flow, micro droplets were introduced into the gas stream. The rib angle of attack was 45°, and the rib spacing-to-height ratios were 10 and 20. The air Reynolds number ranged from 7900 to 24,000, and the water-to-air volume flow ratio was less than 0.1%. The net heat inputs ranged from 1.1–3.1 W/cm² and 3.4–9.4 W/cm² for the air and mist flow cases, respectively. Because the deposited liquid fragments produced uneven temperature distribution on the heated surface, steady-state infrared thermography was used to visualize the heat transfer distribution. Two to seven times higher heat transfer was attained for the broken ribs when using the mist flow than when using air flow. This increase was mainly attributed to the broken structure, which facilitated liquid transport and enhanced liquid coverage. In addition, the broken ribs produced a smaller friction factor than continuous ribs. The broken structures were beneficial for higher thermal performance in the mist flow. Full article