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Dynamic Stiffness (dynamic + stiffness)

Distribution by Scientific Domains

Engineering	81%
Medical Sciences	12%

Selected Abstracts

Dynamic stiffness of deep foundations with inclined piles

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 12 2010
L. A. Padrón
Abstract The influence of inclined piles on the dynamic response of deep foundations and superstructures is still not well understood and needs further research. For this reason, impedance functions of deep foundations with inclined piles, obtained numerically from a boundary element,finite element coupling model, are provided in this paper. More precisely, vertical, horizontal, rocking and horizontal,rocking crossed dynamic stiffness and damping functions of single inclined piles and 2 × 2 and 3 × 3 pile groups with battered elements are presented in a set of plots. The soil is assumed to be a homogeneous viscoelastic isotropic half-space and the piles are modeled as elastic compressible Euler,Bernoulli beams. The results for different pile group configurations, pile,soil stiffness ratios and rake angles are presented. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Dynamic stiffness for piecewise non-uniform Timoshenko column by power series,part I: Conservative axial force

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2001
A. Y. T. Leung
Abstract The dynamic stiffness method uses the solutions of the governing equations as shape functions in a harmonic vibration analysis. One element can predict many modes exactly in the classical sense. The disadvantages lie in the transcendental nature and in the need to solve a non-linear eigenproblem for the natural modes, which can be solved by the Wittrick,William algorithm and the Leung theorem. Another practical problem is to solve the governing equations exactly for the shape functions, non-uniform members in particular. It is proposed to use power series for the purpose. Dynamic stiffness matrices for non-uniform Timoshenko column are taken as examples. The shape functions can be found easily by symbolic programming. Step beam structures can be treated without difficulty. The new contributions of the paper include a general formulation, an extended Leung's theorem and its application to parametric study. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Dynamic stiffness for piecewise non-uniform Timoshenko column by power series,part II: Follower force

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2001
A. Y. T. Leung
Abstract A follower force is an applied force whose direction changes according to the deformed shape during the course of deformation. The dynamic stiffness matrix of a non-uniform Timoshenko column under follower force is formed by the power-series method. The dynamic stiffness matrix is unsymmetrical due to the non-conservative nature of the follower force. The frequency-dependent mass matrix is still symmetrical and positive definite according to the extended Leung theorem. An arc length continuation method is introduced to find the influence of a concentrated follower force, distributed follower force, end mass and stiffness, slenderness, and taper ratio on the natural frequency and stability. It is found that the power-series method can handle a very wide class of dynamic stiffness problem. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Dynamische Steifigkeit und Dämpfung von Pfahlgruppen

BAUTECHNIK, Issue 2 2009
Hamid Sadegh-Azar Dr.-Ing.
Geotechnik; Bodenmechanik Abstract In diesem Beitrag werden die dynamische Steifigkeit und Dämpfung von Pfahlgruppen und ihre Auswirkung auf die Auslegung und Wirtschaftlichkeit der Pfahlgründung selbst und der Bauwerke darauf untersucht. Die Berechungen werden mit der sogenannten "Thin-Layer-Method", einer sehr leistungsfähigen Berechnungsmethode im Frequenzbereich, durchgeführt (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) Dynamic stiffness and damping properties of pile groups. The dynamic stiffness and damping properties of pile-groups have been investigated in this paper. Also, the substantial influence of these properties on an economic structure and foundation design is demonstrated. The analysis has been carried out using the "Thin-Layer-Method", which is a very efficient and powerful analysis procedure in frequency domain. [source]

Dynamic stiffness of deep foundations with inclined piles

A practical method for estimating dynamic soil stiffness on surface of multi-layered soil

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 11 2005
Naohiro Nakamura
Abstract It is important to estimate the influence of layered soil in soil,structure interaction analyses. Although a great number of investigations have been carried out on this subject, there are very few practical methods that do not require complex calculations. In this paper, a simple and practical method for estimating the horizontal dynamic stiffness of a rigid foundation on the surface of multi-layered soil is proposed. In this method, waves propagating in the soil are traced using the conception of the cone model, and the impulse response function can be calculated directly and easily in the time domain with a good degree of accuracy. The characteristics of the impedance, that is the transformed value to the frequency domain of the obtained impulse response, are studied using two- to four-layered soil models. The cause of the fluctuation of impedance is expressed clearly from its relation to reflected waves from the lower layer boundary in the model. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Kinematic response functions and dynamic stiffnesses of bridge embankments

