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CONTENTS
Volume 68, Number 1, October10 2018
 

Abstract
In ocean industry, free surface type ART (Anti Roll tank) system has been widely used to suppress the roll motion of floating structures. In those, various obstacles have been devised to obtain the sufficient damping and to enhance the controllability of freely rushing water inside the tank. Most of previous researches have paid on the development of simple mathematical formula for coupled ship-ARTs analysis although other numerical and experimental approaches exist. Little attention has been focused on the use of 3D panel method for preliminary design of free surface type ART despite its advantages in computational time and general capacity for hydrodynamic damping estimation. This study aims at developing a potential theory based hydrodynamic code for the analysis of floating structure with baffled ARTs. The sloshing in baffled tanks is modeled through the linear potential theory with FE discretization and it coupled with hydrodynamic equations of floating structures discretized by BEM and FEM, resulting in direct coupled FE-BE formulation. The general capacity of proposed formulation is emphasized through the coupled hydrodynamic analysis of floating structure and sloshing inside baffled ARTs. In addition, the numerical methods for natural sloshing frequency tuning and estimation of hydrodynamic damping ratio of liquid sloshing in baffled tanks undergoing wave exiting loads are developed through the proposed formulation. In numerical examples, effects of natural frequency tuning and baffle ratios on the maximum and significant roll motions are investigated.

Key Words
anti roll tank; baffle; linear potential theory; hydrodynamic damping; hydrodynamic analysis; fluid-structure interaction

Address
San Kim: Department of Mechanical Engineering, Korean Advanced Institute for Science and Technology,
291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
Kang-Heon Lee: Korea Atomic Energy Research Institute, 111 Daehak-ro 989 beon-gil, Yuseong-gu, Daejeon 34057, Republic of Korea

Abstract
In this paper, we compare and assess the performance of the standard 3- and 6-node MITC shell elements (Lee and Bathe 2004) with the recently developed MITC triangular elements (Lee et al. 2014, Jeon et al. 2014, Jun et al. 2018) which were based on the partitions of unity approximation, bubble node, or both. The convergence behavior of the shell elements are measured in well-known benchmark tests; four plane stress tests (mesh distortion test, cantilever beam, Cook\'s skew beam, and MacNeal beam), two plate tests (Morley\'s skew plate and circular plate), and six shell tests (curved beam, twisted beam, pinched cylinder, hemispherical shells with or without hole, and Scordelis-Lo roof). To precisely compare and evaluate the solution accuracy of the shell elements, different triangular mesh patterns and distorted element mesh are adopted in the benchmark problems. All shell finite elements considered pass the basic tests; namely, the isotropy, the patch, and the zero energy mode tests.

Key Words
benchmark test; shell structure; triangular shell element; MITC method; partition of unity; bubble-node

Address
Hyungmin Jun: Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Paul Mukai: PVM Associates, Andover, MA 01810, USA
San Kim: Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea

Abstract
In this study, a frequency domain model updating method is presented using power spectral density (PSD) data. It uses the sensitivity of PSD function with respect to the unknown structural parameters through a decomposed form of transfer function. The stiffness parameters are captured with high accuracy through solving the sensitivity equations utilizing the least square approach. Using numerically noise polluted data, the model updating results of a truss model prove robustness of the method against measurement and mass modelling errors. Results prove the capabilities of the method for parameter estimation using highly noise polluted data of low ranges of excitation frequency.

Key Words
power spectral density; model updating; frequency response function; sensitivity-based model updating; modal data

Address
Akbar Esfandiari and Fayaz R. Rofooei: Department of Civil Engineering, Sharif University of Technology, Tehran, Iran
Maryam Ghareh Chaei: Department of Marine Technology, Amirkabir University of Technology, Tehran, Iran

Abstract
This paper presents an analysis of the bending, buckling and free vibration of functionally graded sandwich beams resting on elastic foundation by using a refined quasi-3D theory in which both shear deformation and thickness stretching effects are included. The displacement field contains only three unknowns, which is less than the number of parameters of many other shear deformation theories. In order to homogenize the micromechanical properties of the FGM sandwich beam, the material properties are derived on the basis of several micromechanical models such as Tamura, Voigt, Reuss and many others. The principle of virtual works is used to obtain the equilibrium equations. The elastic foundation is modeled using the Pasternak mathematical model. The governing equations are obtained through the Hamilton\'s principle and then are solved via Navier solution for the simply supported beam. The accuracy of the proposed theory can be noticed by comparing it with other 3D solution available in the literature. A detailed parametric study is presented to show the influence of the micromechanical models on the general behavior of FG sandwich beams on elastic foundation.

