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Documents published in Scipedia

• Probability Analysis and Prevention of Offshore Oil and Gas Accidents: Fire as a Cause and a Consequence

  D. Brkić, P. Praks

  Fire (2021). Brkić, Dejan, and Pavel Praks. 2021. "Probability Analysis and Prevention of Offshore Oil and Gas Accidents: Fire as a Cause and a Consequence" Fire 4, no. 4: 71. https://doi.org/10.3390/fire4040071

  
  

  Abstract

  ailures during the drilling and exploitation of hydrocarbons that result in catastrophic offshore oil and gas accidents are relatively rare but if they occur the consequences can be catastrophic in terms of loss of life and environmental damage. Therefore, to gain insight into their prevention, the largest major offshore oil and gas accidents, those with more than 10 fatalities or with a large environmental impact, are analyzed in this article. Special attention is placed on fire as a cause and a consequence. Relevant technological and legislative changes and updates regarding safety that have followed such accidents and that can prevent potential future similar misfortunes are evaluated. Two main approaches to safety are compared: (1) the American prescriptive vs. (2) the European goal-oriented approach. The main causes of accidents are tested statistically in respect of failure probability, where the exact confidence limits for the estimated probabilities are computed. The results of the statistical test based on exact confidence intervals show that there is no significant difference between the analysed factors, which describe the main causes of offshore oil and gas accidents. Based on the small but carefully chosen group of 24 of the largest accidents, it can be concluded that there is no evidence of a difference between the categories of the main causes of accidents.

  Abstract
  ailures during the drilling and exploitation of hydrocarbons that result in catastrophic offshore oil and gas accidents are relatively rare but if they occur the consequences [...]

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• Excel VBA-based user defined functions for highly precise Colebrook’s pipe flow friction approximations: A comparative overview

  D. Brkić, Z. Stajić

  Facta Universitatis, series: Mechanical Engineering (FU Mech Eng) (2021). Brkić, D. and Stajić, Z., 2021. Excel VBA-Based User Defined Functions for Highly Precise Colebrook’s Pipe Flow Friction Approximations: A Comparative Overview. Facta Universitatis, Series: Mechanical Engineering 9(2):7267. Available from: http://casopisi.junis.ni.ac.rs/index.php/FUMechEng/article/view/7267

  
  

  Abstract

  This review paper gives Excel functions for highly precise Colebrook’s pipe flow friction approximations developed by users. All shown codes are implemented as User Defined Functions – UDFs written in Visual Basic for Applications – VBA, a common programming language for MS Excel spreadsheet solver. Accuracy of the friction factor computed using nine to date the most accurate explicit approximations is compared with the sufficiently accurate solution obtained through an iterative scheme which gives satisfying results after sufficient number of iterations. The codes are given for the presented approximations, for the used iterative scheme and for the Colebrook equation expressed through the Lambert W-function (including its cognate Wright ωfunction). The developed code for the principal branch of the Lambert W-function has additional and more general application for solving different problems from variety branches of engineering and physics. The approach from this review paper automates computational processes and speeds up manual tasks.

  Abstract
  This review paper gives Excel functions for highly precise Colebrook’s pipe flow friction approximations developed by users. All shown codes are implemented as User [...]

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• The volatility of natural gas prices - Structural shocks and influencing factors

  L. Stajić, B. Đorđević, S. Ilić, D. Brkić

  Rev. int. métodos numér. cálc. diseño ing. (2021). Vol. 37, (4), 48

  
  

  Abstract

  The paper examines the primary drivers and factors influencing the volatility of natural gas prices in the world from January 2007 to July 2020. In addition to the narrow dependence between crude oil and natural gas prices, the influence of renewable energy production and coal production on the price of natural gas has been studied. For that purpose, the method of multiple linear regression was used. The results show that the volatility of natural gas prices significantly depends on the type of the shock in the natural gas market and that the total production of energy from renewable sources, production of coal and natural gas and the price of crude oil have a significant impact on the price of gas.

  Abstract
  The paper examines the primary drivers and factors influencing the volatility of natural gas prices in the world from January 2007 to July 2020. In addition to the narrow [...]

