Results 1 - 10 of 6627
Results 1 - 10 of 6627. Search took: 0.035 seconds
|Sort by: date | relevance|
[en] Highlights: • Flow patterns in large cylinder arrays are experimentally studied. • Different flow patterns occur after the first row due to lower turbulence levels. • Bistable flows are identified in the array at a given transversal spacing ratio. • Trends are identified for the turbulence energy distribution along the rows. • The last row is at higher risk of vibration due to turbulent buffeting. - Abstract: Studies on flow-induced vibrations in large tube bundles are usually focused solely on frequency analysis, without considering the flow patterns which are responsible for the fluid forces. Furthermore, investigations which involve variations in the spacing ratios do not separate transversal and longitudinal proximity effects. The purpose of this article is to separately analyze the influence of the transversal (T/D) and longitudinal (L/D) spacing ratios of a confined in-line cylinder array with five rows on the flow characteristics and to identify flow patterns. The laser Doppler anemometry technique was employed to acquire the mean velocity and its fluctuations in the transversal and longitudinal directions between the cylinder rows. Strouhal numbers and regimes reported in the literature were identified in the experiments. The same regime did not always persist along all cylinder rows for a given spacing ratio, as a result of the combined longitudinal and transversal proximity effects and also of the generation of turbulence by the array. For the smallest T/D ratio, a quasi-steady behavior associated with the biased flow pattern was noted in the experimental set-up and flip-flopping was observed in one case. Additionally, the flow characteristics in these arrays diverged from tube bundle classifications described in the literature. The behavior of the fluid forces and susceptibility to vibrations in the array were predicted based on the turbulence intensity of the incident flow of the cylinders. The results reinforced the need to extend flow pattern investigations to arrays with more cylinder rows and to consider both transversal and longitudinal proximity effects, when studying flow-induced vibrations.
[en] In the 1980’s Manchester University carried out over 110 tests on cylinders with a composite wall (steel-concrete-steel) subjected to external pressure as already reported in the literature. This paper describes further tests on 9 cylinders with a composite wall and a dome end subjected to external pressure and reports the results and compares them with theory. The cylinders were 500 mm diameter and 1250 mm long and four of them had penetrations through the cylinder wall. These tests were carried out under contract for Tecnomare SpA of Italy and have not been previously reported because of confidentiality reasons. The agreement between test behaviour, failure load and the theory developed at Manchester University is good. The philosophy for the design of such vessels for seabed structures is discussed and a ‘depth margin’ method proposed as it is a more realistic way of applying safety. Examples of designs for different depths are given and compared with the predicted failure pressure. (Author)
[en] In this paper, we study a thick cylinder with uncertain external pressure. The traditional model was extended in fuzzy context. We use the governing equation which was rewritten as delta operator equation. The interpretations of external pressure are based on triangular, trapezoidal and Gaussian fuzzy numbers. By Adomian Decomposition Method gives an approximate solution. The maximal and minimal radial stresses are obtained, corresponding to the level cut. Finally, we get the methodology for simulating uncertain problems in fuzzy context and utility of each membership function. (paper)
[en] We present an alternative method to determine in a simpler and quicker way the reaction flux in circular loops and saddle-coil sets, as applied in rock magnetometers. The dipole may be in an arbitrary direction and on an arbitrary position with respect to the sensing coil set. After the evaluation of the reaction flux, several test experiments are presented which verify the calculations. Finally, the impact of the image effect on the signal uniformity in commercial rock magnetometers is discussed. (orig./BUD)
[en] Cylindrical structures such as pipes and shafts are widely used in various industrial facilities. Recently, researches on magnetostrictive transduction of torsional waves have been actively reported for the nondestructive evaluation of those cylindrical structures. However, the existing magnetostrictive patch transducer has somewhat inconvenient and time. Consuming process like patch bonding to a structure since it should employ a magnetostrictive patch having strong magnetostriction. To overcome these limitations of the existing transducer, in this work, we develop a novel modular magnetostrictive transducer to generate and measure torsional waves to inspect a cylindrical structure. The proposed transducer can be applied as viscous liquid coupling with shear couplant or dry coupling without coupling media instead of patch bonding to a structure. We describe a detailed structure of the modular transducer and conduct some experiments to verify its performance
[en] This contribution describes the effect of a load shape on load acceleration at the start of an electric hoist. The emphasis is on a comparison of acceleration course of loads. Two loads with entirely different shape-a load with a cuboid shape and one with a cylinder shape, were chosen. Improved mathematical theory for the start of an electric hoist with three degrees of freedom is used. Thus, we measured the acceleration of the electric hoist, the wire rope end and the load center of gravity for two loads with different shape.
[en] Results of the executed researches on prediction of an individual residual operating life of engines are pre-sented in article. Prediction is based on the diagnostic information on technical condition of engines ob-tained during the carrying out their maintenance and repair. The analytical equation, the describing regu-larities of change of diagnostic parameters on an operating time and its graphic interpretation are given. The forecasting technique of a residual operating life of mechanisms of engines with use of the lower fidu-cial bound of distribution of their practices to the limiting condition is offered. The technique is approved on the example of forecasting of a residual operating life of cylinder-piston group of the ZMZ-40524.10 engine. (paper)
[en] The supply of water to the cylinders of the diesel engine is one way to reduce the maximum temperature in the combustion zone of the fuel. A reduction of the maximum combustion temperature allows reducing the formation of nitrogen oxides and improving the environmental characteristics of the engine, which remains one of the urgent tasks at the present stage of their development. The methods of supplying water to the engine together with air at the inlet and with the fuel into the cylinder are well known. This article considers the influence of the way the water is supplied to the engine cylinders on its environmental characteristics. It presents the results of experimental studies on the internal combustion engine and analysis of the method of adding water on the engine performance from exhaust gas toxicity, operating efficiency and its thermal state. There are marked different effects on the motor performance of the method of adding water. (paper)