Abstract
In this paper, a new modified conjugate gradient (MCG) method is presented which is based on a new gradient regularizer, and this method is used to identify the dynamic load on airfoil structure without and with considering random structure parameters. First of all, the newly proposed algorithm is proved to be efficient and convergent through the rigorous mathematics theory and the numerical results of determinate dynamic load identification. Secondly, using the perturbation method, we transform uncertain inverse problem about force reconstruction into determinate load identification problem. Lastly, the statistical characteristics of identified load are evaluated by statistical methods. Especially, this newly proposed approach has successfully solved determinate and uncertain inverse problems about dynamic load identification. Numerical simulations validate that the newly developed method in this paper is feasible and stable in solving load identification problems without and with considering random structure parameters. Additionally, it also shows that most of the observation error of the proposed algorithm in solving dynamic load identification of deterministic and random structure is respectively within 11.13%, 20%.
Key Words
conjugate gradient method; global convergence; Ill-posedness; line search; load identification
Address
Lin J. Wang: Hubei Key Laboratory of Hydroelectric Machinery Design and Maintenance, College of Mechanical and Power Engineering, China Three Gorges University, Yichang, Hubei 443002, PR China; School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane, QLD 4001, Australia
Jia H. Li: Hubei Key Laboratory of Hydroelectric Machinery Design and Maintenance, College of Mechanical and Power Engineering, China Three Gorges University, Yichang, Hubei 443002, PR China
You X. Xie: College of Science Technology, China Three Gorges University, Yichang, Hubei 443002, PR China
Abstract
Riverine flood is one of the critical natural threats to river-crossing bridges. As floods are the most-occurred natural hazard worldwide, survival probability of bridges due to floods must be assessed in a speedy but precise manner. In this regard, the paper presents a reliability-based approach for a rapid assessment of failure probability of vulnerable bridge components under floods. This robust method is generic in nature and can be applied to both concrete and steel girder bridges. The developed methodology essentially utilizes limit state performance functions, expressed in terms of capacity and flood demand, for probable failure modes of various vulnerable components of bridges. Advanced First Order Reliability Method (AFORM), Monte Carlo Simulation (MCS), and Latin Hypercube Simulation (LHS) techniques are applied for the purpose of reliability assessment and developing flood fragility curves of bridges in which flow velocity and water height are taken as flood intensity measures. Upon validating the proposed method, it is applied to a case study bridge that experiences the flood scenario of a river in Gujarat, India. Research outcome portrays how effectively and efficiently the proposed reliability-based method can be applied for a quick assessment of flood vulnerability of bridges in any flood-prone region of interest.
Abstract
The submerged floating tunnel (SFT) infrastructure has been regarded as an emerging technology that efficiently and
safely connects land and islands. The SFT route problem is an essential part of the SFT planning and design phase, with
significant impacts on the surrounding environment. This study aims to develop an optimization model considering
transportation and structure factors. The SFT routing problem was optimized based on two objective functions, i.e., minimizing total travel time and cumulative strains, using NSGA-II. The proposed model was applied to the section from Mokpo to Jeju Island using road network and wave observation data. As a result of the proposed model, a Pareto optimum curve was obtained, showing a negative correlation between the total travel time and cumulative strain. Based on the inflection points on the Pareto
optimum curve, four optimal SFT routes were selected and compared to identify the pros and cons. The travel time savings of the four selected alternatives were estimated to range from 9.9% to 10.5% compared to the non-implemented scenario. In terms of demand, there was a substantial shift in the number of travel and freight trips from airways to railways and roadways. Cumulative strain, calculated based on SFT distance, support structure, and wave energy, was found to be low when the route passed through small islands. The proposed model helps decision-making in the planning and design phases of SFT projects, ultimately contributing to the progress of a safe, efficient, and sustainable SFT infrastructure.
Address
Eun Hak Lee: Multimodal Planning & Environment Division, Texas A&M Transportation Institute, 1111 Rellis Pkwy, 77807, Bryan, Texas, USA
Gyu-Jin Kim: Department of Civil and Environmental Engineering, Korean Advanced Institute for Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea; Department of Ocean Engineering, Texas A&M University, 77843 College Station, Texas, USA
Abstract
In this study, analysis of wave propagation characteristics for functionally graded carbon nanotube-reinforced composite (FG-CNTRC) nanoplates is performed using first-order shear deformation theory (FSDT) and nonlocal strain gradient theory. Uniform distribution (UD) and three types of functionally graded distributions of carbon nanotubes (CNTs) are assumed. The effective mechanical properties of the FG-CNTRC nanoplate are assumed to vary continuously in the thickness direction and are approximated based on the rule of mixture. Also, the governing equations of motion are derived via the extended Hamilton's principle. In numerical examples, the effects of nonlocal parameter, wavenumber, angle of wave propagation, volume fractions, and carbon nanotube distributions on the wave propagation characteristics of the FG-CNTRC nanoplate are studied. As represented in the results, it is clear that the internal length-scale parameter has a remarkable effect on the wave propagation characteristics resulting in significant changes in phase velocity and natural frequency. Furthermore, it is observed that the strain gradient theory yields a higher phase velocity and frequency compared to those obtained by the nonlocal strain gradient theory and classic theory.
