The numerical solution of dynamic response of SDOF systems using cubic B-spline polynomial functions

Shojaee, S.,Rostami, S.,Moeinadini, A. Techno-Press 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.38 No.2

In this paper, we present a new explicit procedure using periodic cubic B-spline interpolation polynomials to solve linear and nonlinear dynamic equation of motion governing single degree of freedom (SDOF) systems. In the proposed approach, a straightforward formulation was derived from the approximation of displacement with B-spline basis in a fluent manner. In this way, there is no need to use a special pre-starting procedure to commence solving the problem. Actually, this method lies in the case of conditionally stable methods. A simple step-by-step algorithm is implemented and presented to calculate dynamic response of SDOF systems. The validity and effectiveness of the proposed method is demonstrated with four examples. The results were compared with those from the numerical methods such as Duhamel integration, Linear Acceleration and also Exact method. The comparison shows that the proposed method is a fast and simple procedure with trivial computational effort and acceptable accuracy exactly like the Linear Acceleration method. But its power point is that its time consumption is notably less than the Linear Acceleration method especially in the nonlinear analysis.

Combination of isogeometric analysis and extended finite element in linear crack analysis

Shojaee, S.,Ghelichi, M.,Izadpanah, E. Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.48 No.1

This paper intends to present an application of isogeometric analysis in crack problems. An isogeometric formula is developed based on NURBS basis functions - enriched and adopted via X-FEM enrichment functions. The proposed method which is represented by the combination of the two above-mentioned methods, first by using NURBS functions models the geometry exactly and then by defining level set function on domain, identifies available discontinuity in elements. Additional DOFs are allocated to elements containing the crack and X-FEM enrichment functions enrich approximate solution. Moreover, a subelement refinement technique is used to improve the accuracy of integration by the Gauss quadrature rule. Finally, several numerical examples are illustrated to demonstrate the effectiveness, robustness and accuracy of the proposed method during calculation of crack parameters.

NURBS-based isogeometric analysis for thin plate problems

Shojaee, S.,Valizadeh, N. Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.41 No.5

An isogeometric approach is presented for static analysis of thin plate problems of various geometries. Non-Uniform Rational B-Splines (NURBS) basis function is applied for approximation of the thin plate deflection, as for description of the geometry. The governing equation based on Kirchhoff plate theory, is discretized using the standard Galerkin method. The essential boundary conditions are enforced by the Lagrange multiplier method. Several typical examples of thin plate and thin plate on elastic foundation are solved and compared with the theoretical solutions and other numerical methods. The numerical results show the robustness and efficiency of the proposed approach.

NURBS-based isogeometric analysis for thin plate problems

S. Shojaee,N. Valizadeh 국제구조공학회 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.41 No.5

An isogeometric approach is presented for static analysis of thin plate problems of various geometries. Non-Uniform Rational B-Splines (NURBS) basis function is applied for approximation of the thin plate deflection, as for description of the geometry. The governing equation based on Kirchhoff plate theory, is discretized using the standard Galerkin method. The essential boundary conditions are enforced by the Lagrange multiplier method. Several typical examples of thin plate and thin plate on elastic foundation are solved and compared with the theoretical solutions and other numerical methods. The numerical results show the robustness and efficiency of the proposed approach.

The numerical solution of dynamic response of SDOF systems using cubic B-spline polynomial functions

S. Shojaee,S. Rostami,A. Moeinadini 국제구조공학회 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.38 No.2

In this paper, we present a new explicit procedure using periodic cubic B-spline interpolation polynomials to solve linear and nonlinear dynamic equation of motion governing single degree of freedom (SDOF) systems. In the proposed approach, a straightforward formulation was derived from the approximation of displacement with B-spline basis in a fluent manner. In this way, there is no need to use a special pre-starting procedure to commence solving the problem. Actually, this method lies in the case of conditionally stable methods. A simple step-by-step algorithm is implemented and presented to calculate dynamic response of SDOF systems. The validity and effectiveness of the proposed method is demonstrated with four examples. The results were compared with those from the numerical methods such as Duhamel integration, Linear Acceleration and also Exact method. The comparison shows that the proposed method is a fast and simple procedure with trivial computational effort and acceptable accuracy exactly like the Linear Acceleration method. But its power point is that its time consumption is notably less than the Linear Acceleration method especially in the nonlinear analysis.

Prediction of Diabetes Using Data Mining and Machine Learning Algorithms: A Cross-Sectional Study

Hassan Shojaee-Mend,Farnia Velayati,Batool Tayefi,Ebrahim Babaee 대한의료정보학회 2024 Healthcare Informatics Research Vol.30 No.1

