Power harvesting using piezoelectric materials: applications in helicopter rotors

The blades of helicopters are heavily loaded and are critical components. Failure of any one blade will lead to loss of the aircraft. Currently, the technical lifespan of helicopter blades is calculated using a worst-case operation scenario. The consequence is that a blade that may be suitable for, for example, ten thousand flight hours is discarded after only three thousand hours. The costs associated with this practice are enormous. For heavily loaded military aircraft this practice may be a reasonable approach. On the other hand, light duty aircraft in civil aviation may only use the blades for half or one third of the total technical lifespan, incurring unnecessarily high costs. Although the blade life could be extended through more advanced materials, extensive inspection regimes and better design, the uncertainty concerning the blade loads and fatigue issues remains. These options are all very costly.\ud Measuring systems are required within the blade in order to more accurately follow the actual loads that it is subjected to. In this manner it is possible to monitor the loads, calculate the actual fatigue within the blade and, finally, the end of life can be predicted far more accurately. This will result in blades being used longer, reducing maintenance costs for the operator and lowering the environmental impact of blade manufacturing.\ud The main challenge is supplying the sensors with electric power. Large rotorcraft have slip rings within the rotor head, supplying power for de-icing systems on the leading edge of the blade. This power is unsuitable for sensing and data processing because it is high voltage, and is not a stable source of power. Additionally, slip rings are maintenance intensive.\ud The idea proposed in this thesis is to generate the power needed for sensing within the blade itself. Many generation methods are available varying from traditional electromagnetic generators to solid state conversion mechanisms. In this work, piezoelectrics are considered as a candidate to harvest power. Piezoelectric material is a material which develops an electrical charge as it is mechanically stressed. It is shown in this thesis that a useful amount of power can be recovered from the blade when combined with the right electric circuit

Power harvesting in a helicopter lag damper

In this paper a new power harvesting application is developed and simulated. Power harvesting is chosen within the European Clean Sky project as a solution to powering in-blade health monitoring systems as opposed to installing an elaborate electrical infrastructure to draw power from and transmit signals to the helicopter body. Local generation of power will allow for a ‘plug and play’ rotor blade and signals may be logged or transmitted wirelessly.\ud The lag damper is chosen to be modified as it provides a well defined loading due to the re-gressive damping characteristic. A piezo electric stack is installed inside the damper rod, effec-tively coupled in series with the damper. Due to the well defined peak force generated in the damper the stack geometry requires a very limited margin of safety. Typically the stack geometry must be chosen to prevent excessive voltage build-up as opposed to mechanical overload.\ud Development and simulation of the model is described starting with a simplified blade and piezo element model. Presuming specific flight conditions transient simulations are conducted using various power harvesting circuits and their performance is evaluated. The best performing circuit is further optimized to increase the specific power output. Optimization of the electrical and mechanical domains must be done simultaneously due to the high electro-mechanical cou-pling of the piezo stack. The non-linear electrical properties of the piezo material, most notably the capacitance which may have a large influence, are not yet considered in this study.\ud The power harvesting lag damper provides sufficient power for extensive health monitoring systems within the blade while retaining the functionality and safety of the standard component. For the 8.15m blade radius and 130 knots flight speed under consideration simulations show 7.5 watts of power is generated from a single damper

Архівна Евристика: практичні аспекти

Для молодої генерації сучасних дослідників здійснення ефективного пошуку інформації для вирішення конкретних завдань набуває надзвичайної ваги та актуальності. Вміння грамотно і професійно шукати достовірну та актуальну інформацію, робити висновки та приймати правильні рішення спонукає фахівця-інтелектуала опановувати спеціальні евристичні методи

Power harvesting using piezomaterial in a helicopter rotor blade

Current power harvesting research has focused on bending beams and determining power output under a given excitation. For the European CleanSky – Green Rotor Craft project a tool is being developed which optimizes the piezoelectric material and placement thereof for power harvesting. It focuses on beam-like structures exhibiting more complex dynamics where the optimum configuration is not evident. In particular helicopter rotor blades are considered where strains are high and frequencies low, stepping away from typical high frequency / low strain harvesting applications. This application will allow for smart rotor blades, alleviate rotor induced vibrations, subsequently increasing comfort and possibly airframe longevity. First an uncoupled model was developed, using an airfoil shape and vibration input from industry. The blade surface is covered with piezo electric patches of which the strain during one cycle is calculated. Materials, either ceramic or piezo polymer, are selected based on a peak strain criterion and the energy of each patch is then evaluated using a specified harvesting circuit. Optimum locations are determined using a minimum desired efficiency relative to the best performing patch. For aircraft application the main performance indicator is clearly the power to weight ratio. Experiments have also been conducted which confirm the piezo polymer performance up in\ud the percentage strain range where piezo ceramics fail. The harvesting performance of ceramic patches has also been evaluated. Measurements will be conducted on a complex beam shape to confirm the theoretical results as well when the theoretical model is completed. Future development encompasses dynamic coupling since the behaviour may be influenced as more energy is extracted. An iteration algorithm will need to be selected for the optimization process. Lastly electrical models will be included as this directly determines the harvesting efficiency. The final tool will be applicable on any slender structure which exhibits complex harmonic loading

Cardiovascular parameters on computed tomography are independently associated with in-hospital complications and outcomes in level-1 trauma patients

