Rigid Cylinder Research Articles

Friction Characteristic Calculations during Cylinder’s Sliding Contact over the Wavy Viscoelastic Base

The formulation and method for solving the contact problem of the rigid cylinder sliding over the wavy surface of the viscoelastic layer bonded to the rigid base is presented under the assumption that the cylinder axis is perpendicular to the surface waviness cross-section. The calculation results allow assessing the effects of sliding velocity, surface layer microgeometry, and its relaxation properties on the contact characteristics (the position and size of the actual contact region and the contact pressure distribution) and on the friction force’s deformation component. Depending on the sliding velocity, the contact region may be solid or consisting of discrete contact spots with high values of the maximum contact pressure for the same surface waviness. It is also established that the friction force increases with increasing waviness amplitude and viscosity of the surface layer.

Towards simulation of force and velocity fluctuations due to turbulence in the relay nozzle jet of an air jet loom

This research was aimed at obtaining a first estimation of the effect of turbulent vortices present in the relay nozzle jets of an air jet loom on the weft. To this end a large eddy simulation (LES) model was set up and validated capable of simulating a highly underexpanded jet up to a point sufficiently far from the nozzle exit such that flow features at the weft location could be analyzed. The quality of the LES was evaluated based on several quality criteria as well as by comparing the results with experiments and data from the literature. The results show that for a free jet substantial velocity fluctuations are present at a representative yarn location. By inserting a rigid cylinder at this location, the corresponding force fluctuations on a smooth yarn were also obtained. The research shows that the unsteadiness in the jet is quite substantial, as are the corresponding force fluctuations. These fluctuations could have a profound impact on the yarn motion and should at least be considered when using numerical tools to evaluate the forces on or the motion of a yarn acted on by a relay nozzle jet.

A sharp-interface immersed boundary method for simulating high-speed compressible inviscid flows

This paper presents a robust sharp-interface immersed boundary method for simulating inviscid compressible flows over stationary and moving bodies. The flow field is governed by Euler equations, which are solved by using the open source library OpenFOAM. Discontinuities such as those introduced by shock waves are captured by using Kurganov and Tadmor divergence scheme. Wall-slip boundary conditions are enforced at the boundary of body through reconstructing flow variables at some ghost points. Their values are obtained indirectly by interpolating from their mirror points. A bilinear interpolation is employed to determine the variables at the mirror points from boundary conditions and flow conditions around the boundary. To validate the efficiency and accuracy of this method for simulation of high-speed inviscid compressible flows, four cases have been simulated as follows: supersonic flow over a 15 ° angle wedge, transonic flow past a stationary airfoil, a piston moving with supersonic velocity in a shock tube and a rigid circular cylinder lift-off from a flat surface triggered by a shock wave. Compared to the exact analytical solutions or the results in literature, good agreement can be achieved.

A simplified model to evaluate peak amplitude for vertical vortex-induced vibration of bridge decks

A simplified model is developed to conveniently evaluate the peak vortex-induced vibration (VIV) amplitudes of a bridge deck at various mass-damping conditions. As a simplified form of the describing function-based model previously developed by the authors, the key innovation of the new model is the introduction of an envelope curve of the aerodynamic describing functions (or amplitude-dependent flutter derivatives), which determines the maximum negative aerodynamic damping versus vibration amplitude in the lock-in range. Based on the envelope curve, the peak VIV amplitudes at different mass-damping conditions can be obtained directly without calculating all the VIV amplitudes in the entire lock-in range. The new model is more practical for engineers in the bridge engineering community since it only contains a single group of aerodynamic parameters which don't vary with the reduced wind speed. The envelope curve can be either identified based on the VIV decay-to-resonance and/or grow-to-resonance signals at a single mass-damping condition, or based on the VIV steady amplitudes at different mass-damping conditions. Numerical examples involving the VIV analyses of a rigid rectangular cylinder and a bridge deck sectional model are utilized to validate the simulation accuracy of the proposed model, and the model is applied to calculate the peak VIV amplitudes of two flexible bridge decks at various mechanical damping levels. The proposed model is capable of accurately and conveniently predicting the peak VIV amplitudes of a bridge deck sectional model at various mass-damping conditions. For a flexible bridge deck, the peak VIV amplitude calculated by the proposed model is slightly conservative due to the overestimated negative aerodynamic damping at some span-wise segments of the bridge deck. The superiority of the proposed model relative to the conventional van der Pol-type model is also demonstrated.

