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[charlie T colton]

Design and AM of 3D-Phononic-Band-Gap-Structures Based on Gradient-Based-Optimization

The mathematics in the design is way beyond me but a useful application of the resulting structure is not. And it's something that GE's been working on. A possible application follows the primary subject's discussion and pictures.

Design and Additive Manufacturing of 3D Phononic Band Gap Structures Based on Gradient Based Optimization

4. Discussion

We have presented a novel modeling for structural optimization that combines features of parametric shape optimization with density based topology optimization. We have successfully applied this approach for a 2D gradient based optimization of PBG structures. A numerical study was performed with a minimal feature size as parameter. The structures where also evaluated numerically to obtain material properties Young’s modulus and Poisson’s ratio where a slight auxetic behaviour could be observed. PBG structures have been designed in the literature manually by gradient free and gradient based optimization, but usually the corresponding stiffness of the structures is not given.
Under the assumption of a reciprocally connection of PBG width and stiffness, the results in literature are therefore difficult to compare. However, the authors believe that the presented results are of unmatched performance. The results reveal a simple, common design principle independent on the parametrization of the optimization problem. Note that we designed our optimization approach intentionally with a rather limited design space to cope with the issues of PBG optimization. Hence, for a different design space competitive alternative designs might exist.
In this work, we successfully transferred the concept of connected masses from the 2D optimization results to a 3D design with connections adapted from earlier studies. Ti-6Al-4V samples were manufactured by selective electron beam melting and tested in a frequency response measurement setup. The obtained frequency response diagrams show reasonable agreement with the numerically obtained PBGs from dispersion relations. The biggest factor for deviations that has to be considered is the difficult-to-measure mechanically active strut diameter of the coarse metal struts. Even computer tomography measurements in the past have shown very high standard deviations in strut diameters, rendering an exact determination impossible [21]. Therefore, the initial estimations for the strut thickness of the samples can be considered a good approximation.
While past studies have shown that cubic lattices with straight struts do not show PBGs [20], the presented structure with straight struts and added masses does have a PBG. This can be attributed to the masses acting as inertial elements connected by the much weaker and more elastic struts.
Sinusoidal struts, however, have more favorable PBG properties. In the three samples with sinusoidal struts and added masses, PBGs inside the audible frequency range were achieved, possibly enabling applications in high-frequency noise isolation. For lower frequencies, the structures would have to become increasingly bigger and therefore more unfeasible.
In future work, we will extend the optimization to obtain 3D designs directly. Additionally, we will seek structures with band gaps in the lower audible frequency range without changing the unit cell size.










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GE is one of a number of companies developing microturbines. The microturbine application possibilities are numerous. Imagineer a household, commercial, or industrial furnace that can heat air, water, or process gasses and liquids AND generate electricity for much less than the cost of the normal technologies.

What's not normally advertized is that turbines, micro or otherwise, are loud. The sound deadening for these applications could be built into the machines themselves using the design structures shown above. Sweet!

The US DOE Combined Heat and Power Technology Fact Sheet on Microturbines


GE's been working on a large microturbine that will be used for distributed power. These could potentially replace some the large inneficient coal burning power plants that are marginally viable. The video included discusses using solar power to provide the heat but more conventional fuels can be used as well.

This Is What We Call Ecomagination: GE Is Building A CO2-Powered Turbine That Generates 10 Megawatts And Fits On A Table - Apr 11, 2017


Supercritical CO2-Brayton Cycle --- The Sandia National Laboratories Solution

The Sandia Solution

Sandia National Laboratories (SNL) is researching a thermal-to-electric power conversion technology in a configuration called the recompression closed Brayton cycle (RCBC) that uses supercritical carbon dioxide (s-CO2) as the working fluid, rather than steam, thereby dramatically increasing conversion efficiency compared to the steam Rankine cycle.

The primary reason for improved power conversion efficiency is simply that the use of s-CO2 as the working fluid in a Brayton cycle requires less work to convert a given thermal input to electricity. In general, increased efficiency represents increased output for the same thermal input, regardless of the thermal source (natural gas, nuclear, solar or coal). Where fuel costs are a significant portion of overall costs (coal and natural gas fired plants), the benefit is reduced fuel costs. Where capital investments are high (nuclear and concentrating solar power), the benefit is increased output for the initial investment.