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Aiming at the cavitations and noise problem of hydraulic cone valve and based on the radial force analysis of the valve core, the radial deviation of the spool is considered to obtain the changing rules of cavitations and noise.

The solid model of the internal flow field of cone valve is established. The mesh models are divided using ICEM-CFD software. The numerical simulation of the liquid-gas two-phase flow is performed on the cavitation and noise of the flow field inside the cone valve based on FLUENT software. The visible experimental platform for cavitation and noise of hydraulic cone valve is built. According to the contrast of the experimental results, the correctness of the simulation results is verified.

The results show that the radial deviation causes the position of the cavitation accumulates in the valve cavity on the side of the upper cone. In addition, the strength of the cavitation changes slowly with the half cone angle of 45°, and the noise level is the smallest. Furthermore, appropriately increasing the opening degree within a reasonable range can effectively suppress cavitation and reduce the noise level.

The cavitation can be suppressed and the noise level can be reduced by means of changing the three factors, which lays the foundation for the design and theoretical research of the cone valve.

Internal leakage is one of the key factors that influence the super-low speed performance of continuous rotary electro-hydraulic servo motor. Therefore, this paper aims to study the change rule of internal leakage for improving the low speed performance of motor.

The mathematical models of internal leakage of continuous rotary electro-hydraulic servo motor were established, and according to the working principle of the motor, the 3D models of internal leakage location were established. Simulation analysis was implemented on the continuous rotary electro-hydraulic servo motor by the finite element analysis software ANSYS based on the fluid-structure interaction theory.

The results show the deformation of motor’s key parts and the changing rule of internal leakage. The effect of the leakage to the low speed performance of electro-hydraulic servo motor was analyzed, and at the same time, the motor’s leakage experiment was also conducted to verify the validity of simulation results.

This paper lays the foundation for improving the low speed performance of motor.

This work aims to demonstrate the vibration suppression of the rotor system with localized defects on bearing using an integral squeeze film damper (ISFD).

Experiments were carried out to study the vibration characteristics of the rotor system with ISFD mounted on fault deep groove ball bearings. Three fault bearings including bearing with outer race defect, inner race defect and ball defect have been used in this paper. The results were compared by use of vibration acceleration level, continuous wavelet transform and envelope spectrum.

It was found that ISFD shows excellent damping and vibration attenuation characteristics of the rotor system with defective bearing. The fault bearing rotor system with external ISFD considerably reduces the vibration energy and amplitude compared with the system without ISFD.

There is a dearth of experimental research pertaining to vibration characteristics of rotor system support by defective bearings with ISFD. Besides, the test provides evidence for the application of ISFD in vibration control of the rotor system with incipient defects on bearing.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2020-0144/

The purpose of this paper is to propose a type of hybrid bearing lubricated with supercritical carbon dioxide (S-CO₂) and to investigate the stiffness and damping characteristics of the bearing under hydrostatic status.

Established a test rig for radial bearings lubricated with S-CO₂ and used it to measure the dynamic coefficients by recording the relative and absolute displacements of bearing. Test bearing is mounted on a nonrotating, stiff shaft. Using static loading experiments to obtain structural stiffness. The dynamic coefficient regularities of the test bearing under hydrostatic status were revealed through dynamic loading experiments.

Experiment results indicate that test bearing displayed increased stiffness when subjected to high excitation frequencies and low excitation forces, as well as elevated damping when exposed to low excitation frequencies and low excitation forces. Additionally, an increase in either environmental pressure or hydrostatic recess pressure can elevate the dynamic coefficient. The effect of temperature on the dynamic coefficient is more pronounced around the critical temperature of S-CO₂.

Designed a type of hybrid bearing for use in the Brayton cycle that is lubricated with S-CO₂ and uses hydrostatic lubrication during start-stop and hydrodynamic lubrication during high-speed operation. The hybrid bearing reduces the wear and friction power consumption of gas bearing. However, few experimental analyses have been conducted by researchers in this field.

Surface texturing has emerged in the past two decades as a viable option of surface engineering, resulting in significant improvement in wear resistance and friction coefficient. The purpose of this study is to find the appropriate surface texture to reduce vibration and improve the stability of journal bearings.

Micro-dimples, evenly distributed in a square array, were selected as the texture pattern and formed on the lower surface of bush by the laser surface texturing technique. Experiments were carried out to evaluate the effects of micro-dimples under different depths, densities and distributions.

The results are summarized in the form of shaft center orbits, waterfall illustrations and Hilbert-Huang transforms. In the entire test, it was found that an optimum geometric and distributive range of micro-dimples exists, where vibration acceleration can be decreased at least 3dB and stability can be greatly improved.

A majority of researchers devoted to studying on static characteristics, such as friction coefficient, load carrying capacity, pressure distribution and cavitation model. Besides, the influence of surface texture on stability of rotor-journal bearing system was rarely investigated and the recent examples can be found in Refs. (Ausas et al. 2007). However, a complete study of textured journal bearings has not been undertaken in the dynamic properties. Therefore, the purpose of this paper is to experimentally investigate the comprehensive effects of density, depth and distribution of micro-dimples on bearing vibration and stability.

