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1

An efficient iteration procedure for form finding of slack cables under concentrated forces

Orynyak Igor, Guarracino Federico, Modano Mariano, Mazuryk Roman

Archives of Civil Engineering

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2022

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Vol. 68, nr 2

645--663

EN

The goal of paper is the development and demonstration of efficiency of algorithm for form finding of a slack cable notwithstanding of the initial position chosen. This algorithm is based on product of two sets of coefficients, which restrict the rate of looking for cable geometry changes at each iteration. The first set restricts the maximum allowable change of absolute values of positions, angles and axial forces. The second set takes into account whether the process is the converging one (the signs of maximal change of parameters remain the same), so that it increases the allowable changes; or it is a diverging one, so that these changes are discarded. The proposed procedure is applied to two different methods of simple slack cable calculation under a number of concentrated forces. The first one is a typical finite element method, with the cable considered as consisting of number of straight elements, with unknown positions of their ends, and it is essentially an absolute coordinate method. The second method is a typical Irvine’s like analytical solution, which presents only two unknowns at the initial point of the cable; due to the peculiarity of implementation it is named here a shooting method. Convergence process is investigated for both solutions for arbitrary chosen, even very illogical initial positions for the ACM, and for angle and force at the left end for SM as well. Even if both methods provide the same correct convergent results, it is found that the ACM requires a much lower number of iterations.

2

A simple technique for approximate evaluation of permeability and skin of a dry gas zone with low to moderate permeability using wellhead pressure data

Szpunar T., Budak P., Dziadkiewicz M.

Nafta-Gaz

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2018

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R. 74, nr 12

905--918

EN

This paper presents a technique for approximate evaluation of permeability and skin of a dry gas zone with low to moderate permeability. The herein given technique may be used for analyzing the wellhead buildup pressure data of a gas well. The results obtained using the presented technique are approximate, because of some simplifying assumptions of the mathematical model and use of the classical method of downhole pressure calculation in static gas column, which is known to be of rather moderate accuracy. In a computer program (not shown) we used the trial and error method to improve the accuracy of down hole pressure calculation and for the evaluation of the average value of gas deviation factor. In the case of thick, highly permeable gas zones, the duration of wellhead pressure build up time may be too short to obtain reliable results. The procedure of execution of the presented technique is very similar to that of the well known “slug test” method, which is used for the evaluation of permeability and skin of reservoirs which do not flow to the surface, or for analyzing the drill stem test flow period data. Contrary to “Horner type” analysis of pressure build up data, neither the flow rate of gas nor the flow duration, need not be known. The procedure of permeability calculation is shown using five examples of gas wells from the domestic oil industry. To facilitate calculations all equations were converted to the engineering system of units.

PL

W artykule zaproponowano sposób obliczania przepuszczalności i skin efektu odwiertu gazowego o niskiej i umiarkowanej przepuszczalności warstwy gazonośnej. Niniejszy sposób można zastosować do analizy krzywej odbudowy ciśnienia głowicowego po krótkotrwałej eksploatacji gazu z odwiertu. W przeciwieństwie do interpretacji danych metodą Hornera nie jest potrzebna znajomość wydatku gazu oraz czasu, przez jaki wydatek ten był utrzymywany. Podano model matematyczny leżący u podstaw proponowanej metody oraz pięć przykładów obliczeń dla odwiertów z krajowego przemysłu naftowego. Należy podkreślić, że do obliczeń przepuszczalności ani wydatek gazu podczas wypływu z odwiertu, ani sumaryczna jego objętość i czas trwania wypływu nie muszą być znane, natomiast konieczna jest znajomość parametrów i składu gazu oraz pojemności odwiertu z uwagi na użycie metod bilansu masowego zamiast zasady superpozycji rozwiązań przyjętej w metodzie Hornera. W przypadku grubych, wysoce przepuszczalnych stref gazowych czas narastania ciśnienia w odwiercie może być zbyt krótki, aby uzyskać wiarygodne wyniki. W programie komputerowym (niezaprezentowany) wykorzystano metodę „prób i błędów”, aby poprawić dokładność obliczeń ciśnienia dennego w odwiercie oraz oszacowania średniej wartości współczynnika ściśliwości gazu. Procedura interpretacji danych za pomocą prezentowanego sposobu jest bardzo podobna do powszechnie znanej metody slug test, która jest używana do oceny przepuszczalności i skin efektu dla złóż cieczy, z których nie ma wypływu na powierzchnię, lub do analizy danych uzyskiwanych podczas opróbowań otworów. Równania przyjęte do obliczeń zostały przeliczone z systemu jednostek SI na system jednostek przyjmowany w przemyśle naftowym.

3

Force-Velocity Characteristics of Individual Human Skeletal Muscles: TBCIat and TBCIong. Outline of the Method

Kornecki S., Siemieński A.

International Journal of Occupational Safety and Ergonomics

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1998

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Vol. 4, No. 1

75--83

EN

The aim of the work is to outline a procedure of finding force-velocity (F-V) characteristics (F = f(V)) of individual skeletal muscles of the human locomotor system. The presentation is based on an example concerning extensors of the elbow joint: the lateral and long heads of triceps brachii (TBCIat and TBCIong). The experimental part of the procedure involves a natural movement of using the upper extremity to push an external object of variable, adjustable load, engaging both the elbow and shoulder joint. Five men aged 23 took part in the experiment. Their task was to push the handle of a physical pendulum whose moment of inertia could be adjusted within the range of 58 kg ∙ m2-450 kg ∙ m2, so as to give it maximum angular velocity. During each trial the movement of the trunk, of the upper extremity and of the pendulum was video recorded and the force applied with the hand to the handle of the pendulum was measured. In order to find the F-V characteristics a simulation model SHOULDER was used, which is capable of solving the synergy problem for muscles of the arm and the shoulder girdle. It was found that despite considerable dispersion of experimental points the respective regression lines revealed a clear tendency of decreasing muscle force for increased shortening velocity of the monoarticular head (TBCIat) and of increasing muscle force for increased lengthening velocity of the Particular head (TBCIong) of the triceps brachii muscle.