Flexible Sidewalls Research Articles

Numerical study of green water loads on a fixed structure with elastic sidewalls by MPS-FEM coupled method

In rough seas, large masses of water will exceed the freeboard and cause violent slamming on the deck, known as green water. Due to its high destructive power, many scientists have devoted themselves to the study of green water. Given the complexity, various simplified methods have been used to study the mechanism and stresses of green water. In this paper, the loads and patterns of green water events on a fixed structure with rigid or flexible sidewalls were investigated using the solver MPSFSI-SJTU based on the Moving Particle Semi-Implicit (MPS) method coupled with the Finite Element Method (FEM). The rapid flow-structure interaction is generated by the wet dam-break method. Firstly, the numerical simulation of the water shipping events with the rigid structure was carried out, which was in good agreement with the existing numerical simulation results. Secondly, numerical simulations were carried out for different cases of fixed structures with elastic side wall and elastic upper wall. The influence of elastic modulus on wave loads and waveform was analyzed.

Case studies on aeroacoustics damping performances of Coupled Helmholtz Resonators over low frequency ranges

Helmholtz resonators are widely applied in industries to reduce the transmission of unwanted noise and passively attenuate tonal noise in pipes/ducts. For example, internal combustion engines take advantage of Helmholtz resonators by combining air box, subwoofers and perforated pipes/plates to reduce engine noise emission nowadays. However, the main drawback of the conventional Helmholtz resonators includes a very narrow bandwidth. To broaden the effective noise damping frequency range of Helmholtz resonators, a number of different improved designs are reported and tested recently in the literature such as applying an array of separated resonators or implementing mechanical-coupled Helmholtz resonators. In this work, we conduct a brief review on the aeroacoustics damping performance of coupled Helmholtz resonators over low frequency range. The noise damping performances could be characterized and quantified in terms of transmission loss and sound absorption coefficient. Both definitions are discussed. Comparison is then made between the separately working resonators and the mechanical-coupled ones. This is achieved by replacing the sharable flexible sidewall with a rigid sidewall. The effect of the mean grazing flow is also discussed and examined on the noise damping performances. An experimental case study of the present authors is included. Additionally, to improve the noise damping performance further, an overview of the resonators neck with different noise damping materials inserted is conducted. Finally, 3D numerical approaches in simulating the aeroacoustics damping performances of coupled Helmholtz resonators are reviewed. This case study and brief overview provides a guidance on improving the design of coupled Helmholtz resonators and an array of Helmholtz resonators.

Mechanical properties of phenine nanotubes

Phenine Nanotubes (PhNT) are cylinder-shaped molecules synthetized from 1,3,5-trisubstituted benzene ring building blocks that can form tubular segments of different sizes. Small nanotube segments have been recently synthetized, and efforts are being made to increase the nanotubes’ length by adding more “phenine” units. To the authors’ best knowledge, a complete characterization of the mechanical properties of these nanotubes has not yet been accomplished. In this work, Reax and AIREBO forcefields were used to model armchair and zigzag PhNTs and Molecular Dynamics simulations were employed to determine their mechanical properties for tensile, compressive, bending and twisting loadings. It was found that PhNTs have a much lower Young’s modulus (about 30%) and tensile strengths (about 45%) than carbon nanotubes (CNTs), but can endure longer tensile strains without breaking apart. Although possessing a lower bending and twisting stiffness than CNTs, PhNT have highly flexible sidewalls due to their superior porosity, and therefore can withstand higher angles of twist and angles of bend without breaking bonds. This extra flexibility; extended porosity; possibility for heteroatom doping and reasonable strength, make PhNTs very promising candidates for a wide range of applications, such as sensing, ionic transistors or molecular sieving. Finally, a brief study on the application of elastic continuum shell formulas to predict the critical stress (compression), critical moment (bending) and critical torque (twisting) is also presented.

