Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, September 1990. / Thesis Advisor(s): Henline, William D. ; Platzer, Max F. Second Reader: Chandrasekhara, M. S. "September 1990." Description based on title screen as viewed on December 21, 2009. DTIC Identifier(s): Ceramic materials, ablative materials, heat shields, reusable equipment, space flight, thermal insulation, atmospheric entry, hypersonic flow, Mars probes, arc heaters, melting, glass, RSI (reusable surface insulaiton), aerodynamic heating, stagnation pressure, mathematical prediction, theses. Author(s) subject terms: Ablative, hypersonic, NASA, Mars, heat shield. Includes bibliographical references (p. 110). Also available in print.

In der vorliegenden Arbeit wurde mit einer Vielzahl an objektiven Messverfahren und subjektiven Einschätzungen, die Wirkungen und Nebenwirkungen von drei unterschiedlichen fraktional ablativen Lasersystemen in der Therapie der gealterten und chronisch lichtgeschädigten Haut einzelner Gesichtsareale, sowie des gesamten Gesichtes dargestellt: CO 2 -Laser; Er:YAG hot Laser; Er:YAG cold Laser. Dabei kamen profilometrische Messungen, Messung von Hautfunktionsparameter (Elastizität, Feuchtigkeit, Sebumgehalt), Bewertungen von Fotografien und Fragebögen zur Erfassungs des Wirkungsprofils einer Lasertherapie zur Anwendung.

Ablative materials can sustain very high temperatures in which surface thermochemical processes are significant enough to cause surface recession. Existence of moving boundary over a wide range of temperatures, temperature-dependent thermophysical properties of ablators, and no prior knowledge about the location of the moving surface augment the difficulty for predicting the exposed heat flux at the receding surface of ablators. In this paper, the conjugate gradient method is proposed to estimate the unknown surface recession and time-varying net surface heat flux for these kinds of problems. The first order Tikhonov regularization is employed to stabilize the inverse solution. Considering the complicated phenomena that are taking place, it is shown via simulated experiment that unknown quantities can be obtained with reasonable accuracy using this method despite existing noises in the measurement data.

A computational model is developed to study the effects of alumina layer formation on an ablative surface when exposed to high temperature particle laden gas flow. The solidification dynamics i.e., the solid and liquid alumina layer growth rate, and the heat transferred to the ablative surface are investigated. A one-dimensional model is developed taking into consideration the thermal loading, particle loading and the temperature dependence of the thermo-physical properties of alumina. A fully implicit finite volume method is used to solve the coupled set of non-linear heat conduction equations. The solidification interface is tracked using the Lagrangian interpolation technique. The particle mass flux was found to be the major factor affecting the solid layer growth rate. The gas heat flux also has a major effect on the solid growth rate and the heat transferred to the ablative surface, but only for lower particle mass fluxes. On other hand the particle temperature has a linear effect on the solidification dynamics and the heat transferred to the ablative surface for all particle mass fluxes. The heat transferred to the ablative surface is reduced by approximately 39% to 88%, depending on the mass fluxes, due to the formation of the alumina layer. / Graduation date: 2003

The objective of this thesis is to predict shape change due to ablation and to find temperature distribution of the thermal protection system of a supersonic vehicle under aerodynamic heating by using finite element method. A subliming ablative is used as thermal protection material. Required material properties for the ablation analyses are found by using DSC (Differential Scanning Calorimetry) and TGA (Thermogravimetric Analysis) thermal analysis techniques. DSC is a thermal analysis technique that looks at how a material&#039 / s specific heat capacity is changed by temperature and TGA is a technique in which the mass of a substance is monitored as a function of temperature. Moreover, oxyacetylene ablation tests are conducted for the subliming ablative specimens and measured recession values are compared with the analytically calculated values. Maximum difference between experimental results and analytical results is observed as 3% as seen in Table 7. For the finite element analyses, ANSYS Software is used. A numerical algorithm is developed by using programming language APDL (ANSYS Parametric Design Language) and element kill feature of ANSYS is used for simulation of ablation process. To see the effect of mesh size and time step on the solution of analyses, oxyacetylene test results are used. Numerical algorithm is also applied to the blunt-nosed section of a supersonic rocket which is made from subliming ablative material. Ablation analyses are performed for the nose section because nose recession is very important for a rocket to follow the desired trajectory and nose temperature is very important for the avionics in the inner side of the nose. By using the developed algorithm, under aerodynamic heating, shape change and temperature distribution of the nose section at the end of the flight are obtained. Moreover, effects of ablation on the trajectory of the rocket and on the flow around the rocket are examined by Missile DATCOM and CFD (computational fluid dynamics) analysis tools.

