Noise reduction of automobile cooling fan based on bio-inspired design

This study aims to minimize the noise generated by automobile cooling fans. Fan blade structures with ridged surfaces based on bio-inspired principles are 3D printed and used to replace the conventional fan blades. The effect of the bio-inspired ridge structures on the noise reduction of the cooling fan is demonstrated by orthogonal experiments in a semi-anechoic chamber. Experimental results show that with an increase in the rotational speed, the effect of the surface textures on the acoustic performance of the cooling fan becomes more significant. For example, at a fan speed of 1750 r/min, all the bio-inspired blade designs reduce noise compared with the original fan and, in particular, the sound pressure level is reduced by 3.83 dB(A) for the design with a ridge width of 4 mm and a ridge pitch of 15 mm. Through variance analysis of the measured noise, the ridge pitch distance has the most significant impact on noise reduction under low speed conditions whilst, under high speed conditions, the ridge width has the most significant influence. In addition to the experimental studies, computational fluid dynamics (CFD) simulations of the cooling fan are carried out to explain the mechanism of noise reduction for the ridged fan blades. When the fan runs, the horseshoe vortexes generated by the ridge structures disturb the flow of the boundary layer, reduce the influence of the fluid flow on the boundary layer, and delay the transition of the fan blade laminar flow to turbulence. It is also seen that there is a reduction of the intensity of the fan blade trailing edge vortices and the scale of the secondary vortices, thereby achieving the overall aim of noise reduction. This research has significance in the noise reduction design of automobile cooling fans.

Ichnofossils, Cracks or Crystals? A Test for Biogenicity of Stick-Like Structures from Vera Rubin Ridge, Mars

New images from Mars rover Curiosity display millimetric, elongate stick- like structures in the fluvio-lacustrine deposits of Vera Rubin Ridge, the depositional environment of which has been previously acknowledged as habitable. Morphology, size and topology of the structures are yet incompletely known and their biogenicity remains untested. Here we provide the first quantitative description of the Vera Rubin Ridge structures, showing that ichnofossils, i.e., the product of life-substrate interactions, are among their closest morphological analogues. Crystal growth and sedimentary cracking are plausible non-biological genetic processes for the structures, although crystals, desiccation and syneresis cracks do not typically present all the morphological and topological features of the Vera Rubin Ridge structures. Morphological analogy does not necessarily imply biogenicity but, given that none of the available observations falsifies the ichnofossil hypothesis, Vera Rubin Ridge and its sedimentary features are here recognized as a privileged target for astrobiological research.

Analysis of the Wear-Resistance Characteristics of Bionic Ridge Structures

HighlightsBionic technology can be applied to resolve agricultural engineering problems.Pangolin Squama and Chlamys Farreri shells possess excellent wear-resistance.Bionic ridges can improve sample wear-resistance.Abstract. Consistent soil contact rapidly wears the soil-engaging components of agricultural machinery, such as ploughs and subsoilers. A bionic method was applied to their structural design to improve component wear resistance. Some animal organs possess excellent wear-resistant structures which can provide design inspiration for improving the wear-resistance of agricultural mechanical parts. Previous research found that many ridges exist on Pangolin squama and Chlamys Farreri shell surfaces. Those ridges cause Pangolin squama and Chlamys Farreri shells to exhibit excellent wear-resistance. Therefore, these ridge structures were applied to the design of experimental subsoiler samples (bionic samples) to enhance their wear-resistance. An abrasive wear tester was utilized to conduct abrasive wear experiments under special experimental conditions. These experimental conditions involved sliding speed, soil particle size, moisture content, and space between the ridges. Finally, nine experiments were conducted that subjected the bionic and flat surface samples to different experimental conditions, and their respective mass-loss quantities were measured. Results show that bionic sample mass loss was less than that of the flat surface samples under the same experimental conditions; bionic sample wear-resistance improved by 77%, 73.8%, 66.9%, 45.4%, 58.9%, 65.5%, 33.1%, 66.4%, and 42.6% when compared with flat surface samples under the same experimental conditions. Orthogonal test results reveal that the soil particle size most significantly affected sample wear-resistance, followed by the space between bionic ridges and the sliding speed. One reason that bionic samples exhibited excellent wear-resistance is that the soil particles underwent a “guiding effect” and a “rolling effect” over the bionic ridge surface, thereby reducing the “micro-plowing” that soil particles generated when moving over the contact surface. Mutual interference among soil particles also reduced wear. Part of the soil particles rushing over the bionic sample surface rebounded back; the rebounded soil particles collided with incoming soil particles, then the speed and kinetic energy of all of the particles decreased and sample surface abrasion declined. Moreover, “vortexes” generated by sample surface air and ridges lead to an “air cushion” effect which can lessen the number of sample surface soil particles, and bionic ridge sample abrasions can be significantly reduced. Abrasion experiment results analysis indicates that bionic ridges distributed on subsoiler sample surfaces can significantly improve wear-resistance. The bionic design method provides a new approach for increasing the wear-resistance of the soil-engaging components of agricultural machinery. Keywords: Abrasive wear, Bionic ridge, Optimal design, Wear-resistance.

