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1
Houdebert, Pierre. "Continuum Random Cluster Model." Thesis, Lille 1, 2017. http://www.theses.fr/2017LIL10042/document.
Full textAbstract:
Cette thèse s'intéresse au Continuum Random Cluster Model (CRCM), modèle gibbsien de boules aléatoires où la densité dépend du nombre de composantes connexes de la structure. Ce modèle est une version continue du Random Cluster Model introduit pour unifier l'étude des modèles d'Ising et de Potts. Le CRCM fut introduit pour sa relation avec le modèle de Widom-Rowlinson, fournissant une nouvelle preuve de la transition de phase pour ce modèle. Dans cette thèse nous étudions dans un premier temps l'existence du CRCM en volume infinie. Dans le cas extrême des rayons non-intégrables, nous démontrons un résultat de non-unicité du CRCM en petite activité. Nous conjecturons de plus que l'unicité serait obtenue en grande activité. Une version faible de cette conjecture est démontré en dimension 1. Dans un second temps nous étudions la percolation du CRCM, qui s'intéresse aux propriétés de connectivité et en particulier à l'existence d'une composante connexe infinie. La percolation est d'autant plus cohérente pour le CRCM dont l'interaction dépend directement de la connectivité de la structure. Nous montrons dans cette thèse l'absence de percolation en petite activité et la percolation en grande activité. Ce résultat permet de généraliser la transition de phase du modèle de Widom-Rowlinson à des rayons non bornésThis thesis focuses on the Continuum Random Cluster Model (CRCM), defined as a Gibbs model of random balls where the density depends on the number of cluster in the structure. This model is a continuum version of the Random Cluster Model introduced to unify the study of the Ising and Potts model. The CRCM was introduced for its links with the Widom-Rowlinson model, which led to a new proof of the phase transition for this model. In this thesis we first study the existence of the model in the infinite volume regime. In the extreme setting of non integrable radii, we prove for small activities the non-uniqueness of a CRCM. We conjecture that the uniqueness would be revovered for large activities. A weak version of the conjecture is proved.We alson study the percolation of the CRCM, which is the existence of at least one unbounded connected component. Percolation is more relevant for the CRCM since the interaction depends on the connectivity of the structure. We prove the absence of percolation for small activities and percolation for large activities. This results leads to the phase transition of the Widom-Rowlinson model with unbounded radii
2
Tashman, Laith. "Microstructural viscoplastic continuum model for asphalt concrete." Diss., Texas A&M University, 2003. http://hdl.handle.net/1969.1/313.
Full textAbstract:
This dissertation presents the development of an anisotropic viscoplastic continuum damage model to describe the permanent deformation of asphalt pavements. The model is developed to account for several phenomena that influence the permanent deformation of Asphalt Concrete (AC) at high temperatures. These phenomena include strain rate dependency, confining pressure dependency, dilation, aggregate friction, anisotropy, and damage. The model is based on Perzyna's theory of viscoplasticity with Drucker-Prager yield function modified to account for the microstructure anisotropy and damage. A parametric study was conducted to study the effect of key factors such as inherent anisotropy and damage on the model response. A preliminary investigation was conducted to demonstrate the capabilities of the model and its sensitivity to changes in the microstructure distribution and loading conditions. The model was used to describe laboratory experimental measurements obtained from the Federal Highway Administration (FHWA) Accelerated Loading Facility (ALF). The model had a good match with these experimental measurements. In particular, using the damage parameter, the model was able to capture the point at which AC experienced tertiary creep in a static creep test. A comprehensive experiment was conducted to systematically determine the model parameters and the evolution laws that describe AC hardening, anisotropy, and damage. The experiment consisted of a set of compressive triaxial strength tests conducted at three confining pressures and five strain rates. Based on these experimental measurements, the model was modified to include a nonassociated flow rule. The model was shown to capture the experimental measurements very well. Furthermore, an experiment was conducted to capture and characterize damage evolution in AC due to permanent deformation. AC specimens were loaded using a triaxial compression setup to four predefined strain levels at three confining pressures. X-Ray computed tomography and image analysis techniques were used to capture and characterize the evolution of cracks and air voids in the deformed specimens. Damage was found to be a localized phenomenon in the sense that there exists a critical section in an AC specimen that is mainly responsible for failure. The results of the damage experiment supported the damage evolution function proposed in the viscoplastic model.
3
Jearanaisilawong, Petch 1979. "A continuum model for needlepunched nonwoven fabrics." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44751.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008."June 2008."
Includes bibliographical references (p. 159-166).
Nonwoven fabrics are sheet structures created by bonding or interlocking a web (network) of fibers through mechanical, thermal or chemical processes. In general, the mechanical response of nonwoven fabrics exhibits two major characteristics. First, the mechanical response can vary significantly when the fabric is loaded along different directions, depending on the existence of a preferential orientation in the fiber arrangement and/or in the pattern of inter-fiber bonding/entanglement. Second, the mechanisms of deformation include elastic and inelastic components, accompanied by an irrecoverable evolution of the texture of the fiber network. In this work, we propose a three-dimensional, large strain continuum model for the constitutive behavior of nonwoven fabrics that accounts for the fiber network characteristics responsible for its anisotropic behavior, and captures the effects of deformation mechanisms at the micro-scale (fiber and bonds/entanglement) level. The model consists of two constitutive components: a nonlinear elastic component representing the resistances to recoverable deformation mechanisms, and a non-linear inelastic component representing the resistances to irrecoverable deformation and texture evolution. For nonwoven fabrics in which the anisotropy of fiber orientation is combined with random entanglement processes, we propose to capture the combined effects of fibers and junctions orientation distributions using a single tensorial representation of the network anisotropy (fabric ellipsoid). An orthotropic elastic constitutive model for the elastic response of nonwoven fabrics is then formulated based on this structural measure and deformation mechanisms of the network structure. The inelastic component of the model is then prescribed in terms of an evolution law for the fabric ellipsoid.
(cont.) A needlepunched web of high strength polyethylene fibers, "Dyneema Fraglight", is selected as the representative material, to be used as a test case to validate the proposed modeling approach. The model is shown to capture the macroscopic nonlinear anisotropic elastic-inelastic response of the fabric in planar deformation, as well as the underlying micromechanical deformation mechanisms, such as fiber stretch, and irrecoverable evolution of fabric texture. The proposed model can be used to predict the mechanical behavior of nonwoven fabrics and can be combined with other continuum models to aid in the design of multi-component structures. In addition, the proposed elastic formulation can be used to model different classes of anisotropic network materials, such as biological tissues, and tissue engineering scaffolds.
bu Petch Jearanaisilawong.
Ph.D.
4
Attaran, Abdolhamid, Jörg Brummund, and Thomas Wallmersperger. "Development of a continuum model for ferrogels." Sage, 2017. https://tud.qucosa.de/id/qucosa%3A35627.
Full textAbstract:
A systematic development of a continuum model is presented, which is capable of describing the magneto-mechanical behavior of magnetic polymer gels commonly referred to as ‘‘ferrogels’’. In the present research, ferrogels are treated as multicomponent, multiphase materials. They consist of a polymer network (P), fixed magnetic particles (f), mobile magnetic particles (m), and liquid (L). By considering ferrogels as multicomponent materials, interaction among constituents of ferrogels can be captured. This helps in understanding the process occurring inside ferrogels under the influence of external stimuli, such as magnetic fields. In our modeling approach, the field equations of ferrogels are derived within the framework of the theory of mixtures. The basic equations include Maxwell’s equations, balance of mass, linear momentum, angular momentum, energy, and entropy. In the framework of the theory of mixtures, balance relations are first presented at the constituent level also referred to as partial balance relations. By summing partial balance relations over all constituents and imposing the restrictions of theory of mixtures, balance relations of mixture (for the ferrogel) are obtained. In the current work the specific magnetization (magnetization per density) is considered as an evolving variable. It is demonstrated that balance of angular momentum is satisfied using the evolution equation of specific magnetization and constitutive laws. In the process of modeling, a suitable free energy function is introduced and thermodynamically consistent constitutive laws are formulated. Introducing certain assumptions, a reduced model of the ferrogel, a coupled magneto-mechanical formulation, is subsequently presented. The reduced model consists only of a polymer network (P) and fixed magnetic particles (f). It is concluded that the reduced model compares well to the existing ones in the literature. The magneto-mechanical problem based on the reduced model is solved in 2D using the finite element method. The only unknowns for the finite element method implementation are mechanical displacement and magnetic potential. Deformation of a ferrogel in a magnetic field is subsequently investigated. Elongation and contraction of a ferrogel are observed when a magnetic field is applied in the x- and y-directions, respectively. The numerical results were compared with existing experimental work in the literature. A good qualitative agreement was found between numerical and experimental results.
