Potential of additively manufactured particle damped compressor blades: A literature review

The high-cycle fatigue of compressors significantly impacts the lifetime of aircraft engines. Excitations in resonance lead to early blade fractures; therefore, vibration reduction measures for blades must be taken. Additively manufactured particle dampers are a suitable measure to suppress vibrations. The focus of this paper is to analyze the applications of additively manufactured particle dampers in compressor blades through a literature review. The design requirements, previous vibration reduction measures for compressor blades and properties of additively manufactured particle dampers are investigated in three studies. In order to evaluate the application of additively manufactured particle dampers in compressor blades, the findings are compared and research demand is derived. The main requirements on compressor blades are stiffness, vibration reduction and wear-resistance. Recent vibration reduction measures are focused on friction dampers. To optimize damping multiple vibration suppression measures shall be used. Few studies exist for additively manufactured particle dampers and some prove their damping improvement in compressor blades. Due to the complicated operation conditions, further studies are needed, which are listed to give researchers an approach for further steps

Design of additively manufacturable injection molds with conformal cooling

Additive manufacturing enables the production of intricate geometries including internal structures. This design freedom can be used advantageously to enhance heat transfer in injection molds by means of conformal cooling. The main goal is to reduce cycle times and to improve part quality through uniform cooling of the plastic products. This paper presents cooling design concepts for mold inserts. Their underlying approaches differ with respect to the shape and the cross-sectional geometries of cooling channels. Distinct inserts are additively manufactured by laser-based powder bed fusion (PBF-LB) of AISI 420 stainless steel. Experiments are carried out on a custom thermal test bench. Infrared thermography is used to examine the surface temperature, showing a reduction in cooling time by up to 41 % compared to conventional concepts. Additionally, the coolant flow is measured. The evaluation of the cooling characteristics reveal a critical trade-off between cycle time and uniformity of the surface temperature

Design Guidelines for Additive Manufactured Particle Dampers: A Review

Recently, additive manufacturing has been used to integrate particle dampers into structural components, particularly by means of laser powder bed fusion (LPBF), in order to significantly reduce component vibrations. The advantage over previous damping mechanisms is that these can be functionally integrated directly into the component during the additive manufacturing process by leaving unmelted powder in the component. This allows local damping effects to be adjusted and low-vibration lightweight structures to be developed and manufactured. In addition, the damping properties act over a wide frequency range and are insensitive to temperature. Despite the positive damping properties, the use of laser beam melted particle dampers is limited at the present time, since there are not yet sufficient design tools available due to the numerous non-linear influences. This is where the current contribution comes in, by developing design guidelines for laser beam melted particle dampers. The results were finally summarised in a design catalogue and support a suitable design of laser beam melted particle dampers

Surfactant function in lung transplantation after 24 hours of ischemia: Advantage of retrograde flush perfusion for preservation

AbstractObjective: Surfactant function was shown to be impaired in clinical and experimental lung transplantation. This study was designed to define the impact of retrograde flush perfusion on graft and surfactant function after an extended period of ischemia. Methods: Left lung transplantation was performed after 24 hours of graft ischemia in 12 pigs. In half of the grafts antegrade cold flush perfusion (Perfadex) was used for preservation. In the second group grafts were flushed in a retrograde fashion via the left atrium. Graft function was monitored for 7 hours after transplantation. Before transplantation (basal) and after 2 hours of reperfusion, bronchoalveolar lavage fluid was obtained. Minimal surface tension of bronchoalveolar lavage fluid was determined and the ratio of small and large surfactant aggregates was calculated. Lung water content was analyzed online in the reperfusion period. Results: Right-sided heart failure developed in 2 animals of group 1 (antegrade perfusion) within 2 and 4.5 hours of reperfusion, respectively. All other pigs survived the observation period. PO2/FIO2 (P =.001) and dynamic lung compliance (P =.001) were superior in retrogradely flushed grafts. A comparable increase of minimal surface tension was found after reperfusion in both groups. Small/large surfactant aggregate ratio after reperfusion (P =.03), as well as extravascular lung water content, was higher in the antegrade perfusion group. Conclusion: Retrograde flush perfusion for 24-hour lung preservation with low-potassium dextran (Perfadex) solution led to better initial graft function than the standard antegrade perfusion technique. A moderate impairment of surfactant function was found in both groups, which was more pronounced in the antegrade perfusion group

Modeling Brain Resonance Phenomena Using a Neural Mass Model

Stimulation with rhythmic light flicker (photic driving) plays an important role in the diagnosis of schizophrenia, mood disorder, migraine, and epilepsy. In particular, the adjustment of spontaneous brain rhythms to the stimulus frequency (entrainment) is used to assess the functional flexibility of the brain. We aim to gain deeper understanding of the mechanisms underlying this technique and to predict the effects of stimulus frequency and intensity. For this purpose, a modified Jansen and Rit neural mass model (NMM) of a cortical circuit is used. This mean field model has been designed to strike a balance between mathematical simplicity and biological plausibility. We reproduced the entrainment phenomenon observed in EEG during a photic driving experiment. More generally, we demonstrate that such a single area model can already yield very complex dynamics, including chaos, for biologically plausible parameter ranges. We chart the entire parameter space by means of characteristic Lyapunov spectra and Kaplan-Yorke dimension as well as time series and power spectra. Rhythmic and chaotic brain states were found virtually next to each other, such that small parameter changes can give rise to switching from one to another. Strikingly, this characteristic pattern of unpredictability generated by the model was matched to the experimental data with reasonable accuracy. These findings confirm that the NMM is a useful model of brain dynamics during photic driving. In this context, it can be used to study the mechanisms of, for example, perception and epileptic seizure generation. In particular, it enabled us to make predictions regarding the stimulus amplitude in further experiments for improving the entrainment effect