Flexibility Of Cage Research Articles

Impact of Vertex Functionalization on Flexibility of Porous Organic Cages.

Efficient carbon capture requires engineered porous systems that selectively capture CO2 and have low energy regeneration pathways. Porous liquids (PLs), solvent-based systems containing permanent porosity through the incorporation of a porous host, increase the CO2 adsorption capacity. A proposed mechanism of PL regeneration is the application of isostatic pressure in which the dissolved nanoporous host is compressed to alter the stability of gases in the internal pore. This regeneration mechanism relies on the flexibility of the porous host, which can be evaluated through molecular simulations. Here, the flexibility of porous organic cages (POCs) as representative porous hosts was evaluated, during which pore windows decreased by 10-40% at 6 GPa. POCs with sterically smaller functional groups, such as the 1,2-ethane in the CC1 POC resulted in greater imine cage flexibility relative to those with sterically larger functional groups, such as the cyclohexane in the CC3 POC that protected the imine cage from the application of pressure. Structural changes in the POC also caused CO2 adsorption to be thermodynamically unfavorable beginning at ∼2.2 GPa in the CC1 POC, ∼1.1 GPa in the CC3 POC, and ∼1.0 GPa in the CC13 POC, indicating that the CO2 would be expelled from the POC at or above these pressures. Energy barriers for CO2 desorption from inside the POC varied based on the geometry of the pore window and all the POCs had at least one pore window with a sufficiently low energy barrier to allow for CO2 desorption under ambient temperatures. The results identified that flexibility of the CC1, CC3, or CC13 POCs under compression can result in the expulsion of captured gas molecules.

Dynamic performance analysis of ball bearings with multi-factor coupling excitation

Skidding behavior and unstable cage whirling of bearings are key factors limiting the service performance of a spindle-bearing system. This study proposes an improved dynamic model of ball bearings focusing on structure deformations and poor lubrication conditions. The ring deformations induced by the radial preload for the spindle-bearing-pedestal mechanical system are first discussed, and the asperity contact and starved lubrication conditions on the traction effect are further considered. Then, the cage flexibility induced by the centrifugal effect is determined by the lumped mass method, and cage clearance deformations are analyzed. On this basis, the dynamic equations are derived by investigating the motions and stress states among the bearing components, and the calculations are compared with experimental data to verify their accuracy and reliability. Finally, the regulatory mechanism of bearing skidding and cage motion stability from the perspective of bearing preload and structural parameters is revealed. The results show that although surface roughness and starved lubrication weaken the lubrication conditions of the ball-race, the traction effect is enhanced to reduce bearing skidding. Compared with the curvature radius of inner race, the groove diameter decreases the cage guiding effect, and ensures cage motion stability by suppressing the collision behavior of the ball-pocket. The system preload is more effective for improving the bearing service performance, which can optimize the collision force of the ball-pocket and increase the cage guiding effect.

A nonlinear dynamic analysis of skidding behavior in rolling bearings using lubricant traction coefficients and cage flexibility

Skidding is a primary cause of rolling element bearing (REB) failure, which is influenced by operating conditions, lubricant properties, and bearing design. This paper presents an improved nonlinear dynamic model of REBs to analyze the impact of lubricant characteristics on REB skidding at different speed states. The model considers time-varying traction coefficient, cage flexibility, and cage pocket clearance. The selected tested lubricants include lithium grease (LGT2), compound calcium sulfonate (CCS) grease, and 4109 Chinese aviation oil. Simulation results show that CCS grease effectively reduces cage skidding, with the lowest load limits (300 N at 2000 RPM) under constant speed conditions and the highest stable limit (2932 RPM) during acceleration. LGT2 grease exhibits minimal sensitivity to acceleration and fluctuation speed parameters change.