ВНЕДРЕНИЕ ТЕХНОЛОГИИ FLEXIBLE SIDEWALL

Studies on increasing the level of yield have the great importance for the Russian Federation as a whole and the Altai Territory in particular as for the agro-industrial complex. LLC “NORTEC” developed and implemented the Flexible sidewall technology in order to reduce tire pressure on the ground. An analysis of the external characteristics, composition of the tire, as well as the impact of its surface on the ground was carried out. It was possible to reduce the operating pressure in the tire to 0.8 kgf / cm2, while increasing the contact patch because of change in the design and composition of rubber compounds. Particular attention in the study was paid to the distribution of material in the tire, which influenced further characteristics and performance. The results of these studies will be further applied to the line of large-sized agricultural tires manufactured by Nortek LLC. The tire 710/70R38 FS, produced using the Flexible sidewall technology, was tested and improved in several stages, after which the tire could be the most competitive with foreign analogues. The article will be useful both to specialists in the production of rubber materials, students, teachers of chemical specialties and to a circle of readers, interested in modern tire production and the prospects for the agricultural industry.

Fluid-structure interaction analysis of entropy generation and mixed convection inside a cavity with flexible right wall and heated rotating cylinder

The current work concentrates on the transient entropy generation and mixed convection due to a rotating hot inner cylinder within a square cavity having a flexible side wall by using the finite element method and arbitrary Lagrangian-Eulerian formulation. Effects of various relevant parameters like Rayleigh number (104⩽Ra⩽107), angular rotational velocity (-1⩽Ω⩽1), dimensionless elasticity modulus (1012⩽E⩽1015) on the convective heat transfer characteristics and entropy generation rates are analyzed for dimensionless time 10-8⩽τ⩽3.5. It is observed that various complex shaped wall deformations are established depending on the non-dimensional elastic modulus of the flexible right wall and cylinder rotation direction. The local and average Nusselt numbers rise with Ra and secondary peaks in the local Nusselt number are established for lower values of Ra. The local heat transfer along the hot cylinder does not change for the case of clockwise rotation of the heated cylinder even if there is a wall deformation in the positive x-direction. The highest average heat transfer and global entropy generation rates are achieved for the case of counter-clockwise rotation of the circular cylinder and for lower values of the flexible wall deformation.

Effect of laminated angle of carbon fiber on interior noise on an enclosure under center point excitation

This paper presents a novel method to control passively the interior noise of an enclosure such as car cabin by using the movement of the peak level and peak frequency according to the laminated angle of carbon fiber reinforced plastic composite plate. Recently, the use of carbon fiber reinforced plastic laminated plates in a car has been increased in order to reduce the weight of a car. For example, the metal plate roof has been replaced by the carbon fiber reinforced plastic plate roof for weight reduction of an electric vehicle. The characteristics of the interior noise inside of a car made of carbon fiber reinforced plastic plate roof can be changed according to the laminated angle of carbon fiber. In this paper, how this characteristic is changed was studied based on the effect of laminated angle of carbon fiber. In order to perform this study, a closed box with one flexible side wall and five acoustically rigid side walls was modelled as the interior compartment of a car. The flexible side wall of the closed box regards as the roof plate of a car. For the flexible side wall of the closed box, three carbon fiber reinforced plastic plates with different angle-ply (± θ) laminates each other were used. Therefore, three carbon fiber reinforced plastic plates with the fiber lamination angles of [−15/15/15/–15]s, [–30/30/30/–30]s, and [–75/75/75/–75]s were fabricated and used as the flexible side wall of the closed box. How the interior noise inside of the closed box was changed according to the laminated angle was studied by theoretical and numerical methods. For the validation of theoretical and numerical methods, the experimental work was performed. Finally, the carbon fiber reinforced plastic plate roof for a passenger car was numerically simulated, and the effect of the laminated angle on the interior noise was studied.

