Cálculo de factores de intensidad de tensión estáticos y dinámicos mediante el método de los elementos de contorno con formulación hipersingular

En el presente trabjo se propone y estudia una metodología de cálculo de Factores de Intensidad de Tensión dinámicos, en el dominio de la frecuencia, basada en el Método de los Elementos de Contorno Mzxto, es decir en la mezcla de ecuaciones correspondientes a las representaciones integrales de los desplazamientos y las tracciones. Se comienza presentando las expresiones de los núcleos hipersingulares y separando sus partes singular y no singular; a coritinucación se construye un elemento Singular Quarter Poznt discontinuo; y se termina realizando estudios paramétricos a aplicaciones que ponen de manifiesto la sencillez y exactitud del método propuesto tanto en problemas estáticos como dinámicos.Peer Reviewe

Efectos dinámicos en grietas en la inmediaciones de una superficie libre

En esta comunicación se presenta una forma de calcular la evolución del Factor de Intensidad de Tensiones con la frecuencia, cuando un tren de ondas que se propaga en un medio elástico semi-infinito, incide en una grieta que está próxima a la superficie libre del mismo. Se emplea el Método de los Elementos de Contorno con un elemento singular, desarrollado con anterioridad para problemas estáticos. Los resultados obtenidos se comparan con los de otros autores.In this paper a procedure for computation of the variation of the Stress Intensity Factor versus frequency is presented. The problem of a crack near the free surface of an uniform half-space when inpinged by harmonic waves is studied. The problem is analysed by means of the Boundary Element Method with a singular element that was previously developed for static problems. Results are compared with other authors

Static and dynamic stress intensity factors computations by the hipersingular element method

En el presente trabajo se propone y estudia una metodología de cálculo de Factores de Intensidad de Tensión dinámicos, en el dominio de la frecuencia, basada en el Método de los Elementos de Contorno Mixto, es decir en la mezcla de ecuaciones correspondientes a las representaciones integrales de los desplazamientos y las tracciones. Se comienza presentando las expresiones de los núcleos hipersingulares y separando sus partes singular y no singular; a continucación se construye un elemento Singular Quarter Point discontinuo; y se termina realizando estudios paramétricos a aplicaciones que ponen de manifiesto la sencillez y exactitud del método propuesto tanto en problemas estáticos como dinámicos.The Mixed Boundary Element Method, a combination of the equations corresponding to the integral representations of displacements and tractions: is used to propose and evaluate a riew methodology for computing dynamic Stress Intensity Factors in the frequency doniain. The paper starts presenting the hypersingular fundamental solution, extracting their singular parts, and constructing a new discontinuous Singular Quarter Point element. Finally, various parametric eornputations and applications are described to illustrate the simplicity and accuracy of the proposed method as applied to both static and dynamic problems

Testicular development in migrant and spawning bluefin tuna (Thunnus thynnus (L.)) from the eastern Atlantic and Mediterranean

Testis histological structure was studied in bluefin tuna (Thunnus thynnus) from the eastern Atlantic and Mediterranean during the reproductive season (from late April to early June). Testicular maturation was investigated by comparing samples from bluefin tuna caught on their eastward reproductive migration off Barbate (Strait of Gibraltar area) with samples of bluefin tuna fished in spawning grounds around the Balearic Islands. Histological evaluations of cross sections showed that the testis consists of two structurally different regions, an outer proliferative region where germ cells develop synchronously in cysts, and a central region made up of a well-developed system of ducts that convey the spermatozoa produced in the proliferative region to the main sperm duct. Ultrastructural features of the different stages of the male germ cell line are very similar to those described in other teleost species. The bluefin tuna testis is of the unrestricted spermatogonial testicular type, where primary spermatogonia are present all along the germinative portion of the lobules. All stages of spermatogenesis were present in the gonad tissue of migrant and spawning bluefin tuna, although spermatids were more abundant in spawning fish. The testis size was found to increase by a factor of four (on average) during migration to the Mediterranean spawning grounds, whereas the fat bodies (mesenteric lipid stores associated with the gonads) became reduced to half their weight, and the liver mass did not change significantly with sexual maturation. Linear regression analysis of the pooled data of migrant and spawning bluefin tuna revealed a significant negative correlation between the gonad index (IG) and the fat tissue index (IF), and a weaker positive correlation between the gonad index (IG) and the liver index (IL). Our analyses indicate that the liver does not play a significant role in the storage of lipids and that mesenteric lipid reserves constitute an important energy source for gametogenesis in bluefin tuna

