Energy conserving time integration scheme for geometrically exact beam

An energy conserving finite-element formulation for the dynamic analysis of geometrically non-linear beam-like structures undergoing large overall motions has been developed. The formulation uses classical displacement-based planar beam finite elements described in an inertial frame. It takes into account finite axial, bending and shear strains. A theoretically consistent approach is used to derive a novel and simple energy conserving scheme, using the unconventional incremental strain update rather than the standard strong form. Numerical examples demonstrate perfect energy and momenta conservation, stability and robustness of the scheme, and good convergence properties in terms of both the Newton-Raphson method and time step size. (c) 2006 Elsevier B.V. All rights reserved

The strain-based beam finite elements in multibody dynamics

We present a strain-based finite-element formulation for the dynamic analysis of flexible elastic planar multibody systems, composed of planar beams. We consider finite displacements, rotations and strains. The discrete dynamic equations of motion are obtained by the collocation method. The strains are the basic interpolated variables, which makes the formulation different from other formulations. The further speciality of the formulation is the strong satisfaction of the cross-sectional constitutive conditions at collocation points. In order to avoid the nested integrations, a special algorithm for the numerical integration over the length of the finite element is proposed. The midpoint scheme is used for the time integration. The performance of the formulation is illustrated via numerical examples, including a stiff multibody system. (c) 2007 Elsevier Ltd. All rights reserved

Compliant Movement Primitives in a Bimanual Setting

Simultaneously achieving low trajectory errors and compliant control \emph{without} explicit models of the task was effectively addressed with Compliant Movement Primitives (CMP). For a single-robot task, this means that it is accurately following its trajectory, but also exhibits compliant behavior in case of perturbations. In this paper we extend this kind of behavior without explicit models to bimanual tasks. In the presence of an external perturbation on any of the robots, they will both move in synchrony in order to maintain their relative posture, and thus not exert force on the object they are carrying. Thus, they will act compliantly in their absolute task, but remain stiff in their relative task. To achieve compliant absolute behavior and stiff relative behavior, we combine joint-space CMPs with the well known symmetric control approach. To reduce the necessary feedback reaction of symmetric control, we further augment it with copying of a virtual force vector at the end-effector, calculated through the measured external joint torques. Real-world results on two Kuka LWR-4 robots in a bimanual setting confirm the applicability of the approach.Comment: 1st, unpolished version, 7 page

Adaptation of the karst land for the agrarian use in the Mediterranean

[cat] En aquest article es revisen els següents mètodes de recerca: 1. Anàlisi de la part superior dels afloraments rocosos. En esser tallats a nivell del sol, la terra s'emprava corn a prat. Quan els tallaven més amunt, la terra s'emprava com a terreny de pastura o com a prat. En el darrer cas, emperò, si la superfície rocosa és llisa, el nivell del sòl ha estat rebaixat per l’erosió; aquest tipus de superfície només es pot formar en contacte amb el sòl. La superfície d'una calcària compacta, exposada a la corrosió causada per les precipitacions i per la meteorització mecànica per damunt del sòl, és cantelluda, clivellada i aspre. 2. Anàlisi de les pedres acumulades per l'home a parets, marges, a la vora inferior de les terrasses a camps rostos, o enterrades sota el sol en aquestes terrasses o sota els prats. La mesura de llur volum i pes, efectuada en algunes illes iugoslaves, ha mostrat que centenars de quilograms de pedres, en casos excepcionals més d'un tona, han estat excavats i trencats per cada metre quadrat de terra “netejada”. 3. Les formes corn cocons (Kamenitza), xaragalls de dissolució (Rundkarren), tubs de dissolució, solcs de dissolució (Korrosionskehle), i especialment els forats de parets llises (Kavernosen Karren), si són trobats a la superfície indiquen una erosió soterrada. 4. Els fragments de pedra amb caires vius deixats en el sol després de “netejar” la superfície rocosa en alguns camps representa mes del 10 % del pes del sòl. Això indica l’extensió de la “netejada”, fins i tot quan les pedres majors s'han retirat de la superfície. Els ocasionals anàlisis professionals realitzats a algunes zones càrstiques de la Mediterrània han mostrat que les zones habilitades per ús agrícola en èpoques antigues eren més grans del que sabíem per la bibliografia. L’època de la netejada no és segura i abarca des de I‘època fenícia (Malta) als temps més recents. A molts de països les modernes tècniques agrícoles destrueixen les antigues formes de preparació de la terra per al conreu amb aixada i càvec. L'article insisteix en la necessitat de l’estudi dels valors ecològics i històrics d'aquests antics testimonis de l’esforç dels nostres avantpassats pel proveïment de menjar per llurs vides, i de la conservació d'aquesta herència natural i cultural.[eng] The following methods of research are reviewed: 1. Analyses of the outcropping tops of stones. When cut off at the level of the soil, the land was used as meadows. When the tops are cut off in higher position, the land was used as a pasture ground or as a meadow. In the latter case, however, the soil level has been lowered by erosion if the stone surface is smooth. This can develope only in contact with the soil. The surface of solid limestone, exposed to corrosion caused by the precipitations and by the mechanical weathering above the soil, is sharply fissured and rough. 2. Analyses of the stones accumulated by man into walls, side walls at the lower edge of the slope field terraces, or buried under the soil in such terraces or under the meadow. Measurements of their volume and weight, made on some Yugoslav islands, have shown that several hundred of kilograms, in exceptional case even more than one ton of stones have been dug out and cut off for one m2 of the “cleared” land. 3. Subsoil forms, such as kamenitza, solution runnel (Rundkarren), solution pipe, solution notche (Korrosionskehle), and especially the rocky holes with smooth walls (Kavernosen Karren) are, when on surface, an indicator of the soil erosion too. 4. The stone fragments with sharp edges left in the soil after the “clearing” of the stony surface represent in come field more than 10 % of the soil weight. They indicate the extent of the “clearing” even when the bigger stones are removed from the surface. The occassional professional analyses, made so fare in some Mediterranean karst areas. have shown much larger adapted areas for agrarian use in ancient times than this is known in the literature. The time of clearing is uncertain and reaches from the Phoenician (Malta) to the recent time. In many countries the modern agricultural techniques, destroy the old forms of land adaptation for the cultivation by hoe and spade. The article stresses the need for the study of the ecological and historical value of these old evidences of the ancient endevour of our ancestors to provide food for their life and for the conservation of this natural and cultural heritage