Address
Mohammad Hosseini, Parisa Chahargonbadizade and Mohammadreza Mofidi: Department of Mechanical Engineering, Sirjan University of Technology, 78137-33385 Sirjan, I.R., Iran
Abstract
Employing the non-local strain gradient theory (NSGT), this paper investigates the nonlinear resonance characteristics of functionally graded material (FGM) nanoshells with initial geometric imperfection for the first time. The effective material properties of the porous FGM nanoshells with even distribution of porosities are estimated by a modified power-law model. With the guidance of Love's thin shell theory and considering initial geometric imperfection, the strain equations of the shells are obtained. In order to characterize the small-scale effect of the nanoshells, the nonlocal parameter and strain gradient parameter are introduced. Subsequently, the Euler-Lagrange principle was used to derive the motion equations. Considering three boundary conditions, the Galerkin principle combined with the modified Lindstedt Poincare (MLP) method are employed to discretize and solve the motion equations. Finally, the effects of initial geometric imperfection, functional
gradient index, strain gradient parameters, non-local parameters and porosity volume fraction on the nonlinear resonance of the porous FGM nanoshells are examined.
Key Words
boundary conditions; FGM; geometrical imperfection; nanoshells; resonance
Address
Wu-Bin Shan: Hunan Electrical College of Technology, School of Elevator Engineering, Xiangtan 411100, China
Gui-Lin She: College of Mechanical and Vehicle Engineering, Chongqing University, Chongqing 400044, China
Abstract
In this study, previously developed algorithm is used for Optimization of hybrid composite plates using Tsai-Wu
criteria. For the stress-based Design Optimization problems, Von-Mises stress uses as design variable for isotropic materials. Maximum stress, maximum strain, Tsai Hill, and Tsai-Wu criteria are generally used to determine failure of composite materials. In this study, failure index value is used as design variable in the optimization algorithm and Tsai-Wu criteria is utilized to calculate this value. In the analyses, commonly used design domains according to different hybrid orientations are optimized and results are presented. When the optimization algorithm was applied, 50% material reduction was obtained without exceeding allowable failure index value.
Key Words
fiber reinforced composites; finite element method (FEM); hybridization; optimization; Tsai-Wu Criteria
Address
Mehmet Hanifi Doğru: Pilotage Department, Aeronautics and Aerospace Faculty, University of Gaziantep, Türkiye
İbrahim Göv, Eyüp Yeter, Kürşad Göv: Aerospace Engineering Department, Aeronautics and Aerospace Faculty, University of Gaziantep, Türkiye
Abstract
Wind and earthquake loads may cause strong vibrations in large-span cable-stayed bridges, leading to the inability of the bridge to operate normally. An improved Pounding Tuned Mass Damper (PTMD) system was designed to improve the safety of the large-span cable-stayed bridge. The vibration control effect of the improved PTMD system on the large-span cablestayed bridge under the combined action of earthquake-wind-traffic was studied. Furthermore, the impact of different parameters on the vibration suppression performance of the improved PTMD system was analyzed. The numerical results indicate that the PTMD system is very effective in suppressing the displacements of the bridge caused by both the traffic-wind coupling and traffic-earthquake coupling. Moreover, the number, mass ratio, pounding stiffness, and gap values have a significant influence on the vibration suppression performance of the improved PTMD system. When the number of PTMD is increased from 3 to 9, the vibration reduction ratio of the vertical displacement is increased from 25.39% to 48.05%. As the mass ratio changes from 0.5% to 2%, the vibration reduction ratio increases significantly from 22.23% to 53.30%.
Key Words
cable-stayed bridge; earthquake-wind-traffic-bridge coupled system; pounding tuned mass damper; vibration
suppression
Address
Xinfeng Yin, Wanli Yan, Yang Liu and Zhou Huang: School of Civil Engineering, Changsha University of Science & Technology, Changsha 410114, Hunan, China
Yong Liu: School of Civil Engineering, Changsha University of Science & Technology, Changsha 410114, Hunan, China; Hubei Communications Investment Construction Group Co. Ltd., Wuhan, 430070, China
Abstract
In order to explore the influence of tooth root cracks on the dynamic characteristics of multi-stage planetary gear transmission systems, a concentrated parameter method was used to construct a nonlinear dynamic model of the system with 30-DOF in bending and torsion, taking into account factors such as crack depth, length, angle, error, time-varying meshing stiffness (TVMS), and damping. In the model, the energy method was used to establish a TVMS model with cracks, and the influence of cracks on the TVMS of the system was studied. By using the Runge- Kutta method to calculate the differential equations of system dynamics, a series of system vibration diagrams containing cracks were obtained, and the influence of different crack parameters on the vibration of the system was analyzed. And vibration testing experiments were conducted on the system with planetary gear cracks. The results show that when the gear contains cracks, the TVMS of the system will decrease, and as the cracks intensify, the TVMS will decrease. When cracks appear on the II-stage planetary gear, the system will experience impact effects with intervals of rotation cycles of the II-stage planetary gear. There will be obvious sidebands near the meshing frequency doubling, and the vibration trajectory of the gear will also become disordered. These situations will become more and more obvious as the degree of cracks intensifies. Through experiments, the theoretical results are in good agreement with experimental results, verifying the correctness of the theoretical model. This provides a theoretical basis for fault diagnosis and reliability research of the system.
Key Words
cracks; planetary gear; time-varying meshing stiffness; vibration
Address
Hao Dong, Yue Bi, Bing-Xing Ren, Zhen-Bin Liu and Yue Li: School of Mechatronic Engineering, Xi'an Technological University, Xi'an 710021, China; Engineering Research Center of Digital Intelligent Technology of High Performance Gear Transmission, University of Shaanxi, Xi'an 710021, China
