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Article
Publication date: 1 September 1997

E. Siebrits and A.P. Peirce

Direct and indirect time marching boundary element methods often become numerically unstable. Evidence of, and reasons for, these instabilities is provided in this paper. Two new…

322

Abstract

Direct and indirect time marching boundary element methods often become numerically unstable. Evidence of, and reasons for, these instabilities is provided in this paper. Two new time stepping schemes are presented, both of which are more stable than the existing standard schemes available. In particular, we introduce the Half‐step scheme, which is more accurate and far more stable than existing methods. This scheme, which is demonstrated on a simple crack problem for the displacement discontinuity method, can also be introduced into the direct boundary element method. Implementation of the Half‐step scheme into existing boundary element codes will allow researchers to attack more challenging problems than before.

Details

Engineering Computations, vol. 14 no. 6
Type: Research Article
ISSN: 0264-4401

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Article
Publication date: 18 October 2018

Xiaoming Tian and Pingchuan Dong

In petroleum industry, hydraulic fracturing is essential to enhance oil productivity. The hydraulic fractures are usually generated in the process of hydraulic fracturing…

116

Abstract

Purpose

In petroleum industry, hydraulic fracturing is essential to enhance oil productivity. The hydraulic fractures are usually generated in the process of hydraulic fracturing. Although some mathematical models were proposed to analyze the well-flow behavior of conventional fracture, there are few models to depict unconventional fracture like reorientation fracture. To figure out the effect of reorientation fracture on production enhancement and guide the further on-site operating, this paper aims to investigate the well-flow behavior of vertical reorientation fracture in horizontal permeability anisotropic reservoir.

Design/methodology/approach

Based on the governing equation considering horizontal permeability anisotropy, the mathematical models for reorientation fractures in infinite reservoir are developed by using the principle of superposition. Furthermore, a rectangular closed drainage area is also considered to investigate the well-flow behavior of reorientation fracture, and the mathematical models are developed by using Green’s and source functions.

Findings

Computational results indicate that the flux distribution of infinite conductivity fracture is uniform at very early times. After a period, it will stabilize eventually. High permeability anisotropy and small inclination angle of reorientation will cause significant end point effect in the infinite conductivity fracture. The reorientation fractures with small inclination angle in high anisotropic reservoir are capable of improving 1-1.5 times more oil productivity in total.

Originality/value

This paper develops the mathematical methods to study the well-flow behavior for unconventional fracture, especially for reorientation fracture. The results validate the production enhancement effect of reorientation fracture and identify the sensitive parameters of productivity.

Details

Engineering Computations, vol. 35 no. 7
Type: Research Article
ISSN: 0264-4401

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Article
Publication date: 20 December 2018

Yuan Li, J. Zhang, Yudong Zhong, Xiaomin Shu and Yunqiao Dong

The Convolution Quadrature Method (CQM) has been widely applied to solve transient elastodynamic problems because of its stability and generality. However, the CQM suffers from…

114

Abstract

Purpose

The Convolution Quadrature Method (CQM) has been widely applied to solve transient elastodynamic problems because of its stability and generality. However, the CQM suffers from the problems of huge memory requirement in case of direct implementation in time domain or CPU time in case of its reformulation in Laplace domain. The purpose of this paper is to combine the CQM with the pseudo-initial condition method (PICM) to achieve a good balance between memory requirement and CPU time.

Design/methodology/approach

The combined methods first subdivide the whole analysis into a few sub-analyses, which is dealt with the PICM, namely, the results obtained by previous sub-analysis are used as the initial conditions for the next sub-analysis. In each sub-analysis, the time interval is further discretized into a number of sub-steps and dealt with the CQM. For non-zero initial conditions, the pseudo-force method is used to transform them into equivalent body forces. The boundary face method is employed in the numerical implementation. Three examples are analyzed. Results are compared with analytical solutions or FEM results and the results of reformulated CQM.

Findings

Results demonstrate that the computation time and the storage requirement can be reduced significantly as compared to the CQM, by using the combined approach.

Originality/value

The combined methods can be successfully applied to the problems of long-time dynamic response, which requires a large amount of computer memory when CQM is applied, while preserving the CQM stability. If the number of time steps is high, then the accuracy of the proposed approach can be deteriorated because of the pseudo-force method.

Details

Engineering Computations, vol. 36 no. 1
Type: Research Article
ISSN: 0264-4401

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Article
Publication date: 19 June 2019

Qinglei Zeng, Zhanli Liu, Tao Wang, Yue Gao and Zhuo Zhuang

The purpose of this paper is to develop a numerical method to model the simultaneous propagation of multiple hydraulic fractures (HFs) with fluid lags driven from a horizontal…

162

Abstract

Purpose

The purpose of this paper is to develop a numerical method to model the simultaneous propagation of multiple hydraulic fractures (HFs) with fluid lags driven from a horizontal wellbore.

