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Internal Forces (internal + force)
Selected AbstractsDexterous manipulation of an object by means of multi-DOF robotic fingers with soft tipsJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 7 2002Pham Thuc Anh Nguyen This article analyzes the dynamics of motion of various setups of two multiple degree-of-freedom (DOF) fingers that have soft tips, in fine manipulation of an object, and shows performances of their motions via computer simulation. A mathematical model of these dynamics is described as a system of nonlinear differential equations expressing motion of the overall fingers-object system together with algebraic constraints due to tight area contacts between the finger-tips and surfaces of the object. First, problems of (1) dynamic, stable grasping and (2) regulation of the object rotational angle by means of a setup of dual two-DOF fingers, are treated. Second, the problem of regulating the position of the object mass center by means of a pair of two-DOF and three-DOF fingers is considered. Third, a set of dual three-DOF fingers is treated, in order to let it perform a sophisticated task, which is specified by a periodic pattern of the object posture and a constant internal force. In any case, there exist sensory-motor coordinations, which are described by analytic feedback connections from sensing to actions at finger joints. In the cases of setpoint control problems, convergences of motion to secure grasping together with the specified object rotational angle and/or the specified object mass center position, are proved theoretically. A constraint stabilization method (CSM) is used for solving numerically the differential algebraic equations to show performances of the proposed sensory-feedback schemes. © 2002 Wiley Periodicals, Inc. [source] A model for the 3D kinematic interaction analysis of pile groups in layered soilsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 11 2009Francesca Dezi Abstract The paper presents a numerical model for the analysis of the soil,structure kinematic interaction of single piles and pile groups embedded in layered soil deposits during seismic actions. A finite element model is considered for the pile group and the soil is assumed to be a Winkler-type medium. The pile,soil,pile interaction and the radiation problem are accounted for by means of elastodynamic Green's functions. Condensation of the problem permits a consistent and straightforward derivation of both the impedance functions and the foundation input motion, which are necessary to perform the inertial soil,structure interaction analyses. The model proposed allows calculating the internal forces induced by soil,pile and pile-to-pile interactions. Comparisons with data available in literature are made to study the convergence and validate the model. An application to a realistic pile foundation is given to demonstrate the potential of the model to catch the dynamic behaviour of the soil,foundation system and the stress resultants in each pile. Copyright © 2009 John Wiley & Sons, Ltd. [source] Analysis and performance of a predictor-multicorrector Time Discontinuous Galerkin method in non-linear elastodynamicsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2002Oreste S. Bursi Abstract A predictor-multicorrector implementation of a Time Discontinuous Galerkin method for non-linear dynamic analysis is described. This implementation is intended to limit the high computational expense typically required by implicit Time Discontinuous Galerkin methods, without degrading their accuracy and stability properties. The algorithm is analysed with reference to conservative Duffing oscillators for which closed-form solutions are available. Therefore, insight into the accuracy and stability properties of the predictor-multicorrector algorithm for different approximations of non-linear internal forces is gained, showing that the properties of the underlying scheme can be substantially retained. Finally, the results of representative numerical simulations relevant to Duffing oscillators and to a stiff spring pendulum discretized with finite elements illustrate the performance of the numerical scheme and confirm the analytical estimates. Copyright © 2002 John Wiley & Sons, Ltd. [source] Three-dimensional finite element analysis of the interaction between tunneling and pile foundationsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2002H. Mroueh Abstract This paper concerns analysis of the impact of construction of urban tunnels on adjacent pile foundations. It is carried out using an elastoplastic three-dimensional finite