Reduced wavelet component energy-based approach for damage detection of jacket type offshore platform

Shahverdi, Sajad,Lotfollahi-Yaghin, Mohammad Ali,Asgarian, Behrouz Techno-Press 2013 Smart Structures and Systems, An International Jou Vol.11 No.6

Identification of damage has become an evolving area of research over the last few decades with increasing the need of online health monitoring of the large structures. The visual damage detection can be impractical, expensive and ineffective in case of large structures, e.g., offshore platforms, offshore pipelines, multi-storied buildings and bridges. Damage in a system causes a change in the dynamic properties of the system. The structural damage is typically a local phenomenon, which tends to be captured by higher frequency signals. Most of vibration-based damage detection methods require modal properties that are obtained from measured signals through the system identification techniques. However, the modal properties such as natural frequencies and mode shapes are not such good sensitive indication of structural damage. Identification of damaged jacket type offshore platform members, based on wavelet packet transform is presented in this paper. The jacket platform is excited by simple wave load. Response of actual jacket needs to be measured. Dynamic signals are measured by finite element analysis result. It is assumed that this is actual response of the platform measured in the field. The dynamic signals first decomposed into wavelet packet components. Then eliminating some of the component signals (eliminate approximation component of wavelet packet decomposition), component energies of remained signal (detail components) are calculated and used for damage assessment. This method is called Detail Signal Energy Rate Index (DSERI). The results show that reduced wavelet packet component energies are good candidate indices which are sensitive to structural damage. These component energies can be used for damage assessment including identifying damage occurrence and are applicable for finding damages' location.

Combined occurrence of Bernard-Soulier syndrome and prekallikrein deficiency

Ehsan Shahverdi,Hassan Abolghasemi,Minoo Ahmadinejad 대한혈액학회 2017 Blood Research Vol.52 No.3

Free vibration analysis of cracked thin plates using generalized differential quadrature element method

Hossein Shahverdi,Mohammad M. Navardi 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.62 No.3

The aim of the present study is to develop an elemental approach based on the differential quadrature method for free vibration analysis of cracked thin plate structures. For this purpose, the equations of motion are established using the classical plate theory. The well-known Generalized Differential Quadrature Method (GDQM) is utilized to discretize the governing equations on each computational subdomain or element. In this method, the differential terms of a quantity field at a specific computational point should be expressed in a series form of the related quantity at all other sampling points along the domain. However, the existence of any geometric discontinuity, such as a crack, in a computational domain causes some problems in the calculation of differential terms. In order to resolve this problem, the multi-block or elemental strategy is implemented to divide such geometry into several subdomains. By constructing the appropriate continuity conditions at each interface between adjacent elements and a crack tip, the whole discretized governing equations of the structure can be established. Therefore, the free vibration analysis of a cracked thin plate will be provided via the achieved eigenvalue problem. The obtained results show a good agreement in comparison with those found by finite element method.

Combined occurrence of Bernard-Soulier syndrome and prekallikrein deficiency

Ehsan Shahverdi,Hassan Abolghasemi,Minoo Ahmadinejad 대한혈액학회 2017 Blood Research Vol.52 No.3

Reduced wavelet component energy-based approach for damage detection of jacket type offshore platform

Sajad Shahverdi,Mohammad Ali Lotfollahi-Yaghin,Behrouz Asgarian 국제구조공학회 2013 Smart Structures and Systems, An International Jou Vol.11 No.6

Identification of damage has become an evolving area of research over the last few decades with increasing the need of online health monitoring of the large structures. The visual damage detection can be impractical, expensive and ineffective in case of large structures, e.g., offshore platforms, offshore pipelines, multi-storied buildings and bridges. Damage in a system causes a change in the dynamic properties of the system. The structural damage is typically a local phenomenon, which tends to be captured by higher frequency signals. Most of vibration-based damage detection methods require modal properties that are obtained from measured signals through the system identification techniques. However, the modal properties such as natural frequencies and mode shapes are not such good sensitive indication of structural damage. Identification of damaged jacket type offshore platform members, based on wavelet packet transform is presented in this paper. The jacket platform is excited by simple wave load. Response of actual jacket needs to be measured. Dynamic signals are measured by finite element analysis result. It is assumed that this is actual response of the platform measured in the field. The dynamic signals first decomposed into wavelet packet components. Then eliminating some of the component signals (eliminate approximation component of wavelet packet decomposition), component energies of remained signal (detail components) are calculated and used for damage assessment. This method is called Detail Signal Energy Rate Index (DSERI). The results show that reduced wavelet packet component energies are good candidate indices which are sensitive to structural damage. These component energies can be used for damage assessment including identifying damage occurrence and are applicable for finding damages' location.

