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Inertia
Kinds of Inertia Terms modified by Inertia Selected AbstractsASSESSING CURRENT ADAPTATION AND PHYLOGENETIC INERTIA AS EXPLANATIONS OF TRAIT EVOLUTION:THE NEED FOR CONTROLLED COMPARISONSEVOLUTION, Issue 10 2005Thomas F. Hansen Abstract The determination of whether the pattern of trait evolution observed in a comparative analysis of species data is due to adaptation to current environments, to phylogenetic inertia, or to both of these forces requires that one control for the effects of either force when making an assessment of the evolutionary role of the other. Orzack and Sober (2001) developed the method of controlled comparisons to make such assessments; their implementation of the method focussed on a discretely varying trait. Here, we show that the method of controlled comparisons can be viewed as a meta-method, which can be implemented in many ways. We discuss which recent methods for the comparative analysis of continuously distributed traits can generate controlled comparisons and can thereby be used to properly assess whether current adaptation and/or phylogenetic inertia have influenced a trait's evolution. The implementation of controlled comparisons is illustrated by an analysis of sex-ratio data for fig wasps. This analysis suggests that current adaptation and phylogenetic inertia influence this trait. [source] ESTIMATING PHYLOGENETIC INERTIA IN TITHONIA (ASTERACEAE): A COMPARATIVE APPROACHEVOLUTION, Issue 2 2000Eduardo Morales Abstract., Phylogenetic inertia is a difficult issue in evolutionary biology because we have yet to reach a consensus about how to measure it. In this study a comparative approach is used to evaluate phylogenetic inertia in 14 demographic and morphological characters in 10 species and one subspecies of the genus Tithonia (Asteraceae). Three different methods, autocorrelational analysis, phylogenetic correlograms, and ancestor-state reconstruction, were used to evaluate phylogenetic inertia in these traits. Results were highly dependent on the method applied. Autoregression and phylogenetic eigenvector regression (PVR) methods found more inertia in morphological traits. In contrast, phylogenetic correlograms and ancestor-state reconstruction suggest that morphological characters exhibit less phylogenetic inertia than demographic ones. The differences between results are discussed and methods are compared in an effort to understand phylogenetic inertia more thoroughly. [source] Dynamic COI-tracking concept for the control of generators in multi-machine power systemsEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 1 2008Zhou Lan Abstract In the conventional excitation control concept, the power angle and frequency of a generator are driven to a pre-designed operation point after the fault occurs. It is named as Constant Point Stabilization (CPS) concept in this paper. A novel concept, called dynamic Center of Inertia (COI)-tracking concept is proposed in this paper. In the concept, the power angle and frequency of each generator track the dynamic COI of the power system. Compared to CPS concept, a salient feature the suggested dynamic COI-tracking concept has is that the generators are not restricted to constant angle point or frequency any longer but track the dynamic COI trajectory of the system to keep synchronous in rotor angle and frequency. Wide area measurement system (WAMS) will be used to transform COI signals to each generator. The time delay within a certain limit of WAMS signals is permitted. To make comparison between the two concepts, the control system models based on the two concepts are first established. Then, using the back-stepping method, two robust controllers are designed to achieve the control objectives of the two concepts. At last, dynamic simulations are carried out based on a 2-area-4-machine test power system, and the control effects of the two controllers, together with that of the conventional AVR,+,PSS excitation system, are compared. Copyright © 2007 John Wiley & Sons, Ltd. [source] Physician or Clinical Inertia: What Is It?JOURNAL OF CLINICAL HYPERTENSION, Issue 1 2009Is It Really a Problem? First page of article [source] Therapeutic Inertia and the Medicare CrisisJOURNAL OF CLINICAL HYPERTENSION, Issue 9 2006DPhil, Thomas G. Pickering MD First page of article [source] The Determinants of Organizational Change and Structural Inertia: Technological and Organizational FactorsJOURNAL OF ECONOMICS & MANAGEMENT STRATEGY, Issue 4 2002Massimo G. Colombo There are a growing body of theoretical work, wide anecdotal evidence, and a few large-scale empirical studies supporting the view that business firms quite rarely change their organizational structure, a phenomenon usually referred to in the literature as structural inertia. The present paper aims to analyze empirically the determinants of structural inertia and organizational change. As far as we know, this work constitutes the first attempt to directly address such issues through econometric estimates based on a large, longitudinal dataset at plant level. For this purpose, we consider changes of the organizational structure within a sample composed of 438 Italian manufacturing plants observed from 1975 to 1996. More precisely, we specify and test a duration model of the likelihood of an individual plant