Particle-resolved simulations of liquid fluidization of rigid and flexible fibers

Particle-resolved, three-dimensional, time-dependent simulations of rigid and flexible cylinders fluidized by a liquid flow in fully periodic domains have been performed by means of the lattice-Boltzmann method supplemented with immersed boundaries. The solids volume fraction ranges from 0.10 to 0.48 and the length-over-diameter aspect ratio of the cylinders from 4 to 12. The bending stiffness of the cylinders is the third major input parameter. The resulting Reynolds numbers based on the average slip velocity of the cylinders and their equivalent diameter range from 6 to 70. It is shown that increasing the flexibility—that is, decreasing the bending stiffness—reduces the Reynolds number, an effect that is most pronounced for low solids volume fractions and long cylinders. As for rigid cylinders, the distribution of the orientation relative to the direction of gravity of the flexible cylinders is a pronounced function of the solids volume fraction and the aspect ratio. Flexibility tends to somewhat randomize the orientation distribution, which could explain the effect of flexibility on the slip velocity and thus the Reynolds number.

Geometric-acoustics analysis of single-scattering of nonlinearly evolving waves by circular cylinders

Geometric acoustics, or acoustic ray theory, is used to analyze the scattering of high-amplitude acoustic waves incident upon rigid circular cylinders. Theoretical predictions of the importance of incorporating nonlinearity in modeling and the nonlinear evolution of the scattered wave field are provided. An analysis of scattering by many cylinders with a dilute concentration is also provided. The nonlinear evolution of the incident wave is shown to be of much greater importance to the overall evolution than the nonlinear evolution of the individual scattered waves. This presentation is based on an article recently published by the Journal of the Acoustical Society of America.

Acoustic wave focusing using a 2.5-D graded metamaterial lens

The creation of a three-dimensional focal spot in air underpins applications in many fields. The literature presents many examples of focusing with acoustic metamaterials, but they are difficult to manufacture in large scale. Sonic crystals, are easier to make—since they are periodic arrangements of simple scatterers—but there are not many studies on achieving 3-D acoustic convergence through a 2-D sonic structure in air. In this study, we exploit the methods of sonic crystals to design the acoustic equivalent of a gradient index (GRIN) lens. We show that an extruded 2-D hexagonal lattice array of rigid cylinders with gradient diameters can be used to achieve the focusing of a 3-D shaped beam at audio frequencies i.e., a 2.5-D lens. We use finite-elements simulations with a commercial software to describe the device's performance in terms of band structure and equifrequency contours. We also present some preliminary measurements taken using a 3-D-printed model of our lens, designed for a focal length of 3.1 cm at 8 kHz. We find our 2.5-D GRIN lens works over a bandwidth of almost one octave. We discuss potential future uses, like in the correction of acoustical aberrations and in devices of flexible focal length.

An experiment study of vortex induced vibration of a steel catenary riser under steady current

The vortex induced vibration (VIV) of marine risers has been investigated by many researchers in experimental studies of a straight flexible riser model as well as a rigid cylinder to reveal the dynamic response characteristic and the mechanics behind it. However, due to the limitation of experimental apparatus, very few studies are about the VIV of a steel catenary riser (SCR) which is with a complex geometry. To investigate the VIV features and to further develop the corresponding numerical predictions of a SCR under steady current, a large-scale model test of a SCR was towed in an ocean basin at various speeds. Fiber Bragg grating strain sensors are instrumented on the riser model to measure both in-plane and out-of-plane responses. The characteristics of oscillating amplitude and dominating frequency response, the phenomenon of mode competition and travelling wave and the fatigue damage of the steel catenary riser in inline and cross-flow direction under steady current are analyzed.