Aplicación del método de los elementos de contorno al estudio de problemas dinámicos de fractura 3-D

XIII Congreso N a c i o n a l de Ingeniería MecánicaEl análisis de problemas tridimensionales dinámicos de mecánica de la fractura requiere del empleo de técnicas numéricas. Entre estas técnicas el Método de los Elementos de Contorno se ha mostrado como una herramienta eficaz y precisa en base a su gran capacidad para representar adecuadamente gradientes de tensión elevados; y a que la implementación de elementos capaces de modelar los campos singulares de tensiones presentes en las inmediaciones del borde de una grieta resulta sencilla y directa. En esta comunicación se extiende la formulación del elemento de contorno tridimensional singular con nodo a un cuarto desarrollado por Ariza, Sáez y Domínguez (1997) para problemas estáticos tridimensionales al estudio de problemas dinámicos en el dominio de la frecuencia. La metodología propuesta se valida mediante el estudio del problema de difracción de ondas planas por una grieta circular inmersa en un dominio infinito. Los resultados obtenidos concuerdan con los disponibles en la literatura.Analysis of dynamic three-dimensional fracture problems requires the use of numerical techniques. Among these techniques, the Boundary Element Method has been shown as an effective approach due to its ability to capture high stress gradients like the ones occuring at a crack front. In this paper, the singular quarter-point boundary element developed by Ariza, Sáez and Domínguez (1997) for static fracture applications is extended to the study of dynamic problems in the frequency domain. Numerical results are obtained for scattering of plane harmonic waves by a penny-shaped crack and compare favorably with those available in the literatureMinisterio de Educación y Cultura PB96-1380Ministerio de Educación y Cultura PB96-1322-C03-0

A polynomial hyperelastic model for the mixture of fat and glandular tissue in female breast

In the breast of adult women, glandular and fat tissues are intermingled and cannot be clearly distinguished. This work studies if this mixture can be treated as a homogenized tissue. A mechanical model is proposed for the mixture of tissues as a function of the fat content. Different distributions of individual tissues and geometries have been tried to verify the validity of the mixture model. A multiscale modelling approach was applied in a finite element model of a representative volume element (RVE) of tissue, formed by randomly assigning fat or glandular elements to the mesh. Both types of tissues have been assumed as isotropic, quasi-incompressible hyperelastic materials, modelled with a polynomial strain energy function, like the homogenized model. The RVE was subjected to several load cases from which the constants of the polynomial function of the homogenized tissue were fitted in the least squares sense. The results confirm that the fat volume ratio is a key factor in determining the properties of the homogenized tissue, but the spatial distribution of fat is not so important. Finally, a simplified model of a breast was developed to check the validity of the homogenized model in a geometry similar to the actual one

Water quality in a reservoir used for carp production

Guadalupe Reservoir, on the San Cayetano river, feeds into the Lerma river about 18 km north of Toluca in the State of Mexico, Mexico. On August 9, 1995, more than 6000 Israeli carp (Cyprinus carpio v. specularis and rubrofruscus) died within a week in this reservoir. We investigated the cause of the fish mortality and we determined whether the reservoir could be used again for carp culture. Five days after the accident the residual chlorine was 4 times higher than the maximum permissible amount. Ammonia nitrogen, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) were also above the recommended levels. Six months later, the amount of some contaminants in the water, such as chlorine, were back to normal ranges of water quality criteria for aquaculture. Ammonia, BOD and COD concentrations were lower to those found in the previous analyses but remained higher than the recommended levels. Most probably, residual chlorine was the cause of carp mortality as the chlorine level was very high when the fishes die

A bone remodelling model including the effect of damage on the steering of BMUs

Bone remodelling in cortical bone is performed by the so-called basic multicellular units (BMUs), which produce osteons after completing the remodelling sequence. Burger et al. (2003) hypothesized that BMUs follow the direction of the prevalent local stress in the bone. More recently, Martin (2007) has shown that BMUs must be somehow guided by microstructural damage as well. The interaction of both variables, strain and damage, in the guidance of BMUs has been incorporated into a bone remodelling model for cortical bone. This model accounts for variations in porosity, anisotropy and damage level. The bone remodelling model has been applied to a finite element model of the diaphysis of a human femur. The trajectories of the BMUs have been analysed throughout the diaphysis and compared with the orientation of osteons measured experimentally. Some interesting observations, like the typical fan arrangement of osteons near the periosteum, can be explained with the proposed remodelling model. Moreover, the efficiency of BMUs in damage repairing has been shown to be greater if BMUs are guided by damage

