Section Of Cylinder Research Articles

Influence of Roughness on the Asymmetric Flow Field of a Slender Body

Low speed and high angle of attack are problems that must be faced in vertical launching missiles. A natural asymmetric vortex phenomenon occurs at a low speed and high angle of attack of a slender body. In this paper, the Detached Eddy Simulation (DES) method is adopted to simulate the asymmetric flow of a slender body at a high angle of attack. The influence of roughness is analysed from the flow field and pressure distribution. And the DES method is verified by comparing it with the wind tunnel test results. The flow fields of the four models with the surface roughness of 0, 0.8, 5, and 100 are compared. The downstream flow still appears asymmetric when the surface is smooth, indicating that the stability of the flow field is not enough to maintain the symmetry of the flow field. The simulation results show that the adverse pressure gradient increases in the region where the boundary layer separates with the roughness greatly increasing, but the structure of the flow field at the head is slightly different. On the whole, the surface pressure and lateral force per unit length ( C f z p m ) transform alternately along the axial direction, and the period of alternating reverses increases with the increase of roughness. Finally, the pressure tends to be in equilibrium, and C f z p m approaches zero. It should be noted that the distribution of C f z p m is slightly different on the head, indicating that the asymmetry of pressure on the cylinder section is an important factor controlling the magnitude and the direction of lateral force. The influence of roughness on the flow around a slender body is acquired in this paper, and it has reference significance to the roughness problem of the actual missile.

Numerical simulations of internal flow fields in a nozzle with liquid fertilizer deep machinery

Fertilizing with water jet is a non-contact fertilization technique that uses high pressure water jet for hole-caving and fertilizing. In this article, an automatic liquid fertilizer deep machinery is proposed. The influences of three typical nozzles on the liquid fertilizer deep machinery were investigated via numerical simulations. The feasible water jet nozzle structures were obtained based on analysis and optimization of the main flaws of the four nozzles. A three-dimensional mathematical model of internal flow field in a high-pressure nozzle was established using the ANSYS software. Using the standard k-ε turbulent model, the internal flow field in the nozzle was simulated and the influences of nozzle parameters on the flow rate isogram and axial flow rate at the outlet of the flow field were studied. The results revealed that the axial flow rate at the outlet increased and then decreased as the convergence angle increased. The effects of cylinder section length on the axial flow rate at the outlet were negligible within a certain range. As the outlet diameter increased, the axial flow rate at the outlet decreased.

Two Dimensional and Stereo PIV Comparison for Port Applications

Fuel-air movements in-cylinder are one of the most critical diesel engine parameters to determine engine performance and emission. Swirling movement in the engine combustion chamber is investigated advanced experimental techniques to improve the air intake design.
 Honeycomb measurement method and PIV (particle image velocimetry) method are used to measure the swirling airflow. The honeycomb measurement method can directly measure the swirl. However, it does not give detail information about the flow field. On the other hand, the PIV technique is one of the non-invasive measurement methods for swirl measurement. PIV can directly measure the velocity vector of the cylinder section. 
 In this study, the honeycomb measurement method was performed to measure the swirl ratio of 13L and 9L engines. The uncertainty analysis was determined for the reliability ratio of the measurement. In addition, PIV measurements are performed to understand the velocity field of the cylinder section. This velocity field gives detailed information about the center of the swirl and the velocity index of the velocity field.

Numerical study on the force distribution on cylindrical structure by internal solitary wave and its prediction with Morison equation

The forces by internal solitary wave on cylinder structure are computed to understand their temporal distribution on different cylinder sections. The results confirm that the total forces could be decomposed into inertial and drag components approximately. Three empirical coefficients determination methods which are referred to as global coefficients, local coefficients, and coefficients based on regression models, are tested to analyze the dependence of the inertial and drag coefficients on the velocity field characteristics. The results show that the layer dependent empirical coefficients could improve the performances of Morison equation in the upper and lower layers, while its advantage in layers close to density interface is not obvious, which is related to the large vertical velocity components in this region. The regression models are derived by fitting selected coefficients samples, and the empirical coefficients predicted are very close to the results by Sarpkaya (1976) for oscillating flows in the same Reynolds number range.