Objectives: This study aimed to develop a model to predict fasting blood glucose status using machine learning and datamining, since the early diagnosis and treatment of diabetes can improve outcomes and quality of life. Methods: This crosssectionalstudy analyzed data from 3376 adults over 30 years old at 16 comprehensive health service centers in Tehran, Iranwho participated in a diabetes screening program. The dataset was balanced using random sampling and the synthetic minorityover-sampling technique (SMOTE). The dataset was split into training set (80%) and test set (20%). Shapley valueswere calculated to select the most important features. Noise analysis was performed by adding Gaussian noise to the numericalfeatures to evaluate the robustness of feature importance. Five different machine learning algorithms, including CatBoost,random forest, XGBoost, logistic regression, and an artificial neural network, were used to model the dataset. Accuracy,sensitivity, specificity, accuracy, the F1-score, and the area under the curve were used to evaluate the model. Results: Age,waist-to-hip ratio, body mass index, and systolic blood pressure were the most important factors for predicting fasting bloodglucose status. Though the models achieved similar predictive ability, the CatBoost model performed slightly better overallwith 0.737 area under the curve (AUC). Conclusions: A gradient boosted decision tree model accurately identified the mostimportant risk factors related to diabetes. Age, waist-to-hip ratio, body mass index, and systolic blood pressure were the mostimportant risk factors for diabetes, respectively. This model can support planning for diabetes management and prevention.

Combination of isogeometric analysis and extended finite element in linear crack analysis

S. Shojaee,M. Ghelichi,E. Izadpanah 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.48 No.1

This paper intends to present an application of isogeometric analysis in crack problems. An isogeometric formula is developed based on NURBS basis functions - enriched and adopted via X-FEM enrichment functions. The proposed method which is represented by the combination of the two abovementioned methods, first by using NURBS functions models the geometry exactly and then by defining level set function on domain, identifies available discontinuity in elements. Additional DOFs are allocated to elements containing the crack and X-FEM enrichment functions enrich approximate solution. Moreover, a subelement refinement technique is used to improve the accuracy of integration by the Gauss quadrature rule. Finally, several numerical examples are illustrated to demonstrate the effectiveness, robustness and accuracy of the proposed method during calculation of crack parameters.

Cut out effect on nonlinear post-buckling behavior of FG-CNTRC micro plate subjected to magnetic field via FSDT

Jamali, M.,Shojaee, T.,Mohammadi, B.,Kolahchi, R. Techno-Press 2019 Advances in nano research Vol.7 No.6

This research is devoted to study post-buckling analysis of functionally graded carbon nanotubes reinforced composite (FG-CNTRC) micro plate with cut out subjected to magnetic field and resting on elastic medium. The basic formulation of plate is based on first order shear deformation theory (FSDT) and the material properties of FG-CNTRCs are presumed to be changed through the thickness direction, and are assumed based on rule of mixture; moreover, nonlocal Eringen's theory is applied to consider the size-dependent effect. It is considered that the system is embedded in elastic medium and subjected to longitudinal magnetic field. Energy approach, domain decomposition and Rayleigh-Ritz methods in conjunction with Newton-Raphson iterative technique are employed to trace the post-buckling paths of FG-CNTRC micro cut out plate. The influence of some important parameters such as small scale effect, cut out dimension, different types of FG distributions of CNTs, volume fraction of CNTs, aspect ratio of plate, magnitude of magnetic field, elastic medium and biaxial load on the post-buckling behavior of system are calculated. With respect to results, it is concluded that the aspect ratio and length of square cut out have negative effect on post-buckling response of micro composite plate. Furthermore, existence of CNTs in system causes improvement in the post-buckling behavior of plate and different distributions of CNTs in plate have diverse response. Meanwhile, nonlocal parameter and biaxial compression load on the plate has negative effect on post-buckling response. In addition, imposing magnetic field increases the post-buckling load of the microstructure.

A direct damage detection method using Multiple Damage Localization Index Based on Mode Shapes criterion

Homaei, F.,Shojaee, S.,Amiri, G. Ghodrati Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.49 No.2

A new method of multiple damage detection in beam like structures is introduced. The mode shapes of both healthy and damaged structures are used in damage detection process (DDP). Multiple Damage Localization Index Based on Mode Shapes (MDLIBMS) is presented as a criterion in detecting damaged elements. A finite element modeling of structures is used to calculate the mode shapes parameters. The main advantages of the proposed method are its simplicity, flexibility on the number of elements and so the accuracy of the damage(s) position(s), sensitivity to small damage extend, capability in prediction of required number of mode shapes and low sensitivity to noisy data. In fact, because of differential and comparative form of MDLIBMS, using noise polluted data doesn't have major effect on the results. This makes the proposed method a powerful one in damage detection according to measured mode shape data. Because of its flexibility, damage detection process in multi span bridge girders with non-prismatic sections can be done by this method. Numerical simulations used to demonstrate these advantages.

Computational fluid dynamics studies of dry and wet pressure drops in structured packings

Seyyed Hossein Hosseini,Saeed Shojaee,Goodarz Ahmadi,Mortaza Zivdar 한국공업화학회 2012 Journal of Industrial and Engineering Chemistry Vol.18 No.4

Computational fluid dynamics was used to study the hydrodynamic of structured packings. The results showed that the k–v was a suitable turbulence model for analyzing the flows in structured packings. A simple method was proposed for evaluating the liquid holdup based on the Iliuta and Larachi (2001)model [25], the calculated liquid film thickness in 2D framework, and the empirical correlation of Brito et al. (1994) [26]. The presented method can be used for estimating the wet pressure drop in 3D structured packings for loading region with good accuracy as well as computational economy. The process of liquid film formation was also discussed.