SPATIO-TEMPORAL PATTERNS OF JUVENILES IN EU PURSE SEINE FLEET CATCHES TARGETING TROPICAL TUNAS OVER THE PERIOD 1990-2019

The knowledge of the juvenile distribution in fisheries is essential to better manage the fishing effort on a stock. The exploration of a large dataset which covers 30 years of the purse seine fishery sampling enabled to study the spatio-temporal dynamic of the juvenile catches of the yellowfin and bigeye tunas. Results showed the existence of several areas of prime importance in terms of catch and concentration in juveniles with seasonal variations. Thus, the south of the fishing ground (Cape Lopez) was fished during winter month and the north during summer months (Cape Verde, Senegal y Mauritania). Offshore coastal zone and Gulf of Guinea were fished almost all along the year. This seasonal pattern is quite stable since the 90s but the proportion of juveniles in schools associated with floating objects tended to increase in both species. This preliminary study opened the way for further research on this important component of the fish stocks. La connaissance de la répartition des juvéniles dans les pêcheries est essentielle pour mieux gérer l'effort de pêche sur un stock. L'exploration d'un vaste jeu de données couvrant 30 ans d'échantillonnage de la pêcherie à la senne a permis d'étudier la dynamique spatio-temporelle des captures de juvéniles d'albacore et de thon obèse. Les résultats ont montré l'existence de plusieurs zones de première importance en termes de capture et de concentration des juvéniles avec des variations saisonnières. Ainsi, le sud de la zone de pêche (Cap Lopez) était pêché pendant les mois d'hiver et le nord pendant les mois d'été (Cabo Verde, Sénégal et Mauritanie). La zone côtière offshore et le golfe de Guinée ont été pêchés presque toute l'année. Bien que ce schéma saisonnier soit stable depuis les années 1990, la proportion de juvéniles dans les bancs associés à des objets flottants avait tendance à augmenter pour ces deux espèces. Cette étude préliminaire a ouvert la voie à d'autres recherches sur cette composante importante des stocks de poissons. El conocimiento de la distribución de los juveniles en las pesquerías es esencial para gestionar mejor el esfuerzo pesquero en un stock. La exploración de un gran conjunto de datos que abarca 30 años de muestreo de la pesquería de cerco permitió estudiar la dinámica espacio-temporal de las capturas de juveniles de rabil y patudo. Los resultados mostraron la existencia de varias zonas de importancia primordial en cuanto a la captura y concentración de juveniles con variaciones estacionales. Así, el sur del caladero (Cabo López) se pescaba durante el mes de invierno y el norte durante los meses de verano (Cabo Verde, Senegal y Mauritania). En la zona costera y en el golfo de Guinea se pescaba casi todo el año. Esta pauta estacional es bastante estable desde los años 90, pero la proporción de juveniles en los cardúmenes asociados a objetos flotantes tendió a aumentar en ambas especies. Este estudio preliminar abrió el camino a nuevas investigaciones sobre este importante componente de los stocks de peces.Versión del edito

Spatio-temporal patterns of juveniles in EU Purse sein fleet catch targetting tropical tunas over the period 1990-2019

The knowledge of the juvenile distribution in fisheries is essential to better manage the fishing effort on a stock. The exploration of a large dataset which covers 30 years of the purse seine fishery sampling enabled to study the spatio-temporal dynamic of the juvenile catches of the yellowfin and bigeye tunas. Results showed the existence of several areas of prime importance in terms of catch and concentration in juveniles with seasonal variations. Thus, the south of the fishing ground (Cape Lopez) was fished during winter month and the north during summer months (Cape Verde, Senegal y Mauritania). Offshore coastal zone and Gulf of Guinea were fished almost all along the year. This seasonal pattern is quite stable since the 90s but the proportion of juveniles in schools associated with floating objects tended to increase in both species. This preliminary study opened the way for further research on this important component of the fish stocks.Versión del edito