Analysis of mixed convection and entropy generation of nanofluid filled triangular enclosure with a flexible sidewall under the influence of a rotating cylinder

In this study, mixed convection and entropy generation in a nanofluid filled triangular cavity under the influence of rotating cylinder and flexible sidewall were numerically analyzed with finite element method. The inclined sidewall was cooled while the left vertical wall is partially heated. Heat transfer rate enhances as the values of Rayleigh number, angular rotational velocity of the cylinder, elastic modulus of the flexible sidewall and solid nanoparticles volume fraction increase. Nusselt number enhances more in the counter-clockwise direction of the cylinder as compared to clockwise directional rotation and 13.55% of average heat transfer enhancement was achieved for $$\varOmega =3000$$ when compared to motionless cylinder. Average Nusselt number increases by about 30.50% when the elastic modulus of the flexible wall is changed from 500 to $$10^5$$ . The changes in the velocity profiles are significant for the lower part of the triangular enclosure with respect to changes in angular rotational velocity and elastic modulus as compared to upper part of the cavity. Adding nanoparticles increases heat transfer especially for the lower part of the cavity and 49.63% of heat transfer enhancement was achieved for the highest volume fraction when compared to base fluid. Normalized total entropy generation rates enhance for higher values of elastic modulus of the flexible wall, angular rotational speed of the circular cylinder and nanoparticle volume fractions.

Peristaltic manipulation of a bio-particle contained in a closed cavity filled with a Bingham fluid: A numerical study

In this study, applicability of peristaltic waves as an efficient means for bio-particle manipulation is numerically investigated using the lattice Boltzmann method (LBM). The analysis is carried out in a flow configuration which comprises a two-dimensional, closed-ended, vertical cavity filled with a Bingham fluid and equipped with two flexible side walls and two rigid upper and lower plates. It is shown that by judicially adjusting the working parameters of the peristaltic waves (e.g., wavelength, amplitude, speed, and/or phase lag) it is possible to control the dynamics/trajectory of a large, circular bio-particle immersed in the fluid. It is also shown that a suspending circular particle moves faster if the surrounding fluid possess a yield-stress. Based on our obtained numerical results, for a given cross-sectional area, circular particles move faster than elliptical particles when excited peristaltically.

Analysis of mixed convection of nanofluid in a 3D lid-driven trapezoidal cavity with flexible side surfaces and inner cylinder

Numerical study of mixed convection in a lid-driven 3D flexible walled trapezoidal cavity with nanofluids was performed by using Galerkin weighted residual finite element method. Effects of various pertinent parameters such as Richardson number (between 0.05 and 50), elastic modulus of the side surfaces (between 1000 and 105), side wall inclination angle (between 0° and 20°) and solid particle volume fraction (between 0 and 0.04) on the fluid flow and heat transfer characteristics in a 3D lid-driven-trapezoidal cavity were numerically examined. It was observed that these characteristics are influenced when the pertinent parameters change. Flexible side surface can be used as control element for heat transfer rate. Increment and reduction in the space which are provided by the flexible side walls result in heat transfer enhancement and deterioration for side wall inclination angle of 0° and 10°. Average Nusselt number enhances by about 9.80% when the value of the elastic modulus is increased from 1000 to 105 for side wall inclination angles of θ=0°. Adding nanoparticles to the base fluid results in linear increment of heat transfer and at the highest volume fraction, 25.30% of heat transfer enhancement is obtained. A polynomial type correlation for the average Nusselt number along the hot wall was proposed and it has a fourth order polynomial dependence upon the Richardson number and first order dependence upon the solid particle volume fraction.

