Numerical investigation of geometrical parameters on the hydrodynamic noise characteristics of submerged bodies and comparisons with experiments

2020 ◽  
pp. 147509022096224
Author(s):  
Sertaç Bulut ◽  
Selma Ergin
Keyword(s):  
Aspect Ratio ◽  
Peak Frequency ◽  
Broadband Noise ◽  
Circular Cylinders ◽  
Main Peak ◽  
Geometrical Parameters ◽  
Square Cylinder ◽  
Side Ratio ◽  
Cylinder Diameter ◽  
Hydroacoustic Measurements

The effects of the geometrical parameters on the hydroacoustic characteristics of the flow over rectangular, square and circular cylinders are investigated by numerical analyses and experiments. The numerical simulations are carried out by using a hybrid method which combines RANS with FWH equation. In order to validate the numerical results, the hydroacoustic measurements are also performed for the circular cylinders. The circular cylinders with diameters of 9.5, 19.0, 38.0 and 65.0 mm and aspect ratios of 2.5, 5.0 and 10.0 are employed for the hydroacoustic measurements and analyses. The rectangular cylinders with side ratios of 0.3, 0.6, 1.8 and 3.0, and also square cylinder with the side ratio of 1.0 are considered in hydroacoustic analyses. The Reynolds numbers are in the range of 2.25 × 104 and 1.7 × 105. The hydroacoustic characteristics of the cylinders are obtained to be completely different due to the differences in the shear layer separation, reattachment mechanism and the intensity of disturbance. The shape of the noise spectrum significantly changes with the geometrical shapes of the cylinders. The spectrum becomes narrower by an increase in the side ratio. The main peak frequency reduces when the side ratio increases. The highest value of the maximum sound pressure level, SPLmax are observed for the square cylinder and the lowest value for the rectangular cylinder with the side ratio of 0.6. The peak spectrum becomes like a line spectrum as the cylinder diameter decreases. The main peak frequency decreases when the cylinder diameter increases but it is almost constant with the aspect ratio. At the constant Reynolds number, the broadband noise level and SPLmax decrease with an increase in the cylinder diameter and decrease in the aspect ratio. A good agreement between the numerical and experimental results are obtained.

scholarly journals Hydromechanics of low-Reynolds-number flow. Part 2. Singularity method for Stokes flows

1975 ◽  
Vol 67 (4) ◽  
pp. 787-815 ◽  
Author(s):  
Allen T. Chwang ◽  
T. Yao-Tsu Wu
Keyword(s):  
Exact Solutions ◽  
Stokes Flow ◽  
Fundamental Solutions ◽  
The Body ◽  
Circular Cylinders ◽  
Geometrical Parameters ◽  
Flow Problems ◽  
Singularity Method ◽  
Wide Range ◽  
Body Shapes

The present study further explores the fundamental singular solutions for Stokes flow that can be useful for constructing solutions over a wide range of free-stream profiles and body shapes. The primary singularity is the Stokeslet, which is associated with a singular point force embedded in a Stokes flow. From its derivatives other fundamental singularities can be obtained, including rotlets, stresslets, potential doublets and higher-order poles derived from them. For treating interior Stokes-flow problems new fundamental solutions are introduced; they include the Stokeson and its derivatives, called the roton and stresson.These fundamental singularities are employed here to construct exact solutions to a number of exterior and interior Stokes-flow problems for several specific body shapes translating and rotating in a viscous fluid which may itself be providing a primary flow. The different primary flows considered here include the uniform stream, shear flows, parabolic profiles and extensional flows (hyper-bolic profiles), while the body shapes cover prolate spheroids, spheres and circular cylinders. The salient features of these exact solutions (all obtained in closed form) regarding the types of singularities required for the construction of a solution in each specific case, their distribution densities and the range of validity of the solution, which may depend on the characteristic Reynolds numbers and governing geometrical parameters, are discussed.

