Cylinder Configuration Research Articles

New analytical solutions to water wave radiation by vertical truncated cylinders through multi-term Galerkin method

New analytical solutions to water wave radiation by vertical truncated circular cylinders are developed based on linear potential flow theory. Two typical cylinder configurations of a surface-piercing cylinder and a submerged floating cylinder are considered. The multi-term Galerkin method is employed in the solution procedure, in which the fluid velocity on the interface between different regions is expanded into a set of basis function involving the Gegenbauer polynomials, and the cube-root singularity of fluid velocity at the side edges of the truncated cylinders is correctly modeled. The present solutions have the merits of very rapid convergence. The results with six-figure accuracy for added mass and radiation damping can be obtained using a few truncated numbers in the basis function for three motions (surge, heave and roll). The calculated results of the present solutions agree well with that by a higher-order boundary element method solution. Calculation examples are presented to investigate the influence of the motion frequency on the added mass and the radiation damping of the truncated cylinders with different geometric parameters. The present solutions can be used as a reliable benchmark for numerical solutions to water wave radiation by complicated structures.

Mutually touching infinite cylinders in the 3D world of lines

Recently we gave arguments that only two unique topologically different configurations of 7 equal all mutually touching round cylinders (the configurations being mirror reflections of each other) are possible in 3D, although a whole world of configurations is possible already for round cylinders of arbitrary radii. It was found that as many as 9 round cylinders (all mutually touching) are possible in 3D while the upper bound for arbitrary cylinders was estimated to be not more than 14 under plausible arguments. Now by using the chirality and Ring matrices that we introduced earlier for the topological classification of line configurations, we have given arguments that the maximal number of mutually touching straight infinite cylinders of arbitrary cross-section (provided that its boundary is a smooth curve) in 3D cannot exceed 10. We generated numerically several configurations of 10 cylinders, restricting ourselves with elliptic cylinders. Configurations of 8 and 9 equal elliptic cylinders (all in mutually touching) are generated numerically as well. A possibility and restriction of continuous transformations from elliptic into round cylinder configurations are discussed. Some curious results concerning the properties of the chirality matrix (which coincides with Seidel's adjacency matrix important for the Graph theory) are presented.

Improvement of the Viscous Penalty Method for Particle-Resolved Simulations

A numerical study of the parameters controlling the viscous penalty method is investigated to better set up Particle-Resolved Direct Numerical Simulations (PR-DNS) of particulate flows. Based on this analysis, improvements of the methods are proposed in order to reach an almost second order convergence in space. The viscous penalty method is validated in Stokes regime by simulating a uniform flow past a fixed isolated cylinder. Moreover, it is also utilized in moderate Reynolds number regime for a uniform flow past a square configuration of cylinder and compared in terms of friction factor to the well-known Ergun correlation.

Numerical investigation of shock wave attenuation in channels using water obstacles

Here, short duration direct numerical simulations of shock water cylinder interaction in a two-dimensional channel are conducted to study shock wave attenuation at time scales smaller than the cylinder convection time. Four different cylinder configurations, i.e., 1 $$\times $$ 1, 2 $$\times $$ 2, 3 $$\times $$ 3, and 4 $$\times $$ 4, are considered, where the total volume of water is kept constant throughout all the cases. Meanwhile, the incident shock Mach number was varied from 1.1 to 1.4. The physical motion of the water cylinders is quantitatively studied. Results show that the center-of-mass velocity increases faster for the cases with more cylinders. In the early stage of breakup, the transfer rate of kinetic energy from the shock-induced flow to the water cylinders increases as the number of cylinders increases. Further, comparing the cases of different incident shock Mach numbers, higher center-of-mass velocity is induced for the cases of lower incident shock Mach numbers. Moreover, the pressure and impulse changes upstream and downstream of the cylinder matrices are tracked as a quantitative evaluation of the shock attenuation.

