Numerical simulation of the upward propagation of a flame in a vertical tube filled with a very lean mixture.

Upwardpropagation of a premixed flame in averticaltubefilled with a very leanmixture is simulated numerically using a single irreversible Arrhenius reaction model with infinitely high activation energy. In the absence of heat losses and preferential diffusion effects, a curved flame with stationary shape and velocity close to those of an open bubble ascending in the same tube is found for values of the fuel mass fraction above a certain minimum that increases with the radius of the tube, while the numerical computations cease to converge to a stationary solution below this minimum mass fraction. The vortical flow of the gas behind the flame and in its transport region is described for tubes of different radii. It is argued that this flow may become unstable when the fuel mass fraction is decreased, and that this instability, together with the flame stretch due to the strong curvature of the flame tip in narrow tubes, may be responsible for the minimum fuel mass fraction. Radiation losses and a Lewis number of the fuel slightly above unity decrease the final combustion temperature at the flame tip and increase the minimum fuel mass fraction, while a Lewis number slightly below unity has the opposite effect.

Desarrollo de nuevos tratamientos térmicos para aleaciones avanzadas de interés aeroespacial

La corrosión bajo tensiones (SCC) es un problema de gran importancia en las aleaciones de aluminio de máxima resistencia (serie Al-Zn-Mg-Cu). La utilización de tratamientos térmicos sobremadurados, en particular el T73, ha conseguido prácticamente eliminar la susceptibilidad a corrosión bajo tensiones en dichas aleaciones pero a costa de reducir su resistencia mecánica. Desde entonces se ha tratado de optimizar simultáneamente ambos comportamientos, encontrándose para ello diversos inconvenientes entre los que destacan: la dificultad de medir experimentalmente el crecimiento de grieta por SCC, y el desconocimiento de las causas y el mecanismo por el cual se produce la SCC. Los objetivos de esta Tesis son mejorar el sistema de medición de grietas y profundizar en el conocimiento de la SCC, con el fin de obtener tratamientos térmicos que aúnen un óptimo comportamiento tanto en SCC como mecánico en las aleaciones de aluminio de máxima resistencia utilizadas en aeronáutica. Para conseguir los objetivos anteriormente descritos se han realizado unos cuarenta tratamientos térmicos diferentes, de los cuales la gran mayoría son nuevos, para profundizar en el conocimiento de la influencia de la microestructura (fundamentalmente, de los precipitados coherentes) en el comportamiento de las aleaciones Al-Zn-Mg-Cu, y estudiar la viabilidad de nuevos tratamientos apoyados en el conocimiento adquirido. Con el fin de obtener unos resultados aplicables a productos o semiproductos de aplicación aeronáutica, los tratamientos térmicos se han realizado a trozos grandes de una plancha de 30 mm de espesor de la aleación de aluminio 7475, muy utilizada en las estructuras aeronáuticas. Asimismo con el objeto de conseguir una mayor fiabilidad de los resultados obtenidos se han utilizado, normalmente, tres probetas de cada tratamiento para los diferentes ensayos realizados. Para la caracterización de dichos tratamientos se han utilizado diversas técnicas: medida de dureza y conductividad eléctrica, ensayos de tracción, calorimetría diferencial de barrido (DSC), metalografía, fractografía, microscopia electrónica de transmisión (MET) y de barrido (MEB), y ensayos de crecimiento de grieta en probeta DCB, que a su vez han permitido hacer una estimación del comportamiento en tenacidad del material. Las principales conclusiones del estudio realizado se pueden resumir en las siguientes: Se han diseñado y desarrollado nuevos métodos de medición de grieta basados en el empleo de la técnica de ultrasonidos, que permiten medir el crecimiento de grieta por corrosión bajo tensiones con la precisión y fiabilidad necesarias para valorar adecuadamente la susceptibilidad a corrosión bajo tensiones. La mejora de medida de la posición del frente de grieta ha dado lugar, entre otras cosas, a la definición de un nuevo ensayo a iniciación en probetas preagrietadas. Asimismo, se ha deducido una nueva ecuación que permite calcular el factor de intensidad de tensiones existente en punta de grieta en probetas DCB teniendo en cuenta la influencia de la desviación del plano de crecimiento de la grieta del plano medio de la probeta. Este aspecto ha sido determinante para poder explicar los resultados experimentales obtenidos ya que el crecimiento de la grieta por un plano paralelo al plano medio de la probeta DCB pero alejado de él reduce notablemente el factor de intensidades de tensiones que actúa en punta de grieta y modifica las condiciones reales del ensayo. Por otro lado, se han identificado los diferentes constituyentes de la microestructura de precipitación de todos los tratamientos térmicos estudiados y, en especial, se ha conseguido constatar (mediante MET y DSC) la existencia de zonas de Guinier-Preston del tipo GP(II) en la microestructura de numerosos tratamientos térmicos (no descrita en la bibliografía para las aleaciones del tipo de la estudiada) lo que ha permitido establecer una nueva interpretación de la evolución de la microestructura en los diferentes tratamientos. Al hilo de lo anterior, se han definido nuevas secuencias de precipitación para este tipo de aleaciones, que han permitido entender mejor la constitución de la microestructura y su relación con las propiedades en los diferentes tratamientos térmicos estudiados. De igual manera, se ha explicado el papel de los diferentes microconstituyentes en diversas propiedades mecánicas (propiedades a tracción, dureza y tenacidad KIa); en particular, el estudio realizado de la relación de la microestructura con la tenacidad KIa es inédito. Por otra parte, se ha correlacionado el comportamiento en corrosión bajo tensiones, tanto en la etapa de incubación de grieta como en la de propagación, con