5
Kulkarni, Sunil B. "A continuum model for foam generating processes /." The Ohio State University, 1999. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488187049540819.
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6
Senozan, Selma. "A Continuum Model For Decoherence In 1d Transport." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606703/index.pdf.
Full textAbstract:
In this thesis we study the conductance of a one dimensional conductor in the presence of dephasing. Dephasing effects are modelled after generalizing Büttiker&rsquo
s dephasing model (Phys. Rev. B 33, 3020 (1986)) to a continuous one. Infinitely many electron reservoirs are coupled to the conductor as phase breakers and the method for calculating the conductance is presented. We investigate how this continuum decoherence effect the conductance of a wire, with single and double rectangular barriers.
7
Su, Cheng Ph D. Massachusetts Institute of Technology. "A continuum constitutive model for amorphous metallic materials." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/38928.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (leaves 153-161).
A finite-deformation, Coulomb-Mohr type constitutive theory for the elastic-viscoplastic response of pressure-sensitive and plastically-dilatant isotropic materials has been developed. The constitutive model has been implemented in a finite element program, and the numerical capability is used to study the deformation response of amorphous nietallic glasses. Specifically, the response of an amorphous metallic glass in tension, compression, strip-bending, and indentation is studied, and it is shown that results from the numerical simulations qualitatively capture major features of corresponding results from physical experiments available in the literature. The response of a Zr-based glass in instrumented plane strain indentation with a cylindrical indenter tip is also studied experimentally. The constitutive model and simulation capability is used to numerically calculate the indentation load versus depth curves, and the evolution of corresponding shear-band patterns under the in-denter. The numerical simulations are shown to compare very favorably with the corresponding experimental results. The constitutive model is subsequently extended to the high homologous temperature regime, and the response of a representative Pd-based metallic glass in tension at various strain rates and temperatures with different pre-annealing histories is studied.
(cont.) The model is shown to capture the major features of the stress-strain response and free volume evolution of this metallic glass. In particular, the phenomena of stress overshoot and strain softening in monotonic experiments at a given strain rate and temperature, as well as strain rate history effects in experiments involving strain rate increments and decrements are shown to be nicely reproduced by the model. Finally, a cavitation mechanism is incorporated in the constitutive model to simulate the failure phenomenon caused by the principal and hydro-static stresses. With the revised theory, the response of a prototypical amorphous grain-boundary is investigated, and the result is later applied to study the deformation and failure behavior of nanocrystalline fcc metals by coupling with appropriate crystal-plasticity constitutive model to represent the grain interior.
by Cheng Su.
Ph.D.
8
Subramaniam, Hari. "VIBRATION ANALYSIS OF CARBON NANOTUBE USING CONTINUUM MODEL AND FINITE ELEMENT MODEL." Master's thesis, University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2268.
Full textAbstract:
The main objective of the thesis is to propose the methods of determining vibration behavior of carbon nanotubes (CNTs) using continuum models and finite element models. Secondary objective is to find the effect of van der Waals force on vibration of multiwalled carbon nanotubes . The study of vibration behavior of CNTs is important because of their potential engineering applications such as nano-mechanical resonators and tips of scanning probe instruments where they are subjected to mechanical vibrations. Continuum modeling is based on an elastic beam model. The interlayer van der Waals interactions are represented by Lennard-Jones potential. In finite element modeling, single walled nanotubes (SWNTs) are modeled as finite beam elements and multi-walled nanotubes (MWNTs) as finite solid elements. The interlayer van der Waals interactions are simulated by distributed springs. The proposed finite element approach and continuum approach for vibration analysis of CNTs are verified by comparing the results with experimental and analytical results available in the literature. The results from both continuum and finite element modeling show that the effect of van der Waals force on vibration of MWNTs are high for smaller aspect ratios irrespective of boundary conditions and number of layers; fixed nanotube than cantilever nanotube for the same dimensions ; five-walled nanotube than a double walled nanotube for the same aspect ratio.M.S.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering
9
Reed, Brandon B. "Continuum Traffic Flow at a Highway Interchange." University of Akron / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1196711036.
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10
Pelà, Luca. "Continuum damage model for nonlinear analysis of masonry structures." Doctoral thesis, Universitat Politècnica de Catalunya, 2009. http://hdl.handle.net/10803/30327.
Full textAbstract:
The present work focuses on the formulation of a Continuum Damage Mechanics model for nonlinear analysis of masonry structural elements. The material is studied at the macro-level, i.e. it is modelled as a homogeneous orthotropic continuum.
The orthotropic behaviour is simulated by means of an original methodology, which is based on nonlinear damage constitutive laws and on the concept of mapped tensors from the anisotropic real space to the isotropic fictitious one. It is based on establishing a one-to-one mapping relationship between the behaviour of an anisotropic real material and that of an isotropic fictitious one. Therefore, the problem is solved in the isotropic fictitious space and the results are transported to the real field. The application of this idea to strain-based Continuum Damage Models is rather innovative.
The proposed theory is a generalization of classical theories and allows us to use the models and algorithms developed for isotropic materials. A first version of the model makes use of an isotropic scalar damage model. The adoption of such a simple constitutive model in the fictitious space, together with an appropriate definition of the mathematical transformation between the two spaces, provides a damage model for orthotropic materials able to reproduce the overall nonlinear behaviour, including stiffness degradation and strain-hardening/softening response.
The relationship between the two spaces is expressed in terms of a transformation tensor which contains all the information concerning the real orthotropy of the material. A major advantage of this working strategy lies in the possibility of adjusting an arbitrary isotropic criterion to the particular behaviour of the orthotropic material. Moreover, orthotropic elastic and inelastic behaviours can be modelled in such a way that totally different mechanical responses can be predicted along the material axes.
The aforementioned approach is then refined in order to account for different behaviours of masonry in tension and compression. The aim of studying a real material via an equivalent fictitious solid is achieved by means of the appropriate definitions of two transformation tensors related to tensile or compressive states, respectively. These important assumptions permit to consider two individual damage criteria, according to different failure mechanisms, i.e. cracking and crushing. The constitutive model adopted in the fictitious space makes use of two scalar variables, which monitor the local damage under tension and compression, respectively. Such a model, which is based on a stress tensor split into tensile and compressive contributions that allows the model to contemplate orthotropic induced damage, permits also to account for masonry unilateral effects. The orthotropic nature of the Tension-Compression Damage Model adopted in the fictitious space is demonstrated. This feature, both with the assumption of two distinct damage criteria for tension and compression, does not permit to term the fictitious space as “isotropic”. Therefore, the proposed formulation turns the original concept of “mapping the real space into an isotropic fictitious one” into the innovative and more general one of “mapping the real space into a favourable (or convenient) fictitious one”. Validation of the model is carried out by means of comparisons with experimental results on different types of orthotropic masonry.
The model is fully formulated for the 2-dimensional case. However, it can be easily extended to the 3-dimensional case. It provides high algorithmic efficiency, a feature of primary importance when analyses of even large scale masonry structures are carried out. To account for this requisite it adopts a strain-driven formalism consistent with standard displacement-based finite element codes. The implementation in finite element programs is straightforward.
Finally, a localized damage model for orthotropic materials is formulated. This is achieved by means of the implementation of a crack tracking algorithm, which forces the crack to develop along a single row of finite elements. Compared with the smeared cracking approach, such an approach shows a better capacity to predict realistic collapsing mechanisms. The resulting damage in the ultimate condition appears localized in individual cracks. Moreover, the results do not suffer from spurious mesh-size or mesh-bias dependence. The numerical tool is finally validated via a finite element analysis of an in-plane loaded masonry shear wall.
