scholarly journals On the Effect of Friction on Tibiofemoral Joint Kinematics

2021 ◽  
Vol 11 (16) ◽  
pp. 7516
Author(s):  
Ehsan Askari ◽  
Michael S. Andersen
Keyword(s):  
Nonlinear Dynamics ◽  
Knee Joint ◽  
Soft Tissues ◽  
Research Work ◽  
Computational Time ◽  
Elastic Model ◽  
Friction Forces ◽  
Normal Contact ◽  
Mesh Density ◽  
Friction Induced Vibration

The effect of friction on nonlinear dynamics and vibration of total knee arthroplasties is yet to be investigated and understood. This research work aims at studying the influence of friction on nonlinear dynamics, friction-induced vibration, and damage of tibiofemoral joints. For this purpose, a spatial dynamic knee model is developed using an asymmetric nonlinear elastic model accounting for knee joint ligaments and a penalty contact model to compute normal contact stresses in the joint while contact detection is treated such that the associated computational time is reduced. Several friction models are considered and embedded in the dynamic model to estimate tangential friction forces in the knee joint. External loads and moments, due to the presence of all soft tissues, e.g., muscles and hip-joint reaction forces, applied to the femoral bone are determined using a musculoskeletal approach. In the post-processing stage, damage, i.e., wear and creep, are estimated using three wear models and an empirical creep formulation, respectively. In addition, a FFT analysis is performed to evaluate likely friction-induced vibration of tibiofemoral joints. Mesh density analysis is performed and the methodology is assessed against outcomes available in the literature. It can be concluded that friction influences not only the tribology, but also dynamics of the knee joint, and friction-induced vibration is likely to take place when the friction coefficient increases.

Effect of Ligament Properties on Nonlinear Dynamics and Wear Prediction of Knee Prostheses

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Ehsan Askari ◽  
Michael S. Andersen
Keyword(s):  
Nonlinear Dynamics ◽  
Soft Tissues ◽  
Cruciate Ligament ◽  
Knee Laxity ◽  
Linear Wear ◽  
Elastic Model ◽  
Knee Prostheses ◽  
Medial Condyle ◽  
Wear Rates ◽  
Stiffness Reduction

Abstract Although wear is known as the primary cause of long-time failure of total knee arthroplasty (TKA), it can be vital in short- and midterm TKA failure due to laxity. One of the reasons leading to joint laxity and instability is ligamentous insufficiency. This study, therefore, aims to investigate the effects of insufficient ligaments-related knee laxity on both nonlinear dynamics and wear of TKA. The study hypothesizes (a) ligamentous insufficiency can increase TKA damage; (b) stiffness reduction of each of the posterior cruciate ligament (PCL) and medial–lateral collateral ligaments (MCL-LCL) can differently contribute to TKA damage. A forward dynamics methodology is developed and the ligament behavior is simulated employing an asymmetric nonlinear elastic model. External loads and moment, due to the presence of all soft tissues, e.g., muscles and hip joint reaction forces, applied to the femoral bone are determined using a musculoskeletal approach linked to the developed model. A mesh density analysis is performed and comparing outcomes with that available in the literature allows for the assessment of our approach. From the results acquired, reduced PCL stiffness leads to an increase in linear wear rates and results in the maximum damage in TKAs. However, the maximum linear wear rates on both condyles occur once the stiffness of all ligaments is reduced. Moreover, the worn area of the tibia surface increases with the reduction in MCL-LCL stiffness on the medial condyle. The joint with insufficient PCL also shows a considerable increase in ligament forces right after toe-off.

Improving the Computational Cost for Copied Region Detection in Forensic Images

2016 ◽  
Vol 2 (1) ◽  
pp. 55
Author(s):  
Tu Huynh-Kha ◽  
Thuong Le-Tien ◽  
Synh Ha ◽  
Khoa Huynh-Van
Keyword(s):  
Wavelet Transform ◽  
Euclidean Distance ◽  
Research Work ◽  
Computational Cost ◽  
Correlation Coefficients ◽  
Zernike Moments ◽  
Computational Time ◽  
Discrete Wavelet ◽  
Feature Vectors ◽  
Region Detection