element modelling. Numerical simulations are performed in two stages, which concern, respectively, the application of the pile axial loading and the construction of the tunnel in presence of the pile foundations. Analysis is carried out for both single piles and groups of piles. Results of numerical simulations show that tunneling induces significant internal forces in adjacent piles. The distribution of internal forces depends mainly on the position of the pile tip regarding the tunnel horizontal axis and the distance of the pile axis from the centre of the tunnel. Analysis of the interaction between tunneling and a group of piles reveals a positive group effect with a high reduction of the internal forces in rear piles. Copyright © 2002 John Wiley & Sons, Ltd. [source] Vertical dynamic responses of a simply supported bridge subjected to a moving train with two-wheelset vehicles using modal analysis methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 9 2005Ping Lou Abstract The vertical dynamic responses of a simply supported bridge subjected to a moving train are investigated by means of the modal analysis method. Each vehicle of train is modelled as a four-degree-of-freedom mass,spring,damper multi-rigid body system with a car body and two wheelsets. The bridge, together with track, is modelled as a simply supported Bernoulli,Euler beam. The deflection of the beam is described by superimposing modes. The train and the beam are regarded as an entire dynamic system, in which the contact forces between wheelset and beam are considered as internal forces. The equations of vertical motion in matrix form with time-dependent coefficients for this system are directly derived from the Hamilton's principle. The equations of motion are solved by Wilson-, method to obtain the dynamic responses for both the support beam and the moving train. Compared with the results previous reported, good agreement between the proposed method and the finite element method is obtained. Finally, the effects of beam mode number, vehicle number, beam top surface, and train velocity on the dynamic responses of the entire train and bridge coupling system are studied, and the dynamic responses of beam are given under the train moving with resonant velocity. Copyright © 2005 John Wiley & Sons, Ltd. [source] Analysis of 3D problems using a new enhanced strain hexahedral elementINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2003P. M. A. Areias Abstract The now classical enhanced strain technique, employed with success for more than 10 years in solid, both 2D and 3D and shell finite elements, is here explored in a versatile 3D low-order element which is identified as HIS. The quest for accurate results in a wide range of problems, from solid analysis including near-incompressibility to the analysis of locking-prone beam and shell bending problems leads to a general 3D element. This element, put here to test in various contexts, is found to be suitable in the analysis of both linear problems and general non-linear problems including finite strain plasticity. The formulation is based on the enrichment of the deformation gradient and approximations to the shape function material derivatives. Both the equilibrium equations and their variation are completely exposed and deduced, from which internal forces and consistent tangent stiffness follow. A stabilizing term is included, in a simple and natural form. Two sets of examples are detailed: the accuracy tests in the linear elastic regime and several finite strain tests. Some examples involve finite strain plasticity. In both sets the element behaves very well, as is illustrated in numerous examples. Copyright © 2003 John Wiley & Sons, Ltd. [source] Delegating Differences: Bilateral Investment Treaties and Bargaining Over Dispute Resolution ProvisionsINTERNATIONAL STUDIES QUARTERLY, Issue 1 2010Todd Allee Bilateral investment treaties (BITs) have become the dominant source of rules on foreign direct investment (FDI), yet these treaties vary significantly in at least one important respect: whether they allow investment disputes to be settled through the International Centre for the Settlement of Investment Disputes (ICSID). Through the compilation and careful coding of the text of nearly 1,500 treaties, we identify systematic variation in "legal delegation" to ICSID across BITs and explain this important variation by drawing upon a bargaining framework. Home governments prefer and typically obtain ICSID clauses in their BITs, particularly when internal forces push strongly for such provisions and when they have significantly greater bargaining power than the