Experimental Research on Polymer-Based Coaxial Sealing Systems of Hydraulic Cylinders for Small Displacement Velocities

Reducing friction in the coaxial sealing systems of hydraulic cylinders is one of the solutions for increasing the energy efficiency of industrial actuations. This is a requirement, particularly in the case of small velocities that carry the risk of eigen-vibrations and/or stick-slip. The authors discuss the experimental research conducted on three coaxial sealing systems made from thermoplastic polymer and polyurethane type materials. The paper presents the equipment and method used for the experimental determination of static and kinematic friction coefficients and discusses the subsequent results obtained to test different working parameters. The experimentally determined friction coefficients yielded a range of materials recommended for coaxial seals such as to minimize the occurrence of jerky operation.

Influence of roundness error screw on running characteristics of sliding bearing based on SDT

In order to study the influence of roundness error on the oil film characteristics of journal bearing rotor system, a dynamic model of journal bearing rotor system with roundness error was established, and a new generalized roundness error equation is derived based on the small displacement screw (SDT) theory. And the influence of roundness error screw parameter dx represented by SDT on critical speed and stability of sliding bearing is analyzed emphatically. The results show that the existence of journal roundness error is beneficial to the bearing capacity and stability of sliding bearing rotor system to a certain extent, and with the increase of roundness error screw parameter, its promoting effect is more obvious; At the same time, the critical speed of the system will increase with the increase of screw parameter, especially when eccentricity ε>0.6; And when Sommerfeld number S>0.6, the roundness error of journal has little influence on stability.

Novel application of mapping method from small displacement torsor to tolerance: Error optimization design of assembly parts

The manufacturing/assembly error of machine parts is a key factor that influences the performance and economy of mechanical systems. To achieve high assembly precision and performance on the basis of low manufacturing accuracy and cost, this study primarily optimizes the assembly error of machine parts. First, the small displacement torsor is used to characterize the small deformation between the mating surfaces of parts. Subsequently, to realize the combination of small displacement torsor and tolerance, the small displacement torsor with manufacturing error and assembly deformation is mapped to the tolerance domain. Second, based on the relationship between small displacement torsor and tolerance, an assembly error optimization model is established on the basis of the conventional tolerance-cost model, considering the emergence of manufacturing error and assembly deformation. Third, aiming at the high-pressure rotor for aeroengines, the error optimization design of assembly is carried out developed with the assembly accuracy requirement as the constraint condition, and the total costs of the manufacturing and assembly processes as the objective. The optimization results indicate that the manufacturing error range of each mating surface after optimization changes, from small to large, under the premise of ensuring the product’s performance, which verifies that the difficulty in processing parts is reduced, and that the efficiency of parts processing is also improved. Meanwhile, the relative manufacturing cost after optimization is reduced by 6.79%, which reflects the economic requirements to a certain extent. The content of this article provides the necessary design basis and reference for the realization of high assembly accuracy of mechanical systems, under low cost requirements from the design perspective.

Generation of Shakedown Boundaries of Thin-Walled 90-Degree Scheduled Pipe Bends Determined via Large and Small Displacement Finite Element Models

The present research investigates the effect of employing large displacement in finite element modelling on the generated shakedown (SD) boundaries of thin-walled 90-degree scheduled pipe bends. A recently developed methodology termed: Shakedown Limit - Plastic Work Dissipation (SDLimit-PWD) method generates the SD boundaries via employing the large displacement in the FE simulations. Additionally, a well-established direct non-cyclic technique termed: Shakedown Direct Noncyclic Technique (SD_DNT) generates the SD boundaries via employing the small displacement formulation in the FE simulations. Comparing the SD boundaries generated via both methods illustrated marked increase in the generated SD domains due to employing large displacement.

Ground Subsidence Evolution from 1000 m Deep Mining: A Case Study in Fengfeng Mining Area

The mining of coal resources in eastern China has entered the stage of deep mining, and many mines have reached the depth of 1000 meters. Different from shallow and moderate depth mining, the temporal and spatial evolution regulation of surface movement and deformation under deep mining has its particularity. Combining with the geological and mining conditions of Fengfeng mining area, this paper systematically studies the characteristics of surface movement under the condition of shallow, moderate, and near kilometer mining depth. By means of field measurement, InSAR monitoring, we get the subsidence data under different mining depth and get the relevant subsidence parameters by inversion. Through comparative analysis, the special law of subsidence under the mining depth of 1000 meters is obtained. The results show that under the condition of nearly 1000 meters mining depth, the surface movement and deformation have the characteristics of large displacement angle, small displacement deformation value, and large main influence radius. The regulation of small proportion of active period of maximum subsidence point, gentle shape of surface movement basin, and low mining adequacy are obtained. The research results provide technical references for deep mining under buildings, railways, and water bodies and provide basis and reference for scientific mining and safe recovery of coal pillars in kilometer deep mine.

Identifying Potential Landslides by Stacking-InSAR in Southwestern China and Its Performance Comparison with SBAS-InSAR

Landslide disasters occur frequently in the mountainous areas in southwest China, which pose serious threats to the local residents. Interferometry Synthetic Aperture Radar (InSAR) provides us the ability to identify active slopes as potential landslides in vast mountainous areas, to help prevent and mitigate the disasters. Quickly and accurately identifying potential landslides based on massive SAR data is of great significance. Taking the national highway near Wenchuan County, China, as study area, this paper used a Stacking-InSAR method to quickly and qualitatively identify potential landslides based on a total of 40 Sentinel SAR images acquired from November 2017 to March 2019. As a result, 72 active slopes were successfully detected as potential landslides. By comparing the results from Stacking-InSAR with the results from the traditional SBAS-InSAR (Small Baselines Subset) time series method, it was found that the two methods had a high consistency, with 81.7% potential landslides identified by both of the two methods. A detailed comparison on the detection differences was performed, revealing that Stacking-InSAR, compared to SBAS-InSAR may miss a few active slopes with small spatial scales, small displacement levels and the ones affected by the atmosphere, while it has good performance on poor-coherence regions, with the advantages of low technical requirements and low computation labor. The Stacking-InSAR method would be a fast and powerful method to qualitatively and effectively identify potential landslides in vast mountainous areas, with a comprehensive understanding of its specialty and limitations.

Ship power plant with reversible shaft generator unit operating by dual-power machine scheme and variable speed diesel generator

The article presents the analysis of the operating modes of small displacement vessels, which states that most of the working time the vessels are in standby mode, or move at low speed. The main ship diesel engines operate at a load of 10-15% (maximum 20%), which impacts the operational performance: the oil and water jacket of the engine do not have time to warm up, fuel and oil consumption increases. There takes place coking of piston rings, intercoolers and other components, which leads to a sharp decrease in the service life of the engine. In order to eliminate the disadvantages happening in the main engines operation in shared load modes, it is considered to use the shaft generator unit as a propeller shaft unit in the prolonged operation of the vessel at passing with a low speed and maneuvering. Such a variant of the shaft generator can be called a reversible shaft generator unit (RSGU) capable of operating in both generator and motor modes. At the same time, it is advisable to power the reversible shaft generator and general ship consumers from a diesel generator, which, in order to save fuel, can be applied as a variable speed diesel generator unit. There is presented a RSGU variant based on an asynchronous machine with a phase rotor and a frequency converter in the rotor (a double power supply machine). The functional and structural schemes of the ship’s electric power system using the variable speed diesel generator and the propulsive system based on the reversible shaft generator are presented. In the Matlab software there are developed the simulation models and presented the results of simulation modeling of the operating modes of the above systems.