Linear sloshing in a 2D rectangular tank with a flexible sidewall

A 2D rectangular sloshing tank with a flexible sidewall have been studied analytically and numerically, with a focus on the coupling between sloshing and the flexible wall. This analysis introduces new knowledge of the effect of internal motions and flow in a membrane structure with a free surface, such as closed flexible fish cages. A framework for analyzing coupled fluid–membrane interaction in the time, and frequency domain in 2D have been developed. The analytical solution gives new knowledge about the effect of the deformations on the linear pressure inside the tank. Coupled eigenfrequencies and the transfer functions for two different membrane lengths due to sway excitation have been found both analytically and numerically. The analytical and numerical results agree. The eigenfrequencies of the system are highly dependent on both the tension and the 2D membrane length. If we consider a given value of tension, then the eigenfrequency of the coupled system is smaller than the sloshing frequency of the rigid tank for any given n. If the tension is small, and we consider a given sloshing frequency of the rigid tank, then there can be more than n eigenfrequencies of the coupled system that is lower than the sloshing frequency of the rigid tank. For large tensions, the eigenfrequencies of the system become the sloshing frequency of a rigid tank. For low tensions, numerical challenges for the direct numerical solution for frequencies close to the natural sloshing frequencies were pointed out.

Piezoelectric energy harvester using impact-driven flexible side-walls for human-limb motion

We present a human-limb driven piezoelectric energy harvester using two mass-loaded unimorph piezoelectric beams clamped on two flexible sidewalls. Since vibration generated by human-limb motion has low-frequency and high amplitude characteristics, the energy harvester has been designed to up-convert the low-frequency human-limb vibration by mechanical impact of a spring less spherical metallic ball. However, instead of direct mechanical impact on the power generating elements (unimorph piezoelectric beams), the ball impacts on the bases (flexible sidewalls) of each beam to avoid mechanical wear of the piezo-materials. While excited by human-limb motion, the ball impacts consecutively on the flexible sidewalls which transfer impulsive forces to the loaded mass of the respective unimorph beam. The beam vibrates at its own resonant frequency and causes voltage generation by virtue of piezoelectric effect. A proof-of-concept prototype has been fabricated and tested. At optimum load condition, each unimorph piezoelectric generator generates 96 µW average power while excited at 4.96 Hz frequency and ~2g acceleration. The device with series connected generators is capable of generating maximum 175 µW average power. Improved design and further optimization would be able to increase its power generation capability (as well as power density) to be used in wearable devices applications.

Fluid–structure-magnetic field interaction in a nanofluid filled lid-driven cavity with flexible side wall

In this study MHD flow in a lid driven nanofluid filled square cavity with a flexible side wall is numerically investigated. The top wall of the cavity is colder than the bottom wall and it moves in the +x direction with constant speed. Other walls of the cavity are insulated. The finite element formulation is utilized to solve the governing equations. The Arbitrary-Lagrangian-Eulerian method is used to describe the fluid motion with the flexible wall of the cavity in the fluid–structure interaction model. The influence of the Young’s modulus of the flexible wall on the flow and heat transfer characteristics are numerically investigated for the following parameters: (104N/m2≤E≤2.5×105N/m2), with a Richardson number of (0.01≤Ri≤5), a Hartmann number of (0≤Ha≤50) and a volume fraction of the solid particles given by (0≤ϕ≤0.04). The effect of Brownian motion on the effective thermal conductivity of the nanofluid is taken into account. Averaged heat transfer decreases with increasing Hartmann number and decreasing Richardson numbers. As the Young’s modulus of the flexible wall decreases, the averaged heat transfer increases and 66.5% of the heat transfer enhancement is obtained for E=104N/m2 compared with E=2.5×105N/m2. An averaged heat transfer enhancement of 33.87% is obtained for a solid volume fraction of 4% compared to the base fluid for the fluid–structure model coupled with the magnetic field.

Mixed convection due to rotating cylinder in an internally heated and flexible walled cavity filled with SiO2–water nanofluids: Effect of nanoparticle shape