Specific Features of the Replacement of the Available Flow Path by the Optimal Flow Path when Upgrading the Steam Turbine High-Pressure Cylinder

This scientific paper gives the main research data obtained during the solution of the search problem to define optimal parameter values for the thermal circuit of the К-540-23.5 turbine unit that would provide the most efficient operation both for the optimal version of the high pressure cylinder (HPC) as part of the turbine unit and the turbine unit on the whole. The effect of the distribution of heat differences in the stages of the optimal flow part of the high pressure cylinder used by the К-540-23.5 turbine on the integral quality factors of the turbine unit has been assessed. The calculation studies of the thermal circuit of the turbine unit with the optimal flow section of the high-pressure cylinder showed that the temperature of the underheated feed water in the high pressure heater (HPH) arranged near the steam generator has the most critical effect on the power and economical efficiency of the high pressure cylinder and entire turbine unit. The two-criterion Pareto problem for the upgrading of the turbine unit was formulated and solved to define optimal underheating temperature values. Consideration was given to the two variants of the solution of the optimization problem for the feed water underheating temperature in the high pressure heater. Comparison and analysis of the two variants of solution for the two-criterion optimization problem showed the identity of the obtained data and it confirms the correctness of the problem formulation and the algorithms used for its solution.

The Effect of Wall Thermal Boundary Condition on Natural Convective Shutdown Cooling in a Gas Turbine

Abstract As a civil gas turbine cools down, asymmetric natural convective heat transfer causes the bottom sector of the rotor to cool faster than the top; this circumferential thermal gradient can potentially cause the shaft to deflect – a phenomenon called thermal or “rotor” bow. Rotor bow is tremendously difficult to predict due to its dependence on a number of engine design parameters, in addition to the complex nature of natural convective flows. A novel experimental facility has been developed to gain further understanding into shutdown cooling of a gas turbine. The scope of this paper is to quantify the effect of basic design features on natural convective cooling in an engine annulus during shut-down; specifically the influence of the thermal boundary wall conditions and the annular diameter ratio. In addition to this, a low-cost, robust thermocouple probe has been developed and validated, which allows for accurate temperature measurements in a natural convective boundary layer. An extensive experimental campaign has been completed. The key finding is that the local radial wall temperature difference was found to be the most influential parameter on the local heat transfer. Non-isothermal walls did not alter the overall distribution of the inner wall equivalent conductivity. This was true for both cylindrical and conical sections. An appropriate characteristic length for use in the Rayleigh number definition for both the concentric cylinder and conical sections have been validated. The conical inner section (5 deg hade angle) did not affect the overall heat transfer in the range of conditions tested. Therefore, the mean surface heat transfer for non-isothermal inner and outer profiles, within the range −0.4<ΔRa/RaLc<0.4, where the thermal gradient is negative in the clockwise from top-dead-center, can be predicted using isothermal correlations for RaLc<5.0×105 and Dr < = 1.5.

Simulation and burst validation of 70 MPa type IV hydrogen storage vessel with dome reinforcement

The dome reinforcement (DR) technology was studied to reduce the amount of carbon fiber of the type IV hydrogen storage vessel in this paper. Firstly, the influence of the angle and thickness of the dome reinforcement part on the stress distribution of the dome section is studied by finite element analysis. Secondly, the weight reduction of carbon fiber composite layer is studied based on the dome reinforcement model. The strain-based Hashin progressive damage model is used to predict the burst pressure and burst mode with user-defined material subroutine (UMAT) of ABAQUS. Finally, the dome reinforcement technology is further verified in comparison with non-dome reinforcement by burst tests. The results show that the progressive damage model can effectively represent matrix cracking and fiber fracture, and the predicted burst pressure and mode is consistent with the test results. The fiber stress near the equator of the dome section affects the burst mode, and the smaller the angle of dome reinforcement parts, the better the reinforcing effect, and the dome reinforcement technology can help to improve the fiber damage state at the dome, transfer the maximum stress to the cylinder section of the vessel, and ensure the burst mode to be a safe mode. Also, it can help to reduce the consumption of carbon fiber by up to 5.5% in composite material.