Dynamic modeling and force-vibration mapping mechanism construction of rolling bearings considering cage flexibility and local faults

Rolling bearings are one of important components of rotating machinery transmissions and thus its health condition is important for the safety of machinery. Thus, rolling bearing vibration analysis is critical for bearing health condition monitoring. Current bearing vibration analysis ignores multiple compound influencing factors for dynamic modeling. Hence, a more accurate bearing dynamic model, considering multiple factors including cage flexibility, time-varying displacement excitations caused by local defects and elastohydrodynamic (EHD) lubrication, is proposed to accurately reflect force states among bearing elements and vibration responses of bearings. Furthermore, the force states and vibration responses of bearings with localized defects in the proposed model are analyzed in details: (1) the main excitation source of the dynamic model under faulty conditions is identified as the contact force between the rolling element and the raceway by analyzing the vibration signals and main physical variables (the contact forces and the friction forces) in numerical values and change trends; (2) the mapping mechanism between the main excitation source and the vibration response is constructed. The force states among bearing elements are detailedly analyzed in the proposed model and the relationship between the forces and bearing vibration responses is revealed, facilitating the bearing health condition monitoring and vibration control of machinery.

The collision and cage stability of cylindrical roller bearing considering cage flexibility

The serious and frequent collisions suffered by cage of cylindrical roller bearing may lead to cage instability, where its flexibility may play an important role but is often neglected. In this paper, a dynamic model of cylindrical roller bearing considering flexible cage constructed by lintels and cross beams flexibilities is established based on the lumped-mass approach. The dynamics between rigid and flexible cage are compared, the collision and trajectory of cage mass center are discussed under different lintel and cross beam flexibility and clearance ratio. It may be beneficial to the cage structural optimization and improve the cage stability of cylindrical roller bearing.

Skidding characteristics of urban rail vehicle axle-box bearings considering surface waviness on races

As one of the core transmission components, axle-box bearings have been widely applied in urban rail vehicles and played a crucial role in their safe and stable operation. No matter in the starting and stopping stage or stable operation stage of the vehicle, the skidding phenomenon in axle-box bearings exists and impacts their own dynamic characteristics. Furthermore, as one of the main shape errors of the bearing surface, waviness may cause fluctuations for skidding characteristics of axle-box bearings. This study investigates the skidding dynamic analysis of axle-box bearings, taking into account race surface waviness. Firstly, a dynamics model for double-row cylindrical roller bearings is established, considering the cage flexibility and friction forces between different components. Then, this model is coupled with a three-dimension vehicle–track model, allowing for more precise dynamic simulation of axle-box bearings under actual running conditions. Furthermore, an excitation related to race surface waviness is added to the coupling model through time-varying displacement and contact stiffness. At last, the influence of race surface waviness on skidding characteristics of axle-box bearings is analyzed. The effectiveness of the proposed model is validated through theoretical analysis and field tests. Simulation results demonstrate that race surface waviness can impact the cage and roller slip ratio of axle-box bearings. Overall, this study provides valuable insights into the skidding dynamic analysis of axle-box bearings, highlighting the importance of considering race surface waviness in designing and maintaining axle-box bearings.

Transient collision behavior and cage instable whirling mechanism in ball bearings: modeling approach and properties investigation

This manuscript presents a dynamic model of ball bearing considering cage flexible deformations and collision behavior of ball-cage pocket. The cage is firstly divided into a series of discrete mass units connected through springs, and the change in cage clearance is then considered to represent cage flexibility. The collision behavior of ball-pocket, the elastic connection force among cage discrete units, and the hydrodynamic action of cage-guiding ring are all analyzed to derive the dynamic equations for bearing components. The cage dynamic properties and instable whirling mechanism are explored. Discussions present that cage motion stability can be effectively improved by adjusting cage flexible characteristics, and appropriate preload and clearance design further optimize bearing service performance.

