On the Application of the Lu-Gre Model to Simulate Joint Friction in Multi-Body Systems

2011 ◽  
Author(s):  
Kedar Gajanan Kale ◽  
Rajiv Rampalli
Keyword(s):  
Friction Model ◽  
Lugre Model ◽  
Friction Forces ◽  
Joint Friction ◽  
Modeling Techniques ◽  
Static Regime ◽  
Increasing Demand ◽  
Automotive Suspension ◽  
Multi Body

Advances in the application of multi-body simulation technology to real world problems have led to an ever increasing demand for higher fidelity modeling techniques. Of these, accurate modeling of friction is of strategic interest in applications such as control system design, automotive suspension analysis, robotics etc. Joints (sometimes referred to as constraints) play an important role in defining the dynamics of a multi-body system. Hence, it is imperative to accurately account for friction forces arising at these joints due to the underlying interface dynamics. In this paper, we discuss the application of LuGre, a dynamic friction model to simulate joint friction. We choose the LuGre model due to its ability to capture important effects such as the Stribeck effect and the Dahl effect. The native 1-d LuGre model is extended to formulate friction computations for non-trivial joint geometries and dynamics in 2 and 3 dimensions. It is also extended to work in the quasi-static regime. Specific applications to revolute, cylindrical and spherical joints in multi-body systems are discussed. Finally, an engineering case study on the effects of joint friction in automotive suspension analysis is presented.

Numerical Analysis of Intermittent Stick-Slip Behaviour of Tube-Support Interaction in Heat-Exchangers

2012 ◽  
Author(s):  
Reza Azizian ◽  
Njuki Mureithi
Keyword(s):  
Heat Exchangers ◽  
Friction Model ◽  
Fretting Wear ◽  
System Response ◽  
Coefficient Function ◽  
Lugre Model ◽  
Stick Slip ◽  
Friction Forces ◽  
Stribeck Effect ◽  
Slip Region

Flow induced excitation forces in heat exchangers cause tube-support interactions. The long-term interaction is an important phenomenon which may cause fretting-wear of the tubes. Experimental tests of the interaction show the occurrence of stick-slip intermittent behavior in the tube response. Many factors are involved to precisely predict the interaction behavior including flow excitation forces, impact and friction forces. One of the explanations behind the intermittent stick-slip behavior may be interpreted by refinements in the conceptual choice of friction model and coefficient of friction. Therefore, among the factors above, the incorporated friction model plays an important role in the determination of the level of fretting-wear in the system. The friction model should satisfy two important criteria: the first important aspect is the strategy of the friction model to detect the cessation of sticking, the beginning of partial slipping and establishment of the sliding region. The second important aspect is defining a friction coefficient function for the entire system response to precisely represent the transient stick-slip regions. In the present work, the velocity limited friction model was compared with the LuGre model which is a rate dependent friction model. The effect of varying the break-away force and Stribeck effect on the stick-slip region was also investigated. Furthermore, the criteria to demarcate the stick-slip region in the LuGre model are discussed and a different method to incorporate the Stribeck effect and presliding damping in the Dahl friction model are proposed. Finally, a new hybrid spring-damper friction model inspired by the Cattaneo-Mindlin stress distribution in the contact region is proposed.

scholarly journals A clarified typology of core-periphery structure in networks

2021 ◽  
Vol 7 (12) ◽  
pp. eabc9800
Author(s):  
Ryan J. Gallagher ◽  
Jean-Gabriel Young ◽  
Brooke Foucault Welles
Keyword(s):  
Dense Core ◽  
Block Model ◽  
Hub And Spoke ◽  
Block Modeling ◽  
Domain Specific ◽  
The Core ◽  
Detailed Case ◽  
Rich Diversity ◽  
Modeling Techniques