las características medidas de los diferentes constituyentes microestructurales de los tratamientos térmicos ensayados, tanto de interior como de límite de grano, habiéndose obtenido que la microestructura de interior de grano tiene una mayor influencia en el comportamiento en corrosión bajo tensiones que la de límite de grano. De forma especial, se ha establecido la importancia capital, y muy negativa, de la presencia en la microestructura de zonas de Guinier-Preston en el crecimiento de la grieta por corrosión bajo tensiones. Finalmente, como consecuencia de todo lo anterior, se ha propuesto un nuevo mecanismo por el que se produce la corrosión bajo tensiones en este tipo de aleaciones de aluminio, y que de forma muy resumida se puede concretar lo siguiente: la acumulación de hidrógeno (formado, básicamente, por un proceso corrosivo de disolución anódica) delante de la zonas GP (en especial, de las zonas GP(I)) próximas a la zona libre de precipitados que se desarrolla alrededor del límite de grano provoca enfragilización local y causa el rápido crecimiento de grieta característico de algunos tratamientos térmicos de este tipo de aleaciones. ABSTRACT The stress corrosion cracking (SCC) is a major problem in the aluminum alloys of high resistance (series Al-Zn-Mg-Cu). The use of overaged heat treatments, particularly T73 has achieved virtually eliminate the susceptibility to stress corrosion cracking in such alloys but at the expense of reducing its mechanical strength. Since then we have tried to simultaneously optimize both behaviors, several drawbacks found for it among them: the difficulty of measuring experimentally the SCC crack growth, and ignorance of the causes and the mechanism by which SCC occurs. The objectives of this thesis are to improve the measurement system of cracks and deeper understanding of the SCC, in order to obtain heat treatments that combine optimum performance in both SCC and maximum mechanical strength in aluminum alloys used in aerospace To achieve the above objectives have been made about forty different heat treatments, of which the vast majority are new, to deepen the understanding of the influence of microstructure (mainly of coherent precipitates) in the behavior of the alloys Al -Zn-Mg-Cu, and study the feasibility of new treatments supported by the knowledge gained. To obtain results for products or semi-finished aircraft application, heat treatments were performed at a large pieces plate 30 mm thick aluminum alloy 7475, widely used in aeronautical structures. Also in order to achieve greater reliability of the results obtained have been used, normally, three specimens of each treatment for various tests. For the characterization of these treatments have been used several techniques: measurement of hardness and electrical conductivity, tensile testing, differential scanning calorimetry (DSC), metallography, fractography, transmission (TEM) and scanning (SEM) electron microscopy, and crack growth tests on DCB specimen, which in turn have allowed to estimate the behavior of the material in fracture toughness. The main conclusions of the study can be summarized as follows: We have designed and developed new methods for measuring crack based on the use of the ultrasound technique, for measuring the growth of stress corrosion cracks with the accuracy and reliability needed to adequately assess the susceptibility to stress corrosion. Improved position measurement of the crack front has resulted, among other things, the definition of a new initiation essay in pre cracked specimens. Also, it has been inferred a new equation to calculate the stress intensity factor in crack tip existing in DCB specimens considering the influence of the deviation of the plane of the crack growth of the medium plane of the specimen. This has been crucial to explain the experimental results obtained since the crack growth by a plane parallel to the medium plane of the DCB specimen but away from it greatly reduces the stress intensity factor acting on the crack tip and modifies the actual conditions of the essay. Furthermore, we have identified the various constituents of the precipitation microstructure of all heat treatments studied and, in particular note has been achieved (by TEM and DSC) the existence of the type GP (II) of Guinier-Preston zones in the microstructure of several heat treatments (not described in the literature for alloys of the type studied) making it possible to establish a new interpretation of the evolution of the microstructure in the different treatments. In line with the above, we have defined new precipitation sequences for these alloys, which have allowed a better understanding of the formation of the microstructure in relation to the properties of different heat treatments studied. Similarly, explained the role of different microconstituents in various mechanical properties (tensile properties, hardness and toughness KIa), in particular, the study of the relationship between the tenacity KIa microstructure is unpublished. Moreover, has been correlated to the stress corrosion behavior, both in the incubation step as the crack propagation, with the measured characteristics of the various microstructural constituents heat treatments tested, both interior and boundary grain, having obtained the internal microstructure of grain has a greater influence on the stress corrosion cracking behavior in the grain boundary. In a special way, has established the importance, and very negative, the presence in the microstructure of Guinier-Preston zones in crack growth by stress corrosion. Finally, following the above, we have proposed a new mechanism by which stress corrosion cracking occurs in this type of aluminum alloy, and, very briefly, one can specify the following: the accumulation of hydrogen (formed basically by a corrosive process of anodic dissolution) in front of the GP zones (especially the GP (I) zones) near the precipitates free zone that develops around grain boundary causes local embrittlement which characterizes rapid crack growth of some heat treatments such alloys.

