Computational Modal Analysis of an Aircraft Hydraulic Pump Support Structure

With the increased size of the finite element model for improved accuracy, the modal frequency response analysis has been one of the common practices of evaluating the performance of vehicle dynamics. However, there is difficulty in predicting the vehicle dynamics response with non-proportional damping regarding performance. The fast frequency response analysis algorithm (FFRA) has been proved to be very effective for partially damped structural system in the modal frequency response analysis. In the fast frequency response analysis algorithm, performance depends mainly on the complex symmetric matrix eigenvalue problem. Therefore, an efficient complex symmetric matrix eigenvalue problem solver is developed in this article. This approach also uses parallel processing in a shared memory machine for more efficient analysis. Numerical examples show that the new complex symmetric matrix eigensolver provides good accuracy and high performance. Then, the fast frequency response analysis algorithm is applied to a full scale vehicle system that includes only a few viscous damping finite elements. The fast frequency response analysis algorithm significantly improves the performance of the modal frequency response analysis compared to conventional method. In addition, parallel processing improves the efficiency of the overall simulation.

An alternative approach to measure similarity between two deterministic transient signals

Analysis of dynamic characteristic was conducted focusing on the transportation of high-pressure storage tanks, covering two scenarios: independent transportation and mixed transportation. For independent transportation, analysis of free modal was carried out to obtain the first four orders of modal shapes. Additionally, the influence of two constraint methods on the modal characteristics and stress distribution was studied, including fixed at both ends and fixed at the cylinder body. Results show that when the tank was fixed at the cylinder body, it had a higher natural frequency and a lower stress level, making it safer. For mixed transportation, a finite element model was built for 6 high-pressure storage tanks, and analysis of random vibration was performed. The results showed that stress was mainly concentrated on the crossbeams and connection nodes, while the stress on the main body of the storage tanks was relatively low. The overall structure exhibited excellent fatigue performance and met the mechanical and safety requirements under random vibration conditions.

Equivalent linear modal parameter estimation for a nonlinear aeroelastic system

Modal analysis is an approach to determine the dynamic behavior of a structure through numerical analysis or experimental approach. Nowadays, numerical analysis has been preferred by most researchers and engineers compared to experimental analysis to analyze the structure due to expenditure and time consuming factors of the research. Recently, numerical analysis is done computationally or well known as Finite Element Analysis (FEA) by using finite element (FE) model to replicate the real test structure. Instead of advantage of FE analysis, the trustworthiness of FE model has been questioned since simplification has been made during design stage for complex structure and inaccurate of geometry input of the model. Hence, this paper is carried out to reduce the discrepancies between numerical prediction results with measured test data on FE model of exhaust structure by implementing FE model updating using SOL200 algorithm. Initially, the FE model is running on normal mode analysis SOL103 to extract the modal parameters such as natural frequency and mode shape. Then, the numerical pre-diction result has been correlated and validated with measured test data obtained through Experimental Modal Analysis (EMA). Due to disagreement between numerical result and experimental data in correlation process, the FE model has been updated using SOL200 algorithm. The percentage error between numerical prediction result and measured test data is minimized from 5.67 to 3.23% after been updated. It’s shown the capability SOL200 algorithm in preparing the reliable FE model before been used for further analysis such as structural dynamic modification.KeywordsDynamic studyJoints strategyFinite element analysisExperimental modal analysisFE model updating

Both Gade & Herlufsen started working for Bruel and Kjaer Company, when the modern era of structural measurements began in the early 1980s. In (Brown and Allemang, Sound Vib Mag 19–25, January 2007), it is even argued that the modern era of Experimental Modal Analysis already started one or maybe two decades earlier. In 1982 we participated at IMAC I, the first international modal analysis conference at Hyatt Orlando, USA—the time considered when modal analysis changed from being a pure scientific concept to be a practical engineering tool. Many tests were at that time limited to Single Input/Single Output, SISO measurements. In 1983, we were involved in the release of Bruel and Kjaer’s first Dual Channel Signal analyzer. Today Dual channel FFT analysis is the established method of performing Frequency Response Function measurements used for what we might call classical mobility based modal testing and analysis. Over the years, we have seen progress and development in all fields of the measurement chain from the input vibration transducers via the signal conditioning to the analog to digital conversion, real time- and post-processing of functions followed by modal parameter estimation and applications of the modal model. This paper will deal with what we see (and we both have been involved with from a Bruel & Kjaer perspective) as some of the most important/biggest steps achieved in this progress. Today it is not unusual that modal analysis is performed using several hundreds of high dynamic range measurement channels connected to dedicated smart modal accelerometers (with build-in Transducer Electronic Data Sheets (TEDS)) doing Multiple Input Multiple Output measurements with automated modal parameters estimation and model correlation with large Finite Element models.