In this study, numerical investigation of mixed convection in a square cavity filled with SiO2 nanofluid and volumetric heat generation is performed under the effect of an inner rotating cylinder and a flexible side wall. The top wall of the cavity is kept at constant cold temperature while the bottom wall is at hot temperature and the other walls of the cavity and the cylinder surface are assumed to be adiabatic. The finite element method is utilized to solve the governing equations. The Arbitrary Lagrangian–Eulerian method is used to describe the fluid motion with the flexible wall of the cavity in the fluid–structure interaction model. The effects of external Rayleigh number (between 103 and 5×105), internal Rayleigh number (between 104 and 106), Young's modulus of the flexible wall (between 5×102 and 106), angular rotational speed of the cylinder (between −2000 and 2000) and nanoparticle volume fraction (between 0 and 0.03) on the fluid flow and heat transfer are numerically studied for different solid nanoparticle shapes (spherical, cylindrical, brick and blade). It is observed that as the value of external Rayleigh number increases, internal Rayleigh number and elastic modulus of the flexible wall decrease, the local and averaged heat transfer enhances. The averaged heat transfer enhances with cylinder rotation in both directions for all nanoparticle types. Among all nanoparticle shapes, cylindrical ones show the best performance and spherical ones show the worst performance for heat transfer enhancement.

Mixed convection in a two-sided elastic walled and SiO2 nanofluid filled cavity with internal heat generation: Effects of inner rotating cylinder and nanoparticle's shape

In this study, mixed convection in a cavity with volumetric heat generation and filled with nanofluid having an inner rotating cylinder and two flexible side walls is numerically investigated. The top wall of the cavity is at constant cold temperature while the bottom wall is kept at hot temperature. Two flexible side walls and the surface of the inner rotating cylinder are accepted as adiabatic. The finite element formulation is used to solve the governing equations. The Arbitrary-Lagrangian–Eulerian method is used to describe the fluid motion with the flexible side walls of the cavity in the fluid–structure interaction model. The influence of external Rayleigh number, elastic modulus pair of the flexible side walls, angular rotational speed of the cylinder, internal Rayleigh number and nanoparticle volume fraction on the fluid flow and heat transfer are numerically simulated by using different solid nanoparticle shapes (spherical, cylindrical, brick and blade type). It is observed that the local and averaged heat transfer enhances as the external Rayleigh number, nanoparticle volume fraction and absolute value of the angular rotational velocity of the cylinder increase and as the internal Rayleigh number decreases. The elastic modulus of the side walls can be used to control the fluid flow and heat transfer inside the cavity. Utilizing cylindrical nanoparticles gives the best performance in terms of heat transfer enhancement.

Piezoelectric energy harvester using mechanical frequency up conversion for operation at low-level accelerations and low-frequency vibration

In this paper, we propose a modified frequency up-conversion mechanism to lower the operational acceleration level for energy harvesting devices using a snap-through buckling phenomenon. The proposed device consists of a buckled bridge beam clamped on flexible sidewalls with a proof mass and cantilever beams attached to the bridge. When subject to a vibration, the buckled bridge beam snaps through between two stable states, inducing impulsive acceleration on the attached piezoelectric cantilevers. During the snap-through transition, the flexible sidewalls deflect outward, thus lowering the threshold acceleration value for the state transition. Various sidewall materials with different flexibilities were tested to determine the maximum output power, bandwidth, and output characteristics for various input acceleration values. The minimum acceleration value for snap-through transition was 0.5g (g = 9.8 m/s2) when using latex sidewalls. A maximum output power of 0.4 mW Hz/cm2--that is 10 μW for test sample at an excitation frequency of 15 Hz--was generated by using the proposed device with latex sidewalls.

Closed form calculation of reverberant sound propagation in a thin duct with flexible walls.

An analytical method for calculating the propagation of reverberant sound between two parallel perfectly reflecting planes in a thin duct with flexible side walls is presented. The flexible walls are modeled with a complex wave number to account for dissipation within the wall material. A mathematical model based on the Euler–Maclaurin sum formula provides an approximate closed form Green’s function for the acoustic space. The method gives a set of two coupled integral equations in acoustic pressure and side wall displacement consisting of convolutions with respect to the spatial dimension along the duct. Laplace transforms for the spatial dimension are applied to the integral equations to solve for the acoustic pressure in terms of the spatial Laplace transforms of the Green functions for the reverberant acoustic space and the mechanical wave in the side wall material. A closed form solution is obtained by considering the first term of a binomial series in the Laplace domain and applying a partial fraction expansion leading to the solution in the spatial dimension along the duct. Numerical simulations show the behavior of the reverberant noise reduction provided by the flexible side walls along the duct.

