scholarly journals On the Mechanical Friction Losses Occurring in Automotive Differential Gearboxes

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Grégory Antoni
Keyword(s):  
Mechanical System ◽  
Automobile Industry ◽  
Sharp Increase ◽  
Analytical Approach ◽  
Surface Damage ◽  
Worst Case ◽  
Local Loss ◽  
Mechanical Assemblies ◽  
Mechanical Elements

In the automobile industry, the mechanical losses resulting from friction are largely responsible for various kinds of surface damage, such as the scuffing occurring in some mechanical assemblies. These scuffing processes seem to be due to a local loss of lubrication between certain mechanical elements of the same assembly, leading to a sharp increase in the friction, which can lead to a surface and volume damage in some of them, and even can cause, in the worst case, the whole destruction of the mechanical system if it has continued to operate. Predicting and checking the occurrence of this kind of undesirable phenomena, especially in some principal systems of the vehicle, represents nowadays, a crucial challenge in terms of automobile reliability and safety. This study focuses on the mechanical friction losses liable to occur in differential automobile gearboxes, which can lead in the long term to the scuffing of these mechanical systems. The friction losses involved were modeled, using a simple analytical approach, which is presented and discussed.

Long-Term Copper Toxicity on Scenedesmus quadricauda and Complexing Polypeptides

1995 ◽  
Vol 30 (2) ◽  
pp. 265-276 ◽  
Author(s):  
Denis Bussières ◽  
Raynald Côté ◽  
Clément Richard ◽  
Édith St-Pierre
Keyword(s):  
Heavy Metal ◽  
Sharp Increase ◽  
Copper Ions ◽  
Copper Toxicity ◽  
Scenedesmus Quadricauda ◽  
Continuous Exposure ◽  
Exponential Curve ◽  
Negative Exponential

Abstract Long-term copper toxicity has been demonstrated in Scenedesmus quadricauda. Upon continuous exposure to copper ions at 250 μg/L, the algae responded by a sharp increase in the synthesis of complexing polypeptides to chelate Cu. Complexing polypeptides gradually decreased, as observed by six sampling tests over 732 h, resembling to a negative exponential curve. This gradual diminution is considered to be a prime mechanism of acclimation or of adaptation to a heavy metal contaminated environment.

Strict Frequency Reuse Algorithm in Downlink 3GPP Random Cellular Networks

2019 ◽  
Vol 9 (3) ◽  
pp. 404-413
Author(s):  
Sinh C. Lam ◽  
Kieu T. Nguyen
Keyword(s):  
Cellular Networks ◽  
Coverage Probability ◽  
Rayleigh Fading ◽  
Analytical Approach ◽  
Frequency Reuse ◽  
Network Modelling ◽  
Cell Edge ◽  
Term Evolution ◽  
Establishment Phase

Background & Objective: In this work, we introduced a mathematical network model which follows on the recommendations of 3GPP to evaluate the downlink Long Term Evolution (LTE) network utilizing Strict Frequency Reuse (FR) scheme. The network modelling bases on the establishment phase and communications of the FR scheme. The user average coverage probability is derived and analysed under Rayleigh fading environment and furthermore the closed-form formulations of the performance are found using Gauss Quadratures. Through the Monte Carlo simulation, it is proved that the proposed analytical approach is more accurate than other approaches in the literature. Conclusion: Furthermore, this paper stated that the overall system can achieve the better performance with a higher number of Cell-Edge Users (CEUs), which contrasts with other works in the literature.

Efficient Analysis of a Catenary Riser

2006 ◽  
Author(s):  
Elizabeth Passano ◽  
Carl M. Larsen
Keyword(s):  
Operating Conditions ◽  
Stochastic Simulations ◽  
Worst Case ◽  
Nonlinear Structure ◽  
Tension Response ◽  
Extreme Response ◽  
Analysis Strategies ◽  
Low Tension ◽  
Term Response

The paper deals with the challenge of predicting the extreme response of catenary risers, a topic of both industry and academic interest. Large heave motions introduced at the upper end of a catenary riser can lead to compression and large bending moments in the region immediately above the touch down area. In the worst case, dynamic beam buckling may occur. The focus of the paper will be on understanding the riser behaviour in extreme, low-tension response and in establishing suitable analysis strategies to predict the extreme response. Results from long nonlinear stochastic simulations of many sea states with varying environmental and operating conditions may be combined to describe the long-term response of a nonlinear structure such as a catenary riser. However, this theoretically straight-forward approach is very demanding computationally and ways to limit the extent of nonlinear stochastic simulations are therefore sought. The usefulness of simpler methods such as regular wave analysis to improve understanding of the physical behaviour and to aid in concentrating the nonlinear simulations to where they are most useful, will be demonstrated.