changing the number of hierarchical tiers after a spell r, provided that no change has occurred up to T. We also analyze the direction of change, distinguishing increases from decreases of the number of managerial layers. We consider a set of plant- and industry-specific explanatory variables that are expected to induce or oppose organizational change. The findings show that the adoption of advanced manufacturing technologies and new human-resources management practices favors organizational change. On the contrary, the presence of sunk costs and the extent of influence activities figure prominently in explaining structural inertia of business organizations. [source] From Mass Production to Mass Customization: Hindrance Factors, Structural Inertia, and Transition HazardPRODUCTION AND OPERATIONS MANAGEMENT, Issue 3 2008M. Johnny Rungtusanatham Research on mass customization has largely overlooked the issue of organizational change associated with the mass production-to-mass customization transition. To address this gap in the literature, we conduct a longitudinal case study of a manufacturing facility belonging to a division of a Fortune 1000 discrete manufacturing firm as it seeks to transition from mass production to mass customization. We empirically identify five factors hindering the mass production-to-mass customization transition within the research site and articulate five corresponding generalizations explaining how and why these hindrance factors relate to the mass production-to-mass customization transition hazard beyond the research site (i.e., how and why the five hindrance factors, in general, threaten the likelihood of a successful mass production-to-mass customization transition). We then theoretically validate the five hindrance factors and corresponding generalizations by mapping them onto the antecedents and tenets of structural inertia theory. We conclude with a brief discussion of the scientific and pragmatic significance of the findings and highlight opportunities for future research. [source] Design Inertia: Designing for Life-Cycle Flexibility in Internet-Based Services,THE JOURNAL OF PRODUCT INNOVATION MANAGEMENT, Issue 3 2005Roberto Verganti Managing innovation in rapidly moving environments, such as Internet-based services, is a major challenge in theory and in practice. Most of the existing literature focuses on the development process as the main area in which innovation takes place. However, in environments where the pace of change of technology and market needs is extremely high, managing service innovations means not only being able to design a good service but also, more importantly, continuously redesigning and adapting the service in order to deal with frequent exogenous changes and opportunities. A high number of innovations therefore must be introduced throughout the entire life cycle of a service. This capability of introducing incremental and radical innovations during the service life cycle (i.e., to adapt a service to contextual changes and opportunities after it has been first released onto the market) at low costs and in the shortest possible time is what is defined here as service life-cycle flexibility. This process of service adaptation and upgrading implies significant challenges that can be traced back to when a service is first conceived and designed. In fact, many decisions made during the first design process (i.e., the choice of a given database environment) involve a low reversibility rate and may reduce the possibility of taking advantage of future unpredictable opportunities, creating what is called inertia toward innovation. In other words, service life-cycle flexibility largely depends on how a service has been first designed. This article analyzes two in-depth case studies of Italian online newspapers and identifies five possible inertia factors that may influence service life-cycle flexibility, namely (1) technological inertia; (2) internal organizational inertia; (3) external organizational inertia; (4) customer inertia toward changes in the service package; and (5) customer inertia toward changes in the service interaction design. These inertia factors are traced back to the service development process in order to suggest design practices that may increase the service life-cycle flexibility. [source] Rapid Human-Assisted Creation of Bounding Models for Obstacle Avoidance in ConstructionCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 1 2004J. McLaughlin A practical, interactive method for doing so is described here. The method: (1) exploits a human operator's ability to quickly recognize significant objects or clusters of objects in a scene, (2) exploits the operator's ability to acquire sparse range point clouds of the objects quickly, and then (3) renders models, such as planes, boxes, and generalized convex hulls, to be displayed graphically as visual feedback during equipment operation and/or for making proximity calculations in an obstacle detection system. Experiments were performed in which test subjects were asked to model objects of varying complexity and clutter. These models were then compared to control models using a ray-tracing algorithm to determine the operator's ability to create conservative models that are critical to construction operations. To demonstrate the applicability of the modeling method to