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Collaborating Authors
The idea of the present study is to apply the advantages of neural networks to the choice of an optimum ship screw propeller as an introduction to more complex ship design problems. The neural network was created and trained to provide the characteristics of the maximum efficiency propeller. To train the network, data regarding the blade number, advance speed, delivered power, rate of revolution, diameter, pitch ratio, and expanded area ratio as well as thrust and efficiency were set as inputs and outputs. The testing of the network proved its efficiency, which makes it a reliable tool for the preliminary screw propeller selection.
Study on the Ultimate Strength of Welded Thin-Walled Square Tubes Under Axial Compression
Xu, Liang (Key Laboratory of High Performance Ship Technology (Wuhan University of Technology) / Ocean and Structural Engineering, School of Transportation, Wuhan University of Technology) | Zhu, Ling (Key Laboratory of High Performance Ship Technology (Wuhan University of Technology) / Ocean and Structural Engineering, School of Transportation, Wuhan University of Technology) | Zhang, Shengming (Global Technology Centre, Lloyd’s Register EMEA) | Sun, Kun (Key Laboratory of High Performance Ship Technology (Wuhan University of Technology))
ABSTRACT This paper investigates the ultimate bearing capacity of welded thinwalled square tubes with small aspect ratios under axial compression, by experimental and numerical methods. Three groups of square tubes with different sizes were tested in the experiments. Based on the experimental model, the finite element software ABAQUS was applied to perform numerical simulations of the ultimate bearing capacity of square tubes subjected to the axial compression. In numerical simulations, the real material properties and the initial imperfection of the tested model were taken into account. In addition, the influence of the welding residual stress on the accuracy of the numerical calculations was considered. The numerical results were compared with the experiments to validate the accuracy and applicability of the established numerical model, which was then applied to investigate the effect of slenderness parameter on the ultimate bearing capacity of the welded thin-walled square tubes. INTRODUCTION Welded thin-walled square tube structures are widely used in ship structures. Much literature has been devoted to investigating the ultimate bearing capacity of such structures under axial compression. Chiew et al (1987) verified the calculation formula of the ultimate bearing capacity of thin-walled square tubes under axial pressure and bending moment at the same time, and carried out parameter analyses such as width to thickness ratio, slenderness parameter and section shape. Based on Johnson Ostenfeld's formula, Faulkner (1973) presented an analytical method of critical stress for inelastic buckling of stiffened plate structures, which took into account the effective strip width and welding residual stress. This method was accepted by the British navy and applied to the structural design of the box girders. Imtazkhan, Zhang (2011) studied the influence of welding induced geometric deformation and residual stress on the ultimate longitudinal compressive strength of plates and stiffened plates by nonlinear finite element analysis considering the thickness range of plates with different residual stress levels. The residual stresses of plates and stiffened plates were simulated in detail, and the influence of welding defects on the structure was studied. Pircher et al (2002) thought that the square tube was usually obtained by plate welding, and the welding would make the residual stress and initial deformation have a greater impact on its strength. The finite element analysis method considering geometric nonlinearity and material nonlinearity was used to simulate the welding process and behavior of the square tube under axial pressure, which had a good correlation with the test results. The condition of model buckling in welding process was established, and the design method of welded square tubes was put forward based on it. Shen (2015) developed a finite element model with ANSYS software which considering the nonlinearity of materials and geometric defects to study the deformation and ultimate strength of welded thin-walled rectangular section beams and columns. And the parameter analysis was carried out and the formula for calculating the maximum in-plane stress of the model was put forward. Usami and Fukumoto (1984) studied the strength of welded box compression members made of high strength steel. In the theoretical study, according to the concept of effective width, an approximate method to calculate the local buckling of plates was obtained, and compared with the experimental results, the accuracy of the method was verified.
Optimization of CO2 WAG Processes in a Selected Carbonate Reservoir-An Experimental Approach
Amin, Mohamed E. (United Arab Emirates University) | Zekri, Abdulrazag Y. (United Arab Emirates University) | Almehaideb, Reyadh (United Arab Emirates University) | Al-Attar, Hazim (United Arab Emirates University)
Abstract Miscible gas flooding using carbon dioxide is currently being investigated as a possible EOR process for a number of United Arab Emirates (UAE) reservoirs. It has high potential to improve oil recovery in addition to possibly utilizing most of the carbon dioxide emissions from industrial sources. The major factors affecting implementation of CO2 floods are the availability of CO2 at economic prices (generally within 2-3 $/MSCF) and the net utilization ratio of CO2 per barrel of additional oil recovered. Typical net utilization of CO2 for well-designed floods vary from field to field but on average has been estimated at 5.5 MSCF CO2 per additional barrel of oil in a US EOR overview study by Broome et al.1 and between 4-6 MSCF/barrel by a more recent study by Jeschke et al.. At other fields it might be as high as 15 MSCF/barrel or more. Minimizing net utilization requires controlling the high mobility ratio for miscible gas injection which causes lower sweep due to gas channeling and by-passing of the oil in the reservoir. To control the mobility ratio, the Water-Alternating CO2-Gas (WAG) technique is proposed by injecting alternately small solvent [CO2] and water slugs. The slug of water reduces the speed of the solvent and solvent fingering thus improving the mobility ratio of the injected