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The latest studies on failures in steel truss-type bridge found that they are highly vulnerable to damage and thus prone to potential local or total collapse. Many authors recommend monitoring the critical elements in the existing steel truss-type bridges in real time to anticipate any failures in local members. Although mechanical strain is the most frequently used variable for this purpose, this method also happens to be the most expensive monitoring strategy. This paper describes a case study of failure scenarios assessment in a steel truss-type railway bridge after extensive long-term monitoring conducted by the authors, based on measuring vertical deflections and modal frequencies. The structure has both an isostatic and a hyperstatic configuration, and was assessed by means of a combination of: (i) long-term monitoring results, and (ii) a finite element analysis to simulate several failure scenarios. A sensitivity study of the different failure scenarios has been carried out, identifying those that can be detected. The results are used to define practical recommendations for failure detection by measuring vertical deflections and modal frequencies.

[EN] The monitoring of bridges is a crucial operation for their maintenance and safe operation. Several methodologies have been developed the last decades, where different sensors are deployed to measure the bridge response (displacement, acceleration, tilt, strain, etc.). GNSS technology is one of the methods which are applied with the main advantage the direct measurement of the bridge displacement is carried out in an independent global coordinate system. However, the high cost of the GNSS stations, consisted of dual frequency receiver and geodetic GNSS antenna, is the main reason of the limited application of GNSS for bridge monitoring. In the current study, we assess the accuracy of low-cost multi-GNSS receivers in monitoring dynamic motion, similar to that of bridge response. The precision of low-cost GNSS receivers was assessed against high-performance dual frequency GNSS receivers, by executing controlled circular motion of predefined radius, of amplitude ranging between 5 to 50 cm, and frequency of 0.363 Hz. From the analysis of the GNSS measurements it was assessed the precision of GPS-only and the potential beneficial contribution of multi-GNSS constellation by enhancing the accuracy of GNSS solution. Then, a low-cost monitoring system formed by two closely-spaced low-cost GNSS receivers was applied in dynamic displacement monitoring of the Wilford pedestrian bridge. The analysis from low-cost GNSS data shows similar accuracy in monitoring the bridge dynamic response to that of the survey-grade GNSS receiver, with same main modal frequency of the bridge identified.

A method to estimate modal frequency based on empirical mode decomposition (EMD) and ensemble empirical mode decomposition (EEMD) is proposed. This method can decrease the difficulties in identifying modal frequency of combine harvesters. First, we used 16 acceleration sensors installed at different test points to collect vibration signals of a corn combine harvester under operating conditions (mass time-varying conditions). Second, we calculated mean value, variance and root mean square (RMS) value of the vibration signals, and analyzed its stationarity of vibration signals. Third, the main frequencies of the 16 points were extracted using the EMD and EEMD methods. Finally, we considered modal frequencies identified by the SSI algorithm as standard, and calculated the fitting degrees of the EMD and EEMD methods. The results show that in different time periods (0~60 s and 60~120 s), the maximum differences of the mean value, variance and RMS value of signals were 0.8633, 171.1629 and 11.3767, and the vibration signal under the operating condition of field harvesting can be regarded as a typical non-stationary random vibration signal. The EMD method had more modal aliasing than EEMD, and when we obtained the fitting equations of EMD, EEMD and SSI methods, the value of the Euler distance between the EMD fitting equation and the SSI fitting equation was 446.7883, while that for EEMD and SSI was 417.2845. The vibration frequencies calculated by the EEMD method is closer to the modal frequencies identified by SSI algorithm. The proposed method provides a reference for modal frequency identification and vibration control in a complex working environment.

Metallic-ceramic functionally graded materials have potential application value in the design of thermal barrier systems for aircraft panels due to their ultrahigh temperature resistant and high strength properties. In this article, the FGMs plate was used as the object to study the influence of parameters such as the volume fraction index, the geometric size of the plate and the thermal environment on the modal frequencies of a FGMs plate. Firstly, the power law distribution function was employed to discuss the influence of thermal environment on the physical properties of FGMs plates. Thereafter, the FGMs linear layered model dependent on temperature field was established by using the temperature continuously changing with the spatial position trait in the finite element, and the validity of this model in dynamic analysis was verified. Finally, the effects of ceramic volume fraction index, FGMs plate length-to-width ratio, temperature gradient and other variables on the modal frequencies of a FGMs plate were comprehensively analyzed and discussed. Results indicate that the higher order modes are mostly impacted by the uniform temperature field, while the linear and nonlinear temperature fields have the greatest impact on the first-order modes. In linear and nonlinear temperature fields, the volume fraction index is the most sensitive one to the effects of modal frequency drop ratio, while the modal frequency drop ratio is mainly affected by the coupling effect of the volume fraction index and the temperature gradient in uniform temperature field.