In der vorliegenden Arbeit wurde mit einer Vielzahl an objektiven Messverfahren und subjektiven Einschätzungen, die Wirkungen und Nebenwirkungen von drei unterschiedlichen fraktional ablativen Lasersystemen in der Therapie der gealterten und chronisch lichtgeschädigten Haut einzelner Gesichtsareale, sowie des gesamten Gesichtes dargestellt: CO 2 -Laser; Er:YAG hot Laser; Er:YAG cold Laser. Dabei kamen profilometrische Messungen, Messung von Hautfunktionsparameter (Elastizität, Feuchtigkeit, Sebumgehalt), Bewertungen von Fotografien und Fragebögen zur Erfassungs des Wirkungsprofils einer Lasertherapie zur Anwendung.:Inhaltsverzeichnis 1 EINLEITUNG 1 1.1 EINFÜHRUNG IN DIE THEMATIK 1 1.2 Darstellung der Lasersysteme für die Therapie der gealterten Haut 2 1.3 Darstellung von Verfahren zur Evaluation der Therapieergebnisse 6 1.4 Zielstellung 9 1.5 Fragestellungen 9 2. MATERIAL UND METHODEN 10 2.1 Studiendesign und Studienprotokoll 10 2.2 Probanden 11 2.3 Randomisierung 11 2.4 Versicherung und Ethik 11 2.5 Ablauf der Behandlung 12 2.6 Angewandte Lasersysteme 13 2.7 Messgeräte zur Erfassung von Hautveränderungen 15 2.8 Patientenfragebögen 23 2.9 Digitale Fotografien 24 2.10 STATISTIK 24 3 ERGEBNISSE 26 3.1 Hautveränderungen nach 3 Behandlungen gemessen mit PRIMOS 28 3.2 Veränderung der Hautfunktionsparameter nach 3 Behandlungen gemessen mit MPA 5 37 3.3 Auswertung der digitalen Fotografien: Blinded Evaluation 43 3.4 Auswertung der Patientenfragebögen 47 4 DISKUSSION 71 4.1 Evaluation der mit PRIMOS gewonnenen Messergebnisse 71 4.2 Evaluation der mit MPA 5 gewonnenen Messergebnisse 74 4.3 Evaluation subjektiver Behandlungseindrücke mittels Fragebögen 76 4.4 Vergleich der Ergebnisse der digitalen Fotografien mit ausgewählten objektiven Parametern und subjektiven Probandenbeurteilungen 81 4.5 Beantwortung der Fragestellungen 84 4.6 Schlussfolgerungen 85 5 ZUSAMMENFASSUNG DER ARBEIT 86 6 LITERATURVERZEICHNIS 90 7 ANHANG 97

The Space Shuttle Columbia accident and the recent excitement surrounding Discovery's return to space brought excessive media attention to the foam products used on the External Tank (ET). In both cases, videos showed chunks of foam or ablative material falling away from the ET during lift off. This led to several years of investigation and research into the exact cause of the accident and potential solutions to avoid the problem in the future. Several design changes were made prior to the return to flight this year, but the ET still shed foam during lift off. Since the Columbia accident, the loss of foam on ETs has been a significant area of interest for NASA, United Space Alliance, and Lockheed Martin. The Columbia Accident Investigation Board did not evaluate alternative materials but certainly highlighted the need for change. The majority of the research previously concentrated on improving the design and/or the application process of the current materials. Within recent years, some research and testing has been done to determine if a glass microsphere composite foam would be an acceptable alternative, but this work was overcome by the need for immediate change to return the shuttle to flight in time to deliver supplies to the International Space Station. Through a better understanding of the foam products currently used on the ET, other products can be evaluated for future space shuttle flights and potential applications on new space vehicles. The material properties and the required functionality of alternative materials can be compared to the current materials to determine if suitable replacement products exist. This research also lends itself to the development of future space flight and unmanned launch vehicles. In this paper, the feasibility of alternative material for the space shuttle's external tank will be investigated. Research on what products are used on the ET and a set of functional requirements driving the selection of those materials will be presented. The material properties of the current ET foam products will be collected and an evaluation of how those materials' properties meet the functional requirements will be accomplished. Then significant research on polymeric foams and ablative materials will be completed to learn how these various products can be applied in this industry. With this research and analysis, the knowledge gained will be used to select and evaluate the effectiveness of an alternate product and to determine feasibility of a product change with the current ET and the importance of maintaining the shuttle launch schedule. This research will also be used to evaluate the potential application of the alternative product on future platforms. There are several possible outcomes to this research. This research could result in a recommended change to the ET foam material or a perfectly acceptable alternative material that could result in a cost or schedule impact if implemented. It is also possible that there exists no suitable alternative material given the existing functional requirements. In any case, the alternative material could have future applications on new space vehicles. A set of results from the research and analysis will be provided along with a recommendation on a future material for use on space vehicles.