Geometric diagnostics of complex patterns: Spiral defect chaos

Motivated by the observation of spiral patterns in a wide range of physical, chemical, and biological systems, we present an automated approach that aims at characterizing quantitatively spiral-like elements in complex stripelike patterns. The approach provides the location of the spiral tip and the size of the spiral arms in terms of their arc length and their winding number. In addition, it yields the number of pattern components (Betti number of order 1), as well as their size and certain aspects of their shape. We apply the method to spiral defect chaos in thermally driven Rayleigh- Bénard convection and find that the arc length of spirals decreases monotonically with decreasing Prandtl number of the fluid and increasing heating. By contrast, the winding number of the spirals is nonmonotonic in the heating. The distribution function for the number of spirals is significantly narrower than a Poisson distribution. The distribution function for the winding number shows approximately an exponential decay. It depends only weakly on the heating, but strongly on the Prandtl number. Large spirals arise only for larger Prandtl numbers. In this regime the joint distribution for the spiral length and the winding number exhibits a three-peak structure, indicating the dominance of Archimedean spirals of opposite sign and relatively straight sections. For small Prandtl numbers the distribution function reveals a large number of small compact pattern components.

Modelos predictivos y preventivos para una Administración Pública sostenible

Con la finalidad de ayudar a la creación y desarrollo de modelos de predicción y simulación que permitan al ciudadano/administraciones publicas gestionar el consumo energético de forma más eficiente y respetuosa con el medio ambiente, se ha implementado un sistema de gestión de datos de indicadores energéticos. En 2007 la UE creó una directiva conocida como "20/20/20" en la que la Unión Europea se compromete a ahorrar un 20% del consumo anual de energía primaria desde esa fecha a 2020. En 2009 la Comisión Europea ha llegado a la conclusión de que con las medidas propuestas en dicha directiva no se podría alcanzar el objetivo de reducción del 20% del consumo energético previsto para el 2020, quedándose en menos de la mitad. Para dar un nuevo impulso a la eficiencia energética se redacta una propuesta de directiva: 2011/0172(COD). En esta directiva se obliga a los estados miembros a potenciar y ampliar la información estadística agregada sobre sus clientes finales (los perfiles de carga, la segmentación de los clientes, su ubicación geográfica, etc ). La Unión Europea plantea que incrementar el volumen y la accesibilidad de los datos de consumo energético, ayudará de forma significativa a alcanzar los objetivos. En este marco, parece lógico afirmar que un banco de datos de indicadores energéticos universalmente accesible puede contribuir de un modo efectivo al aumento de la eficiencia energética. Como aplicativo de este PFC se ha desarrollado una aplicación que permite la definición y almacenamiento de indicadores energéticos, en la que los diferentes sistemas, propietarios o abiertos, pueden volcar y extraer datos de una forma poco costosa. Se ha pretendido realizar una aplicación lo más abierta posible, tanto desde el punto de vista de la funcionalidad, permitiendo la definición del propio indicador a través del sistema, como desde el punto de vista de la implementación, usando únicamente código abierto para el desarrollo de la misma. ABSTRACT. In order to assist in the creation and development of forecasting and simulation models that enable citizens / public authorities manage energy consumption more efficient and environmentally friendly, we have implemented a data management system of energy indicators. In 2007 the EU created a policy known as " 20/20/20 " in which the European Union is committed to saving 20 % of the annual primary energy consumption from that date to 2020 . In 2009 the European Commission has concluded that the measures proposed in the directive could not achieve the goal of 20% reduction in energy consumption expected for 2020 , staying in less than half. To give new impetus to energy efficiency is drawn up a draft directive : 2011/0172 ( COD ) . This directive obliges member states to strengthen and expand aggregate statistical information on their final customers ( load profiles , customer segmentation , geographic location, etc. ) . The European Union argues that increasing the volume and accessibility ofenergy data , will significantly help to achieve the objectives . In this context , it seems logical to say that a database of universally accessible energy indicators can contribute in an effective way to increase energy efficiency. As of this PFC application has developed an application that allows the definition and storage of energy indicators , in which different systems, proprietary or open, can tip and extract data from an inexpensive way. We have tried to make an application as open as possible , both from the point of view of functionality , allowing the definition of the indicator itself through the system , and from the point of view of implementation, using only open source development thereof.

Método computacional para la aceleración de análisis paramétricos de modificaciones locales en estructuras complejas sometidas a cargas dinámicas