11
Druet, Thomas. "Reactions involving exotic nuclei in a discretized-continuum model." Doctoral thesis, Universite Libre de Bruxelles, 2013. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209367.
Full textAbstract:
The structure of exotic nuclei is one of the main interests in current nuclear physics. Exotic nuclei present unusual properties, such as a low breakup energy, a short lifetime and/or a halo structure. Because of their short lifetimes, they can not be studied by usual spectroscopic techniques. Indeed, targets of such nuclei are impossible to build. But since the availability of radioactive beams, nuclear reactions have provided possibilities of exploring nuclei far from stability.The investigation of exotic nuclei has been recently reactivated by the development of intense radioactive nuclear beams. As firstly observed for the deuteron, and then for other exotic projectiles such as $^6$He and $^{11}$Be, the internal structures of the interacting nuclei can have a significant effect on the elastic cross sections. Due to their low binding energy, the projectile dissociation process, leaving the target in its ground state, highly affects elastic cross sections but also other measurements such as transfer and fusion reactions. Accurate reaction theories are therefore needed. The coupled discretized-continuum channel (CDCC) method is one of those theories and assumes a projectile made of N clusters (usually N=2 or 3) impinging on a target which is structureless. The N+1-body Schrödinger equation is approximately solved by expanding the total wave function over the bound and continuum states of the projectile. These latter take into account the dissociation events and are approximately described by a truncated set of square-integrable wave functions. There are two available methods for discretizing the continuum, the pseudostate method where the projectile Hamiltonian is diagonalized within a finite basis of square-integrable functions, or the bin method where exact scattering wave functions of the projectile are averaged over bins in a finite region of space. In both cases, the N+1-body Schrödinger equation is replaced by a set of coupled-channel differential equations, which provides the physical quantities such as the collision matrix. In principle, the CDCC method can be very close to the exact N+1-body wave function and is adapted to low as well as to high energy reactions. However, its main interest consists in the low-energy domain.
In the present work, we propose a new approach to solve the CDCC equations. This method is based on the R-matrix theory associated with a Lagrange mesh basis. We will show that the combination of both approaches provides a fast and accurate technique to solve the CDCC equations, even for large systems, where traditional methods meet convergence problems. Before investigating collisions with exotic projectiles, we restrict ourselves to the simplest nucleus, the deuteron. Then we make a step towards a more complicated system, the $^6$Li which is a well known stable nucleus. We apply the CDCC method to the d + $^{58}$Ni and $^6$Li + $^{40}$Ca elastic scattering and breakup. These systems are considered in the literature as test cases. They have been investigated by several authors who showed the importance of the breakup channels in the elastic cross sections.
After having validated the present version of the CDCC method, we focus on $^{11}$Be, a typical example of a halo nucleus, with low binding energy and large quadrupole moment. Elastic, inelastic and breakup cross sections are computed in the CDCC formalism, at energies near the Coulomb barrier, where continuum effects in the scattering of exotic nuclei, and more specifically on the $^{11}$Be + $^{64}$Zn scattering, are observed. We show that converged cross sections need high angular momenta as well as large excitation energies in the wave functions of the projectile.
A Borromean nucleus is made of three constituents which are weakly linked together, but where each pair of those three constituents does not form a bound system. The name "Borromean" comes from the Borromean rings where, if any one of three rings is removed, the remaining two become unbound. Collisions with $^6$He and $^9$Be Borromean projectiles are studied in the present work. Again we compare our method with the $^6$He + $^{208}$Pb and $^6$He + $^{12}$C benchmark calculations. Afterwards, the convergence against the parameters of the description of the $^9$Be projectile is tested for the elastic cross section. The sensitivity to the technique employed to remove the forbidden states and also the sensitivity to the collision energy are investigated.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
12
Yates, Keith William. "Optimization of slender space trusses utilizing a continuum model." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-11242009-020159/.
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13
Jiang, Qing Knowles James K. Knowles James K. "A continuum model for phase transformation in thermoelastic solids /." Diss., Pasadena, Calif. : California Institute of Technology, 1990. http://resolver.caltech.edu/CaltechETD:etd-02232007-155324.
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14
PELA', Luca. "CONTINUUM DAMAGE MODEL FOR NONLINEAR ANALYSIS OF MASONRY STRUCTURES." Doctoral thesis, Università degli studi di Ferrara, 2009. http://hdl.handle.net/11392/2389195.
Full textAbstract:
The present work focuses on the formulation of a Continuum Damage Mechanics
model for nonlinear analysis of masonry structural elements. The material is
studied at the macro-level, i.e. it is modelled as a homogeneous orthotropic
continuum.
The orthotropic behaviour is simulated by means of an original methodology,
which is based on nonlinear damage constitutive laws and on the concept of
mapped tensors from the anisotropic real space to the isotropic fictitious one. It is
based on establishing a one-to-one mapping relationship between the behaviour of
an anisotropic real material and that of an isotropic fictitious one. Therefore, the
problem is solved in the isotropic fictitious space and the results are transported to
the real field. The application of this idea to strain-based Continuum Damage
Models is rather innovative.
The proposed theory is a generalization of classical theories and allows us to use
the models and algorithms developed for isotropic materials. A first version of the
model makes use of an isotropic scalar damage model. The adoption of such a
simple constitutive model in the fictitious space, together with an appropriate definition of the mathematical transformation between the two spaces, provides a
damage model for orthotropic materials able to reproduce the overall nonlinear
behaviour, including stiffness degradation and strain-hardening/softening response.
The relationship between the two spaces is expressed in terms of a transformation
tensor which contains all the information concerning the real orthotropy of the
material. A major advantage of this working strategy lies in the possibility of
adjusting an arbitrary isotropic criterion to the particular behaviour of the
orthotropic material. Moreover, orthotropic elastic and inelastic behaviours can be
modelled in such a way that totally different mechanical responses can be predicted
along the material axes.
The aforementioned approach is then refined in order to account for different
behaviours of masonry in tension and compression. The aim of studying a real
material via an equivalent fictitious solid is achieved by means of the appropriate
definitions of two transformation tensors related to tensile or compressive states,
respectively. These important assumptions permit to consider two individual
damage criteria, according to different failure mechanisms, i.e. cracking and
crushing. The constitutive model adopted in the fictitious space makes use of two
scalar variables, which monitor the local damage under tension and compression,
respectively. Such a model, which is based on a stress tensor split into tensile and
compressive contributions that allows the model to contemplate orthotropic
induced damage, permits also to account for masonry unilateral effects. The
orthotropic nature of the Tension-Compression Damage Model adopted in the
fictitious space is demonstrated. This feature, both with the assumption of two
distinct damage criteria for tension and compression, does not permit to term the
fictitious space as “isotropic”. Therefore, the proposed formulation turns the
original concept of “mapping the real space into an isotropic fictitious one” into
the innovative and more general one of “mapping the real space into a favourable (or convenient) fictitious one”. Validation of the model is carried out by means of
comparisons with experimental results on different types of orthotropic masonry.
The model is fully formulated for the 2-dimensional case. However, it can be easily
extended to the 3-dimensional case. It provides high algorithmic efficiency, a
feature of primary importance when analyses of even large scale masonry
structures are carried out. To account for this requisite it adopts a strain-driven
formalism consistent with standard displacement-based finite element codes. The
implementation in finite element programs is straightforward.
Finally, a localized damage model for orthotropic materials is formulated. This is
achieved by means of the implementation of a crack tracking algorithm, which
forces the crack to develop along a single row of finite elements. Compared with
the smeared cracking approach, such an approach shows a better capacity to predict
realistic collapsing mechanisms. The resulting damage in the ultimate condition
appears localized in individual cracks. Moreover, the results do not suffer from
spurious mesh-size or mesh-bias dependence. The numerical tool is finally
validated via a finite element analysis of an in-plane loaded masonry shear wall.
15
Donolo, Marcos A. "A continuum Approach to Power system simulation." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/29002.