Influence of nozzle exit geometrical parameters on supersonic jet decay

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Prasanta Kumar Mohanta ◽  
B. T. N. Sridhar ◽  
R. K. Mishra
Keyword(s):  
Aspect Ratio ◽  
Nozzle Exit ◽  
Ambient Air ◽  
Schlieren Image ◽  
Geometrical Parameters ◽  
Image Study ◽  
Aspect Ratios ◽  
Core Length ◽  
Supersonic Core Length ◽  
The Impact

Abstract Experiments and simulations were carried on C-D nozzles with four different exit geometry aspect ratios to investigate the impact of supersonic decay characteristics. Rectangular and elliptical exit geometries were considered for the study with various aspect ratios. Numerical simulations and Schlieren image study were studied and found the agreeable logical physics of decay and spread characteristics. The supersonic core decay was found to be of different length for different exit geometry aspect ratio, though the throat to exit area ratio was kept constant to maintain the same exit Mach number. The impact of nozzle exit aspect ratio geometry was responsible to enhance the mixing of primary flow with ambient air, without requiring a secondary method to increase the mixing characteristics. The higher aspect ratio resulted in better mixing when compared to lower aspect ratio exit geometry, which led to reduction in supersonic core length. The behavior of core length reduction gives the identical signature for both under-expanded and over-expanded cases. The results revealed that higher aspect ratio of the exit geometry produced smaller supersonic core length. The aspect ratio of cross section in divergent section of the nozzle was maintained constant from throat to exit to reduce flow losses.

scholarly journals J091043 Numerical simulation of broadband noise generated from a square cylinder

2011 ◽  
Vol 2011 (0) ◽  
pp. _J091043-1-_J091043-3
Author(s):  
Naoki MASUDA ◽  
Chisachi KATO ◽  
Yasumasa SUZUKI
Keyword(s):  
Numerical Simulation ◽  
Broadband Noise ◽  
Square Cylinder

Hierarchical Structure Enhances and Tunes the Damping Behavior of Load-Bearing Biological Materials

2016 ◽  
Vol 83 (5) ◽  
Author(s):  
Mahan Qwamizadeh ◽  
Pan Liu ◽  
Zuoqi Zhang ◽  
Kun Zhou ◽  
Yong Wei Zhang
Keyword(s):  
Aspect Ratio ◽  
Biological Materials ◽  
Damping Capacity ◽  
Geometrical Parameters ◽  
Loading Frequency ◽  
Load Bearing ◽  
Damage And Fracture ◽  
Damping Behavior ◽  
Specific Loading ◽  
Self Similar

One of the most crucial functionalities of load-bearing biological materials such as shell and bone is to protect their interior organs from damage and fracture arising from external dynamic impacts. However, how this class of materials effectively damp stress waves traveling through their structure is still largely unknown. With a self-similar hierarchical model, a theoretical approach was established to investigate the damping properties of load-bearing biological materials in relation to the biopolymer viscous characteristics, the loading frequency, the geometrical parameters of reinforcements, as well as the hierarchy number. It was found that the damping behavior originates from the viscous characteristics of the organic (biopolymer) constituents and is greatly tuned and enhanced by the staggered and hierarchical organization of the organic and inorganic constituents. For verification purpose, numerical experiments via finite-element method (FEM) have also been conducted and shown results consistent with the theoretical predictions. Furthermore, the results suggest that for the self-similar hierarchical design, there is an optimal aspect ratio of reinforcements for a specific loading frequency and a peak loading frequency for a specific aspect ratio of reinforcements, at which the damping capacity of the composite is maximized. Our findings not only add valuable insights into the stress wave damping mechanisms of load-bearing biological materials, but also provide useful guidelines for designing bioinspired synthetic composites for protective applications.

Estimation of Maximum Flow Length for CF-PEEK Overmolded Grid Structures Using the Finite Element Method

2021 ◽  
Author(s):  
Carlos Rodríguez-Mondéjar ◽  
Álvaro Rodríguez-Prieto ◽  
Ana María Camacho
Keyword(s):  
Aspect Ratio ◽  
Injection Molding ◽  
Cross Section ◽  
Maximum Flow ◽  
Thermoplastic Composites ◽  
Injection Molding Process ◽  
Geometrical Parameters ◽  
Molding Process ◽  
Support Tool ◽  
Flow Length