other signatory. Yet some home governments are less likely to insist upon ICSID clauses if they have historical or military ties with the other government. On the other hand, although host governments are often hostile toward ICSID clauses, particularly when sovereignty costs are high, they are more likely to consent to such clauses when they are heavily constrained by their dependence on the global economy. Our findings have significant implications for those interested in FDI, legalization, international institutions, and interstate bargaining. [source] The voice of historical biogeographyJOURNAL OF BIOGEOGRAPHY, Issue 2 2001Jorge V. Crisci Historical biogeography is going through an extraordinary revolution concerning its foundations, basic concepts, methods, and relationships to other disciplines of comparative biology. There are external and internal forces that are shaping the present of historical biogeography. The external forces are: global tectonics as the dominant paradigm in geosciences, cladistics as the basic language of comparative biology and the biologist's perception of biogeography. The internal forces are: the proliferation of competing articulations, recourse to philosophy and the debate over fundamentals. The importance of the geographical dimension of life's diversity to any understanding of the history of life on earth is emphasized. Three different kinds of processes that modify the geographical spatial arrangement of the organisms are identified: extinction, dispersal and vicariance. Reconstructing past biogeographic events can be done from three different perspectives: (1) the distribution of individual groups (taxon biogeography) (2) areas of endemism (area biogeography), and (3) biotas (spatial homology). There are at least nine basic historical biogeographic approaches: centre of origin and dispersal, panbiogeography, phylogenetic biogeography, cladistic biogeography, phylogeography, parsimony analysis of endemicity, event-based methods, ancestral areas, and experimental biogeography. These nine approaches contain at least 30 techniques (23 of them have been proposed in the last 14 years). The whole practice and philosophy of biogeography depend upon the development of a coherent and comprehensive conceptual framework for handling the distribution of organisms and events in space. [source] Sensory-motor control mechanism for reaching movements of a redundant musculo-skeletal armJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 11 2005Kenji Tahara This paper studies the human arm's sensory-motor control mechanism in reaching movements. First, we formulate both the kinematics and dynamics of a two-link planar arm model with six redundant muscles. The nonlinear muscle dynamics is modeled based on several biological understandings. We then show the stability of the overall system and perform some numerical simulations. By considering the internal forces induced by the redundant muscles, we show that the damping factors in each joint can be regulated, and as the result, it can realize humanlike quasistraight line reaching movements. In addition, we also propose the gravity compensation method at the muscle input level and present the result of numerical simulation to verify the usefulness of this method. © 2005 Wiley Periodicals, Inc. [source] The Teaching of Denture Marking Methods in Dental Schools in the United Kingdom and the United States,JOURNAL OF FORENSIC SCIENCES, Issue 6 2009M.Phil, Raymond Richmond B.Sc. Abstract:, Forensic organizations worldwide have recommended that dental prostheses should be marked with, at a minimum, the patient's name and preferably with further unique identifiers such as a social security number. The current study aimed to assess the denture marking practice of dental schools within the United States and the United Kingdom. A questionnaire-based survey was employed to gain both quantitative and qualitative data on the methods, practices, and ethos behind denture marking in 14 U.K. and 32 U.S. dental schools. One hundred percent of U.K. and 87.5% of U.S. schools returned surveys and the results suggest that, for dental schools where there is no legal or legislative need for denture marking, the practice is inconsistently taught and appears to be reliant on internal forces within the school to increase awareness. Among those schools practicing marking, only 18% employ a technique likely to withstand common postmortem assaults; this is a concern. [source] Organizational Transformation in Transition Economies: Resource-based and Organizational Learning PerspectivesJOURNAL OF MANAGEMENT STUDIES, Issue 2 2003Klaus Uhlenbruck