Dentro del análisis y diseño estructural surgen frecuentemente problemas de ingeniería donde se requiere el análisis dinámico de grandes modelos de elementos finitos que llegan a millones de grados de libertad y emplean volúmenes de datos de gran tamaño. La complejidad y dimensión de los análisis se dispara cuando se requiere realizar análisis paramétricos. Este problema se ha abordado tradicionalmente desde diversas perspectivas: en primer lugar, aumentando la capacidad tanto de cálculo como de memoria de los sistemas informáticos empleados en los análisis. En segundo lugar, se pueden simplificar los análisis paramétricos reduciendo su número o detalle y por último se puede recurrir a métodos complementarios a los elementos .nitos para la reducción de sus variables y la simplificación de su ejecución manteniendo los resultados obtenidos próximos al comportamiento real de la estructura. Se propone el empleo de un método de reducción que encaja en la tercera de las opciones y consiste en un análisis simplificado que proporciona una solución para la respuesta dinámica de una estructura en el subespacio modal complejo empleando un volumen de datos muy reducido. De este modo se pueden realizar análisis paramétricos variando múltiples parámetros, para obtener una solución muy aproximada al objetivo buscado. Se propone no solo la variación de propiedades locales de masa, rigidez y amortiguamiento sino la adición de grados de libertad a la estructura original para el cálculo de la respuesta tanto permanente como transitoria. Adicionalmente, su facilidad de implementación permite un control exhaustivo sobre las variables del problema y la implementación de mejoras como diferentes formas de obtención de los autovalores o la eliminación de las limitaciones de amortiguamiento en la estructura original. El objetivo del método se puede considerar similar a los que se obtienen al aplicar el método de Guyan u otras técnicas de reducción de modelos empleados en dinámica estructural. Sin embargo, aunque el método permite ser empleado en conjunción con otros para obtener las ventajas de ambos, el presente procedimiento no realiza la condensación del sistema de ecuaciones, sino que emplea la información del sistema de ecuaciones completa estudiando tan solo la respuesta en las variables apropiadas de los puntos de interés para el analista. Dicho interés puede surgir de la necesidad de obtener la respuesta de las grandes estructuras en unos puntos determinados o de la necesidad de modificar la estructura en zonas determinadas para cambiar su comportamiento (respuesta en aceleraciones, velocidades o desplazamientos) ante cargas dinámicas. Por lo tanto, el procedimiento está particularmente indicado para la selección del valor óptimo de varios parámetros en grandes estructuras (del orden de cientos de miles de modos) como pueden ser la localización de elementos introducidos, rigideces, masas o valores de amortiguamientos viscosos en estudios previos en los que diversas soluciones son planteadas y optimizadas, y que en el caso de grandes estructuras, pueden conllevar un número de simulaciones extremadamente elevado para alcanzar la solución óptima. Tras plantear las herramientas necesarias y desarrollar el procedimiento, se propone un caso de estudio para su aplicación al modelo de elementos .nitos del UAV MILANO desarrollado por el Instituto Nacional de Técnica Aeroespacial. A dicha estructura se le imponen ciertos requisitos al incorporar un equipo en aceleraciones en punta de ala izquierda y desplazamientos en punta de ala derecha en presencia de la sustentación producida por una ráfaga continua de viento de forma sinusoidal. La modificación propuesta consiste en la adición de un equipo en la punta de ala izquierda, bien mediante un anclaje rígido, bien unido mediante un sistema de reducción de la respuesta dinámica con propiedades de masa, rigidez y amortiguamiento variables. El estudio de los resultados obtenidos permite determinar la optimización de los parámetros del sistema de atenuación por medio de múltiples análisis dinámicos de forma que se cumplan de la mejor forma posible los requisitos impuestos con la modificación. Se comparan los resultados con los obtenidos mediante el uso de un programa comercial de análisis por el método de los elementos .nitos lográndose soluciones muy aproximadas entre el modelo completo y el reducido. La influencia de diversos factores como son el amortiguamiento modal de la estructura original, el número de modos retenidos en la truncatura o la precisión proporcionada por el barrido en frecuencia se analiza