obstacle avoidance, a scripted motion robot simulation was conducted using an artificial potential formulation that monitors position (closest point on manipulator link to nearest obstacle) as well as velocity (link inertia). Experimental results indicate that bounding models can be created rapidly and with sufficient accuracy for obstacle avoidance with the aid of human intelligence and that human-assisted modeling can be very beneficial for real-time construction equipment control. [source] Body size and host range in European HeteropteraECOGRAPHY, Issue 1 2000Martin Brändle We used data on body size and host range of phytophagous Heteroptera in central Europe, an inverse measure of specialisation, to analyse the relationship of body size vs specialisation: 1) we found a clear positive relationship between body size and host range using species as independent data points. 2) However, a nested analysis of variance shows that most of the variance in body size occurred at higher taxonomic levels whereas most of the variance in host specialisation occurred between species. This suggests different phylogenetic inertia of body size and specialisation. Nevertheless, using means of different higher taxonomic levels there is still a significant positive correlation between body size and host range. 3) With more sophisticated methods of correcting for the phylogenetic relatedness between species, the positive correlation between body size and host range still holds, despite the different assumptions of each method. Thus, the relationship between body size and host range is a very robust pattern in true bugs. [source] A Nolan Committee for the German ethics infrastructure?EUROPEAN JOURNAL OF POLITICAL RESEARCH, Issue 5 2002Nathalie Behnke An international trend towards establishing and conforming standards of ethical behaviour in the public sector has repeatedly been stated. Germany, however, remains surprisingly reluctant to adopt such recommendations. This article argues that the likelihood of German decision makers implementing new, and especially soft, ethics measures depends on the demand for such measures, on the one hand, and their supply, on the other. The analysis shows that contradictory forces have an impact on Germany. The demand for new ethics measures is relatively low as a high level of hard ethics measures incorporated in the longstanding formal legal system of rules and regulations make the implementation of new measures seem unnecessary. Also, the demand for soft ethics measures is less marked in Germany than in the United Kingdom. This comparatively weak pressure meets the natural inertia caused by cognitive and institutional path,dependency in institutional choices of political decision makers. On the other hand, external bodies (such as the Organisation for Economic Cooperation and Development , OECD) provide blueprints for soft ethics measures and encourage the implementation of uniform standards across countries. Which of these forces will prevail in the long run, however, cannot be deduced from the present situation. [source] A COMPARATIVE METHOD FOR STUDYING ADAPTATION TO A RANDOMLY EVOLVING ENVIRONMENTEVOLUTION, Issue 8 2008Thomas F. Hansen Most phylogenetic comparative methods used for testing adaptive hypotheses make evolutionary assumptions that are not compatible with evolution toward an optimal state. As a consequence they do not correct for maladaptation. The "evolutionary regression" that is returned is more shallow than the optimal relationship between the trait and environment. We show how both evolutionary and optimal regressions, as well as phylogenetic inertia, can be estimated jointly by a comparative method built around an Ornstein,Uhlenbeck model of adaptive evolution. The method considers a single trait adapting to an optimum that is influenced by one or more continuous, randomly changing predictor variables. [source] ASSESSING CURRENT ADAPTATION AND PHYLOGENETIC INERTIA AS EXPLANATIONS OF TRAIT EVOLUTION:THE NEED FOR CONTROLLED COMPARISONSEVOLUTION, Issue 10 2005Thomas F. Hansen Abstract The determination of whether the pattern of trait evolution observed in a comparative analysis of species data is due to adaptation to current environments, to phylogenetic inertia, or to both of these forces requires that one control for the effects of either force when making an assessment of the evolutionary role of the other. Orzack and Sober (2001) developed the method of controlled comparisons to make such assessments; their implementation of the method focussed on a discretely varying trait. Here, we show that the method of controlled comparisons can be viewed as a meta-method, which can be implemented in many ways. We discuss which recent methods for the comparative analysis of continuously distributed traits can generate controlled comparisons and can thereby be used to properly assess whether current adaptation and/or phylogenetic inertia have influenced a trait's evolution. The implementation of controlled comparisons is illustrated by an analysis of sex-ratio data for fig wasps. This analysis suggests that current adaptation and phylogenetic inertia influence this trait. [source] ESTIMATING PHYLOGENETIC INERTIA IN TITHONIA (ASTERACEAE): A COMPARATIVE APPROACHEVOLUTION, Issue 2 2000Eduardo Morales Abstract., Phylogenetic inertia is a difficult issue in