Rotordynamic Analysis of the AM600 Turbine-Generator Shaftline

The AM600 represents the conceptual design and layout of a Nuclear Power Plant Turbine Island intended to address challenges associated with emerging markets interested in nuclear power. When coupled with a medium sized nuclear reactor plant, the AM600 is designed with a unit capacity that aligns with constraints where grid interconnections and load flows are limiting. Through design simplification, the baseline turbine-generator shaftline employs a single low-pressure turbine cylinder, a design which to date has not been offered commercially at this capacity. Though the use of a ‘stiffer’ design, this configuration is intended to withstand, with a margin, the damage potential of torsional excitation from the grid-machine interface, specifically due to transient disturbances and negative sequence currents. To demonstrate the robust nature of the design, torsional rotordynamic analysis is performed for the prototype shaftline using three dimensional finite element modelling with ANSYS® software. The intent is to demonstrate large separation of the shaftline natural frequencies from the dominant frequencies for excitation. The analysis examined both welded drum and monoblock type Low Pressure Turbine rotors for single cylinder and double cylinder configurations. For each, the first seven (7) torsional natural frequencies (ranging from zero–190 Hz) were extracted and evaluated against the frequency exclusion range (i.e., avoidance of 1× and 2× grid frequency). Results indicate that the prototype design of AM600 shaftline has adequate separation from the dominant excitation frequencies. For verification of the ANSYS® modelling of the shaftline, a simplified lumped mass calculation of the natural frequencies was performed with results matching the finite element analysis values.

Hydrostatics and stability of a floating elliptical cylinder with surface tension effects for different eccentricities and Bond numbers

A model dealing with the conditions of equilibrium and initial stability of floating bodies in two dimensions with an arbitrary cross-section has been proposed recently (J. Fluid Mech. 847:489-519, 2018). The method is applied to investigate the hydrostatics and stability of the configuration of an elliptical cylinder floating on an infinite liquid bath for a range of two dimensionless parameters: the eccentricity of the elliptical cross-section e and the Bond number Bo. It is shown that the prolate cylinder with a greater eccentricity e can bear a greater pressing force and a greater moment and therefore is more stable. For a great Bond number, the greater the eccentricity e of the cylinder, the greater the inclination angle corresponding to maximum moment. For a small Bond number, the opposite is true. However, the inclination angle of the cylinder corresponding to the maximum moment does not obey this rule. The maximum inclination angle occurs at an intermediate Bond number.

Experimental investigation of aerodynamic energy harvester with different interference cylinder cross-sections

Collecting kinetic energy from ambient vibrations for sustainably powering microelectronics becomes favoured in recent years. Yet the distribution of environmental oscillations is generally over a wide frequency spectrum which limits harvesting purpose of current energy harvesters. This work reports an optimal experimental design of piezoelectric energy generator for efficiently harvesting from aerodynamic oscillations. Various cross-sections of an interference cylinder (IC) are proposed so that the designed energy harvester operates under small wind speeds over a wide bandwidth. Average power of 803.4 μW at wind speed of 2.36 m/s with spacing ratio of 0.9 for the square interference cylinder configuration is achieved, and the synchronization region is increased 380% compared to that without the interference cylinder. It is observed that the harvester with circular or triangular interference cylinder at a certain value of spacing ratio displays a quenching behavior, resulting in quite a small output average power, which needs to be avoided. Transferring mechanism of dynamic behaviors for the energy generator equipped with an IC is determined and closely related with variations of the vibration frequency. Experimental results show that the plate interference configuration for the energy harvester has a superior harvesting performance over other configurations, especially in the occurrence of vortex-induced vibrations.

Transient behaviors of mixed convection in a square enclosure with an inner impulsively rotating circular cylinder

This work numerically investigated the unsteady mixed convective heat transfer between a square enclosure and an inner concentric circular cylinder maintained at different temperatures. The cylinder undergoes a transition of motion whose physics is significant for engineering applications such as cooling of rotating shaft and lubricating of journal bearing. It keeps stationary at first and steady-state natural convective flow is achieved, then impulsively rotates at a constant angular velocity and the flow arrives at a new final steady-state. Although the mixed convective heat transfer for rotating cylinder configurations are analyzed in a number of works, the transient behaviors of the thermal and flow characteristics from the onset of cylinder rotation to the final steady-state are not investigated, which restrains the thorough understandings on the relevant flow physics and mechanisms. The present work performs the first numerical investigation on the targeted physical problem. The objective is to explore the transient characteristics of the mixed convective heat transfer, and to identify the effects of cylinder rotation and rotation speed (tangential velocity at cylinder surface, V0) on the flow and heat transfer behaviors. The results are presented and analyzed by the temporal variations and spatial distributions of the thermal field, mean heat transfer rate, local heat transfer rate and velocity/temperature in certain regions where the flow is significantly affected. Our numerical results for the first time identify two flow regimes depending on the tangential velocity: mixed buoyancy-shear stress dominated flow for V0 ≤ 1.0 where the effect of natural convection is pronounced and the flow is driven by both buoyancy and shear stress from the cylinder surface, and shear stress dominated flow for V0 ≥ 2.0 where the flow is almost entirely driven by rotating cylinder and heat transfer is realized by conduction. The transient behaviors of the thermal and flow quantities are characterized and categorized based on the two regimes.

