Mathematical modelling of shallow flows: Closure models drawn from grain-scale mechanics of sediment transport and flow hydrodynamicsThis paper is one of a selection of papers in this Special Issue in honour of Professor M. Selim Yalin (1925–2007).

2009 ◽  
Vol 36 (10) ◽  
pp. 1605-1621 ◽  
Author(s):  
Rui M. L. Ferreira ◽  
Mário J. Franca ◽  
João G. A. B. Leal ◽  
António H. Cardoso
Keyword(s):  
Sediment Transport ◽  
Mathematical Modelling ◽  
Conceptual Models ◽  
Numerical Solutions ◽  
Shear Stresses ◽  
Shallow Flows ◽  
River Modelling ◽  
Morphologic Evolution ◽  
Sediment Mixtures ◽  
Selection Of

Mathematical modelling of river processes is, nowadays, a key element in river engineering and planning. River modelling tools should rest on conceptual models drawn from mechanics of sediment transport, river mechanics, and river hydrodynamics. The objectives of the present work are (i) to describe conceptual models of sediment transport, deduced from grain-scale mechanics of sediment transport and turbulent flow hydrodynamics, and (ii) to present solutions to specific river morphology problems. The conceptual models described are applicable to the morphologic evolution of rivers subjected to the transport of poorly sorted sediment mixtures at low shear stresses and to geomorphic flows featuring intense sediment transport at high shear stresses. In common, these applications share the fact that sediment transport and flow resistance depend, essentially, on grain-scale phenomena. The idealized flow structures are presented and discussed. Numerical solutions for equilibrium and nonequilibrium sediment transport are presented and compared with laboratory and field data.

2D and 3D CFD Investigations of Seabed Shear Stresses Around Subsea Pipelines

2013 ◽  
Author(s):  
Wenwen Shen ◽  
Terry Griffiths ◽  
Mengmeng Xu ◽  
Jeremy Leggoe
Keyword(s):  
Sediment Transport ◽  
Suspended Sediment ◽  
Interaction Model ◽  
Suspended Sediment Transport ◽  
Shear Stresses ◽  
Parametric Function ◽  
Ample Evidence ◽  
North West ◽  
Wide Range ◽  
Subsea Pipelines

For well over a decade it has been widely recognised that existing models and tools for subsea pipeline stability design fail to account for the fact that seabed soils tend to become mobile well before the onset of pipeline instability. Despite ample evidence obtained from both laboratory and field observations that sediment mobility has a key role to play in understanding pipeline/soil interaction, no models have been presented previously which account for the tripartite interaction between the fluid and the pipe, the fluid and the soil, and the pipe and the soil. There are numerous well developed and widely used theories available to model pipe-fluid and pipe-soil interactions. A challenge lies in the way to develop a satisfactory fluid-soil interaction algorithm that has the potential for broad implementation under both ambient and extreme sea conditions due to the complexity of flow in the vicinity of a seabed pipeline or cable. A widely used relationship by Shields [1] links the bedload and suspended sediment transport to the seabed shear stresses. This paper presents details of computational fluid dynamics (CFD) research which has been undertaken to investigate the variation of seabed shear stresses around subsea pipelines as a parametric function of pipeline spanning/embedment, trench configuration and wave/current properties using the commercial RANS-based software ANSYS Fluent. The modelling work has been undertaken for a wide range of seabed geometries, including cases in 3D to evaluate the effects of finite span length, span depth and flow attack angle on shear stresses. These seabed shear stresses have been analysed and used as the basis for predicting sediment transport within the Pipe-Soil-Fluid (PSF) Interaction Model [2] in determining the suspended sediment concentration and the advection velocity in the vicinity of pipelines. The model has significant potential to be of use to operators who struggle with conventional stabilisation techniques for the pipelines, such as those which cross Australia’s North West Shelf, where shallow water depths, highly variable calcareous soils and extreme metocean conditions driven by frequent tropical cyclones result in the requirement for expensive and logistically challenging secondary stabilisation measures.

