Cage Rotation Research Articles

Generation of broadband airborne ultrasound using an Harmonic Acoustic Pneumatic Source

This paper presents a new type of airborne transducer for generating broadband ultrasound with a high Sound Pressure Level (SPL). The concept is based on the Harmonic Acoustic Pneumatic Source (HAPS) that uses pressurized air in conjunction with a flow chopper made up of a rotating cage with slots connected to a specific exhaust. The fundamental frequency depends on the number of slots and the rotation speed of the cage. An analytical model of the HAPS coupled with a numerical model of the exhaust is used to predict the radiated acoustic pressure and to estimate the influence of dimensional parameters on pressure level generated by the source. Experiments are conducted with two cages: one with one slot in order to generate pulses periodically and one with 122 slots to generate periodic sound. The level of sound pressure is measured as a function of distance (0.004 to 0.5 m), the cage rotation (up to 11 krpm) and directivity (0 to 90°). For the fundamental frequency at 22 kHz, the maximum SPL of 150 dB (632 Pa rms) is /measured at 0.004 m, and decreases to 122 dB (35 Pa rms) at 0.5 m. At 0.5 m, the second and third harmonics can generate a SPL equal or greater than 115 dB above 22 kHz and up to 66 kHz. Discrepancies between the experiments results and numerical model are observed in terms of SPL, directivity and in-axis pressure.

Trunk kinematic analysis of ascent and descent stairs in college students with idiopathic scoliosis: a case-control study

BACKGROUND CONTEXTTraditional 3D motion analysis typically considers the spine as a rigid entity. Nevertheless, previous single-joint models have proven inadequate in evaluating the movement across different spinal segments in patients with idiopathic scoliosis (IS). Scoliosis significantly impairs movement functions, especially during activities such as ascending and descending stairs. There is a lack of research on the patterns of stair movement specifically for patients with IS. PURPOSEThis study aims to investigate trunk kinematics in college students with IS during stair ascent and descent tasks. A total of 56 participants, 28 with IS and 28 with healthy controls, were recruited for this case-control study. The trunk movements were analyzed using a motion analysis system that incorporated a multisegment spine model. Understanding the multi-segment spine kinematics during stair tasks can contribute to the development of effective rehabilitation programs for individuals with IS. STUDY DESIGNCase-control study. SAMPLE SIZETwenty-eight IS and 28 controls. OUTCOME MEASURESCobb angle, spinal curvature, spinal active range of motion (ROM), Kinematics. METHODSThe Qualisys system (Gothenburg, Sweden) was utilized in this study with a sampling frequency of 150 Hz. It recorded the kinematics in the thoracic, lumbar, thoracic cage, and pelvis while ascending and descending stairs for both the 28 IS individuals and the 28 control participants. Additionally, clinical parameters such as the Cobb angle, curvature of the spine, spinal range of motion (ROM), and other relevant factors were concurrently assessed among the subjects. Project supported by the National Natural Science Foundation of China (Grant No. 82205306). The authors declare no conflict of interest in preparing this article. RESULTSThe findings of this study revealed that IS individuals exhibited reduced kyphotic curvature in the sagittal plane (p<.05) when compared to the control group. In contrast, these IS patients displayed greater coronal curvature (Cobb angle) in the frontal plane and a more substantial difference in thoracic side bending range of motion in comparison to the control group (p.05). Moreover, during the ascending stair activity, IS patients showed reduced thoracic cage flexion-extension range of motion (p<.05), while displaying increased lumbar rotation range of motion and anterior-posterior pelvic tilt range of motion (p<.05) in contrast to the control group. Notably, the kinematic analysis during the descent of stairs indicated that IS patients exhibited a larger range of motion in thoracic flexion-extension, thoracic side bending, thoracic cage side bending, thoracic rotation, and thoracic cage rotation when compared to the control group (p<.05). CONCLUSIONSThe results showed significant differences in trunk kinematics between the two groups during both stair ascent and descent tasks. The utilization of the "multisegment spine model" facilitates the acquisition of motion information across multiple segments of the spine in patients diagnosed with IS, effectively enhancing the assessment outcomes derived from imaging information. The three-dimensional structural deformity in the trunk affects both static and dynamic activity patterns. In different activity states, IS patients demonstrate stiff movements in certain segments while experiencing compensatory instability in others. In the future, clinical rehabilitation programs for IS should prioritize stair-related activity training.

