Topology optimization design for buckling analysis related to the size effect

Owing to the excellent performance of microstructures or nanomaterials with well-designed topological configuration, the characteristic scale of structural design is gradually shifting from macroscopic to nanoscale or microscale structural design. However, the size effect that emerges from the small-scale structures may not be explained effectively with the hypothesis of classical mechanics owing to the lack of microscopic parameters in the classical constitutive model. In addition, slender beams within such small-scale structures are prone to buckling failure, which puts forward additional requirements for the stability design of the structure except for the overall compliance of the structure. Therefore, a topology optimization framework combining the modified couple stress theory with the solid isotropic material penalization (SIMP) model is constructed to illustrate the size effect on topology optimization. Numerical results show that the size effect affects the compliance, buckling performance, and topological configurations of the evolutionary structures.

Influence of the Nonaxisymmetric Dark Halo Shape on Galaxies Outer Spiral Pattern Morphology

The results of numerical simulations of a gaseous galactic disk rotating in an external nonaxisymmetric potential of a dark halo are presented in the article. Analysis of two models of a nonaxisymmetric dark halo, in which a gaseous galactic disk rotates, has been carried out. In the first case, the halo is nonaxisymmetric within the optical radius of the disk, where the bulk of the visible matter of the galaxy is located, including the stellar disk. The model is ineffective for the external long-lived spiral structure formation in the disk periphery due to the nonaxisymmetry of dark halo. In the second series of calculations, we have employed the model with a symmetric halo inside the optical radius and a non-axisymmetric one outside of it. The results of the simulations confirm that nonaxisymmetry in the halo matter distribution is effectively generating the global spiral pattern at the periphery of the galaxy. One may observe such spiral structures in some galaxies, mainly in the ultraviolet range. Analysis of various model parameters has showed that the value of parameter " is the primary characteristic affecting the morphology of the forming spiral pattern. This value determines the degree of nonaxisymmetry of the halo. The Le parameter introduced in this work and responsible for the formation of small-scale structures in the transition region does not significantly affect the disk periphery. Moreover, the larger the value of Le, the smoother spirals are formed. As it has shown in this work the size of the computational grid does not significantly influence on the simulation results, revealing only small-scale structures which are not the subject of current work.

Additive Manufacture of Small-Scale Metamaterial Structures for Acoustic and Ultrasonic Applications

Acoustic metamaterials are large-scale materials with small-scale structures. These structures allow for unusual interaction with propagating sound and endow the large-scale material with exceptional acoustic properties not found in normal materials. However, their multi-scale nature means that the manufacture of these materials is not trivial, often requiring micron-scale resolution over centimetre length scales. In this review, we bring together a variety of acoustic metamaterial designs and separately discuss ways to create them using the latest trends in additive manufacturing. We highlight the advantages and disadvantages of different techniques that act as barriers towards the development of realisable acoustic metamaterials for practical audio and ultrasonic applications and speculate on potential future developments.

Use of Genetic Algorithms to Optimize Efficiency in Small-Scale Structures

The prevalence of algorithms and computational tools in the modern-day has intersected with nearly every field. Generative design, specifically those using genetic algorithms, is an increasingly effective, yet cost efficient way to generate architectural designs in modern engineering. Thus, we adopt a genetic algorithm model in pursuit of maximizing the durability of a structure when it is stressed while minimizing the material cost. After the model is formulated, the algorithm is able to approximate with high accuracy the load a small-scale structure is able to bear, as well as iterate upon its designs to maximize a fitness function.

Small scale structures in the footprint tails of the Galilean moons observed by JIRAM

<p>The Jovian Infrared Auroral Mapper (JIRAM) on board Juno is a spectro-imager which is observing the<br>atmosphere of Jupiter and its auroral emission using its two imagers in the L (3.3-3.6μm) and M bands (4.5-<br>5.0μm) and a spectrometer (2-5 μm spectral range).<br>The highly elliptic orbit of Juno and the unprecedented resolution of the JIRAM imager allowed to retrieve<br>wealth of details about the morphology of moon-related aurorae. This phenomenon is due to the jovian magnetic<br>field sweeping past the Galiean moons, which generate Alfven waves travelling towards the ionosphere and set<br>up field aligned currents. When the associated electrons reach the ionosphere, they interact with the hydrogen<br>and make it to glow. In particular, the tails of the footprints showed a spot-like substructure consistently, which<br>were investigated using the L-band of the imager from perijove 4 to perijove 30. This feature was observed close<br>to the footprints, where the the typical distance between spots lies between 250km and 500km. This distance<br>decreases to 150km in a group of three observations in the northern emisphere when each moon is close to 250 ◦<br>west longitude. No correlation with orbital parameters such as the longitude of the moons was found so far,<br>which suggests that such morphology is almost purely due to ionospheric processes.<br>Moreover, during PJ 13 a long sequence of images of the Io footprint was shot and it revealed that the<br>secondary spots appears to corotate with Jupiter. This behaviour is observed also during orbits 14 and 26.<br>During these sequences JIRAM clearly observed the Io footprint leaving behind a trail of ”footsteps” as bright<br>spots.<br>The characteristics of these spots are incompatible with multiple reflection of Alfven waves between the two<br>emispheres. Instead, we are currently investigating ionospheric processes like the feedback instability (FI) as a<br>potential candidate to explain the generation of the observed small scale structure. This process relies on local<br>enhacement of conductivity in the ionosphere, which is affected by electron precipitation. Order of magnitude<br>estimates from the FI are compatible with the inter-spot distance and the stillness of the spots.</p>

Waves at the edge of space revealed by noctilucent cloud observations using camera and lidar

<p>Noctilucent clouds (NLC) exist at an altitude of about 83 km during the summer season at middle and polar latitudes. They consist of icy particles that exist in the polar summer mesopause region where the atmosphere is about 100 K colder than expected from pure radiative forcing. Dynamical effects, for example the dissipation of gravity waves, play an important role in the global circulation finally leading to the cold summer mesopause region. Ever since the first reports on the occurrence of NLC in 1885 the observers noticed distinct structures in the clouds that are most often wave-like. However at times the wave field becomes seemingly chaotic. <br><br>State of the art lidar and camera observations of NLC allow studying small-scale structures of tens of meters in the vertical and horizontal direction. Given a high time resolution (about one second), the development of these structures is measured on temporal scales spanning the range from inertia gravity waves to acoustic gravity waves. We will show observations with the RMR-lidars at ALOMAR (Northern Norway at 69°N) and Kühlungsborn (54°N) as well as cameras located nearby these stations. Using these combined observations we study waves and their transition to turbulence.</p>