Sedimentation in Storage Tank Structures

1994 ◽  
Vol 29 (1-2) ◽  
pp. 363-372 ◽  
Author(s):  
Virginia R. Stovin ◽  
Adrian J. Saul
Keyword(s):  
Numerical Models ◽  
Effective Means ◽  
Design Guidelines ◽  
Laboratory Model ◽  
Shear Stresses ◽  
Model Situation ◽  
Combined Sewer ◽  
Urban Watercourse ◽  
Storage Structures ◽  
Selection Of

Although storage tanks provide an effective means of reducing the magnitude and frequency of combined sewer overflow discharges, and thereby of alleviating urban watercourse pollution, poorly designed storage structures frequently suffer from maintenance problems arising from sedimentation. The development of design guidelines that optimise the self-cleansing operation of storage structures is clearly a priority for urban drainage research. This paper describes a system that has been developed to study sediment deposition in laboratory model-scale storage structures. The patterns of deposition resulting from a selection of flow regimes are described, and the need for time-varying and time series storm tests is highlighted. Sedimentation patterns are shown to predominantly depend on the flow field, and the critical bed shear stresses for deposition and erosion in the model situation are identified. Hence, the potential application of numerical models to the design problem is discussed.

QualViz: a tool for visual representation of water quality models

2011 ◽  
Vol 63 (1) ◽  
pp. 171-177
Author(s):  
G. T. Parker
Keyword(s):  
Water Quality ◽  
Conceptual Models ◽  
Dynamic Behaviour ◽  
Specific Model ◽  
Model Complexity ◽  
Proof Of Concept ◽  
Quality Models ◽  
Biochemical Kinetics ◽  
Water Quality Models ◽  
Selection Of

As water quality models and their implementation have become increasingly diverse, complex and proprietary, a need for more thorough understanding of the differences between each alternative arises. The work presented here proposes a novel visualization paradigm for water quality applications which can be used to understand difference between implementations of identical and different conceptual models. A proof-of-concept visualization tool was developed and tested again three scenarios for four different conceptual models of biochemical kinetics. Results show representative figures illustrating how the approach can communicate differences in model complexity and dynamic behaviour. The proposed tool should help ensure more suitable application of water quality models in varied contexts. A discussion of quantifying model complexity in a single metric is also presented, and recommendations are made on the selection of various representational forms for communicating and exploring specific model characteristics.

Utilizing Modeling in a Reliability Study of ACA Joints in Humidity Tests

2013 ◽  
Vol 10 (1) ◽  
pp. 30-39 ◽  
Author(s):  
Kirsi Saarinen ◽  
Laura Frisk
Keyword(s):  
Radio Frequency Identification ◽  
Cost Savings ◽  
Experimental Tests ◽  
Shear Stresses ◽  
Cycling Test ◽  
Humidity Level ◽  
Anisotropic Conductive Adhesive ◽  
Frequency Identification ◽  
Identification Tags ◽  
Selection Of

Radio frequency identification tags (RFID) with anisotropic conductive adhesive (ACA) joints are used in various applications where the environmental conditions may impair their reliability. Thus the effects of different environmental stresses on reliability need to be investigated. The purpose of this work was to study whether a relatively simple shear stress model can be utilized in reliability prediction of anisotropically conductive paste (ACP) joints in an accelerated humidity test on the basis of the information obtained from another humidity test. If modeling gives accurate results when studying reliability, the need for actual testing would decrease and thereby time and cost savings could be achieved. In this study, finite element models were made to calculate shear stresses in ACP joints induced by two different humidity tests. Additionally, experimental tests were performed and the results were compared with those of modeling. The test samples were RFID tags whose microchips were attached with ACP. A constant humidity test was used to study the effects of high humidity level and a humidity cycling test was used to examine the effects of constantly varying humidity. In the modeling it was observed that the selection of the stress-free temperature has a significant effect on the results. With three different stress-free temperatures, three different sets of results were obtained. Although the tags saturated in the extreme conditions of the humidity cycling test, according to modeling, the change in relative humidity level in the humidity cycling test did not increase the harshness of the test. However, the temperature change in the humidity cycling test increased the harshness.