Extremely compact and lightweight triboelectric nanogenerator for spacecraft flywheel system health monitoring

The abnormal state of supporting bearings significantly affects the directional accuracy of spacecraft flywheel systems. A self-sensing triboelectric nanogenerator (TENG) offers a desirable route for on-orbit health monitoring and can potentially improve the intelligence level of spacecraft. Here, an extremely compact and lightweight TENG (CL-TENG) for the nonguided clearance of bearings is proposed and fabricated for the condition monitoring of a flywheel assembly. Using the bearing radial space allows the CL-TENG to perceive the revolution and whirling behavior of the cage; therefore, the output of the CL-TENG is simultaneously affected by the bearing speed and load. A test platform for capturing the kinematic of the cage is established to validate the effectiveness of the CL-TENG based on bearing skidding, cage rotation, and whirling instability. A negative exponential correlation between the output voltage and dynamic whirling clearance index is shown to be the basis of cage whirling sensing. The internal clearance and materials of the CL-TENG are optimized to enhance the output performance while preventing wear on the flexible electrodes. The application of the CL-TENG to an actual flywheel system in a simulated space environment and nonstationary operating conditions demonstrate its advantages in detecting the abnormal operating state of the cage.

Ortho-Carborane Decorated Multi-Resonance TADF Emitters: Preserving Local Excited State and High Efficiency in OLEDs.

A novel class of o-carboranyl luminophores, 2CB-BuDABNA (1) and 3CB-BuDABNA (2) is reported, in which o-carborane moieties are incorporated at the periphery of the B,N-doped multi-resonance thermally activated delayed fluorescence (MR-TADF) core. Both compounds maintain the inherent local emission characteristics of their MR-emitting core, exhibiting intense MR-TADF with high photoluminescence quantum yields in toluene and rigid states. In contrast, the presence of the dark lowest-energy charge transfer state, induced by cage rotation in THF, is suggested to be responsible for emission quenching in a polar solvent. Despite the different arrangement of the cage on the DABNA core, both 1 and 2 show red-shifted emissions compared to the parent compound BuDABNA (3). By utilizing 1 as the emitter, high-efficiency blue organic light-emitting diodes (OLEDs) are achieved with a remarkable maximum external quantum efficiency of 25%, representing the highest reported efficiency for OLEDs employing an o-carboranyl luminophore as the emitter.

CFD simulation and optimization of an industrial cement gas–solid air classifier

An air classifier is one of the main and effective devices in cement industry. In this study, a three-dimensional, steady and two-phase (solid-gas) computational fluid dynamics (CFD) simulation was performed to optimize the performance of this device in the Kerman Momtazan cement plant, Iran. After the validation of CFD results, the air flow field and air path lines between fixed blades were checked carefully and the non-uniformity in velocity distribution and the formation of vortex flows between the blades close to particle inlets were observed. The study tried to improve the device efficiency by changing the method of entering particles into the device, resulting in a reduction in air classifier electrical energy consumption (from 41 to 35 (kW h)/t) and an increase in production rate (from 203 to 214 t/h). Additionally, the study investigated the effects of other modifiable operating conditions like rotary cage rotation speed, pressure difference, and inlet air temperature on the particle size distribution and classifier efficiency. The results showed that increasing the cage rotation speed decreased the product rate and the product particles mean diameter while increasing pressure difference or increasing temperature increased the product rate and the product particles mean diameter. It was concluded that these modifiable operating conditions can significantly affect the performance of the air classifier in the cement industry.