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• Offshore Oil and Gas Safety: Protection against Explosions

  D. Brkić, Z. Stajić

  Journal of Marine Science and Engineering (2021). 9(3), article 331.

  
  

  Abstract

  Offshore oil and gas operations carry a high risk of explosions, which can be efficiently prevented in many cases. The two most used approaches for prevention are: (1) the “International Electrotechnical Commission System for Certification to Standards Relating to Equipment for Use in Explosive Atmospheres” (IECEx) and (2) European “Atmosphere Explosible” (ATEX) schemes. The main shortcoming for the IECEx scheme is in the fact that it does not cover nonelectrical equipment, while for the ATEX scheme, it is due to the allowed self-certification for a certain category of equipment in areas with a low probability of explosions, as well as the fact that it explicitly excludes mobile offshore drilling units from its scope. An advantage of the IECEx scheme is that it is prescribed by the US Coast Guard for protection against explosions on foreign mobile offshore drilling units, which intend to work on the US continental shelf but have never operated there before, with an additional requirement that the certificates should be obtained through a US-based Certified Body (ExCB). Therefore, to avoid bureaucratic obstacles and to be allowed to operate with minimized additional costs both in the US and the EU/EEA’s offshore jurisdictions (and very possibly worldwide), all mobile offshore drilling units should be certified preferably as required by the US Coast Guard.

  Abstract
  Offshore oil and gas operations carry a high risk of explosions, which can be efficiently prevented in many cases. The two most used approaches for prevention are: (1) the [...]

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• Simplified Indirect Estimation of Pump Flow Discharge: An Example from Serbia

  M. Amon, M. Radić, Z. Stajić, D. Brkić, P. Praks

  Water (2021). 13(6), article 796.

  
  

  Abstract

  In the absence of a flowmeter or due to its inaccuracy, the flow rate at the discharge section of the pipeline following the observed pump can be roughly estimated if the pressure can be measured instead. To use the proposed procedure two main conditions should be achieved: (1) a manometer should be installed at the discharge pipeline between the pump and the flow regulation valve, and (2) the actual curve that relates pressure and flow for the observed pump unit should be known in advance. The described example is from Serbia, but it is of interest for any water pumping station with a submersible pump (installed in wells or tanks) where a limited number of adequate places for the measuring of flow are available (if any are available at all), but where the pressure at the discharge pipe of the observed pump can be measured. This simplified method can find applicability in installations in remote rural regions where limited resources are available. The results show that the calculated values of the flow obtained by the presented method deviate greatly in relation to the measured values provided by the portable ultrasonic flowmeter, up to 60% at one of the measuring points. However, in relation to the measured values provided by the permanently installed flowmeter the discrepancy is significantly lower (0.6–6.8%).

  Abstract
  In the absence of a flowmeter or due to its inaccuracy, the flow rate at the discharge section of the pipeline following the observed pump can be roughly estimated if the [...]

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• Suitability for coding of the Colebrook’s flow friction relation expressed by symbolic regression approximations of the Wright-ω function

  P. Praks, D. Brkić

  Reports in Mechanical Engineering (2020). Vol. 1, No. 1, 2020, pp. 174-179. ISSN: 2683-5894

  
  

  Abstract

  This article analyses a form of the empirical Colebrook’s pipe flow friction equation given originally by the Lambert W-function and recently also by the Wright ω-function. These special functions are used to explicitly express the unknown flow friction factor of the Colebrook equation, which is in its classical formulation given implicitly. Explicit approximations of the Colebrook equation based on approximations of the Wright ω-function given by an asymptotic expansion and symbolic regression were analyzed in respect of speed and accuracy. Numerical experiments on 8 million Sobol’s quasi-Monte points clearly show that also both approaches lead to the approximately same complexity in terms of speed of execution in computers. However, the relative error of the developed symbolic regression-based approximations is reduced significantly, in comparison with the classical basic asymptotic expansion. These numerical results indicate promising results of artificial intelligence (symbolic regression) for developing fast and accurate explicit approximations.