Key Words
FG sandwich beam, micromechanical model; quasi 3D shear deformation theory; stretching effect; bending; buckling; free vibration; Pasternak foundation

Address
Mohammed Yahiaoui and Samir Benyoucef: Department of Civil Engineering, Material and Hydrology Laboratory, Faculty of Technology, University of Sidi Bel Abbes, Algeria
Abdelouahed Tounsi:
1) Department of Civil Engineering, Material and Hydrology Laboratory, Faculty of Technology, University of Sidi Bel Abbes, Algeria
2) Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia
Bouazza Fahsi: Laboratoire de Modelisation et Simulation Multi-echelle, Faculte des Sciences Exactes, Universite de Sidi Bel Abbes, Algeria
Rabbab Bachir Bouiadjra: Department of Civil Engineering, University Mustapha Stambouli of Mascara, Algeria

Abstract
Recently, U-section decks have been more and more used in metro and light rail bridges as an innovative concept in bridge deck design and a successful alternative to conventional box girders because of their potential advantages. U-section may be viewed as a single vent box girder eliminating the top slab connecting the webs, with the moving vehicles travelling on the lower deck. U-section bridges thus solve many problems like limited vertical clearance underneath the bridge lowest point, besides providing built-in noise barriers. Beam theory in mechanics assumes that plane section remains plane after bending, but it was found that shearing forces produce shear deformations and the plane section does not remain plane. This phenomenon leads to distortion of the cross section. For a box or a U section, this distortion makes the central part of the slab lagging behind those parts closer to the webs and this is known as shear lag effect. A sample real-world double-track U-section metro bridge is modelled in this paper using a commercial finite element analysis program and is analysed under various loading conditions and for different geometric variations. The three-dimensional finite element analysis is used to demonstrate variations in the transverse bending moments in the deck as well as variations in the longitudinal normal stresses induced in the cross section along the U-girder\'s span thus capturing warping and shear lag effects which are then compared to the stresses calculated using conventional beam theory. This comparison is performed not only to locate the distortion, warping and shear lag effects typically induced in U-section bridges but also to assess the main parameters influencing them the most.

Key Words
U-section bridge; metro bridge; shear lag; pre-stressed concrete; finite element analysis; beam theory

Address
Philopateer F. Boules, Sameh S.F. Mehanny and Mourad M. Bakhoum: Department of Structural Engineering, Faculty of Engineering, Cairo University, Gamaa Street, Giza, Egypt

Abstract
This paper uses the finite element method (FEM) considering geometrically nonlinear strains to study the first ply failure of laminated composite skewed hypar shell roofs through well-established failure criteria along with the serviceability criterion of deflection. Apart from validating the approach through solution of benchmark problems, skewed hypars with different practical parametric variations are studied for failure loads and tendencies. First ply failure zones are also identified to suggest design and non-destructive monitoring guidelines to the practising engineers. Recommendation tables regarding the design approaches to be adopted in specific cases and factor of safety values needed to be imposed on first ply failure load values for varying shell curvatures are also suggested in this paper. Providing practical inputs to design engineers is the main achievement of the present study.

Key Words
laminated composites; failure analysis; skewed hypar shell; FEM; nonlinear analysis; design guidelines

Address
Arghya Ghosh and Dipankar Chakravorty: Department of Civil Engineering, Jadavpur University, Kolkata – 700032, India

Abstract
The low rate of penetration and short lifetime of drilling bit served as the most common problems encountered in hard formation drilling, thus leading to severe restriction of drilling efficiency in oil and gas reservoir. This study developed a new local impact drilling method to enhance hard formation drilling efficiency. The limitation length formulas of radial/lateral cracks under static indentation and dynamic impact are derived based on the experimental research of Marshall D.B considering the mud column pressure and confining pressure. The local impact rock breaking simulation model is conducted to investigate its ROP raising effect. The results demonstrate that the length of radial/lateral cracks will increase as the decrease of mud pressure and confining pressure, and the local impact can result in a damage zone round the impact crater which helps the rock cutting, thus leading to the ROP increase. The numerical results also demonstrate the advantages of local impact method for raising ROP and the vibration reduction of bit in hard formation drilling. This study has shown that the local impact method can help raising the ROP and vibration reduction of bit, and it may be applied in drilling engineering.