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 11 2002
Jian Zhang
Abstract Recognizing that soil,structure interaction affects appreciably the earthquake response of highway overcrossings, this paper compares approximate analytical solutions and finite element results to conclude on a simple procedure that allows for the estimation of the kinematic response functions and dynamic stiffnesses of approach embankments. It is shown that the shear-wedge model yields realistic estimates for the amplification functions of typical embankments and reveals the appropriate levels of dynamic strains which are subsequently used to estimate the stiffness and damping coefficients of embankments. The shear-wedge model is extended to a two-dimensional model in order to calculate the transverse static stiffness of an approach embankment loaded at one end. The formulation leads to a sound closed-form expression for the critical length, Lc, that is the ratio of the transverse static stiffness of an approach embankment and the transverse static stiffness of a unit-width wedge. It is shown through two case studies that the transverse dynamic stiffness (,spring' and ,dashpot') of the approach embankment can be estimated with confidence by multiplying the dynamic stiffness of the unit-width wedge with the critical length, Lc. The paper concludes that the values obtained for the transverse kinematic response function and dynamic stiffness can also be used with confidence to represent the longitudinal kinematic response function and dynamic stiffness, respectively. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Response of unbounded soil in scaled boundary finite-element method

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2002
John P. Wolf
Abstract The scaled boundary finite-element method is a powerful semi-analytical computational procedure to calculate the dynamic stiffness of the unbounded soil at the structure,soil interface. This permits the analysis of dynamic soil,structure interaction using the substructure method. The response in the neighbouring soil can also be determined analytically. The method is extended to calculate numerically the response throughout the unbounded soil including the far field. The three-dimensional vector-wave equation of elasto-dynamics is addressed. The radiation condition at infinity is satisfied exactly. By solving an eigenvalue problem, the high-frequency limit of the dynamic stiffness is constructed to be positive definite. However, a direct determination using impedances is also possible. Solving two first-order ordinary differential equations numerically permits the radiation condition and the boundary condition of the structure,soil interface to be satisfied sequentially, leading to the displacements in the unbounded soil. A generalization to viscoelastic material using the correspondence principle is straightforward. Alternatively, the displacements can also be calculated analytically in the far field. Good agreement of displacements along the free surface and below a prism foundation embedded in a half-space with the results of the boundary-element method is observed. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Functional consequences of cartilage degeneration in the equine metacarpophalangeal joint: quantitative assessment of cartilage stiffness

EQUINE VETERINARY JOURNAL, Issue 5 2005
H. BROMMER
Summary Reasons for performing study: No quantitative data currently exist on the relationship of the occurrence of cartilage degeneration and changes in site-specific biomechanical properties in the metacarpophalangeal (MCP) joint in the horse. Objectives: To gain insight into the biomechanical consequences of cartilage deterioration at 2 differently loaded sites on the proximal articular surface of the proximal phalanx (P1). Hypothesis: Static and dynamic stiffness of articular cartilage decreases significantly in degenerated cartilage. Methods: Cartilage degeneration index (CDI) values were measured at the lateral dorsal margin (Site 1), lateral central fovea (Site 2) and entire joint surface of P1 (CDIP1) in 30 horses. Group 1 contained joints without (CDIP1 values <25%, n = 22) and Group 2 joints with (CDIP1 values >25%, n = 8) signs of cartilage degeneration. Cartilage thickness at Sites 1 and 2 was measured using ultrasonic and needle-probe techniques. Osteochondral plugs were drilled out from Sites 1 and 2 and subsequently tested biomechanically in indentation geometry. Young's modulus at equilibrium and dynamic modulus were determined. Results: Cartilage thickness values were not significantly different between the 2 groups and sites. Young's modulus at Site 1 was significantly higher in Group 1 than in Group 2; at Site 2, the difference was not significant. Dynamic modulus values were significantly higher in Group 1 than in Group 2 at both sites. Conclusions: Degenerative cartilage changes are clearly related to loss of stiffness of the tissue. Absolute changes in cartilage integrity in terms of CDI are greatest at the joint margin, but concomitant changes are also present at the centre, with a comparable decrease of the biomechanical moduli at the 2 sites. Therefore, significant cartilage degradation at the joint margin not only reflects local deterioration of biomechanical properties, but is also indicative of the functional quality in the centre. Potential relevance: These findings may be important for improving prognostication and developing preventative measures. [source]

A continued-fraction-based high-order transmitting boundary for wave propagation in unbounded domains of arbitrary geometry