Stability analysis of the wake-induced vibration of tandem circular and square cylinders

We present a stability analysis to investigate the underlying fluid–structure modes during transverse wake-induced vibration (WIV) of an elastically mounted downstream cylinder in a tandem arrangement at low Reynolds number. The upstream cylinder with an equal diameter is kept stationary, whereas the downstream cylinder in the tandem arrangement is free to vibrate in the transverse direction. The WIV involves complex interaction dynamics of the upstream wake with the freely vibrating downstream cylinder, which leads to a relatively large transverse force and vibration in the post-lock-in region. We consider a data-driven model reduction approach to construct an eigenvalue representation of WIV system and perform the stability analysis to examine the underlying process of WIV for the tandem circular and square cylinders. The model reduction of the fluid system is constructed by the eigensystem realization algorithm (ERA) and coupled with a transversely vibrating bluff body in a state-space format. Unlike the wake-oscillator model, the ERA-based ROM does not rely on any empirical formulation and captures naturally the essential linear fluid dynamics through the solution of the Navier–Stokes equations. Results show that the WIV region and the onset reduced velocity can be predicted accurately by tracing the eigenvalue trajectories of the ERA-based low-dimensional model for a range of reduced velocities. The stability analysis reveals that there exists a persistently unstable eigenvalue branch that sustains WIV, which also implies that the highly nonlinear behavior of WIV has its linear origin. The sharp corner of the square cylinder is found to have the stabilizing effects, namely (i) the reduced velocity for the WIV onset is larger than its circular cylinder counterpart, (ii) the transverse response amplitude and the lift force are consistently lesser in both lock-in and post-lock-in regimes for the square cylinder configuration. This work has a potential impact on the development of control strategies for reducing undesired vibrations and loads in flexible structures undergoing wake interference effects.

Wake behind a concave curved cylinder

The wake behind a concave, curved cylinder configuration is investigated at different Reynolds numbers. Distinctly different wake flow regimes were observed in the computed flow field, including oblique vortex shedding and dislocations. The crucial influence of a straight vertical extension is explored.

Influence of rounded corners on flow interference between two tandem cylinders using FVM and IB-LBM

PurposeThe purpose of this study is to numerically investigate the influence of corner radius on the flow around two square cylinders in tandem arrangements at a Reynolds number of 100.Design/methodology/approachSix models of square cylinders with corner radii R/D = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 (where R denotes the corner radius and D denotes the characteristic dimension of the body) were studied using an immersed boundary-lattice Boltzmann method, and the results were compared with those obtained using a two-dimensional unsteady finite volume method. The cylinders were mounted in a tandem configuration (1.5 ≤ L/D ≤ 10 where L denotes the in-line separation between the cylinder centers). The simulated models were quantitatively compared to the aerodynamic force coefficients and Strouhal number. Furthermore, qualitative analysis is presented in the form of flow streamlines and vorticity contours.FindingsThe R/D and L/D values were varied to observe the variation in the flow characteristics in the gap and wake regions. The numerical results revealed two different regimes over the spacing range. The drag force on the downstream cylinder was negative for all corner radii values when the cylinders were placed at L/D = 3.0 (a single-body system). Subsequently, a sudden increase was observed in the aerodynamic forces (drag and lift) when L/D increased. A different gap value was identified in the transformation from a single-body to a two-body system for different corner radii. To verify the single-body system, a simulation was carried out with a single cylinder having a longitudinal geometric dimension equal to the tandem arrangement (L/D + D). Furthermore, in a single-body regime, the total drag of a tandem cylinder was less than that of a single cylinder, thus demonstrating the benefits of using tandem structures. A significant reduction in the aerodynamic forces and drag force was achieved by rounding the sharp corners and placing the cylinders in close proximity. An appropriate configuration of the tandem cylinders with a rounded corner of R/D = 0.4 and 0.5 at L/D = 3.0 and the range is enhanced to L/D = 4.0 for 0.0 ≤ R/D < 0.4 to achieve adequate drag reduction.Originality/valueTo the best of the author’s knowledge, there is a paucity of studies examining the effect of corner radius on bluff bodies arranged in a tandem configuration.