Key Words
local impact; acceleration mechanism; rock-breaking mechanism; hard formation

Address
Weiji Liu:
1) School of Mechatronic Engineering, Southwest Petroleum University, Chengdu, 610500, China
2) The key laboratory of well stability and fluid & rock mechanics in Oil and gas reservoir of Shaanxi Province, Xi\'an Shiyou University, Xi\'an, 710065, China
Xiaohua Zhu: School of Mechatronic Engineering, Southwest Petroleum University, Chengdu, 610500, China
Yunlai Zhou and Xiannan Meng: Department of Civil and Environmental Engineering, National University of Singapore, 117576, Singapore
Liu Mei: Guangdong Provincial Key Laboratory of Durability for Marine Civil Engineering, Shenzhen University, Shenzhen, 518060, China
Cheng Jiang: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong SAR, China

Abstract
In the present research, an attempt is made to obtain a semi analytical solution for both nonlinear natural frequency and forced vibration of embedded functionally graded double layered nanoplates with all edges simply supported based on nonlocal strain gradient elasticity theory. The interaction of van der Waals forces between adjacent layers is included. For modeling surrounding elastic medium, the nonlinear Winkler-Pasternak foundation model is employed. The governing partial differential equations have been derived based on the Mindlin plate theory utilizing the von Karman strain-displacement relations. Subsequently, using the Galerkin method, the governing equations sets are reduced to nonlinear ordinary differential equations. The semi analytical solution of the nonlinear natural frequencies using the homotopy analysis method and the exact solution of the nonlinear forced vibration through the Harmonic Balance method are then established. The results show that the length scale parameters give nonlinearity of the hardening type in frequency response curve and the increase in material length scale parameter causes to increase in maximum response amplitude, whereas the increase in nonlocal parameter causes to decrease in maximum response amplitude. Increasing the material length scale parameter increases the width of unstable region in the frequency response curve.

Key Words
nonlinear vibration; FG double layered nanoplate; nonlocal strain gradient theory; homotopy analysis method; nonlinear elastic medium

Address
E. Mahmoudpour and S. A. Faghidian: Department of Mechanical Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
SH. Hosseini-Hashemi: School of Mechanical Engineering, Iran University of Science and Technology, Tehran, Iran

Abstract
This study deals with optimum geometry design of laterally loaded piles in a Winkler\'s medium through the Fully Stressed Design (FSD) method. A numerical algorithm distributing the mass by means of the FSD method and updating the moment by finite elements is implemented. The FSD method is implemented here using a simple procedure to optimise the beam length using an approach based on the calculus of variations. For this aim two conditions are imposed, one transversality condition at the bottom end, and a one sided constraint for moment and mass distribution in the lower part of the beam. With this approach we derive a simple condition to optimise the beam length. Some examples referred to different fields are reported. In particular, the case of laterally loaded piles in Geotechnics is faced.

Key Words
Winkler\'s soil model; fully stressed beam; FSD method; optimum length

Address
Luigi Fenu: Department of Civil & Environment Engineering and Architecture, University of Cagliari, Via Marengo 2, 09123 Cagliari, Italy
Bruno Briseghella and Giuseppe Carlo Marano: College of Civil Engineering, Fuzhou University, No. 2 Xue Yuan Road, University Town, Fuzhou 350108 - Fujian, China

Abstract
In this study, Eringen nonlocal elasticity theory in conjunction with surface elasticity theory is employed to study nonlinear free vibration behavior of FG nano-plate lying on elastic foundation, on the base of Reddy\'s plate theory. The material distribution is assumed as a power-law function and effective material properties are modeled using Mori-Tanaka homogenization scheme. Hamilton\'s principle is implemented to derive the governing equations which solved using DQ method. Finally, the effects of different factors on natural frequencies of the nano-plate under hygrothermal situation and various boundary conditions are studied.

Key Words
nanomechanics; rectangular plate; hygro-thermo-mechanical; surface effect; generalized differential quadrature method; high shear deformation plate theory; thermal loading; elastic medium; nonlocal

Address
Farzad Ebrahimi and Ebrahim Heidari: Department of Mechanical Engineering, Faculty of Engineering, Imam Khomeini International University, Qazvin, Iran


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