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Article
Publication date: 11 January 2024

Vahid Lotfi and Hesamedin Abdorazaghi

The response of the Pine Flat dam–water–foundation rock system is studied by a new described approach (i.e. FE-(FE-TE)-FE). The initial part of study is focused on the time…

Abstract

Purpose

The response of the Pine Flat dam–water–foundation rock system is studied by a new described approach (i.e. FE-(FE-TE)-FE). The initial part of study is focused on the time harmonic analysis. In this part, it is possible to compare the transfer functions against corresponding responses obtained by the FE-(FE-HE)-FE approach (referred to as exact method which employs a rigorous fluid hyper-element). Subsequently, the transient analysis is carried out. In that part, it is only possible to compare the results for low and high normalized reservoir length cases. Therefore, the sensitivity of results is controlled due to normalized reservoir length values.

Design/methodology/approach

In the present study, dynamic analysis of a typical concrete gravity dam–water–foundation rock system is formulated by the FE-(FE-TE)-FE approach. In this technique, dam and foundation rock are discretized by plane solid finite elements while, water domain near-field region is discretized by plane fluid finite elements. Moreover, the H-W (i.e. Hagstrom–Warburton) high-order condition is imposed at the reservoir truncation boundary. This task is formulated by employing a truncation element at that boundary. It is emphasized that reservoir far-field is excluded from the discretized model.

Findings

High orders of H-W condition, such as O5-5 considered herein, generate highly accurate responses for both possible excitations under both types of full reflective and absorptive reservoir bottom conditions. It is such that transfer functions are hardly distinguishable from corresponding exact responses obtained through the FE-(FE-HE)-FE approach in time harmonic analyses. This is controlled for both low and high normalized reservoir length cases (L/H = 1 and 3). Moreover, it can be claimed that transient analysis leads practically to exact results (in numerical sense) when one is employing high order H-W truncation element. In other words, the results are not sensitive to reservoir normalized length under these circumstances.

Originality/value

Dynamic analysis of concrete gravity dam–water–foundation rock systems is formulated by a new method. The salient aspect of the technique is that it utilizes H-W high-order condition at the truncation boundary. The method is discussed for all types of excitation and reservoir bottom conditions.

Article
Publication date: 26 November 2021

Liancheng Xiu, Zhiye Du, Yu Tian, Jingxuan He, Hongwei Cai and Fan Yi

The purpose of this paper is to develop a numerical simulation method based on the transient upstream finite element method (FEM) and Schottky emission theory to reveal the…

Abstract

Purpose

The purpose of this paper is to develop a numerical simulation method based on the transient upstream finite element method (FEM) and Schottky emission theory to reveal the distribution characteristics of space charge in oil-paper insulation.

Design/methodology/approach

The main insulation medium of the converter transformer in high voltage direct current transmission is oil-paper insulation. However, the influence of space charge is difficult to be fully considered in the insulation design and simulation of converter transformers. To reveal the influence characteristics of the space charge, this paper proposes a numerical simulation method based on Schottky emission theory and the transient upstream FEM. This method considers the influence of factors, such as carrier mobility, carrier recombination coefficient, trap capture coefficient and diffusion coefficient on the basis of multi-physics field coupling calculation of the electric field and fluid field.

Findings

A numerical simulation method considering multiple charge states is proposed for the space charge problem in oil-paper insulation. Meanwhile, a space charge measurement platform based on the electrostatic capacitance probe method for oil-paper insulation structure is built, and the effectiveness and accuracy of the numerical simulation method is verified.

Originality/value

A variety of models are calculated and analyzed by the numerical simulation method in this paper, and the distribution characteristics of the space charge and total electric field in oil-paper insulation medium with single-layer, polarity reversal of plate voltage and double-layer are obtained. The research results of this paper have the guiding significance for the engineering application of oil-paper insulation and the optimal design of converter transformer insulation.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering , vol. 41 no. 1
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 1 April 2014

Anis Younes, Ahmed Makradi, Ali Zidane, Qian Shao and Lyazid Bouhala

– The purpose of this paper is to develop an efficient non-iterative model combining advanced numerical methods for solving buoyancy-driven flow problems.

Abstract

Purpose

The purpose of this paper is to develop an efficient non-iterative model combining advanced numerical methods for solving buoyancy-driven flow problems.

Design/methodology/approach

The solution strategy is based on two independent numerical procedures. The Navier-Stokes equation is solved using the non-conforming Crouzeix-Raviart (CR) finite element method with an upstream approach for the non-linear convective term. The advection-diffusion heat equation is solved using a combination of Discontinuous Galerkin (DG) and Multi-Point Flux Approximation (MPFA) methods. To reduce the computational time due to the coupling, the authors use a non-iterative time stepping scheme where the time step length is controlled by the temporal truncation error.