Hydrodynamic Response Analysis of a Fixed Aquaculture Platform with a Horizontal Cylindrical Cage in Combined Waves and Currents

Biofouling on net cages adversely affects structural safety and the growth of aquacultural fish. Therefore, a novel fixed aquaculture platform with a rotatable horizontal cylindrical cage is proposed in this study, which is convenient for the cleaning of biofouling. Based on ANSYS, the numerical model of the fixed aquaculture platform was established. The response results of the strain, acceleration, and displacement of the structure under the combined action of waves and currents at three typical attack angles were calculated. The effects of water depth and cage rotation on the hydrodynamic response of the structure are discussed. The results show that the strain, acceleration, and displacement of the cage increase with the increase in wave height; however, the change with the wave period is not obvious. The direction perpendicular to the long axis of the cage is the most unfavorable load direction. The acceleration of each position increases with the increase in water depth; however, the strain response has the opposite trend. When the rotation constraint of the horizontal cylindrical cage is released, the acceleration of the cage is larger than that when the cage is fixed. The rotation of the cage has a tiny effect on the structural strain and load acting on the structure.

Cage Obliquity and Radiological Outcomes in Oblique Lateral Interbody Fusion.

Retrospective radiological study. This study aimed to examine whether cage obliquity affects radiological outcomes in oblique lateral interbody fusion (OLIF). The OLIF cage enters the disk space in the oblique direction and is then turned to the true orthogonal orientation. However, orthogonal cage placement is often hindered by cage rotation limitations. Few studies have examined the degree of cage obliquity and its effects in OLIF. This study involved 171 levels in 118 consecutive patients who underwent OLIF between L2-L3 and L4-L5 with a minimum two-year follow-up. Cage obliquity was divided into three groups on postoperative axial computed tomography images; cage obliquity <10° (group 1), cage obliquity ≥10° and <20° (group 2), and cage obliquity ≥20° (group 3). The radiological outcomes included anterior/posterior disk height, intervertebral disk angle, foraminal height, fusion, and cage subsidence. Postoperative complications related to cage obliquity were examined. The mean cage obliquity of the 171 cages was 11.3±6.9°. Cage obliquity was greater at the L4-L5 level (13.4±6.4°) than at other levels (L2-L3 and L3-L4: 6.5±7.0° and 10.1±6.2°, respectively) ( P <0.05). There were no significant differences in radiological outcomes among the groups. There were two cases of postoperative contralateral neurological symptoms in group 3. Our study showed that the orthogonal cage rotation in OLIF achieved adequate lateral cage placement. Although accurate cage rotation can be limited at the lower lumbar segments, radiological outcomes were not affected by cage obliquity.

A complete dynamics model of defective bearings considering the three-dimensional defect area and the spherical cage pocket

In current studies of dynamics of the defective bearing, the lumped-parameter model of the rolling element bearing is widely used, which is a simplified bearing vibration model consisting of the rigid masses connected by springs and dampers and is not a complete bearing dynamics model. In this paper, based on Gupta's bearing dynamics model, a complete dynamics model of the defective bearing is developed. The dynamics model includes the translational and rotational motion of all components in the bearing and fully considers the contact and friction forces between each component, especially the interaction between the rolling element and spherical pocket of the cage when the cage is guided by the rolling element. Different from the lumped-parameter model which needs to pre-plan the motion path of the rolling element in the defect area, the dynamics model can solve the motion path directly based on the three-dimensional geometric relationship and mechanical mechanism between the rolling element and defect area. The vibration responses of the defective bearing simulated by the dynamics model are in good agreement with the measured vibration responses in the time, frequency, and time-frequency domain, and the double-impulse phenomenon exists in the vibration response of the defective bearing with either outer or inner raceway defect, and the average value of the dynamically varying cage rotation speed solved by the dynamics model is consistent with the theoretical calculation, which verifies the accuracy of the model. The effect of raceway defects on the cage motion state is also studied, and the cage stability index is given by combining the cage whirl instantaneous angular velocity and cage rotation angular velocity, and the cage stability index is quantified and analyzed. The analysis results show that the bearing with inner raceway defects has worse cage stability than the bearing with outer raceway defects, and there is no obvious regularity for the effect of changes in the geometry of the defect area on cage stability.