This paper aims to propose novel flexible structure-supported tilting-pad aerostatic bearings and to improve operational stability and vibration reduction of aerostatic bearings.

The authors established an aerostatic bearing-rotor test rig and designed two aerostatic tilting-pad bearings with different flexible support structure and an ordinary aerostatic tilting-pad bearing and then examined their effects in dynamic performance to assess the vibration reduction performance of different flexible structures. Furthermore, the authors proposed three gas supply methods and conducted experiments to study the influence of gas supply methods in the performance of bearings.

The experimental results show that among the three structures, the double-layer flexible structure-supported tilting-pad bearing demonstrates outstanding vibration damping performance and it significantly enhances the operational stability of the bearing-rotor system. Furthermore, the experimental results indicate that the gas supply method has a significant impact on the performance of the aerostatic bearing. There is a certain pressure difference between the gas supply pressure for the loading pads and that for the nonloading pads, which is advantageous for increasing the operational stability and reducing system vibration.

The authors designed novel flexible aerostatic tilting-pad journal bearing structures, which can enhance the operational stability and reduce vibrations of the bearing. Additionally, this article proposes an air supply method advantageous for increasing the stability of the bearing and reducing system vibrations.

This study aims to present a novel hydrostatic squeeze film-metal mesh journal bearing (HS-MMJB), which uses both hydrostatic squeeze film damper (HSFD) and metal mesh damper (MMD), to suppress the vibration of rotor-bearing systems.

The lubrication equations were introduced to calculate the dynamic characteristics of HS-MMJB, and the response analyses of rotor systems were carried out. Experiments were conducted to study the vibration reduction of a rotor system with HS-MMJB. In addition, experiments for different oil supply pressures in the HS-MMJB were conducted.

The theoretical and experimental results show that the HS-MMJB exhibits excellent damping and vibration attenuation characteristics. Moreover, the stability of the rotor system can be improved by controlling the oil supply pressure.

There is a dearth of research on vibration characteristics of rotor system support by journal bearing combining HSFD and MMD. Moreover, the active oil pressure control is implemented to improve the stability of rotor system.

The purpose of this paper is to use systemic thinking to explain and predict the cost of logistics outsourcing, and to devise policies to minimize the cost of risk.

A method of system dynamics is adopted to capture the dynamic interaction of logistics outsourcing systems and to analyze the impact of some factors in the system on policy decisions over a long‐term horizon.

This paper illustrates the internal mechanism of the logistics outsourcing cost of risk systems by virtue of system dynamic principles, to develop a system dynamics model, and to give a quite detailed description of how the model could work.

The results of the simulation analysis provide useful information for logistics outsourcing risk managers.

This paper contributes to the discussion on the use of system dynamics for studying logistics outsourcing cost of risk.

This study aimed to investigate the learning strategies adopted by Saudi university students and explore the differences in the use of learning strategies due to gender and academic achievement.

The study utilized a cross-sectional descriptive analytic approach and adopted the brief “ACRA-C” learning strategies scale. The study sample consisted of 365 students enrolled at a Saudi university selected using the random clustering technique.

The study revealed that microstrategies and study habits are the most preferred strategies by Saudi university students. Statistically significant differences in the use of learning strategies were found between male and female students in favor of the female students. The study also found that learning strategies are a significant predictor of students' academic achievement.

The study was limited to one college in one Saudi university. Future studies should use larger samples from different colleges and universities in Saudi Arabia and incorporate a variety of measures of academic achievement, such as students' grades in specific courses rather than the overall grade average.

While there are a number of studies that investigated the use of learning strategies by students, there is a lack of such research in the higher education context of Saudi Arabia. Hence, the current study contributes to closing this gap in the literature by looking at the use of learning strategies by university students in Saudi Arabia and the relationship between strategy use, gender and academic achievement.

This paper aims to investigate the modification of surface of a copper alloy by friction stir surface processing (FSSP).

The metallographic condition of the surface modification was observed using microscopy. Electrochemical corrosion tests were carried out on the modified surface and the corroded surface was observed by scanning electron microscopy (SEM).

The test results showed that FSSP resulted in refinement of the surface grains of the copper alloy. The degree of refinement was increased with rotation speed and increased in the descending distance of the stirring tool. The corrosion resistance of the modified surface was superior to the base metal except for the surface generated by a rotation speed of 800 rpm and a descending distance 0.1 mm. For the surface modification of the rotation speed of 800 rpm, its corrosion resistance was lower than for the other two rotation speeds. When the rotation speed is specified, the corrosion resistance is improved with increased descending distance. When the descending distance is specified, the corrosion resistance is improved with the rotation speed.

In this study, it was confirmed that the corrosion resistance of the surface modification was best at the rotation speed 1200 rpm and descending distance 0.2 mm.