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1
Alzaharnah, Iyad T. „Thermal Stresses in Thick Walled Cylinders due to a Periodic Moving Heat Source: Effect of Material Properties“. Advanced Materials Research 445 (Januar 2012): 627–30. http://dx.doi.org/10.4028/www.scientific.net/amr.445.627.
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nternal heating of hollow cylinders with moving periodic heat source is examined in relation to surface treatment applications. This study includes three different cylinder materials, namely aluminum, nickel and titanium. Effective stresses in the cylinder wall are found to be mainly attributed to longitudinal temperature gradients. The aluminum cylinder shows sharper longitudinal temperature gradients as compared to the nickel and the titanium cylinders, which is due to the high value of the aluminum specific heat capacity. However, the larger Eα (elasticity modulus × thermal expansion coefficient) values for nickel cylinder result in higher levels of stress although nickel and titanium cylinders exhibit similar longitudinal temperature profiles. During dwelling time for the heating source at a certain spot, titanium cylinder exhibits lower levels of temperature increase as compared to aluminum and nickel cylinders, due to its lower value of thermal conductivity.
2
Willems, Harco. „“Cylinder seals for the lower classes”“. Zeitschrift für Ägyptische Sprache und Altertumskunde 145, Nr. 2 (02.11.2018): 187–204. http://dx.doi.org/10.1515/zaes-2018-0017.
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Summary Egyptologists have paid much attention to inscribed administrative seals and their impressions. By contrast, the so-called figure seals, which render no or hardly any text, but instead use icons and signs inspired on hieroglyphs which however yield no coherent sense, have received far less attention. Usually this material is related to the lower strata of society. According to current interpretations, it is rooted in the Egyptian culture of the later Old Kingdom and First Intermediate Period. The phenomenon would be a corollary of the decreasing prominence of central state authority in this era. Proceeding from a number of recent early Old Kingdom finds from al-Shaykh Saʽīd/Wādī Zabaydā, the present article argues that a) figure seals were continually in use from the late Predynastic until the late Old Kingdom and b) different from what is commonly assumed, stamp seals were in existence long before the late Old Kingdom. The article challenges the relationship between these object categories and developments specifically in late Old Kingdom Egypt.
3
Li, Zhihua, Jane H. Davidson und Susan C. Mantell. „Numerical Simulation of Flow Field and Heat Transfer of Streamlined Cylinders in Cross Flow“. Journal of Heat Transfer 128, Nr. 6 (23.12.2005): 564–70. http://dx.doi.org/10.1115/1.2188463.
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The drag and convective heat transfer coefficients along the outer surface of lenticular and elliptical tubes with minor-to-major axis ratios of 0.3, 0.5, and 0.8 were determined numerically for cross-flow Reynolds numbers from 500 to 104. The two-dimensional, unsteady Navier-Stokes equations and energy equation were solved using the finite volume method. Laminar flow was assumed from the front stagnation point up to the point of separation. Turbulent flow in the wake was resolved using the shear stress transport k-ω model. Local heat transfer, pressure and friction coefficients as well as the total drag coefficient and average Nusselt number are presented. The results for streamlined tubes are compared to published data for circular and elliptical cylinders. Drag of the elliptical and lenticular cylinders is similar and lower than a circular cylinder. Drag can be reduced by making the streamlined cylinders more slender. Drag is relatively insensitive to Reynolds number over the range studied. An elliptical cylinder with an axis ratio equal to 0.5 reduces pressure drop by 30–40% compared to that of a circular cylinder. The Nusselt numbers of lenticular and elliptical cylinders are comparable. The average Nusselt number of an elliptical or lenticular cylinder with axis ratio of 0.5 and 0.3 is 15–35% lower than that of a circular cylinder.
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Wailanduw, A. Grummy, Triyogi Yuwono und Wawan Aries Widodo. „Flow Characteristics around Four Circular Cylinders in Equispaced Arrangement near a Plane Wall“. Applied Mechanics and Materials 493 (Januar 2014): 245–50. http://dx.doi.org/10.4028/www.scientific.net/amm.493.245.
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The flow characteristics around four circular cylinders in equispaced arrangement located near a plane wall were investigated experimentally. The pressure distributions on the each cylinder surface and on the plane wall were measured for a spacing ratio L/D= 1.5 (L, center to center spacing between cylinders; D, diameter) and G/D= 0.2 (G, gap spacing between cylinder surface and the plane wall) in a uniform flow at a Reynolds Number of 5.3 x 104. The 2D U-RANS numerical simulation with k-ω SST as viscous model was used to visualize the flow phenomena occured around the cylinders. The results showed that the flow tend to be biased on the upper side of cylinders configuration. It causes the stagnation at the upstream cylinders occured at lower side of cylinders and results a formation of a narrower wake behind the third cylinder and a wider wake behind the fourth cylinder.Keywords: equispaced arrangement, circular cylinders, plane wall
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Qin, Bin, Md Mahbub Alam und Yu Zhou. „Free vibrations of two tandem elastically mounted cylinders in crossflow“. Journal of Fluid Mechanics 861 (21.12.2018): 349–81. http://dx.doi.org/10.1017/jfm.2018.913.
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The paper presents an experimental investigation on the flow-induced vibrations of two tandem circular cylinders for spacing ratio $L/D=1.2{-}6.0$ and reduced velocity $U_{r}=3.8{-}47.8$, where $L$ is the cylinder centre-to-centre spacing and $D$ is the cylinder diameter. Both cylinders are allowed to vibrate only laterally. Extensive measurements are conducted to capture the cylinder vibration and frequency responses, surface pressures, shedding frequencies and flow fields using laser vibrometer, hotwire, pressure scanner and PIV techniques. Four vibration regimes are identified based on the characteristics and generation mechanisms of the cylinder galloping vibrations. Several findings are made on the mechanisms of vibration generation and sustainability. First, the initial states (vibrating or fixed) of a cylinder may have a pronounced impact on the vibration of the other. Second, alternating reattachment, detachment, rolling up and shedding of the upper and lower gap shear layers all contribute to the vibrations. Third, the gap vortices around the base surface of the upstream cylinder produce positive work on the cylinder, sustaining the upstream cylinder vibration. Fourth, reattachment, detachment and switching of the gap shear layers result in largely positive work on the downstream cylinder, playing an important role in sustaining its vibration.
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Hattori, Yuji, und Ryu Komatsu. „Mechanism of aeroacoustic sound generation and reduction in a flow past oscillating and fixed cylinders“. Journal of Fluid Mechanics 832 (26.10.2017): 241–68. http://dx.doi.org/10.1017/jfm.2017.668.
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The aeroacoustic sound generated in a flow past two cylinders, one of which is oscillating and the other is fixed, is studied by direct numerical simulation. This problem involves key ingredients of the aeroacoustic noise generated from wind turbines, helicopters, axial flow fans and other turbomachinery: flow, a moving body and a fixed body. The corrected volume penalization method is successfully applied to resolve the sound pressure of aeroacoustic waves as a solution of the compressible Navier–Stokes equations. The sound pressure was shown to be in good agreement with the prediction by the Ffowcs Williams–Hawkings aeroacoustic analogy, which takes account of the cylinder motion, confirming the accuracy of the corrected volume penalization method. Prior to the case of two cylinders, sound generation in flow past a single oscillating cylinder is considered. The fluid motion can be either periodic or non-periodic depending on the frequency and the amplitude of cylinder oscillation. The acoustic power is significantly reduced when the fluid motion locks in to a frequency lower than the natural frequency of vortex shedding from a fixed cylinder. When a fixed cylinder is added, the acoustic power depends strongly on the distance between the cylinders, since that determines whether synchronization occurs and the phase difference between the three forces: the lift forces exerted on the two cylinders and the inertial force due to volume displacement effect of the oscillating cylinder. In particular, significant sound reduction is observed when the fixed cylinder is placed upstream and the frequency of the cylinder oscillation is set to the frequency for which the acoustic power is minimized in the single-cylinder case.
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Garg, Manish, Dharmpal Deepak und V. K. Gupta. „FE modeling of creep in linear and non-linear FGM cylinder under internal pressure“. Multidiscipline Modeling in Materials and Structures 10, Nr. 1 (03.06.2014): 94–105. http://dx.doi.org/10.1108/mmms-10-2012-0016.
