Laser-Heating for Thermo-Mechanical Fatigue Simulation

The strong demand for light-weight structures, which is typical for space transportation systems, leads to a close-to-the-limit design of all involved components – including the rocket engines. The combined thermally and mechanically induced Low Cycle Fatigue and creep failure of hot gas walls is one of the strongest limiting factors of the life time of key rocket engine components like combustion chambers and expansion nozzles. The development and flight qualification of such components includes on top of many other actions CFD, structural and life time analyses of the key components and full scale tests of the whole rocket engine. Thermo-Mechanical Fatigue (TMF)-tests can provide essential validation data for these numerical analyses and reduce the need for full scale tests. Therefore, TMF-tests have the potential of both, avoiding failure due to non-validated design analyses as well as saving full scale testing cost. During a TMF test, only a small section of the hot gas wall of the real engine (the so called TMF panel) is tested. For this TMF panel, realistic cooling conditions like in the full scale rocket engine are chosen. In Europe, the concept of TMF-panel testing has been first very successfully applied to rocket thrust chamber structures in the frame of the Ariane 5 Flight Recovery Programme in 2003 and 2004. During this programme, TMF tests were performed by EADS Astrium Space Transportation in cooperation with Volvo Aero Corporation, Snecma Safran and Fraunhofer Institute Dresden to demonstrate the life margin of dump-cooled nozzle structures under relevant thermo-mechanical loading conditions. These encouraging results have motivated the partners DLR Lampoldshausen and EADS Astrium to jointly investigate again the TMF test concept with special focus on meeting relevant requirements for future liquid propulsion needs. The key component of a TMF test facility is a heating device for the hot gas side of the tested wall component. For the TMF test facility at DLR Lampoldshausen, a diode Laser with a wave length of 940 nm was chosen. This Laser was especially designed by the diode laser producer DILAS in order to obtain an optical output of 11 kW. In combination with a built in modular optics system, this results in an energy density of up to 8 MW per square meter at the focal plane (18 mm x 50 mm). The presentation at the IAA 2008 will show details of the TMF test facility such as the Laser, the TMF panel housing, the fluid system, the MCC system as well as numerical analyses for an experimental TMF panel

Evaluation of Different Positive End-Expiratory Pressures Using Supreme™ Airway Laryngeal Mask during Minor Surgical Procedures in Children

Background and objectives: The laryngeal mask is the method of choice for airway management in children during minor surgical procedures. There is a paucity of data regarding optimal management of mechanical ventilation in these patients. The Supreme™ airway laryngeal mask offers the option to insert a gastric tube to empty the stomach contents of air and/or gastric juice. The aim of this investigation was to evaluate the impact of positive end-expiratory positive pressure (PEEP) levels on ventilation parameters and gastric air insufflation during general anesthesia in children using pressure-controlled ventilation with laryngeal mask. Materials and Methods: An observational trial was carried out in 67 children aged between 1 and 11 years. PEEP levels of 0, 3 and 5 mbar were tested for 5 min in each patient during surgery and compared with ventilation parameters (dynamic compliance (mL/cmH2O), etCO2 (mmHg), peak pressure (mbar), tidal volume (mL), respiratory rate (per minute), FiO2 and gastric air (mL)) were measured at each PEEP. Air was aspirated from the stomach at the start of the sequence of measurements and at the end. Results: Significant differences were observed for the ventilation parameters: dynamic compliance (PEEP 5 vs. PEEP 3: p < 0.0001, PEEP 5 vs. PEEP 0: p < 0.0001, PEEP 3 vs. PEEP 0: p < 0.0001), peak pressure (PEEP 5 vs. PEEP 3: p < 0.0001, PEEP 5 vs. PEEP 0: p < 0.0001, PEEP 3 vs. PEEP 0: p < 0.0001) and tidal volume (PEEP 5 vs. PEEP 3: p = 0.0048, PEEP 5 vs. PEEP 0: p < 0.0001, PEEP 3 vs. PEEP 0: p < 0.0001). All parameters increased significantly with higher PEEP, with the exception of etCO2 (significant decrease) and respiratory rate (no significant difference). We also showed different values for air quantity in the comparisons between the different PEEP levels (PEEP 5: 2.8 ± 3.9 mL, PEEP 3: 1.8 ± 3.0 mL; PEEP 0: 1.6 ± 2.3 mL) with significant differences between PEEP 5 and PEEP 3 (p = 0.0269) and PEEP 5 and PEEP 0 (p = 0.0209). Conclusions: Our data suggest that ventilation with a PEEP of 5 mbar might be more lung protective in children using the Supreme™ airway laryngeal mask, although gastric air insufflation increased with higher PEEP. We recommend the use of a laryngeal mask with the option of inserting a gastric tube to evacuate potential gastric air