Design/methodology/approach

Fracture propagation in solid medium is modeled with the extended finite element method and fluid flow is modeled with finite volume method. Three iteration loops are introduced to solve the nonlinear system within each time increment, i.e. a Newtonian iteration to solve the solid-fluid coupling system, a Picard iteration to determine fluid front positions and a secant iteration to update fracture lengths.

Findings

The propagation of one single HF with a fluid lag is simulated and agrees well with semi-analytical solutions or other numerical results in the literature. The simultaneous propagation of two HFs are then investigated, which demonstrates the ability of the proposed method in capturing the hydraulic fracturing process with multiple fractures and fluid lags.

Originality/value

With the proposed method, one can simulate the simultaneous propagation of multiple HFs with fluid lags, which play a significant role during early-time propagation or when the confinement stress is relatively low (shallow HFs). Solid deformation and fracturing, fluid flow in fractures and in the wellbore are fully coupled, and three iteration loops are introduced to solve the nonlinear system.

Details

Engineering Computations, vol. 36 no. 8
Type: Research Article
ISSN: 0264-4401

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Article
Publication date: 31 December 2024

Yanan Sun, Guoyin Zhang, Michael G. Edwards and Chenfeng Li

The purpose of this paper is to systematically investigate the hydraulic fracture branching phenomena in porous media under different loading conditions and the stepwise…

33

Abstract

Purpose

The purpose of this paper is to systematically investigate the hydraulic fracture branching phenomena in porous media under different loading conditions and the stepwise phenomenon. The effect of the pore pressure in hydraulic fracturing branching is studied, and more evidence for the stepwise phenomenon with the peridynamics approach is provided.

Design/methodology/approach

A fully coupled fluid-filled explicit peridynamics model is developed to simulate the complex evolution of crack branching and stepwise phenomena in saturated porous media. Based on the peridynamics theory, an explicit time integration scheme is used to solve the coupled equation system including rock deformation, fluid flow and fracture propagation. Using the proposed model, a series of peridynamic computational tests are performed to examine two common kinds of phenomena observed in hydraulic fracturing: the crack branching phenomenon and the stepwise phenomenon.

Findings

For crack branching phenomenon, the results obtained indicate that sufficient loading is required in order to initiate the crack branching process. Compared with the stress applied on crack surfaces condition, crack branching is more easily induced with the stress applied on boundaries. In addition, for the fluid-driven crack (stress applied on crack surfaces), the existence of pore pressure will depress the growth and branching of the crack. For stepwise phenomena, the results obtained indicate that the peridynamics is a promising tool to study the stepwise phenomenon. The stepwise phenomenon is more distinct under mechanical loading conditions due to the solid behaviour. A sudden jump or crack extension will happen when enough energy is accumulated in the hydraulic fracturing system.

Research limitations/implications

In this study, the explicit method is used, which means it is conditionally stable, and the critical time step needs to be decided. The reason to use the explicit method is for the study purpose; the explicit method is faster and has no need for matrix inversions.

Originality/value

This study helps to understand the effect of the pore pressure in hydraulic fracturing branching and provides more evidence for the stepwise phenomenon with peridynamics.

Details

Engineering Computations, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 0264-4401

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Article
Publication date: 23 July 2024

Yongliang Wang, Liangchun Li and Nana Liu

With the development of fracturing technology, the research of multi-well hydrofracturing becomes the key issue. Frac-hits in multi-well hydrofracturing has an important effect on…

119

Abstract

Purpose

With the development of fracturing technology, the research of multi-well hydrofracturing becomes the key issue. Frac-hits in multi-well hydrofracturing has an important effect on fracture propagation and final production of fractured well; in the process of hydrofracturing, there are many implement parameters that can affect frac-hits, and previous studies in this area have not systematically targeted the influence of a single parameter on multi-well hydrofracturing. Therefore, it is of great significance to study the occurrence rule and influence of frac-hits for optimizing the design of fracturing wells.

Design/methodology/approach

Based on the proposed numerical models, the effects of different fracturing implement parameters (perforation cluster spacing, well spacing and injection rate) on frac-hits are compared in numerical cases. Through the analysis of fracture network, stress field and microseismic, the effects of different fracturing implement parameters on frac-hits and connections are compared.