A modeling of synthetic aperture Image of a partially buried rigid cylinder on a flat boundary

Synthetic Aperture Sonar is a side-looking sonar that can obtain the equal resolution of the sonar images in lower frequencies than the conventional frequency ranges of Side Scan Sonar. The current study shows a part of the works being developed in the incorporation of the prototypes of Synthetic Aperture Sonar. As well as the conventional 2-D SAS, the system also has the bathymetric imaging in mind. In order to test the parameters and the algorithms imbedded in the system, a partially buried rigid cylinder was adopted as a simulation target for the broadside incident and the scattering amplitude by the cylinder was calculated by the Kirchhoff approximation. The features of monostatic scattering by a partially buried objects on the boundary are heavily dependent on its exposed surface out of the boundary [K. Baik and P. L. Marston, IEEE J. Ocean. Eng. 33, 368 (2008)] due to the contributions by the flat boundary to the scattered direction. Delay of the reverberation between the boundary and the cylinder was considered by the inverse Fourier transform of total scattering form function [L. G. Zhang etal., J. Acoust. Soc. Am. 91, 1862 (1992)] in the modeling. Current study shows the effects the parameters of the scattering by the partially buried cylinder on the resulting simulated SAS images. [This work is supported by the project of “Development of towed interferometric Synthetic Aperture Sonar” (15-CM-SS-01).]

Broadband acoustic lens design using the principle of reciprocity and gradient-based optimization

In this work, we will present a gradient-based optimization method for the design of an acoustic lens. This design is based on an optimization process using the semi-analytical optimization approach and applying the principle of reciprocity. Here, we will illustrate the use of acoustic reciprocity to define the pressure at the focal point due to a source located in a far-field. The reciprocity enables us to relate the response by configuration of scatterers for an incident plane wave in terms of the far-field Green's function. The idea differs from earlier inverse designs that use topology optimization tools and generic algorithms. The gradient-based optimization algorithm maximizes the sound amplification at the focal point by evaluating pressure derivative with respect to the cylinder positions and then perturbatively optimizing the position of each cylinder in the lens while taking into account acoustic the multiple scattering between the cylinders. Computations are performed on MATLAB using “fmincon” function with a MultiStart optimization solver, and supplying the gradient of pressure at the focus. The reciprocal formulation of inverse design of acoustic lens leads to the closed-form solution that takes lesser time to compute the absolute pressure and it gradients at the focal point. The numerical results for the optimization of the broadband acoustic lens will be illustrated for configurations of uniform rigid cylinders.

Numerical investigation of solitary wave attenuation and resistance induced by rigid vegetation based on a 3-D RANS model

Mangrove forests can significantly attenuate tsunami waves and thus play an important role in coastal protection. As a first approximation, the problem is modeled utilizing solitary waves impinging on emergent/submerged rigid cylinders. A three-dimensional (3-D) numerical model using cyclic boundary conditions was developed based on the IHFOAM solver to investigate the effects of wave nonlinearity and vegetation configuration on the solitary wave attenuation. The numerical model was established based on the Reynolds Averaged Navier-Stokes (RANS) equations combined with the standard k – ω shear stress transport (SST) turbulence model and the volume of fluid (VOF) surface capturing schemes. The results indicate that different patterns are found in terms of flow field characteristics (velocity and turbulent kinetic energy) and forces exerted on the cylinders for various wave nonlinearity and vegetation configuration, which helps to better understand wave dissipation mechanism induced by vegetation. Different from the bulk drag coefficient derived by the conventional wave dissipation models, the direct force method was applied to quantify the time-varying and period-averaged drag coefficients (CD) of individual cylinders. The time-varying CD associated with maximum force and local velocity is defined as the representative CD, for comparison with the period-averaged CD in detail. Besides, by considering the submergence ratio, new generic CD formulas are proposed as functions of the modified Reynolds number (Re) and Keulegan-Carpenter number (KC) for illustrating the CD dynamics under solitary wave conditions. Finally, a preliminary comparison between the proposed CD formulas and existing formulas are given to reveal the intrinsic CD law, which may lead to improved understanding and modeling concerning wave-vegetation interaction.

Vortex-induced vibrations of a flexible cylinder at subcritical Reynolds number

Abstract

Predictions of the transient loading exerted on circular cylinders by arbitrary pressure waves in air

Abstract

How does three-dimensional canopy geometry affect the front propagation of a gravity current?