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Purpose – The purpose of this paper is to investigate creep in an internally pressurized thick-walled, closed ends cylinder made of functionally graded composite, having linear and non-linear distribution of reinforcement, using finite element (FE) analysis. Design/methodology/approach – FE-based Abaqus software is used to investigate creep behavior of a functionally graded cylinder. The cylinder is made of composite containing linear and non-linearly varying distributions of reinforcement along the radius. The creep behavior has been described by Norton's power law. The creep stresses and strains have been estimated in linear and non-linear functionally graded materials (FGM) cylinders and compared with those estimated for a similar composite cylinder but having uniform distribution of reinforcement. Findings – The radial stress in the composite cylinder is observed to decreases over the entire radius upon imposing linear or non-linear reinforcement gradients. However, the tangential stress in the cylinder increases near the inner radius but decreases toward the outer radius, on imposing linear or non-linear reinforcement gradients. The creep strains in the FGM cylinders are significantly lower than those observed in a uniform composite cylinder. Originality/value – The creep strains in an internally pressurized functionally graded thick composite cylinder could be reduced significantly by employing non-linear distribution of reinforcement along the radial direction.
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Tang, Zhong, Haotian Zhang, Yuepeng Zhou und Yu Li. „Mutual Interference and Coupling Response of Multicylinder Vibration among Combine Harvester Co-Frame“. Shock and Vibration 2019 (16.06.2019): 1–14. http://dx.doi.org/10.1155/2019/1584391.
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Unbalanced vibrations of axial threshing cylinders on a combine harvester were coupled to each other through a frame. The intensified unbalanced vibration will shorten the working life of the axial threshing cylinder. In this paper, the theoretical modes of the axial threshing cylinder were carried out by using finite element analysis software ANSYS. The axis trajectory and speed fluctuation of the axial threshing cylinder under no-load state and threshing state were tested and analyzed. According to the amplitude and axis trajectory of the transmission shaft, as well as the variation law of the axial threshing cylinder speed, the influence of rice straw on the vibration under the threshing state was revealed. The rotation speeds of cylinder I and cylinder III were adjusted, and the amplitude of cylinder II transmission shaft was analyzed when cylinder II was under stable condition. Then the disturbance and coupling relationships among the unbalanced vibration of axial threshing cylinders were compared. Test results showed that the rotational frequency of the axial threshing cylinder was not in its resonance interval at rated speed. When the axial threshing cylinder was threshing, the horizontal amplitude increased by 0.366 mm. The vertical amplitude increased by 0.697 mm. The speed decreased from 763 rpm to about 750 rpm. The rotational frequency of the axial threshing cylinder would not cause the resonance. With the feeding of rice, the amplitude of the axial threshing cylinder increased slightly and the operating speed was lower than the rated speed. The unbalanced vibration of the axial threshing cylinder transmitted along the frame and coupled with each other, causing the vibration of the axial threshing cylinder to be intensified.
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Попиков, Viktor Popikov, Жданов, Yuriy Zhdanov, Канищев und Denis Kanishchev. „Improvement of technological equipment of the unit for removal of logging residues from the forest fringe in the thinnin“. Forestry Engineering Journal 5, Nr. 3 (15.11.2015): 210–19. http://dx.doi.org/10.12737/14169.
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The technique of optimization of the provisions of attachment points of hydraulic cylinders lifting mechanism, which takes into account, the fact that using standard cylinders with certain minimum and maximum length and stroke, when the distance from the axis of rotation of the boom to the upper hinge cylinder also changes the distance from the axis of rotation of the boom to the lower hinge cylinder. The tests described and tech-nology unit carried out in the areas of protective forest plantations, showed results that match the original requirements, which indicates the effectiveness of the work.
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LOCK, G. S. H., und W. J. O’CALLAGHAN. „FLOW THROUGH A ROW OF CLOSELY-SPACED CIRCULAR CYLINDERS NORMAL TO A COLD WATER STREAM“. Transactions of the Canadian Society for Mechanical Engineering 12, Nr. 3 (September 1988): 139–47. http://dx.doi.org/10.1139/tcsme-1988-0020.
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Flow near a row of parallel circular cylinders standing normal to a cross flow has been investigated experimentally. The cylinders spanned the height of the test section in a water tunnel in which the temperature was maintained close to the freezing point. Reynolds numbers, based on the mean bulk water velocity and the cylinder diameter, ranged between 3 x 103 and 3 x 104. The gap-diameter ratio g/D was set at five nominal values: 0.49, 0.20, 0.15, 0.10 and 0.06. For this range of conditions, static pressure readings were taken around the cylinder surfaces and at points well upstream and downstream of the cylinders. The overall static pressure change was converted into a pressure loss coefficient whose dependency on Reynolds number and gap-diameter ratio has been studied. The cylinder surface pressure profiles were used to determine flow behaviour in the gap region and in the wake. A critical transition at free stream Reynolds numbers much lower than that corresponding to a single cylinder was evident; a gap-diameter ratio near to 0.15 appeared to separate two different flow regimes. A cellular wake was often observed and found to be either metastable or bistable.
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Guo, Hui Fen, Chenxiao Yang und Li Li. „Study on the dynamics of chitosan/cotton fiber in an airflow around two rotating cylinders“. Textile Research Journal 88, Nr. 18 (20.06.2017): 2035–43. http://dx.doi.org/10.1177/0040517517715082.
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To predict chitosan/cotton yarn properties in ring spinning, a particle-level simulation method has been used to simulate the dynamics of the fibers with different initial positions in three-dimensional airflow around counter-rotating cylinders. The results show that the fibers near the cylinder end-face can leave two cylinders’ nip and move around the top cylinder, thus form fly waste. It is good to entangle other fibers as this gives the fiber greater bending energy. Compared with cotton fiber, the axial-direction deflections of the tail-ends of chitosan fibers near the cylinder center are much greater, while their bending energies are much lower, thus forming a wide triangle zone and reduced fiber–fiber cohesion force and yarn strength. To demonstrate the simulation results, a series of spinning experiments are completed, which tally with the predictions.
12
Praburam, G. „Lower‐hybrid quasimode decay in a plasma cylinder“. Physics of Fluids B: Plasma Physics 3, Nr. 7 (Juli 1991): 1576–78. http://dx.doi.org/10.1063/1.859676.
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13
Hamilton, R., D. Mackenzie, J. Shi und J. T. Boyle. „Simplified lower bound limit analysis of pressurised cylinder/cylinder intersections using generalised yield criteria“. International Journal of Pressure Vessels and Piping 67, Nr. 2 (Juli 1996): 219–26. http://dx.doi.org/10.1016/0308-0161(95)00063-1.
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14
Chamberlain,, J. A., D. J. Horrobin,, K. A. Landman, and und J. E. Sader. „Upper and Lower Bounds for Incipient Failure in a Body Under Gravitational Loading“. Journal of Applied Mechanics 71, Nr. 4 (01.07.2004): 586–89. http://dx.doi.org/10.1115/1.1767164.
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Recent numerical work has investigated incipient failure of yield stress materials under gravitational loading, for both the rectangular block and cylinder geometries [Chamberlain et al.; 2001, Int. J. Mech. Sci. 43(3):793-815, 2002, Int. J. Mech. Sci. 44(8):1779-1800]. While the rectangular block solution is exact, the cylinder solutions give lower bounds on the height of incipient failure. Consequently, we construct upper bound solutions for the height of incipient failure of a cylinder under gravitational loading. This closes the cylinder problem and quantifies the accuracy of the Haar-Karman hypothesis used in slip-line analysis. For completeness, we also give a simple lower bound solution for the cylinder, as well as upper and lower bound solutions for the two-dimensional rectangular block. These results have the advantage of being analytical, in contrast to the previous purely numerical results.
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HU, J. C., und Y. ZHOU. „Flow structure behind two staggered circular cylinders. Part 1. Downstream evolution and classification“. Journal of Fluid Mechanics 607 (30.06.2008): 51–80. http://dx.doi.org/10.1017/s0022112008001808.