Abstract Injection overmolding process is a high versatile process that permits, when used in combination with fiber reinforced thermoplastic composites, the obtaining of high mechanical properties structures with complex geometries in short time cycles. The maximum flow length is a parameter that reflects the success of filling in a polymer injection molding process. Geometry of the part, rheological properties of the polymer and process parameters, such as injection pressure and temperature, are involved on the value of this parameter and therefore on the viability of a certain configuration. For injection molding manufacturing, the understanding of the relation between maximum flow length and main geometrical parameters of the molded part is fundamental to approach the product design, which is conditioned severely by processing capabilities. In this work, the maximum flow length is obtained for different geometries of an overmolded rectangular stiffener grid of carbon fiber filled polyether eter ketone (CF-PEEK) using the software Moldflow© Adviser© for calculations. Value of maximum flow length is provided as a function of cross section aspect ratio for gate diameters between 0.8 mm and 1.4 mm and cross section areas from 10 to 50 mm2. An exponential decrement of maximum flow length has been observed with the increment of aspect ratio of the cross section as well as a linear increment with the increment of cross section area. Gate diameter variation is slightly related with maximum flow length for the simulated values. These results provide a support tool for geometry sizing in overmolded rectangular grid parts at preliminary design stages.

scholarly journals Biomimetic Functional Surfaces towards Bactericidal Soft Contact Lenses

Micromachines ◽  
2020 ◽  
Vol 11 (9) ◽  
pp. 835
Author(s):  
Tianyu Mao ◽  
Fengzhou Fang
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Contact Lenses ◽  
Influence Factors ◽  
Interaction Mechanism ◽  
Holistic Approach ◽  
Geometrical Parameters ◽  
Physical Interaction ◽  
Soft Contact ◽  
Soft Contact Lenses

The surface with high-aspect-ratio nanostructure is observed to possess the bactericidal properties, where the physical interaction between high-aspect-ratio nanostructure could exert sufficient pressure on the cell membrane eventually lead to cell lysis. Recent studies in the interaction mechanism and reverse engineering have transferred the bactericidal capability to artificial surface, but the biomimetic surfaces mimicking the topographical patterns on natural resources possess different geometrical parameters and surface properties. The review attempts to highlight the recent progress in bactericidal nanostructured surfaces to analyze the prominent influence factors and cell rupture mechanism. A holistic approach was utilized, integrating interaction mechanisms, material characterization, and fabrication techniques to establish inclusive insights into the topographical effect and mechano-bactericidal applications. The experimental work presented in the hydrogel material field provides support for the feasibility of potentially broadening applications in soft contact lenses.

Experimental Study on Flow-Induced Vibration of Floating Squared Section Cylinders With Low Aspect Ratio: Part I — Effects of Incidence Angle

2015 ◽  
Author(s):  
Rodolfo T. Gonçalves ◽  
Dênnis M. Gambarine ◽  
Felipe P. Figueiredo ◽  
Fábio V. Amorim ◽  
André L. C. Fujarra
Keyword(s):  
Aspect Ratio ◽  
Incidence Angle ◽  
Ocean Basin ◽  
Circular Cylinders ◽  
Structural Damping ◽  
Flow Induced Vibration ◽  
Double Frequency ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Elastically Supported

Experiments regarding flow-induced vibration on floating squared section cylinders with low aspect ratio were carried out in an ocean basin with rotating-arm apparatus. The floating squared section cylinders were elastically supported by a set of linear springs to provide low structural damping to the system. Three different aspect ratios were tested, namely L/D = 1.0, 2.0 and 3.0, and two different incidence angles, namely 0 and 45 degrees. The aims were to understanding the flow-induced vibration around single columns of multi-column platforms, such as semi-submersible and TLP. VIV on circular cylinders were also carried out to compare the results. The range of Reynolds number covered was 2,000 < Re < 27,000. The in-line and transverse amplitude results showed to be higher for 45-degree incidence compared with 0-degree, but the maximum amplitudes for squared section cylinders were lower compared with the circular ones. The double frequency in the in-line motion was not verified as in circular cylinders. The yaw amplitudes cannot be neglected for squared section cylinders, maximum yaw amplitudes around 10 degrees were observed for reduced velocities up to 15.

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