  Abstract
  This article analyses a form of the empirical Colebrook’s pipe flow friction equation given originally by the Lambert W-function and recently also by the Wright ω-function. [...]

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• List of Equations in https://doi.org/10.23967/j.rimni.2020.09.001

  P. Praks, D. Brkić

  Dejan Brkić's personal collection (2020). 59

  
  

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• Proper Use of Technical Standards in Offshore Petroleum Industry

  D. Brkić, P. Praks

  Journal of Marine Science and Engineering (2020). 8(8), article 555

  
  

  Abstract

  Ships for drilling need to operate in the territorial waters of many different countries which can have different technical standards and procedures. For example, the European Union and European Economic Area EU/EEA product safety directives exclude from their scope drilling ships and related equipment onboard. On the other hand, the EU/EEA offshore safety directive requires the application of all the best technical standards that are used worldwide in the oil and gas industry. Consequently, it is not easy to select the most appropriate technical standards that increase the overall level of safety and environmental protection whilst avoiding the costs of additional certifications. We will show how some technical standards and procedures, which are recognized worldwide by the petroleum industry, can be accepted by various standardization bodies, and how they can fulfil the essential health and safety requirements of certain directives. Emphasis will be placed on the prevention of fire and explosion, on the safe use of equipment under pressure, and on the protection of personnel who work with machinery. Additionally considered is how the proper use of adequate procedures available at the time would have prevented three large scale offshore petroleum accidents: the Macondo Deepwater Horizon in the Gulf of Mexico in 2010; the Montara in the Timor Sea in 2009; the Piper Alpha in the North Sea in 1988.

  Abstract
  Ships for drilling need to operate in the territorial waters of many different countries which can have different technical standards and procedures. For example, the European [...]

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• Air-Forced Flow in Proton Exchange Membrane Fuel Cells: Calculation of Fan-Induced Friction in Open-Cathode Conduits with Virtual Roughness

  D. Brkić, P. Praks

  Processes (2020). 8(6), article 686

  
  

  Abstract

  Measurements of pressure drop during experiments with fan-induced air flow in the open-cathode proton exchange membrane fuel cells (PEMFCs) show that flow friction in its opencathode side follows logarithmic law similar to Colebrook’s model for flow through pipes. The stable symbolic regression model for both laminar and turbulent flow presented in this article correlates air flow and pressure drop as a function of the variable flow friction factor which further depends on the Reynolds number and the virtual roughness. To follow the measured data, virtual inner roughness related to the mesh of conduits of fuel cell used in the mentioned experiment is 0.03086, whereas for pipes, real physical roughness of their inner pipe surface goes practically from 0 to 0.05. Numerical experiments indicate that the novel approximation of the Wright-ω function reduced the computational time from half of a minute to fragments of a second. The relative error of the estimated friction flow factor is less than 0.5%.

  Abstract
  Measurements of pressure drop during experiments with fan-induced air flow in the open-cathode proton exchange membrane fuel cells (PEMFCs) show that flow friction in its [...]

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• Artificial neural network as a tool for estimation of hydraulic resistance

  Ž. Ćojbašić, D. Brkić

  Tehnika (2011). 66 (6), 947-952,

  
  

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Articles (Documents not available in Scipedia)

• Discussion of “Friction modeling of flood flow simulations” by Vasilis Bellos, Ioannis Nalbantis, and George Tsakiris

  D Brkić, P Praks

  Journal of Hydraulic Engineering 146 (5), article 07020007, 2020

• Discussion of “Approximate analytical solutions for the Colebrook equation” by Ali R. Vatankhah

  D Brkić, P Praks

  Journal of Hydraulic Engineering 146 (2), article 07019011, 2020

• A possible publishing model profitable for authors

  D Brkić

  GRIN Verlag, 2019

• Correction: Brkić, D., and Praks, P. Accurate and efficient explicit approximations of the Colebrook flow friction equation based on the Wright ω-function. Mathematics 2019, 7, 34