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Flow structures, Strouhal numbers and their downstream evolutions in the wake of two-staggered circular cylinders are investigated at Re=7000 using hot-wire, flow-visualization and particle-image velocimetry techniques. The cylinder centre-to-centre pitch, P, ranges from 1.2d to 4.0d (d is the cylinder diameter) and the angle (α) between the incident flow and the line through the cylinder centres is 0° ~ 90°. Four distinct flow structures are identified at x/d ≥ 10 (x is the downstream distance from the mid-point between the cylinders), i.e. two single-street modes (S-I and S-II) and two twin-street modes (T-I and T-II), based on Strouhal numbers, flow topology and their downstream evolution. Mode S-I is further divided into two different types, i.e. S-Ia and S-Ib, in view of their distinct vortex strengths. Mode S-Ia occurs at P/d ≤ 1.2. The pair of cylinders behaves like one single body, and shear layers separated from the free-stream sides of the cylinders roll up, forming one street of alternately arranged vortices. The street is comparable to that behind an isolated cylinder in terms of the topology and strength of vortices. Mode S-Ib occurs at α ≤ 10° and P/d > 1.5. Shear layers separated from the upstream cylinder reattach on or roll up to form vortices before reaching the downstream cylinder, resulting in postponed flow separation from the downstream cylinder. A single vortex street thus formed is characterized by significantly weakened vortices, compared with Mode S-Ia. Mode S-II is identified at P/d=1.2~2.5 and α>20° or 1.5≤P/d≤4.0 and 10° < α≤20°, where both cylinders generate vortices, with vortex shedding from the upstream cylinder at a much higher frequency than from the downstream, producing two streets of different widths and vortex strengths at x/d≤5.0. The two streets interact vigorously, resulting in a single street of the lower-frequency vortices at x/d≥10. The vortices generated by the downstream cylinder are significantly stronger than those, originating from the upstream cylinder, in the other row. Mode T-I occurs at P/d≥2.5 and α=20°~88°; the two cylinders produce two streets of different vortex strengths and frequencies, both persisting beyond x/d=10. At P/d≥2.5 and α≥88°, the two cylinders generate two coupled streets, mostly anti-phased, of the same vortex strength and frequency (St≈0.21), which is referred to as Mode T-II. The connection of the four modes with their distinct initial conditions, i.e. interactions between shear layers around the two cylinders, is discussed.
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Huera-Huarte, Francisco J. „Dynamics and excitation in a low mass-damping cylinder in cross-flow with side-by-side interference“. Journal of Fluid Mechanics 850 (04.07.2018): 370–400. http://dx.doi.org/10.1017/jfm.2018.469.
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Experiments have been conducted with a low mass-damping circular cylinder, elastically supported in a cross-flow, in the vicinity of a second stationary cylinder. The dynamic response, including amplitudes and frequencies of oscillation, together with the fluid excitation, were measured covering a large parametric space, consisting of variations in the gap distance between the cylinders as well as in the reduced velocity and Reynolds number. The flow dynamics in the near wake was also measured using planar particle image velocimetry. The results show how there is a strong wake interaction between the cylinders that greatly modifies the vortex-induced vibrations (VIV) of the elastically mounted cylinder when the centre-to-centre distance between the models is initially set to values smaller than $3.5D$, where $D$ is the external diameter. The wake interference leads to responding amplitudes that are reduced if compared to those of isolated cylinders undergoing VIV, while responding frequencies are increased. The transverse force coefficients observed in the lock-in region increase and the upper branch shifts to smaller reduced velocities. The phase between motion and excitation is also shifted and values measured in the lower branch of the response tend to be smaller than those typical of isolated cylinders. At the smallest separation distances investigated, the wakes of the cylinders are synchronised in an out-of-phase mode of shedding, characterised by a biased flow towards the oscillating cylinder.
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Jiang, Jinlin, Yu Wang, Heng Cao, Jun Zhu und Xinbin Zhang. „A novel pump-valve coordinated controlled hydraulic system for the lower extremity exoskeleton“. Transactions of the Institute of Measurement and Control 42, Nr. 15 (16.06.2020): 2872–84. http://dx.doi.org/10.1177/0142331220930623.
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In order to reduce the weight and improve the energy efficiency of the lower extremity exoskeleton, a novel pump-valve coordinated controlled (PVCC) hydraulic system is presented. This hydraulic system only uses one electro-hydrostatic unit (EHU) and two valves to drive two hydraulic cylinders at the hip and knee of the lower extremity exoskeleton. The PVCC hydraulic system has the advantage of high energy conversion efficiency of the electro-hydrostatic actuator (EHA), which consists of one EHU and one hydraulic cylinder. To meet the requirements of the moment and speed of each joint of the exoskeleton, the proportional valve and on-off valve are added to adjust the flow into two hydraulic cylinders. The performance of EHU is tested by some hydraulic experiments, and the performance of the PVCC hydraulic system is analyzed by AMESim. The results show that the novel hydraulic system can only use one EHU to drive two hydraulic cylinders simultaneously under the premise of meeting the functional requirements of the exoskeleton.
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Leung, Y. C., N. W. M. Ko und K. M. Tang. „Flow Past Circular Cylinder With Different Surface Configurations“. Journal of Fluids Engineering 114, Nr. 2 (01.06.1992): 170–77. http://dx.doi.org/10.1115/1.2910012.
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Measurements of the mean pressure distributions and Strouhal numbers on partially grooved cylinders with different groove subtend angles were made over a Reynolds number range of 2.0×104 to 1.3×105 which was within the subcritical regime of smooth cylinder. The Strouhal number, pressure distributions, and their respective coefficients were found to be a function of the groove subtend angles. In general, a progressive shift of the flow regime to lower Reynolds number was observed with higher subtend angle and a subtend angle of 75 deg was found for optimum drag reduction. With the configuration of asymmetrical groove surface, lower drag, and higher lift coefficients were obtained within the same Reynolds number range. Wake traverse and boundary layer results of the asymmetric grooved cylinder indicated that the flows at the smooth and groove surfaces lied within different flow regimes and a downward shift of the wake.
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Dong, Xinlong, Xinlu Yu und Shunjie Pan. „Analysis of Fracture Behaviour of Exploded Metal Cylinders with Varied Charge“. EPJ Web of Conferences 183 (2018): 01036. http://dx.doi.org/10.1051/epjconf/201818301036.
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Explosively driven fragmentation of ductile metals cylinders is a highly complex phenomenon. In this work, the fracture characteristics of exploded TA2 titanium alloy cylinder with varied charge were investigated numerically and experimentally. The results show that the fracture surfaces of fragments lie along planes of maximum shear stress for either a higher or a lower detonation pressure, but their mechanism is different. The finite element analysis demonstrated that the equivalent plastic strain in the middle of the wall is always larger than that of inner and outer wall for metal cylinder during the stage of shock wave driven period. For the high explosive pressures, the micro-cracks originated firstly in middle zone of wall during the stage of shock wave driven, and extend to the inner and outer wall in the direction of maximum shear stress. Explosives which generate lower detonation pressures, the shear fracture of cylinder originated from the inner wall and propagate to the outer wall in an angle of 45° or 135° to radial, the crack begin at the stage of free expansion. The simulated analysis of the process of deformation and fragmentation for exploded metal cylinder agree with the experimental results.
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Lu, Xiao Yang, Xiao Wei Zhao, Shi Ying Chen, Rong Li und Qiao Sha Wang. „ANSYS Parametric Design of Double Layer Cylinder Reticulated Shell by the Upper and Lower Translation“. Applied Mechanics and Materials 470 (Dezember 2013): 489–92. http://dx.doi.org/10.4028/www.scientific.net/amm.470.489.
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The five double layer cylinder reticulated shells (single diagonal rod cylinder reticulated shell, Foeppl cylinder reticulated shell, double diagonal rod cylinder reticulated shell, lamella cylinder reticulated shell and three way grid of cylinder reticulated shell) are developed by adopting the upper and lower translation method. Five connection forms of web member (cross truss, positive four pyramidal, upend four pyramidal, evacuated positive four pyramidal, evacuated upend four pyramidal) and the methods of the node generation and element connection are established in the cylindrical coordinate system. By using the ANSYS parametric design language APDL, the corresponding parametric design macro program is developed so that the five double-layer cylindrical shells can be parametrically modeled under the given parameters such as shell type, shell span D, rise high t, thickness h, length L and number of grids m and n, etc. Examples prove that this method is simple, efficient and pragmatic, which provides great convenience for the force analysis and the optimization scheme comparison.