en detalle para, por último, señalar la eficiencia en términos de tiempo y volumen de datos de computación que ofrece el método propuesto en comparación con otras aproximaciones. Por lo tanto, puede concluirse que el método propuesto se considera una opción útil y eficiente para el análisis paramétrico de modificaciones locales en grandes estructuras. ABSTRACT When developing structural design and analysis some projects require dynamic analysis of large finite element models with millions of degrees of freedom which use large size data .les. The analysis complexity and size grow if a parametric analysis is required. This problem has been approached traditionally in several ways: one way is increasing the power and the storage capacity of computer systems involved in the analysis. Other obvious way is reducing the total amount of analyses and their details. Finally, complementary methods to finite element analysis can also be employed in order to limit the number of variables and to reduce the execution time keeping the results as close as possible to the actual behaviour of the structure. Following this third option, we propose a model reduction method that is based in a simplified analysis that supplies a solution for the dynamic response of the structure in the complex modal space using few data. Thereby, parametric analysis can be done varying multiple parameters so as to obtain a solution which complies with the desired objetive. We propose not only mass, stiffness and damping variations, but also addition of degrees of freedom to the original structure in order to calculate the transient and steady-state response. Additionally, the simple implementation of the procedure allows an in-depth control of the problem variables. Furthermore, improvements such as different ways to obtain eigenvectors or to remove damping limitations of the original structure are also possible. The purpose of the procedure is similar to that of using the Guyan or similar model order reduction techniques. However, in our method we do not perform a true model order reduction in the traditional sense. Furthermore, additional gains, which we do not explore herein, can be obtained through the combination of this method with traditional model-order reduction procedures. In our procedure we use the information of the whole system of equations is used but only those nodes of interest to the analyst are processed. That interest comes from the need to obtain the response of the structure at specific locations or from the need to modify the structure at some suitable positions in order to change its behaviour (acceleration, velocity or displacement response) under dynamic loads. Therefore, the procedure is particularly suitable for parametric optimization in large structures with >100000 normal modes such as position of new elements, stiffness, mass and viscous dampings in previous studies where different solutions are devised and optimized, and in the case of large structures, can carry an extremely high number of simulations to get the optimum solution. After the introduction of the required tools and the development of the procedure, a study case is proposed with use the finite element model (FEM) of the MILANO UAV developed by Instituto Nacional de Técnica Aeroespacial. Due to an equipment addition, certain acceleration and displacement requirements on left wing tip and right wing tip, respectively, are imposed. The structure is under a continuous sinusoidal wind gust which produces lift. The proposed modification consists of the addition of an equipment in left wing tip clamped through a rigid attachment or through a dynamic response reduction system with variable properties of mass, stiffness and damping. The analysis of the obtained results allows us to determine the optimized parametric by means of multiple dynamic analyses in a way such that the imposed requirements have been accomplished in the best possible way. The results achieved are compared with results from a commercial finite element analysis software, showing a good correlation. Influence of several factors such as the modal damping of the original structure, the number of modes kept in the modal truncation or the precission given by the frequency sweep is analyzed. Finally, the efficiency of the proposed method is addressed in tems of computational time and data size compared with other approaches. From the analyses performed, we can conclude that the proposed method is a useful and efficient option to perform parametric analysis of possible local modifications in large structures.

