An Experimental Method to Identify the Effects of Joints on Structures Using Laser Vibrometry

2001 ◽  
Author(s):  
Xianghong Ma ◽  
Alexander F. Vakakis ◽  
Lawrence A. Bergman
Keyword(s):  
Complex Modulus ◽  
Nonlinear Effects ◽  
Mode Shapes ◽  
Joint Interface ◽  
Laser Vibrometry ◽  
Post Process ◽  
Structural Responses ◽  
The Difference ◽  
As Effects ◽  
Dynamic Phenomena

Abstract A technique based on laser vibrometry is outlined for identifying the effects of bolted joints on the structural dynamics. The method is based on the comparison of the dynamics of the bolted structure to that of a “baseline” structure; e.g., a structure with similar geometry and material characteristics but no jointed interface. Hence, under identical forcing conditions, the difference in the dynamics between the actual and baseline structures can be attributed solely to the joint interface effects. Non-contacting laser vibrometry is utilized to experimentally measure these differences in the structural responses at specific frequencies. A numerical algorithm is then developed to post-process the experimental data and identify the joint effects on the dynamics. The method provides estimates for the equivalent, frequency and amplitude dependent complex modulus of the joint interface. The laser scans of the mode shapes of the systems under consideration reveal interesting dynamic phenomena such as nonlinear effects due to micro-impacts at the bolted joint as well as effects due to non-proportional damping distribution.

An Investigation of the Structural Dynamics of a Racing Yacht

1999 ◽  
Author(s):  
Frederic Louarn ◽  
Pandeli Temarel
Keyword(s):  
Dynamic Properties ◽  
Three Dimensional ◽  
Element Model ◽  
Point Of View ◽  
Mode Shapes ◽  
Function Technique ◽  
Operational Conditions ◽  
Principal Coordinates ◽  
Modal Summation ◽  
Structural Responses

The dynamic behaviour of a WOR 60 is investigated using three dimensional hydroelasticity theory. Global structural responses (e.g. stresses) in waves are obtained corresponding to the upright as well as to the more realistic heeled sailing configurations, revealing the connection between the ballast keel and the hull as being a critical area of the structure. For the "dry hull" analysis, a global finite element model has been developed, incorporating the hull and deck shell, the internal structure, the ballast keel and the rig together with rigging loads. The modular nature of the model has been used to assess the relative influence of each of the aforementioned components upon the required characteristic dynamic properties (e.g. natural frequencies and principal mode shapes). Regarding the "wet hull" analysis, a three dimensional Green's function technique, using pulsating sources distributed over the wetted surface, provides a numerical solution to the case of the yacht sailing in regular waves at arbitrary heading. Principal coordinates for the rigid body motions and flexible distortions of interest are evaluated and the latter are used to obtain the dynamic stresses in waves using modal summation. This paper will describe the modelling techniques used and discuss the applicability / limitations of hydroelasticity theory regarding this type of structures in the light of the results obtained for the upright and heeled operational conditions, as well as from the point of view of design aspects such as "L" and "T" keel configurations. The ABS design criteria will provide a practical reference for comparing the results from the dynamic analysis.

Analytical Solution for Vibration of a Rotating Delaminated Composite Beam with End Mass

2016 ◽  
Vol 16 (06) ◽  
pp. 1550013 ◽  
Author(s):  
Ramazan-Ali Jafari-Talookolaei
Keyword(s):  
Analytical Solution ◽  
Natural Frequencies ◽  
Laminated Composite ◽  
Mode Shapes ◽  
Material Anisotropy ◽  
Rotating Speed ◽  
Multipliers Method ◽  
Free Mode ◽  
The Difference ◽  
Laminated Composite Beams