scholarly journals Amplified bioproductivity during Transition IV (332 000–342 000 yr ago): evidence from the geochemical record of Lake El'gygytgyn

2013 ◽  
Vol 9 (2) ◽  
pp. 679-686 ◽  
Author(s):  
L. Cunningham ◽  
H. Vogel ◽  
V. Wennrich ◽  
O. Juschus ◽  
N. Nowaczyk ◽  
...  
Keyword(s):  
Sharp Increase ◽  
Biogenic Silica ◽  
Ice Cores ◽  
Climatic Conditions ◽  
The Arctic ◽  
Significant Shift ◽  
Geochemical Parameters ◽  
Lake El’Gygytgyn ◽  
Arctic Russia

Abstract. To date, terrestrial archives of long-term climatic change within the Arctic have widely been restricted to ice cores from Greenland and, more recently, sediments from Lake El'gygytgyn in northeast Arctic Russia. Sediments from this lake contain a paleoclimate record of glacial-interglacial cycles during the last three million years. Low-resolution studies at this lake have suggested that changes observed during Transition IV (the transition from marine isotope stage (MIS) 10 to MIS 9) are of greater amplitude than any observed since. In this study, geochemical parameters are used to infer past climatic conditions thus providing the first high-resolution analyses of Transition IV from a terrestrial Arctic setting. These results demonstrate that a significant shift in climate was subsequently followed by a rapid increase in biogenic silica (BSi) production. Following this sharp increase, bioproductivity remained high, but variable, for over a thousand years. This study reveals differences in the timing and magnitude of change within the ratio of silica to titanium (Si/Ti) and BSi records that would not be apparent in lower resolution studies. This has significant implications for the increasingly common use of Si/Ti data as an alternative to traditional BSi measurements.

scholarly journals Exposure of Ceramics and Ceramic Matrix Composites in Simulated and Actual Combustor Environments

2000 ◽  
Vol 122 (2) ◽  
pp. 212-218 ◽  
Author(s):  
Karren L. More ◽  
Peter F. Tortorelli ◽  
Mattison K. Ferber ◽  
Larry R. Walker ◽  
James R. Keiser ◽  
...  
Keyword(s):  
Ceramic Matrix Composite ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Surface Damage ◽  
Operating Conditions ◽  
Matrix Composites ◽  
Long Term Stability ◽  
Recession Rates ◽  
Combustor Liner

A high-temperature, high-pressure, tube furnace has been used to evaluate the long term stability of different monolithic ceramic and ceramic matrix composite materials in a simulated combustor environment. All of the tests have been run at 150 psia, 1204°C, and 15 percent steam in incremental 500 h runs. The major advantage of this system is the high sample throughput; >20 samples can be exposed in each tube at the same time under similar exposure conditions. Microstructural evaluations of the samples were conducted after each 500 h exposure to characterize the extent of surface damage, to calculate surface recession rates, and to determine degradation mechanisms for the different materials. The validity of this exposure rig for simulating real combustor environments was established by comparing materials exposed in the test rig and combustor liner materials exposed for similar times in an actual gas turbine combustor under commercial operating conditions. [S0742-4795(00)02402-9]

Long-Term Destructive SEE Risk and Calculations Using Multiple “Worst-Case” Events Versus Modelling

2014 ◽  
Vol 61 (4) ◽  
pp. 1695-1702
Author(s):  
Piers Jiggens ◽  
Hugh Evans ◽  
Pete Truscott ◽  
Daniel Heynderickx ◽  
Fan Lei ◽  
...  
Keyword(s):  
Worst Case

A Case Study - Life Extension of Offshore Bridge Bearings

2021 ◽  
Author(s):  
Ahmed Abdelkhalek ◽  
Govindavilas Sudhesh ◽  
Anjan Sarkar ◽  
Mohammed Eissa
Keyword(s):  
Cost Savings ◽  
Holistic Approach ◽  
Life Extension ◽  
Case Scenario ◽  
Worst Case ◽  
Maintenance And Repair ◽  
Seasonal Monitoring ◽  
The Impact ◽  
Bridge Bearings