An Experimental and Numerical Study of Ballistic Impacts on a Turbine Casing Material at Varying Temperatures

An experimental and numerical study of ballistic impacts on steel plates at various temperatures (700ºC, 400ºC and room temperature) has been carried out. The motivation for this work is the blade‐off event that may occur inside a jet engine turbine. However, as a first attempt to understand this complex loading process, a somewhat simpler approach is carried out in the present work. The material used in this study is the FV535 martensitic stainless steel, which is one of the most commonly used materials for turbine casings. Based on material test data, a Modified Johnson‐Cook (MJC) model was calibrated for numerical simulations using the LS‐DYNA explicit finite element code (see Figure 1). To check the mesh size sensitivity, 2D axisymmetric finite element models with three different mesh sizes and configurations were used for the various temperatures. Two fixed meshes with 64 and 128 elements over the 2mm thick plate and one mesh with 32 elements over the thickness with adaptive remeshing were used in the simulations. The formation of adiabatic shear bands in the perforation process has been found critical in order to achieve good results. Adiabatic shear bands are formed by the temperature rise due to the accumulation of plastic strain during impact (see Figure 2). The influence of the thermal softening in the plastic model has hence been analyzed for the room temperature impact tests, where the temperature gradient is highest

Distribution of indole-3-acetic acid in Petunia hybrida shoot tip cuttings and relationship between auxin transport, carbohydrate metabolism and adventitious root formation.

To determine the contribution of polar auxin transport (PAT) to auxin accumulation and to adventitious root (AR) formation in the stem base of Petunia hybrida shoot tip cuttings, the level of indole-3-acetic acid (IAA) was monitored in non-treated cuttings and cuttings treated with the auxin transport blocker naphthylphthalamic acid (NPA) and was complemented with precise anatomical studies. The temporal course of carbohydrates, amino acids and activities of controlling enzymes was also investigated. Analysis of initial spatial IAA distribution in the cuttings revealed that approximately 40 and 10% of the total IAA pool was present in the leaves and the stem base as rooting zone, respectively. A negative correlation existed between leaf size and IAA concentration. After excision of cuttings, IAA showed an early increase in the stem base with two peaks at 2 and 24h post excision and, thereafter, a decline to low levels. This was mirrored by the expression pattern of the auxin-responsive GH3 gene. NPA treatment completely suppressed the 24-h peak of IAA and severely inhibited root formation. It also reduced activities of cell wall and vacuolar invertases in the early phase of AR formation and inhibited the rise of activities of glucose-6-phosphate dehydrogenase and phosphofructokinase during later stages. We propose a model in which spontaneous AR formation in Petunia cuttings is dependent on PAT and on the resulting 24-h peak of IAA in the rooting zone, where it induces early cellular events and also stimulates sink establishment. Subsequent root development stimulates glycolysis and the pentosephosphate pathway

Uso de DES y RANS no estacionario para la simulación del flujo alrededor de una carena Wigley - Use of Unsteady RANS and DES to simulate flows around a Wigley Hull)