Core-periphery structure, the arrangement of a network into a dense core and sparse periphery, is a versatile descriptor of various social, biological, and technological networks. In practice, different core-periphery algorithms are often applied interchangeably despite the fact that they can yield inconsistent descriptions of core-periphery structure. For example, two of the most widely used algorithms, the k-cores decomposition and the classic two-block model of Borgatti and Everett, extract fundamentally different structures: The latter partitions a network into a binary hub-and-spoke layout, while the former divides it into a layered hierarchy. We introduce a core-periphery typology to clarify these differences, along with Bayesian stochastic block modeling techniques to classify networks in accordance with this typology. Empirically, we find a rich diversity of core-periphery structure among networks. Through a detailed case study, we demonstrate the importance of acknowledging this diversity and situating networks within the core-periphery typology when conducting domain-specific analyses.

Boundary and Mixed Friction in the Presence of Dynamic Normal Loads: Part I—System Model

1995 ◽  
Vol 117 (2) ◽  
pp. 255-260 ◽  
Author(s):  
Andreas A. Polycarpou ◽  
Andres Soom
Keyword(s):  
Important Variable ◽  
Friction Model ◽  
System Model ◽  
Dynamic Friction ◽  
Discrete Elements ◽  
Friction Forces ◽  
Contact Compliance ◽  
Stiffness Characteristics ◽  
Nonlinear Normal ◽  
Linearized Model

The instantaneous normal motion between bodies in a sliding contact is an important variable in determining dynamic friction under unsteady sliding conditions. In order to model friction under dynamic conditions, it is therefore necessary to combine a dynamic model of the sliding system with an accurate model of the friction process. In the present work, the nonlinear normal dynamics of a friction test apparatus are described by a linearized model at a particular steady loading and sliding condition in a mixed or boundary-lubricated regime. The geometry is a line contact. The Hertzian bulk contact compliance and film and asperity damping and stiffness characteristics are included as discrete elements. In Part I of the paper, a fifth-order model is developed for the normal dynamics of the system, using both the Eigensystem Realization Algorithm (ERA) and classical experimental modal analysis techniques. In Part II, this system model is combined with a friction model, developed independently, to describe dynamic friction forces under both harmonic and impulsive applied normal loads.

Direct Sensitivity Analysis of Spatial Multibody Systems With Joint Friction Using Index-1 Formulation

2021 ◽  
Author(s):  
Adwait Verulkar ◽  
Corina Sandu ◽  
Daniel Dopico ◽  
Adrian Sandu
Keyword(s):  
Sensitivity Analysis ◽  
Dynamic Systems ◽  
Multibody Systems ◽  
Friction Model ◽  
Design Parameters ◽  
Adjoint Sensitivity ◽  
Joint Friction ◽  
Multibody Dynamic ◽  
Model Dynamics ◽  
Direct Sensitivity

Abstract Sensitivity analysis is one of the most prominent gradient based optimization techniques for mechanical systems. Model sensitivities are the derivatives of the generalized coordinates defining the motion of the system in time with respect to the system design parameters. These sensitivities can be calculated using finite differences, but the accuracy and computational inefficiency of this method limits its use. Hence, the methodologies of direct and adjoint sensitivity analysis have gained prominence. Recent research has presented computationally efficient methodologies for both direct and adjoint sensitivity analysis of complex multibody dynamic systems. The contribution of this article is in the development of the mathematical framework for conducting the direct sensitivity analysis of multibody dynamic systems with joint friction using the index-1 formulation. For modeling friction in multibody systems, the Brown and McPhee friction model has been used. This model incorporates the effects of both static and dynamic friction on the model dynamics. A case study has been conducted on a spatial slider-crank mechanism to illustrate the application of this methodology to real-world systems. Using computer models, with and without joint friction, effect of friction on the dynamics and model sensitivities has been demonstrated. The sensitivities of slider velocity have been computed with respect to the design parameters of crank length, rod length, and the parameters defining the friction model. Due to the highly non-linear nature of friction, the model dynamics are more sensitive during the transition phases, where the friction coefficient changes from static to dynamic and vice versa.