ABSTRACT The capitalist and socialist societies of the twentieth century assigned firms different roles within their economic systems. Enterprises transforming from socialist to market economies thus face fundamental organizational restructuring. Many former state-owned firms in the transition economies of Central and Eastern Europe have failed at this task. These firms have pursued primarily defensive downsizing, rather than strategic restructuring, as a result of both internal and external constraints on restructuring strategies. Building on the organizational learning and resource-based theories, we analyse strategies available to management in privatized, former state-owned enterprises in transition economies to restructure their organization. Both internal forces promoting or inhibiting the restructuring process, and external constraints arising in the transition context are examined. A model and testable propositions are developed that explain post-privatization performance. Implications of our research point to the ways in which firms should manage and develop their resource base to transform to competitive enterprises. [source] Linking planning, quality improvement, and institutional researchNEW DIRECTIONS FOR INSTITUTIONAL RESEARCH, Issue 123 2004Daniel Seymour External and internal forces are driving institutions not only to create departments and positions that specialize in planning, quality improvement, and institutional research but also to link them within a systems context. [source] Zur maßgebenden Verkehrslaststellung bei SchrägseilbrückenBAUTECHNIK, Issue 4 2004Harald Unterweger ao. Als Grundlage der Bemessung erfordert die Systemberechnung im Brükkenbau auch die Auffindung der ungünstigsten Verkehrslaststellung für jeden betrachteten Brückenquerschnitt. Insbesondere beim Fahrbahnbalken von Schrägseilbrücken ergibt sich die Gesamtbeanspruchung aus einem komplexen Zusammenwirken aus Normalkräften, Querkräften und Biegemomenten. In der Praxis erfolgt üblicherweise eine Selektion jener Verkehrslaststellungen, die eine der Teil beanspruchungen am Querschnitt (meist ausgedrückt durch Schnittkräfte) maximieren, wodurch jedoch für die nachfolgend betrachteten Stahl- bzw. Verbundbrücken nicht immer die höchsten Beanspruchungen entstehen. Einleitend erfolgt die Darstellung eines einfachen und anschaulichen Verfahrens, um , unabhängig von der Komplexität der Grenzzustandsfunktion, die auch das Beulen des Hauptträgerstegs beinhalten kann , die ungünstigste Verkehrslaststellung am Querschnitt zu finden. Dies stellt eine Verallgemeinerung des in [1] vorgestellten Verfahrens dar. Der Hauptteil beinhaltet ein Anwendungsbeispiel einer Schrägseilbrücke mit Verbundquerschnitt, wobei zwei repräsentative Fahrbahnquerschnitte näher untersucht werden. Einerseits werden die Gesamtbeanspruchungen der konventionellen und der genauen Vorgehensweise anhand von Einflußlinien erläutert, und andererseits lassen sich daraus Hinweise für die Praxis ableiten. Die dargestellte ingenieurmäßige Vorgehensweise kann alle Arten der Einwirkungen beinhalten und ist grundsätzlich auch auf andere Bauwerke sowie Baustoffe (z. B. Stahlbeton) direkt anwendbar. Appropriate traffic load cases for steel and composite cable , stayed bridges. A significant problem in the global analysis of bridge structures is to find the most unfavourable position of the traffic loads for each cross-section. In practice usually those traffic load cases are chosen which maximise one part of stresses at the cross-section (often expressed in form of internal forces). First of all a simple method is presented to find out the most unfavourable traffic load position, also applicable for complex interaction formulae including web buckling. Secondly an example of a cable-stayed bridge is analysed. For two significant sections of the bridge deck the results are presented. The stresses due to the conventional practical procedure are compared with the more accurate ones. The behaviour is explained by the corresponding influence lines. Based on these results some proposals for practical work are given. The presented procedure is also applicable to other types of construction works and materials (e.g. reinforced concrete). [source] Bemessungsvorschlag für Holz/Beton-Verbundbalken unter Beachtung abgestufter VerbindungsmittelabständeBAUTECHNIK, Issue 3 2004Jörg Schmidt Dr.