Investigations on effect of cylinder configuration of rectangular spiked tooth thresher on threshing performance of wheat crop

Nearly 90% of wheat threshers are spike tooth type and majority of them are operated by a prime mover of 3-4 kW. These threshers available in the market have cylinder and blower on the same shaft and hence are not suitable for threshing other crops. The machine factors which affect the quality and efficiency of threshing are feeding chute angle, spike shape, size and numbers, cylinder type, cylinder diameter, concave size, shape and clearance. In the threshing, standardization and improvement of critical component viz threshing cylinder configuration can bring down the total power consumption to 2/3. Therefore investigation was taken for manufacturing of threshing cylinders with different configuration and their testing for standardization. The threshing cylinder of rectangular spike of 6 mm thickness and 600 mm tip diameter yielded maximum output capacity (372 kg/h) with minimum specific power consumption (0.971 kWh/q) at maximum feed rate ((780 kg/h). The maximum threshing efficiency (99.91%) and minimum wheat straw length (21 mm) was obtained corresponding to the same configuration and feed rate. The minimum broken grain (0.20%) and total loss (0.43%) were at tip diameter of 500 mm and spike thickness of 6 mm corresponding to maximum feed rate (780 kg/h). The output capacity was above 300 kg/h at maximum feed rate (780 kg/h) for all the tip diameter and spike thickness. The maximum wheat straw split (88.60%) was at 780 kg/h feed rate corresponding to tip diameter of 550 mm and spike thickness of 6 mm. The maximum cleaning efficiency (99.52%) was at maximum feed rate (780 kg/h) corresponding to tip diameter of 550 mm and spike thickness of 6 mm. The wheat straw size for maximum output capacity and threshing efficiency were 22.43 mm at tip diameter of 600 mm and spike thickness of 6 mm corresponding to maximum feed rate (780 kg/h). For higher threshing efficiency, fine straw quality and minimum specific power consumption, rectangular spiked threshing cylinder of 600 mm tip diameter and spike thickness of 6 mm gave best performance results with total grain loss within permissible limit.

Performance investigation of NIM’s small force device based on electrostatic force principle

A small force device based on electrostatic force principle was developed by NIM. A flexure hinge mechanism with a balance lever is used as a force transmission unit. Inner and outer electrodes with thin cylinders configuration are assembled coaxially. The inner electrode is joined to the end of the flexure hinge mechanism. While a voltage is applied between inner and outer electrodes, an electrostatic force is generated. The force measurement range is from 10−8 N to 10−4 N. The main characteristics of the small force device such as creep, capacitance gradient and stiffness of flexure hinge mechanism were investigated. Force measurement uncertainty of the small force device is evaluated. The relative combined uncertainty of electrostatic force is less than 3.6×10−4 in the force range of 10μN to 100μN.

Method for combining valves with symmetric and asymmetric cylinders for hydraulic systems

Electro-hydraulic position control systems are widely applied in several fields. The valve and cylinder configuration and the dimensioning of these systems is dependent on the requested transient r...

Near field underwater explosion response of polyurea coated composite cylinders

The response of composite cylinders to near field underwater explosive (UNDEX) loading, including the effects of polyurea coatings, have been studied through experiments with corresponding computational simulations. Experiments were conducted on woven E-glass/epoxy roll wrapped cylinders in three unique configurations: (1) base composite, (2) base composite with a thin (100% composite thickness) coating, and (3) base composite with a thick (200% composite thickness) coating. Each cylinder configuration was subjected to near field underwater explosive loading in a large diameter test tank at charge standoff distances of 2.54 cm and 5.08 cm. The response of the cylinders on the non-loaded side was evaluated through high speed photography coupled with three-dimensional Digital Image Correlation (DIC). Transient deformation and Post-mortem damage comparisons were made to evaluate the effects of the applied coatings. The LS-Dyna finite element code has been utilized to conduct corresponding computational simulations of the experiments to allow for additional evaluations of the cylinder response. The simulations are shown to provide high correlation to the experiments in terms of pressure loading and final damage mechanisms. Results for the internal / kinetic energy levels and the material strains as determined through the simulations are presented. The experimental and numerical results show that the application of a polyurea coating is effective for significantly reducing damage in the cylinders. It is also shown that there is in increase in both material internal energies as well as overall strains with increasing coating thickness.

POD-Kriging Reduced Method's Application in Tandem Cylinders' Flow

The configuration of Tandem Cylinders is a typical one in researching noise and interactions between different components, where the distance-diameter ratio is a very significant parameter with which the flow form varies a lot. To clearly research the ratio's effect on tandem cylinders flow as well as the unsteady flow physics, a reduced-order model is built where Proper orthogonal Decomposition(POD) is usedto extract reduced basis modes, and Kriging model is used to train sample data and interpolate projection coefficents for each reduced basis. To ensure the snapshots' accuracy, the scale-adaptive simulation (SAS) model based on SST turbulence model is used to predict time-dependent flow field. By comparing with solutions provided by the numerical solver as well as experimental data, the reduced model presents a good accuracy and efficiency. And then based on the reduced basis, the change regulation of the time-average flow is summarized.