This paper adopts composite structure system analysis method to perform modal analysis of high-speed face milling cutter which is mounted on the machine tool through FEM modal analysis. The key problem of this method is to obtain joint surface parameters between the machine tool spindle and face milling cutter through experimental modal analysis and MATLAB software. The joint surface parameters consist of linear stiffness, linear damping, rotation stiffness and rotation damping. After getting the frequency response function (FRF) at the tool tip of the face milling system through experimental modal analysis, the contact surface parameters can be used to eliminate the influence of the machine tool to get modal parameters of the face-milling cutter itself. Based on the finite element model of face milling cutter, composite structure system analysis method can be used easily to acquire the dynamic performance of the face milling system through FEM modal analysis, greatly to improve the reliability of modal analysis, and is helpful to the dynamic design and the structure improvement of high speed face milling cutter.

A technique for structural analysis of transformer cores in terms of magnetostriction is proposed. The magnetic flux density of each element is first calculated by the finite element method (FEM). Then the magnetostrictive force on each element is calculated from measurements. The magnetostriction is specified as the initial strain and is converted into the force on each node, and a structural analysis is performed. The advantage of specifying the magnetostriction as the initial strain is that it is possible to obtain the force at the location of each element as a vector. Modal analysis and frequency response analysis were also performed and it was shown that resonance is related to the magnetostrictive frequency and the natural mode. Thus, it becomes possible to forecast the frequency at which the core vibrates most strongly which makes the proposed technique of analysis is very useful. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 172(1): 19–26, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20947

The insulator strings in substation which are long time exposed in the outdoor environment are easily accumulation industrial and natural filth. So they need to be cleaned regularly to prevent the power outages and other incidents because of flashover phenomenon which occurs in the weather of rain and fog and other inclement weather. The substation equipment water washing robot with hot-line is employed in the substation to clean the insulator strings with the same method of artificial flushing. The theory of finite element analysis and modal analysis are based in this paper. The reliability and precision of robot's structural in the process of washing operation are ensured by stress distribution and deformation from the static analysis; The low order natural frequencies and mode shapes are carried out through modal analysis and a vibration control and optimization scheme is proposed to reduce the effects of vibration in the condition of the flushing operation, and the robot's stability can be improved.

We theoretically investigate a new type of piezoelectric actuator with tubular interdigitated electrodes. A partial model is adopted due to the axial symmetry of the actuator, which is divided into non-overlapping opposing electrode pairs on the center plane of the branch electrode. We present a finite element model of actuator and analyze its static-dynamic properties by using the commercially available finite element software ABAQUS. The length-to-diameter ratio of the tubular actuator can be as larger as necessary, so we are more concerned with the axial mechanical properties of the actuator. Thus we studied the influence of the electrode’s shape and structure size on the clamping stress and free strain of the partial models. We also analyzed an ordinary piezoelectric model of the same size. We demonstrated that the partial model displayed significantly improved axial performance over the ordinary one. The axial stress of the partial model can reach 2.75 times that of the ordinary one, and the axial free strain can reach 1.55 times that of the ordinary one. According to the results of the static analysis, appropriate electrodes and structural parameters were selected to establish a tubular actuator model, with which modal and harmonic response analysis were performed. A modal analysis was used to obtain the frequencies and the shapes of the axial vibration. Each pair of electrodes is shunted to a sinusoidal varying voltage. Using the results of the harmonic response analysis, we obtained the actuator’s axial resonance curve.

