Thermal Distortion Compensation for Improving Electrical Performance of Reflector Antennas

Aiming at the problem of the surface accuracy and electrical performance of the antenna in space environment are reduced due to thermal deformation caused by temperature load. This paper presents a method to compensate the thermally induced shape distortion of antenna reflector by actively adjusting actuators in order to improve the electrical performance. The adjustment of each actuator is related to the local deformation of the panel. Then, taking a space deployable antenna with a diameter of 5 meters as an example, the finite element model is established. According to the range of the temperature variation in space (−180°C - 200°C), different temperature loads are applied to the antenna. The variation of electrical properties and surface accuracy is analyzed and the worst working condition is determined, and the antenna is compensated based on this condition. Then, four different electrical performance parameters are used as the optimization objectives, and the electromechanical coupling optimization model is established, and the PSO algorithm is used to optimize the actuators adjustments. The results show that the method can effectively improve the electrical performance of the deformed reflector antenna.

Numerical Investigation of the Thermal Distortion in Multi-Laser Powder Bed Fusion(ML-PBF)Additive Manufacturing of Inconel 625

Metal additive manufacturing,especially laser powder bed fusion(L-PBF),is increasingly being used to fabricate complex parts with fine features.Emerging L-PBF systems have large build volumes and several lasers that op-erate simultaneously.Hence,they can produce large and complex parts at reduced costs and short build times.However,the thermal distortion remains a critical challenge.Hence,a thorough understanding of the impact of multiple lasers on part distortion in multi-laser PBF(ML-PBF)is imperative.Although experimental investigation is possible,a more conducive approach is to design and create suitable predictive models to understand the impact of multiple lasers consolidating a part into layers.To fulfill this goal,in this study,a commercially available and widely used thermo-mechanical model,Netfabb,was used to investigate the effects of multiple lasers for com-plex scan patterns such as raster,spiral,and Hilbert on the temperature distribution and thermal distortion.The results show that the thermal distortion is minimal for the spiral scan pattern.Additionally,multiple lasers were found to decrease the build time(as expected)while maintaining or reducing the thermal distortion compared with their single-laser counterparts for all scan patterns(except Hilbert).Therefore,the newly developed ML-PBF predictive model is capable of providing critical insights into the effects of using multiple lasers,thereby opening new possibilities for the faster production of complex parts.In the future,small-scale computational models will be expanded to include large-scale parts,and probabilistic models will be developed to establish correlations.

Non-standard tests for process control in chemically bonded sands

Chemically bonded sand cores and molds are more commonly referred to as precision sand systems in the high production automotive powertrain sector. Their behavior in contact with molten metal can lead to casting defects. Consequently, the interaction is of great interest and an important part of metal casting technology. The American Foundry Society(AFS) sand testing is based on physical, mechanical, thermal and chemical properties of the sand system. Foundry engineers have long known that certain AFS sand tests provide limited information regarding control of molding and casting quality. The inadequacy is due to the fact that sand casting processes are inherently thermo-mechanical, thermo-chemical and thermo-physical. Non-standard foundry sand testing has proven useful for laboratory measurement of these characteristics in foundry sand using a disc-shaped specimen. Similarly, the equivalent disc-shaped specimens are used for casting trials. In order to accomplish near-net-shape casting with minimal defects, it is necessary to understand both the properties of the sand system, as well as the interface of molten metal when different binders, additives and/or refractory coatings are used. The methodology for the following non-standard chemically bonded sand tests is described:(1) disc transverse;(2) impact;(3) modified permeability;(4) abrasion;(5) thermal distortion;(6) quick loss on ignition. The data related to the non-standard sand tests were analyzed and interpreted. The test results indicate that there is relatively lower test-to-test variability with the disc-shaped specimens. The non-standard tests were able to discriminate between the chemically bonded polyurethane cold box sand specimens. Further studies should be conducted on various other sand and binder systems as well as on different specimen thicknesses.

Thermoelastohydrodynamic behaviour of inclined-ellipse dimpled gas face seals

The thermoelastohydrodynamic performance of an inclined-ellipse dimpled gas face seal is analyzed. The pressure distributions of the gas film and temperature fields of the seal rings and gas film are presented considering thermal and elastic distortions.Then, the influences of texturing parameters, including dimple inclination angle and dimple depth, on sealing performance are investigated under different operating parameters such as rotational speeds and seal pressures. The results show that face distortions lead to a decrease in the hydrodynamic effect at high rotational speed. The analysis shows that the opening force can decrease by more than 50% as the rotational speed increases from 0 to 35000 r min^(-1). The influence of face distortion on the seal performance, such as opening force and leakage characteristic, gradually increases with the rotational speed.