Findings

The simulation results show that the effect of perforation cluster spacing and well spacing on frac-hits is greater than that of injection rate. Smaller well spacing makes it easier for fractures between adjacent wells to interact with each other, which increases the risk of frac-hits and reduces the risk of fracture connections. Smaller perforation cluster spacing results in larger individual fracture lengths and greater deflection angles, which makes the possibility of frac-hits and connections greater. The lower the injection rate, the lower the probability of frac-hits.

Originality/value

In this study, the influence of different fracturing implement parameters on frac-hits and connections in multi-well hydrofracturing is studied, and the mechanism of frac-hits and connections is analyzed through fracture network, stress field and microseismic analysis. Different simulation results are compared to optimize fracturing well parameter design and provide reference for engineering application.

Details

Engineering Computations, vol. 41 no. 6
Type: Research Article
ISSN: 0264-4401

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Article
Publication date: 24 December 2019

Tausi Ally Mkasiwa

The purpose of this paper is to investigate how the new Budget Act (2015) and the new budget cycle influence and were influenced by the contextual environment of the Tanzanian…

325

Abstract

Purpose

The purpose of this paper is to investigate how the new Budget Act (2015) and the new budget cycle influence and were influenced by the contextual environment of the Tanzanian parliament and how this changed parliamentarians’ (MPs) budgetary oversight roles.

Design/methodology/approach

The paper employed analytical concepts explained in the contextual framework proposed by Alsharari et al. (2015) to explore changes in budgetary oversight roles after the implementation of the reforms. Interviews, video clips and document review were employed in the data collection. Data were analyzed using the thematic approach.

Findings

The values of the new Budget Act and the new budget cycle were in conflict with the prevailing institutions, political and power aspects. The MPs modified a few provisions in the new Budget Act and in the new budget cycle. Legitimating budgetary oversight roles as a result of institutional pressure emerged but stopped. Although there was a change in MPs formal powers and MPs involvement in budgetary oversight, there was stability as the change was ineffective.

Research limitations/implications

The paper only extracted relevant aspects of the contextual framework, which were sufficient to achieve the objective of the paper. Moreover, the study was conducted only a few years after the implementation of the reforms. Therefore, it might be too early to reach conclusions. Yet, the paper serves as the basis for further studies investigating changes in budgetary oversight roles after the implementation of the reforms.

Practical implications

In order for the parliament to hold the government accountable to the electorate, there is a need for reforming the nature of the government system, improving MPs capacity, harmonizing Budget Act with prevailing constitution and demonstrating the political will to use MPs’ formal powers. The findings suggest that effective change in budgetary oversight by focusing on formal institutions only is unlikely.

Originality/value

This paper provides a more robust explanation on how the integration of institutional, political and power aspects shape budgetary oversight roles in parliaments. It is the first paper to explore accounting change using the contextual theoretical framework in an organization of a parliamentary nature. The paper responds to Kim’s (2018) call for conducting case studies to explore changes in budgetary oversight roles by investigating potential attributes of institutions when operating in practice.

Details

Journal of Public Budgeting, Accounting & Financial Management, vol. 32 no. 1
Type: Research Article
ISSN: 1096-3367

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Article
Publication date: 12 June 2020

Mabel K. Majanja

To determine the perceived self-efficacy of South African LIS academics in e-teaching as a co-requisite to imparting relevant ICT knowledge and skills to LIS students.

816

Abstract

Purpose

To determine the perceived self-efficacy of South African LIS academics in e-teaching as a co-requisite to imparting relevant ICT knowledge and skills to LIS students.

Design/methodology/approach

The study was underpinned by the pragmatic world view, which allows a researcher to choose a combination of methods, techniques and procedures that best meets the needs and purposes of the study. Based on the purpose and objectives of the study, and the type of data needed, a quantitative approach, employing the descriptive survey design was used. An online questionnaire with both structured and unstructured questions was distributed to 79 LIS academics in 8 universities and attracted a 68.4% response rate. Structured responses were computed directly as quantitative data, while the unstructured answers were aggregated under themes and analysed quantitatively.

Findings

The findings show that LIS academics in South Africa have not been left behind in the trends regarding e-teaching, and most of them feel quite confident about their self-efficacy in e-teaching. A variety of Learning Management Systems and e-tools are in use and relevant policies and technical support available. Most LIS academics, to re-/up-skill themselves, employ diverse heutagogical strategies. However, the e-teaching support in terms of resources and technical support are inadequate because some universities are deficient in their provision of ICTs and e-learning guidelines.

Research limitations/implications

The limitations of the study is that this was a time-bound study that focused merely on the basic level investigation A further in-depth probing of the real (as opposed to self) levels of e-teaching efficacy and how heutagogy can be explored or advocated is necessary.

