Effects of Modelling Assumptions on the Plan Irregularity Criteria for Single Storey Buildings

Within an aero-engine bearing chamber oil is provided to components to lubricate and cool. This oil must be efficiently removed (scavenged) from the chamber to ensure it does not overheat and degrade. Bearing chambers typically contain a sump section with an exit pipe leading to a scavenge pump. In this paper a simplified geometry of a sump section, here simply made of a radial off-take port on a walled inclined plane, is analysed computationally. This paper follows on work presented within GT2008-50634. In the previous paper it was shown that simple gravity draining from a static head of liquid cold be modelled accurately, for what was akin to a deep sump situation fond in integrated gear boxes for example. The work within this paper will show that the draining of flow perpendicular to a moving film can be modelled. This situation is similar to the arrangements found in transmission bearing chambers. The case modelled is of a walled gravity driven film running down a plane with a circular off-take port, this replicates experimental work similar to that reported in GT2008-50632. The commercial computational fluid dynamics (CFD) code, Fluent 6 [1] has been employed for modelling, sing the Volume of Fluid (VOF) approach of Hirt and Nichols [2, 3] to capture the physics of both the film motion and the two phase flow in the scavenge pipe system. Surface tension [4] and a sharpening algorithm [5] are used to complement the representation of the free surface and associated effects. This initial CFD investigation is supported and validated with experimental work, which is only depicted briefly here as it is mainly sued to support the CFD methodology. The case has been modelled in full as well as with the use of a symmetry plane running down the centre of the plane parallel to the channel walls. This paper includes details of the meshing methodology, the boundary conditions sued, which will be shown to be of critical importance to accurate modelling, and the modelling assumptions. Finally, insight into the flow patterns observed for the cases modelled are summarised. The paper further reinforces that CFD is a promising approach to analysing bearing chamber scavenge flows although it can still be relatively costly.

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Quirky patterns in time-series of estimates of recruitment could be artefacts

ICES Journal of Marine Science ◽

10.1093/icesjms/fsu022 ◽

2014 ◽

Vol 72 (1) ◽

pp. 111-116 ◽

Cited By ~ 14

Author(s):

M. Dickey-Collas ◽

N. T. Hintzen ◽

R. D. M. Nash ◽

P-J. Schön ◽

M. R. Payne

Keyword(s):

Time Series ◽

Stock Assessment ◽

Meta Analysis ◽

Reference Points ◽

Fish Stocks ◽

Stock Recruitment ◽

Modelling Assumptions ◽

Meta Analyses ◽

Recruitment Model ◽

Recruitment Time

Abstract The accessibility of databases of global or regional stock assessment outputs is leading to an increase in meta-analysis of the dynamics of fish stocks. In most of these analyses, each of the time-series is generally assumed to be directly comparable. However, the approach to stock assessment employed, and the associated modelling assumptions, can have an important influence on the characteristics of each time-series. We explore this idea by investigating recruitment time-series with three different recruitment parameterizations: a stock–recruitment model, a random-walk time-series model, and non-parametric “free” estimation of recruitment. We show that the recruitment time-series is sensitive to model assumptions and this can impact reference points in management, the perception of variability in recruitment and thus undermine meta-analyses. The assumption of the direct comparability of recruitment time-series in databases is therefore not consistent across or within species and stocks. Caution is therefore required as perhaps the characteristics of the time-series of stock dynamics may be determined by the model used to generate them, rather than underlying ecological phenomena. This is especially true when information about cohort abundance is noisy or lacking.

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Effects of finite-rate chemistry and detailed transport on the instability of jet diffusion flames

Journal of Fluid Mechanics ◽

10.1017/jfm.2014.95 ◽

2014 ◽

Vol 745 ◽

pp. 647-681 ◽

Cited By ~ 5

Author(s):

Yee Chee See ◽

Matthias Ihme

Keyword(s):