Aeroelastic Stability Analysis of Curved Composite Blades in Hover Using Fully Intrinsic Equations

M. R. Amoozgar,H. Shahverdi 한국항공우주학회 2019 International Journal of Aeronautical and Space Sc Vol.20 No.3

In this paper, the aeroelastic stability of a curved composite hingeless rotor blade in hovering condition is investigated. The composite blade is modeled using the geometrically exact fully intrinsic beam equations, and the aerodynamic loads are simulated by using the two-dimensional quasi-steady strip theory combined with the uniform inflow. The nonlinear governing equations are discretized using a time–space scheme, and the stability of the system is determined by inspecting the eigenvalues of the linearized system. The obtained results are compared with those reported in the literature, and an excellent agreement is observed. It is found that the ply angle of the composite layup and the blade precone angle affect the aeroelastic stability of the blade dramatically. Finally, the effect of initial curvatures on the aeroelastic stability of the composite blade is analyzed. The results highlight the importance of the initial curvature combined with ply angle on the aeroelastic stability of composite blades.

A four-variable plate theory for thermal vibration of embedded FG nanoplates under non-uniform temperature distributions with different boundary conditions

Mohammad Reza Barati,Hossein Shahverdi 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.60 No.4

In this paper, thermal vibration of a nonlocal functionally graded (FG) plates with arbitrary boundary conditions under linear and non-linear temperature fields is explored by developing a refined shear deformation plate theory with an inverse cotangential function in which shear deformation effect was involved without the need for shear correction factors. The material properties of FG nanoplate are considered to be temperature-dependent and graded in the thickness direction according to the Mori-Tanaka model. On the basis of non-classical higher order plate model and Eringen’s nonlocal elasticity theory, the small size influence was captured. Numerical examples show the importance of non-uniform thermal loadings, boundary conditions, gradient index, nonlocal parameter and aspect and side-to-thickness ratio on vibrational responses of size-dependent FG nanoplates.

Equivalent material properties of perforated metamaterials based on relative density concept

Mohammad Reza Barati,Hossein Shahverdi 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.44 No.5

In this paper, the equivalent material properties of cellular metamaterials with different types of perforations have been presented using finite element (FE) simulation of tensile test in Abaqus commercial software. To this end, a Representative Volume Element (RVE) has been considered for each type of cellular metamaterial with regular array of circular, square, oval and rectangular perforations. Furthermore, both straight and perpendicular patterns of oval and rectangular perforations have been studied. By applying Periodic Boundary conditions (PBC) on the RVE, the actual behavior of cellular material under uniaxial tension has been simulated. Finally, the effective Young’s modulus, Poisson’s ratio and mass density of various metamaterials have been presented as functions of relative density of the RVE.

Flutter behavior of graded graphene platelet reinforced cylindrical shells with porosities under supersonic airflow

Mohammad Mashhour,Mohammad Reza Barati,Hossein Shahverdi 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.46 No.5

In the present work, the flutter characteristics of porous nanocomposite cylindrical shells, reinforced with graphene platelets (GPLs) in supersonic airflow, have been investigated. Different distributions for GPLs and porosities have been considered which are named uniform and non-uniform distributions thorough the shell’s thickness. The effective material properties have been determined via Halpin-Tsai micromechanical model. The cylindrical shell formulation considering supersonic airflow has been developed in the context of first-order shell and first-order piston theories. The governing equations have been solved using Galerkin’s method to find the frequency-pressure plots. It will be seen that the flutter points of the shell are dependent on the both amount and distribution of porosities and GPLs and also shell geometrical parameters.

Aeroelastic stability analysis of a two-stage axially deploying telescopic wing with rigid-body motion effects

Sayed Hossein Moravej Barzani,Hossein Shahverdi Techno-Press 2023 Advances in aircraft and spacecraft science Vol.10 No.5

This paper presents the study of the effects of rigid-body motion simultaneously with the presence of the effects of temporal variation due to the existence of morphing speed on the aeroelastic stability of the two-stage telescopic wings, and hence this is the main novelty of this study. To this aim, Euler-Bernoulli beam theory is used to model the bending-torsional dynamics of the wing. The aerodynamic loads on the wing in an incompressible flow regime are determined by using Peters' unsteady aerodynamic model. The governing aeroelastic equations are discretized employing a finite element method based on the beam-rod model. The effects of rigid-body motion on the length-based stability of the wing are determined by checking the eigenvalues of system. The obtained results are compared with those available in the literature, and a good agreement is observed. Furthermore, the effects of different parameters of rigid-body such as the mass, radius of gyration, fuselage center of gravity distance from wing elastic axis on the aeroelastic stability are discussed. It is found that some parameters can cause unpredictable changes in the critical length and frequency. Also, paying attention to the fuselage parameters and how they affect stability is very important and will play a significant role in the design.