Full textAbstract:
The behavior of large and tightly interconnected power systems resembles, in certain circumstances, the behavior of a continuously distributed system. This resemblance motivated the derivation of continuum models, which were used to explain and predict disturbance propagation, un-damped power oscillations, and the stability of power systems. In this dissertation, we propose a one-dimensional continuum representation suitable for meshed power systems. Previous continuous representations of meshed power systems used two-dimensional spatial domains. Thus our approach has the potential to provide better resolution for comparable computational burden. It is important to note that, the computational burden required to obtain solutions for PDEs involved in the continuum representation varies notably with the solver implementation.
The contributions of this dissertation are: a) Reviewing a previous continuum model and providing a detailed derivation for the one-dimensional version of it. b) Providing and describing in detail a parameter distribution technique adequate for the continuum approach. c) Identifying and documenting limitations on the continuum model voltage calculation. e) Providing a procedure to simulate the behavior of meshed power systems using the one dimensional continuum model. And f) Identifying and applying a numerical PDE solver for the continuum approach.Ph. D.
16
Bingham, Richard John. "A continuum model of the electroporation of bilayer lipid membranes." Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.535113.
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17
Kang, Jae-Sun. "A finite element continuum model for consolidation due to pumpage." Thesis, Swansea University, 2005. https://cronfa.swan.ac.uk/Record/cronfa42218.
Full textAbstract:
Modelling the mechanical behaviour of engineering phenomena has occupied the attention of researchers since Karl Terzaghi's pioneering work on settlement due to consolidation in 1925. Soil improvement methods using vertical drains in combination with pre-loading were used for soil stabilization at the San Francisco- Oakland Bay Bridge in 1926. Over the next decades, other drain methods, including prefabricated and pack drains, were developed and used for practical purposes. In the mid-1990s, vacuum-induced consolidation became a reliable technology, thanks to a rethinking of theoretical principles that led to the Menard vacuum system. The Menard system was used successfully, for the first time in South Korea, for construction of the Kimhae sewage treatment plant. The drain method is based on Terzaghi's one-dimensional consolidation theory and Barron's vertical drain. Even when using finite element simulation, numerical solution for consolidation problems involves averaging material properties such as elastic modulus, Poisson's ratio, and coefficients of permeability. But the results are too unreliable to use for practical purposes. Classical mechanics alone do not provide sufficient information on the global motion equation of fluid in a porous media. A new approach is presented in this paper to the problem of continuum modelling of vacuum-induced consolidation due to pumpage. This finite element continuum model uses the interior boundary condition instead of installed vacuum tube as a line, with changing pore pressures at the installed material being treated as boundary conditions of the interior part. An innovative linear equation solution method for separate fixed boundary conditions is presented. The efficacy of this model for field construction is shown by comparing results with the results obtained from field measurements at the Jangyoo sewage plant. Because the properties of material are not exact in their natural states, the results of the calculated finite modelling are similar but not a mirror image of field measurements. Whereas conventional one-dimensional calculation uses only one point, the finite element continuum model shows displacements and pore pressures for a whole section. Once the exact material properties have been determined, the model can be applied effectively to field analyses, predicting settlements due to pumpage and facilitating decision making about when pumpage should start and stop. The finite continuum model for consolidation due to pumpage can be applied to other soil improvement methods, such as prefabricated and pack vertical drain, with some modification.
18
Kopp, A. M., and D. L. Orlovskyi. "A role of business process model repository in enterprise continuum." Thesis, NTU "KhPI", 2018. http://repository.kpi.kharkov.ua/handle/KhPI-Press/36873.
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Huang, Kai. "Continuum MDOF model for seismic analysis of wall-frame structures /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202009%20HUANG.
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Damman, Alix. "Microscopic description of three-body continuum states." Doctoral thesis, Universite Libre de Bruxelles, 2011. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209807.
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Durant le milieu des années quatre-vingt, le développement des faisceaux radioactifs a permis l’étude de noyaux exotiques situés à la limite de la stabilité nucléaire. Parmi ceux-ci, l’6He possède une structure particulière constituée d’un cœur α et de deux neutrons de valence faiblement liés. Il fait partie des noyaux à halo. Il s’agit également d’un système possédant au moins un état lié à trois amas (α+n+n) alors qu’aucun des sous-systèmes à deux amas (α+n ou n+n) n’est lié. Un tel système est dit borroméen. Deux autres exemples de systèmes borroméens sont le 9Be=n+α+α et le 12C=α+α+α. Les noyaux borroméens possèdent un ou deux états liés dont les propriétés sont maintenant bien connues. En revanche, les propriétés des états du continu le sont moins. Il existe aussi des systèmes à trois amas non liés mais caractérisés par une ou plusieurs résonances étroites à basse énergie. Par exemple, nous pouvons citer le 6Be=α+p+p et le 9B=p+α+α qui sont les noyaux miroirs de l’6He et du 9Be. L’étude des états du continu à trois corps est un sujet important de la recherche en physique nucléaire actuelle.D’un point de vue théorique, les modèles en amas permettent de décrire les noyaux possédant une structure à plusieurs corps. En particulier, les modèles en amas microscopiques tiennent compte de tous les nucléons et le principe de Pauli est traité de manière exacte à l’aide de l’opérateur d’antisymmétrisation. Les modèles microscopiques, plus réalistes, requièrent de longs temps de calculs et sont difficiles à implémenter.
Dans le présent travail, nous avons développé une méthode de calcul semi-analytique plus rapide et plus précise qu’une méthode purement numérique. Notre modèle est basé sur la méthode des coordonnées génératrices dans le formalisme hypersphérique. Les états du continu sont étudiés à l’aide de la méthode des déphasages. Ces derniers sont obtenus à partir de la méthode de la matrice R microscopique.
Avec ce modèle, nous avons étudié les effets d’antisymmétrisation dans les noyaux d’6He, 6Be, 9Be, 9B et 12C. Nous avons montré que ces effets restent non négligeables mêmes à grandes distances dans le cas des noyaux 9Be, 9B et du 12C.
Nous avons ensuite étudié les états du continu du 6He et du 6Be. Nous avons déterminé des valeurs théoriques pour les propriétés des résonances connues expérimentalement. Nos résultats sont en bon accord avec l’expérience. Nous avons également observé des structures larges dans les déphases associés aux états 0+ et 1- de l’6He et 1- du 6Be.
Finalement, nous avons étudié les états du 12C à travers la collision 8Be+α. Dans notre calcul, le 8Be est considéré comme un système comportant deux amas α. Nous avons montré que les états 2+ et 4+ du 8Be devaient être pris en compte pour une étude appropriée des états 0+, 2+ et 4+ du 12C.
Doctorat en Sciences
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Dondeti, Piyush Prashant. "Rate-Dependent Homogenization based Continuum Plasticity Damage Model for Dendritic Cast Aluminum Alloys." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1308245866.
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Ren, Zhen. "Modular model assembly from finite element models of components." Diss., Connect to online resource - MSU authorized users, 2008.
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王軍 and Chun Wang. "Development of an anisotropic damage mechanics model in ductile fracture." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1987. http://hub.hku.hk/bib/B31231378.
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Wang, Chun. "Development of an anisotropic damage mechanics model in ductile fracture /." [Hong Kong : University of Hong Kong], 1987. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12362864.
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Berg, Peter. "Optimal-velocity models of motorway traffic." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367664.
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Crooks, Matthew Stuart. "Application of an elasto-plastic continuum model to problems in geophysics." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/application-of-an-elastoplastic-continuum-model-to-problems-in-geophysics(56bc2269-3eb2-47f9-8482-b62e8e053b76).html.
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A model for stress and strain accumulation in strike slip earthquake faults is presented in which a finite width cuboidal fault region is embedded between two cuboidal tectonic plates. Elasto-plastic continuum constitutive equations model the gouge in the fault and the tectonic plates are linear elastic solids obeying the generalised Hooke's law. The model predicts a velocity field which is comparable to surface deformations. The plastic behaviour of the fault material allows the velocities in the tectonic plate to increase to values which are independent of the distance from the fault. Both of the non-trivial stress and strain components accumulate most significantly in the vicinity of the fault. The release of these strains during a dynamic earthquake event would produce the most severe deformations at the fault which is consistent with observations and the notion of an epicenter. The accumulations in the model, however, are at depths larger than would be expected. Plastic strains build up most significantly at the base of the fault which is in yield for the longest length of time but additionally is subject to larger temperatures which makes the material more ductile. The speed of propagation of the elasto-plastic boundary is calculated and its acceleration towards the surface of the fault may be indicative of a dynamic earthquake type event.