Research on the Instantaneous Slip Ratio Monitoring of Rolling Bearing Based on Variable Reluctance Sensor

The bearing slip ratio is an effective index for bearing slip evaluation, and is also of great significance for bearing design and condition monitoring. In this paper, we proposed a slip monitoring method based on the variable reluctance sensor (VRS). A magnetoelectric probe is directly aligned with the outer ring to obtain the instantaneous rotation frequency of the inner ring, cage rotation frequency, and rolling element revolution frequency. In addition, a method based on frequency-shifting filter and spectrum correction (FSF-SC) is used to evaluate the instantaneous slip ratio, and a test rig was developed to verify the effectiveness of the proposed method under different speeds, workloads, and oil levels. Experimental results show that the slip ratio measured by the proposed method is very close to that measured by ultrasonic, and the deviation is only 0.02%. Moreover, the proposed instantaneous slip ratio is useful for bearing condition monitoring.

Triboelectric based high-precision self-powering cage skidding sensor and application on main bearing of jet engine

Monitoring the dynamic behavior of rolling bearings is important to ensure the reliability of rotating machinery. In this study, a novel, high-precision, self-powering triboelectric bearing skidding sensor (HP-TEBSS) is developed for the real-time monitoring of bearing skidding degree and cage stability characteristics. A floating sweeping, freestanding mode is adopted to ensure long-term reliability, and the HP-TEBSS does not affect the bearing structure and dynamic behavior. The proposed sensor consists of an interdigital electrode plate, a dielectric ring with a protruding surface, and a fixed ring. The dielectric ring, which is pasted to the side surface of the integral copper cage, rotates synchronously with the cage and sweeps to the electrode plate. The HP-TEBSS generates Ne (number of electrode finger pairs) times of instantaneous cage speed information than that of commercial sensor, and the deviation between these two sensors is less than 1%. This shows the advanced real-time performance and monitoring accuracy of the proposed sensor. Experiments are conducted under variable working conditions with different structural parameters to optimize the sensor output performance. The self-powering and 50 h durability capabilities of the HP-TEBSS are demonstrated. Bearing skidding and cage rotation stability under variable spindle rotation speeds and bearing axial loads are systematically evaluated. It was found that in the light-load range, the skidding degree showed an increasing trend as the speed increased, whereas it showed the opposite trend under the heavy-load range. The monitoring results of cage speed fluctuations, which indicate running stability, provide recommendations for preventing bearing operation in the vulnerable range. Furthermore, the proposed bearing dynamic model is validated using the HP-TEBSS test results to demonstrate the wide applicability, high portability, and high-speed performance of the HP-TEBSS prototype. The application of the HP-TEBSS on a high-speed jet engine test bench is analyzed. It is found that cage skidding shows a certain degree of hysteresis in the deceleration stage, as compared to the acceleration stage, owing to cage inertia. Finally, theoretical and experimental aspects of the presented self-powering multifunctional HP-TEBSS that can be applied in the smart rolling bearing field are presented.

Establishing an inexpensive, space efficient colony of Bemisia tabaci MEAM1 utilizing modelling and feedback control principles.

A stable, synchronized colony of whitefly (Bemisia tabaci MEAM1 Gennadius) was established in a single ~30 cu.ft. reach‐in incubator and supported on cabbage host plants which were grown in a 2 × 2′ mesh cage without the need for a greenhouse or dedicated growth rooms. The colony maintenance, including cage cleaning and rotation of plants, was reduced to less than 10 h per week and executed by minimally experienced researchers. In our hands, this method was approximately 10‐fold less expensive in personnel and materials than current typical implementations. A predator‐prey model of whitefly colony maintenance that included whitefly proliferation and host plant health was developed to better understand and avoid colony collapse. This quantitative model can be applied to inform decisions such as inoculum planning and is a mathematical framework to assess insect control strategies. Extensive measurements of colony input and output (such as image analysis of leaf area and whitefly population size) were performed to define basic ‘feedback control’ parameters to gain reproducibility of this inherently unstable scaled‐down whitefly colony. Quantitative transfer of ~100 whiteflies repeatedly produced more than 5000 adult whiteflies over a 6‐week, two‐generation period. Larger scale experimentation could be easily accommodated by transferring adult whiteflies from the maintenance colony with a low flow vacuum capture device. This approach to colony maintenance would be useful to programs that lack extensive plant growth room or greenhouse access and require a “clean” implementation that will not contaminate an axenic tissue culture laboratory.