Transport Properties ◽

Diffusion Flames ◽

Diffusive Transport ◽

Mean Flow ◽

Stability Behaviour ◽

Jet Diffusion Flames ◽

One Step ◽

The Mean ◽

Modelling Assumptions ◽

The Stability

AbstractLocal linear stability analysis has been shown to provide valuable information about the response of jet diffusion flames to flow-field perturbations. However, this analysis commonly relies on several modelling assumptions about the mean flow prescription, the thermo-viscous-diffusive transport properties, and the complexity and representation of the chemical reaction mechanisms. In this work, the effects of these modelling assumptions on the stability behaviour of a jet diffusion flame are systematically investigated. A flamelet formulation is combined with linear stability theory to fully account for the effects of complex transport properties and the detailed reaction chemistry on the perturbation dynamics. The model is applied to a methane–air jet diffusion flame that was experimentally investigated by Füriet al.(Proc. Combust. Inst., vol. 29, 2002, pp. 1653–1661). Detailed simulations are performed to obtain mean flow quantities, about which the stability analysis is performed. Simulation results show that the growth rate of the inviscid instability mode is insensitive to the representation of the transport properties at low frequencies, and exhibits a stronger dependence on the mean flow representation. The effects of the complexity of the reaction chemistry on the stability behaviour are investigated in the context of an adiabatic jet flame configuration. Comparisons with a detailed chemical-kinetics model show that the use of a one-step chemistry representation in combination with a simplified viscous-diffusive transport model can affect the mean flow representation and heat release location, thereby modifying the instability behaviour. This is attributed to the shift in the flame structure predicted by the one-step chemistry model, and is further exacerbated by the representation of the transport properties. A pinch-point analysis is performed to investigate the stability behaviour; it is shown that the shear-layer instability is convectively unstable, while the outer buoyancy-driven instability mode transitions from absolutely to convectively unstable in the nozzle near field, and this transition point is dependent on the Froude number.

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Validating and Updating Finite Element Models Using Experimental Measurements of Dynamics

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

10.1243/pime_proc_1990_204_208_02 ◽

1990 ◽

Vol 204 (1) ◽

pp. 45-50

Author(s):

C F McCulloch ◽

P Vanhonacker ◽

E Dascotte

Keyword(s):

Finite Element ◽

Structural Dynamics ◽

Model Updating ◽

Measured Data ◽

Physical Parameters ◽

Experimental Measurements ◽

Finite Element Models ◽

Data Sets ◽

Modal Data ◽

Modelling Assumptions

A method is proposed for updating finite element models of structural dynamics using the results of experimental modal analysis, based on the sensitivities to changes in physical parameters. The method avoids many of the problems of incompatibility and inconsistency between the experimental and analytical modal data sets and enables the user to express confidence in measured data and modelling assumptions, allowing flexible but automated model updating.

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An investigation into the effects of modelling assumptions on sound power radiated froma high-speed train wheelset

Journal of Sound and Vibration ◽

10.1016/j.jsv.2020.115910 ◽

2021 ◽

Vol 495 ◽

pp. 115910

Author(s):

Gong Cheng ◽

Yuanpeng He ◽

Jian Han ◽

Xiaozhen Sheng ◽

David Thompson

Keyword(s):

High Speed ◽

Sound Power ◽

High Speed Train ◽

Modelling Assumptions

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Design capacities of joints with laterally loaded nails

Canadian Journal of Civil Engineering ◽

10.1139/l00-088 ◽

2001 ◽

Vol 28 (2) ◽

pp. 282-290 ◽

Cited By ~ 6

Author(s):

Ian Smith ◽

Steven T Craft ◽

Pierre Quenneville

Keyword(s):

Limit State ◽

Ultimate Limit State ◽

Joint Models ◽

Yield Model ◽

Rigid Plastic ◽

Double Shear ◽

Modelling Assumptions ◽

Ultimate Limit State Design ◽

Laterally Loaded ◽

The Impact

Capacities of joints with laterally loaded nails may be predicted using "European yield" type models (EYMs) with various levels of complexity. EYMs presume that a nail and the wood on which it bears exhibit a rigidplastic stressstrain response. Consideration is given in this paper to the "original" model published by K.W. Johansen in 1949, an empirical approximation proposed by L.R.J. Whale and coworkers in 1987, and a curtailed and "simplified" model proposed by H.J. Blass and coworkers in 1999. Predictions from the various EYMs are compared with experimentally determined ultimate capacities of single and double shear joints. Experiments covered a range of combinations of member thicknesses and two nail sizes. The impact of modelling assumptions is illustrated in the context of the Canadian timber design code. Suggestions are made regarding the necessary level of complexity for nailed joint models used in design.Key words: timber, joints, nails, yield model, ultimate limit state, design.

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MATHEMATICAL MODELING SINGULARLY PERTURBED PROCESSES OF WATER SOFTENING ON SODIUM-CATIONITE FILTERS

Informatyka Automatyka Pomiary w Gospodarce i Ochronie Środowiska ◽

10.5604/01.3001.0013.0901 ◽

2019 ◽

Vol 9 (1) ◽

pp. 37-40 ◽

Cited By ~ 1

Author(s):

Andrij Safonyk ◽

Ihor Prysiazhniuk ◽

Olena Prysiazhniuk ◽

Oleksandr Naumchuk

Keyword(s):

Ion Exchange ◽

Asymptotic Approximation ◽

Model Problem ◽

Initial Boundary ◽

Theoretical Description ◽

Water Softening ◽

Operational Conditions ◽

Calcium And Magnesium ◽

Pre Treatment ◽

Modelling Assumptions

Mathematical model of the process of water softening using ion exchange pre-treatment of waters to desalination, with a view to removal of scale forming components, such as calcium and magnesium, are formed in the paper. In this process, no additional chemicals, except for brines formed during desalination, are required for regeneration of ion-exchanger in operation cycles. An asymptotic approximation of a solution of a corresponding model problem is constructed. Theoretical description and modelling assumptions included the set of differential equations of mass balance, initial, boundary and operational conditions. The paper deals with the development of a computer model for description and prediction of the performance of ion exchange columns.