Oscillations of two superposed fluids in an open and flexible container

The interaction of two superposed inviscid liquids with a flexible side wall of a rectangular container is considered. The governing equations describing the behaviour of the system are analyzed using the concept of normal modes, and their solutions presented in the form of infinite series. The expansion coefficients for the velocity potentials are calculated by employing a new inner product which allows orthogonalizing the fluid shape modes. An eigenfrequency equation is then derived from the requirement for a nontrivial solution exists. The influence of the governing parameters on the coupled frequencies is illustrated in the case of water–mercury system. To cite this article: M. Amaouche, B. Meziani, C. R. Mecanique 336 (2008).

Diethyl 1,4-dioxo-6-(3-pyridyl)perhydro-2,3,4a,6,7a-pentaazacyclopenta[cd]indene-2a,7b-dicarboxylate 1,2-dichoroethane solvate

The main residue of the title compound, C18H22N6O6·C2H4Cl2, is a derivative of glycoluril. The six-membered heterocycle adopts a chair conformation and shares two N atoms with two five-membered rings of the glycoluril unit to form the flexible sidewalls of a mol­ecular clip. Two ethyl fragments and the solvent mol­ecule are disordered; the site occupancy factors for the ethyl groups are 0.72/0.28 and 0.75/0.25 and for the solvent molecule 0.54/0.46. Inter­molecular N—H⋯O and N—H⋯N hydrogen bonds link the cyclo­penta­[cd]indene mol­ecules into two-dimensional layers parallel to the bc plane.

Diethyl 2,6-diethyl-4,8-dioxo-2,3,6,7-tetrahydro-1H,5H-2,3a,4a,6,7a,8a-hexaazacyclopenta[def]fluorene-8b,8c-dicarboxylate

The title compound, C18H28N6O6, is a derivative of glycoluril, with two ethyl acetate substituents on the convex face of the glycoluril system. Two equivalent six-membered rings bind the N atoms from separate rings of the glycoluril unit to form the flexible sidewalls of a mol­ecular clip. One N atom from each ring carries an ethyl substituent. The crystal packing is stabilized by non-classical C—H⋯O hydrogen bonds.

Turbulent Jet Mixing Enhancement and Control Using Self-Excited Nozzles

A new self-excited jet methodology was developed for the mixing enhancement of jet fluid with its surrounding, quiescent, stagnant, or coflowing fluid. The nozzles, of a square or rectangular cross section, featured two flexible side walls that could go into aerodynamically-induced vibration. The mixing of nozzle fluid was measured using planar laser-induced fluorescence (PLIF) from acetone seeded into the nozzle fluid. Overall, the self-excited jet showed enhanced mixing with the ambient fluid; for example, at 390Hz excitation a mixing rate enhancement of 400% at x∕D=4 and 200% at x∕D=20 over the unexcited jet. The mixing rate was sensitive to the excitation frequency, increasing by 60% with the frequency changing from 200 to 390Hz (corresponding to a Strouhal number from 0.052 to 0.1). It was also observed that the mixing rate increased with the coflow velocity. To explain the observed mixing enhancement, the flow field was studied in detail using four-element hot wire probes. This led to the observation of two pairs of counter rotating large-scale streamwise vortices as the dominant structures in the excited flow. Shedding right from the nozzle exit, these inviscid vortices provided a rapid transport of the momentum and mass between the jet and the surrounding fluid at a length scale comparable to half-nozzle diameter. Moreover, the excited jet gained as much as six times the turbulent kinetic energy at the nozzle exit over the unexcited jet. Most of the turbulent kinetic energy is concentrated within five diameters from the nozzle exit, distributed across the entire jet width, explaining the increased mixing in the near field.