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Saha, Reema. "Investigation of a continuum damage model using experimental and numerical techniques." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/12542.
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Ho, Kwang-Il. "An anisotropic continuum damage model for creep-dominated, multiaxial loading histories." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/20043.
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Fleming, Michael P. "Deconstructing Schizophrenia : uncovering evidence of a severity continuum model of psychosis." Thesis, University of the West of Scotland, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.568814.
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The schizophrenia syndrome was developed with the aim of distinguishing between those people that have the syndrome and those people that do not and between those people with the syndrome and those people with other distinct syndromes. The basis for syndromes to be recognised is that they are made up of symptoms unique to that syndrome and that the pattern between those symptoms determines onset, course and prognosis. Valid syndromes are then used to identify the disease agent that causes these symptoms to occur and vary together. Once a disease agent is identified, it is possible to develop treatments that eliminate the disease agent. In the hundred years since its development, the schizophrenia syndrome has failed to deliver these expected outcomes. Problems remain regarding reliability of diagnosis, aetiology and the effective treatment. Despite these shortcomings, the Syndrome Model of schizophrenia continues to have a monopoly in terms of research into aetiology and dominates clinical practice. It has failed to establish a cause and leading biological researchers have acknowledged this deficit. The reason for these deficits is a flaw in the validity of the syndrome. Poor validity is inferred by the lack of uniqueness of symptoms and variations in symptoms across different populations. One of the main principles that protect syndrome validity is the notion of discontinuity. In order for a syndrome to make a distinction between those with the syndrome and those that do not, a discontinuum between these two groups is required. If a syndrome is not supported by this discontinuum this would seriously impinge on its ability to effectively function as syndrome and would account for the deficiencies noted above. Compelling evidence is emerging that members of the general population experience the symptoms of psychosis. Studies have found that the prevalence of auditory hallucinations and delusions are experienced in rates higher than those found in clinical populations. This is evidence that would suggest a Severity Continuum of Psychosis exists rather than the assumed discontinuum.
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Sears, Aaron Thomas. "Carbon Nanotube Mechanics: Continuum Model Development from Molecular Mechanics Virtual Experiments." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/29959.
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Carbon Nanotubes (CNTs) hold great promise as an important engineering material for future applications. To fully exploit CNTs to their full potential, it is important to characterize their material response and ascertain their material properties. We have used molecular mechanics (MM) simulations to conduct virtual experiments on single-wall and multi-wall carbon nanotubes (SWNTs and MWNTs respectively) similar to those performed in the mechanics of materials laboratory on a continuum structure. The output (energy and deformation rather than the load and deflection) is used to understand the material response and formulate macroscopic constitutive relations.
From results of MM simulations of axial and torsional deformations on SWNTs, Young's modulus, the shear modulus and the wall thickness of an equivalent continuum tube made of a linear elastic isotropic material were found. These values were used to compare the response of the continuum tube, modeled as an Euler-Bernoulli beam, in bending and buckling with those obtained from the MM simulations.
MM simulations have been carried out to find energetically favorable double-walled carbon nanotube (DWNT) configurations, and analyze their responses to extensional, torsional, radial expansion/contraction, bending, and buckling deformations. Loads were applied either to one wall or simultaneously to both walls of an open-ended DWNT. These results were compared against SWNT results. It was found that for simple tension and torsional deformations, results for a DWNT can be derived from those for its constituent SWNTs within 3% error. Radial deformations of a SWNT were achieved by considering a DWNT with the SWNT as one of its walls and moving radially through the same distance all atoms of the other wall of the DWNT thereby causing a pseudo-pressure through changes in the cumulative van der Waals forces which deform the desired wall. Results of radial expansion/contraction of a SWNT were used to deduce an expression for the van der Waals forces, and find through-the-thickness elastic moduli (Young's modulus in the radial direction, Er, and Poisson's ratio ?r?) of the SWNT. We have found four out of the five elastic constants of a SWNT taken to be transversely isotropic about a radial line.
MWNTs were studied using the same testing procedures as those used SWNTs. Based on the results from those simulations a continuum model is proposed for a MWNT whose response to mechanical deformations is the same as that of the MWNT. The continuum structure is comprised of concentric cylindrical tubes interconnected by truss elements. Young's modulus, Poisson's ratio, the thickness of each concentric tube, and the stiffness of the truss elements are given. The proposed continuum model is validated by studying its bending and buckling deformations and comparing these results to those from MM simulations.
The major contributions to the field on nanotubes and the scientific literature is a simple and robust continuum model for nanotubes. This model can be used to study both SWNTs and MWNTs in either global or local responses by applying different analytic techniques. This model was developed using a consistent engineering methodology that mimicked traditional engineering testing, assumptions and constraints.Ph. D.
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Hale, Christine Anne. "The Chinese continuum of self-cultivation: a Confucian-Deweyan learning model." Thesis, The University of Sydney, 2014. http://hdl.handle.net/2123/13354.
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This thesis explores a transcultural philosophy of education based on the Neo-Confucian concepts of the universal nature of self (ren xing人性), as positioned with self-in-the-world (ren 人) and humanity (ren 仁) in the co-creative process of self-cultivation (xiushen 修身). This approach to knowledge synthesis and consolidation informs and enhances the educational theories of John Dewey (1859-1952) and presents a philosophy of education which has a dynamic self interacting with and becoming in the world as an evolving process of knowledge schematization and application. The Confucian-Deweyan educational model explored herein is presented as, not only a transcultural educational approach in the changing face of globality, but also a means to encourage and foster humanitarian and communitarian values in the student to be applied in life-long learning. That is, a wholistic approach to education whereby the individual considers the other – human and natural – tantamount to the self in an increasingly shifting world. This concept is in direct opposition to the anthropocentric approach of egoistic individualism currently prevalent in post-modern societies. Hence, the model developed herein is a pragmatic response to 21st century globality, fostering cooperation, rather than competition; an anthropocosmic vision of life and living, enabling non-European indigenous values to co-exist in a global arena. The specific elements addressed for the contextual background of the thesis is the history and influence of Deweyan thought in China (Dewey lectured in China for two years – 1919-1921), the history of China’s educational systems, and the PRC’s current education reform initiatives. China, with a community-based culture and growing global presence, offers a real-world context for exploring the viability of such a Confucian-Deweyan model of education as a confluence of Western and Eastern approaches to learning, self, community, creativity and knowledge.
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Xin, W. (Weidong). "Continuum electrostatics of biomolecular systems." Doctoral thesis, University of Oulu, 2008. http://urn.fi/urn:isbn:9789514287602.
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Abstract
Electrostatic interactions are very important in biomolecular systems. Electrostatic forces have received a great deal of attention due to their long-range nature and the trade-off between desolvation and interaction effects. It remains a challenging task to study and to predict the effects of electrostatic interactions in biomolecular systems. Computer simulation techniques that account for such interactions are an important tool for the study of biomolecular electrostatics.
This study is largely concerned with the role of electrostatic interactions in biomolecular systems and with developing novel models to estimate the strength of such interactions.
First, a novel formulation based upon continuum electrostatics to compute the electrostatic potential in and around two biomolecules in a solvent with ionic strength is presented. Many, if not all, current methods rely on the (non)linear Poisson-Boltzmann equation to include ionic strength. The present formulation, however, describes ionic strength through the inclusion of explicit ions, which considerably extends its applicability and validity range. The method relies on the boundary element method (BEM) and results in two very similar coupled integral equations valid on the dielectric boundaries of two molecules, respectively. This method can be employed to estimate the total electrostatic energy of two protein molecules at a given distance and orientation in an electrolyte solution with zero to moderately high ionic strength.
Secondly, to be able to study interactions between biomolecules and membranes, an alternative model partly based upon the analytical continuum electrostatics (ACE) method has been also formulated. It is desirable to develop a method for calculating the total solvation free energy that includes both electrostatic and non-polar energies. The difference between this model and other continuum methods is that instead of determining the electrostatic potential, the total electrostatic energy of the system is calculated by integrating the energy density of the electrostatic field. This novel approach is employed for the calculation of the total solvation free energy of a system consisting of two solutes, one of which could be an infinite slab representing a membrane surface.