No description available.

O esôfago de Barrett é o principal fator de risco para o adenocarcinoma e resulta da agressão crônica causada pelo refluxo gastroesofágico. A abordagem terapêutica é controversa, e o tratamento cirúrgico, na presença de neoplasia intraepitelial de alto grau, pode estar indicado. A abordagem endoscópica apresenta-se como a alternativa com menor morbimortalidade e resultados favoráveis. Método: Realizou-se revisão sistemática nas bases de informação científica, com seleção de artigos randomizados e controlados, possibilitando metaanálise e avaliação isolada dos resultados das terapias ablativas da metaplasia intestinal. Considerou-se como terapias ablativas a crioterapia, laser, terapia fotodinâmica, eletrocoagulação multipolar, ablação por plasma de argônio e radiofrequência. Resultados: A revisão sistemática da literatura através do PUBMED recuperou os estudos com maior força de evidência e grau de recomendação disponíveis referentes ao tratamento ablativo do esôfago de Barrett. Nenhuma outra base de dados pesquisada adicionou outros artigos. Os artigos selecionados são estudos randomizados e controlados, classificados como A ou B pela tabela de Oxford. A terapia fotodinâmica apresenta no estudo meta-analítico aumento do risco de falha terapêutica em relação à ablação por plasma de argônio, NNH = -7. Os efeitos colaterais considerados foram dor torácica e estenose, com aumento do risco de dor torácica quando a ablação é realizada por terapia fotodinâmica e números semelhantes de estenoses para as duas terapias. A ablação do esôfago de Barrett por eletrocoagulação multipolar ou plasma de argônio apresenta risco de falhas terapêuticas semelhantes, assim como do efeito colateral de dor torácica na meta-análise. A terapia fotodinâmica associada ao inibidor da bomba de prótons apresenta benefício, em meta-análise, para a ablação do esôfago de Barrett em relação ao uso isolado do inibidor, NNT = 2. Dor torácica, estenose e fotossensibilidade estão associadas à intervenção endoscópica e, desta forma, a terapia fotodinâmica está associada ao aumento do risco com NNH entre - 2 e -3. Não houve aumento do risco de falha terapêutica entre a ablação do esôfago de Barrett por plasma de argônio e inibidor da bomba de prótons versus uso isolado do inibidor da bomba de prótons, em estudo isolado. A radiofrequência associada ao inibidor da bomba de prótons apresenta-se como método eficaz na redução do risco de falha terapêutica, NNT = 1. Conclusões: Não há estudos que demonstrem benefício na indicação da crioterapia ou laser para a abordagem endoscópica do esôfago de Barrett. A ablação por plasma de argônio apresenta eficácia superior à terapia fotodinâmica e a ablação por plasma de argônio e eletrocoagulação multipolar apresentam resultados efetivos e semelhantes. A terapia fotodinâmica apresenta menor número de falhas terapêuticas em relação ao uso isolado do inibidor da bomba de prótons. Não há dados suficientes para demonstrar a eficácia da ablação por plasma de argônio em relação ao uso isolado do inibidor da bomba de prótons. A radiofrequência é a abordagem mais recente e requer estudos comparativos para sua indicação. Os tratamentos endoscópicos ablativos estão associados a um maior risco de eventos colaterais como dor torácica, estenose e fotossensibilidade em relação ao tratamento clínico isolado, embora tais eventos não sejam graves ou limitantes / Barrett´s esophagus is the main risk factor for adenocarcinoma and it results from the chronic aggression produced by gastroesophageal reflux. Its therapeutic approach is controversial and surgical treatment in the presence of high-grade intraepithelial neoplasia may be indicated. Endoscopic approach is an alternative with lower mortality and morbidity rates and favorable results. Methods: A systematic review of scientific databases was conducted and articles of randomized, controlled studies were selected, enabling meta-analysis and the isolated evaluation of the results concerning ablative therapies of intestinal metaplasia. Cryotherapy, laser therapy, photodynamic therapy, multipolar electrocoagulation, and ablation through argon plasma coagulation and radiofrequency were considered ablation therapies. Results: The systematic review through PUBMED retrieved results with higher strength of evidence and available recommendation level regarding the ablative therapy of Barrett´s esophagus. No other database in the research yielded additional articles. The selected articles are randomized, controlled studies classified as A or B according to the Oxford table. Photodynamic therapy was found to present an increase in treatment failure compared to argon plasma coagulation in the meta-analysis, NNH = -7. Chest pain and stenosis were considered side effects with higher risk of chest pain whenever ablation is conducted through photodynamic therapy and similar figures of stenoses for both therapies. Ablation of Barrett´s esophagus with multipolar electrocoagulation or argon plasma was found to have similar risk of treatment failure, as well as the side effect of chest pain in the meta-analysis. Photodynamic therapy associated with proton pump inhibitor is beneficial, in the meta-analysis, for the ablation of Barrett´s esophagus regarding the isolated use of the inhibitor, NNT = 2. Chest pain, stenoses and photosensitivity were found to be associated with the endoscopic intervention and, therefore, photodynamic therapy was found to be associated with higher risk with NNH ranging between -2 and -3. No increase of treatment failure risk between Barrett´s esophagus ablation with argon plasma and proton pump inhibitor versus the isolated use of proton pump inhibitor was verified, in isolated study. Radiofrequency associated with proton pump inhibitor is an efficient method to reduce the risk of treatment failure, NNT = 1. Conclusions: There are no studies demonstrating the benefit of indicating cryotherapy or laser therapy for the endoscopic approach of Barrett´s esophagus. Ablation with argon plasma coagulation was found to have superior efficacy compared to photodynamic therapy and the ablation through argon plasma coagulation and multipolar electrocoagulation was found to present effective and similar results. Photodynamic therapy was found to have lower occurrences of treatment failure compared to the isolated use of proton pump inhibitor. No sufficient data were found to demonstrate the efficacy of ablation with argon plasma compared to the isolated use of proton pump inhibitor. Radiofrequency is the most recent approach and requires comparative studies in order to be indicated. Ablative endoscopic therapies are associated with higher risk of side effects, for instance chest pain, stenoses and photosensitivity compared to clinical treatment alone, although such events are neither severe nor limiting