Rolling Bearing Condition Monitoring Technique Based on Cage Rotation Analysis and Acoustic Emission

The objective of this paper is to present an approach for the detection of change in rolling element bearings (REB) operating conditions that can lead to premature failure. The developed technique is based on the measurement of the kinematics of the bearing cage. The rotational motion of the cage is driven by the traction forces produced in the contacts of the rolling elements with the races. It is known that the cage angular frequency relative to shaft angular frequency is dependent of the bearing load, the bearing speed and the lubrication condition, as these factors are determinant for the lubricant film thickness and the associated traction forces. As an important part of REB failures are caused by misalignment or lubrication problems, any evidence of these conditions should be interpreted as an incipient fault. In this paper a novel method for the determination of the instantaneous angular speed (IAS) of the cage is developed. The method is evaluated in a deep grove ball bearing test rig equipped with the cage IAS sensor, as well as custom acoustic emission (AE) transducer and a piezoelectric accelerometer. The cage IAS is analyzed under different bearing loads and shaft speed, showing the dependence of the cage angular speed with the calculated lubricant film thickness. Typical bearing faulty operating conditions (mixed lubrication regime, lubricant depletion and misalignment) are recreated and it is shown that the cage IAS is dependent on the lubrication regime and is sensitive to misalignment. The AE signal is used as a lubrication regime evaluator as well. Experimental results show that the proposed technique can be used as a condition monitoring tool to detect abnormal REB conditions that can lead to premature failure.

СОВЕРШЕНСТВОВАНИЕ АКСИАЛЬНО-РОТОРНЫХ МОЛОТИЛЬНО-СЕПАРИРУЮЩИХ УСТРОЙСТВ

The authors studied the model of an axial-rotary threshing-and-separating unit (RF Patent No. 1665246) to expand the technological capabilities and adapt it to the changing conditions of grain harvesting. In the developed unit, the cage parts (a feeder, a threshing and separating part, a straw separating part and a straw unloading part) are freely connected with one another and can rotate independently. The unit also provides changing rotation speed of the cage parts relative to the rotor as they counter-rotate, co-rotate, or are at a complete stop. The study results describing the threshing and separation of the Rostovchanka and Severodonskaya wheat varieties and lupine-grass mixed crops with different moisture content can prove the validity of the developed scheme with independent rotation of the cage parts. The treshing and separation of the Rostovchanka and Severodonskaya wheat varieties and mixed lupine-grass crops were studied at grain moisture content of 9.6…13.0%, straw moisture content of 10.3…15.0%, ratio of grain-to-straw mass of 1:1.6…1.8. The authors have found that the operation of the rotor and the rotating cage in each separate part of the threshing unit has an impact on the threshing process. The best capacity results of the axial-flow threshing-and-separating unit are obtained when the rotor, the feeder cage and the threshing and separating cage co-rotate, or when the rotor and the cage of the straw separating part counter-rotate. The study has revealed that an effective separation and the least grain crushing are observed at a cage rotation speed of 28…42 min–1, a rotor speed of 870…1000 min–1, and set feed rates of 8.5…12.3 kg/s. The developed design provides more intensive operation of the threshing-and-separating unit, due to the increased number of the options for adjusting the thresher, and also facilitates cleaning the separating gratings and prevents stem mass bundling.