Simulating the passive confinement of circular concrete cylinders allowing for size effect

ABSTRACT There are innumerable tests on small stocky circular cylinders with either internal passive encasement of the concrete with circular stirrups or spirals, or external passive encasement through fibre-reinforced polymer (FRP) wrapping or through the use of FRP tubes or steel tubes. These tests have shown that passive confinement can increase the strength but, in particular, can substantially increase the ductility of concrete cylinders. Because of these important benefits, the effect of passive confinement on the concrete stress/strain in a particular cylinder section is invariably derived from tests such that substantial member testing is required. In this paper, it is shown how the passive stress/strain of the concrete for a particular circular member can theoretically be determined directly from their partial-interaction shear-friction and partial-interaction bond-slip material properties for any reinforcement arrangement and geometry of the circular cylinder. This procedure provides tools for designing for the benefits of passive confinement directly without the need for member testing.

Effect of Strain Measurement Layout on Damage Detection and Localization in a Free Falling Compliant Cylinder Impacting a Water Surface

The need for effective and reliable damage detection and localization systems is growing in several engineering fields, in particular in water impact problems characterized by impulsive loading conditions, high amplitude vibrations and large local deformations. In this paper, we further develop the approach presented in previous works to detect damage of water-impacting structures. Specifically, we provide a set of experimental tests on a flexible plastic cylinder impacting the water after a 50 cm free fall. The cylindrical specimen is artificially damaged in a known position. Strain measurements are performed through a set of nine fiber Bragg gratings distributed along the circumference of a cylinder section. We show that strain sensors can be used as reference sensors, for structure displacements reconstruction, and control sensors, for damage detection purposes, and the computation of the difference between measured and expected deformation may allow damage detection. Moreover, we investigate how exchanging control and reference sensors in the same sensor arrangement affect damage detection and localization.

약한 천이영역에서 정사각형 기둥 단면 외팔보의 유체-구조 연성 해석

In this paper, the flow phenomena around a beam with a square cylinder section were verified through a CFD technology to study the fluid-structure interaction related with the instability flow induced from Kármán vortex shedding. The Strouhal numbers obtained from the unsteady time history of lift coefficient are plotted for several Reynolds numbers ranged from 1,280 to 38,400, and the result shows a good agreement with the experiment in the reasonable error bounds of 2% for the three-dimensional model. From the fully-coupled simulation on the abruptly starting fluid-structure interaction of the present square beam shape, the cantilever beam is vibrated in a specified natural frequency, but did not reach the resonance of frequency locking, which had been expected to be affected by the dynamic behavior of the beam structure.

Numerical study on load characteristics by internal solitary wave on cylinder sections at different depth and its parameterization

The current field induced by internal solitary wave could cause destruction to marine structures. Morison equation is widely used in estimating forces by internal solitary waves on cylinder structure. Zan and Lin (2020) utilize numerical simulation to check the applicability of Morison equation on force estimation by internal solitary wave on cylindrical structure and conclude that nonlinearity is important for the force estimation induced by internal solitary wave. However, Wang et al. (2019) analyze experimental data on pile sections and find that the original Morison equation could fit measured forces reasonably well if local coefficients are used. In this study numerical simulations are used to illustrate the significance of nonlinear acceleration terms, and explain contradictions between these two studies. The results show that nonlinear terms could not be neglected even if local coefficients are adopted, and the significance of nonlinear contribution at different layers is exemplified. The pros and cons of using local versus global coefficients are also discussed.

Coral larvae avoid substratum exploration and settlement in low-oxygen environments

Oxygen is a critical resource that mediates a multitude of essential processes and interactions at multiple scales on coral reefs. In adult corals, it can directly or indirectly impact physiological processes, such as photosynthesis, respiration, and calcification. Moreover, many corals bleach as a consequence of being exposed to low oxygen. The sessile adult phase of corals makes habitat selection crucial for post-settlement survival and thus their pelagic larvae use a diverse array of cues to determine a suitable spot for settlement. However, the effects of oxygen on the early life stages of corals are still poorly known. This study investigated the importance of oxygen as a potential settlement cue and its effect on swimming and settlement behavior of coral larvae of two Acropora species. Two experiments were performed, one investigating coral larval swimming behavior under different oxygen conditions and the other studying coral larval settlement along an oxygen gradient. Bottom exploration, expressed as the percent of A. cytherea and A. pulchra larvae in the bottom section of experimental cylinders, was reduced by 96% and 100%, respectively, in hypoxic water compared to normoxic water. When offered the choice to settle on an otherwise preferred settlement substrate (Titanoderma prototypum) along an oxygen gradient, larvae of both coral species settled almost exclusively on T. prototypum fragments placed in well-oxygenated environments, with settlement rates increasing nonlinearly with oxygen concentrations. These results suggest that low-oxygen areas can negatively influence the settlement success of coral larvae and that oxygen concentration may be used as a cue for coral larval swimming and settlement behavior.