Dynamic modeling and properties analysis for ball bearing driven by structure flexible deformations

A comprehensive dynamic model of ball bearing focusing on structure flexible deformations is developed in this paper. The cage is split into several discrete segments linked by nonlinear springs to indicate the cage flexibility. The effect of cage flexibility on cage clearance is further considered. The race flexibility generated by assembly status variation of the shaft-bearing-housing system are then deduced, and the interplay mechanism between the race and other bearing components is analyzed. Finally, the effect of structure flexible deformations on bearing dynamic properties is investigated. The results indicate that rational design for structure flexibility can optimize bearing rotary performance.

Dynamic interaction between the rolling element and cage of rolling bearing considering cage flexibility and clearance

The dynamic interaction between the rolling element and cage has a significant effect on the bearing performances. However, there have been few investigations of this interaction. Hence, this study analyzes this interaction based on dynamic simulations. A dynamic model is proposed considering both the cage flexibility and variable pocket clearance. A comparative analysis is implemented of the proposed model and two widely used models, namely the rigid-cage model and flexible-cage model under a clearance-free assumption. This reveals the necessity of considering the cage flexibility and pocket clearance when estimating ball-cage impacts. Then, the transient response of ball-cage contact impacts is investigated under different cage flexibility and initial pocket clearance values. The coupled influences of these two parameters and operating conditions are evaluated and discussed. The results indicate that it is imperative to consider the cage flexibility and pocket clearance simultaneously to obtain an accurate estimate of the ball-cage interaction. The circumferential stiffness of the cage, initial pocket clearance, and speed of the bearing play a dominant role in the ball-cage dynamic interaction.

Exploring aromatic cage flexibility of the histone methyllysine reader protein Spindlin1 and its impact on binding mode prediction: an in silico study

Some of the main challenges faced in drug discovery are pocket flexibility and binding mode prediction. In this work, we explored the aromatic cage flexibility of the histone methyllysine reader protein Spindlin1 and its impact on binding mode prediction by means of in silico approaches. We first investigated the Spindlin1 aromatic cage plasticity by analyzing the available crystal structures and through molecular dynamic simulations. Then we assessed the ability of rigid docking and flexible docking to rightly reproduce the binding mode of a known ligand into Spindlin1, as an example of a reader protein displaying flexibility in the binding pocket. The ability of induced fit docking was further probed to test if the right ligand binding mode could be obtained through flexible docking regardless of the initial protein conformation. Finally, the stability of generated docking poses was verified by molecular dynamic simulations. Accurate binding mode prediction was obtained showing that the herein reported approach is a highly promising combination of in silico methods able to rightly predict the binding mode of small molecule ligands in flexible binding pockets, such as those observed in some reader proteins.

Skidding dynamic performance of rolling bearing with cage flexibility under accelerating conditions

Rolling bearings are widely used in rotating machinery and its dynamic performance plays a significant effect on the stability, reliability and even safety of the machine. Presence of the skidding is likely to cause damages to the surfaces of the inner race, the outer race, the rolling elements, and/or the cage. In this paper, a skidding dynamics model of a rolling bearing is established to reveal the skidding characteristics. In the dynamics model, the cage is discretized into several segments having the same number of the rolling elements so as to introduce the flexibility of the cage represented by springs connecting the adjacent segments. And the nonlinear contact forces between the rolling elements and inner\\outer races and the cage, the corresponding friction forces, and the gravity and centrifugal forces of the rolling elements are considered comprehensively. The simulation results are compared with the traditional dynamics model with rigid cage. By using the dynamics model, effects of the radial load, the inner ring acceleration, and the connect stiffness between the mass blocks of the cage on the bearing skidding are investigated. The results indicate that the rolling element skidding generally happens at the time instant that the rolling element is entering or leaving the loaded region. The smaller radial load or the higher angular acceleration of inner ring are the primary causes of the bearing skidding. In addition, increasing the connect stiffness could effectively alleviate the skidding phenomenon. Therefore, the proposed bearing dynamics model is proven to be capable of making a reasonable prediction on the bearing skidding with a more realistic flexible cage.

Flexibility of the Sec13/31 cage is influenced by the Sec31 C-terminal disordered domain.

