Characteristics and outcomes of patients with chronic obstructive pulmonary disease admitted to the intensive care unit due to acute hypercapnic respiratory failure

Türkay Akbaş,Harun Güneş 대한중환자의학회 2023 Acute and Critical Care Vol.38 No.1

Background The study aimed to describe the clinical course, outcomes, and prognostic factors of chronic obstructive pulmonary disease (COPD) patients with acute hypercapnic respiratory failure. Methods This retrospective study involved patients with acute hypercapnic respiratory failure due to COPD of any cause admitted to the intensive care unit (ICU) for non-invasive or invasive mechanical ventilation (IMV) support between December 2015 and February 2020. Results One hundred patients were evaluated. The main causes of acute hypercapnic respiratory failure were bronchitis, pneumonia, and heart failure. The patients’ mean Acute Physiology and Chronic Health Evaluation (APACHE) II score was 23.0±7.2, and their IMV rate was 43%. ICU, in-hospital, and 90-day mortality rates were 21%, 29%, and 39%, respectively. Non-survivors had more pneumonia, shock within the first 24 hours of admission, IMV, vasopressor use, and renal replacement therapy, along with higher APACHE II scores, lower admission albumin levels and PaO2/FiO2 ratios, and longer ICU and hospital stays than survivors. Logistic regression analysis identified APACHE II scores (odds ratio [OR], 1.157; 95% confidence interval [CI], 1.017–1.317; P=0.026), admission PaO2/FiO2 ratio (OR, 0.989; 95% CI, 0.978–0.999; P=0.046), and vasopressor use (OR, 8.827; 95% CI, 1.650–47.215; P=0.011) as predictors of ICU mortality. APACHE II scores (OR, 1.099; 95% CI, 1.021–1.182; P=0.011) and admission albumin level (OR, 0.169; 95% CI, 0.056–0.514; P=0.002) emerged as predictors of 90-day mortality. Conclusions APACHE II scores, the PaO2/FiO2 ratio, vasopressor use, and albumin levels are significant short-term mortality predictors in severely ill COPD patients with acute hypercapnic respiratory failure.

Wave propagation of a functionally graded beam in thermal environments

Şeref Doğuşcan Akbaş 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.19 No.6

In this paper, the effect of material-temperature dependent on the wave propagation of a cantilever beam composed of functionally graded material (FGM) under the effect of an impact force is investigated. The beam is excited by a transverse triangular force impulse modulated by a harmonic motion. Material properties of the beam are temperature-dependent and change in the thickness direction. The Kelvin–Voigt model for the material of the beam is used. The considered problem is investigated within the Euler-Bernoulli beam theory by using energy based finite element method. The system of equations of motion is derived by using Lagrange's equations. The obtained system of linear differential equations is reduced to a linear algebraic equation system and solved in the time domain and frequency domain by using Newmark average acceleration method. In order to establish the accuracy of the present formulation and results, the comparison study is performed with the published results available in the literature. Good agreement is observed. In the study, the effects of material distributions and temperature rising on the wave propagation of the FGM beam are investigated in detail.

Geometrically nonlinear analysis of a laminated composite beam

Şeref D. Akbaş 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.1

The objective of this work is to analyze geometrically nonlinear static analysis a simply supported laminated composite beam subjected to a non-follower transversal point load at the midpoint of the beam. In the nonlinear model of the laminated beam, total Lagrangian finite element model of is used in conjunction with the Timoshenko beam theory. The considered non-linear problem is solved considering full geometric non-linearity by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. There is no restriction on the magnitudes of deflections and rotations in contradistinction to von-Karman strain displacement relations of the beam. In the numerical results, the effects of the fiber orientation angles and the stacking sequence of laminates on the nonlinear deflections and stresses of the composite laminated beam are examined and discussed. Convergence study is performed. Also, the difference between the geometrically linear and nonlinear analysis of laminated beam is investigated in detail.

Post-buckling responses of a laminated composite beam

Şeref D. Akbaş 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.26 No.6

This paper presents post-buckling responses of a simply supported laminated composite beam subjected to a non-follower axially compression loads. In the nonlinear kinematic model of the laminated beam, total Lagrangian approach is used in conjunction with the Timoshenko beam theory. In the solution of the nonlinear problem, incremental displacement-based finite element method is used with Newton-Raphson iteration method. There is no restriction on the magnitudes of deflections and rotations in contradistinction to von-Karman strain displacement relations of the beam. The distinctive feature of this study is post-buckling analysis of Timoshenko Laminated beams full geometric non-linearity and by using finite element method. The effects of the fibber orientation angles and the stacking sequence of laminates on the post-buckling deflections, configurations and stresses of the composite laminated beam are illustrated and discussed in the numerical results. Numerical results show that the above-mentioned effects play a very important role on the post-buckling responses of the laminated composite beams.