Stability and skidding behavior of spacecraft porous oil-containing polyimide cages based on high-speed photography technology

The stability and skidding degree of the porous oil-containing polyimide cage used in the rolling bearing in spacecraft as a function of cage oil-content ratio, applied load, and rotation speed was experimentally studied. The internal and surface topography of cage has been analyzed to explain the lubrication mechanism. A non-invasive material-independent high-speed (10 kHz) photography technology that can obtain the instantaneous cage state was adopted in test rig. Three indicators were defined to characterize the cage stability and skidding. The results show that the vibration level of the cage with 60% oil content ratio is 2 dB lower than that without oil. The bearing skidding ratio under axial force of 60 N is 4% higher than that of 210 N. The fluctuation amplitude of the cage whirl radius at 5000 r/min is about 3 times that of 1000 r/min.

Modeling structural behavior of precast concrete pipe with single elliptical steel cage reinforcement

Using single elliptical (SE) cage reinforcement in reinforced concrete pipes (RCP) can reduce both the needed reinforcing steel and labor for manufacturing double and triple steel reinforcing cages. However, there is currently no robust tools to predict the structural behavior of RCP with SE reinforcement. In this study, non-linear 3D finite element model was developed to evaluate the load capacity of SE reinforced RCP. Model predictions were validated using experimental results on corresponding full-scale pipes. The model simulated load–deflection curves of RCP under the three-edge bearing test (TEBT) and predicted its load capacity with an average error of 9%. A parametric study was conducted to investigate the effects of SE cage rotation on the load capacity of RCP. It was found that rotation had minimal effect on the elastic behavior and stiffness of the pipe up to 1 mm vertical deflection. However, SE cage rotation had greater significance on the plastic response of the pipe when the steel reinforcement became fully engaged. The proposed model could provide a basis for developing design charts for RCP with SE reinforcement and quantify possible effects of SE reinforcing cage rotation on pipe load capacity.

Ftir and Raman Spectroscopic Study of a Complex Perovskite: Ca0.91-XCe0.09Rb0.04Csx[(Zr0.50Ti0.45)Al0.05]O3, X=0.2 to 0.4, Dedicated for Radioactive Waste Confinement

Abstract Perovskite is able to sequester simultaneously, in its structure, both actinides and alkaline-earth elements. This study is an attempt to synthesize a complex perovskite Ca0.91-xCe0.09Rb0.04Csx[(Zr0.50Ti0.45)Al0.05]O3 (0.2≤x≤0.4), doped in the same time, with Ce, Cs and Rb. The synthesis is conducted by sintering at 1150°C during 16h. XRX analysis confirms the perovskite formation. SEM observations show a less porous microstructure. FTIR analysis reveals TiO6, Ti-O-Ti, Ti-O and Zr-O vibrations. Raman spectroscopy indicates many orthorhombic perovskite active modes, as: Ti-O6 and Ti-O3 torsions, ZrO7, CaO8 vibrations, the totally symmetric oxygen, and the O-octahedron cage rotation.

Exploring Cage‐warped Rotation Isomers of C20 Fullerene: MP2 and Density Functional Calculations

Using the density functional methods B3LYP, M06‐2X, PBE1PBE, B3LYP D3, M06‐2X D3, and PBE1PBE D3, and the ab initio MP2 calculations, the optimized atomic structures and energies of C20 cage rotation isomers without a constraint were obtained. The reaction path between the two rotational isomers was then studied, in which there are three local stable atomic structures. One is the most stable fullerene structure with the D2h point group staggered between the upper and bottom pentagons (ST) and the other is the second lowest energy rotational isomer with the Cs point group eclipsed between the upper and bottom pentagons (EC) with a torn fullerene structure (M1) between ST and EC. The first transition structure T1 between the ST and the M1, and the second transition structure T2 between the M1 and the EC were then obtained along the reaction coordinate between these three structures. Vibration analysis of all optimized structures including the transition structures without a constraint was carried out. For each of the rotational isomers obtained by our calculations, thermodynamic stability was explained with the relative energy difference, and then the kinetic stability was analyzed as the HOMO–LUMO energy difference.

