Effects of structural coupling on mistuned cascade flutter and response

The effects of structural coupling on mistuned cascade flutter and response are analytically investigated using an extended typical section model. This model includes both structural and aerodynamic coupling between the blades. The model assumes that the structurally coupled system natural modes were determined and are represented in the form of N bending and N torsional uncoupled modes for each blade, where N is the number of blades and, hence, is only valid for blade dominated motion. The aerodynamic loads are calculated by using two dimensional unsteady cascade theories in the subsonic and supersonic flow regimes. The results show that the addition of structural coupling can affect both the aeroelastic stability and frequency. The stability is significantly affected only when the system is mistuned. The resonant frequencies can be significantly changed by structural coupling in both tuned and mistuned systems, however, the peak response is significantly affected only in the latter

Coupled bending-bending-torsion flutter of a mistuned cascade with nonuniform blades

A set of aeroelastic equations describing the motion of an arbitrarily mistuned cascade with flexible, pretwisted, nonuniform blades is developed using an extended Hamilton's principle. The derivation of the equations has its basis in the geometric nonlinear theory of elasticity in which the elongations and shears are negligible compared to unity. A general expression for foreshortening of a blade is derived and is explicity used in the formulation. The blade aerodynamic loading in the subsonic and supersonic flow regimes is obtained from two dimensional, unsteady, cascade theories. The aerodynamic, inertial and structural coupling between the bending (in two planes) and torsional motions of the blade is included. The equations are used to investigate the aeroelastic stability and to quantify the effect of frequency mistuning on flutter in turbofans. Results indicate that a moderate amount of intentional mistuning has enough potential to alleviate flutter problems in unshrouded, high aspect ratio turbofans

Flutter of swept fan blades

The effect of sweep on fan blade flutter is studied by applying the analytical methods developed for aeroelastic analysis of advance turboprops. Two methods are used. The first method utilizes an approximate structural model in which the blade is represented by a swept, nonuniform beam. The second method utilizes a finite element technique to conduct modal flutter analysis. For both methods the unsteady aerodynamic loads are calculated using two dimensional cascade theories which are modified to account for sweep. An advanced fan stage is analyzed with 0, 15 and 30 degrees of sweep. It is shown that sweep has a beneficial effect on predominantly torsional flutter and a detrimental effect on predominantly bending flutter. This detrimental effect is shown to be significantly destabilizing for 30 degrees of sweep

Effects of mistuning on bending-torsion flutter and response of a cascade in incompressible flow

The effect of small differences between the individual blades (mistuning) on the aeroelastic stability and response of a cascade were studied. The aerodynamic, inertial, and structural coupling between the bending and torsional motions of each blade and the aerodynamic coupling between the blades was considered. A digital computer program was developed to conduct parametric studies. Results indicate that the mistuning has a beneficial effect on the coupled bending torsion and uncoupled torsion flutter. On forced response, however, the effect may be either beneficial or adverse, depending on the engine order of the forcing function. The results also illustrate that it may be feasible to utilize mistuning as a passive control to increase flutter speed while maintaining forced response at an acceptable level

Aeroelastic characteristics of a cascade of mistuned blades in subsonic and supersonic flows

The effects of mistuning on flutter and forced response of a cascade in subsonic in subsonic and supersonic flow were investigated. The aerodynamic and structural coupling between the bending and torsional motions and the aerodynamic coupling between the blades were studied. It is shown that frequency mistuning always has a beneficial effect on flutter. For the cascade considered, the potential for raising flutter speed is greater in subsonic than in supersonic flow. Preliminary results for structural damping mistuning show that there are no additional benefits over adding damping mistuning may have either a beneficial or an adverse effect on forced response, depending on the engine order of the excitation and Mach number