evolutionary biology because we have yet to reach a consensus about how to measure it. In this study a comparative approach is used to evaluate phylogenetic inertia in 14 demographic and morphological characters in 10 species and one subspecies of the genus Tithonia (Asteraceae). Three different methods, autocorrelational analysis, phylogenetic correlograms, and ancestor-state reconstruction, were used to evaluate phylogenetic inertia in these traits. Results were highly dependent on the method applied. Autoregression and phylogenetic eigenvector regression (PVR) methods found more inertia in morphological traits. In contrast, phylogenetic correlograms and ancestor-state reconstruction suggest that morphological characters exhibit less phylogenetic inertia than demographic ones. The differences between results are discussed and methods are compared in an effort to understand phylogenetic inertia more thoroughly. [source] Machine Tools With Metal Foams,ADVANCED ENGINEERING MATERIALS, Issue 9 2006R. Neugebauer Abstract Machine tool construction calls for subassemblies with reduced weight while retaining excellent dynamic properties. Modern frame components do always meet required static stiffness but often display oscillation problems due to low component wall thicknesses. Breaking down solid steel structure into wide-area sandwich designs such as steel-aluminum foam-steel panels results in good static properties to be combined with excellent properties since these sandwiches have 30 to 40 times the flexural strength. This is due to their major geometrical moment of inertia in relation to adequate-mass steel sheet metals. In addition, the foam core dampens oscillations. Studies on foamed steel sections indicate that 2 to 3 times higher damping is likely in relation to unfoamed steel sections. These benefits were the motivation for the Chemnitz Metal Foam Center to accelerate development of extremely large-format sandwiches with dimensions of 1,500,×,1,000,mm2. [source] Axial Rotation of the Lower Human Spine by Rhythmic Torques Automatically Generated at the Resonant FrequencyEXPERIMENTAL PHYSIOLOGY, Issue 3 2003E. Geoffrey Walsh Subjects sat on a ,Balans' chair supported by the shaft of a large torque generator. The lower but not the upper part of the body was free to make to/fro movements maintained by feeding back a modified velocity signal to the generator. The stiffness could be increased by the use of a position signal. Using the equations for a torsion pendulum the good linearity observed in relationship to the applied forces allowed stiffness, inertia, damping, critical damping and the damping factor to be determined in absolute terms. The method enables parameters relevant to back function and problems to be evaluated. Eleven adults acted as subjects. [source] Inherent flammability parameters,Room corner test applicationFIRE AND MATERIALS, Issue 8 2009J. G. Quintiere Abstract It has been hypothesized that four parameters are solely responsible for a material's performance in a flammability scenario. This excludes effects of material physical integrity, i.e. melting, delamination, etc. They are (1) the critical heat flux below which piloted ignition cannot occur (CHF), (2) the ratio of heat of combustion to heat of gasification (HRP), (3) the thermal response parameter related to the thermal inertia and the ignition temperature (TRP), and (4) the available energy per unit area (AEP). The fire scenario controls the process by its initial heat flux and region of ignition. The hypothesis is applied to 54 tests of the ISO Room Corner Test to assess its validity. It is shown that these four parameters give good correlations in predicting the time to flashover and whether it occurs. In principle, different correlations could be developed for other scenarios of tests and fire configurations. Copyright © 2009 John Wiley & Sons, Ltd. [source] The loose coupling mechanism in molecular machines of living cellsGENES TO CELLS, Issue 1 2000Fumio Oosawa Living cells have molecular machines for free energy conversion, for example, sliding machines in muscle and other cells, flagellar motors in bacteria, and various ion pumps in cell membranes. They are constructed from protein molecules and work in the nm (nanometer), pN (piconewton) and ms (millisecond) ranges, without inertia. In 1980s, a question was raised of whether the input,output or influx,efflux coupling in these molecular machines is tight or loose, and an idea of loose coupling was proposed. Recently, the long-distance multistep sliding of a single myosin head on an actin filament, coupled with the hydrolysis of one ATP molecule, was observed by Yanagida's group using highly developed techniques of optical microscopy and micromanipulation. This gave direct evidence for the loose coupling between the chemical reaction and the mechanical event in the sliding machine. In this review, I will briefly describe a historical overview of the input,output problem in the molecular machines of living cells. [source] Partitioning phylogenetic and adaptive components of the geographical body-size pattern of New World birdsGLOBAL ECOLOGY, Issue 1 2008Lizabeth Ramirez ABSTRACT Aim To evaluate seasonal body-size patterns for New World birds in geographical space, to develop environmental models to explain the gradients, and to estimate phylogenetic and