Research Papers - Department of Civil Engineering
Permanent URI for this collectionhttps://rda.sliit.lk/handle/123456789/598
Browse
13 results
Filters
Advanced Search
Filter by
Settings
Search Results
Publication Open Access Visibility of pharyngeal structures as a predictor of difficult intubation(Blackwell Publishing Ltd, 1987-10) Charters, P; Perera, S. V. T; Horton, W. AVisibility of pharyngeal structures as a predictor of difficult intubation Page 1 Correspondence 1115 Visibility of pharyngeal structures as a predictor of difficult intubation We would like to comment on the study by Samsoon and Young (Anuesihesh 1987; 42: 487-90) since we also have experience with the test which forms the basis of their report. Mallampati’s test scores the visibility of pharyngcal structures (faucial pillars, soft palate and uvula) in an attempt to predict difficult tracheal intubation. Three of us used this test as part of a pre-operative asscssmcnt in a study about tracheal intubation. Sainsoon and Young did not make it clear in their paper hut thcy did not make the assessment in the way described by Mallampati. We also chosc to examine our patients with ‘the head in the neutral position’ and the observer sitting ‘opposite at eye level’. We graded paticiits class 1 to 3 as originally described because Mallampati …Publication Open Access Visibility of pharyngeal structures as a predictor of difficult intubation(Blackwell Publishing Ltd, 1987-10) Charters, P; Perera, S. V. T; Horton, W. AVisibility of pharyngeal structures as a predictor of difficult intubation Page 1 Correspondence 1115 Visibility of pharyngeal structures as a predictor of difficult intubation We would like to comment on the study by Samsoon and Young (Anuesihesh 1987; 42: 487-90) since we also have experience with the test which forms the basis of their report. Mallampati’s test scores the visibility of pharyngcal structures (faucial pillars, soft palate and uvula) in an attempt to predict difficult tracheal intubation. Three of us used this test as part of a pre-operative asscssmcnt in a study about tracheal intubation. Sainsoon and Young did not make it clear in their paper hut thcy did not make the assessment in the way described by Mallampati. We also chosc to examine our patients with ‘the head in the neutral position’ and the observer sitting ‘opposite at eye level’. We graded paticiits class 1 to 3 as originally described because MallampatiPublication Embargo Elastodynamic Green's functions of orthotropic half plane(American Society of Civil Engineers, 1991-03-01) Rajapakse, R.K.N.D; Wang, Y.The dynamic response of an orthotropic elastic half plane subjected to a set of time‐harmonic buried loadings is investigated. The governing differential equations are established in terms of displacements and a general solution is derived using Fourier integral transforms with respect to the x‐coordinate. The boundary‐value problems corresponding to time‐harmonic vertical and horizontal loads acting in the interior of the half plane are solved. Explicit analytical solutions are presented for displacements and stresses due to buried uniformly distributed and concentrated loadings. Some characteristics of the analytical solution are investigated, and its numerical evaluation is also discussed. Selected numerical results for displacements and stresses of isotropic, ice, layered soil, and cadmium half‐plane regions are presented. A discussion of these numerical solutions is presented to investigate the influence of the degree of material anisotropy, frequency of excitation, and the type of loading on the response of the elastic half plane.Publication Open Access Vertical vibrations of a rigid disk embedded in a poroelastic medium(John Wiley & Sons, Ltd., 1999-12-25) Zeng, X; Rajapakse, R. K. N. Dhis paper considers the steady-state vertical vibrations of a rigid circular disk embedded at a finite depth below the free surface of a poroelastic medium. Biot's elastodynamic theory for porous media is used in the analysis. General solutions for axisymmetric poroelastic fields are obtained by using Hankel integral transforms. Analytical solutions for influence functions corresponding to four types of buried axisymmetric excitations are derived. The embedded disk problem is fomulated in terms of a set of coupled integral equations for unknown traction and pore pressure jumps across the disk. The kernel functions of the integral equations are the influence functions corresponding to buried vertical, radial and pore pressure ring loads. The system of integral equations is solved numerically by discretizing the disk into several concentric annular rings. Selected numerical solutions for displacements, vertical stress and pore pressure due to a buried fully flexible