Large-eddy simulations are performed to investigate how three-dimensional canopy geometry affects the front propagation of an incoming gravity current under a given initial forcing. A regular array of rigid square cylinders are used to represent the distributed canopy elements. It is shown that the conventional geometrical parameter of submerged canopies in constant-density flows (ah, where a is the frontal area per canopy volume and h is the canopy height) is misleading when applied to buoyancy-driven flows due to the additional complexity arising from the internal density gradients. Instead, the present study suggests a new geometrical framework consisting of a canopy density (ϕ) and a canopy-to-current height ratio (h̃), which can jointly provide an unambiguous description of the state of the current–canopy interaction. Two propagation regimes of the gravity current are identified, either along the channel bed (through-flow) or above the canopy’s top boundary (over-flow). Our analysis reveals that ϕ and h̃ counteract each other’s effect on the transition of flow regimes. Large ϕ implies a strong suppression of horizontal advection within the canopy and thus promotes the through-to-over flow transition; in contrast, large h̃ tends to promote the over-to-through flow transition due to the lack of sufficient potential energy to overcome the height jump. The end product is a complex variation pattern of a propagation regime and front velocity in the two-dimensional ϕ–h̃ parameter space.

Modelling of Cylinder Indentation into a Viscoelastic Layer

The indentation of a rigid cylinder with a flat base into a viscoelastic layer situated without friction on a rigid base is considered. The interaction process consists of two stages: indentation of a cylinder at a constant speed to a certain depth and its further holding in this depth. The mechanical behavior of a viscoelastic layer is described by equations of linear viscoelasticity with relaxation functions of two types: exponential and power. The solution of the problem is based on the application of the Volterra principle and the use of an elastic solution constructed by the asymptotic “methods of large and small λ” that were developed by I. I. Vorovich and his students. On the basis of the solution obtained, the nature of the time variation in contact stresses and loads during the indentation of the cylinder has been studied for both relatively small and relatively large layer thicknesses. A comparison of the time variation of the studied quantities for two different relaxation functions and with the results of calculations based on a simplified one-dimensional model used to describe the behavior of a viscoelastic layer during indentation is performed.

Circular Shell Gripper for Handling Food Products.

Pneumatically driven soft robotic grippers have been extensively studied in recent years. A majority of the grippers, especially those entirely composed of soft materials, can adapt to and handle various objects. However, there are limited studies regarding the realization of arbitrary grasping postures and twisting manipulation. Furthermore, the handling efficiency or the takt time of a handling task has not been investigated frequently. Therefore, this article proposes a circular shell gripper that consists of a rigid external shell and four soft internal air chambers. The soft chambers can be pneumatically inflated, thereby enabling it to grasp an object with a large contact area. The rigid shell allows the gripper to generate a large grasping force, while providing rigidity. This allows it to achieve arbitrary handling postures and twisting manipulations. A finite element model was constructed to simulate the chamber inflation, contact area upon grasping, lifting force, and twisting torque. An analytical model was formulated to quickly predict the lifting force and the twisting torque required to manipulate a known object. The models were validated via experimental tests on the lifting and twisting of a rigid cylinder. The experimental results indicate that the shell gripper can generate a maximum lifting force and twisting torque of 50.97 N and 0.73 Nm, respectively, with an input pressure of 10 kPa. Experimental tests on a variety of food and drink products revealed that the gripper could handle deformable, heavy, and irregularly shaped objects as well as realize arbitrary manipulation posture and twisting motion. The takt time for a pick-and-place task was found to be ∼2-5 s, using an SCARA robot; this time can be further optimized (less than 1 s) by using a parallel robot. However, the gripper was unable to handle low-profile objects, due to the downward pressing force; this was identified as a limitation of the proposed design.

Wave Attenuation by Spartina alterniflora under Macro-Tidal and Storm Surge Conditions

Salt marshes are coastal wetlands that provide many ecosystem services. They protect coasts from erosion, storm surge, and small tsunami by dissipating wave energy. Plant flexibility has been reported to reduce drag force on and wave attenuation of marsh plants. In this study, we proposed a new drag coefficient formula to account plant flexibility so that the classical theory based on rigid cylinders can be extended to predict wave decay by flexible plants. To validate this new formula, the field survey was conducted in the North Hangzhou Bay, China. The wave attenuation was measured in a Spartina alterniflora marsh under a combined macro-tidal and storm surge condition, during which strong bending motions of the plants were observed. The new formula provided better predictions of wave decay than that by the traditional drag formula when compared to the field data measured in both the present study and the earlier studies.

