Proof-of-Concept Design for MPP Acoustic Absorbers with Elements of Art

A micro-perforated plate or panel (MPP) is a device used to absorb sound. It consists of a thin flat plate made from several different materials with small holes and a back cavity. Several reported modifications and enhancements to the original design of the MPP acoustic absorber were modified by the holes or the back-cavity shape and sizes following the original idea. The present study attempts to artistically beautify the MPP acoustic absorbers by incorporating dotted arts into the design of MPP. The perforation for micro-perforated panels could be dotted arts with a perforation size smaller than 1 mm for enhanced acoustic absorption performance in the form of various artistic designs. Small LED lights could be placed inside the acoustic chamber to create the color lights emanating from the perforations instead of dots with different colors. Several MPP incorporated artistic designs of dotted patterns were presented and their acoustic absorption performance was analyzed using impedance tube in this paper.

An Adjoint Optimization Prediction Method for Partially Cavitating Hydrofoils

Much work has been done over the past years to obtain a better understanding, predict and alleviate the effects of cavitation on the performance of lifting surfaces for hydrokinetic turbines and marine propellers. Lifting-surface sheet cavitation, when addressed as a free-streamline problem, can be predicted up to a desirable degree of accuracy using numerical methods under the assumptions of ideal flow. Typically, a potential solver is used in conjunction with geometric criteria to determine the cavity shape, while an iterative scheme ensures that all boundary conditions are satisfied. In this work, we propose a new prediction model for the case of partially cavitating hydrofoils in a steady flow that treats the free-streamline problem as an inverse problem. The objective function is based on the assumption that on the cavity boundary, the pressure remains constant and is evaluated at each optimization cycle using a source-vorticity BEM solver. The attached cavity is parametrized using B-splines, and the control points are included in the design variables along with the cavitation number. The sensitivities required for the gradient-based optimization are derived using the continuous adjoint method. The proposed numerical scheme is compared against other methods for the NACA 16-series hydrofoils and is found to predict well both the cavity shape and cavitation number for a given cavity length.

Thermal simulation of cavity shape and its impact on solar and terrestrial radiation measurement in space

<p>In order to upgrade the technology readiness lever of the solar and terrestrial radiation measurement from space, in this paper, we started detailed thermal analysis and modeling of the Bolometric Oscillation Sensor (BOS) using the finite element method (FEM)<sup> [1]</sup><sup></sup>. Four cavity shapes (cylindrical, conical, inverted conical and hemispherical) are tested to compare their thermal and optical characteristics under different radiation and thermal environment, which helps to gain a better understanding of the mechanisms of BOS. We examined the absorptivity and emissivity of each cavity shape by applying the same amount of radiation power. Especially, when the ambient temperature maintains at a stable and low value, such as 20K, it produces the most accurate reconstruction of the input power. In this presentation, we will introduce the detailed simulation result and how to apply it to correct the ambient thermal radiation on each type of detector.</p><p><strong>Reference:</strong></p><p>[1] P. Zhu, M. Wild, M. van Ruymbeke, G. Thuillier, M. Meftah, and O. Karatekin. Interannual variation of globe net radiation flux as measured from space. J. Geophys. Res. doi:10.1002/2015JD024112, 121:6877-6891, 2016.</p><p><strong>Acknowledgement: </strong>This work has been supported by the National Natural Science Foundation of China (NO. 41904163, 41974207), Natural Science Foundation of Hunan Province (NO. 2020JJ5483), and Research Foundation of Education Bureau of Hunan Province (NO. 18C0416). We also thank the financial support from China Scholarship Council (No. 201908430058).</p>