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2008
Mohammad Hossein Bazyar
Abstract A high-order local transmitting boundary is developed to model the propagation of elastic waves in unbounded domains. This transmitting boundary is applicable to scalar and vector waves, to unbounded domains of arbitrary geometry and to anisotropic materials. The formulation is based on a continued-fraction solution of the dynamic-stiffness matrix of an unbounded domain. The coefficient matrices of the continued fraction are determined recursively from the scaled boundary finite element equation in dynamic stiffness. The solution converges rapidly over the whole frequency range as the order of the continued fraction increases. Using the continued-fraction solution and introducing auxiliary variables, a high-order local transmitting boundary is formulated as an equation of motion with symmetric and frequency-independent coefficient matrices. It can be coupled seamlessly with finite elements. Standard procedures in structural dynamics are directly applicable for evaluating the response in the frequency and time domains. Analytical and numerical examples demonstrate the high rate of convergence and efficiency of this high-order local transmitting boundary. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Fractional calculus applied to radiation damping

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003
C. Trinks Dipl.-Ing.
Separate treatment of the low, and high,frequency part of the dynamic stiffness is essential when approximating the latter in the frequency,domain. In this paper, a doubly,asymptotic rational approximation of the low,frequency part is combined with an analytical interpretation of the asymptotic part leading to a system of fractional differential equations to represent the force,displacement relationship. Here, an analogy between fading memory of viscoelastic materials and radiation damping of unbounded domains is visible. [source]

Polymorphisms in eggshell organic matrix genes are associated with eggshell quality measurements in pedigree Rhode Island Red hens

ANIMAL GENETICS, Issue 1 2009
I. C. Dunn
Summary Novel and traditional eggshell quality measurements were made from up to 2000 commercial pedigree hens for a candidate gene association analysis with organic eggshell matrix genes: ovocleidin-116, osteopontin (SPP1), ovocalyxin-32 (RARRES1), ovotransferrin (LTF), ovalbumin and ovocalyxin-36, as well as key genes in the maintenance and function of the shell gland [estrogen receptor (ESR1) and carbonic anhydrase II (CAII)]. Associations were found for (i) ovalbumin with breaking strength and shell thickness; (ii) ovocleidin-116 with elastic modulus, shell thickness and egg shape; (iii) RARRES1 with mammillary layer thickness; (iv) ESR1 with dynamic stiffness; (v) SPP1 with fracture toughness and (vi) CAII with egg shape. The marker effects are as large as 17% of trait standard deviations and could be used to improve eggshell quality. [source]

Vulnerability of the superficial zone of immature articular cartilage to compressive injury

ARTHRITIS & RHEUMATISM, Issue 10 2010
Bernd Rolauffs
Objective The zonal composition and functioning of adult articular cartilage causes depth-dependent responses to compressive injury. In immature cartilage, shear and compressive moduli as well as collagen and sulfated glycosaminoglycan (sGAG) content also vary with depth. However, there is little understanding of the depth-dependent damage caused by injury. Since injury to immature knee joints most often causes articular cartilage lesions, this study was undertaken to characterize the zonal dependence of biomechanical, biochemical, and matrix-associated changes caused by compressive injury. Methods Disks from the superficial and deeper zones of bovine calves were biomechanically characterized. Injury to the disks was achieved by applying a final strain of 50% compression at 100%/second, followed by biomechanical recharacterization. Tissue compaction upon injury as well as sGAG density, sGAG loss, and biosynthesis were measured. Collagen fiber orientation and matrix damage were assessed using histology, diffraction-enhanced x-ray imaging, and texture analysis. Results Injured superficial zone disks showed surface disruption, tissue compaction by 20.3 ± 4.3% (mean ± SEM), and immediate biomechanical impairment that was revealed by a mean ± SEM decrease in dynamic stiffness to 7.1 ± 3.3% of the value before injury and equilibrium moduli that were below the level of detection. Tissue areas that appeared intact on histology showed clear textural alterations. Injured deeper zone disks showed collagen crimping but remained undamaged and biomechanically intact. Superficial zone disks did not lose sGAG immediately after injury, but lost 17.8 ± 1.4% of sGAG after 48 hours; deeper zone disks lost only 2.8 ± 0.3% of sGAG content. Biomechanical impairment was associated primarily with structural damage. Conclusion The soft superficial zone of immature cartilage is vulnerable to compressive injury, causing superficial matrix disruption, extensive compaction, and textural alteration, which results in immediate loss of biomechanical function. In conjunction with delayed superficial sGAG loss, these changes may predispose the articular surface to further softening and tissue damage, thus increasing the risk of development of secondary osteoarthritis. [source]