Abstract Structural bearings of 47 offshore platform-link bridges with average age of 40 years were inspected and recommended for replacements due to their poor condition. Replacement of bridge bearings involves major risk and production interruptions given the structural modifications, and critical piping and E&I disconnections required for safe jacking-lifting activities required during the process. This paper presents the approach adopted to assure the integrity of the bridges and extend their lives without the need to replace the bearings. The approach employed failure mode and effect analysis to identifying and narrowing down areas that need focused efforts while tackling the problem. Scenario based structural assessments were carried out to examine the impact of the level of movement-allowing bearings functionality on the integrity of the bridge and its supporting structures; identify critical locations to be targeted during focused inspections; and establish envelopes for monitoring thermal expansion and contraction of the bridges. Guidelines were developed and implemented for integrated inspection-maintenance and repair campaign, which aimed to tackle corrosion issues and to install movement-monitoring indicators. Indicator seasonal monitoring is employed to establish the functionality of bearings on the long-term. The what-if structural assessments revealed that even in the worst-case scenario (in which the bearing are completely jammed) the option of local strengthening of the bridge and its supporting elements is more attractive than bearing replacement. The integrated inspection-maintenance and repair campaigns revealed that excessive corrosion levels observed from historic visual inspections on external non-critical bearing components (e.g: guide plates, angles, etc.) is not indicative of the condition of the internal load-bearing components (pedestals) which experienced much lower corrosion levels. The seasonal monitoring of bridge movements revealed that the 40+ years old Teflon pads are still functional and allow the bridges expansion and contraction. The developed holistic approach enabled demonstration of the fitness for service of the bearings, and provided means for assuring their long-term performance through monitoring. The results assured safety, integrity and delivered significant cost savings through aversion brownfield modifications, and production loss associated with bridge jacking and bearing replacement operations.

A trajectories' guide to the state space - learning missing terms in bifurcating ecological systems

2021 ◽  
Author(s):  
Rahel Vortmeyer-Kley ◽  
Pascal Nieters ◽  
Gordon Pipa
Keyword(s):  
Machine Learning ◽  
Differential Equations ◽  
Algal Blooms ◽  
Ecological Systems ◽  
Short Term ◽  
Specific System ◽  
Worst Case ◽  
System Components ◽  
Full Knowledge

<p>Ecological systems typically can exhibit various states ranging from extinction to coexistence of different species in oscillatory states. The switch from one state to another is called bifurcation. All these behaviours of a specific system are hidden in a set of describing differential equations (DE) depending on different parametrisations. To model such a system as DE requires full knowledge of all possible interactions of the system components. In practise, modellers can end up with terms in the DE that do not fully describe the interactions or in the worst case with missing terms.</p><p>The framework of universal differential equations (UDE) for scientific machine learning (SciML) [1] allows to reconstruct the incomplete or missing term from an idea of the DE and a short term timeseries of the system and make long term predictions of the system’s behaviour. However, the approach in [1] has difficulties to reconstruct the incomplete or missing term in systems with bifurcations. We developed a trajectory-based loss metric for UDE and SciML to tackle the problem and tested it successfully on a system mimicking algal blooms in the ocean.</p><p>[1] Rackauckas, Christopher, et al. "Universal differential equations for scientific machine learning." arXiv preprint arXiv:2001.04385 (2020).</p>

The effect of the financing structure on the return on the market share in Saudi companies An Empirical Study: أثر هيكل التمويل على عائد السهم السوقي في الشركات السعودية: دراسة تطبيقية

2020 ◽  
Vol 4 (11) ◽  
Author(s):  
Fatimah Mohammad Asiri
Keyword(s):  
Market Share ◽  
Food Production ◽  
Analytical Approach ◽  
Negative Impact ◽  
Short Term ◽  
Financing Structure ◽  
Time Period ◽  
Comprehensive Survey ◽  
Study Population

The study aimed to identify the influence of the financing structure on the return of the market share in Saudi corporations/companies. The study applied the descriptive-analytical approach, and the study population consisted of some joint-stock companies in the Saudi stock market, where the study sample consisted of (75) companies in five productive sectors where concentration was made on the following sectors: (basic materials, long-term commodities, energy, food production, capital goods). Method of the comprehensive survey was used for all companies. The data was analyzed using the Panel Data method through the STATA program. The study concluded several findings, the most important of which are that short-term debt (liabilities) have a negative impact on the return on the market share, as increasing short debts (liabilities) lead to a decrease in the return on the market share, and that long-term debt (liabilities) have no effect on the return on the market share, and equity has a negative impact on the return on the market share, as the increase in financing through equity leads to a decrease in the return on the market share. The study recommended the necessity of diversification between sources of financing and not limited to debt and long & short-term liabilities only. It also recommended conducting such a study on other sectors or conducting it on the whole market which may result in improving results, and also recommends expanding the time period more than five years, which may lead to improve results.

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