-Ing. Die Abstände der Verbindungsmittel von Holz/Beton-Verbundbalken werden i. allg. vorrangig aus Kostengründen entsprechend dem Querkraftverlauf abgestuft. Das Tragvermögen gemäß Bemessungsgrundlagen nach DIN 1052 bzw. EC 5 mit linear ermittelten Schnittgrößen (Näherungsverfahren/,-Verfahren) wird gegenüber Balken ohne die o. g. Abstufung deutlich reduziert. Da das tatsächliche Last-Verformungsverhalten jedoch deutliche Nichtlinearitäten aufweist und die Verbundsteifigkeit hinsichtlich des Tragvermögens nur einen geringen Einfluß besitzt, wird in diesem Beitrag der Einfluß der Abstufung der Verbindungsmittelabstände auf das Tragverhalten von Verbundbalken mittels nichtlinearer FE-Analysen untersucht. Im Ergebnis ist festzustellen, daß der Sicherheitsabstand zwischen Gebrauchslast gemäß E DIN 1052 und Versagenslastniveau mit zunehmendem Abstufungsgrad zunimmt, weil das tatsächliche Tragvermögen weniger , als durch das derzeitige Bemessungsmodell unterstellt , reduziert wird. Somit weisen also die Systeme, deren Verbinderabstände mehrmals abgestuft sind, den größten Sicherheitsabstand auf, könnten also noch wirtschaftlicher bemessen werden. Deshalb wird im Ergebnis der Untersuchungen ein neuer Bemessungsvorschlag unterbreitet und verifiziert, der die Nichtlinearitäten berücksichtigt, einen gleichmäßigen Sicherheitsabstand zum Versagenslastniveau gewährleistet und eine deutlich wirtschaftlichere Bemessung erlaubt. Design proposal for timber/concrete composite beams with graded connnector distances. The distance of connections of timber/concrete composite beams is often graded for economical reasons according the shear force distribution. The load-carrying capacity of composite beams according to DIN 1052 respectively E DIN 1052 with internal forces, which are linearly determined, (,-procedure) are clearly reduced compared to beams without graded distances of connectors. The actual load-bearing behaviour distinctly shows non-linearities. The influence of the gradations of the connectors on the load-bearing behaviour of composite beams is investigated, because the influence of the stiffness of connections on the load-bearing capacity of composite beams is small. The paper presents a comparison between failure loads determined by FE-analysis and the working loads according to the current design rule. It is shown that the decrease of load-bearing capacity is smaller than assumed by current code of practice. Structures with several different distances of connections have the largest safety-factor. These systems can more economically be designed. As the result of the investigations, a new design proposal is presented, which takes non-linearities into account and guarantees a constant safety-zone between failure load and working load. These proposal permits an economic design of timber/concrete composite beams. [source] Zur Querkraftgefährdung bestehender SpannbetonbrückenBETON- UND STAHLBETONBAU, Issue 6 2010Teil II: Empfehlungen zur Vorgehensweise bei Sichtung und Überprüfung Brückenbau; Spannbeton; Normen; Berechnungs- und Bemessungsverfahren Abstract Zur Formulierung einer Handlungsanweisung wurden in Teil I die geänderten Lastannahmen für Brücken nach DIN Fachbericht 101 mit den Belastungsklassen nach alten Normen verglichen und gezeigt, wie anhand aktueller Verkehrszahlen die Lastansätze modifiziert werden können. Der aktuelle Brückenbestand in Hessen wurde mit der Straßeninformationsbank (Teilprojekt Bauwerksdaten) ausgewertet, um Klassifizierungs- und Bewertungskriterien zu erarbeiten. Zur Beurteilung des Querkraftwiderstandes wurden die Grundlagen der Querkraftbemessung nach DIN 1045, DIN 4227, DIN Fachbericht 102 und aus der Literatur gegenübergestellt. In Teil II werden Verfahren zur nachträglichen Verstärkung von Querschnitten und Tragsystemen mit zu geringer Querkrafttragfähigkeit zusammengestellt. Des Weiteren werden verschiedene Varianten der Modellierung verglichen, die bei der linearelastischen Schnittgrößenermittlung nach der Finite-Elemente- Methode verwendet werden. Auf Grundlage der gewonnenen Erkenntnisse werden schließlich Empfehlungen für eine Handlungsanweisung zur Beurteilung querkraftgefährdeter Brückenbauwerke formuliert. Shear-Vulnerability of Existing Pre-Stressed Concrete Bridges In Part I, to formulate an operation directive the revised load assumptions for bridges of DIN Technical Report 101 are compared with the loading classes according to old standards and it is demonstrated, how the loading models can be modified based on actual traffic data. The current bridge asset in the Federal State of Hesse is evaluated using the "Road Information Database (Sub-Project: Structural Data)" in order to work out classification and evaluation criteria. Regarding the assessment of the shear load-bearing capacity the fundamentals of the shear load design models of DIN 1045, DIN 4227, DIN TR 102 and from the literature are compared. In Part II, the procedures for the subsequent strengthening of cross-sections and structural systems with a low shear load-bearing capacity are compiled. In addition, different types of finite element modelling are compared used for the calculation of the linear-elastic internal forces. Finally, based on the findings recommendations are formulated for an operation directive in regard to the assessment of shear-vulnerable bridges. [source] Kombiniertes Verfahren zur wirklichkeitsnahen Berechnung schlanker StahlbetonstabtragwerkeBETON- UND STAHLBETONBAU, Issue 10 2006Uwe Starossek Univ.