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Kirby, Nicholas O. "Modeling, Analysis, and Simulation of Discrete-Continuum Models of Step-Flow Epitaxy: Bunching Instabilities and Continuum Limits." UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_diss/187.
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Vicinal surfaces consist of terraces separated by atomic steps. In the step-flow regime, deposited atoms (adatoms) diffuse on terraces, eventually reaching steps where they attach to the crystal, thereby causing the steps to move. There are two main objectives of this work. First, we analyze rigorously the differences in qualitative behavior between vicinal surfaces consisting of infinitely many steps and nanowires whose top surface consists of a small number of steps bounded by a reflecting wall. Second, we derive the continuum model that describes the macroscopic behavior of vicinal surfaces from detailed microscopic models of step dynamics.
We use the standard theory of Burton-Cabrera-Frank (BCF) to show that in the presence of an Ehrlich-Schwoebel barrier, i.e., a preferential attachment of adatoms from the lower terraces, N-periodic step motions are stable with respect to step collisions. Nonetheless, for N > 2 step collisions may occur. Moreover, we consider a single perturbed terrace, in which we distinguish three cases: no attachment from the upper terraces (perfect ES barrier), no attachment from the lower terraces (perfect inverse ES barrier), and symmetric attachment. For a perfect ES barrier, steps never collide regardless of the initial perturbation. In contrast, for a perfect inverse ES barrier, collisions occur for any nonzero perturbation. Finally, for symmetric attachment, step collisions occur for sufficiently large outward perturbations.
To model nanowire growth, we consider rectilinear steps and concentric steps bounded by reflecting walls. In contrast to a vicinal surface with infinitely many steps, we prove analytically that the Ehrlich-Schwoebel barrier is destabilizing with respect to step collisions. We further consider nanowire growth with desorption, and prove that the initial conditions that lead to step collisions are characterized by a unique step motion trajectory.
We take as our starting point a thermodynamically consistent (TC) generalization of the BCF model to derive PDE that govern the evolution of the vicinal surface at the macroscale. Whereas the BCF model yields a fourth-order parabolic equation for the surface height, the TC model yields a system of coupled equations for the surface height and the surface chemical potential.
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Skoog, Rebecka. "Records continuum i arkivvetenskaplig forskning : Kontinuummodellens och kontinuumidéernas användning i 22 arkivvetenskapliga artiklar publicerade 2005 - 2018." Thesis, Uppsala universitet, Institutionen för ABM, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-401059.
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This study examines uses of the records continuum model and related continuum concepts and ideas within the broader field of archival research. By analysing the different ways researchers understand and use the model and related concepts the study aims to contribute new knowledge regarding the records continuum model and its roles in contemporary archival science. The study is a literature review within a qualitative, interpretative paradigm. The review method shares some traits with a systematic literature review through systematicity in the search process and the procedure of selecting articles for the study. These were delimited to English written, peer reviewed, archival science articles published 2005-2018 which use the records continuum model (RCM) in their own studies. Systematicity is also present in analysis through a set of questions that seek to link the research goals within the studies with the purposes of using the RCM and the perceived value of its application. This combination of questions offers a method to get hold of some of the functions and roles of the RCM in archival science. An analysis of the research goals within the articles revealed societal as well as theoretical/methodological goals. Different uses of the RCM were further explored – by analysing motives for including the RCM and related concepts as well as the authors descriptions of their application. The identified goals and an interpretation of the ways the RCM and related ideas were used were then connected, and further interpreted with the help of a theoretical framework consisting of (1) the abilities of theoretical frameworks (according to Anfara 2008), (2) a typology of theories in Information Systems studies (according to Gregor 2006) and (3) the purposes of modelling in science (according to Hofman 2017). The results enabled a discussion on the roles of the RCM in archival research. The study is of value since it identifies the goals within some RCM research and connects these goals with the purposes of using the RCM and related ideas, which might support a continuing discussion on the roles of the RCM in archival science. The study further has a merit in providing a survey of the RCM in contemporary research through a perspective “from without”. This perspective is arrived at partly by including studies from both continuum researchers in the know, as well as from individual researchers of different proximity to continuum thinking and the RCM as a theoretical model; partly by the fact that the author is not a researcher within a community of continuum thinkers or researchers. This is a two years master’s thesis in Archival Science.
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Gray, Jr Ricky Lee. "VERIFICATION OF A THREE-DIMENSIONAL STATICS MODEL FOR CONTINUUM ROBOTICS AND THE DESIGN AND CONSTRUCTION OF A SMALL CONTINUUM ROBOT (SCR)." MSSTATE, 2009. http://sun.library.msstate.edu/ETD-db/theses/available/etd-11062009-155747/.
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Continuum robots are biologically inspired robots that capture the extraordinary abilities of biological structures such as elephant trunks, octopus tentacles, and mamma-lian tongues. They are given the term continuum robots due to their ability to bend conti-nuously rather than at specific joints such as with traditional rigid link robots. They are used in applications such as search and rescue operations, nuclear reactor repairs, colo-noscopies, minimal invasive surgeries, and steerable needles. In this thesis, a model that predicts the shape of a continuum robot is presented and verified. A verification system to verify the validity and accuracy of the model is presented which allows easy and accu-rate measurement of a continuum robot tip position. The model was verified against a flexible rod, the core component of a continuum robot, resulting in an accuracy of 0.61%. Finally, this thesis introduces a novel robot design, consisting of a single rod for the backbone which can be manipulated by applying external forces and torques.
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Sheldon, Timothy John. "Design of optimal solvent molecules using a quantum mechanical continuum solvation model." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415228.
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Custer, Melba G. "DEVELOPING A MODEL OF CLIENT SATISFACTION WITH A REHABILITATION CONTINUUM OF CARE." UKnowledge, 2012. http://uknowledge.uky.edu/rehabsci_etds/7.
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Client satisfaction is an important outcome indicator because it measures multiple domains of the quality of healthcare and rehabilitation service delivery. It is especially important in occupational therapy because it is also client-centered. There are multiple domains of satisfaction and findings described in previous research; however, there is no single standard of measuring client satisfaction or any single working model describing the relationship among variables influencing satisfaction. This research was designed to apply a measure of satisfaction in rehabilitation and to develop a working model of satisfaction.
This study was an exploratory and predictive study using a large existing dataset to test a working logic model of client satisfaction, determine the best predictors of satisfaction, and then to revise the model for future research. After developing the Satisfaction with a Continuum of Care (SCC) in a pilot study, the SCC was completed by 1104 clients from a large Midwest rehabilitation hospital. The SCC results were paired with administrative data with client demographics, functional status, and measures of the` rehabilitation process. Six research questions on the predictors of satisfaction with client-centeredness and clinical quality were answered using logistic regression.
Significant predictors of satisfaction were having a neurological disorder, total rehabilitation hours, and admission to rehabilitation within 15 days of onset. The most robust and consistent predictors of satisfaction in this study were aspects of functional status as measured by the Functional Independence Measure especially improvement in overall and self-care functioning.
The results in the study were consistent with some previous research and inconsistent with others. The finding that improvements in functional status were highly predictive of satisfaction supports the worth that clients place on rehabilitation results including the self-care improvements focused on by occupational therapy.
This study was a partnership involving occupational therapy and a rehabilitation hospital. The finding that changes in self-care function were predictive of satisfaction was intended to isolate the effects of OT. There is a need to demonstrate outcomes and link these to occupational therapy and other rehabilitation disciplines to continue to identify best practices and contribute to the rehabilitation literature.
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Meder, Markus. "A continuum approximation of the Fermi-Pasta-Ulam-Tsingou model with Langevin dynamics." Thesis, KTH, Matematisk statistik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-220353.