Fretting studies on electroplated brass contacts

This article describes frictional and electrical contact behaviors of electroplated brass under fretting conditions. Fretting tests using a crossed cylinder configuration are conducted. Cylindrical-type specimens are made of tin-plated and gold-plated brass. The ratio of the maximum tangential force to normal force is calculated. The ratio is 0.85 for the self-mated tin-plated brass and 0.55–0.6 for the self-mated gold-plated brass. The results show that the evolution of the dimensionless electrical resistance can be described with a Kachanov-type damage form. Two parameters, the electrical resistance rate constant and electrical resistance exponent, are determined to describe the evolution of the electrical resistance. The results also reveal that the rate constant is affected by the test temperature.

Measuring the charge density along the radius in concentric cylinders configuration by sensing system

The measurement of space charge density caused by the corona discharge around the overhead transmission line is a tough problem till nowadays. For this problem, a system for measuring the one-dimensional (1D) distribution of space charge density in a coaxial cylinder model under negative corona discharge in ambient air is developed. This system is a scale model which can provide research basis for actual overhead line measurement. The system consists of acoustic emission, space charge generation, and signal-receiving systems. The sound wave of an ultrasonic transducer is used to stimulate space charge generated by a small corona cage, and the applied voltage ranges from −34 kV to −38 kV. Charge vibration produces an electrical field (E-field) that can be measured with an E-field antenna. After obtaining the E-field signal, the adaptive noise cancellation method is adopted to eliminate noise interference so that the accuracy of charge density can be improved. The Townsend's analysis solution is used to calculate the theoretical value of space charge density. Experimental results are consistent with the simulation value and thus confirm the validity of the proposed adaptive noise cancellation method and sensing system.

Development of High-Powered Steam Turbines by OAO NPO Central Research and Design Institute for Boilers and Turbines

The article provides an overview of the developments by OAO NPO TsKTI aimed at improvement of components and assemblies of new-generation turbine plants for ultra-supercritical steam parameters to be installed at the power-generating facilities in service. The list of the assemblies under development includes cylinder shells, the cylinder’s flow paths and rotors, seals, bearings, and rotor cooling systems. The authors consider variants of the shafting–cylinder configurations for which advanced high-pressure and intermediate-pressure cylinders with reactive blading and low-pressure cylinders of conventional design and with counter-current steam flows are proposed and high-pressure rotors, which can increase the economic efficiency and reduce the overall turbine plant dimensions. Materials intended for the equipment components that operate at high temperatures and a steam cooling technique that allows the use of cheaper steel grades owing to the reduction in the metal’s working temperature are proposed. A new promising material for the bearing surfaces is described that enables the operation at higher unit pressures. The material was tested on a full-scale test bench at OAO NPO TsKTI and a turbine in operation. Ways of controlling the erosion of the blades in the moisture–steam turbine compartments by the steam heating of the hollow guide blades are considered. To ensure the dynamic stability of the shafting, shroud and diaphragm seals that prevent the development of the destabilizing circulatory forces of the steam flow were devised and trialed. Advanced instrumentation and software are proposed to monitor the condition of the blading and thermal stresses under transient conditions, to diagnose the vibration processes, and to archive the obtained data. Attention is paid to the normalization of the electromagnetic state of the plant in order to prevent the electrolytic erosion of the plant components. The instrumentation intended for monitoring the relevant electric parameters is described.

Characteristics of negative DC discharge in a wire-cylinder configuration under coal pyrolysis gas components at high temperatures.

This work aims to provide a comprehensive understanding of negative DC discharge under coal pyrolysis gas components (CO2, H2, N2, CH4, CO) and air. The characteristics of negative DC discharge were studied in a wire–cylinder configuration at an ambient temperature range of 20–600 °C by analyzing V–I characteristics, discharge photographs, and gas composition. With increasing temperature, corona onset voltage, spark breakdown voltage and operational voltage range for corona discharge decrease, but discharge current and electron current ratio increase. Discharge current of CO2 is higher than that of air due to the difference of electronegativity. During CO2 discharge, with the increase of output voltage, three types of discharge are successively observed, namely corona, glow and arc. However, during H2 discharge, only glow discharge is observed. Temperatures significantly affect the capability of CO to attach electrons. The discharge characteristic of CO is similar to the electronegative gas media at 20 °C and the non-electronegative gas media when the temperature exceeds 350 °C. Chemical reactions and carbon generation are observed during the CH4 and CO discharge process. The product of carbon filaments under the CH4 gas medium leads to discharge current volatility and short circuit. These results assist in understanding the property of ESP at high temperatures.