This research work develops a new method to detect the forgery in image by combining the Wavelet transform and modified Zernike Moments (MZMs) in which the features are defined from more pixels than in traditional Zernike Moments. The tested image is firstly converted to grayscale and applied one level Discrete Wavelet Transform (DWT) to reduce the size of image by a half in both sides. The approximation sub-band (LL), which is used for processing, is then divided into overlapping blocks and modified Zernike moments are calculated in each block as feature vectors. More pixels are considered, more sufficient features are extracted. Lexicographical sorting and correlation coefficients computation on feature vectors are next steps to find the similar blocks. The purpose of applying DWT to reduce the dimension of the image before using Zernike moments with updated coefficients is to improve the computational time and increase exactness in detection. Copied or duplicated parts will be detected as traces of copy-move forgery manipulation based on a threshold of correlation coefficients and confirmed exactly from the constraint of Euclidean distance. Comparisons results between proposed method and related ones prove the feasibility and efficiency of the proposed algorithm.

scholarly journals Region Filling with Super Resolution Algorithm

2021 ◽  
Vol 9 (VI) ◽  
pp. 3557-3564
Author(s):  
Darakhshan R. Khan
Keyword(s):  
Patch Size ◽  
Research Work ◽  
Super Resolution ◽  
Input Image ◽  
Computational Time ◽  
Low Resolution ◽  
Resolution Image ◽  
Resolution Algorithm ◽  
Region Filling

Region filling which has another name inpainting, is an approach to find the values of missing pixels from data available in the remaining portion of the image. The missing information must be recalculated in a distinctly convincing manner, such that, image look seamless. This research work has built a methodology for completely automating patch priority based region filling process. To reduce the computational time, low resolution image is constructed from input image. Based on texel of an image, patch size is determined. Several low resolution image with missing region filled is generated using region filling algorithm. Pixel information from these low resolution images is consolidated to produce single low resolution region filled image. Finally, super resolution algorithm is applied to enhance the quality of image and regain all specifics of image. This methodology of identifying patch size based on input fed has an advantage over filling algorithms which in true sense automate the process of region filling, to deal with sensitivity in region filling, algorithm different parameter settings are used and functioning with coarse version of image will notably reduce the computational time.

Analysis of Elastic Machinery With Clearances

1973 ◽  
Vol 95 (3) ◽  
pp. 695-703 ◽  
Author(s):  
R. C. Winfrey ◽  
R. V. Anderson ◽  
C. W. Gnilka
Keyword(s):  
Computer Program ◽  
Valve Train ◽  
Computational Time ◽  
Elastic Model ◽  
Elastic Link

Previous work on the analysis of elastic link mechanisms has been enlarged upon so as to include the effect of intermittent separation and impact between members. A cam-driven valve train is used as an example to demonstrate the methods for analyzing an elastic machine with clearances. Also demonstrated is a method for bookkeeping, or keeping track of the various configurations which the machine can assume due to the clearances. The methods presented here are sufficiently general to be applied to a variety of machinery; however, a cam-driven valve train was selected as an example because (1) it could be represented by a relatively simple elastic model, thus reducing the size of the computer program, and (2) an essentially constant geometry could be assumed, thus saving considerable computational time.

scholarly journals A New Approach for Solving Rub-Impact Dynamic Characteristics of Shrouded Blades Based on Macroslip Friction Model

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Guofang Nan ◽  
Jianyang Lou ◽  
Chuanchong Song ◽  
Min Tang
Keyword(s):  
Contact Angle ◽  
Vibration Amplitude ◽  
Research Work ◽  
Friction Model ◽  
Rotating Machinery ◽  
Equivalent Stiffness ◽  
Normal Contact ◽  
New Approach ◽  
Damping Characteristics ◽  
The Impact

Based on the macroslip friction model, a new dynamic model of the shrouded blades for rotating machinery is developed to study the impact vibration between the adjacent blades. Unlike the traditional analytical method of the shrouded blade based on the simple Coulomb friction model, a new approach is developed that the macroslip friction model is used to represent a more accurate rubbing behavior (more closer to reality) between the shrouds. By means of the harmonic balance method, the friction force and the normal pressure are translated into the equivalent stiffness and the equivalent damping. The Galerkin method is adopted to reduce the dimension of the equation to obtain the 1-DOF equation of motion, and the dynamic response of the shrouded blade is solved by Runge–Kutta numerical method. The effects of parameters such as the gap of shrouds, the mass of the tip, the contact angle, and the normal stiffness between the shrouded blades on the damping characteristics are discussed. The results show that the gap of tips has a significant effect on the vibration amplitude of the blade. Within a certain range, with the decrease of the gap, the amplitude of the blade tip is getting smaller while the resonant speed is increasing. The mass of the shroud has little effect on the damping characteristics, while the contact angle has a great influence on the equivalent stiffness and damping. Increasing the contact angle to a certain extent can effectively reduce the vibration amplitude of the blade, and the normal contact stiffness also has an important influence in reducing the vibration. The research results based on the new method in this paper are compared with the published articles and agree well. The research work is important to the accurate calculations and design and control of the shrouded blades for rotating machinery.