adaptive contributions. Location The Western Hemisphere. Methods We used range maps to generate gridded geometric mean body masses. Summer and winter patterns were distinguished based on breeding and non-breeding ranges. We first generated the geographical gradients, followed by phylogenetic eigenvector regression to generate body sizes predicted by the birds' positions in a phylogenetic tree, which were used to generate the expected phylogenetic gradient. Subtracting the expected pattern from the observed pattern isolated the adaptive component. Ordinary least squares multiple-regression models examined factors influencing the phylogenetic, adaptive and combined components of the seasonal body-size patterns, and non-spatial and spatial models were compared. Results Birds are larger in the temperate zones than in the tropics. The gradient is quantitatively stronger in winter than in summer. Regression models explained 66.6% of the variance in summer mass and 45.9% of the variance in winter mass. In summer, phylogenetic and adaptive responses of birds contribute equally to the gradient. In winter, the gradient in North America is much stronger than that expected by taxonomic turnover, and responses of species independent of their family membership drive the overall pattern. Main conclusions We confirm Bergmann's rule in New World birds and conclude that winter temperatures ultimately drive the pattern, exerting selection pressures on birds that overwhelm patterns expected by phylogenetic inertia at the family level. However, in summer, the movement of migratory species into the temperate zone weakens the gradient and generates a pattern more congruent with that expected from the taxonomic composition of the fauna. The analytical method we develop here represents a useful tool for partitioning the phylogenetic and non-phylogenetic components of spatially explicit macroecological data. [source] Mammals in South American drylands: faunal similarity and trophic structureGLOBAL ECOLOGY, Issue 2 2000Ricardo A. Ojeda Abstract We compared the fauna of small mammals (less than 500 g body weight) among five major South American drylands (Atacama, Altiplano, Monte, Patagonia and Caatinga) and found considerable heterogeneity and distinctiveness in species richness and composition between these biomes. From a total of 89 recorded species, 76 of them are restricted to only one of these drylands. The highland desert, or Altiplano, is the biome with the highest number of species. Despite the marked differences in the composition of the mammalian fauna, the trophic structure shows a rather consistent pattern: herbivores are the most important trophic group in all drylands. This consistency seems to be more the result of phylogenetic inertia than of similar ecological processes. Our results are compared with recent studies on desert small mammals across continents. [source] A Closed Form Slug Test Theory for High Permeability AquifersGROUND WATER, Issue 1 2005David W. Ostendorf We incorporate a linear estimate of casing friction into the analytical slug test theory of Springer and Gelhar (1991) for high permeability aquifers. The modified theory elucidates the influence of inertia and casing friction on consistent, closed form equations for the free surface, pressure, and velocity fluctuations for overdamped and under-damped conditions. A consistent, but small, correction for kinetic energy is included as well. A characteristic velocity linearizes the turbulent casing shear stress so that an analytical solution for attenuated, phase shifted pressure fluctuations fits a single parameter (damping frequency) to transducer data from any depth in the casing. Underdamped slug tests of 0.3, 0.6, and 1 m amplitudes at five transducer depths in a 5.1 cm diameter PVC well 21 m deep in the Plymouth-Carver Aquifer yield a consistent hydraulic conductivity of 1.5 × 10,3 m/s. The Springer and Gelhar (1991) model underestimates the hydraulic conductivity for these tests by as muchas 25% by improperly ascribing smooth turbulent casing friction to the aquifer. The match point normalization of Butler (1998) agrees with our fitted hydraulic conductivity, however, when friction is included in the damping frequency. Zurbuchen et al. (2002) use a numerical model to establish a similar sensitivity of hydraulic conductivity to nonlinear casing friction. [source] Poverty and Local Governments: Economic Development and Community Service Provision in an Era of DecentralizationGROWTH AND CHANGE, Issue 3 2009LINDA LOBAO ABSTRACT Social scientists have given substantial attention to poverty across U.S. localities. However, most work views localities through the lens of population aggregates, not as units of government. Few poverty researchers question whether governments of poorer localities have the capacity to engage in economic development and service activities that might improve community well-being. This issue is increasingly important as responsibilities for growth and redistribution are decentralized to local governments that vary dramatically in resources. Do poorer communities have less activist local governments? Are they more likely to be engaged in a race to the bottom, focusing on business attraction activities but neglecting services for families and working people? We bring together two distinct literatures, critical