Numerical modelling of cohesive sediment transport in rivers

2004 ◽  
Vol 31 (5) ◽  
pp. 749-758 ◽  
Author(s):  
David H Willis ◽  
B G Krishnappan
Keyword(s):  
Sediment Transport ◽  
Three Dimensional ◽  
Cohesive Sediment ◽  
Low Flow ◽  
Shear Stresses ◽  
Hydrodynamic Models ◽  
Coupled Models ◽  
Time Step ◽  
Water And Sediment ◽  
Sediment Model

Techniques available to practicing civil engineers for numerically modelling cohesive mud in rivers and estuaries are reviewed. Coupled models, treating water and sediment as a single process, remain research tools but are usually not three-dimensional. The decoupled approach, which separates water and sediment computations at each model time step, allows the three-dimensional representation of at least the bed and the use of well-proven, commercial, numerical, hydrodynamic models. Most hydrodynamic models compute sediment transport in suspension but may require modification of the dispersion coefficients to account for the presence of sediment. The sediment model deals with the sediment exchange between the water column and the bed using existing equations for erosion and deposition. Both equations relate the sediment exchange rates to the shear stress in the bottom boundary layer. In real rivers and estuaries, a depositional bed layer is associated with a period of low flow and shear, at slack tide for example, whereas in numerical models a layer is defined by the model time step. The sediment model keeps track of the uppermost layers at each model grid point, including consolidation and strengthening. Although numerical hydrodynamic models are based strongly on physics, sediment models are only numerical frameworks for interpolating and extrapolating full-scale field or laboratory measurements of "hydraulic sediment parameters," such as threshold shear stresses. Calibration and verification of models against measurement are therefore of prime importance.Key words: cohesive sediment, mathematical modelling, settling velocity, erosion, resuspension, deposition, fluid mud, bed layers.

scholarly journals OC-25 Bio-mathematical modelling provides the most accurate selection of HCV-G1 patients for triple-therapy

2013 ◽  
Vol 45 ◽  
pp. S9 ◽  
Author(s):  
P. Colombatto ◽  
F. Oliveri ◽  
G. Ricco ◽  
P. Ciccorossi ◽  
B. Coco ◽  
...  
Keyword(s):  
Mathematical Modelling ◽  
Triple Therapy ◽  
Selection Of

scholarly journals Numerical Simulation of Soil Water Movement under Subsurface Irrigation

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Xinqiang Qin ◽  
Xianbao Duan ◽  
Lijun Su ◽  
Xiaoqin Shen ◽  
Gang Hu
Keyword(s):  
Soil Water ◽  
Difference Method ◽  
Existence And Uniqueness ◽  
Nonlinear Term ◽  
Numerical Solutions ◽  
Water Movement ◽  
High Dimensional ◽  
Uniqueness Of The Solution ◽  
Selection Of ◽  
Soil Water Movement

By constructing a radial basis function collocation method combined with a difference method, a two-dimensional mathematical model with boundary conditions of soil water movement under irrigation is proposed. The nonlinear term is dealt with a difference method and the equation is solved using an implicit scheme. In addition, the existence and uniqueness of the solution to the soil water movement equation are proven. Numerical results show that the proposed method has high precision and is easier to use than traditional methods. Moreover, the selection of parametercplays an important role in guaranteeing calculation precision. It lays the foundation for the numerical solutions to high-dimensional soil water movement equations.

Self-consistent estimates for the viscoelastic creep compliances of composite materials

1978 ◽  
Vol 359 (1697) ◽  
pp. 251-273 ◽  
Keyword(s):  
Composite Materials ◽  
Numerical Solutions ◽  
The Self ◽  
Inclusion Problem ◽  
Inclusion Problems ◽  
Viscoelastic Creep ◽  
Self Consistent ◽  
Title Problem ◽  
Consistent Method ◽  
Selection Of

In this paper the viscoelastic creep compliances of various composites are estimated by the self-consistent method. The phases may be arbitrarily anisotropic and in any concentrations but we demand that one of the phases be a matrix and the remaining phases consist of ellipsoidal inclusions. The theory is succinctly formulated with the help of Stieltjes convolutions. In order to solve the title problem, we first solve the misfitting viscoelastic inclusion problem. Numerical solutions are given for a selection of inclusion problems and for two common composite materials, namely an isotropic dispersion of spheres, and a uni-directional fibre reinforced material.

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