Non-linear piezoelectric fluidic energy harvesters: The mutual interaction of two oscillating cylinders

The presence of a bluff body upstream of a cantilever beam promotes persistent, aero-elastic vibrations of the beam. Vortex-induced vibration in an array of two mutually interacting bluff bodies in such configurations undergoing two-degrees of freedom transverse oscillation has not been investigated before. In the present work, we have studied experimentally, the unsteady response of an array of two similar rigid cylinders, positioned side-by-side in reference to the freestream velocity, each one mounted on the upstream end of an elastic cantilever beam. By fitting the beams with piezoelectric layers, these configurations are converted to piezoelectric fluid energy harvesters (PFEH) that can extract small amounts of energy from the flow. Comparing the performance of linear (L-PFEH), non-linear (NL-PFEH), and a non-linear array (NLA-PFEH) of harvesters show that NLA-PFEH has the widest broadband operating velocity range and the greatest generated power followed by NL-PFEH and then L-PFEH. The maximum electric power output of NLA-PFEH was ~1000% greater than for NL-PFEH with a corresponding ~250% increase in the operating velocity range. Different cylinder configurations reveal the presence of hysteresis in the behavior of NLA-PFEH when the distance between the cylinders (so-called cylinder gap to diameter ratio), G/ D < 0.5. At large distances from each other ( G/ D ≥ 4), the two cylinders behave like independent, isolated harvester units with rather weak mutual interaction.

Wake behavior analysis for two circular cylinders placed at several angles to the flow

This paper presents an experimental study performed in an aerodynamic channel using hot-wire anemometers and flow visualization by injection of dye in water in a hydraulic channel of the flow on two rigid cylinders placed at several angular positions to the flow, from 0° (side-by-side) to 90° (tandem). The main objective is to analyze the effects of the angular positions on the wake flow and the occurrence of bistability. Signal analysis was performed by means of Fourier and discrete and continuous wavelets transform. Time series of the angle of the flow emanating from the cylinder gap related to the main flow direction were obtained from flow visualization analysis to track the flow mode change in the water flow. Results from the aerodynamic channel showed the presence of bistability only for side-by-side configuration, and some attempts to modify the flow mode for 2.5° and 5° while through the flow visualization the flow mode changes were present for side-by-side and for 2.5° configurations. For the other angles investigated, the presence of a narrow and a wide wake without flow mode changes was observed. The difference between the results for 2.5° suggests that the scales and inertia involved in bistability phenomenon may affect the phenomenon. For 75°, the wide wake is so vigorous that it overwhelmed the narrow wake, displacing it downwards, and increasing the amplitude of the vertical component of the wake compared to smaller angles. The phenomena analyzed can be seen as two-dimensional for all cases, but the presence of vertical components shows that the resulting flow is three-dimensional.

Acoustic Doppler velocimetry (ADV) data on flow-vegetation interaction with natural-like and rigid model plants in hydraulic flumes.

Vegetation, generally present along river margins and floodplains, governs key hydrodynamic processes in riverine systems. Despite the flow-influencing mechanisms exhibited by natural vegetation and driven by its complex morphology and flexibility, vegetation has been conventionally simulated by using rigid cylinders. This article presents a dataset obtained from hydraulic experiments performed for investigating the flow-vegetation interaction in partly vegetated channels. Vegetation was simulated by using both natural-like and rigid model plants. Specifically, two sets of experiments are described: in the first, vegetation was simulated with natural-like flexible foliated plants standing on a grassy bed; in the second, rigid cylinders were used. Experiments with rigid cylinders were designed to be compared against tests with natural-like plants, as to explore the effects of vegetation representation. The following experimental data were produced: 3D instantaneous velocity measured by acoustic Doppler velocimetry, vegetation motion video recordings, and auxiliary data including detailed vegetation characterization. These experiments are unique both for the use of natural-like flexible woody vegetation in hydraulic experiments and for the similarity achieved between the resulting observed vegetated shear layers. These data are expected to be useful in vegetated flows model development and validation, and represent a unique benchmark for the interpretation of the flow-vegetation interaction in partly vegetated channels.