Findings

Advanced numerical methods have been successfully combined to solve buoyancy-driven flow problems on unstructured triangular meshes. The accuracy of the results has been verified using three test problems: first, a synthetic problem for which the authors developed a semi-analytical solution; second, natural convection of air in a square cavity with different Rayleigh numbers (103-108); and third, a transient natural convection problem of low Prandtl fluid with horizontal temperature gradient in a rectangular cavity.

Originality/value

The proposed model is the first to combine advanced numerical methods (CR, DG, MPFA) for buoyancy-driven flow problems. It is also the first to use a non-iterative time stepping scheme based on local truncation error control for such coupled problems. The developed semi analytical solution based on Fourier series is also novel.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 24 no. 3
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 31 May 2021

Farid Terbouche, Ali Hamza and Smail Gabi

The purpose of this paper is the analysis of the dissipation of pore water pressures in the core of an earth dam, under the effect of water level fluctuations in the reservoir…

Abstract

Purpose

The purpose of this paper is the analysis of the dissipation of pore water pressures in the core of an earth dam, under the effect of water level fluctuations in the reservoir under operating conditions, taking into account the partial emptying and filling.

Design/methodology/approach

The Taksebt Dam, Tizi-Ouzou, Algeria was chosen as a case study, using a two-dimensional transient finite element numerical model. The GeoStudio calculation software is used through the SEEP/W. The latter takes into account the flow in the saturated and unsaturated zone, the formulation of SEEP/W allows the analysis of the dissipation of pore water pressures in the dyke. Starting from the maximum level of the reservoir, at least one cycle of partial emptying-filling was modelled over an eight-year operating period from 2011 to 2019. The input variables were the water level variation curve, material properties and boundary conditions.

Findings

It can be concluded that the numerical results obtained from the simulation model on the different points studied, namely, the pore water pressures are satisfactory as long as they are close to those recorded in the field by the pore pressure cells with an average error not exceeding 10% except for some measurements where the error is 20%. When the water level in the reservoir varies, the pore water pressures vary and their behaviour follows these fluctuations. Some points in the dam are affected by negative pore water pressures. No abnormal situations have been detected pore water pressures.

Originality/value

The numerical results of the simulation are analysed and validated against actual pore pressure cell measurements under operating conditions.

Details

World Journal of Engineering, vol. 19 no. 4
Type: Research Article
ISSN: 1708-5284

Keywords

Article
Publication date: 8 February 2023

Solmaz Dehghanmarvasty and Vahid Lotfi

The response of an idealized triangular concrete gravity dam is studied due to horizontal and vertical ground motions for both fully reflective and absorptive reservoir bottom…

Abstract

Purpose

The response of an idealized triangular concrete gravity dam is studied due to horizontal and vertical ground motions for both fully reflective and absorptive reservoir bottom conditions. For each combination, in this paper different orders of Givoli-Neta (G-N) high-order truncation condition are aimed to be evaluated from accuracy point of view by comparing the results against corresponding exact solutions which relies on utilizing a two-dimensional fluid hyper-element.

Design/methodology/approach

In present study, the dynamic analysis of concrete gravity dam-reservoir systems is formulated by Finite Element (FE)-(FE-TE) approach. In this technique, dam and reservoir are discretized by plane solid and fluid finite elements. Moreover, the G-N high-order condition imposed at the reservoir truncation boundary. This task is formulated by employing a truncation element at that boundary. It is emphasized that reservoir far-field is excluded from the discretized model.

Findings

It was observed that trend in gaining accuracy with increase in the order of G-N condition were basically the same for both horizontal and vertical ground motions under full reflective reservoir bottom condition. Moreover, convergence rate increases for absorptive reservoir bottom condition cases in comparison with fully reflective cases. It is also noticed that in certain cases, the responses are hardly distinguishable from corresponding exact responses. This reveals that proposed FE-(FE-TE) analysis technique based on G-N condition is quite successful, and one may fully rely on that for accurate and efficient analysis of concrete gravity dam-reservoir systems.

Originality/value

Dynamic analysis of concrete gravity dam-reservoir systems are formulated by a new method. The salient aspect of the technique is that it utilizes G-N high-order condition at the truncation boundary. This is achieved by developing a special truncation element which its generalized matrices are derived for Finite Element Method (FEM) programmers. The method is discussed for all types of excitation and reservoir bottom conditions. It must be emphasized that although time harmonic analysis is considered in the present study, the main part of formulation is explained in the context of time domain. Therefore, the approach can easily be extended for transient type of analysis.