In this paper, the free vibration of rotating laminated composite beams (LCBs) with general lay-ups and single through-the-width delamination is analytically investigated. The Hamilton’s principle is used to derive the coupled governing differential equations and boundary conditions for the rotating delaminated beam, considering the effects of shear deformation, rotary inertia, material couplings (bending–tension, bending–twist and tension–twist couplings), and Poisson’s effect. Both the free mode and constrained mode assumptions are adopted. Analytical solution for the natural frequencies and mode shapes are presented by incorporating the constraint conditions using the Lagrange multipliers method. The accuracy is assured by the convergence of the natural frequencies, as well as by comparison with published results. The effects of various factors such as delamination parameter, fiber angle, hub radius, material anisotropy, end mass and rotating speed are studied in detail. The difference between the results based on the free mode and constrained mode assumptions is also investigated.

scholarly journals Pressure Wave in Liquid Generated by Pneumatic Pistons and Its Interaction with a Free Surface

2017 ◽  
Vol 09 (03) ◽  
pp. 1750037 ◽  
Author(s):  
Victoria Suponitsky ◽  
David Plant ◽  
Eldad J. Avital ◽  
Ante Munjiza
Keyword(s):  
Free Surface ◽  
Pressure Wave ◽  
Equations Of State ◽  
Current System ◽  
Nonlinear Effects ◽  
Compression Process ◽  
Double Peak Structure ◽  
Peak Structure ◽  
Westervelt Equation ◽  
The Difference

Numerical analysis of a pressure wave generated in a liquid [Formula: see text] upon impact of the pneumatic pistons and its interaction with a free surface has been performed for the geometry and parameters of the plasma compression system prototype constructed by General Fusion Inc. Stress wave developing in the hammer–anvil piston assembly is first simulated using high-fidelity structural mechanics research code, then propagated through the liquid [Formula: see text] with several solvers within OpenFOAM[Formula: see text] software and also with nonlinear acoustics in-house code based on the Westervelt equation. In the current system, a pressure wave transmitted into the liquid [Formula: see text] is characterized by a complex temporal double peak structure and strong spatial amplitude variation. An imprint of discrete pulses remains detectable during the entire propagation of the combined wave. An excellent agreement between the results produced with different numerical codes is obtained. Nonlinear effects associated with equation of state are found to be significant at impact velocities of [Formula: see text], while at lower velocities of [Formula: see text] the difference between the results obtained with linear and nonlinear equations of state is negligible. Liquid–gas interface dynamics during the compression process of a spherical gas cavity is captured very well by the compressibleInterFoam within OpenFOAM.

Updating the Mathematical Model of a Structure Using Vibration Data

2005 ◽  
Vol 11 (12) ◽  
pp. 1469-1486 ◽  
Author(s):  
Ashutosh Bagchi
Keyword(s):  
Mathematical Model ◽  
Model Updating ◽  
Three Dimensional ◽  
Field Tests ◽  
Mode Shapes ◽  
Actual Structure ◽  
Shell Elements ◽  
Vibration Data ◽  
The Difference ◽  
The Mathematical Model

Model updating is an important step for correlating the mathematical model of a structure to the real one. There are a variety of techniques available for model updating using dynamic and static measurements of the structure’s behavior. This paper concentrates on the model updating techniques using the natural frequencies or frequencies and mode shapes of a structure. An iterative technique is developed based on the matrix update method. The method hasbeenappliedtothefiniteelement models of a three span continuous steel free deck bridge located in western Canada. The finite element models of the bridge have been constructed using three-dimensional beam and facet shell elements and the models have been updated using the measured frequencies. From the study it is clear that the initial model needs to be built such that it represents the actual structure as closely as possible. The results demonstrate that the difference between the modal parameters from the model and field tests affect the quality of the model updating process.

Conditional Nonlinear Optimal Perturbations of a Two-Dimensional Quasigeostrophic Model

2006 ◽  
Vol 63 (6) ◽  
pp. 1587-1604 ◽  
Author(s):  
Mu Mu ◽  
Zhiyue Zhang
Keyword(s):  
Singular Vector ◽  
Nonlinear Evolution ◽  
Initial Perturbation ◽  
Nonlinear Effects ◽  
Two Dimensional ◽  
Physical Problems ◽  
Maximum Value ◽  
The Difference ◽  
Quasigeostrophic Model ◽  
The Cost

Abstract Conditional nonlinear optimal perturbations (CNOPs) of a two-dimensional quasigeostrophic model are obtained numerically. The CNOP is the initial perturbation whose nonlinear evolution attains the maximum value of the cost function, which is constructed according to the physical problems of interests with physical constraint conditions. The difference between the CNOP and a linear singular vector is compared. The results demonstrate that CNOPs catch the nonlinear effects of the model on the evolutions of the initial perturbations. These results suggest that CNOPs are applicable to the study of predictability and sensitivity analysis when nonlinearity is of importance.

