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Thermal fluid-structure interaction and coupled thermal-stress analysis in a cable stayed bridge exposed to fire

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Frontiers of Structural and Civil Engineering 2018年第4期12卷 609-628页

作者： nazim Abdul nariman Institute of Structural Mechanics Faculty of Civil EngineeringBauhaus Universitat WeimarMarienstrasse 1599423WeimarGermany

In this paper, thermal fluid structure-interaction (TFSI) and coupled thermal-stress analysis are utilized to identify the effects of transient and steady-state heat-transfer on the vortex induced vibration and fatigue of a segmental bridge deck due to fire incidents. Numerical simulations of TFSI models of the deck are dedicated to calculate the lift and drag forces in addition to determining the lock-in regions once using fluid-structure interaction (FSI) models and another using TFSI models. Vorticity and thermal convection fields of three fire scenarios are simulated and analyzed. Simiu and Scanlan benchmark is used to validate the TFSI models, where a good agreement was manifested between the two results. Extended finite element method (XFEM) is adopted to create 3D models of the cable stayed bridge to simulate the fatigue of the deck considering three fire scenarios. Choi and Shin benchmark is used to validate the damaged models of the deck in which a good coincide was seen between them. The results revealed that TFSI models and coupled thermal-stress models are significant in detecting earlier vortex induced vibration and lock-in regions in addition to predicting damages and fatigue of the deck due to fire incidents.

关键词： fire scenario transient heat transfer TFSI model coupled thermal-stress XFEM

A novel structural modification to eliminate the early coupling between bending and torsional mode shapes in a cable stayed bridge

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Frontiers of Structural and Civil Engineering 2017年第2期11卷 131-142页

作者： nazim Abdul nariman Institute of Structural Mechanics Faculty of Civil Engineering Bauhaus University Weimar Weimar 99423 Germany

In this paper, a novel structural modification approach has been adopted to eliminate the early coupling between the bending and torsional mode shapes of vibrations for a cable stayed bridge model generated using ABAQUS software. Two lateral steel beams are added to the middle span of the structure. Frequency analysis is dedicated to obtain the natural frequencies of the first eight mode shapes of vibrations before and after the structural modification approach. Numerical simulations of wind excitations are conducted for the 3D model of the cable stayed bridge with duration of 30 s supporting on real data of a strong wind from the literature. Both vertical and torsional displacements are calculated at the mid span of the deck to analyze both the bending and the torsional stiffness of the system before and after the structural modification. The results of the frequency analysis after applying lateral steel beams declared a safer structure against vertical and torsional vibrations and rarely expected flutter wind speed. Furthermore, the coupling between the vertical and torsional mode shapes has been removed to larger natural frequencies magnitudes with a high factor of safety. The novel structural approach manifested great efficiency in increasing vertical and torsional stiffness of the structure.

关键词： aeroelastic instability structural damping flutter wind speed bending stiffness torsional stiffness

Control efficiency optimization and Sobol＇s sensitivity indices of MTMDs design parameters for buffeting and flutter vibrations in a cable stayed bridge

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Frontiers of Structural and Civil Engineering 2017年第1期11卷 66-89页

作者： nazim Abdul nariman Institute of Structural Mechanics School of Civil Engineering Bauhaus University Weimar Weimar 99423 Germany

This paper studies optimization of three design parameters （mass ratio, frequency ratio and damping ratio） of multiple tuned mass dampers MTMDs that are applied in a cable stayed bridge excited by a strong wind using minimax optimization technique. ABAQUS finite element program is utilized to run numerical simulations with the support of MATLAB codes and Fast Fourier Transform FFT technique. The optimum values of these three parameters are validated with two benchmarks from the literature, first with Wang and coauthors and then with Lin and coauthors. The validation procedure detected a good agreement between the results. Box-Behnken experimental method is dedicated to formulate the surrogate models to represent the control efficiency of the vertical and torsional vibrations. Sobol＇s sensitivity indices are calculated for the design parameters in addition to their interaction orders. The optimization results revealed better performance of the MTMDs in controlling the vertical and the torsional vibrations for higher mode shapes. Furthermore, the calculated rational effects of each design parameter facilitate to increase the control efficiency of the MTMDs in conjunction with the support of the surrogate models.