Compact Modeling of a Telecommunication Cabinet

2008 ◽  
Author(s):  
Aalok Trivedi ◽  
Dereje Agonafer ◽  
Deepak Sivanandan ◽  
Mark Hendrix ◽  
Akbar Sahrapour
Keyword(s):  
Heat Exchanger ◽  
Computation Time ◽  
Time Frame ◽  
Thermal Design ◽  
Compact Model ◽  
Computational Time ◽  
Compact Modeling ◽  
Thermal System ◽  
Mesh Density ◽  
Product Test

Computational Fluid Dynamics (CFD) is widely used in the telecommunication industry to validate experimental data and obtain both qualitative and quantitative results during product development. A typical outdoor telecommunications cabinet requires the modeling of a large number of components in order to perform the required air flow and thermal design. Among these components, the heat exchanger is the most critical to thermal performance. The cabinet heat exchanger and other thermal components make up a complex thermal system. This thermal system must be characterized and optimized in a short time frame to support time-to-market requirements. CFD techniques allow for completing system thermal optimization long before product test data can be available. However, the computational model of the complex thermal system leads to a large mesh count and corresponding lengthy computational times. The objective of this paper is to present an overview of techniques to minimize the computational time for complex designs such as a heat exchanger used in telecommunication cabinets. The discussion herein presents the concepts which lead to developing a compact model of the heat exchanger, reducing the mesh count and thereby the computation time, without compromising the acceptability of the results. The model can be further simplified by identifying the components significantly affecting the physics of the problem and eliminating components that will not adversely affect either the fluid mechanics or heat transfer. This will further reduce the mesh density. Compact modeling, selective meshing, and replacing sub-components with simplified equivalent models all help reduce the overall model size. The model thus developed is compared to a benchmark case without the compact model. Given that the validity of compact models is not generalized, it is expected that this methodology can address this particular class of problems in telecommunications systems. The CFD code FLOTHERM™ by Flomerics is used to carry out the analysis.

Basic Optimization Methodology for the Design of Friction Damping in Blade Shrouds

2013 ◽  
Author(s):  
Michal Hajžman ◽  
Luděk Pešek ◽  
Jan Brůha ◽  
Vladimír Zeman ◽  
Drahomír Rychecký
Keyword(s):  
Vibration Suppression ◽  
Harmonic Balance Method ◽  
Rigid Bodies ◽  
Geometrical Parameters ◽  
Bending Vibration ◽  
Friction Forces ◽  
Normal Contact ◽  
Friction Element ◽  
Experimental Stand ◽  
Optimization Methodology

This paper is focused on the optimization of friction element parameters in blade shrouds for various types of excitation. In order to create and validate a proper modelling methodology an experimental stand and a numerical simulation of blades interaction by means of a friction element placed in the shrouds were prepared. Mathematical models are based on the finite element method combined with rigid bodies. The interaction of the friction element and blades is described by normal contact and tangential friction forces derived for particular geometrical parameters of the studied mechanical system. The models can be analyzed both in frequency domain (by the harmonic balance method) or in time domain (by the numerical integration). The results of the optimization of friction element parameters with respect to the bending vibration suppression are documented in the paper. Another contact modelling approach intended for more complex contact surfaces is based on the decomposition of a contact surface into a set of elementary areas and on the expression of contact and friction forces between these areas. All methodologies are implemented in the MATLAB system and the results for the chosen test cases are compared with the results obtained by a measurement or by the ANSYS software.