Bending-torsion flutter of a highly swept advanced turboprop

Experimental and analytical results are presented for a bending-torsion flutter phenomena encountered during wind-tunnel testing of a ten-bladed, advanced, high-speed propeller (turboprop) model with thin airfoil sections, high blade sweep, low aspect ratio, high solidity and transonic tip speeds. Flutter occurred at free-stream Mach numbers of 0.6 and greater and when the relative tip Mach number (based on vector sum of axial and tangential velocities) reached a value of about one. The experiment also included two- and five-blade configurations. The data indicate that aerodynamic cascade effects have a strong destabilizing influence on the flutter boundary. The data was correlated with analytical results which include aerodynamic cascade effects and good agreement was found

Recent coastline changes of fan-deltas in the Western Gulf of Corinth, Central Greece

Στην παρούσα εργασία επιχειρείται η εκτίμηση των πρόσφατων μεταβολών της ακτογραμμής των δελταϊκών ριπιδίων των ποταμών Φοίνικα, Θολοπόταμο, Λαγκάδι, Μεγανίτα, Σελινούντα, Κερυνίτη και Βουραϊκού, με τη χρήση μεθόδων τηλεπισκόπησης και ΣΓΠ. Τα δελταϊκά αυτά ριπίδια ηλικίας Ανώτερου Ολόκαινου έχουν σχηματισθεί από ποτάμια μεγάλης μορφολογικής κλίσης που αποθέτουν το αδρομερές φορτίο ιζημάτων τους κατά μήκος των νότιων ακτών του δυτικού Κορινθιακού κόλπου (Β. Πελοπόννησος). Για τους σκοπούς της εργασίας δημιουργήθηκε και οργανώθηκε μια ψηφιακή βάση δεδομένων για την περιοχή αποτελούμενη από λεπτομερή (κλίμακας 1:5.000) τοπογραφικά διαγράμματα και γεωμετρικά διορθωμένες και γεωαναφερμένες αεροφωτογραφίες λήψης 1945, 1996 και 2008. Η σύγκριση των ακτογραμμών των δελταϊκών ριπιδίων κατά τα έτη 1945, 1996 και 2008 οδήγησε στον προσδιορισμό των τμημάτων της ακτογραμμής πουυπόκεινται σε διάβρωση καθώς και εκείνων που προελαύνουν. Η κύρια διεργασία κατά μήκος του μεγαλύτερου μήκους της ακτογραμμής είναι η διάβρωση. Ομεγαλύτερος ρυθμός διάβρωσης ήταν 2,44 m/έτος (μεταξύ των ετών 1945 και 1996) και σημειώθηκε περίπου 150 m δυτικά των εκβολών του ποταμού Φοίνικα. Αντίθετα οι υψηλότεροι ρυθμοί προέλασης μετά το 1945 ήταν 3,10 και 3,00 m/έτος και σημειώθηκαν στις περιοχές των ενεργών εκβολών των ποταμών Βουραϊκού και Σελινούντα αντίστοιχα.This study deals with the assessment of recent shoreline change rates along the fandeltas of Finix, Tholopotamo, Lagadi, Meganitas, Selinous, Kerinitis, and Vouraikos streams by using GIS and Remote Sensing techniques. These Late Holocene fandeltas have been formed by high gradient braided streams that deposit their coarse sediment load along the southern coast (North Peloponnese) of the western Gulf of Corinth. For the purposes of the study a spatial database was constructed, organized and implemented consisting of analogue detailed (at the scale of 1:5000) topographic diagrams, and orthorectified aerial photos taken in 1945, 1996 and 2008. Comparisons of fan-deltas shoreline positions for the periods 1945 vs. 1996 and 1945 vs. 2008 were made and the segments of the coastline along the aprons of the fan-deltas which are subject to erosion accretion were defined. Coastal erosion is the main dominant geomorphic process along a significant part of the fan deltas coastline. The highest retreat rate value (2.44 m/yr for the period 1945-1996) was estimated for the Finix stream fan delta, about 150 m west of the river mouth, while the highest accretion rates since 1945 (3.10 and 3.00 m/yr) occurred at the mouths of Vouraikos and Selinous rivers respectively

Analysis of the US Food and Drug Administration Manufacturer and User Facility Device Experience database for adverse events involving Amplatzer septal occluder devices and comparison with the Society of Thoracic Surgery congenital cardiac surgery database