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Widodo, Wawan Aries, und Nuzul Hidayat. „Experimental Study of Drag Reduction on Circular Cylinder and Reduction of Pressure Drop in Narrow Channels by Using a Cylinder Disturbance Body“. Applied Mechanics and Materials 493 (Januar 2014): 198–203. http://dx.doi.org/10.4028/www.scientific.net/amm.493.198.
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This paper present the results of drag reduction on circular cylinder and reduction of pressure drop in narrow rectangular channels by using circular disturbance body. This study focused on the phenomenon when the flow through the arrangement of the circular cylinder, separation will occur at a specific point on a circular cylinder resulting drag force. When the separation can be delayed so that the resulting drag force will be smaller. This can be done in various ways, one of which is by using a cylinder disturbance body on the upper and lower side near the bluff body. This study will be conducted in a wind tunnel experiments which have narrow channels with a square cross-sectional area of 125 mm x 125 mm and a blockage ratio of 26.4% and 36.4%. Specimens used circular cylinder with 25 mm diameter (d/D= 0.16) and 37.5 mm (d/D= 0.107) as well as the circular disturbance body with a diameter of 4 mm. cylinder disturbance body placed on the upper and lower side with the position α=200 to 600 and spacing (δ=0.4 mm) to the main circular cylinder. Reynolds number based on the hydraulic diameter of 5.21×104 to 15.6×104. The results of this research show the effect of using circular disturbance body on circular cylinder and the characteristics of fluid flow on a narrow channel square cross section. At a certain position of the circular disturbance body provide value pressure drop reduction on narrow channels and drag reduction when compared to a single circular cylinder. From the experimental data presented in this paper it is observed that the position angle of circular disturbance body to reduce drag force on a circular cylinder and reducing the pressure drop in the channel are at angle 200 and 300 for D=25 mm, and 200, 300 and 400, respectively, for D= 37.5 mm then the best reduction for both cylinders are at an angle of 300.
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He, Yuhai, Peilin Zhou, Liangtao Xie und Jiyun Zhang. „New concept and design of electronically controlled cylinder lubrication system for large two-stroke marine diesel engines“. International Journal of Engine Research 20, Nr. 8-9 (07.01.2019): 967–85. http://dx.doi.org/10.1177/1468087418822634.
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Lubrication of cylinders between liners and rings is one of the crucial factors that affects the efficient operation of diesel engines. Marine diesel engines usually use inferior heavy fuel oil with high sulphur content, and the acidic substances formed by fuel combustion need alkaline cylinder oil to neutralize. For the operational cost to a marine engine, besides fuel oil, cylinder oil also takes a big share. This article first analyses the advantages and disadvantages of existing cylinder lubrication systems with regard to oil injection control. Second, the control parameters and variables such as the oil injection pressure, timing, oil feed rate and reliability are analysed, and the corresponding control schemes formulated. Third, the control strategies are developed in detail. Finally, verification tests are carried out on an actual engine, with the results showing that the control strategies developed in this article provide a stable, cost-effective, creative and excellent solution for cylinder lubrication with reduced cylinder wear. A thin and uniform oil film distribution is retained on the liner surface, with savings in cylinder oil consumption, lower particulate matter emission levels and improved cylinder liner and piston rings running conditions. The experimental results show that the oil consumption could be reduced by up to 50%.
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Qi, Jiyang, Yuyao Shao, Qunyan Chen, Ping Liu, Chen Chen, Deqiang Wang, Haifeng Yang und Fei Yan. „Dynamic Analysis of Wake Characteristics of the Circular Cylinder with a Dimpled Surface“. Water 13, Nr. 16 (12.08.2021): 2197. http://dx.doi.org/10.3390/w13162197.
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In order to understand the wake characteristics for the circular cylinder with the dimpled structure, particle image velocimetry (PIV) and proper orthogonal decomposition (POD) method are used to measure and analyze the flow field velocity and the flow characteristic of the wake flow of the circular cylinder with the dimpled surface. This study focuses on the distribution of Reynolds stress and turbulent kinetic energy, the velocity profiles and recirculation zones, and the velocity fluctuating characteristics of flow field with POD technology. It is found that the equivalent high-intensity Reynolds stress and turbulent kinetic energy regions of the circular cylinder with the dimpled surface are smaller, and the peak values are lower, and the velocity gradient in the wake region of the circular cylinder with the dimpled surface is larger. Otherwise, the energy contained by the dominant modes of the smooth cylinder is larger than that contained by the dominant modes of the circular cylinders with the dimpled surface, which means the energy of the dimpled cylinder is more distributed. At the same time, it is observed that the dimpled structure will decrease the vortex shedding intensity, but may increase the vortex shedding frequency, and destroy the inherent flow mode of the flow field around the cylinder.
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Law, C. W., und N. W. M. Ko. „Bistable flow in lower transition regime of circular cylinder“. Fluid Dynamics Research 29, Nr. 6 (Dezember 2001): 313–44. http://dx.doi.org/10.1016/s0169-5983(01)00034-x.
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Liu, Xiao Xu, und Min Chen. „CFD Analysis for Cooling Water Cavity of a Four-Cylinder Gasoline Engine“. Advanced Materials Research 940 (Juni 2014): 184–87. http://dx.doi.org/10.4028/www.scientific.net/amr.940.184.
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s: The 3D model of cooling water cavity was set up, which was in a four cylinders gasoline engine, and the CFD analysis was done after setting the CFD calculation model and boundary conditions. The CFD analysis results shows that the structure design of engine’s cooling water cavity can meet the requirements basically, but there are some zone in which the water speed is lower than 0.5m/s, and there are some whirlpools in cylinder water jacket. In order to improve the cooling effect of the engine, the cooling water inlet channel and cylinder head should be improved.
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Barber, G. C., J. C. Lee und K. C. Ludema. „Materials and Surface Finish Effects in the Breaking-in Process of Engines“. Journal of Engineering for Gas Turbines and Power 109, Nr. 4 (01.10.1987): 380–87. http://dx.doi.org/10.1115/1.3240052.
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In this investigation, three materials and several surface finishes on cylinder walls were compared in laboratory tests that simulate the running-in behavior of fired engines. The three materials were the conventional cast gray iron, a sintered graphite-iron powder, and a cast aluminum-silicon alloy. The surface finishes were formed by various types of polishing and honing, including “plateau honing.” The run-in behavior of these materials was indicated by a laboratory simulator that is known to correlate with the early wear seen in fired engines. Two test sequences were used. One is a scuff test, in which a quick succession of increasing contact pressure is applied between a piston ring and a cylinder wall until surface failure occurs. The other is a “normal” wear test in which a lower contact pressure is applied, for a longer term study of surface change and coefficient of friction. Scuff load and midstroke friction were found to be dependent on roughness but independent of the amount of plateauing, as measured by skewness of the height distribution in the surface roughness trace. Plateau-honed cylinders were found to run in no more quickly than uniform-honed cylinders. Graphite-iron powder and aluminum-silicon cylinder walls had lower scuff resistance than did gray iron, but their “normal” wear behavior and midstroke friction performance were about the same as gray iron.
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Semin, B., A. Decoene, J. P. Hulin, M. L. M. François und H. Auradou. „New oscillatory instability of a confined cylinder in a flow below the vortex shedding threshold“. Journal of Fluid Mechanics 690 (24.11.2011): 345–65. http://dx.doi.org/10.1017/jfm.2011.435.