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In continuum mechanics, the conservation laws for mass, momentum and energy coupled with the constitutive relations of the stress and heat flux could be a powerful solution method for continuum systems. However, it is required that the equations form a closed system, i.e. that the stress and heat flux are formulated as functions of the conserved variables. This thesis studies the constitutive relations of the stress and heat flux in the Fermi-Pasta-Ulam-Tsingou model with Langevin dynamics, by the means of molecular dynamics simulations. In essence, the model consists of a many particle system in the presence of a heat bath, where each particle is chained to its two neighbors by a nonlinear quadratic spring force. A numerical method is implemented to propagate the particle dynamics. Following Hardy [7], formulas relating the macroscopic entities to the particle dynamics are employed in order to study the behavior of the stress and heat flux in relation to the mass, momentum and energy. In fact, the numerical result show that the stress appears as a linear function of the energy.En värdefull lösningsmetod för kontinuumsystem är att lösa det system av partiella differentialekvationer som utgörs av konserveringslagarna för massa, rörelsemängd och energi tillsammans med två konstitutiva relationer för spänning och värmeflöde. För detta krävs det att ekvationerna bildar ett slutet system, dvs. att spänningen och värmeflödet är funktioner av de konserverade storheterna. Detta examensarbete studerar de konstitutiva relationerna för spänningen och värmeflödet i Fermi-Pasta-Ulam-Tsingou modellen med Langevindynamik, som bestäms genom simulering av molekyldynamiken. Modellen består väsentligen av många partiklar som är kopplade till ett värmebad, där varje partikel är länkad till sina två grannar genom en ickelinjär fjäderkraft. En numerisk metod implementeras för att propagera partikeldynamiken. Baserat på Hardys arbete [7] bestäms först spänningen och värmeflödet, sedan studeras deras beroende av konserveringsvariablerna. De numeriska resultaten visar att spänningen är en linjär funktion av energin.
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Hou, Tian. "Fatigue Performance Prediction of North Carolina Mixtures Using Simplified Viscoelastic Continuum Damage Model." NCSU, 2009. http://www.lib.ncsu.edu/theses/available/etd-07102009-011752/.
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Fatigue performance modeling is one the major topics in asphalt concrete modeling work. Currently the only standard fatigue test available for asphalt concrete mixtures is the flexural bending fatigue test, AASHTO T-321. There are several issues associated with flexural fatigue testing, the most important of which are the stress state is not uniform but varies over the depth of the specimen and equipment for fabricating beam specimens is not widely available. Viscoelastic continuum damage (VECD) fatigue testing is a promising alternative to flexural fatigue testing. Different researchers have successfully applied the VECD model to asphalt concrete mixtures using constant crosshead rate direct tension test. However, due to the load level limitation of the new coming Asphalt Mixture Performance Tester (AMPT) testing equipment, there is an immediate need to develop a model that can characterize fatigue performance quickly using cyclic test data. In this study, a simplified viscoelastic continuum damage model developed at NCSU is applied to various North Carolina mixtures, which are used in the NCDOT HWY-2007-7 MEPDG local calibration project. It is shown that the simplified VECD model can predict fatigue tests fairly accurately under various temperature conditions and strain levels. It is also shown that the model can be further utilized to simulate both the strain controlled direct tension fatigue test and the traditional beam fatigue test. In this thesis, simulation results are presented. Conclusions regarding the applicability of the new model are advanced as well as suggestions for further work.
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Josefsson, Axel, and Johan Wedin. "Convergence properties of a continuum damage mechanics model for fatigue of adhesive joints." Thesis, Högskolan i Skövde, Institutionen för ingenjörsvetenskap, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-10188.
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The effect of the element length is examined in modelling crack growth in fatigue loading of an adhesive joint. This is done for a cohesive element using an expression for the damage evolution developed at the University of Skövde which is implemented using the UMAT subroutine in the FE-solver Abaqus. These analyses are done for pure mode I loading by analysing a DCB-specimen loaded by a pure moment. An expression is developed in which the critical element length is dependent on the geometry of the specimen (in the form of the wave number of the adhesive joint), the element length, the material properties of the adhesive (in form of the material parameters , , ), the load applied (in form of the stress in the crack tip), the time step used in the analysis and the crack growth rate. It is shown that the results converge by decreasing the element length and the time step used. Therefore an expression for the crack growth rate as a function of the remaining parameters can be determined. Another expression is thereafter developed for the element length needed in order to get a crack growth rate within a certain range of the critical element length. The results show a regular pattern but are not monotone. Therefor two different definitions of the critical element length are tested, either by defining the critical element length as the point where the error is greater than an arbitrary boundary of 1 % of a converged result or where a least square approximation of the error is within 1 % of the converged results. The first method shows a highly irregular result which makes it difficult to develop an expression out of these results. The second method on the other hand gives results that are predictable enough to develop a function out of them. This is done using a regression analysis with all parameters of a third order expression in order to get an expression.
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Wood, Cody. "A Continuum Model for the van der Waals Interaction Energy of Carbon Nanotubes." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1493376354522434.
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Bai, Jie. "A Homogenization based Continuum Plasticity-Damage Model for Ductile Frature of Materials Containing Heterogeneities." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1211910660.
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Reberg, Andrew Steven. "An Anisotropic Damage Mechanics Model for Concrete with Applications for Fatigue Loading and Freeze-Thaw Effects." Thesis, North Dakota State University, 2013. https://hdl.handle.net/10365/26994.
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It is well known that the formation and propagation of microcracks within concrete is anisotropic in nature, and has a degrading effect on its mechanical performance. In this thesis an anisotropic damage mechanics model is formulated for concrete which can predict the behavior of the material subjected to monotonic loading, fatigue loading, and freeze-thaw cycles. The constitutive model is formulated using the general framework of the internal variable theory of thermodynamics. Kinetic relations are used to describe the directionality of damage accumulation and the associated softening of mechanical properties. The rate independent model is then extended to cover fatigue loading cycles and freeze-thaw cycles. Two simple softening functions are used to predict the mechanical properties of concrete as the number of cyclic loads as well as freeze-thaw cycles increases. The model is compared with experimental data for fatigue and freeze-thaw performance of plain concrete.DOT-MPC grant
Department of Civil Engineering, North Dakota State University
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Momoti, Nikiwe Gloria. "A model to foster the use of records for evidence-based decision-making by senior managers in western cape governmental bodies, South Africa." University of the Western Cape, 2021. http://hdl.handle.net/11394/8118.
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Philosophiae Doctor - PhDSouth Africa has placed emphasis on evidence-based decision-making for justifying service delivery improvement decisions. Evidence-based decision-making entails decisions made by referring to verifiable facts and figures available from a variety of sources of evidence such as organizational records. Records are created or received during the conduct of business and contain evidence of organizational activities. Their use as sources of evidence is continuous. Most records management scholars hypothesize that the use of records as sources of evidence for decision-making contributes to improved service delivery. In the same breath, some scholars lament their minimal use as sources of evidence for decision-making in the South African public sector due to poor records management. This descriptive, positivist quantitative study used a cross-sectional survey to determine the extent to which records as sources of evidence were used for evidence-based decision-making by senior managers in Western Cape governmental bodies,
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Sharma, Ity. "Developing and validating Fuzzy-Border continuum solvation model with POlarizable Simulations Second order Interaction Model (POSSIM) force field for proteins." Digital WPI, 2015. https://digitalcommons.wpi.edu/etd-dissertations/393.
