Vibration attenuation and bandgap characteristics in plates with periodic cavities

Plates with periodic cavities show excellent vibration attenuation characteristics. This behavior can be attributed to the presence of frequency bandgaps on account of interference between the incident wave and the reflected wave from the cavities. The present work investigates the vibration attenuation/bandgap characteristics of plates with varying shapes of periodic cavities, such as square, circular, vertical rectangle, and horizontal rectangle, through experiments and simulation. Vibration responses of different periodic plates have been studied by carrying out frequency sweep on a vibration shaker. The investigation has been restricted to flexural vibrations of the plates, which are the predominant mode of vibration in many practical vibration scenarios. The frequency bandgaps, observed through the experiment, have been compared with the numerical simulation by harmonic analysis and by carrying out dispersion analysis on a unit cell of the periodic structure using Floquet–Bloch theory. Dispersion curves of the periodic plates yielded bandgaps, which were observed to be in agreement with the bandgaps from the experiment. The effect of variation in the aspect ratio of the cavities, that is length-to-width ratio, on the bandgaps has also been examined. It has been demonstrated that by suitable selection of the shape/size of the periodic cavity, desired vibration attenuation bandgaps can be realized for a 2-dimensional structure.

Linear Buckling Behaviour of Composite Laminate [(Θ/-Θ)] with Various Shaped Cutout using Fem

In this paper, the buckling behavior has been investigated on square laminate made of Woven-glass-polyester composite with various shaped cutouts (i.e., circle, square, vertical rectangle, horizontal rectangle, vertical ellipse, horizontal ellipse) numerically. The composite laminates have been arranged in asymmetrical order as [(θ/-θ)]. The laminated plate that is subjected to uniaxial compression has been emphasized on the laminate along with the effect of layer orientation, effect of cutout ratio and effect of cutout angle. The result shows that the minimum buckling load is obtained at 45° and the maximum buckling load attained at 0° and 90°for all laminates by increasing the layer orientation. For cutout ratio, the maximum and minimum load is obtained for the smallest and largest cutout ratio in all cutout shapes. Increasing the cutout angle, the square cutout exhibits the minimum load at 60°. In elliptical cutouts, the load is decreasing and increasing gradually while they are aligned in along and perpendicular to the loading directions. The rectangular cutouts positioned vertically and horizontally the load is decreasing up to 30° and 60°and then increasing up to 90°.

Revealing Mechanical Strength of Nanopores Using Atomic Finite Element Techniques

Graphene nanopore has been widely employed in nanofilter or nanopore devices due to its outstanding properties. The understanding of its mechanical properties at nanoscale is crucial for device improvement. In this work, the mechanical properties of graphene nanopore is thus investigated using atomistic finite element method (AFEM). Four graphene models with different pore shapes (circular (CR), horizontal rectangle (RH), and vertical rectangle (RV)) in sub-nm size which could be successfully fabricated experimentally have been studied here. The force normal to a pore surface is applied to mimic the impact force due to a fluid flow. Increasing pore size results in the reduction in its strength. Comparing among different pore shapes with comparable sizes, the order of pore strength is CR>RH>RV>SQ. In addition, we observe that the direction of pore alignment and geometries of pore edge also play a key role in mechanical strength of nanopores.

Effect of the Asymmetric Baffle Shape on the Thermal Performance Using Non-Newtonian Fluids

The efficiency of industrial heat equipment can be increased using baffles. The shape of baffles is one of the effective parameters. In this work, the effect of shapes of asymmetric baffles on the thermal performance has been investigated. Four different shapes as rectangular diagonal, trapezoidal, triangular and semi-ellipsoid, as well as, vertical rectangle (as the base model) were used. Also, four non-Newtonian fluids were used as the working fluid. The governing equation, which models the physical phenomenon, was solved with the finite volume method. The results showed that better thermal performance could be observed with semi-ellipsoid baffle for all four non-Newtonian fluids. However, for different models of non-Newtonian fluids, the average of increasing of thermal performance with different percent was achieved. By comparing different models of non-Newtonian fluids, shear-thinning model shows better thermal performance than other models.

Evidence that Octopus is Colour Blind

1. Six octopuses were trained on a series of visual discrimination tasks where the discriminanda were presented simultaneously, and where different tasks alternated in a single training session. 2. All the octopuses could make discriminations based on brightness and orientation over the same period of time. 3. Over a period in which all octopuses discriminated a black from a white vertical rectangle none discriminated a yellow vertical rectangle from a grey (of matching brightness). 4. Over a period in which all octopuses discriminated a vertical from a horizontal grey rectangle none discriminated a violet vertical rectangle from a matching grey. 5. The behaviour of the octopuses was qualitatively different in the hue versus grey situations, their attacks being considerably slower and less certain. 6. These results, which agree with previous behavioural findings and a variety of morphological, physiological and biochemical evidence, make it increasingly probable that Octopus vulgaris is colour blind.

Influence of Previous Preferences on the Memory of Octopus Vulgaris After Removal of the Vertical Lobe

1. Octopuses from which the vertical lobe had been removed attacked a vertical rectangle more readily than a horizontal one when both shapes were moved vertically. 2. During discrimination training the results differed markedly according to which figure was rewarded with food. 3. When a vertical rectangle was positive the excess of attacks at this figure increased both within and between sessions, the animals showing considerable ability to learn. 4. When a horizontal rectangle was the positive figure the responses to it were at first ‘paradoxical’, the negative shape being attacked more often. There was then improvement within each session, but little if any between the sessions. 5. Octopuses without the vertical lobe quickly ceased to attack crabs shown at 4 min. intervals when shocks were given for attacks, and the effect could still be detected 4 hr. later. 6. When crabs were shown at 8 min. intervals, and shocks given for attacks, there was no decline in attacks over fourteen trials. Fifteen hours later, however, some residual signs of the shocks were evident when trials were resumed at 8 min. intervals. Although all of the animals at first attacked they soon stopped doing so. After a further 15 hr. all attacked again but soon ceased to do so after receiving shocks. 7. Normal animals, by contrast, all ceased to attack the crabs shown at 8 min. intervals after receiving four or five shocks. The memory is much more retentive in normal animals, so that 2 days after receiving shocks the octopuses seldom attacked the crabs.

Interference in Learning and Lesions in the Visual System of Octopus Vulgaris

Two groups of Octopuses, one normal and one with lesions in the optic lobe system, were trained on a discrimination between horizontal and vertical rectangles followed by a discrimination with a square and a diamond. They were then retrained on the original horizontal and vertical discrimination. A further group of normal animals were trained on a discrimination between the square and the diamond followed by a discrimination with the horizontal and vertical rectangles. They were then retrained on the original square and diamond discrimination. Results were as follows: 1. Animals with lesions in the optic lobe system showed impairment of relearning following the different and more difficult square and diamond discrimination. Normal animals, on the other hand, showed improved performance under these conditions. 2. In the case of both normal and operated animals the square and diamond discrimination (square positive - diamond negative) was learned less well following the horizontal and vertical rectangle discrimination than when it was learned as a first discrimination by the normal animals. The level of learning with diamond positive- square negative was, however, maintained at the same level as the first discrimination. 3. When the square and diamond discrimination was relearned by the normal group, square positive - diamond negative was relearned less well than first learning, and diamond positive-square negative was not affected by previous learning, thus confirming point 2. 4. At the end of training the operated animals discriminated between black and white circles better than they had re-learned the horizontal and vertical rectangles. These findings have been related to theories of analysing mechanisms in the nervous system of octopus.