  D Brkić, P Praks

  Mathematics 7 (10), article 951, 2019

• Discussion of “Economics and statistical evaluations of using Microsoft Excel Solver in pipe network analysis”

  D Brkić

  Journal of Pipeline Systems Engineering and Practice 9 (3), article 07018002, 2018

• Discussion of “Exact analytical solutions of the Colebrook-White equation”

  D Brkić

  Journal of Hydraulic Engineering ASCE 143 (9), article 07017007, 2017

• Discussion of “Gene expression programming analysis of implicit Colebrook–White equation in turbulent flow friction factor calculation”

  D Brkić

  Journal of Petroleum Science and Engineering 124, 399-401, 2014

• Discussion of “Method to cope with zero flows in Newton solvers for water distribution systems”

  D Brkić

  Journal of Hydraulic Engineering 140 (4), 456-459, 2014

• Very accurate explicit approximations for calculation of the Colebrook friction factor

  Ž Ćojbašić, D Brkić

  International Journal of Mechanical Sciences 67, 10-13, 2013

• Discussion of “Sustainable electric power system: Is it possible? Case study: Croatia”

  D Brkić

  Journal of Energy Engineering 138 (3), 163-164, 2012

• Discussion of “Jacobian matrix for solving water distribution system equations with the Darcy-Weisbach head-loss model”

  D Brkić

  Journal of Hydraulic Engineering 138 (11), 1000-1001, 2012

• Discussion of “Water distribution system analysis: Newton-Raphson method revisited”

  D Brkić

  Journal of Hydraulic Engineering 138 (9), 822-824, 2012

• Can pipes be actually really that smooth?

  D Brkić

  International Journal of Refrigeration 35 (1), 209-215, 2012

• Comparison of the Lambert W‐function based solutions to the Colebrook equation

  D Brkić

  Engineering Computations, 2012

• Determining friction factors in turbulent pipe flow

  D Brkić

  Chemical Engineering N.Y. 119 (3), 34-39, 2012

• Comments on "Experimental study of the pressure drop in the cathode side of air-forced open-cathode proton exchange membrane fuel cells"

  D Brkić

  International Journal of Hydrogen Energy 37 (14), 10963-10964, 2012

• Discussion of “Classroom activities to illustrate concepts of Darcy’s Law and hydraulic conductivity”

  D Brkić, V Mitrović

  Journal of Professional Issues in Engineering Education and Practice 137 (1 …, 2011

• Iterative methods for looped network pipeline calculation

  D Brkić

  Water Resources Management 25 (12), 2951-2987, 2011

• An explicit approximation of Colebrook's equation for fluid flow friction factor

  D Brkić

  Petroleum Science and Technology 29 (15), 1596-1602, 2011

• New explicit correlations for turbulent flow friction factor

  D Brkić

  Nuclear Engineering and Design 241 (9), 4055-4059, 2011

• Review of explicit approximations to the Colebrook relation for flow friction

  D Brkić

  Journal of Petroleum Science and Engineering 77 (1), 34-48, 2011

• Comments on “Settling velocities of particulate systems 15: Velocities in turbulent Newtonian flows”

  D Brkić

  International Journal of Mineral Processing 92 (3-4), 201-202, 2009

• Serbian gas sector in the spotlight of oil and gas agreement with Russia

  D Brkić

  Energy Policy 37 (5), 1925-1938, 2009

• An improvement of Hardy Cross method applied on looped spatial natural gas distribution networks

  D Brkić

  Applied Energy 86 (7-8), 1290-1300, 2009

• Serbian, Russian pipeline accord enhances European gas security

  D Brkić

  Oil & Gas Journal 106 (48), 52-54, 2008

• Systematic approach to natural gas usage for domestic heating in urban areas

  D Brkić, TI Tanasković

  Energy 33 (12), 1738-1753, 2008

• Prirodni gas kao gorivo za grejanje

  D Brkić

  Zadužbina Andrejević, 2006

• Određivanje graničnih parametara upotrebe prirodnog gasa u Beogradu

  D Brkić

  University of Belgrade, Faculty of Mining and Geological Engineering, 2005