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"The accurate, fast and low cost computational tools are indispensable for studying the structure and dynamics of biological macromolecules in aqueous solution. The goal of this thesis is development and validation of continuum Fuzzy-Border (FB) solvation model to work with the Polarizable Simulations Second-order Interaction Model (POSSIM) force field for proteins developed by Professor G A Kaminski. The implicit FB model has advantages over the popularly used Poisson Boltzmann (PB) solvation model. The FB continuum model attenuates the noise and convergence issues commonly present in numerical treatments of the PB model by employing fixed position cubic grid to compute interactions. It also uses either second or first-order approximation for the solvent polarization which is similar to the second-order explicit polarization applied in POSSIM force field. The FB model was first developed and parameterized with nonpolarizable OPLS-AA force field for small molecules which are not only important in themselves but also building blocks of proteins and peptide side chains. The hydration parameters are fitted to reproduce the experimental or quantum mechanical hydration energies of the molecules with the overall average unsigned error of ca. 0.076kcal/mol. It was further validated by computing the absolute pKa values of 11 substituted phenols with the average unsigned error of 0.41pH units in comparison with the quantum mechanical error of 0.38pH units for this set of molecules. There was a good transferability of hydration parameters and the results were produced only with fitting of the specific atoms to the hydration energy and pKa targets. This clearly demonstrates the numerical and physical basis of the model is good enough and with proper fitting can reproduce the acidity constants for other systems as well. After the successful development of FB model with the fixed charges OPLS-AA force field, it was expanded to permit simulations with Polarizable Simulations Second-order Interaction Model (POSSIM) force field. The hydration parameters of the small molecules representing analogues of protein side chains were fitted to their solvation energies at 298.15K with an average error of ca.0.136kcal/mol. Second, the resulting parameters were used to reproduce the pKa values of the reference systems and the carboxylic (Asp7, Glu10, Glu19, Asp27 and Glu43) and basic residues (Lys13, Lys29, Lys34, His52 and Lys55) of the turkey ovomucoid third domain (OMTKY3) protein. The overall average unsigned error in the pKa values of the acid residues was found to be 0.37pH units and the basic residues was 0.38 pH units compared to 0.58pH units and 0.72 pH units calculated previously using polarizable force field (PFF) and Poisson Boltzmann formalism (PBF) continuum solvation model. These results are produced with fitting of specific atoms of the reference systems and carboxylic and basic residues of the OMTKY3 protein. Since FB model has produced improved pKa shifts of carboxylic residues and basic protein residues in OMTKY3 protein compared to PBF/PFF, it suggests the methodology of first-order FB continuum solvation model works well in such calculations. In this study the importance of explicit treatment of the electrostatic polarization in calculating pKa of both acid and basic protein residues is also emphasized. Moreover, the presented results demonstrate not only the consistently good degree of accuracy of protein pKa calculations with the second-degree POSSIM approximation of the polarizable calculations and the first-order approximation used in the Fuzzy-Border model for the continuum solvation energy, but also a high degree of transferability of both the POSSIM and continuum solvent Fuzzy Border parameters. Therefore, the FB model of solvation combined with the POSSIM force field can be successfully applied to study the protein and protein-ligand systems in water. "
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Tigabu, Romel. "Modeling static creep with stress reversals of mastic asphalt." Thesis, KTH, Transportvetenskap, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-50950.
Full textAbstract:
This thesis studies the strain response of mastic asphalt to arbitrary tension, arbitrary compression, alternating tension/compression, loading, zigzag loading and sinusoidal loading. In order to model the strain response to different loading histories, the scissors model is employed. Matlab modules are developed that are able to predict strain response not only for creep loading but also for other types of non constant stress loading such as zigzag loading and sinusoidal loading. In addition, another phenomological model, i.e. the viscoelastoplastic continuum damage model, is summarized and discussed in detail with respect to its applicability for the available data set.
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Tyagi, Vipin. "A non-continuum approach to obtain a macroscopic model for the flow of traffic." Texas A&M University, 2003. http://hdl.handle.net/1969.1/5913.
Full textAbstract:
Existing macroscopic models for the flow of traffic treat traffic as a continuum or
employ techniques similar to those used in the kinetic theory of gases. Spurious two-
way propagation of disturbances that are physically unacceptable are predicted by
continuum models for the flow of traffic. The number of vehicles in a typical section
of a freeway does not justify traffic being treated as a continuum. It is also important
to recognize that the basic premises of kinetic theory are not appropriate for the flow
of traffic. A model for the flow of traffic that does not treat traffic as a continuum
or use notions from kinetic theory is developed in this dissertation and corroborated
with traffic data collected from the sensors deployed on US 183 freeway in Austin,
Texas, USA.
The flow of traffic exhibits distinct characteristics under different conditions and
reflects the congestion during peak hours and relatively free motion during off-peak
hours. This requires one to use different governing equations to describe the diverse
traffic characteristics, namely the different traffic flow regimes of response. Such
an approach has been followed in this dissertation. An observer based on extended
Kalman filtering technique has been utilized for the purpose of estimating the traffic state. Historical traffic data has been used for model calibration. The estimated
model parameters have consistent values for different traffic conditions. These esti-
mated model parameters are then subsequently used for estimation of the state of
traffic in real-time.
A short-term traffic state forecasting approach, based on the non-continuum
traffic model, which incorporates weighted historical and real-time traffic information
has been developed. A methodology for predicting trip travel time based on this
approach has also been developed. Ten and fifteen minute predictions for traffic state
and trip travel time seem to agree well with the traffic data collected on US 183.
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Bai, Jie. "A homogenization based continuum plasticity-damage model for ductile fracture of materials containing heterogeneities." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1211910660.
Full text
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Laurie, Henri De Guise. "The general continuum model for structured populations, with two case studies in plant ecology." Doctoral thesis, University of Cape Town, 1994. http://hdl.handle.net/11427/18243.
Full textAbstract:
Bibliography: p. 129-143.The broad aim of this thesis is to investigate the formulation and usefulness of a very general model for plant population dynamics. In chapter 1, the goal of generality is discussed, particularly in the light of the lack of interaction between field and experimental population studies on the one hand and theoretical population dynamics on the other hand. A distinction is ma.de between descriptive and axiomatic theories, and it is suggested that they serve different purposes. The advantages of a. rigorous framework are pointed out and the basic elements of the continuum approach are introduced. In chapter 2, the model is proposed, the existence and uniqueness of solutions to its equations is proved, and an algorithm for numerically -approximating transient solutions is discussed. The question of generality is addressed in two places, and it is argued that the basic framework presented here is in principle adequate to model the processes of plant population dynamics in full detail, though the existence proof cannot to accommodate all possible models. In particular, models with time lags are excluded. Further limitations of the existence proof ill terms of constitutive relations are pointed out. In consequence, the theory here presented does not fully exploit the possibilities for generality inherent in the basic equations. In chapter 3, the question of what data would allow identification of factors determining somatic growth and mortality is investigated computationally. It is shown that using only the average size is insufficient. A class of models which includes all possible combinations of three types of size dependence in somatic growth and mortality is formulated. Qualitative parameter estimation for the various models yields size distributions that can be classified into the following biologically meaningful groups: group (i) has no models that use dependence on relative size; group (ii) has all the models in which somatic growth depends on relative size group (iii) has the models where only mortality depends on relative size. Thus it appears that size distribution may be used to distinguish various forms of size dependence in somatic growth and mortality. In chapter 4, a lottery model criterion for coexistence of plants with disjoint generations is developed, which is shown to require relative density dependence. Computer simulations aiming to initiate the use of exploratory calculations in studies of coexisting serotinous proteoids in fynbos indicate that the aspect of plant population dynamics most sensitive to density dependence is seed production, then somatic growth, while mortality is least sensitive to density dependence.
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Armstrong, Kenneth Weber. "A Microscopic Continuum Model of a Proton Exchange Membrane Fuel Cell Electrode Catalyst Layer." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/10080.
Full textAbstract:
A series of steady-state microscopic continuum models of the cathode catalyst layer (active layer) of a proton exchange membrane fuel cell are developed and presented. This model incorporates O₂ species and ion transport while taking a discrete look at the platinum particles within the active layer. The original 2-dimensional axisymmetric Thin Film and Agglomerate Models of Bultel, Ozil, and Durand [8] were initially implemented, validated, and used to generate various results related to the performance of the active layer with changes in the thermodynamic conditions and geometry. The Agglomerate Model was then further developed, implemented, and validated to include among other things pores, flooding, and both humidified air and humidified O₂. All models were implemented and solved using FEMAP™ and a computational fluid dynamics (CFD) solver, developed by Blue Ridge Numerics Inc. (BRNI) called CFDesign™. The use of these models for the discrete modeling of platinum particles is shown to be beneficial for understanding the behavior of a fuel cell. The addition of gas pores is shown to promote high current densities due to increased species transport throughout the agglomerate. Flooding is considered, and its effect on the cathode active layer is evaluated. The model takes various transport and electrochemical kinetic parameters values from the literature in order to do a parametric study showing the degree to which temperature, pressure, and geometry are crucial to overall performance. This parametric study quantifies among a number of other things the degree to which lower porosities for thick active layers and higher porosities for thin active layers are advantageous to fuel cell performance. Cathode active layer performance is shown not to be solely a function of catalyst surface area but discrete catalyst placement within the agglomerate.Master of Science