Behavior of Fully Encapsulated Cable Bolt in Various Double-Shear Methods and the Sequence of Wire Failure in the Newly Developed Shear Apparatus

The use of long-tendon ground support elements (cable bolts) is now a common practice in modern underground coal mines, hard rock mines, tunnels, and other underground structures. The paper briefly introduces the development of test methods for rock and cable bolts, including single- and double-shear methods, in the last 30 years and focuses on the novel development of the fourth generation of cylindrically shaped shear test apparatus (MK-IV Double Shear Box) for assessing tendon performance in shear based on the experience gained from the development of previous versions of shear experiment apparatus. The results were compared with similar test findings using a rectangular-shaped double-shear apparatus with and without friction across joint faces. The sequence of wire failure was studied by using the newly developed double-shear test apparatus, and the performance of abnormal phenomena in the double-shear tests was analyzed. The sequence of wire failure can be inferred based on the positive and negative values of strain gauge readings, and the wire of cable bolt under shearing may be broken in the joint area. The failure possibly occurred from one side to the other instead of from top to bottom. The modified double-shear test apparatus with a long section of concrete cylinder was proposed to conduct further research on cable bolt debonding.

Progressive damage analysis for multiscale modelling of composite pressure vessels based on Puck failure criterion

This study proposed a method for progressive failure analysis to investigate the failure modes of 35 MPa Type III composite pressure vessels during hydraulic burst tests. Representative volume elements (RVEs) were introduced, and the degraded elastic parameters of composite, which include fibre and matrix failure modes, were calculated by the finite element analysis (FEA) method to obtain the macroscopic stiffness degradation parameters. The Puck failure criterion was adopted, and the effective elastic parameters calculated from RVEs was introduced by the UDSLFD subroutine to simulate the multiscale progressive damage of composite layers during hydraulic burst test. Combined with acoustic emission detection, composite microscopic photos and hydraulic burst test, the burst pressure and failure modes of the vessels were analysed. The results showed that meso-macroscopic finite element models could effectively predict the progressive damage of composite pressure vessel, such as matrix crack, interlaminar failure and fiber fracture under internal pressure loading. Finally, the predicted burst pressure was about 5.4% average difference of the actual experimental results. Besides, cylinder section of the vessels was the predicted blasting position, which was close to the actual tests. Thus, the proposed method can provide theoretical reference for the design and optimisation of composite pressure vessels.

Study on particle movement characteristics in sandblast cylinder based on PIV technology

Abstract PIV technology was used to investigate the influence of the particles’ relevant parameters on the instantaneous movement characteristics in the sandblast cylinder under the circumstance of different particle sizes, different section heights and different stacking conditions. As the diameter increased, particles had a greater velocity and energy when approaching the wall, which would cause a serious abrasion. The influence of test selection factors on the particles’ radial velocity of particles was greater than that on axial velocity. The radial velocity and axial velocity on the surface of the cylindrical section were all reduced to a lower level when the particles approach the tank wall. When r > 0.3 R, the particle velocity maintained at a higher level, but then decreased slowly when r > 0.7 R. Therefore, the abrasion of the conical section of the sandblast cylinder when r > 0.3 R should be paid more attention to.

Controlling the shape of a tapered nanowire: lessons from the Burton-Cabrera-Frank model

The propagation of sidewall steps during the growth of nanowires is calculated in the frame of the Burton-Cabrera-Frank model. The stable shape of the nanowire comprises a cylinder section on top of a cone section: their characteristics are obtained as a function of the radius of the catalyst-nanowire area, the desorption-limited diffusion length of adatoms on the terraces, and the sticking of adatoms at step edges. The comparison with experimental data allows us to evaluate these last two parameters for InP and ZnTe nanowires; it reveals a different behavior for the two materials, related to a difference by an order of magnitude of the desorption-limited diffusion length.