Using MR Imaging and X-Ray Fluoroscopy to Quantify the Effects of Soft-Tissue Artifact on Measurement of Knee-Joint Kinematics

2009 ◽  
Author(s):  
Massoud Akbarshahi ◽  
Justin W. Fernandez ◽  
Anthony Schache ◽  
Richard Baker ◽  
Marcus G. Pandy
Keyword(s):  
Soft Tissue ◽  
Knee Joint ◽  
Soft Tissues ◽  
Surgical Techniques ◽  
Joint Kinematics ◽  
Segmental Motion ◽  
Coordinate Systems ◽  
Knee Joint Kinematics ◽  
Soft Tissue Artifact

The ability to accurately measure joint kinematics in vivo is of critical importance to researchers in the field of biomechanics [1]. Applications range from the quantitative evaluation of different surgical techniques, treatment methods and/or implant designs, to the development of computer-based models capable of simulating normal and pathological musculoskeletal conditions [1,2]. Currently, non-invasive marker-based three dimensional (3D) motion analysis is the most commonly used method for quantitative assessment of normal and pathological locomotion. The accuracy of this technique is influenced by movement of the soft tissues relative to the underlying bones, which causes inaccuracies in the determination of segmental anatomical coordinate systems and tracking of segmental motion. The purpose of this study was to quantify the errors in the measurement of knee-joint kinematics due solely to soft-tissue artifact (STA) in healthy subjects. To facilitate valid inter-subject comparisons of the kinematic data, relevant anatomical coordinate systems were defined using 3D bone models generated from magnetic resonance imaging (MRI).

scholarly journals Computational Evolving Technique for Casting Process of Alloys

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Amir M. Horr
Keyword(s):  
Heat Transfer ◽  
Continuous Casting ◽  
Numerical Simulations ◽  
Computational Models ◽  
Cooling System ◽  
Research Work ◽  
Industrial Process ◽  
Casting Process ◽  
Computational Time ◽  
Mechanical Coupling

The challenging task of bringing together the advanced computational models (with high accuracy) with reasonable computational time for the practical simulation of industrial process applications has promoted the introduction of innovative numerical methods in recent decades. The time and efforts associated with the accurate numerical simulations of manufacturing processes and the sophisticated multiphysical and multiscale nature of these processes have historically been challenging for mainstream industrial numerical tools. In particular, the numerical simulations of industrial continuous and semicontinuous casting processes for light metal alloys have broadly been reinvigorated to investigate the optimization of casting processes. The development of advanced numerical techniques (e.g., multiscale/physical, finite zoning, and evolving domain techniques) for industrial process simulations including the transient melt flow, heat transfer, and evolution of stress/strain and damage during continuous casting processes have endeavored many new opportunities. However, smarter and broader improvements are needed to capture the underlying physical/chemical phenomena including multiscale/physical transient fluid-thermal-mechanical coupling and dynamic heat-transfer changes during these processes. Within this framework, the cooling system including its fluid flow and its characteristic heat transfer has to be modelled. In the research work herein, numerical studies of a novel transient evolving technique including the thermal-mechanical phenomena and Heat Transfer Coefficient (HTC) estimation using empirical and reverse analyses are presented. The phase change modeling during casting process including liquid/solid interface and also the implementation of dynamic HTC curves are also considered. One of the main contributions of this paper is to show the applicability and reliability of the newly developed evolving numerical simulation approach for in-depth investigations of continuous casting processes.

The Contribution of the Cruciate Ligaments to the Load-Displacement Characteristics of the Human Knee Joint

1980 ◽  
Vol 102 (4) ◽  
pp. 277-283 ◽  
Author(s):  
R. L. Piziali ◽  
J. Rastegar ◽  
D. A. Nagel ◽  
D. J. Schurman
Keyword(s):  
Knee Joint ◽  
Soft Tissues ◽  
Lateral Load ◽  
Flexion Angle ◽  
Cruciate Ligaments ◽  
Significant Percentage ◽  
Human Knee ◽  
Human Knee Joint ◽  
Torsional Loads ◽  
Anterior Posterior

Human knee specimens were subjected to anterior-posterior, medial-lateral, varus-valgus, and torsional displacement tests. Loads were recorded for the intact joint and for the joint with all soft tissues cut except for the cruciate ligaments. The effect of condylar interference was determined for anterior-posterior, medial-lateral, and torsional displacements. The variation in load with flexion angle was considerable for medial-lateral (0–90-deg flexion) displacements, and less for varus-valgus (0–45-deg flexion) displacements. The cruciates were found to carry almost the entire anterior-posterior load; they carried a significant percentage of the medial-lateral load which varied considerably with flexion angle. A small, but not insignificant percentage of the varus-valgus load was carried by the cruciates and the variations with flexion angle were small. In torsion, the cruciates resisted only internal rotation. In the tested displacement ranges, condylar interference had a small effect on the medial-lateral load but did not affect anterior-posterior or torsional loads.

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