Computer Fluid Dynamics tools have already become a valuable instrument for Naval Architects during the ship design process, thanks to their accuracy and the available computer power. Unfortunately, the development of RANSE codes, generally used when viscous effects play a major role in the flow, has not reached a mature stage, being the accuracy of the turbulence models and the free surface representation the most important sources of uncertainty. Another level of uncertainty is added when the simulations are carried out for unsteady flows, as those generally studied in seakeeping and maneuvering analysis and URANS equations solvers are used. Present work shows the applicability and the benefits derived from the use of new approaches for the turbulence modeling (Detached Eddy Simulation) and the free surface representation (Level Set) on the URANS equations solver CFDSHIP-Iowa. Compared to URANS, DES is expected to predict much broader frequency contents and behave better in flows where boundary layer separation plays a major role. Level Set methods are able to capture very complex free surface geometries, including breaking and overturning waves. The performance of these improvements is tested in set of fairly complex flows, generated by a Wigley hull at pure drift motion, with drift angle ranging from 10 to 60 degrees and at several Froude numbers to study the impact of its variation. Quantitative verification and validation are performed with the obtained results to guarantee their accuracy. The results show the capability of the CFDSHIP-Iowa code to carry out time-accurate simulations of complex flows of extreme unsteady ship maneuvers. The Level Set method is able to capture very complex geometries of the free surface and the use of DES in unsteady simulations highly improves the results obtained. Vortical structures and instabilities as a function of the drift angle and Fr are qualitatively identified. Overall analysis of the flow pattern shows a strong correlation between the vortical structures and free surface wave pattern. Karman-like vortex shedding is identified and the scaled St agrees well with the universal St value. Tip vortices are identified and the associated helical instabilities are analyzed. St using the hull length decreases with the increase of the distance along the vortex core (x), which is similar to results from other simulations. However, St scaled using distance along the vortex cores shows strong oscillations compared to almost constants for those previous simulations. The difference may be caused by the effect of the free-surface, grid resolution, and interaction between the tip vortex and other vortical structures, which needs further investigations. This study is exploratory in the sense that finer grids are desirable and experimental data is lacking for large α, especially for the local flow. More recently, high performance computational capability of CFDSHIP-Iowa V4 has been improved such that large scale computations are possible. DES for DTMB 5415 with bilge keels at α = 20º were conducted using three grids with 10M, 48M and 250M points. DES analysis for flows around KVLCC2 at α = 30º is analyzed using a 13M grid and compared with the results of DES on the 1.6M grid by. Both studies are consistent with what was concluded on grid resolution herein since dominant frequencies for shear-layer, Karman-like, horse-shoe and helical instabilities only show marginal variation on grid refinement. The penalties of using coarse grids are smaller frequency amplitude and less resolved TKE. Therefore finer grids should be used to improve V&V for resolving most of the active turbulent scales for all different Fr and α, which hopefully can be compared with additional EFD data for large α when it becomes available.

Molecular analysis of endo-β-mannanase genes upon seed imbibition suggest a cross-talk between radicle and micropylar endosperm during germination of Arabidopsis thaliana.

The endo-β-mannanase (MAN) family is represented in the Arabidopsis genome by eight members, all with canonical signal peptides and only half of them being expressed in germinating seeds. The transcripts of these genes were localized in the radicle and micropylar endosperm (ME) before radicle protrusion and this expression disappears as soon as the endosperm is broken by the emerging radicle tip. However, only three of these MAN genes, AtMAN5, AtMAN7 and especially AtMAN6 influence the germination time (t50) as assessed by the analysis of the corresponding knock-out lines. The data suggest a possible interaction between embryo and ME regarding the role of MAN during the Arabidopsis germination process.

Curvature and velocity of methane-air Bunsen flame tips.

PIV and photographic recording are used to measure the velocity of the fresh gas and the shape of the reaction layer in a region around the tip of a methane-air Bunsen flame attached to a cylindrical burner. The results compare well with numerical simulations carried out with an infinite activation energy reaction model. The experimental and numerical results confirm that the well-known linear relation between flame velocity and flame stretch derived from asymptotic theory for weakly curved and strained flames is valid for small and moderate values of the flame stretch if the modified definition of stretch introduced by Echekki and Mungal (Proc Combust Inst 23:455–461, 1990) and Poinsot et al. (Combust Sci Technol 81:45–73, 1992) is used. However, the relation between flame velocity and modified stretch ceases to be linear and approaches a square root law for large values of the stretch, when the curvature of the flame tip becomes large compared to the inverse of the thickness of a planar flame.