Details

Engineering Computations, vol. 40 no. 2
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 1 May 1998

Ezzeddine Hadj‐Taieb and Taieb Lili

To accurately predict transient flow in homogeneous gas‐liquid mixtures in rigid and quasi‐rigid pipes, two mathematical models based on the gas‐fluid mass ratio are presented…

Abstract

To accurately predict transient flow in homogeneous gas‐liquid mixtures in rigid and quasi‐rigid pipes, two mathematical models based on the gas‐fluid mass ratio are presented. The fluid pressure and velocity are considered as two principal dependent variables and the gas‐fluid mass ratio is assumed to be constant. By application of the conservation of mass and momentum laws, non‐linear hyperbolic systems of two differential equations are obtained and integrated numerically by a finite difference conservative scheme. The fluid density is defined by an expression averaging the two‐component densities where a polytropic process of the gaseous phase is admitted. The rigid model is deduced by neglecting the liquid compressibility and the pipe wall elasticity against the gas deformability. The quasi‐rigid model takes into account these two parameters. The effect of fluid compressibility on transient pressure behaviour is then analysed and confronted to the pipe wall elasticity. Numerical solutions are compared with numerical results available in literature and experiment developed in the laboratory. The results show that the pressure wave propagation is significantly influenced by the gas‐fluid mass ratio and the elasticity of the pipe wall. They indicate that the pipe elasticity and liquid compressibility may be neglected for great values of gas‐fluid mass ratio but not for the smaller ones.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 8 no. 3
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 January 1990

S.K.W. Tou

This paper presents a mixed Eulerian and Lagrangian finite element method for solving 2‐D transient flows involving a moving/free boundary. The method combines the simplicity of a…

Abstract

This paper presents a mixed Eulerian and Lagrangian finite element method for solving 2‐D transient flows involving a moving/free boundary. The method combines the simplicity of a solution with a fixed computational grid associated with the Eulerian concept and the computational power of Lagrangian approach which is especially effective for a moving grid defined in the physical domain. The method employs a time‐dependent boundary‐fitted coordinate transformation to allow the physical grid to follow the moving boundary which remains always an element boundary while the computational grid is held fixed. The method is demonstrated by an example in which transient wave propagation in an open channel is simulated. The method is efficient and requires no iterative procedures and no mesh re‐zoning.

Details

Engineering Computations, vol. 7 no. 1
Type: Research Article
ISSN: 0264-4401

Article
Publication date: 1 March 1996

A. Tahani, S.J. Salon and M.V.K. Chari

Proposes a coupled finite element and Laplace transform algorithm for the numerical modelling of the electrification phenomena and the transient analysis of the flow‐induced…

472

Abstract

Proposes a coupled finite element and Laplace transform algorithm for the numerical modelling of the electrification phenomena and the transient analysis of the flow‐induced electric fields in insulating tubes carrying charged dielectric liquid. Checks the validity and accuracy of the method by applying it to certain models, for which the experimental results have been documented and other models for which analytical solutions can be found.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 15 no. 1
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 1 August 2003

Nahidh Hamid Sharif and Nils‐Erik Wiberg

A numerical model is presented for the computation of unsteady two‐fluid interfaces in nonlinear porous media flow. The nonlinear Forchheimer equation is included in the…

Abstract

A numerical model is presented for the computation of unsteady two‐fluid interfaces in nonlinear porous media flow. The nonlinear Forchheimer equation is included in the Navier‐Stokes equations for porous media flow. The model is based on capturing the interface on a fixed mesh domain. The zero level set of a pseudo‐concentration function, which defines the interface between the two fluids, is governed by a time‐dependent advection equation. The time‐dependent Navier‐Stokes equations and the advection equation are spatially discretized by the finite element (FE) method. The fully coupled implicit time integration scheme and the explicit forward Eulerian scheme are implemented for the advancement in time. The trapezoidal rule is applied to the fully implicit scheme, while the operator‐splitting algorithm is used for the velocity‐pressure segregation in the explicit scheme. The spatial and time discretizations are stabilized using FE stabilization techniques. Numerical examples of unsteady flow of two‐fluid interfaces in an earth dam are investigated.

Details

Engineering Computations, vol. 20 no. 5/6
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 1 September 2000

B.S.V. Patnaik, P.A.A. Narayana and K.N. Seetharamu

Flow past an isolated circular cylinder and two cylinders in tandem is numerically simulated, under the influence of buoyancy aiding and opposing the flow. A modified velocity…

1436

Abstract

Flow past an isolated circular cylinder and two cylinders in tandem is numerically simulated, under the influence of buoyancy aiding and opposing the flow. A modified velocity correction method is employed, which has second order accuracy in both space and time. The influence of buoyancy on the temporal fluid flow patterns is investigated, with respect to streamlines, isotherms and streaklines. Comparisons are made with respect to mean center line velocities, drag coefficients, Strouhal number and streakline patterns. Degeneration of naturally occurring Kármán vortex street into a twin eddy pattern is noticed in the Reynolds number (Re) range of 41‐200, under buoyancy aided convection. On the contrary, buoyancy opposed convection could trigger vortex shedding even at a low Re range of 20‐40, where only twin eddies are found in the natural wake. Temporal evolution of unsteady eddy patterns is visualized by means of numerical particle release (NPR). Zones of vortex shedding and twin vortices are demarcated on a plot of Richardson number against Strouhal number. Root mean square (RMS) lift coefficients (CL,RMS) and average drag coefficient (\overline Cd) are obtained as a function of Richardson number (Ri).

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 10 no. 6
Type: Research Article
ISSN: 0961-5539

Keywords

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