Geometrically nonlinear analysis of functionally graded porous beams

Şeref D. Akbaş 한국풍공학회 2018 Wind and Structures, An International Journal (WAS Vol.27 No.1

In this paper, geometrically non-linear analysis of a functionally graded simple supported beam is investigated with porosity effect. The material properties of the beam are assumed to vary though height direction according to a prescribed power-law distributions with different porosity models. In the nonlinear kinematic model of the beam, the total Lagrangian approach is used within Timoshenko beam theory. In the solution of the nonlinear problem, the finite element method is used in conjunction with the Newton-Raphson method. In the study, the effects of material distribution such as power-law exponents, porosity coefficients, nonlinear effects on the static behavior of functionally graded beams are examined and discussed with porosity effects. The difference between the geometrically linear and nonlinear analysis of functionally graded porous beam is investigated in detail. Also, the effects of the different porosity models on the functionally graded beams are investigated both linear and nonlinear cases.

Size dependent vibration of laminated micro beams under moving load

Ş.D. Akbaş 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.46 No.2

The goal of this paper is to investigate dynamic responses of simply-supported laminated micro beams under moving load. In the considered micro-scale problem, the modified coupled stress theory which includes the length scale parameter is used. The governing equations of problem are derived by using the Lagrange procedure. In the solution of the problem the Ritz method is used and algebraic polynomials are used with the trivial functions for the Ritz method. In the solution of the moving load problem, the Newmark average acceleration method is used in the time history. In the numerical examples, the effects of stacking sequence of laminas, fibre orientation angles and the length scale parameter on the dynamic responses of laminated micro beams are examined and discussed.

Nonlinear static analysis of laminated composite beams under hygro-thermal effect

Şeref D. Akbaş 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.72 No.4

In this paper, geometrically nonlinear static analysis of laminated composite beams is investigated under hygrothermal effect. In the solution of problem, the finite element method is used within the first shear beam theory. Total Lagrangian approach is used nonlinear kinematic model. The geometrically nonlinear formulations are developed for the laminated beams with hygro-thermal effects. In the nonlinear solution of the problem, the Newton-Raphson method is used with incremental displacement. In order to verify of obtained formulations, a comparison study is performed. The effects of the fiber orientation angles, the stacking sequence of laminates, temperature rising and moisture changes on the nonlinear static displacements and configurations of the composite laminated beam are investigated in the numerical results.

Dynamic responses of laminated beams under a moving load in thermal environment

Şeref D. Akbaş 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.35 No.6

The goal of this study is to investigate dynamic responses of laminated composite beams under a moving load with thermal effects. The governing equations of problem are derived by using the Lagrange procedure. The transverse-shear strain and rotary inertia are considered within the Timoshenko beam theory. The material properties of laminas are considered as the temperature dependent physical property. The differential equations of the problem are solved by the Ritz method. The solution step of dynamic problem, the Newmark average acceleration method is used in the time history. A compassion study is performed for accuracy of used formulations and method. In the numerical results, the effects of velocity of moving load, temperature values, the fiber orientation angles and the stacking sequence of laminas on the dynamic responses of the composite laminated beam are investigated.

Large deflection analysis of edge cracked simple supported beams

Şeref Doğuşcan Akbaş 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.54 No.3

This paper focuses on large deflection static behavior of edge cracked simple supported beamssubjected to a non-follower transversal point load at the midpoint of the beam by using the total Lagrangian Timoshenko beam element approximation. The cross section of the beam is circular. The cracked beam is modeled as an assembly of two sub-beams connected through a massless elastic rotational spring. It is known that large deflection problems are geometrically nonlinear problems. The considered highly nonlinear problem is solved considering full geometric non-linearity by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. There is no restriction on the magnitudes of deflections and rotations in contradistinction to von-Karman strain displacement relations of the beam. The beams considered in numerical examples are made of Aluminum. In the study, the effects of the location of crack and the depth of the crack on the non-linear static response of the beam are investigated in detail. The relationships between deflections, end rotational angles, end constraint forces, deflection configuration, Cauchy stresses of the edge- cracked beams and load rising are illustrated in detail in nonlinear case. Also, the difference between the geometrically linear and nonlinear analysis of edge-cracked beam is investigated in detail.

Large deflection analysis of a fiber reinforced composite beam

Şeref D. Akbaş 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.27 No.5

The objective of this work is to analyze large deflections of a fiber reinforced composite cantilever beam under point loads. In the solution of the problem, finite element method is used in conjunction with two dimensional (2-D) continuum model. It is known that large deflection problems are geometrically nonlinear problems. The considered non-linear problem is solved considering the total Lagrangian approach with Newton-Raphson iteration method. In the numerical results, the effects of the volume fraction and orientation angles of the fibre on the large deflections of the composite beam are examined and discussed. Also, the difference between the geometrically linear and nonlinear analysis of fiber reinforced composite beam is investigated in detail.