关键词： MTMDs power spectral density fast Fourier transform minimax optimization technique Sobol's sensitivityindices Box-Behnken method

Uncertainty quantification of stability and damage detection parameters of coupled hydrodynamic-ground motion in concrete gravity dams

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Frontiers of Structural and Civil Engineering 2019年第2期13卷 303-323页

作者： nazim Abdul nariman Tom LAHMER Pevman KARAMPOUR Institute of Structural Mechanics Faculty of Civil EngineeringBauh aus Universitat Weimar99423 WeimarGermany Department of Mechanical Engineering Faculty of EngineeringArak UniversityArak 38156-8-8849Iran

In this paper, models of the global system of the Koyna dam have been created using ABAQUS software considering the dam-reservoir-fbundation interaction. Non coupled models and the coupled models were compared regarding the horizontal displacement of the dam crest and the differential settlement of the dam base in clay foundation. Meta models were constructed and uncertainty quantification process was adopted by the support of Sobol's sensitivity in dices considering five un certain parameters by exploiting Box-Behnken experimental method. The non coupled models results determined overestimated predicted stability and damage detection in the dam. The rational effects of the reservoir height were very sensitive in the variation of the horizontal displacement of the dam crest with a small interaction effect with the beta viscous damping coefficient of the clay fbundation. The modulus of elasticity of the clay foundation was the decisive parameter regarding the variation of the differential settlement of the dam base. The XFEM approach has been used for damage detection in relation with both minimum and maximum values of each uncertain parameter. Finally the effects of clay and rock foundations were determined regarding the resistance against the propagation of cracks in the dam, where the rock fbundation was the best.

关键词： massed foundation hydrodynamic pressure Box-Behnken method meta model Sobol's sensitivity indices

Application of coupled XFEM-BCQO in the structural optimization of a circular tunnel lining subjected to a ground motion

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Frontiers of Structural and Civil Engineering 2019年第6期13卷 1495-1509页

作者： nazim Abdul nariman Ayad Mohammad RAMADAN Ilham Ibrahim MOHAMMAD Department of Civil Engineering Tishk International University-SulaimaniSulaimaniya 46001Iraq Mathematics Department-College of Science Sulaimani UniversitySulaimaniya 46001Iraq

A new structural optimization method of coupled extended finite element method and bound constrained quadratic optimization method(XFEM-BCQO)is adopted to quantify the optimum values of four design parameters for a circular tunnel lining when it is subjected to *** parameters are:tunnel lining thickness,tunnel diameter,tunnel lining concrete modulus of elasticity and tunnel lining concrete ***-Carlo sampling method is dedicated to construct the meta models so that to be used for the BCQO method using matlab *** simulations of the tensile damage in the tunnel lining due to a real earthquake in the literature are created for three design *** approach is used to show the cracks for the mentioned design *** results of the BCQO method for the maximum design case for the tunnel tensile damage was matching the results obtained from XFEM approach to a fair *** new coupled approach manifested a significant capability to predict the cracks and spalling of the tunnel lining concrete under the effects of dynamic earthquakes.

关键词： ovaling deformation monte carlo sampling XFEM-BCQO maximum principal stress

Global sensitivity analysis of certain and uncertain factors for a circular tunnel under seismic action

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Frontiers of Structural and Civil Engineering 2019年第6期13卷 1289-1300页

作者： nazim Abdul nariman Raja Rizwan HUSSAIN Ilham Ibrahim MOHAMMAD Peyman KARAMPOUR Department of Civil Engineering Tishk International University SulaimaniSulaimaniya 46001Iraq Civil Engineering Department College of EngineeringKing Saud UniversityRiyadh 11421Saudi Arabia Department of Mechanical Engineering Faculty of EngineeringArak UniversityArak 38156-875Iran

There are many certain and uncertain design factors which have unrevealed rational effects on the generation of tensile damage and the stability of the circular tunnels during seismic *** this research paper,we have dedicated three certain and four uncertain design factors to quantify their rational effects using numerical simulations and the Sobol's sensitivity *** effects and interaction effects between the design factors have been determined supporting on variance-based global sensitivity *** results detected that the concrete modulus of elasticity for the tunnel lining has the greatest effect on the tensile damage generation in the tunnel lining during the seismic *** the other direction,the interactions between the concrete density and both of concrete modulus of elasticity and tunnel diameter have appreciable effects on the tensile ***,the tunnel diameter has the deciding effect on the stability of the tunnel *** the interaction between the tunnel diameter and concrete density has appreciable effect on the stability *** is worthy to mention that SoboFs sensitivity indices manifested strong efficiency in detecting the roles of each design factor in cooperation with the numerical simulations explaining the responses of the circular tunnel during seismic actions.