Curvature and velocity of methane-air Bunsen flame tips

PIV and photographic recording are used to measure the velocity of the fresh gas and the shape of the reaction layer in a region around the tip of a methane- air Bunsen flame attached to a cylindrical burner. The results compare well with numerical simulations carried out with an infinite activation energy reaction model. The experimental and numerical results confirm that the well-known linear relation between flame velocity and flame stretch derived from asymptotic theory for weakly curved and strained flames is valid for small and moderate values of the flame stretch if the modified definition of stretch introduced by Echekki and Mungal (Proc Combust Inst 23:455–461,1990) and Poinsot et al. (Combust Sci Technol 81:45–73,1992) is used. However, the relation between flame velocity and modified stretch ceases to be linear and approaches a square root law for large values of the stretch, when the curvature of the flame tip becomes large compared to the inverse of the thickness of a planar flame

Flow and fracture behaviour of FV535 steel at different triaxialities, strain rates and temperatures

The new generation jet engines operate at highly demanding working conditions. Such conditions need very precise design which implies an exhaustive study of the engine materials and behaviour in their extreme working conditions. With this purpose, this work intends to describe a numerically-based calibration of the widely-used Johnson–Cook fracture model, as well as its validation through high temperature ballistic impact tests. To do so, a widely-used turbine casing material is studied. This material is the Firth Vickers 535 martensitic stainless steel. Quasi-static tensile tests at various temperatures in a universal testing machine, as well as dynamic tests in a Split Hopkinson Pressure Bar, are carried out at different triaxialities. Using ABAQUS/Standard and LS-DYNA numerical codes, experimental data are matched. This method allows the researcher to obtain critical data of equivalent plastic strain and triaxility, which allows for more precise calibration of the Johnson–Cook fracture model. Such enhancement allows study of the fracture behaviour of the material across its usage temperature range.

Intraply fracture of fiber-reinforced composites: microscopic mechanisms and modeling

The fracture behavior parallel to the fibers of an E-glass/epoxy unidirectional laminate was studied by means of three-point tests on notched beams. Selected tests were carried out within a scanning electron microscope to ascertain the damage and fracture micromechanisms upon loading. The mechanical behavior of the notched beam was simulated within the framework of the embedded cell model, in which the actual composite microstructure was resolved in front of the notch tip. In addition, matrix and interface properties were independently measured in situ using a nanoindentor. The numerical simulations very accurately predicted the macroscopic response of the composite as well as the damage development and crack growth in front of the notch tip, demonstrating the ability of the embedded cell approach to simulate the fracture behavior of heterogeneous materials. Finally, this methodology was exploited to ascertain the influence of matrix and interface properties on the intraply toughness.

Differences in the structural response of 'granny-smith' apples under mechanical impact and compression

Apple fruits, cv. Granny Smith, were subjected to mechanical impact and compression loads utilizing a steel rod with a spherical tip 19 mm diameter, 50.6 g mass. Energies applied were low enough to produce enzymatic reaction: 0.0120 J for impact, and 0.0199 J for compression. Bruised material was cut and examined with a transmission electron microscope. In both compression and impact, bruises showed a central region located in the flesh parenchyma, at a distance that approximately equalled the indentor tip radius. The parenchyma cells of this region were more altered than cells from the epidermis and hypodermis. Tissues under compression presented numerous deformed parenchyma cells with broken tonoplasts and tissue degradation as predicted by several investigators. The impacted cells supported different kinds of stresses than compressed cells, resulting in the formation of intensive vesiculation, either in the vacuole or in the middle lamella region between cell walls of adjacent cells. A large proportion of parenchyma cells completely split or had initiated splitting at the middle lamella. Bruising may develop with or without cell rupture. Therefore, cell wall rupture is not essential for the development of a bruise, at least the smallest one, as predicted previously

Fracture propagation and stress corrosion in the case of dissimilar laser hybrid welded joints

The paper addresses the fracture propagation and stress corrosion behaviour of laser hybrid welds achieved between low carbon steel and stainless steel thin sheets. The crack propagation within these overmatched in strength welds was investigated by crack tip opening displacement (CTOD) on CT specimens notched transverse to the weld. A Digital Image Correlation System was used to qualify and estimate the initial crack length obtained by fatigue. The results are associated with the fractographic examinations of various regions of laser hybrid joints. Stress corrosion behaviour of the joint is also discussed.