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AbstractA new type of flow-induced oscillation is reported for a tethered cylinder confined inside a Hele-Shaw cell (ratio of cylinder diameter to cell aperture, $D/ h= 0. 66$) with its main axis perpendicular to the flow. This instability is studied numerically and experimentally as a function of the Reynolds number $\mathit{Re}$ and of the density ${\rho }_{s} $ of the cylinder. This confinement-induced vibration (CIV) occurs above a critical Reynolds number ${\mathit{Re}}_{c} \ensuremath{\sim} 20$ much lower than for Bénard–Von Kármán vortex shedding behind a fixed cylinder in the same configuration (${\mathit{Re}}_{\mathit{BV K}} = 111$). For low ${\rho }_{s} $ values, CIV persists up to the highest $\mathit{Re}$ value investigated ($\mathit{Re}= 130$). For denser cylinders, these oscillations end abruptly above a second value of $\mathit{Re}$ larger than ${\mathit{Re}}_{c} $ and vortex-induced vibrations (VIV) of lower amplitude appear for $\mathit{Re}\ensuremath{\sim} {\mathit{Re}}_{\mathit{BV K}} $. Close to the first threshold ${\mathit{Re}}_{c} $, the oscillation amplitude variation as $ \mathop{ (\mathit{Re}\ensuremath{-} {\mathit{Re}}_{c} )}\nolimits ^{1/ 2} $ and the lack of hysteresis demonstrate that the process is a supercritical Hopf bifurcation. Using forced oscillations, the transverse position of the cylinder is shown to satisfy a Van der Pol equation. The physical meaning of the stiffness, amplification and total mass coefficients of this equation are discussed from the variations of the pressure field.
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Guo, Qing, und Dan Jiang. „The Lower Extremity Exoskeleton Coordinated Control Method Based on Human Electromechanical Coupling“. Applied Mechanics and Materials 220-223 (November 2012): 1012–17. http://dx.doi.org/10.4028/www.scientific.net/amm.220-223.1012.
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This paper has introduced electromechanical coupling characteristics in the lower extremity exoskeleton systems, considered model ,according to legs supporting gait when people walking, established the load torque compensation model , and a mathematical model of knee position control system which is made of the servo valve, hydraulic cylinders and other hydraulic components, designed hydraulic cylinder position control loop in case of existing load force interference compensation, and used the method of combining the PID and lead correction network for frequency domain design ,ensured system to meet a certain stability margin. The simulation results show that this position control method can servo on the knee angular displacement of normal human walking, reached a certain exoskeleton boost effect, at the same time, met the needs of human-machine coordinated motion.
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Xiaobing, Ma, und Zhang Yongbo. „Life Prediction on a T700 Carbon Fiber Reinforced Cylinder with Limited Accelerated Life Testing Data“. Mathematical Problems in Engineering 2015 (2015): 1–9. http://dx.doi.org/10.1155/2015/902157.
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An accelerated life testing investigation was conducted on a composite cylinder that consists of aluminum alloy and T700 carbon fiber. The ultimate failure stress predictions of cylinders were obtained by the mixing rule and verified by the blasting static pressure method. Based on the stress prediction of cylinder under working conditions, the constant stress accelerated life test of the cylinder was designed. However, the failure data cannot be sufficiently obtained by the accelerated life test due to the time limitation. Therefore, most of the data presented to be high censored in high stress level and zero-failure data in low stress level. When using the traditional method for rupture life prediction, the results showed to be of lower confidence. In this study, the consistency of failure mechanism for carbon fiber and cylinder was analyzed firstly. According to the analysis result, the statistical test information of carbon fiber could be utilized for the accelerated model constitution. Then, rupture life prediction method for cylinder was proposed based on the accelerated life test data and carbon fiber test data. In this way, the life prediction accuracy of cylinder could be improved obviously, and the results showed that the accuracy of this method increased by 35%.
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Aldoss, Taha K., und Awad Mansour. „Theoretical Calculations of the Flow Around a Rotating Circular Cylinder Placed in a Uniform Flow“. Journal of Fluids Engineering 110, Nr. 1 (01.03.1988): 96–98. http://dx.doi.org/10.1115/1.3243518.
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The rotation of a circular cylinder placed in a uniform flow is assumed to add a circulation to the flow around the cylinder proportional to the product of the angular velocity of the cylinder and the front area between upper and lower separation points. Adding the velocity due to this induced circulation to the base velocity distribution of the non-rotating cylinder the new velocity distribution on the rotating cylinder is formed. Thwaites’ method is then used to calculate the laminar boundary layer on the upper and on the lower sides of the cylinder. The stagnation point, and the upper and lower separation points are also calculated at different values of rotational speed. The calculated lift and drag coefficients using a linear pressure distribution on the wake part of the cylinder with the calculated pressure dstribution on the front part between the two separation points show the same trend as the measured values. The torque coefficient is also calculated to estimate the necessary power required to rotate the cylinder to produce the needed lift.
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CARBERRY, J., und J. SHERIDAN. „Wake states of a tethered cylinder“. Journal of Fluid Mechanics 592 (14.11.2007): 1–21. http://dx.doi.org/10.1017/s0022112007007707.
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This paper describes an experimental investigation of a buoyant, m*<1, tethered cylinder which is free to move in an arc about its pivot points. The response of the cylinder, in particular its layover angle and flow-induced motion, is considered for a range of flow velocities and mass ratios. At pertinent parameters, the flow fields were also measured using particle image velocimetry (PIV). At lower mass ratios, 0.54≤m*≤0.72, two distinct states are observed, the low-amplitude and upper states. The transition from the low-amplitude state to the upper state is characterized by abrupt jumps in the amplitude of oscillation, the mean tether angle and the drag coefficient as well as distinct changes in the cylinder's wake. At higher mass ratios, the jump does not occur; however, as m* approaches unity at low flow velocities the cylinder's motion is more periodic than that observed at lower m*. The flow fields indicate that the low-amplitude state exhibits a 2S Kármán wake. The wake of the upper state has long shear layers extending well across the wake centreline, is not fully symmetric and is often consistent with either the 2P or P+S shedding modes. There is a collapse of the response data, in particular an excellent collapse of the mean layover angle, when the response parameters are plotted against the buoyancy Froude number, Frbuoyancy=U/((1-m*) gD)0.5. When the data collapses, the two states described above are clearly delineated.
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Lee, Young Shin, Jae Hyun Park, Jae Hoon Kim, Ki Up Cha und Suk Kyun Hong. „Bauschinger Effect’ Influence on the Componud Cylinder Containing an Autofrettaged Layer“. Key Engineering Materials 345-346 (August 2007): 149–52. http://dx.doi.org/10.4028/www.scientific.net/kem.345-346.149.
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Autofrettage is used to introduce advantageous residual stresses into cylinders. The Bauschinger effect can produce less compressive residual hoop stresses near the bore than are predicted “ideal” autofrettage solutions. A723 steel is used for compound cylinder. This paper extends the analysis to material the addition of pressure or of shrink-fitting to the cylinders, providing associated residual stress profiles following various amounts of further yielding due to a net external pressure. The Bauschinger effects for “realistic” – Bauschinger effect dependent autofrettage are obtained. The 2-D analysis is performed via the finite element method. The Bauschinger effect is found to significantly lower the beneficial stress due to autofrettage.
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Parker, Michael, und Douglas Bohl. „Experimental Investigation of Finite Aspect Ratio Cylindrical Bodies for Accelerated Wind Applications“. Fluids 5, Nr. 1 (17.02.2020): 25. http://dx.doi.org/10.3390/fluids5010025.
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The placement of a cylindrical body in a flow alters the velocity and pressure fields resulting in a local increase in the flow speed near the body. This interaction is of interest as wind turbine rotor blades could be placed in the area of increased wind speed to enhance energy harvesting. In this work the aerodynamic performance of two short aspect ratio (AR = 0.93) cylindrical bodies was evaluated for potential use in “accelerated wind” applications. The first cylinder was smooth with a constant diameter. The diameter of the second cylinder varied periodically along the span forming channels, or corrugations, where wind turbine blades could be placed. Experiments were performed for Reynolds numbers ranging from 1 × 105 to 9 × 105. Pressure distributions showed that the smooth cylinder had lower minimum pressure coefficients and delayed separation compared to the corrugated cylinder. Velocity profiles showed that the corrugated cylinder had lower peak speeds, a less uniform profile, and lower kinetic energy flux when compared to the smooth cylinder. It was concluded that the smooth cylinder had significantly better potential performance in accelerated wind applications than the corrugated cylinder.
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Nordsiek, Freja, Sander G. Huisman, Roeland C. A. van der Veen, Chao Sun, Detlef Lohse und Daniel P. Lathrop. „Azimuthal velocity profiles in Rayleigh-stable Taylor–Couette flow and implied axial angular momentum transport“. Journal of Fluid Mechanics 774 (09.06.2015): 342–62. http://dx.doi.org/10.1017/jfm.2015.275.