The advancement of each component of aerospace vehicles is necessary as the continual demand for more aggressive missions are created. Improvements in propulsion and guidance system electronics are invaluable; however without material development to protect the vehicle from its environment those advances will not have a practical application. Thermal protection systems (TPS) are required in both external applications; for example on reentry vehicles, as well as in internal applications; to protect the casing of rockets and missiles. This dissertation focuses on a specific type of internal solid rocket motor TPS, ablatives. Ablatives have been used for decades on aerospace vehicles. To protect the motor from the hostile environment, these materials pyrolyze and char. Both of these mechanisms produce a boundary between the combustion gases and the motor as well as release the heat that the decomposed material has absorbed. These sacrificial materials are intended to protect the casing that it is attached to. With the development of polymer nanocomposites (PNCs) in the last couple of decades, it is of interest to see how these two fields can merge. Three different nanomaterials (carbon nanofibers, multiwall carbon nanotubes, and nanoclays) are examined to observe how each behaves in environments that simulate the motor firing conditions. These nanomaterials are individually added to a thermoplastic polyurethane elastomer (TPU) at different loadings, creating three distinct families of polymer nanocomposites. To describe a materials ablative performance, a number of material properties must be individually studied; such as thermal, density, porosity, char strength, and rheology. Different experiments are conducted to isolate specific ablative processes in order to identify how each nanomaterial affects the ablative performance. This dissertation first describes each material and the ablative processes which are characterized by each experiment. Then basic material properties of each family of materials are described. Degradation and flammability experiments then describe the degassing processes. Studies of the material char are then performed after full blown rocket experiments are done. These tests have shown that of the three nanomaterials, nanoclay enhances the TPU ablative performance the most while the CNF provides the least enhancement. / text