scholarly journals Assessing Natural Gas Versus CO2 Potential Underground Storage Sites in Greece: A Pragmatic Approach †

2022 ◽  
Vol 5 (1) ◽  
pp. 98
Author(s):  
Vagia Ioanna Makri ◽  
Spyridon Bellas ◽  
Vasilis Gaganis
Keyword(s):  
Natural Gas ◽  
Co2 Storage ◽  
Sedimentary Basins ◽  
Hydrocarbon Exploration ◽  
Greenhouse Gas Mitigation ◽  
Underground Storage ◽  
Pragmatic Approach ◽  
Increasing Demand ◽  
Salt Caverns

Although subsurface traps have been regularly explored for hydrocarbon exploration, natural gas and CO2 storage has drawn industrial attention over the past few decades, thanks to the increasing demand for energy resources and the need for greenhouse gas mitigation. With only one depleted hydrocarbon field in Greece, saline aquifers, salt caverns and sedimentary basins ought to be evaluated in furtherance of the latter. Within this study the potential of the Greek subsurface for underground storage is discussed. An overview and re-evaluation of the so-far studied areas is implemented based on the available data. Lastly, a pragmatic approach for the storage potential in Greece was created, delineating gaps and risks in the already proposed sites. Based on the above details, a case study for CO2 storage is presented, which is relevant to the West Katakolo field saline aquifer.

scholarly journals Is There a Need to Conduct Water Rights Transactions in the Water-Rich Areas of China? A Case Study of the Taihu Basin

2018 ◽  
Author(s):  
Fengping Wu ◽  
Min Zhu ◽  
Shang Luo ◽  
Junyuan Shen ◽  
Xia Xu ◽  
...  
Keyword(s):  
Institutional Environment ◽  
Water Rights ◽  
Chinese Government ◽  
Trading System ◽  
Water Management System ◽  
Taihu Basin ◽  
Total Water Consumption ◽  
Resource Endowment ◽  
Increasing Demand

To alleviate the contradiction between the increasing demand for water and the shortage of resources and to provide a favorable institutional environment for water rights trading, the Chinese government has strengthened the top-level design of water management system. However, the water-rich regions (southern regions of China) have good water resource endowment and a surplus of total water consumption indicators. Does this mean that there is no incentive and no need to conduct water rights trading in these regions? Through the investigation of water rights circulation cases in the Taihu Basin, a typical water-rich region of China, we established the existence of trading demand and some difficulties in conducting transactions. This paper argues that the needs of trading include alleviating the water gap in regional development, solving the water demand for large new projects, coordinating trans-jurisdiction water disputes. The plight of trading includes the lack of awareness, irregular process, excessive administrative intervention, and imperfect trading system.

scholarly journals Urban Villages, Their Redevelopment and Implications for Inequality and Integration

2021 ◽  
pp. 99-120
Author(s):  
Ya Ping Wang
Keyword(s):  
Migrant Workers ◽  
Urban Expansion ◽  
Local Population ◽  
Large Cities ◽  
Public Projects ◽  
Urban Village ◽  
Study Village ◽  
Increasing Demand ◽  
Urban Villages

AbstractUrbanvillages are a unique product of China’s rapid urban expansion. They provide a new way of life sustained by property rental income for local villagers. More importantly, urban villages provide cheap accommodation for millions of rural migrant workers in most large cities. Recently, with the increasing demand for land by commercialdevelopers and public projects, urban villages have become the targets for redevelopment. This chapter uses a case study village in Beijing as an example to assess the social and economic impacts of urban village redevelopment on both the original local inhabitants and migrants in rented accommodation. The case study village went through a very long and complicated redevelopment process from 2004 to 2017 involving different stages of demolition and relocation. It provided a rare opportunity to evaluate the effects on the local population, both pre- and post-redevelopment. The study involved several field visits, observation and interviews with village residents. It shows that urban village redevelopment offered no positive benefits for migrant workers who often lost their homes to demolition. For local villagers, redevelopment and relocation into new flats may improve their living conditions. However, most suffer from the loss of long-term economic and income generation opportunities. Moreover, the new property rights for the replacement flats confer no additional rights of citizenship for the relocated villagers who remain ‘second-class citizens’ within Chinese cities.