ObjectiveAmplatzer (AGA Medical Corporation, Plymouth, Minn) septal and vascular occluder devices have significantly altered the care of patients with congenital heart disease. The relative frequency and consequence of complications resulting from the attempted placement of such devices, however, have not been well assessed. The purpose of this study is to use large databases to assess the frequency and severity of such complications and compare them with those of surgical atrial septal defect closure.MethodsThe US Food and Drug Administration Manufacturer and User Facility Device Experience database was quarried for all adverse events for Amplatzer septal occluder devices, which were categorized and analyzed with particular emphasis on management and outcome. The Society of Thoracic Surgery database was likewise quarried for the same data regarding atrial septal defect closures over a contemporaneous time period. By using a literature-derived denominator for total Amplatzer implant numbers, the results of the 2 therapies were compared.ResultsSince July 1, 2002, 223 adverse events in patients undergoing Amplatzer atrial septal defect closure were submitted to the Food and Drug Administration, resulting in 17 deaths (7.6%) and 152 surgical rescue operations (68.2%). Society of Thoracic Surgery data demonstrated 1537 primary operations with 2 deaths (0.13%) and 6 reoperations (0.39%). By extrapolating on published estimates of Amplatzer implantation to provide an implant denominator (n = 18,333), there was no difference between overall mortality for surgical (0.13%) and device closure (0.093%, P = .649). Rescue operation for device adverse events (0.83%) was 2.1 times more likely than reoperation for surgical closure (0.39%, P = .063). Mortality per adverse event was higher for device closure (7.6%) than for surgical closure (1.2%, P = .004), and the need for surgery per adverse event was higher for device closure (68.2%) than for surgical closure (3.6%, P < .001). The mortality for surgical management of a device adverse event (2.6%) was 20-fold higher than for primary elective atrial septal defect closure (0.13%, P < .0001).ConclusionOverall crude mortality for device and surgical closure atrial septal defect closure is equivalent, and the need for subsequent operation (surgical rescue) is more common in patients undergoing device closure than reoperation is in patients undergoing surgical closure. Complications from device closure tend to be serious and most often require urgent or emergency operative management, whereas the mortality for surgical management of a device complication appears higher than that of elective atrial septal defect closure. Further information is required in the form of postmarketing surveillance, such as a mandatory user registry with periodic end-user notification

Reproducibility of the lung anatomy under Active Breathing Coordinator control: Dosimetric consequences for scanned proton treatments.

Purpose/Objective The treatment of moving targets with scanning proton beams is challenging. By controlling lung volumes, Active Breathing Control (ABC) assists breath-holding for motion mitigation. The delivery of proton treatment fractions often exceeds feasible breath-hold durations, requiring high breath-hold reproducibility. Therefore, we investigated dosimetric consequences of anatomical reproducibility uncertainties in the lung under ABC, evaluating robustness of scanned proton treatments during breath-hold. Material/Methods T1-weighted MRIs of five volunteers were acquired during ABC, simulating image acquisition during four subsequent breath-holds within one treatment fraction. Deformation vector fields obtained from these MRIs were used to deform 95% inspiration phase CTs of 3 randomly selected non-small-cell lung cancer patients (Figure 1). Per patient, an intensity-modulated proton plan was recalculated on the 3 deformed CTs, to assess the dosimetric influence of anatomical breath-hold inconsistencies. Results Dosimetric consequences were negligible for patient 1 and 2 (Figure 1). Patient 3 showed a decreased volume (95.2%) receiving 95% of the prescribed dose for one deformed CT. The volume receiving 105% of the prescribed dose increased from 0.0% to 9.9%. Furthermore, the heart volume receiving 5 Gy varied by 2.3%. Figure 2 shows dose volume histograms for all relevant structures in patient 3. Conclusion Based on the studied patients, our findings suggest that variations in breath-hold have limited effect on the dose distribution for most lung patients. However, for one patient, a significant decrease in target coverage was found for one of the deformed CTs. Therefore, further investigation of dosimetric consequences from intra-fractional breath-hold uncertainties in the lung under ABC is needed