research on decentralization and research on local development efforts, that provide contrasting views about the penalty of poverty. Data are from a unique, national survey of county governments measuring activity across two time points. The most consistent determinants of activity are local government capacity, devolutionary pressures, and inertia or past use of strategies. Net of these factors, levels and changes in poverty do not significantly impact government activity. There is no evidence the nations' poorest counties are racing to the bottom. Findings challenge views that poverty is a systematic structural barrier to pursuing innovative economic development policies and suggest that even poorer communities can take steps to build local capacity, resources, and networks that expand programs for local businesses and low-wage people. [source] European health policy challengesHEALTH ECONOMICS, Issue S1 2005Alan Maynard Abstract Few countries are immune to the international health care ,virus' of reform, with many countries regularly re-cycling changes that shift costs and benefits in ways that are arbitrary, inefficient and offer short term political palliation. Much of this activity has little evidence base and reveals lack of clarity in defining public policy goals, establishing trade-offs and aligning incentive structures with these objectives. Well established failures in health care delivery systems such as variations in medical practice and continuing absence of systematic outcome measurement, have persisted for decades as nations grapple inefficiently with recurring problems of expenditure inflation and waiting times. The lack of emphasis on evidence to inform the efficient management of chronic disease and the reduction of health inequalities is a product of perverse incentives and managerial inertia that maintains the incomes of powerful interest groups. Copyright © 2005 John Wiley & Sons, Ltd. [source] Analysis of flow and heat transfer in evaporator porous wicking structure of a flat heat pipeHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2009Congxiang Hu Abstract With a specified pressure distribution, an analytical investigation was conducted to explore the flow and heat transfer characteristics in an evaporator porous wicking structure of a flat heat pipe. The boundary effect on the flow rate is more significant than the inertia, and both the boundary and inertia effects exert very little influence on fluid layer thickness and velocity distribution. The bottom of the porous layer is at a quite uniform temperature, and the heat flux is almost normal to the solid boundary. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20237 [source] HR, ERP, and knowledge for competitive advantageHUMAN RESOURCE MANAGEMENT, Issue 2 2006Cynthia A. Lengnick-Hall Enterprise resource planning (ERP) systems are a strong fit with organizations dominated by routine, highly programmed technologies, and tightly regulated operations. However, while these settings are best suited for ERP implementation, they also have the greatest difficulty making use of the knowledge ERP systems generate because of their inherent rigidity, inertia, and resistance to change. This article examines how human resource management practices can help a firm overcome the problems and capitalize on the opportunities that ERP technology presents by facilitating an effective dual-core structure through an emphasis on knowledge management, human capital stewardship, and relationship building. © 2006 Wiley Periodicals, Inc. [source] Ultrasonic Nanofabrication with an AFMIMAGING & MICROSCOPY (ELECTRONIC), Issue 4 2007Nanomanipulation, Ultrasound Facilitates Nanolithography Abstract Ultrasonic AFM may improve fabrication technologies on the nanometer scale. In the presence of ultrasonic vibration, hard surfaces can be indented and scratched with the tip of a soft cantilever, due to its inertia. Ultrasound reduces or even eliminates friction, and hence modifies the tip-nanoparticle-surface interactions in AFM manipulation. The subsurface sensitivity of the technique makes feasible the purposed manipulation of subsurface nanoscale features by ultrasonic actuation. [source] Indentation of a free-falling lance penetrometer into a poroelastic seabedINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2005Derek Elsworth Abstract A solution is developed for the build-up, steady and post-arrest dissipative pore fluid pressure fields that develop around a blunt penetrometer that self-embeds from freefall into the seabed. Arrest from freefall considers deceleration under undrained conditions in a purely cohesive soil, with constant shear strength with depth. The resulting decelerating velocity field is controlled by soil strength, geometric bearing capacity factors, and inertial components. At low impact velocities the embedment process is controlled by soil strength, and at high velocities by inertia. With the deceleration defined, a solution is evaluated for a point normal dislocation penetrating in a poroelastic medium with a prescribed decelerating velocity. Dynamic steady pressures, PD, develop relative to the penetrating tip geometry with their distribution conditioned by the non-dimensional penetration rate, UD, incorporating impacting penetration rate, consolidation coefficient and penetrometer radius, and the