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Proof and Uncertainty in Causal Claims

Exchanges The Interdisciplinary Research Journal ◽

10.31273/eirj.v5i2.238 ◽

2018 ◽

Vol 5 (2) ◽

pp. 72-89

Author(s):

Martine Jayne Barons ◽

Rachel L Wilkerson

Keyword(s):

Graphical Models ◽

Mathematical Proof ◽

Statistical Modelling ◽

Causal Mechanisms ◽

Science Domain ◽

History Of ◽

New Methodologies ◽

Mathematical Sciences ◽

Modelling Assumptions ◽

Causal Theories

Causal questions drive scientific enquiry. From Hume to Granger, and Rubin to Pearl the history of science is full of examples of scientists testing new theories in an effort to uncover causal mechanisms. The difficulty of drawing causal conclusions from observational data has prompted developments in new methodologies, most notably in the area of graphical models. We explore the relationship between existing theories about causal mechanisms in a social science domain, new mathematical and statistical modelling methods, the role of mathematical proof and the importance of accounting for uncertainty. We show that, while the mathematical sciences rely on their modelling assumptions, dialogue with the social sciences calls for continual extension of these models. We show how changing model assumptions lead to innovative causal structures and more nuanced casual explanations. We review differing techniques for determining cause in different disciplines using causal theories from psychology, medicine, and economics.

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crestr An R package to perform probabilistic climate reconstructions using fossil proxies

10.5194/cp-2021-153 ◽

2021 ◽

Author(s):

Manuel Chevalier

Keyword(s):

R Package ◽

Climate Reconstruction ◽

Diagnostic Tools ◽

Calibration Data ◽

Reconstruction Process ◽

Climate Reconstructions ◽

Reconstruction Software ◽

Modelling Assumptions ◽

The Many ◽

Data Collections

Abstract. Statistical climate reconstruction techniques are practical tools to study past climate variability from fossil proxy data. In particular, the methods based on probability density functions (PDFs) are powerful at producing robust results from various environments and proxies. However, accessing and curating the necessary calibration data, as well as the complexity of interpreting probabilistic results, often limit their use in palaeoclimatological studies. To address these problems, I present a new R package (crestr) to apply the CREST method (Climate REconstruction SofTware) on diverse palaeoecological datasets. crestr includes a globally curated calibration dataset for six common climate proxies (i.e. plants, beetles, chironomids, rodents, foraminifera, and dinoflagellate cysts) that enables its use in most terrestrial and marine regions. The package can also be used with private data collections instead of, or in combination with, the provided dataset. It also includes a suite of graphical diagnostic tools to represent the data at each step of the reconstruction process and provide insights into the effect of the different modelling assumptions and external factors that underlie a reconstruction. With this R package, the CREST method can now be used in a scriptable environment, thus simplifying its use and integration in existing workflows. It is hoped that crestr will contribute to producing the much-needed quantified records from the many regions where climate reconstructions are currently lacking, despite the existence of suitable fossil records.

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Interpolation of spatial data – A stochastic or a deterministic problem?

European Journal of Applied Mathematics ◽

10.1017/s0956792513000016 ◽

2013 ◽

Vol 24 (4) ◽

pp. 601-629 ◽

Cited By ~ 31

Author(s):

M. SCHEUERER ◽

R. SCHABACK ◽

M. SCHLATHER

Keyword(s):

Spatial Data ◽

Convergence Rates ◽

Mathematical Problem ◽

Computer Experiments ◽

Underlying Structure ◽

Kernel Selection ◽

Deterministic Problem ◽

Interpolation Accuracy ◽

Interpolation Procedure ◽

Modelling Assumptions

Interpolation of spatial data is a very general mathematical problem with various applications. In geostatistics, it is assumed that the underlying structure of the data is a stochastic process which leads to an interpolation procedure known as kriging. This method is mathematically equivalent to kernel interpolation, a method used in numerical analysis for the same problem, but derived under completely different modelling assumptions. In this paper we present the two approaches and discuss their modelling assumptions, notions of optimality and different concepts to quantify the interpolation accuracy. Their relation is much closer than has been appreciated so far, and even results on convergence rates of kernel interpolants can be translated to the geostatistical framework. We sketch different answers obtained in the two fields concerning the issue of kernel misspecification, present some methods for kernel selection and discuss the scope of these methods with a data example from the computer experiments literature.

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