Waveguide Structures with Improved Cut-off Frequency and Bandwidth

The wave transmission characteristics of rectangular, double-ridge, trapezoidal-ridge and anti-trapezoidal ridge waveguides are analyzed using the finite-element method. The cut-off wavelength and attenuation of these waveguides are calculated. The result shows that anti-trapezoidal ridge waveguides perform better than rectangular, double-ridge and trapezoidal-ridge waveguides. The variation of bandwidth and attenuation with respect to change in the angle of physical ridge structures has been studied while migrating from rectangular to anti-trapezoidal ridge structures.

A methodology for the production of microfabricated electrospun membranes for the creation of new skin regeneration models

The continual renewal of the epidermis is thought to be related to the presence of populations of epidermal stem cells residing in physically protected microenvironments (rete ridges) directly influenced by the presence of mesenchymal fibroblasts. Current skin in vitro models do acknowledge the influence of stromal fibroblasts in skin reorganisation but the study of the effect of the rete ridge-microenvironment on epidermal renewal still remains a rich topic for exploration. We suggest there is a need for the development of new in vitro models in which to study epithelial stem cell behaviour prior to translating these models into the design of new cell-free biomaterial devices for skin reconstruction. In this study, we aimed to develop new prototype epidermal-like layers containing pseudo-rete ridge structures for studying the effect of topographical cues on epithelial cell behaviour. The models were designed using a range of three-dimensional electrospun microfabricated scaffolds. This was achieved via the utilisation of polyethylene glycol diacrylate to produce a reusable template over which poly(3-hydrroxybutyrate- co-3-hydroxyvalerate) was electrospun. Initial investigations studied the behaviour of keratinocytes cultured on models using plain scaffolds (without the presence of intricate topography) versus keratinocytes cultured on scaffolds containing microfeatures.

AEGA: A New Real-Coded Genetic AlgorithmTaking Account of Extrapolation

This study proposes a new real-coded genetic algorithm (RCGA) taking account of extrapolation, which we call adaptive extrapolation RCGA (AEGA). Real-world problems are often formulated as black-box function optimization problems and sometimes have ridge structures and implicit active constraints. mAREX/JGG is one of the most powerful RCGAs that performs well against these problems. However, mAREX/JGG has a problem of search inefficiency. To overcome this problem, we propose AEGA that generates offspring outside the current population in a more stable manner than mAREX/JGG. Moreover, AEGA adapts the width of the offspring distribution automatically to improve its search efficiency. We evaluate the performance of AEGA using benchmark problems and show that AEGA finds the optimum with fewer evaluations than mAREX/JGG with a maximum reduction ratio of 45%. Furthermore, we apply AEGA to a lens design problem that is known as a difficult real-world problem and show that AEGA reaches the known best solution with approximately 25% fewer evaluations than mAREX/JGG.