Mitral Annular Forces and Their Potential Impact on Annuloplasty Ring Selection

Objectives: To provide an overview that describes the characteristics of a mitral annuloplasty device when treating patients with a specific type of mitral regurgitation according to Carpentier's classification of mitral regurgitation.Methods: Starting with the key search term “mitral valve annuloplasty,” a literature search was performed utilising PubMed, Google Scholar, and Web of Science to identify relevant studies. A systematic approach was used to assess all publications.Results: Mitral annuloplasty rings are traditionally categorised by their mechanical compliance in rigid-, semi-rigid-, and flexible rings. There is a direct correlation between remodelling capabilities and rigidity. Thus, a rigid annuloplasty ring will have the highest remodelling capability, while a flexible ring will have the lowest. Rigid- and semi-rigid rings can furthermore be divided into flat and saddled-shaped rings. Saddle-shaped rings are generally preferred over flat rings since they decrease annular and leaflet stress accumulation and provide superior leaflet coaptation. Finally, mitral annuloplasty rings can either be complete or partial.Conclusions: A downsized rigid- or semi-rigid ring is advantageous when higher remodelling capabilities are required to correct dilation of the mitral annulus, as seen in type I, type IIIa, and type IIIb mitral regurgitation. In type II mitral regurgitation, a normosized flexible ring might be sufficient and allow for a more physiological repair since there is no annular dilatation, which diminishes the need for remodelling capabilities. However, mitral annuloplasty ring selection should always be based on the specific morphology in each patient.

Collective Motion of Cells Modeled as Ring Polymers

In this article, we use a coarse-grained model of disjoint semi-flexible ring polymers to investigate computationally the spatiotemporal collective behavior of cell colonies. A ring polymer in this model is...

Virtual Generation of Flexible Ring Tire Models Using Finite Element Analysis: Application to Dynamic Cleat Simulations

ABSTRACT The main goal of this work is to investigate if finite element (FE) model techniques with special applications of material properties accurately estimate the parameters of flexible ring tire models. It is known that commercially available ring tire models are used as standard tools for simulating and predicting vehicle ride and durability, e.g., rigid ring MF-Swift [1] and flexible ring Flexible Structure Tire Model (FTire) [2–5]. Despite wide acceptance of these models, difficulty in model parameterization limits their application in the vehicle development process. For estimation of tire dynamic stiffnesses and inertial properties, rolling tire cleat test data are required for most ring models. Although this test method produces reliable models, the parameterization is not time and cost effective as it requires measurement and processing of cleat data at multiple speeds and loads and is prone to test rig dynamic compliance variations. This approach also limits the ability to evaluate tire performances during the virtual stages of tire design. The objective of this work is to develop virtual data using time and cost effective FE-based methods towards the estimation of flexible ring model parameters rather than relying on measured cleat data on physical tires. Commercial product ABAQUS is used for the FE simulations and FTire for tire flexible ring model simulations. Two FE modeling techniques are utilized in this work. Firstly, it is shown that the dynamic stiffness of a rolling tire can be estimated from a steady state eigensolution modal analysis of a static tire using material properties characterized for a rolling tire. Secondly, a method of separation of the sidewall from the tread band is developed for the estimation of mass and bending properties of the tread band. The estimated stiffnesses, inertias, and dimensions from the FE model results are converted into FTire model parameters. Finally, to validate the virtually generated FTire model, simulated dynamic cleat data response trends at multiple inflation pressures and velocities are compared with measurements. The virtual FE based techniques presented in this work can be applied to other ring based models as well.

Characteristics analysis of the new flexible ring gear for helicopter reducer

As a key component of the vibration generation and transmission of planetary transmission system, the design of ring gear will directly affect the vibration of the system. After considering the advantages and disadvantages of the traditional ring gear structure, the new flexible ring gear was designed by scholars and applied to helicopter reducer. There is a dearth of reported analysis in the meshing characteristics of the new flexible ring gear, which leads to the blind selection of the ring gear. By building an accurate parametric finite element model, the meshing characteristics of the new flexible ring gear and the difference in dynamic characteristics between the new flexible ring gear and the traditional ring gear are obtained. The analysis shows that the new ring gear is superior to the traditional ring gear in many aspects, but it also has the characteristic of unbalance loading on the tooth surface. In addition, a test method is proposed to accurately measure the load sharing coefficient and dynamic load factor of planetary transmission and the simulation results of flexible ring gear are verified by comparison.

Coupling effects of manufacturing error and flexible ring gear rim on dynamic features of planetary gear

Manufacturing errors widely exist in and deteriorate the dynamic property of planetary gear train (PGT). To solve this problem, the ring gear is often designed with a thin rim to compensate for the effects of manufacturing errors via the elastic deflections of the rim. Existing dynamic models of the PGT only consider the effects of either the elasticity of the rim of the ring gear or the manufacturing errors. The coupling effects of manufacturing errors and the flexible ring gear are ignored. To understand the dynamic behaviors of the PGT better, a dynamic model of the PGT coupled with typical manufacturing error and flexible ring gear is developed in this study. The tooth contact analysis of the ring-planet mesh, which is calculated based on the potential energy method and uniformly curved Timoshenko beam theory, is studied using the influence coefficient method. A numerical algorithm is proposed to solve the integrated dynamic equations of the PGT. Calculated results show that the dynamic features of the PGT are complex, and the load sharing characteristic is improved when the flexible ring gear is incorporated.

Effects of molecule force on free vibration for a micro electromagnetic harmonic drive system

In this paper, a micro electromagnetic harmonic drive system is proposed. Considering Van der Waals force, dynamics equation of the flexible ring for the micro drive system is deduced and resolved. Using the equations, the effects of the molecule force on the natural frequencies and vibration modes of the drive system are investigated. Results show that considering molecule force, natural frequencies of the flexible ring are reduced and its vibration modes are changed. For lower order modes, smaller clearance between the flexible ring and stator, smaller thickness of the flexible ring and larger radius of the flexible ring, the effects of the molecule force on the natural frequencies and vibration modes are more obvious.

Intrinsic structure and dynamics of monolayer ring polymer melts

We present the general structural and dynamical characteristics of flexible ring polymers in narrowly confined two-dimensional (2D) melt systems using atomistic molecular dynamics simulations. The results are further analyzed via...