Numerical procedure for the vibration analysis of arbitrarily constrained stiffened panels with openings

조대승,Nikola Vladimir,최태묵 대한조선학회 2014 International Journal of Naval Architecture and Oc Vol.6 No.4

A simple and efficient vibration analysis procedure for stiffened panels with openings and arbitraryboundary conditions based on the assumed mode method is presented. Natural frequencies and modes are determinedby solving an eigenvalue problem of a multi-degree-of-freedom system matrix equation derived by using Lagrange'sequations of motion, where Mindlin theory is applied for plate and Timoshenko beam theory for stiffeners. The effect ofstiffeners on vibration response is taken into account by adding their strain and kinetic energies to the correspondingplate energies whereas the strain and kinetic energies of openings are subtracted from the plate energies. Differentstiffened panels with various opening shapes and dispositions for several combinations of boundary conditions areanalyzed and the results show good agreement with those obtained by the finite element analysis. Hence, the proposedprocedure is especially appropriate for use in the preliminary design stage of stiffened panels with openings.

Hydroelastic response of 19,000 TEU class ultra large container ship with novel mobile deckhouse for maximizing cargo capacity

임홍일,Nikola Vladimir,Sime Malenica,조대승 대한조선학회 2017 International Journal of Naval Architecture and Oc Vol.9 No.3

This paper is related to structural design evaluation of 19,000 TEU ultra large container ship, dealing with hydroelastic response, i.e. springing and whipping. It illustrates application of direct calculation tools and methodologies to both fatigue and ultimate strength assessment, simultaneously taking into account ship motions and her elastic deformations. Methodology for springing and whipping assessment within so called WhiSp notation is elaborated in details, and in order to evaluate innovative container ship design with increased loading capacity, a series of independent hydroelastic computations for container ship with mobile deckhouse and conventional one are performed with the same calculation setup. Fully coupled 3D FEM e 3D BEM model is applied, while the ultimate bending capacity of hull girder is determined by means of MARS software. Beside comparative analysis of representative quantities for considered ships, relative influence of hydroelasticity on ship response is addressed.

Approximate natural vibration analysis of rectangular plates with openings using assumed mode method

조대승,Nikola Vladimir,최태묵 대한조선학회 2013 International Journal of Naval Architecture and Oc Vol.5 No.3

Natural vibration analysis of plates with openings of different shape represents an important issue in naval architecture and ocean engineering applications. In this paper, a procedure for vibration analysis of plates with openings and arbitrary edge constraints is presented. It is based on the assumed mode method, where natural frequencies and modes are determined by solving an eigenvalue problem of a multi-degree-of-freedom system matrix equation derived by using Lagrange's equations of motion. The presented solution represents an extension of a procedure for natural vibration analysis of rectangular plates without openings, which has been recently presented in the literature. The effect of an opening is taken into account in an intuitive way, i.e. by subtracting its energy from the total plate energy without opening. Illustrative numerical examples include dynamic analysis of rectangular plates with rectangular,elliptic, circular as well as oval openings with various plate thicknesses and different combinations of boundary conditions. The results are compared with those obtained by the finite element method (FEM) as well as those available in the relevant literature, and very good agreement is achieved.

Numerical simulations of hydrodynamic loads and structural responses of a Pre-Swirl Stator

Bakica Andro,Vladimir Nikola,Jasak Hrvoje,김은수 대한조선학회 2021 International Journal of Naval Architecture and Oc Vol.13 No.1

This paper investigates the effect of different flow models on the Pre-Swirl-Stator structural response from the perspective of a non-existing unified design procedure. Due to viscous effects near the propeller plane, the hydrodynamic solution is calculated by Computational Fluid Dynamics (CFD). Three different models are analysed: without the propeller, with the actuator disk and with the propeller. The main intention of this paper is to clarify the effects of the propeller model on the structural stresses in calmwater and waves which include the ship motion. CFD simulations are performed by means of OpenFOAM, while the structural response is calculated by means of the Finite Element Method (FEM) solver NASTRAN. Calm-water results have shown the inclusion of the propeller necessary from the design perspective, while the wave simulations have shown negligible propeller influence on the resulting stresses arising from the ship motions.

Physical insight into Timoshenko beam theory and its modification with extension

Senjanovic, Ivo,Vladimir, Nikola Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.48 No.4

An outline of the Timoshenko beam theory is presented. Two differential equations of motion in terms of deflection and rotation are comprised into single equation with deflection and analytical solutions of natural vibrations for different boundary conditions are given. Double frequency phenomenon for simply supported beam is investigated. The Timoshenko beam theory is modified by decomposition of total deflection into pure bending deflection and shear deflection, and total rotation into bending rotation and axial shear angle. The governing equations are condensed into two independent equations of motion, one for flexural and another for axial shear vibrations. Flexural vibrations of a simply supported, clamped and free beam are analysed by both theories and the same natural frequencies are obtained. That fact is proved in an analytical way. Axial shear vibrations are analogous to stretching vibrations on an axial elastic support, resulting in an additional response spectrum, as a novelty. Relationship between parameters in beam response functions of all type of vibrations is analysed.