non-dimensional strength, ND, additionally incorporating undrained shear strength of the sediment. Pore pressures develop to a steady peak magnitude at the penetrometer tip, and drop as PD=1/xD with distance xD behind the tip and along the shaft. Peak induced pressure magnitudes may be correlated with sediment permeabilities, post-arrest dissipation rates may be correlated with consolidation coefficients, and depths of penetration may be correlated with shear strengths. Together, these records enable strength and transport parameters to be recovered from lance penetrometer data. Penetrometer data recorded off La Palma in the Canary Islands (J. Volcanol. Geotherm. Res. 2000; 101:253) are used to recover permeabilities and consolidation coefficients from peak pressure and dissipation response, respectively. Copyright © 2004 John Wiley & Sons, Ltd. [source] Instationary aeroelastic computation of yacht sailsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 8 2001Heinrich Schoop Abstract Effective schemes exist to calculate aerodynamic forces for thin bodies and structural dynamics of flexible membranes. The fluid dynamic of thin wings in a irrotational flow leads to the lifting surface theory. Neglecting the inertia of the membrane the structural dynamics are solved by the non-linear (FEM). But the interaction of flexible membranes and an irrotational flow causes problems due to the different nature of the mathematical equations. On the one hand, there is a partial differential equation for the structural dynamics and on the other hand, there is a singular integral equation for the aerodynamics. The numerical discretization scheme has to fit these different types of equation. Our work introduces a new interaction scheme to couple the singular integral equation of the lifting surface theory with the non-linear FEM of the membrane static. The fundamental examinations, showed by Schoop et al. (International Journal for Numerical Methods in Engineering 1998; 41: 217,219), are applied to realistic sail geometries and the aerodynamics is extended to instationary flow conditions. Copyright © 2001 John Wiley & Sons, Ltd. [source] Free vibrations of shear-flexible and compressible arches by FEMINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2001Przemyslaw Litewka Abstract The purpose of this paper is to analyse free vibrations of arches with influence of shear and axial forces taken into account. Arches with various depth of cross-section and various types of supports are considered. In the calculations, the curved finite element elaborated by the authors is adopted. It is the plane two-node, six-degree-of-freedom arch element with constant curvature. Its application to the static analysis yields the exact results, coinciding with the analytical ones. This feature results from the use of the exact shape functions in derivation of the element stiffness matrix. In the free vibration analysis the consistent mass matrix is used. It is obtained on the base of the same functions. Their coefficients contain the influences of shear flexibility and compressibility of the arch. The numerical results are compared with the results obtained for the simple diagonal mass matrix representing the lumped mass model. The natural frequencies are also compared with the ones for the continuous arches for which the analytically determined frequencies are known. The advantage of the paper is a thorough analysis of selected examples, where the influences of shear forces, axial forces as well as the rotary and tangential inertia on the natural frequencies are examined. Copyright © 2001 John Wiley & Sons, Ltd. [source] Transient free-surface flow of a viscoelastic fluid in a narrow channelINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2004Roger E. Khayat Abstract The interplay between inertia and elasticity is examined for transient free-surface flow inside a narrow channel. The lubrication theory is extended for the flow of viscoelastic fluids of the Oldroyd-B type (consisting of a Newtonian solvent and a polymeric solute). While the general formulation accounts for non-linearities stemming from inertia effects in the momentum conservation equation, and the upper-convected terms in the constitutive equation, only the front movement contributes to non-linear coupling for a flow inside a straight channel. In this case, it is possible to implement a spectral representation in the depthwise direction for the velocity and stress. The evolution of the flow field is obtained locally, but the front movement is captured only in the mean sense. The influence of inertia, elasticity and viscosity ratio is examined for pressure-induced flow. The front appears to progress monotonically with time. However, the velocity and stress exhibit typically a strong overshoot upon inception, accompanied by a plug-flow behaviour in the channel core. The flow intensity eventually diminishes with time, tending asymptotically to Poiseuille conditions. For highly elastic liquids the front movement becomes oscillatory, experiencing strong deceleration periodically. A multiple-scale solution is obtained for fluids with no inertia and small elasticity. Comparison with the exact (numerical) solution indicates a wide range of validity for the analytical result. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||||||||||||||||||||||||||