disk (uniform pressure) are also presented. The vertical compliances of a rigid disk are examined for different depths of embedment, poroelastic materials and hydraulic boundary conditions. Solutions for traction and pore pressure jumps are also examined. The present results are useful in the study of dynamic response of embedded foundations and anchors in poroelastic soils.Publication Embargo On the longitudinal harmonic motion of an elastic bar embedded in an elastic half-space(Pergamon, 1987-01-01) Shah, A.H; Rajapakse, R. K. N. DThe present study is concerned with the motion of a long cylindrical elastic bar which is partially embedded in a homogeneous elastic half-space and subjected to a harmonic axial load. Initially Green's functions corresponding to axisymmetric harmonic ring loads are derived and presented explicitly. It is found that the direct extension of elastostatic solution schemes to solve elastodynamic problems may lead to erroneous solutions due to the inability of these algorithms to properly account for inertia effects. Some discrepancies in existing solutions with respect to the inertia component of the bar are shown. An efficient solution scheme, based on Lagrange's equation of motion and a discretization technique, is presented to solve the title problem. Numerical results are presented to illustrate the influence of bar flexibility, mass density, geometry, and frequency of excitation on the axial impedance of the system.Publication Embargo Exact stiffness method for quasi-statics of a multi-layered poroelastic medium(Pergamon, 1995-06-01) Senjuntichai, T; Rajapakse, R. K. N. DA method is presented to study the three-dimensional quasi-static response of a multi-layered poroelastic half-space with compressible constituents. The system under consideration consists of N layers of different thickness and material properties overlying a homogeneous half-space. Fourier expansion, Laplace transforms and Hankel transforms with respect to the circumferential, time and radial coordinates, respectively, are used in the formulation. Laplace-Hankel transforms of displacements and pore pressure at layer interfaces are considered as the basic unknowns. Exact stiffness matrices describing the relationship between generalized displacement and force vectors of a finite layer and a half-space are derived explicitly in the transform space. The global stiffness matrix of a layered system is assembled by considering the continuity of tractions and fluid flow at layer interfaces. The time histories of displacements, stresses and pore pressure are obtained by solving the stiffness equation system for discrete values of Laplace and Hankel transform parameters, and using numerical quadrature schemes for Laplace and Hankel transform inversions. Selected numerical results for different layered systems are presented to portray the influence of layering and poroelastic material properties. The advantage of the present method is that for an N-layered system, it yields a numerically stable symmetric stiffness matrix of order 4N × 4N when compared to the unsymmetric and numerically unstable coefficient matrix of order 8N × 8N associated with the conventional method based on the determination of layer arbitrary coefficients.Publication Embargo A coupled thermoporoelastic model with thermo-osmosis and thermal-filtration(Pergamon, 1998-12-01) Rajapakse, R. K. N. D; Zhou, Y; Graham, JA coupled thermoporoelastic model accounting for compressibility and thermal expansion of constituents, convective heat flow and changing porosity and related properties of a saturated soil is presented. The model also considers thermodynamically coupled water and heat flow (thermal-filtration and thermo-osmosis that are analogous to Sorêt and Dufour effects in solutions) . These coupling effects are reported to be significant in the case of semi-impermeable clay barriers used in waste repositories. The governing equations derived in terms of displacements, temperature and pore water pressure are non-linear. A mixed finite element formulation is presented to obtain numerical solutions. An exact analytical solution for a 1-D soil column is presented for a simplified linear case that includes thermodynamic coupling. Selected numerical solutions for soil columns and radially symmetric plane strain problems are presented to demonstrate the principle features of the coupled model and the significance of thermodynamic coupling.Publication Embargo Transient response of a circular cavity in a poroelastic medium(John Wiley & Sons, Ltd, 1993-06) Rajapakse, R. K. N. D; Senjuntichai, TThis paper considers the transient response of a pressurized long cylindrical cavity in an infinite poroelastic medium. To obtain transient solutions, Biot's equations for