Stator current model for detecting rolling bearing faults in induction motors using magnetic equivalent circuits

Stator current modeling for defective induction motor rolling bearings (IMRBs) based on magnetic equivalent circuits (MEC) is carried out. A dynamic model of rotor system supported by defective IMRBs is established to numerically obtain the non-uniform time-varying air gap length. MEC modeling of a induction motor (IM) is then conducted and a magnetic equivalent network is formed by connecting the flux tubes with nodes. After considering the nonlinear air gap permeance, nonlinear iron material and magnetic saturation, an iterative numerical integration method is proposed to solve the stator current model. Finite element analysis and dynamic tests on a typical IM are carried out for verification. Based on these, the fault characteristic frequencies in stator current spectra are, respectively, identified for outer race spall, inner race spall and ball spall. Fault-related frequencies are basically represented by the combinations between the passing frequency (outer race, inner race or ball), its harmonics and power supply frequency. Due to the modulation of rotor (or cage) rotation, higher harmonics of rotor frequency (or cage frequency) participate in the fault-related frequencies of the inner race (or ball) spall. Some fault-related frequencies, which might be more suitable for condition monitoring of induction motors, are recommended by comparing the slope of each spectral amplitude varying with spall width.

Experimental study on dynamic behavior of ball bearing cage in cryogenic environments, Part I: Effects of cage guidance and pocket clearances

Abstract In cryogenic environments, it is not possible to apply oil or grease to ball bearings, owing to the extreme temperature conditions. Thus, polytetrafluoroethylene (PTFE) cages are used as solid lubricants in such environments, because PTFE has a low coefficient of friction. PTFE cages increase the rotational stability of the ball bearings by reducing the frictional force of the rolling elements. In addition, design parameters such as the cage guidance and ball-pocket clearances significantly affect the stability of the ball bearings. In this study, the dynamic behavior of a ball bearing cage submerged in a cryogenic fluid was investigated for different cage clearances and rotation speeds. For experimental verification, a test rig was designed to realize a cryogenic environment. The test rig could be driven to 11,000 rpm using a DC motor and provided loads of up to 20 kN using a pneumatic cylinder. A metal ring was employed to measure the cage whirling amplitude using a fiber optic displacement sensor. The parameters considered included the cage whirling amplitude, ball bearing torque, and cage wear. The effects of the clearances and rotation speed on the cage stability and performance were analyzed using the probability density function of the cage whirling frequency, and the standard deviation of this function decreased as the outer guidance clearance decreased. In addition, the cage wear loss increased with decreasing cage ball-pocket clearance, owing to the collisions between the balls and cage pocket. The experimental results agreed partially with the existing theory and demonstrated that the cage instability increased as the cage guidance clearance increased.

Numerical Study of Cage Dynamics Focused on Hydrodynamic Effects of Guidance Land Clearances for Different Ball-Pocket Clearances in Cryogenic Environments

This study presents the dynamic motion of a ball bearing cage submerged in a cryogenic fluid under high-speed conditions. The dynamic motion of the cage has been studied as a function of the race land-cage and ball-cage pocket clearances for different inner race rotation speeds under light load conditions. In addition, this study conducted computational fluid dynamics (CFD) analysis using commercial software to analyze the fluid dynamic forces on the cage. The hydraulic force obtained from the CFD analysis was coded in commercial ball bearing analysis software as a function of the eccentricity ratio and rotation speed of the cage. Finally, the dynamic motion of the ball bearing cage considering the effects of fluid dynamic forces has been studied. The results include the cage whirling amplitude, fluctuation of cage whirling speed, and cage wear for various cage clearances and rotation speeds. The cage whirling amplitude decreases as the outer guidance clearance decreases, and it decreases as the rotation speed increases up to 11,000 rpm because of the increasing hydrodynamic force of the liquid nitrogen (LN2). However, the probability density function curves indicate that an increase in the rotor speed increases the standard deviation in the cage whirling frequency. The wear loss of the cage was greatest for the largest race land-cage and the smallest ball-cage pocket clearances. Consequently, the analysis results for various operating conditions (inner race rotation speeds, cage clearances, traction coefficients, etc.) are in good agreement with the reference results.