Time-Accurate Evaluation of Film Cooling Jet Characteristics for Plenum and Crossflow Coolant Supplies

2019 ◽  
Author(s):  
Spencer J. Sperling ◽  
Randall M. Mathison
Keyword(s):  
Film Cooling ◽  
Momentum Flux ◽  
Flux Ratio ◽  
Fast Response ◽  
Mode Shapes ◽  
Momentum Flux Ratio ◽  
Cooling Hole ◽  
The Difference ◽  
Response Pressure ◽  
Jet Characteristics

Abstract Gas turbine film cooling creates complicated and highly unsteady flow structures. This study seeks to examine the unsteady characteristics created by different film hole inlet geometries using a fast-response pressure sensitive paint (PSP) technique able to capture time-accurate measurements at 2000 frames per second, resolving frequencies up to 1000 Hz. Time accurate and time-averaged measurements are used to evaluate the performance of a plenum-style inlet and a crossflow-style inlet in varying turbulence environments over a flat plate. The results of this study are intended to begin the process of breaking down widely accepted time-averaged film effectiveness contours into the cumulative effects of smaller oscillating cooling jets. Jet behaviors observed in this study include a sweeping oscillation, unsteady attachment and separation from the plate, and time accurate and time average flow bias. The behavior and performance of higher blowing ratio, separated film cooling jets depend heavily on the momentum flux ratio. Crossflow fed cooling holes show bias to the upstream side of the cooling hole with respect to the internal crossflow direction. Plenum fed cooling holes outperform crossflow fed cooling holes, and the difference increases with increasing momentum flux ratio. Cooling hole inlet geometry and momentum flux ratio affect the core of the jet, and freestream turbulence affects the periphery of the jet. Fluctuating frequencies of plenum fed and crossflow fed cooling holes were seen to be influenced by the turbulent velocity fluctuation frequency. The resulting mode shapes showed dominant side-to-side fluctuations for higher turbulence environments and a separation and reattachment motion for lower turbulence environments.

Horizontal and Torsional Modes of an Ultra Large Container Ship (ULCS)

2020 ◽  
Author(s):  
P. P. Vijith ◽  
Suresh Rajendran
Keyword(s):  
Numerical Model ◽  
Numerical Method ◽  
Natural Frequency ◽  
Flexible Structures ◽  
Complex Problem ◽  
Mode Shapes ◽  
Beam Model ◽  
Torsional Vibrations ◽  
Hydrodynamic Loads ◽  
Structural Responses

Abstract The hydro elastic responses of flexible structures under fluid loading is an important concern during the design of large ocean structures. The two-way coupling between the structural responses and the hydrodynamic loads is a complex problem in large flexible floating structures since the structures can vibrate in longitudinal, vertical, horizontal, or torsional modes. The antisymmetric distortion modes may be coupled depending on the location of the centroid and the shear centre. In the case of thin walled open structures, horizontal and torsional vibrations are usually coupled due to the asymmetry of cross section as well as eccentricity between centroid of the section and shear deformation centres. The acurate estimation of dry natural frequency and modes shapes of structure is indispensable since it helps to validate the accuracy of the structural modelling. A numerical method available from one of the existing literatures is used for the estimation of dry and wet natural frequencies, and mode shapes of horizontal and torsional vibrations of an ULCS. The natural frequency and modes are essential parameters for the analysis of interaction between structural responses and hydrodynamic loads. The numerical method is based on a 1D FEM beam model. Distortion due to warping is included in the numerical model since it is well known that containerships with large hatch opening are susceptible to warping. The numerical model is subdivided into 50 stations and the mass distribution and the sectional properties are calculated in order to match the bending, shear, torsion and warping moduli of the experimental model. The dry and wet natural frequency and mode shapes for the horizontal and torsional vibrations of the ULCS is numerically calculated and compared with the experimental results.