fluids to fluids in place. The objective of this work is to experimentally assess the recovery of oil with CO2 injection in a selected UAE carbonate reservoir. Two types of CO2-flooding experiments were conducted, continuous miscible CO2 injection and CO2-WAG injection using a specialized experimental rig. The effects of changing the CO2-Water ratio and WAG timing on the overall performance of the flood were investigated. All laboratory tests were conducted under controlled conditions of pressure and temperature corresponding to field conditions. Results of this laboratory investigation reveal a general trend of improved oil recovery with increased volume of CO2 inside core samples during the flood process. The observed ultimate oil recoveries range from 52 percent with continuous water injection to 72 percent of the original oil in place with continuous CO2 injection over the full period of the experiment with recoveries of the CO2-WAG floods falling in between. The optimum CO2-WAG ratio was found to occur at 1:2. The outcomes of this work should contribute to our understanding of WAG CO2 floods for the UAE reservoirs and supports the ongoing R&D efforts made by the operating oil companies in the UAE towards application of CO2-WAG floods
- North America (1.00)
- Asia > Middle East > UAE > Abu Dhabi Emirate > Abu Dhabi (0.29)
- North America > United States > California > Sacramento Basin > 4 Formation (0.99)
- Asia > Middle East > UAE > Abu Dhabi > Rub' al Khali Basin > Bu Hasa Field > Thamama Group > Shuaiba Formation (0.99)
Laboratory Investigation of Static Elastic Properties Assessment With Pressuremeter Testing
Elkhoury, Jean E. (Schlumberger-Doll Research) | Elias, Quincy K. (Schlumberger-Doll Research) | Bรฉrard, Thomas (Schlumberger-Riboud Product Center) | Peyret, Emilie (Schlumberger Wireline) | Prioul, Romain (Schlumberger-Doll Research)
ABSTRACT: Pressuremeter testing (PMT) is a formation test that consists of inflating a cylindrical packer inside a borehole, while measuring radial deformation or injected volume as a function of packer pressure. Measurement of packer pressure and injected volume provides the required data to infer formation shear modulus (G), if the packer stiffness is known. PMT is a well-established technique in soil mechanics and has been extensively used in mining and civil engineering. However, its application to rock mechanics has so far remained limited to small diameter packers and very shallow boreholes, mainly due to a lack of sufficiently stiff packer systems. PMT could provide an in-situ measurement of G on the meter length scale, for typical field scale packers. Moreover, if the Poisson ratio is known or estimated a priori, then the Young Modulus (E) can be obtained without resorting to sample coring and laboratory testing. To gain insight into PMT and its potential applicability to deep downhole formations, we explore PMT at the laboratory scale. We present results of experiments that use a stiff, custom-built packer to infer G from the applied pressure and injected fluid volume. Packer calibration was performed in stainless steel cylinder with known elastic properties and geometry. And, a variety of analog samples, such as Lexan and Plexiglass were tested. We explored the influence of packer aspect ratio L/D (by varying packer length, L while maintaining packer diameter D) on the inferred shear moduli. Our lab-scale PMT measurements and the interpretation framework provide precise estimates of G, while the accuracy increases with increasing packer length. Further parameter space exploration, including rock samples, would provide additional insight into the approaches of static elastic properties assessment using PMT. Our experimental results support the feasibility of PMT for inferring G and E. Additionally, the experimental results provide an indication of possible challenges that field scale trials might encounter. 1 Introduction Pressuremeter testing (PMT) is a formation test that consists of inflating a cylindrical packer inside a borehole, while measuring the radial deformation or injected volume as a function of packer pressure. Knowing the stiffness of the packer, PMT provides in situ static shear modulus, G, on the meter length scale, for typical field scale packers (Figure 1). Furthermore, if the Poisson ratio is known or estimated a priori, then the Young Modulus can also be obtained, without resorting to sample coring and laboratory tests.
- Europe (0.68)
- North America > United States > Texas (0.46)
ABSTRACT This research performed undrained cyclic shear tests on remolded specimens of Taipei sand by a hollow cylindrical torsional shear apparatus to obtained their liquefaction resistance. The maximum shear moduli were obtained by resonant column tests. RemoIded samples with different fines contents were prepared. The influences of fines content on the relationship between maximum shear modulus and liquefaction resistance were studied. To obtain a unique relationship between maximum shear modulus and liquefaction resistance, the maximum shear modulus is to be normalized by the effective confining pressure and a fabric factor. Under the conditions of same maximum shear modulus, liquefaction resistance decreases with increasing fines content. INTRODUCTION Liquefaction generally includes all phenomena involving excessive deformations as a result of transient or repeated disturbance of saturated granular soils. Initial liquefaction indicates a condition where, during the course of cyclic stress applications, the residual pore water pressure on completion of any full stress cycle becomes equal to the applied confining pressure. Cyclic mobility represents a condition in which cyclic stress applications develop a peak cyclic pore pressure ratio of 100% and subsequent cyclic stress applications cause limited strains to develop because the soil dilates during the deformation. In this paper liquefaction resistance is defined as the cyclic stress ratio required to cause soil to reach initial liquefaction at a certain number of cyclic loading. The first approach is to assume that the factors of stress history and density, which control liquefaction resistance, also affect penetration resistance. The blow count obtained by the standard penetration test or the cone tip resistance is related to the liquefaction resistance of the deposit by means of empirical equations based on penetrometer measurements at sites that did (or did not) liquefy, supplemented by the results of large-scale liquefaction tests.