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We present azimuthal velocity profiles measured in a Taylor–Couette apparatus, which has been used as a model of stellar and planetary accretion disks. The apparatus has a cylinder radius ratio of ${\it\eta}=0.716$, an aspect ratio of ${\it\Gamma}=11.74$, and the plates closing the cylinders in the axial direction are attached to the outer cylinder. We investigate angular momentum transport and Ekman pumping in the Rayleigh-stable regime. This regime is linearly stable and is characterized by radially increasing specific angular momentum. We present several Rayleigh-stable profiles for shear Reynolds numbers $\mathit{Re}_{S}\sim O(10^{5})$, for both ${\it\Omega}_{i}>{\it\Omega}_{o}>0$ (quasi-Keplerian regime) and ${\it\Omega}_{o}>{\it\Omega}_{i}>0$ (sub-rotating regime), where ${\it\Omega}_{i,o}$ is the inner/outer cylinder rotation rate. None of the velocity profiles match the non-vortical laminar Taylor–Couette profile. The deviation from that profile increases as solid-body rotation is approached at fixed $\mathit{Re}_{S}$. Flow super-rotation, an angular velocity greater than those of both cylinders, is observed in the sub-rotating regime. The velocity profiles give lower bounds for the torques required to rotate the inner cylinder that are larger than the torques for the case of laminar Taylor–Couette flow. The quasi-Keplerian profiles are composed of a well-mixed inner region, having approximately constant angular momentum, connected to an outer region in solid-body rotation with the outer cylinder and attached axial boundaries. These regions suggest that the angular momentum is transported axially to the axial boundaries. Therefore, Taylor–Couette flow with closing plates attached to the outer cylinder is an imperfect model for accretion disk flows, especially with regard to their stability.
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Hashemian, Amir H., Mohammad Hossein Kargarnovin und Jafar E. Jam. „Accurate Calculation of the Natural Frequencies of Reticulated and Solid Cylindrical Composite Shells“. Applied Mechanics and Materials 110-116 (Oktober 2011): 4598–606. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.4598.
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There are hundreds models of reticulated structures including the squared reticulated cylindrical shells. It is considered as comprising of a number of circumferential and longitudinal rods. Analytical governing equation for natural frequencies has been derived for this type of structures and to verify the validity of solutions, Finite Element Method (FEM) is used. The comparison of results demonstrate close agreement between analytical and FE solutions. Also a comparison is preformed between a reticulated and equivalent solid hollow cylinder shell. The equivalent solid hollow cylinder has equal weight, length and outer diameter with the squared reticulated cylindrical shell. This comparison shows that the natural frequencies of squared reticulated shells are lower than the hollow solid cylinders.
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Praburam, G., V. K. Tripathi und V. K. Jain. „Lower hybrid suppression of drift waves in a plasma cylinder“. Physics of Fluids 31, Nr. 10 (1988): 3145. http://dx.doi.org/10.1063/1.866972.
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Bao, Zhenzhong, Guoliang Qin, Wenqiang He und Yazhou Wang. „Spectral Element Numerical Investigation of Flow between Three Cylinders in an Equilateral-Triangular Arrangement with Different Spacing Distances“. Shock and Vibration 2018 (2018): 1–11. http://dx.doi.org/10.1155/2018/6358949.
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Two-dimensional incompressible Navier-Stokes equations are numerically solved using the high resolution spectral element method at Reynolds number 200. The flow between three cylinders in an equilateral-triangular arrangement is investigated. The center-to-center spacing distance ratio between two circular cylinders is varied from 1.5 to 12. Present numerical results show that the flow patterns and force characteristics are the result of the combined effects of Reynolds number, spacing distance, configuration arrangement, and incident angle. For the small spacing distance ratio of 1.5, the well-known biased flow phenomenon in the gap of downstream cylinders is found. And the biased flow is bistable in our study but not monostable. A small spacing distance means lower Strouhal number, drag, and root-mean-square lift coefficients. In the medium spacing distance ratio of 4.0, the suppressed effect of vortex shedding for the presence of the side-by-side downstream cylinders disappeared. Mean drag coefficients of downstream cylinders are basically identical to the value of flow past around a single circular cylinder. For the large spacing distance ratio of 8.0, the effects between three cylinders basically disappeared. The mean drag and lift coefficients, root-mean-square lift coefficients, and Strouhal number of three cylinders are essentially equivalent to those values of a single circular cylinder.
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Levy, C., M. Perl und Q. Ma. „Erosions and Their Effect on the Fatigue Life of Thick Walled, Autofrettaged, Pressurized Vessels“. Journal of Pressure Vessel Technology 125, Nr. 3 (01.08.2003): 242–47. http://dx.doi.org/10.1115/1.1593698.
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This paper summarizes the results that have been found in evaluating the effect of erosions on thick walled, autofrettaged, pressurized, cracked vessels. The problem is solved numerically via the FEM method. Autofrettage, based on von Mises yield criterion, is simulated by thermal loading and stress intensity factors (SIF’s) are determined by the nodal displacement method. SIF’s were evaluated for a variety of relative crack depths a/t and crack ellipticities a/c emanating from the tip of the erosion of various geometries, namely, (a) semi-circular erosions of small relative depths of the cylinder’s wall thickness t; (b) arc erosions for several dimensionless radii of curvature r′/t; and (c) semi-elliptical erosions with ellipticities of d/h. Other parameters evaluated were, in the cases of finite erosions, the semi-erosion length to the semicrack length Le/c, the erosion angular spacing α, and the autofrettage level. First, we summarize the differences found between a vessel with one erosion and one with multiple erosions. We show that for full cylinder length erosions, the erosions tend to make smaller cracks more dangerous than larger cracks in fully autofrettaged vessels and that as the crack grows the stress intensity factor initially decreases. We then show that as the crack grows further, the effect is to increase the effective stress intensity factor (SIF) but also to practically void the existence of the erosion. We show further that lower levels of autofrettage will lead to higher effective SIF’s but that partially eroded cylinders (cylinders where erosions are a fraction of the cylinder length) lead to lower SIF’s. Affecting these values in all cases, of course, are the erosion geometry and depth as well as the crack geometry and depth.
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An, Xuanyi, Ping Ye, Jiayun Liu, Chao Tian, Shunshan Feng und Yongxiang Dong. „Dynamic Fracture and Fragmentation Characteristics of Metal Cylinder and Rings Subjected to Internal Explosive Loading“. Materials 13, Nr. 3 (08.02.2020): 778. http://dx.doi.org/10.3390/ma13030778.
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Dynamic fracture and fragmentation characteristics of explosively driven rings and cylinders are important issues in the field of weapon effectiveness and protection. However, the comparison of fracture characteristics between metal cylinder and rings, and the fracture characteristics of the metal shells at different axial positions, are rarely touched. In the present work, a recovery tank was used to collect fragments, and witness plates were used to investigate the fragment spatial distributions. Before the test, the representative positions of metal shells were plated with copper layers to locate the original position of the recovered fragments. After the test, scanning electron microscopy and optical microscope were used for characterizing the microstructure of the recovered fragments from different positions. Then, the recovered fragments were weighed and measured to investigate their mass and size characteristics. In addition, numerical simulation was used to further investigate the fracture mechanisms of explosively driven cylinders and rings. It was found that the projection angle axial distribution of the fragments for the metal cylinder was similar to that of the fragments for the metal rings. However, the fracture characteristics of the metal rings were significantly different from those of the metal cylinder. The adiabatic shear band played a key role in the fracture process of the metal cylinder, whereas the adiabatic shear band had little chance to initiate in the fracture process of the metal rings because the metal rings could deform uniformly with much fewer strain localizations due to their much lower length. The fracture surfaces of the fragments from different positions of the metal cylinder were very smooth, whereas dimples were found in the fracture surfaces of the fragments from different positions of the metal rings. The mass distribution of the fragments from the metal rings was more uniform than that of the fragments from the metal cylinder, and the circumferential rupture strains of the metal rings were much larger than those of the metal cylinder.
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Tzou, Gow-Yi, Yeong-Maw Hwang und Sai-Chih Pan. „Investigation on rotating compression of porous cylinder under constant shear friction using FEM simulation“. MATEC Web of Conferences 185 (2018): 00040. http://dx.doi.org/10.1051/matecconf/201818500040.
