Search Results (5)

Introduction: Cold welding is an anecdotally well-known complication of removal of metalwork, most commonly at the screw–plate interface, and can often complicate extraction of implants after fracture fixation. Even though this phenomenon is familiar amongst the orthopedic community, there is relatively little formalized discussion or literature pertaining to its identification and management clinically. In addition, as far as we can establish, there does not seem to be a paper that discusses the various techniques described in the literature that are employed to combat cold welding. Methods: A systematic review was carried out in accordance with the PRISMA guidance, with two independent reviewers and a third person to arbitrate for any discrepancies. Manuscripts were identified using a search of PubMed/MEDLINE and Google Scholar. Studies eligible for inclusion were tabulated and the results categorized qualitatively with respect to the technique described for removal of the implants. Results: A total of 272 manuscripts were identified using a search of PubMed/MEDLINE and Google Scholar, and of these 14 were ruled to be eligible for inclusion reporting on 292 patients. Common locations of the cold-welded screws included femur, tibia, distal radius and clavicle. The most common technique for metalwork removal was using either bolt cutters or burrs to cut the plates between the screws and mobilize the screw and plate as one unit. Other techniques included using specialized removal tools and cutting between the screw head and body. There was no appreciable correlation between the specific anatomic location of the welded implant and the technique used in its removal. From the studies, it was found that, of the total number of screws (n = 1654), 58 (3.5%) were cold welded. The mean time to metalwork removal was 1104 days (36.8 months). Conclusions: As far as we can tell, this is the first systematic review pertaining to the phenomenon of cold welding specifically, and with this project we have collated the techniques used to remove implants affected by cold welding from a variety of different articles. Our work aims to highlight the relative paucity of literature in this area and provide a number of accessible and safe techniques to facilitate the removal of cold-welded implants in fracture fixation. Full article

Accurate evaluation of cutter life at different cutter positions on the cutter head is helpful to determine the time of cutter change and reduce the time of cutter wear measurement, which is of great significance to improve the tunneling efficiency of tunnel boring machine (TBM) projects. Unfortunately, there is no unified cutter life evaluation index now. The field data of cutter wear are collected from a section of a long TBM tunneling water conveyance tunnel in China. Two kinds of cutter life evaluation indexes (based on the radial wear extent of cutter rings and replacement number of cutter rings) are selected and the variation rule between these two kinds of indexes with cutter installation radius is statistically analyzed. The results show that the regression relationships between the two kinds of cutter life evaluation indexes and installation radius mainly present linear functions and quadratic functions. Those regression relationships are affected by factors such as wear type, installation angle, cutter spacing, influence width, and allowable limit wear extent of cutter rings. Considering the calculation accuracy of the evaluation index, the actual working conditions of the disc cutter, and ignoring the influence of tunnel diameter, it is recommended to preferentially choose the radial wear extent of cutter rings per unit rolling distance as the evaluation index of cutter life. The research results can provide a reference for the selection of cutter life evaluation index, prediction of disc cutter life at different cutter positions, and establishment of cutter life prediction mode. Full article

At present, the determination of tunnel parameters mainly rely on engineering experience and human judgment, which leads to the subjective decision of parameters and an increased construction risk. Machine learning algorithms could provide an objective theoretical basis for tunnel parameter decision making. However, due to the limitations of a machine learning model’s performance and parameter selection methods, the prediction model had poor prediction results and low reliability for parameter research. To solve the above problems, based on a large number of construction parameters of a composite section subway in Shenzhen, this paper combined dimensionality reduction data with service analysis to optimize the selection process of shield tunneling parameters, and determined the total propulsion force, cutter head torque, cutter head speed, and advance rate as key tunneling parameters. Based on an LGBM algorithm and Bayesian optimization, the prediction model of key tunneling parameters of an earth pressure balance shield was established. The results showed that the average error of the LGBM model on the test set was 8.18%, the average error of the cutter head torque was 13.93%, the average error of the cutter head speed was 3.16%, and the average error of advance rate was 13.35%. Compared with the RF model, the prediction effect and the generalization on the test set were better. Therefore, an LGBM algorithm could be used as an effective prediction method for tunneling parameters in tunnel construction and provide guidance for the setting of tunneling parameters. Full article

As the urban underground space environment gets more complex, the cases of shield machines encountering and cutting through piles are becoming more common. The interaction between the cutter head and pile foundation directly affects the tunneling performance of the shield machine and the safety of the existing structure. To study the interaction between the pile and the shield machine, a calculation model of the interaction force is established. A field test of cutting two piles was conducted and the rationality of the model is verified by comparing the calculation results with field test data. The model is applied in the project of a shield machine cutting bridge piles in Harbin Metro Line 3, China. The shield operation parameters are predicted and compared with field test results. Besides, the impacts of cutting surface width and eccentric distance on interaction force are discussed. The study shows that there is a significant interaction between the cutter head and the piles when the shield machine cuts reinforced concrete piles, which causes obvious changes in the shield operation parameters and shield performance. The number of tools that are inside the cutting area has a significant effect on the additional torque. The additional torque fluctuates with the rotation of cutter head and increases with the increase of the number of tools. The number of these tools is determined by factors such as the layout of tools in the cutter head, cutting surface width and eccentric distance, which influence the position of each tool relative to the cutting area. As the cutting distance increase, the additional torque of the cutter head shows a trend of first increasing and then decreasing and reaches the maximum value when the cutting distance reaches the radius of the pile. Besides, the additional force and additional moment of the cutter head increase with the increase of the cutting surface width. The impacts of eccentric distance on additional force and additional moment are complicated. The results in this paper can provide reference for similar engineering. Full article

For the investigation of the cavitation of non-jammed submersible grinder pumps, a GSP-22 model pump was numerically simulated based on CFX. ICEM-CFD was applied to a structured mesh for the flow components. Pump performance and the influence of the cutter head on cavitation with different cutter head numbers and shapes were investigated. The results were as follows: with increases in the number of cutter heads, the effects of the cutter heads on the water increased, and the flow rate near the cutter head increased correspondingly—which eventually led to aggravated cavitation near the cutter head of the non-jammed submersible grinder pump. The head of the submersible grinder pump with a streamlined cutter changed little compared to the pump with a non-streamlined cutter; the overall power declined by 13.2% and the highest efficiency increased by 6%. For all pumps with different numbers of cutter heads, the vapor volume fraction of the streamlined cutter head was lower than that of the non-streamlined cutter head, and the vapor distribution area size of the streamlined cutter head was smaller than that of the non-streamlined cutter head. This means that changing the cutter head shape to streamlined can effectively control the cavitation intensity near the cutter head. Full article