Dynamic Assessment and Modeling of the Modal Frequencies and Shapes of Bovine Tibia

2018 ◽  
Vol 1 (4) ◽  
Author(s):  
Reem Yassine ◽  
Ali Fakhreddine ◽  
Mohammad Sayegh ◽  
Samir Mustapha ◽  
Ramsey F. Hamade
Keyword(s):  
Dynamic Assessment ◽  
Indicator Function ◽  
Mode Shapes ◽  
Bone Length ◽  
Impact Location ◽  
The Difference ◽  
Highly Correlated ◽  
Simple Equations ◽  
Correlated Parameters

Thirteen long tibia (bovine) bones were utilized in vitro to experimentally extract modal frequencies in the cranial-caudal (C-C) and medial–lateral (M–L) planes. Bones were instrumented with four single-axis accelerometers uniformly placed along the length of the bone and hammer impacted at different locations in both planes. Frequency response function (FRF) and complex mode indicator function (CMIF) techniques were used to identify the modal frequencies. CMIF has an advantage of detecting closely spaced modes by excluding misinterpreted peaks. It was found that the difference between the two methods did not exceed 2.98%. CMIF data were more consistent when varying impact location. The effect of bone's geometrical attributes on modal frequencies was statistically scrutinized and highly correlated parameters were identified. Bone length exhibited high correspondence to frequencies (p < 0.05) for practically all modes. Also, four simple equations were developed, relating modes 1 and 2 in the C-C and M-L planes to bone length. To determine the first and second modal shapes, subset of 6 tibia bones was further instrumented. Mode shapes were extracted in the C-C and M-L planes.

Amplification and attenuation of waves of finite duration by means of a bubble zone in the one-dimensional approximation

2012 ◽  
Vol 9 (2) ◽  
pp. 33-37
Author(s):  
M.N. Galimzyanov
Keyword(s):  
Solid Wall ◽  
Nonlinear Effects ◽  
Uneven Distribution ◽  
Pressure Waves ◽  
One Dimensional ◽  
Finite Duration ◽  
Dimensional Approximation ◽  
The One ◽  
Bubble Zone ◽  
As Effects

Some peculiarities of the dynamics of pressure waves in a fluid containing bubble zone of finite dimensions in the one-dimensional approximation are studied. The problem is considered taking into account nonlinear effects. The results of the action of wave pulses on a bubble area with an uneven distribution of bubbles are presented, as well as effects on a solid wall covered with a bubble area.

Vibration analysis of an idealized vertical pump model

2005 ◽  
Vol 219 (2) ◽  
pp. 169-181 ◽  
Author(s):  
J M Lee ◽  
C-G Pak ◽  
H S Lee ◽  
H G Choi
Keyword(s):  
Mathematical Model ◽  
Analytical Models ◽  
Mode Shapes ◽  
Design Strategies ◽  
Test Operation ◽  
Design Variables ◽  
Parametric Studies ◽  
The Difference ◽  
Pump Assembly ◽  
Flexible Foundation

Vertical pumps have intrinsically weak structures for vibration resonance because of their long slender shapes. Therefore, it is important to estimate the vibration characteristics of a vertical pump analytically and/or experimentally before its final installation. Sometimes, however, unexpected resonances arise after the installation. The unexpected resonance is found to be due to the difference between the boundary condition of a vertical pump for rigid-foundation test operation and for flexible-foundation real operation. In order to examine this problem and quantify the effect of the foundation condition on the natural frequencies and mode shapes of the entire pump assembly, a mathematical model using a Euler-Bernoulli beam with a flexible foundation is presented. This model combines the lower and upper parts of a vertical pump, distinguishing it from previous analytical models. Experiments and simulations have been performed to validate this mathematical model and to evaluate the effect of foundation stiffness on vibration behaviour. Parametric studies have also been carried out to investigate the effects of other design variables on the dynamic characteristics of the pumps and to propose design strategies for improvement in the dynamics.

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