Fungicide resistance among Cladobotryum spp. – causal agents of cobweb disease of the edible mushroom Agaricus bisporus

A survey of fungicide resistance among isolates of the mushroom pathogens Cladobotryum mycophilum and C. dendroides Types I and II was undertaken, with respect to the active ingredients thiabendazole, carbendazim (benzimidazoles) and prochloraz manganese following an epidemic in Britain and Ireland in 1994/95. The majority of isolates (41/57) were strongly resistant to thiabendazole (ED50 > 200 ppm) and were exclusively C. dendroides Type II. All C. mycophilum and C. dendroides Type I isolates, and four C. dendroides Type II isolates, were weakly resistant to thiabendazole (ED50 1–10 ppm). Thiabendazole-resistant C. dendroides Type II isolates were only weakly resistant to carbendazim (ED50 2–10 ppm) and isolates which were weakly resistant to thiabendazole were carbendazim-sensitive (ED50 < 1 ppm), demonstrating a lack of complete cross resistance between these two benzimidazole fungicides. The ED50 values for all isolates with respect to prochloraz manganese ranged from 0.14 to 7.8 ppm. Benzimidazole resistance was considered to have been an important factor influencing the severity of the 1994/95 cobweb epidemic but 25% of isolates collected were benzimidazole sensitive

Differential Geometry applied to Acoustics : Non Linear Propagation in Reissner Beams

Although acoustics is one of the disciplines of mechanics, its "geometrization" is still limited to a few areas. As shown in the work on nonlinear propagation in Reissner beams, it seems that an interpretation of the theories of acoustics through the concepts of differential geometry can help to address the non-linear phenomena in their intrinsic qualities. This results in a field of research aimed at establishing and solving dynamic models purged of any artificial nonlinearity by taking advantage of symmetry properties underlying the use of Lie groups. The geometric constructions needed for reduction are presented in the context of the "covariant" approach.Comment: Submitted to GSI2013 - Geometric Science of Informatio

Family Functioning and Secondary Traumatic Stress in Military Families: A Qualitative Study

The purpose of this study was to explore secondary traumatic stress and family functioning in military families. Six licensed mental health professionals, including social workers and a marriage and family therapist with experience working directly with military families participated in this study. Using a qualitative design, participants were interviewed regarding their experience working with these families. Five themes emerged from the data including: (1) strength of communication within the family can impact functioning; (2) the non-veteran parent often takes on various aspect in the role of both parents; (3) children often present secondary traumatic stress symptoms outside of the home; (4) family functioning and responses to trauma are unique to each family; and, (5) family and couples counseling is an essential treatment tool for these families. Limitations were lack of discussion surrounding female veteran to male spouses, as well as same sex partnerships. This study presents information through the personal and professional lens of the participants and draws awareness to PTSD and secondary traumatic stress in military families