poroelastodynamics are specialized for this problem. A set of exact general solutions for radial displacement, stresses, pore pressure and discharge are derived in the Laplace transform space by using analytical techniques. Solutions are presented for three different types of prescribed transient radial pressures acting on the surface of a permeable as well as an impermeable cavity surface. Time domain solutions are obtained by inverting Laplace domain solutions using a reliable numerical scheme. A detailed parametric study is presented to illustrate the influence of poroelastic material parameters and hydraulic boundary conditions on the response of the medium. Comparisons are also presented with the corresponding ideal elastic solutions to portray the poroelastic effects. It is noted that the maximum radial displacement and hoop stress at the cavity surface are substantially higher than the classical static solutions and differ considerably from the transient elastic solutions. Time histories and radial variations of displacement, hoop stress, pore pressure and fluid discharge corresponding to a cavity in two representative poroelastic materials are also presented.Publication Embargo Dynamic Green's functions of homogeneous poroelastic half-plane(American Society of Civil Engineers, 1994-11) Rajapakse, R. K. N. D; Senjuntichai, TThis paper presents a comprehensive analytical and numerical treatment of two‐dimensional dynamic response of a dissipative poroelastic half‐plane under time‐harmonic internal loads and fluid sources. General solutions for poroelastodynamic equations corresponding to Biot's theory are obtained by using Fourier integral transforms in the x‐direction. These general solutions are used to solve boundary‐value problems corresponding to vertical and horizontal loads, and fluid sources applied at a finite depth below the surface of a poroelastic half‐plane. Explicit analytical solutions corresponding to above‐boundary‐value problems are presented. The solutions for poroelastic fields of a half‐plane subjected to internal excitations are expressed in terms of semiinfinite Fourier type integrals that can only be evaluated by numerical quadrature. The integration path is free from any singularities due to the dissipative nature of the elastic waves propagating in a poroelastic medium, and the Fourier integrals are evaluated by using an adaptive version of the trapezoidal rule. The accuracy of present numerical solutions are confirmed by comparison with existing solutions for ideal elasticity and poroelasticity. Selected numerical results are presented to portray the influence of the frequency of excitation, poroelastic material properties and types of loadings on the dynamic response of a poroelastic half‐plane. Green's functions presented in this paper can be used to solve a variety of elastodynamic boundary‐value problems and as the kernel functions in the boundary integral equation method.Publication Embargo Dynamic response of a multi‐layered poroelastic medium(John Wiley & Sons, Ltd, 1995-05) Rajapakse, R. K. N. D; Senjuntichai, TAn exact stiffness matrix method is presented to evaluate the dynamic response of a multi-layered poroelastic medium due to time-harmonic loads and fluid sources applied in the interior of the layered medium. The system under consideration consists of N layers of different properties and thickness overlying a homogeneous half-plane or a rigid base. Fourier integral transform is used with respect to the x-co-ordinate and the formulation is presented in the frequency domain. Fourier transforms of average displacements of the solid matrix and pore pressure at layer interfaces are considered as the basic unknowns. Exact stiffness (impedance) matrices describing the relationship between generalized displacement and force vectors of a layer of finite thickness and a half-plane are derived explicitly in the Fourier-frequency space by using rigorous analytical solutions for Biot's elastodynamic theory for porous media. The global stiffness matrix and the force vector of a layered system is assembled by considering the continuity of tractions and fluid flow at layer interfaces. The numerical solution of the global equation system for discrete values of Fourier transform parameter together with the application of numerical quadrature to evaluate inverse Fourier transform integrals yield the solutions for poroelastic fields. Numerical results for displacements and stresses of a few layered systems and vertical impedance of a rigid strip bonded to layered poroelastic media are presented. The advantages of the present method when compared to existing approximate stiffness methods and other methods based on the determination of layer arbitrary coefficients are discussed.