Model-Based Analysis of Friction-Induced Sub-Synchronous Whirl for a Rotor Contacting With Clearance Bearings Under Axial Load

2015 ◽  
Author(s):  
Matthew O. T. Cole ◽  
Lawrence Hawkins
Keyword(s):  
Axial Load ◽  
Coulomb Friction ◽  
Friction Forces ◽  
Root Finding ◽  
Model Based ◽  
Simple Physical Interpretation ◽  
Level Of Agreement ◽  
Model Based Analysis

For rotors supported by active magnetic bearings (AMBs), clearance bearings are commonly used to provide backup support under loss of AMB functionality. Test data from real machines shows that rotor vibration during touchdown on backup bearings may involve steady forward whirling at a sub-synchronous frequency. This excitation is believed to be due to friction forces transmitted between the rotor and a bearing end-face under axial load. This paper proposes a new analytical approach to model and predict such friction-driven forward whirl behaviors. A set of constraint equations are derived that relate a circular whirl motion of arbitrary orbital speed to the frequency response functions of the rotor-housing structure. This model is coupled with an evaluation of Coulomb friction associated with slip between the rotor and the supporting end-face of a thrust bearing. The resulting equations can be used to compute a set of possible whirl motions via a root-finding procedure. A case study is undertaken for a 140 kW energy storage flywheel. Model-based predictions are compared with measured data from spin-down tests and show a good level of agreement. The study confirms the role of friction-related forces in driving forward-whirl response behaviors. It also highlights the key role of housing and machine support characteristics in response behavior. This influence is shown to be complex and not open to simple physical interpretation. Therefore, the proposed analytical method is seen as a useful tool to investigate this influence while avoiding the need for time consuming numerical simulations.

Successful Application of Geological Process Modeling Techniques for a Offshore Deltaic Reservoir: A Case Study from Western Offshore Basin, India

2020 ◽  
Author(s):  
Abhishek Moharana ◽  
Mahabir Prasad Mahapatra ◽  
Subrata Chakraborty ◽  
Debakanta Biswal ◽  
Khushboo Havelia
Keyword(s):  
Process Modeling ◽  
Geological Process ◽  
Modeling Techniques

Readiness in Systems Implementation

2011 ◽  
pp. 15-51
Author(s):  
Eric Lou ◽  
Hafez Salleh
Keyword(s):  
Higher Education ◽  
International Students ◽  
Industrial Sector ◽  
Business Law ◽  
Systems Implementation ◽  
Education Organization ◽  
Health Related ◽  
Student Information ◽  
Increasing Demand

Higher education sector is notorious for lagging behind the industrial sector in the application of IT/IS systems and infrastructure. This chapter presents the application of the IT/IS readiness model in a higher education organization. This organisation was established in 1967 and currently has about 2,500 staff and 18,000 students, of which, 3,000 are international students from all over the world. The organization comprises of 14 schools and 13 research institutes and offers programmes various fields, which include virtual reality, magnetic and optics, business, law, genetic algorithms, health-related studies, and building construction. In 1996, Academic Division (AD) identified the need to improve the management of the student database due to the increase of students and programs offered by the organization. AD also identified that the Legacy Student Information System (SIS) was unable to cope with the increasing demand of data administration. This case study presents the overview of issues encountered while assessing the e-readiness of the organisation after most of the systems went live. Post implementation, the system has been able to reduce the redundancies in processes and has been able to provide a more effective support to students and staff. However, still there are several issues and conflicts that need to be resolved, and a radical rethink of the processes supporting the IT system is needed to achieve any further efficiency.

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