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In this paper, a series of systematic studies on the rotating compression of porous cylinders by the FEM using DEFORM-3D analysis software are carried out. For a series of simulations, the forming conditions such as (1) the angular velocities from small to large are 0, 0.1, 0.25, 0.5, and 1 (rad/sec), respectively;(2) aspect ratio of porous cylinder (height-diameter ratio) are 0.75, 1, and 1.25, respectively;(3) the frictional factors are 0.3 and 0.7. Through different combinations of the above-mentioned variation factors, the characteristics of the rotating compression of porous cylinder can be explored. These rotating forming characteristics such as the compression force, the bulging ratio, the change in density, the rotating torque and so on can be investigated. The rotating compression characteristics of both porous and sound cylinders reveal lots of similarities and some differences. The main conclusions of this study are as follows: (1) as the rotating speed increases fast, the compression force of porous cylinder is whereas reduced. This phenomenon is different from the compression of sound cylinder; (2)the compression force under the lower aspect ratio can be reduced by the lubrication; (3)the relative density can be increased by increasing the rotating speed and reduction ratio; (4)the rotating torque is increased with higher rotating speed, higher frictional factor, and higher aspect ratio; (5)the bulging effect can be reduced by increasing the rotating speed, however it is increased by increasing the frictional factor.
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Wang, Jialu, Fabo Chen, Chen Shi und Jiuzheng Yu. „Mitigation of Vortex-Induced Vibration of Cylinders Using Cactus-Shaped Cross Sections in Subcritical Flow“. Journal of Marine Science and Engineering 9, Nr. 3 (07.03.2021): 292. http://dx.doi.org/10.3390/jmse9030292.
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Flexible cylinders, such as marine risers, often experience sustained vortex-induced vibrations (VIVs). Installing helical strakes on a riser is the most widely used technique to mitigate VIVs. This study was inspired by the giant Saguaro Cacti which can withstand strong wind with a shallow root system. In this study, numerical simulations of flow past a stationary cylinder of a cactus-shaped cross-section in a two-dimensional flow field at a subcritical Reynolds number of 3900 were performed. Results show that cylinders of a cactus-shaped cross-section have a lower lift coefficient without increasing drag compared to those of a circular cylinder. VIV experiments on a single flexible pipe as well as on a set of two tandem-arranged flexible pipes were conducted at different reduced velocities to investigate the effects of the streamwise spacing and wake of the cactus-like body shape on VIV mitigation. Experimental results show that the cactus-like body shape can mitigate VIV responses of the cylinder at upstream position with no cost of increased drag; however, similar to helical strakes, the efficiency of VIV mitigation for the cylinder at downstream position is reduced. Although the cactus-like body shapes tested in this study were not optimized for oscillation suppression, still this study suggests that modification of the cross-sectional shape to a well-designed cactus-like shape has potentials to be used as an alternative technology to mitigate VIV of marine risers.
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Wong, K. W. L., J. Zhao, D. Lo Jacono, M. C. Thompson und J. Sheridan. „Experimental investigation of flow-induced vibration of a rotating circular cylinder“. Journal of Fluid Mechanics 829 (21.09.2017): 486–511. http://dx.doi.org/10.1017/jfm.2017.540.
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While flow-induced vibration of bluff bodies has been extensively studied over the last half-century, only limited attention has been given to flow-induced vibration of elastically mounted rotating cylinders. Since recent low-Reynolds-number numerical work suggests that rotation can enhance or suppress the natural oscillatory response, the former could find applications in energy harvesting and the latter in vibration control. The present experimental investigation characterises the dynamic response and wake structure of a rotating circular cylinder undergoing vortex-induced vibration at a low mass ratio ($m^{\ast }=5.78$) over the reduced velocity range leading to strong oscillations. The experiments were conducted in a free-surface water channel with the cylinder vertically mounted and attached to a motor that provided constant rotation. Springs and an air-bearing system allow the cylinder to undertake low-damped transverse oscillations. Under cylinder rotation, the normalised frequency response was found to be comparable to that of a freely vibrating non-rotating cylinder. At reduced velocities consistent with the upper branch of a non-rotating transversely oscillating cylinder, the maximum oscillation amplitude increased with non-dimensional rotation rate up to $\unicode[STIX]{x1D6FC}\approx 2$. Beyond this, there was a sharp decrease in amplitude. Notably, this critical value corresponds approximately to the rotation rate at which vortex shedding ceases for a non-oscillating rotating cylinder. Remarkably, at $\unicode[STIX]{x1D6FC}=2$ there was approximately an 80 % increase in the peak amplitude response compared to that of a non-rotating cylinder. The observed amplitude response measured over the Reynolds-number range of ($1100\lesssim Re\lesssim 6300$) is significantly different from numerical predictions and other experimental results recorded at significantly lower Reynolds numbers.
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Trenc, Ferdinand, Francˇisˇek Bizjan, Brane Sˇirok und Alesˇ Hribernik. „Influence of the Exhaust System Design on Scavenging Characteristic and Emissions of a Four-Cylinder Supercharged Engine“. Journal of Engineering for Gas Turbines and Power 122, Nr. 4 (09.05.2000): 556–61. http://dx.doi.org/10.1115/1.1289387.
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A four-stroke four-cylinder turbocharged engine can be fitted with two different types exhaust system: a simple common manifold fed by all cylinders, or a twin-branch manifold, where two selected cylinders, directed by the firing order, feed two separate turbine entries. In this case good utilization of the exhaust pressure pulse energy can be achieved at higher loads and lower engine speeds, leading to good overall turbocharger efficiency and favorable pressure distribution during the gas-exchange period. Improved engine scavenging capability affects quality and quantity of the fresh charge and consequently influences the exhaust gas emissions. If, in addition, valve overlap period is increased the benefit of this system is still more evident. Common manifold exhaust system shows its advantage through lower pumping losses at higher engine speeds and lower loads. Both systems were optimized and the results of numerical and experimental work are presented in the paper. [S0742-4795(00)00404-X]
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Ragui, Karim, Abdelkader Boutra und Youb Khaled Benkahla. „The Impact of Cylindrical Fuel Assemblies’ Arrangement on the Heat and Mass Transfers into an Horizontal Porous Circular Cylinder“. International Letters of Chemistry, Physics and Astronomy 58 (September 2015): 66–76. http://dx.doi.org/10.18052/www.scipress.com/ilcpa.58.66.
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The present work refers to the investigation of natural convection into an horizontal porous circular cylinder, driven by cooperating thermal and solutal buoyancy forces. The circular cylinder is maintained at constant temperature and concentration lower than that of four inner, heat and solute, ones which are arranged in two different manners. The physical model for the momentum conservation equation makes use of the Brinkman extension of the classical Darcy equation, the set of coupled equations is solved using the finite volume method and the SIMPLER algorithm. Through a parametric study, the effects of the distance between the cylinders on the thermal and solutal characteristics are widely inspected. Then, powerful correlations predicting the mean transfer inside the porous medium as a function of the cylinders’ disposition are proposed, which predict within ±1% the numerical results. It is to note that the validity of the computing code used was ascertained by comparing our results with the experimental and the numerical ones already available in the literature.
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HOVER, F. S., A. H. TECHET und M. S. TRIANTAFYLLOU. „Forces on oscillating uniform and tapered cylinders in cross flow“. Journal of Fluid Mechanics 363 (25.05.1998): 97–114. http://dx.doi.org/10.1017/s0022112098001074.
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Forces are measured at both ends of rigid cylinders with span 60 cm, performing transverse oscillations within an oncoming stream of water, at Reynolds number Re≈3800. Forced harmonic motions and free vibrations of uniform and tapered cylinders are studied. To study free motions, a novel force-feedback control system has been developed, consisting of: (a) a force transducer, which measures forces on a section of a cylinder moving forward at constant speed; (b) a computer using the measured force signal to drive in real time a numerical simulation of an equivalent mass-dashpot-spring system; (c) a servomotor and linear table which impose, also in real time, the numerically calculated motion on the cylinder section. The apparatus allows very low equivalent system damping and strict control of the parametric values and structure of the equivalent system.Calculation of the cross-correlation coefficient between forces at the two ends of the uniform cylinder reveals five distinct regimes as a function of the nominal reduced velocity Vrn: two regimes, for low and high values of Vrn, and far away from the value of VrS corresponding to the Strouhal frequency, show small correlation; two regimes immediately adjacent to, but excluding, VrS show strong correlation, close to 1; surprisingly, there is a regime containing the Strouhal frequency, within which correlation is low. Free vibrations with a 40[ratio ]1 tapered cylinder show that the regime of low correlation, containing the Strouhal frequency, stretches to higher reduced velocities, while lock-in starts at lower reduced velocities.When comparing the amplitude and phase of the lift coefficient measured for free and then for forced vibrations, we obtain close agreement, both for tapered and uniform cylinders. When comparing the cross-correlation coefficient, however, we find that it is much higher in the forced oscillations, especially for the uniform cylinder. Hence, although the force magnitude and phase may be replicated well in forced vibrations, the correlation data suggest that differences exist between free and forced vibration cases.