Background: In-hospital complications after trauma may result in prolonged stays, higher costs, and adverse functional outcomes. Among reported risk factors for complications are pre-existing cardiopulmonary comorbidities. Objective and quick evaluation of cardiovascular risk would be beneficial for risk assessment in trauma patients. Studies in non-trauma patients suggested an independent association between cardiovascular abnormalities visible on routine computed tomography (CT) imaging and outcomes. However, whether this applies to trauma patients is unknown.Purpose: To assess the association between cardiopulmonary abnormalities visible on routine CT images and the development of in-hospital complications in patients in a level-1 trauma center.Methods: All trauma patients aged 16 years or older with CT imaging of the abdomen, thorax, or spine and admitted to the UMC Utrecht in 2017 were included. Patients with an active infection upon admission or severe neurological trauma were excluded. Routine trauma CT images were analyzed for visible abnormalities: pulmonary emphysema, coronary artery calcifications, and abdominal aorta calcification severity. Drug-treated complications were scored. The discharge condition was measured on the Glasgow Outcome Scale.Results: In total, 433 patients (median age 50 years, 67% male, 89% ASA 1–2) were analyzed. Median Injury Severity Score and Glasgow Coma Scale score were 9 and 15, respectively. Seventy-six patients suffered from at least one complication, mostly pneumonia (n = 39, 9%) or delirium (n = 19, 4%). Left main coronary artery calcification was independently associated with the development of any complication (OR 3.9, 95% CI 1.7–8.9). An increasing number of calcified coronary arteries showed a trend toward an association with complications (p = 0.07) and was significantly associated with an adverse discharge condition (p = 0.02). Pulmonary emphysema and aortic calcifications were not associated with complications.Conclusion: Coronary artery calcification, visible on routine CT imaging, is independently associated with in-hospital complications and an adverse discharge condition in level-1 trauma patients. The findings of this study may help to identify trauma patients quickly and objectively at risk for complications in an early stage without performing additional diagnostics or interventions.</p

Hearing loss and cognitive decline in the general population: a prospective cohort study

Background: Previous studies identifying hearing loss as a promising modifiable risk factor for cognitive decline mostly adjusted for baseline age solely. As such a faster cognitive decline at a higher age, which is expected considering the non-linear relationship between cognition and age, may have been overlooked. Therefore it remains uncertain whether effects of hearing loss on cognitive decline extend beyond age-related declines of cognitive function. Methods: 3,590 non-demented participants were eligible for analysis at baseline, and a maximum of 837 participants were eligible for the longitudinal analysis. Hearing loss was defined at baseline. Cognitive function was measured at baseline and at follow-up (4.4 years [SD: 0.2]). Multivariable linear regression analysis was used for the cross-sectional analysis. Linear mixed models were used to assess the longitudinal association between hearing loss and cognitive decline over time while adjusting for confounders and the interaction of age and follow-up time. Results: Hearing loss was associated with lower cognitive function at baseline. Moreover, hearing loss was associated with accelerated cognitive decline over time on a memory test. After additionally adjusting for the interaction between age and follow-up time, we found that hearing loss did not accelerate cognitive decline anymore. Conclusions: Hearing loss was associated with lowe

Is a chest radiograph indicated after chest tube removal in trauma patients? A systematic review

PURPOSE The aim of this systematic review was to assess the necessity of routine chest radiographs after chest tube removal in ventilated and nonventilated trauma patients. METHODS A systematic literature search was conducted in MEDLINE, Embase, CENTRAL, and CINAHL on May 15, 2020. Quality assessment was performed using the Methodological Index for Nonrandomized Studies criteria. Primary outcome measures were abnormalities on postremoval chest radiograph (e.g., recurrence of a pneumothorax, hemothorax, pleural effusion) and reintervention after chest tube removal. Secondary outcome measures were emergence of new clinical symptoms or vital signs after chest tube removal. RESULTS Fourteen studies were included, consisting of seven studies on nonventilated patients and seven studies on combined cohorts of ventilated and nonventilated patients, all together containing 1,855 patients. Nonventilated patients had abnormalities on postremoval chest radiograph in 10% (range across studies, 0-38%) of all chest tubes and 24% (range, 0-78%) of those underwent reintervention. In the studies that reported on clinical symptoms after chest tube removal, all patients who underwent reintervention also had symptoms of recurrent pathology. Combined cohorts of ventilated and nonventilated patients had abnormalities on postremoval chest radiograph in 20% (range, 6-49%) of all chest tubes and 45% (range, 8-63%) of those underwent reintervention. CONCLUSION In nonventilated patients, one in ten developed recurrent pathology after chest tube removal and almost a quarter of them underwent reintervention. In two studies that reported on clinical symptoms, all reinterventions were performed in patients with symptoms of recurrent pathology. In these two studies, omission of routine postremoval chest radiograph seemed safe. However, current literature remains insufficient to draw definitive conclusions on this matter, and future studies are needed. LEVEL OF EVIDENCE Systematic review study, level IV

Dendritic position is a major determinant of presynaptic strength

Different regulatory principles influence synaptic coupling between neurons, including positional principles. In dendrites of pyramidal neurons, postsynaptic sensitivity depends on synapse location, with distal synapses having the highest gain. In this paper, we investigate whether similar rules exist for presynaptic terminals in mixed networks of pyramidal and dentate gyrus (DG) neurons. Unexpectedly, distal synapses had the lowest staining intensities for vesicular proteins vGlut, vGAT, Synaptotagmin, and VAMP and for many nonvesicular proteins, including Bassoon, Munc18, and Syntaxin. Concomitantly, distal synapses displayed less vesicle release upon stimulation. This dependence of presynaptic strength on dendritic position persisted after chronically blocking action potential firing and postsynaptic receptors but was markedly reduced on DG dendrites compared with pyramidal dendrites. These data reveal a novel rule, independent of neuronal activity, which regulates presynaptic strength according to dendritic position, with the strongest terminals closest to the soma. This gradient is opposite to postsynaptic gradients observed in pyramidal dendrites, and different cell types apply this rule to a different extent