In COPII mediated vesicle formation, Sec13/Sec31 heterotetramers play a role in organizing the membranes into a spherical vesicle. There they oligomerize into a cage that interacts with the other COPII proteins to direct vesicle formation and concentrate cargo into a bud. In this role they must be flexible to accommodate different sizes and shapes of cargo, but also have elements that provide rigidity to help deform the membrane. Here we characterize the influence the C-terminal disordered region of Sec31 has on cage flexibility and rigidity. After deleting this region (residues 820-1220), we characterized Sec13/Sec31ΔC heterotetramers biophysically and structurally through cryo-EM. Our results show that Sec13/31ΔC self-assembles into canonical cuboctahedral cages in vitro at buffer conditions similar to wild type. The distribution of cage sizes indicated that unlike the wild type, Sec13/31ΔC cages have a more homogeneous geometry. However, the structure of cuboctahedrons exhibited more conformational heterogeneity than wild type. Through localized reconstruction of cage vertices and molecular dynamics flexible fitting we found a new hinge for the flexing of Sec31 β-propeller domain and more flexibility of the previously known hinge. Together, these results show that the C-terminal region of Sec31 regulates the flexing of other domains such that flexibility and rigidity are not compromised during transport of large and/or asymmetric cargo.

A New Approach for Including Cage Flexibility in Dynamic Bearing Models by Using Combined Explicit Finite and Discrete Element Methods

In this investigation, a new approach was developed to study the influence of cage flexibility on the dynamics of inner and outer races and balls in a bearing. A 3D explicit finite element model (EFEM) of the cage was developed and combined with an existing discrete element dynamic bearing model (DBM) with six degrees of freedom. The EFEM was used to determine the cage dynamics, deformation, and resulting stresses in a ball bearing under various operating conditions. A novel algorithm was developed to determine the contact forces between the rigid balls and the flexible (deformable) cage. In this new flexible cage dynamic bearing model, the discrete and finite element models interact at each time step to determine the position, velocity, acceleration, and forces of all bearing components. The combined model was applied to investigate the influence of cage flexibility on ball-cage interactions and the resulting ball motion, cage whirl, and the effects of shaft misalignment. The model demonstrates that cage flexibility (deflection) has a significant influence on the ball-cage interaction. The results from this investigation demonstrate that the magnitude of ball-cage impacts and the ball sliding reduced in the presence of a flexible cage; however, as expected, the cage overall motion and angular velocity were largely unaffected by the cage flexibility. During high-speed operation, centrifugal forces contribute substantially to the total cage deformation and resulting stresses. When shaft misalignment is considered, stress cycles are experienced in the bridge and rail sections of the cage where fatigue failures have been observed in practice and in experimental studies.

A Discrete Element Approach for Modeling Cage Flexibility in Ball Bearing Dynamics Simulations

A model for deep-groove and angular-contact ball bearings was developed to investigate the influence of a flexible cage on bearing dynamics. The cage model introduces flexibility by representing the cage as an ensemble of discrete elements that allow deformation of the fibers connecting the elements. A finite element model of the cage was developed to establish the relationships between the nominal cage properties and those used in the flexible discrete element model. In this investigation, the raceways and balls have six degrees of freedom. The discrete elements comprising the cage each have three degrees of freedom in a cage reference frame. The cage reference frame has five degrees of freedom, enabling three-dimensional motion of the cage ensemble. Newton’s laws are used to determine the accelerations of the bearing components, and a fourth-order Runge–Kutta algorithm with constant step size is used to integrate their equations of motion. Comparing results from the dynamic bearing model with flexible and rigid cages reveals the effects of cage flexibility on bearing performance. The cage experiences nearly the same motion and angular velocity in the loading conditions investigated regardless of the cage type. However, a significant reduction in ball-cage pocket forces occurs as a result of modeling the cage as a flexible body. Inclusion of cage flexibility in the model also reduces the time required for the bearing to reach steady-state operation.