1,721,177 research outputs found
Smart-tuned liquid column damper for reducing structural vibrations in offshore structures
No full textThis paper describes the dynamic behaviour of offshore structures modelled as discrete dynamic systems with the installation of innovative smart-tuned liquid column dampers (TLCDs). The use of advanced nano-fluids enhances the mechanical properties of the TLCD and allows the conventional passive system to be modified into a semi-active damping system. The magnetic force is modelled as an additional non-linear stiffness applied on the main structure once the magnetic field is activated. This new approach brings novel perspectives in reducing structural vibrations with respect to conventional TLCD systems. The aim of the study is to present a numerical investigation of the parameters involved in the dynamic behaviour of these systems subjected to random forces. In particular, a comprehensive analysis of a simplified structural model as a two-degrees-of-freedom system is given. Mathematical details and procedures using magneto-rheological-TLCD dampers without the need for commercial frameworks are presented. The present coupled system of ordinary differential equations is solved in a Matlab environment by using the built-in Runge-Kutta implementations for the solution of non-linear equations. This allows engineers and designers to obtain an initial estimation of the structural behaviour prior to in-depth simulations and analysis
Free vibrations of conical shells via Ritz method
Full text linkA formulation is presented for the investigation of the free vibrations of open and closed conical shells. Cylindrical ones are derived as a special case. The approach relies upon an efficient implementation of the Ritz method and allows any set of boundary conditions to be accounted for. In addition, the shells can be stiffened via stringers and/or rings, which are modeled by smearing the properties or by accounting for their discreteness. The resulting models are characterized by relatively few degrees of freedom and reduced computational effort. No meshing is required, so even the modeling phase is conducted quickly. A number of test cases is presented, revealing the accuracy of the proposed strategy and suggesting its use a mean for performing preliminary calculations and assisting the analysis and design process of composite shell structures
Analysis of unreinforced and reinforced tubular T-joints structures with open source finite element software
No full textTubular Joints play quite a vital role in most marine structures. It is obvious that having full control about the capacity and strength of tubular joints would be very worthy to have good knowledge about the total performance of the structure. In recent years, the application of the finite element method has become very popular in the analyses of different types of welded circular tubular joints and many commercial and open-source FE systems have been profoundly involved in these regards. Most of these software shares so much in common that it is difficult to differentiate them. This study was performed to investigate and report the usefulness of the open-source software programs in implementing finite element modeling for design applications. In this regard, with aid of the open-source finite element package Code_Aster and its user-friendly interface Salome-Meca, the behavior of reinforced and unreinforced T-joint specimens subjected to axial brace load with different geometry and material property has been studied. In addition, different types of shell and solid finite elements with various mesh densities are considered in this research. In order to overlap the outcomes, the numerical results of this research are present in terms of load-ovalization curves along with the results of other references. Due to mesh sizes and the element types, 144 different simulations have been performed on 12 different specimens. The results show that Code_Aster can satisfactorily predict the nonlinear static behavior of reinforced and unreinforced joints under both tension and compression load. Hence, Code_Aster can be used as a reliable tool for the evaluation and analysis and design of complex offshore joints
Strong Formulation: A Powerful Way for Solving Doubly Curved Shell Structures
No full textA theoretical framework based on an Equivalent Single Layer (ESL) approach is proposed in this chapter to develop several Higher-order Shear Deformation Theories (HSDTs) in a unified and compact manner. In particular, the maximum order of kinematic expansion can be arbitrarily chosen in order to define more refined displacement fields. The Murakami’s function can be also included in the model to take into account the so-called zig-zag effect. The proposed theory is employed to describe the mechanical behavior of doubly-curved shell structures made of composite materials. In particular, the differential geometry is used to define accurately the curved surfaces at issue. The strong formulation of the governing equation is solved by means of a numerical approach based on the Generalized Differential Quadrature (GDQ) method. The accuracy of both the theoretical model and the numerical method is shown through some applications, in which the solutions are compared with the results obtained by means of a three-dimensional finite element model
Discrete systems
No full textIn this chapter some basic concepts of the finite element method are illustrated by solving basic discrete systems built from springs and bars. Generation of element stiffness matrix and assembly for the global system is performed. First basic steps on finite element programs are described
Plane stress
No full textThis chapter deals with the static and dynamic analysis of 2D solids, particularly in plane stress. Plane stress analysis refers to problems where the thickness is quite small when compared to other dimensions in the reference plane x–y. The loads and boundary conditions are applied at the reference or middle plane of the structure. In this chapter we consider isotropic, homogeneous materials four-node (Q4), eight-node (Q8) and nine-node (Q9) quadrilateral elements
Bernoulli 3D frames
No full textThe analysis of three dimensional frames is quite similar to the analysis of 2D frames. In the 2-node 3D frame finite element we now consider in each node three displacements and three rotations with respect to the three global cartesian axes. However, the complexity in such structures is due to the orientation of the beam in space other than in 2D plane. Before introducing the stiffness and mass matrices in the global reference system rotation matrices for vectors in 3D space are firstly introduced
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