Physical insight into Timoshenko beam theory and its modification with extension

Ivo Senjanović,Nikola Vladimir 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.48 No.4

An outline of the Timoshenko beam theory is presented. Two differential equations of motion in terms of deflection and rotation are comprised into single equation with deflection and analytical solutions of natural vibrations for different boundary conditions are given. Double frequency phenomenon for simply supported beam is investigated. The Timoshenko beam theory is modified by decomposition of total deflection into pure bending deflection and shear deflection, and total rotation into bending rotation and axial shear angle. The governing equations are condensed into two independent equations of motion, one for flexural and another for axial shear vibrations. Flexural vibrations of a simply supported, clamped and free beam are analysed by both theories and the same natural frequencies are obtained. That fact is proved in an analytical way. Axial shear vibrations are analogous to stretching vibrations on an axial elastic support, resulting in an additional response spectrum, as a novelty. Relationship between parameters in beam response functions of all type of vibrations is analysed.

A new finite element formulation for vibration analysis of thick plates

Ivo Senjanović,Nikola Vladimir,조대승 대한조선학회 2015 International Journal of Naval Architecture and Oc Vol.7 No.2

A new procedure for determining properties of thick plate finite elements, based on the modified Mindlin theory for moderately thick plate, is presented. Bending deflection is used as a potential function for the definition of total (bending and shear) deflection and angles of cross-section rotations. As a result of the introduced interdependence among displacements, the shear locking problem, present and solved in known finite element formulations, is avoided. Natural vibration analysis of rectangular plate, utilizing the proposed four-node quadrilateral finite element, shows higher accuracy than the sophisticated finite elements incorporated in some commercial software. In addition, the relation between thick and thin finite element properties is established, and compared with those in relevant literature.

Natural vibration analysis of stiffened panels with arbitrary edge constraints using the assumed mode method

Cho, Daeseung,Vladimir, Nikola,Choi, Taemuk SAGE Publications 2015 Proceedings of the Institution of Mechanical Engin Vol.229 No.4

<P>Natural vibration analysis of stiffened panels represents an important issue in different kinds of engineering applications. In this article, a procedure for the vibration analysis of stiffened panels with arbitrary edge constraints is presented. It is based on the assumed mode method, where natural frequencies and modes are determined by solving an eigenvalue problem of a multi-degree-of-freedom system matrix equation derived by using Lagrange’s equations of motion. The Mindlin thick plate theory is applied for a plate, while the effect of stiffeners having the properties of Timoshenko beams is accounted for by adding their strain and kinetic energies to the corresponding plate energies. The accuracy of the proposed procedure is justified by several numerical examples which include the natural vibration analysis of stiffened panels with different framing sizes, their lengths and orientations, plate thicknesses and different combinations of boundary conditions. A comparison of results with those obtained by the finite element method is provided, and good agreement is achieved.</P>

A new finite element formulation for vibration analysis of thick plates

Senjanovic, Ivo,Vladimir, Nikola,Cho, Dae Seung The Society of Naval Architects of Korea 2015 International Journal of Naval Architecture and Oc Vol.7 No.2

A new procedure for determining properties of thick plate finite elements, based on the modified Mindlin theory for moderately thick plate, is presented. Bending deflection is used as a potential function for the definition of total (bending and shear) deflection and angles of cross-section rotations. As a result of the introduced interdependence among displacements, the shear locking problem, present and solved in known finite element formulations, is avoided. Natural vibration analysis of rectangular plate, utilizing the proposed four-node quadrilateral finite element, shows higher accuracy than the sophisticated finite elements incorporated in some commercial software. In addition, the relation between thick and thin finite element properties is established, and compared with those in relevant literature.

Global hydroelastic analysis of ultra large container ships by improved beam structural model

Ivo Senjanović,Nikola Vladimir,Marko Tomić,Neven Hadžić,Šime Malenica 대한조선학회 2014 International Journal of Naval Architecture and Oc Vol.6 No.4

Some results on the hydroelasticity of ultra large container ships related to the beam structural modeland restoring stiffness achieved within EU FP7 Project TULCS are summarized. An advanced thin-walled girder theorybased on the modified Timoshenko beam theory for flexural vibrations with analogical extension to the torsionalproblem, is used for formulation of the beam finite element for analysis of coupled horizontal and torsional ship hullvibrations. Special attention is paid to the contribution of transverse bulkheads to the open hull stiffness, as well as tothe reduced stiffness of the relatively short engine room structure. In addition two definitions of the restoring stiffnessare considered: consistent one, which includes hydrostatic and gravity properties, and unified one with geometric stiffnessas structural contribution via calm water stress field. Both formulations are worked out by employing the finiteelement concept. Complete hydroelastic response of a ULCS is performed by coupling 1D structural model and 3Dhydrodynamic model as well as for 3D structural and 3D hydrodynamic model. Also, fatigue of structural elementsexposed to high stress concentration is considered.