Numerical study of roundness effect on flow around a circular cylinder

Imperfectly round bridge stay cable cross section is speculated to be a key factor for wind-induced large-amplitude cable vibrations observed on site. A delayed detached eddy simulation implemented in Open source Field Operation and Manipulation is used to investigate the flow structure around and in the near-wake of an imperfectly round circular cylinder and the corresponding aerodynamic forces at a Reynolds number of 104 and an attack angle of 0° or 45°. With the increase in roundness imperfection, both monotonic and non-monotonic changes of the mean surface pressure and the wake velocity are found when the cylinder is normal to the flow. At an attack angle of 45° and when the roundness ratio is e/D = 4%, it is found that the geometric imperfection in the cross-sectional shape of the cylinder allows it to the retention of more axial flow in the proximity of the cylinder leeward surface due to a shorter recirculation length. The vortex formed by the intensified axial flow would interact with the conventional von Kármán vortex formation at a frequency a few times lower than that of the latter and lead to intermittently amplified transverse lift. This reveals that imperfect roundness in the cross section of a circular cylinder could be an excitation source of low frequency vibration. Thus, it provides evidence that this kind of geometric imperfection, which commonly exists in real stay cables, could contribute to the mechanisms that trigger large-amplitude or even divergent cable motion, such as dry inclined cable galloping on site.

The magnetic field from a homogeneously magnetized cylindrical tile

The magnetic field of a homogeneously magnetized cylindrical tile geometry, i.e. an angular section of a finite hollow cylinder, is found. The field is expressed as the product between a tensor field describing the geometrical part of the problem and a column vector holding the magnetization of the tile. Outside the tile, the tensor is identical to the demagnetization tensor. We find that four components of the tensor, Nxy,Nxz,Nyz and Nzy, can be expressed fully analytically, while the five remaining components, Nxx,Nyx,Nyy,Nzx and Nzz, contain integrals that have to be evaluated numerically. When evaluated numerically the tensor is symmetric. A comparison between the found solution, implemented in the open source magnetic framework MagTense, and a finite element calculation of the magnetic flux density of a cylindrical tile shows excellent agreement.

3D thermodynamic analysis of superhydrophobicity of cylinder microtextured surfaces

Superhydrophobic surfaces have attracted great interest due to their self-cleaning, dust-proofing and friction-reducing properties. Related papers have proposed methods and theoretical bases for preparing these surfaces in order to achieve excellent superhydrophobicity. However, the influence of the roughness of the solid surface structure on its superhydrophobicity requires further in-depth thermodynamic analysis. In this paper, three-dimensional (3D) cylinder microtextured surface models are selected based on thermodynamic analysis. On this basis, a simulation diagram of the three-phase contact line of a circular cylinder section in a 3D model is presented. The effects of the intrinsic contact angle and geometrical parameters of the cylinder microtexture on free energy and the free energy barrier, as well as contact angle hysteresis, are theoretically investigated. The obtained results reveal the necessity of the transition between the non-composite state and composite state. The transition criteria between the non-composite and composite wetting states are obtained from the perspective of thermodynamic analysis and theoretical equations. The calculated results are basically consistent with the theoretical calculations and experimental results. This method provides theoretical guidance for the design of superhydrophobic surfaces.

Experimental study on the dynamic characteristics of wall normal stresses during silo discharge

The characteristics and mechanisms of stress fluctuation are not fully understood, especially for the large fluctuation at the cylinder/hopper transition. In this paper, we performed wall normal stress tests in a laboratory-scale silo which consisted of the cylinder section and hopper section. The amplitude and period characteristics of wall normal stress fluctuation at the top of the hopper were investigated. The result shows that the peak of the stress fluctuation and the maximum of the fluctuation range at the hopper top can reach 1.60 times and 0.64 times of the theoretical value, respectively. The amplitude of the stress fluctuation at the hopper top is independent of the outlet diameter, while the period of the stress fluctuation decreases with the increase of the outlet diameter. Furthermore, the stress-state transition and the shear zones in bulk solids are reasonably responsible for the periodic stress fluctuation at the hopper top.