Practical implications

The implications of the results are that (1) South African LIS academics are well fairly well prepares to face the impact of COVID-19, which has forced universities to turn to virtual/online education (2) Heutagogical approach should be explored as a method of further improving the capabilities of e-teachers, in order to (3) pass forward a positive impact on LIS graduates by preparing them to be agile for a modern work environment. (4) universities have to provide sufficient resources to support academics in their endeavour to continually improve their teaching.

Social implications

Topical in the face of the novel coronavirus.

Originality/value

Optimal

Details

Library Management, vol. 41 no. 6/7
Type: Research Article
ISSN: 0143-5124

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Book part
Publication date: 14 December 2023

Fazlyn Petersen

Business simulation games (BSGs) are gaining popularity in higher education as tools for entrepreneurial education. However, there are challenges in using BSGs for large classes…

Abstract

Background

Business simulation games (BSGs) are gaining popularity in higher education as tools for entrepreneurial education. However, there are challenges in using BSGs for large classes of students in historically disadvantaged institutions (HDIs). The challenges include limited resources and digital literacy skills.

Purpose

The living standards measure (LSM) indicates socioeconomic status by measuring the degree of urbanisation, access to services and possession of assets, such as mobile phones. This research investigated the impact of students' living standards on their intention to use BSGs, as there is limited research.

Methodology

This study used positivism and added LSM to the Unified Theory of Acceptance and Use of Technology (UTAUT) model. Quantitative data from 224 third-year information system students at an HDI were collected through an online survey. Structured Equation Modelling was used to analyse the data.

Findings

Results indicated that performance expectancy and social influence significantly influenced the intention to use BSGs. However, the relationship between effort expectancy and behavioural intention facilitating conditions was not significant. The introduction of LSM as a moderator for the relationships between all variables and behavioural intention also proved to be insignificant.

Implications and Conclusion

The result was unexpected, as we posited that a lower LSM would affect students' intention to use BSGs. This was not proven in this study and could be related to students accessing campus resources. However, during times when access to campus is restricted, such as protest action, the result may change for students with lower LSM.

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Article
Publication date: 6 October 2020

Chantel De Vos, Lawrence Ogechukwu Obokoh and Babatunde Abimbola Abiola

This paper examines the determinants of savings among low-income households, regarded as non-Ricardian households (NRHs), in South Africa. NRHs comprise low-income households…

361

Abstract

Purpose

This paper examines the determinants of savings among low-income households, regarded as non-Ricardian households (NRHs), in South Africa. NRHs comprise low-income households largely depending on government welfare benefits for sustenance. This research investigates socio-economic factors determining savings pattern of low-income households in South Africa.

Design/methodology/approach

The research makes use of the National Income Dynamics Study (NIDS) data set wave one to five. The longitudinal survey models are analysed in determining the socio-economic characteristics of NRH in South Africa. The estimators include Pooled ordinary least square (OLS), fixed and random effects methods.

Findings

The household grant contributes positively to the level of savings, but the savings level is still considerably low: majority of the low-income households have zero or negative savings. The average size of a NRH is about twice the size of the Ricardian, despite the NRHs’ debt burden impoverishing them.

Research limitations/implications

The self-perpetuated poverty problem makes every factor in the vicious cycle both cause and effect of another factor, warranting reverse causality and threatening the reliability of Pooled OLS estimates for the research.

Practical implications

The growing cost of government grant hinges on the increased level of inflation while largely depending on the number of households entering the low-income threshold.

Social implications

The study recommends that the government creates a more enabling environment for NRHs to engage in productive activities. Also they create more low-skilled jobs and encourage reduction of birth rate among low-income households; this will reduce their expenditure and increase their level of savings and will assist in pulling them out of the vicious circle of poverty. Government can boost NRHs’ savings through increase in various grants.

Originality/value

The study makes significant contribution towards addressing the unfortunate situation of household savings among low-income brackets in South Africa. The research corroborates other studies on the effectiveness of the fiscal stimulus package to boost the welfare and savings condition of NRHs in South Africa. The result explicitly confirmed the redistribution policy of the grant to the low-income household. The grant has a significant positive effect on the savings pattern of the household. An increase in it beyond the poverty threshold could indeed break the vicious circle of poverty since the effect does not only stop at expenditure but also pass through to savings, which may ultimately boost investment. Further studies should continue the investigation of grant transmission channels to investment and income.

Peer review

The peer review history for this article is available at: https://publons.com/publon/10.1108/IJSE-11-2019-0692

Details

International Journal of Social Economics, vol. 47 no. 11
Type: Research Article
ISSN: 0306-8293

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