关键词： shear waves SoboFs sensitivity indices maximum principal stress maximum overall displacement tensile damage

Kinetic energy based model assessment and sensitivity analysis of vortex induced vibration of segmental bridge decks

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Frontiers of Earth Science 2017年第4期11卷 480-501页

作者： nazim Abdul nariman Institute of Structural Mechanics Faculty of Civil Engineering Bauhaus Universitat Weimar Weimar 99423 Germany

In this paper, semi 3D models for segmental Bridge decks are created in ABAQUS CFD program with the support of MATLAB codes to simulate and analyze vortex shedding generated due to wind excitation through considering the stationary position of the deck. Three parameters （wind speed, deck streamlined length and dynamic viscosity of the air） are dedicated to study their effects on the kinetic energy of the system in addition to the shapes and patterns of the vortices. Two benchmarks from the literature Von Karman and Dyrbye and Hansen are considered to validate the vortex shedding aspects for the CFD models. Good agreement between the results of the benchmarks and the semi 3D models has been detected. Latin hypereube experimental method is dedicated to generate the surrogate models for the kinetic energy of the system and the lift forces. Variance based sensitivity analysis is utilized to calculate the main sensitivity indices and the interaction orders for all the three parameters. The kinetic energy approach performed very well in revealing the rational effects and the roles of each parameter in the generation of vortex shedding and predicting vortex induced vibration of the deck.

关键词： vortex induced vibration reynolds number kinetic energy vorticity latin hypercube sampling

Prediction meta-models for the responses of a circular tunnel during earthquakes

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Underground Space 2019年第1期4卷 31-47页

作者： nazim Abdul nariman Raja Rizwan Hussain Mohammed A Msekh Peyman Karampour Engineering Department Sulaimaniya Health General DirectorateMinistry of HealthKurdistan RegionIraq Civil Engineering Department College of EngineeringKing Saud University11421 RiyadhSaudi Arabia Civil Engineering Department College of EngineeringUniversity of BabylonBabylonIraq Department of Mechanical Engineering Faculty of EngineeringArak UniversityArakIran

Three uncertain parameters(peak ground acceleration,soil density,and soil modulus of elasticity)have been studied with regard to their effects on the stability and damage of a circular tunnel during an earthquake.A time history of an actual earthquake in the literature with modification has been adopted in the numerical simulation and analysis of the tunnel ***-models have been constructed based on an experimental method with quadratic and interaction terms using matlab codes in order to predict the compressive damage,tensile damage,and the overall displacement of the *** results of the meta-models predicted a highly reasonable response of the tunnel with regard to the maximum principal stresses in the tunnel lining and predicted a remarkable response of the tunnel with respect to the overall displacement of the ***,the peak ground acceleration was observed to exert the highest effect on the overall displacement of the tunnel,compared to the soil density and soil modulus of ***,the metamodels revealed the inverse relationship between the soil modulus of elasticity and the compressive and tensile damages of the tunnel *** meta-models exhibited high efficiency of representation of the behavior of the structural system during earthquakes.

关键词： Peak ground acceleration Ovalization Meta-model Least squares method Compressive damage Tensile damage

Analysis of stiffness and flexural strength of a reinforced concrete beam using an invented reinforcement system

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Frontiers of Structural and Civil Engineering 2021年第2期15卷 378-389页

作者： nazim Abdul nariman Martin HUSEK Ilham Ibrahim MOHAMMAD Kaywan Othman AHMED Diyako DILSHAD Ibrahim KHIDR Department of Civil Engineering Tishk International UniversitySulaimani46001Iraq Institute of Structural Mechanics Faculty of Civil EngineeringBrno University of TechnologyBrno331/95-60200Czech Republic

In this study,we conducted experimental tests on two specimens of reinforced concrete beams using a three-point bending test to optimize the flexure and stiffness *** first specimen is a reinforced concrete beam with an ordinary reinforcement,and the second specimen has an invented reinforcement system that consists of an ordinary reinforcement in addition to three additional bracings using steel bars and steel *** results of the flexure test were collected and analyzed,and the flexural strength,the rate of damage during bending,and the stiffness were *** element modeling was applied for both specimens using the LS-DYNA program,and the simulation results of the flexure test for the same outputs were *** results of the experimental tests showed that the flexural strength of the invented reinforcement system was significantly enhanced by 15.5%compared to the ordinary ***,the flexural cracks decreased to a significant extent,manifesting extremely small and narrow cracks in the flexure spread along the bottom face of the *** addition,the maximum deflection for the invented reinforced concrete beam decreased to 1/3 compared to that of an ordinary reinforced concrete *** results were verified through numerical simulations,which demonstrated excellent similarities between the flexural failure and the stiffness of the *** invented reinforcement system exhibited a high capability in boosting the flexure design and stiffness.

关键词： three-point flexure test softening stage flexural crack flexural strain