-Prof. Der wirklichkeitsnahen und damit nichtlinearen Berechnung von allgemeinen Stahlbetontragwerken kommt eine wachsende Bedeutung zu. Eine Kombination des allgemeinen Weggrößenverfahrens, des Übertragungsverfahrens und eines Querschnittsmoduls führt zu einem effektiven Berechnungsverfahren für allgemeine Stabtragwerke aus Stahl- und Spannbeton. Neben der stofflichen Nichtlinearität berücksichtigt das Verfahren auch geometrische Nichtlinearität mit großen Verformungen. Die übergeordnete Berechnung des Systems erfolgt inkrementell und iterativ mit dem allgemeinen Weggrößenverfahren. Auf Stabebene wird ein erweitertes Übertragungsverfahren zur Bestimmung der Stabendschnittgrößen und der Steifigkeitsmatrix eingesetzt. Die Formulierung des Übertragungsverfahrens erfolgt in einem rekursiven Schema für einen verformten Stab, der in Abhängigkeit vom Steifigkeitsgradienten in einzelne Abschnitte diskretisiert wird. Das nichtlineare Materialverhalten einschließlich Rißbildung, Entfestigung und Fließen der Bewehrung wird im Querschnittsmodul über eine Querschnittsintegration erfaßt. Combined method for a realistic analysis of slender reinforced concrete frames A more realistic and, hence, nonlinear analysis of reinforced concrete structures is becoming increasingly important. A combination of the displacement method, the transfer matrix method, and a cross section module is suggested which leads to an effective analysis method for general reinforced and prestressed concrete frames. The combined method considers both material and geometrical nonlinearities including large deformations. The first level computation of the system is incrementally and iteratively carried out by the displacement method. At element level, an extended transfer matrix method is used for determining both the internal forces at the element end nodes and the stiffness matrix. The transfer matrix method is recursively applied to the deformed element, which is discretized into individual segments whose number and lengths depend on the stiffness gradient. The cross section module is based on cross-sectional integration. It takes into account nonlinear material behavior including cracking, softening, and yielding of reinforcement. [source] Einfluß der Elementfugen auf die Durchbiegung von FlachdeckenBETON- UND STAHLBETONBAU, Issue 3 2006Manfred Curbach Prof. Dr.-Ing. Das Verformungsverhalten von Flachdecken in Elementbauweise unterscheidet sich von einer reinen Ortbetondecke aufgrund der vorhandenen Elementfugen. Die damit verbundenen lokalen Querschnittsschwächungen erfordern schon auf niedrigem Lastniveau eine Umlagerung der Belastung in angrenzende Feld- und Stützbereiche. Die Folge der Lastumlagerung sind anfänglich höher beanspruchte Deckenbereiche und eine frühere Rißbildung im Vergleich zu einer reinen Ortbetondecke. Mit steigender Belastung kommt es jedoch zur Annäherung der Rißzustände von Fertigteil- und Ortbetondecken, wie anhand nichtlinearer Berechnungen nachgewiesen werden konnte. Der relative Unterschied in der Durchbiegung wird deutlich reduziert. Auf Gebrauchslastniveau liegen die Verformungen der Fertigteildecken etwa 5% über denen der reinen Ortbetondecke. Influence of Bond Joints on Deformation of precast Slabs Precast slabs and in-situ concrete slabs vary in their deflection behaviour due to the bond joints between the precast concrete units. The diminished cross section of the bond joints require a redistribution of internal forces to adjoining field and support areas already at a small load. The consequence of this redistribution are higher demands in these slab areas and an earlier crack initiation in comparison to the in-situ concrete slabs. With an increase of the loading the cracking pattern of the precast slabs and the in-situ concrete slabs converge as the nonlinear FE-calculation have shown. The relative difference in deformation is clearly reduced. At the service load the deformation of the precast slabs is only 5% higher than the deformation of the in-situ concrete slabs. [source] | ||||||||||||||||||||||||||||