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Sakai, A., H. Takeyama, H. Ogawa und N. Miyamoto. „Improvements in premixed charge compression ignition combustion and emissions with lower distillation temperature fuels“. International Journal of Engine Research 6, Nr. 5 (01.10.2005): 433–42. http://dx.doi.org/10.1243/146808705x58288.
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The charge mixture in a premixed charge compression ignition (PCCI) engine with direct in-cylinder injection early in the compression stroke is still heterogeneous even at the compression end. Direct injection of a low-volatility fuel, such as diesel fuel, early in the compression stroke results in adhesion of unevaporated fuel on the cylinder liner wall. It may be possible to improve both mixture formation and homogeneity, and decrease wall wetting by using higher-volatility fuels with distillation temperatures lower than the in-cylinder gas temperature early in the compression stroke. This research addressed the potential for improvements in early direct injection type PCCI combustion with a higher-volatility fuel, experimentally and computationally. A normal heptane + isooctane blended fuel with ignitability similar to diesel fuel in PCCI operation was used as the higher-volatility fuel. The experimental results showed that the deterioration in thermal efficiency that occurs with advanced injection timings with ordinary diesel fuel could be eliminated with the higher-volatility fuel without significantly altering the total hydrocarbons (THC) and CO emissions. With early injection timings, the rate of heat release with diesel fuel is smaller than with higher-volatility fuels. This result suggests that with diesel fuel there is significant fuel adhesion to the cylinder liner wall and also absorption into the lubricating oil.
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BORAZJANI, IMAN, und FOTIS SOTIROPOULOS. „Vortex-induced vibrations of two cylinders in tandem arrangement in the proximity–wake interference region“. Journal of Fluid Mechanics 621 (12.02.2009): 321–64. http://dx.doi.org/10.1017/s0022112008004850.
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We investigate numerically vortex-induced vibrations (VIV) of two identical two-dimensional elastically mounted cylinders in tandem in the proximity–wake interference regime at Reynolds number Re = 200 for systems having both one (transverse vibrations) and two (transverse and in-line) degrees of freedom (1-DOF and 2-DOF, respectively). For the 1-DOF system the computed results are in good qualitative agreement with available experiments at higher Reynolds numbers. Similar to these experiments our simulations reveal: (1) larger amplitudes of motion and a wider lock-in region for the tandem arrangement when compared with an isolated cylinder; (2) that at low reduced velocities the vibration amplitude of the front cylinder exceeds that of the rear cylinder; and (3) that above a threshold reduced velocity, large-amplitude VIV are excited for the rear cylinder with amplitudes significantly larger than those of the front cylinder. By analysing the simulated flow patterns we identify the VIV excitation mechanisms that lead to such complex responses and elucidate the near-wake vorticity dynamics and vortex-shedding modes excited in each case. We show that at low reduced velocities vortex shedding provides the initial excitation mechanism, which gives rise to a vertical separation between the two cylinders. When this vertical separation exceeds one cylinder diameter, however, a significant portion of the incoming flow is able to pass through the gap between the two cylinders and the gap-flow mechanism starts to dominate the VIV dynamics. The gap flow is able to periodically force either the top or the bottom shear layer of the front cylinder into the gap region, setting off a series of very complex vortex-to-vortex and vortex-to-cylinder interactions, which induces pressure gradients that result in a large oscillatory force in phase with the vortex shedding and lead to the experimentally observed larger vibration amplitudes. When the vortex shedding is the dominant mechanism the front cylinder vibration amplitude is larger than that of the rear cylinder. The reversing of this trend above a threshold reduced velocity is associated with the onset of the gap flow. The important role of the gap flow is further illustrated via a series of simulations for the 2-DOF system. We show that when the gap-flow mechanism is triggered, the 2-DOF system can develop and sustain large VIV amplitudes comparable to those observed in the corresponding (same reduced velocity) 1-DOF system. For sufficiently high reduced velocities, however, the two cylinders in the 2-DOF system approach each other, thus significantly reducing the size of the gap region. In such cases the gap flow is entirely eliminated, and the two cylinders vibrate together as a single body with vibration amplitudes up to 50% lower than the amplitudes of the corresponding 1-DOF in which the gap flow is active. Three-dimensional simulations are also carried out to examine the adequacy of two-dimensional simulations for describing the dynamic response of the tandem system at Re = 200. It is shown that even though the wake transitions to a weakly three-dimensional state when the gap flow is active, the three-dimensional modes are too weak to affect the dynamic response of the system, which is found to be identical to that obtained from the two-dimensional computations.
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Wang, Hong Jun, und Hao Wu. „The Design of New Lock Keyhole and Cylinder“. Applied Mechanics and Materials 635-637 (September 2014): 219–22. http://dx.doi.org/10.4028/www.scientific.net/amm.635-637.219.
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This essay will find a new way to prevent technical unlocking and violence through the cylinder lock through the narrow cylinder bore for the purpose of improving the performance of the theft. The miniaturization of the keyhole and cylinder locks, it makes the lock cylinder by means of the implementation does not have enough space, greatly limits the unlocking illegal activities. Meanwhile, the new lock cylinder has the advantage of mutual opening rate lower.
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Siddiqui, Abuzar Abid, und Ali J. Chamkha. „Thermo-magnetohydrodynamic effects on Cu + engine oil/water nanofluid flow in a porous media-filled annular region bounded by two rotating cylinders“. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 234, Nr. 12 (16.02.2020): 2360–75. http://dx.doi.org/10.1177/0954406220906435.
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We examine the thermo-magnetohydrodynamic effects on nanofluid flow in a porous circular annular region bounded by two rotating cylinders in the presence of a constant radial magnetic field but variable thermal conductivity. The nanofluid consists of a sample liquid (water/ engine oil) along with suspended copper nanoparticles. This physical problem is formulated and analytical solutions for the governing equations are obtained by using the homotopy analysis method in the form of the physical variables such as, the pressure, fluid speed, temperature, shear stress, heat transfer, and the concentration of nanoparticles. The obtained results are compared with the existing results for the clear fluid and are found in excellent agreement. The effects of the field parameters on these physical variables are studied. It is found that the fluid speed (pressure) increases (decreases) with the Forchheirmer coefficient, porosity, applied magnetic field intensity, and the angular speed of the outer cylinder, but it decreases with the angular speed of the inner cylinder for both liquids. The reverse flow exists if the inner and outer cylinders are rotating in the opposite directions for both the liquids. Furthermore, the thermal transfer rate in the engine oil is lower than that in water. If the annulus region is squeezed, then the fluid speed decays while the pressure rises. The temperature and the thermal transfer rate decay if we march from the inner cylinder to the outer one. The porosity and the angular speed of the outer cylinder enhance the viscous dissipation and shear stress.
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Croll, J. G. A., und C. P. Ellinas. „A Design Formulation for Axisymmetric Collapse of Stiffened and Unstiffened Cylinders“. Journal of Energy Resources Technology 107, Nr. 3 (01.09.1985): 350–55. http://dx.doi.org/10.1115/1.3231198.
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A procedure, developed for predicting the elastic-plastic general axisymmetric collapse of stiffened and unstiffened cylinders, is presented. This permits the formulation of reliable lower bounds to collapse loads for any combination of radial pressure and axial loadings, with any prescribed forms and levels of initial geometric imperfection, in a simple, “column-type,” analysis. The approach provides a unified format for the treatment of isotropic and orthotropic cylinder buckling, which is compact and design orientated.