A reliable and accurate analytical model is desired for the printed circuit board (PCB) with IC package to predict the system response due to loadings such as shock and vibration simulation or even with thermal effect. This work addresses the procedure of model verification by the adoption of experimental modal analysis (EMA) to validate the finite element (FE) model constructed by FE commercial software. The PCB with one package adhered with the heating pad to emulate the heat effect is first considered for completely free boundary condition. The refined FE model of the PCB consists of detail components, such as the chip, substrate, compound and solder balls. The thermal effect on the PCB is simulated to conduct the temperature field analysis as well as the thermal stress. The modal analysis on the PCB with the heating in steady state is then performed to obtain the structural modal parameters, i.e. natural frequencies and mode shapes. The EMA is also carried out to determine the system modal properties that are used to update the analytical FE model. Through the comparison of frequency response functions and modal parameters between the analytical FE model and the real PCB structure, the refined FE model can be verified for material properties and thermal boundary conditions. The same procedure for model verification is then conducted via both EMA and FEA on the PCB in the fixed boundary that complies with the test fixture for the random vibration test of JEDEC specification. The verified equivalent FE model of the PCB can then be adopted to perform spectrum response analysis accordingly.

The possibility of characterising the dynamics of rotating machinery structures using modal analysis is explored. The paper is based on a recently-developed method by which the left-eigenvectors can be computed from their right counterparts and their corresponding eigenvalues. This method is aimed at obtaining the complete set of modal parameters of a machine without the need to measure a complete row plus a complete column of the frequency response function (FRF) matrix, as is customary for non-self-adjoint systems. The applicability of the method to the derivation of reduced-order modal models of continuous systems from measured FRFs is discussed. It is shown that the new method is applicable if the response of the continuous system at hand is only affected significantly by a limited number of modes within the frequency interval of interest. It is also shown that a simplification of the measurement scheme made available by this new method depends on the selection of degrees of freedom used to study the structure. A numerical example is given to illustrate this point.

Identification of modal parameters of unmeasured modes using multiple FRF modal analysis method

Traumatic brain injury (TBI) may happen due to loads at high rates. Due to the limitations in experimental approaches, computational methods can simulate and quantify mechanical properties. The experiments show that the human skull has nonlinear mechanical behavior and is significantly strain rate dependent. In this study, we implement Mooney-Rivlin nonlinear hyper and linear-elastic constitutive models to the experimental tensile data at different strain rates; 0.005, 0.1, 10, and 150 1/sec. A dried human skull including frontal, parietal, and occipital bones, was modeled by the 3D laser scanner and discretized by HyperMesh software to perform modal analysis using LS-Dyna finite element software. Using a roving hammer experimental modal analysis scheme, the frequency response function (FRF) and the first three natural frequencies of the skull will be measured. We found these natural frequencies are 496.9 Hz, 560.9 HZ, and 1246 Hz. Performing numerical modal analysis on the skull with pre-assumed linear elastic properties at high strain rate showed close natural frequencies as obtained by experiments. This study provides a new insight into a better understanding of the nonlinearity dynamical behavior of the human skull.

In recent years composites have progressively been used for large-scale structures such as aircraft, ships, ground vehicles, and wind turbine blades. Traditional Nondestructive Evaluation (NDE) techniques have various limitations in assessing the performance of the large-scale composite structures. For instance, many techniques have the ability to measure either global or local properties but cannot measure both simultaneously. Nondestructive vibration detection techniques present a potential solution for evaluating both local and global large-scale composite structures, which are largely based on the fact that damage in a structure influences its dynamic characteristics such as modal parameters and Frequency Response Functions (FRF). This study investigates locating delamination in composite laminate plates under dynamic loading utilizing accelerometers during dynamic response as an alternative structural health monitoring method in composite structures. The test specimens were manufactured using unidirectional carbon fiber/epoxy creating 11 cross-ply composite laminate plates with [0,90,0,90]s orientation. Delaminated regions were placed at one inch increments, horizontally along the specimen. During testing, one side of each composite laminate plates were clamped using a custom fabricated fixture, cantilevered leaving the remaining edges free. An Unholtz-Dickie shake system excited the specimens. Dynamic response measurements using teardrop style piezoelectric accelerometers were taken along the surface face of each specimen, individually located along a 3 X 10 grid. Each response was compared collectively to examine any acceleration differences and damping between specimens. Finite element Modeling (FEM) ensured correlation of the flexural bending mode shapes between theoretical, analytical, and experimental. It was found that, the comparison between the results of the theoretical, Finite Element Analysis, and experimental data were in good agreement and delamination can be detected.