TMF: Laser Application for a Close-to-Reality Simulation of Thermo-Mechanical Fatigue Processes in Rocket Engines

The concept of a thermo-mechanical fatigue (TMF) - test bench is discussed in this paper. Motivation for the TMF tests are two-fold: to assess the life expectation of structures being exposed to extreme thermo-mechanical loads first on subcomponent or panel level, and to serve as validation experiment for life-prediction models. In Europe, the concept of TMF-panel testing has been first very successfully applied to rocket thrust chamber structures in the frame of the Ariane 5 Flight Recovery Programme in 2003 and 2004. These encouraging results have motivated the partners DLR Lampoldshausen and EADS Astrium to jointly investigate again the TMF-bench concept with special focus on meeting relevant requirements for future liquid propulsion needs. The following key elements of a TMF test bench are presented in the paper: • the TMF heating device – a diode Laser, which is available already at DLR Lampoldshausen, • the design of the panel housing, • a tentative design of the TMF panel. Furthermore, numerical analyses of this tentative TMF panel – such as a CFD analysis of the coolant flow in the core part of the TMF panel and a thermal as well as a structural Finite Element analysis of the sandwich part of the TMF panel during the hot run are shown

Incidence of severe critical events in paediatric anaesthesia (APRICOT): a prospective multicentre observational study in 261 hospitals in Europe

Background Little is known about the incidence of severe critical events in children undergoing general anaesthesia in Europe. We aimed to identify the incidence, nature, and outcome of severe critical events in children undergoing anaesthesia, and the associated potential risk factors. Methods The APRICOT study was a prospective observational multicentre cohort study of children from birth to 15 years of age undergoing elective or urgent anaesthesia for diagnostic or surgical procedures. Children were eligible for inclusion during a 2-week period determined prospectively by each centre. There were 261 participating centres across 33 European countries. The primary endpoint was the occurence of perioperative severe critical events requiring immediate intervention. A severe critical event was defined as the occurrence of respiratory, cardiac, allergic, or neurological complications requiring immediate intervention and that led (or could have led) to major disability or death. This study is registered with ClinicalTrials.gov, number NCT01878760. Findings Between April 1, 2014, and Jan 31, 2015, 31 127 anaesthetic procedures in 30 874 children with a mean age of 6.35 years (SD 4.50) were included. The incidence of perioperative severe critical events was 5.2% (95% CI 5.0-5.5) with an incidence of respiratory critical events of 3.1% (2.9-3.3). Cardiovascular instability occurred in 1.9% (1.7-2.1), with an immediate poor outcome in 5.4% (3.7-7.5) of these cases. The all-cause 30-day in-hospital mortality rate was 10 in 10 000. This was independent of type of anaesthesia. Age (relative risk 0.88, 95% CI 0.86-0.90; p<0.0001), medical history, and physical condition (1.60, 1.40-1.82; p<0.0001) were the major risk factors for a serious critical event. Multivariate analysis revealed evidence for the beneficial effect of years of experience of the most senior anaesthesia team member (0.99, 0.981-0.997; p<0.0048 for respiratory critical events, and 0.98, 0.97-0.99; p=0.0039 for cardiovascular critical events), rather than the type of health institution or providers. Interpretation This study highlights a relatively high rate of severe critical events during the anaesthesia management of children for surgical or diagnostic procedures in Europe, and a large variability in the practice of paediatric anaesthesia. These findings are substantial enough to warrant attention from national, regional, and specialist societies to target education of anaesthesiologists and their teams and implement strategies for quality improvement in paediatric anaesthesia