Cylindrical roller bearing is an important component of the airflow root blower of a power generation plant, and its malfunction has been identified as one of the root causes of poor quality demineralized water produced during operation. Hence, there is need to study the dynamic behaviour of a typical cylindrical roller bearing of an airflow root blower. In this study, the dynamic analysis of a cylindrical roller bearing subjected to different rotational speeds was simulated using finite element analysis software, Abaqus. The frequency response of the bearing was determined experimentally and analytically, and the modal frequency results obtained from both analyses were compared. The outcome of the dynamic analysis showed that the maximum temperature and Hertzian stress was developed on the outer ring of the bearing during operation, thus making this component most prone to failure. It was observed that the value of the temperature and stress developed increase with an increase in rotational speed. However, at a rotational speed greater than 503 rad/s, a drop in the Hertzian stress was developed due to the stress relaxation the bearing experience at the higher temperatures. A good agreement was obtained when the modal frequency of the frequency response obtained numerically was compared with those obtained experimentally.

This paper examines the influence of the equipment considered as a DVA (Dynamic Vibration Absorber) upon the mode of vertical vibrations of the car body in high-speed vehicles. The car body is represented as an Euler-Bernoulli beam to minimize flexible vibration. The DVA approach is used to find the appropriate suspension frequencies for various types of equipment. A vertical mathematical model with a flexible car body and equipment is developed to investigate the effect of equipment mass, suspension stiffness, damping, and mounting location on car-body flexible vibrations. A three-dimensional, rigid-flexible coupled vehicle system dynamics model is developed to simulate the car body and equipment’s response to track irregularities. The experimental result was considered to verify the theoretical analysis and dynamic simulation. The mathematical analysis demonstrates that the DVA theory can be used to design the suspension parameters of the equipment and that it is suitable and effective in reducing the flexible vibration of the car body in which the vertical bending mode is greatly affected. Heavy equipment should be mounted as close to the car body’s center as possible to achieve significant flexible vibration reduction, whereas light equipment contributes very little flexible vibration reduction.

Modal frequencies are often used in structural model updating based on the finite element model, and metamodel technique is often applied to the corresponding optimization process. In this work, the Kriging model is used as the metamodel. Firstly, the influence of different correlation functions of Kriging model is inspected, and then the approximate capability of Kriging model is investigated via inspecting the approximate accuracy of nonlinear functions. Secondly, a model updating procedure is proposed based on the Kriging model, and the samples for constructing Kriging model are generated via the method of Optimal Latin Hypercube. Finally, a typical frame structure is taken as a case study and demonstrates the feasibility and efficiency of the proposed approach. The results show the Kriging model can match the target functions very well, and the finite element model can achieve accurate frequencies and can reliably predict the frequencies after model updating.

In field harvesting conditions, the non-stationary random vibration characteristics of the harvester are rarely considered, and the results of vibration frequency calculated by different time–frequency transformation methods are different. In this paper, the harvester’s vibration characteristics under the time-varying mass were studied, and the correlation between vibration frequency and modal frequency was analyzed. Firstly, under the conditions of time-varying mass (field harvesting conditions) and non-time-varying mass (empty running condition), the non-stationarity characteristics of vibration signals at 16 measurement points of a combined corn harvester frame were studied. Then, fast Fourier transform (FFT), short-time Fourier transform (STFT), and continuous wavelet transform (CWT) were used to calculate the vibration frequency distribution characteristics of the corn harvester. Finally, based on the EFDD (enhanced frequency domain decomposition) algorithm, the correlation between the primary vibration frequency and the operating mode frequency is studied. The results show that the mean, variance, and maximum difference of the vibration amplitude under harvesting conditions (mass time-varying system) are 0.10, 26.5, and 1.0, respectively, at different harvesting periods (0~10 s, 10~20 s, 20~30 s). The harvesting conditions’ vibration signals conform to the characteristics of non-stationary randomness. The FFT algorithm is used to obtain more dense vibration frequencies, while the frequencies based on STFT and CWT algorithms are sparse. The correlation between the FFT method and the EFDD algorithm is 0.98, and the correlation between the STFT, CWT, and the EFDD algorithm is 0.99 and 0.98. Therefore, the primary frequency of the STFT methods is closer to the modal frequency. Our research laid the foundation for further study and application of mass time-varying combined harvester system non-stationary random vibration modal frequency identification and vibration control.

In this article, the mechanical properties of large-scale rack structures are analysed by MSC Marc analysis software is verified through the modal test. The modal frequency and modal shape are obtained through the finite element analysis and LMS data acquisition system for modal test verification. It is showed that the modal shape of the modal test and the calculation by finite element analysis are consistent, which verifies the inherent characteristics of the frame structure effectively and provides reliability parameters of the manipulator for the space station in the zero-gravity test.

Structural health monitoring (SHM) has been widely used for the performance assessment of bridges, especially the methods based on dynamic characteristics. Meanwhile, bridge modal frequency is influenced significantly by environmental factors, such as temperature and humidity. Combined with SHM, a reliability assessment of bridges with the temperature and humidity effects eliminated is proposed. Firstly, the bridge deflection verification coefficient is adopted as the evaluation indicator for bridge condition, which is the ratio of deflection-measured value to deflection-calculated value. It is obtained from the relationship between verification coefficient and modal frequency through theoretical derivation. Secondly, a back propagation (BP) neural network is improved by using an artificial bee colony algorithm and employed as a surrogate model to eliminate the effect of temperature and humidity on frequency. Thirdly, a dynamic Bayesian network is applied to establish the reliability analysis model combined with the monitoring results, so that the probability distribution of bridge parameters is updated to improve the accuracy of the reliability analysis. Finally, a simply supported bridge is used as the case study, based on the proposed method in this work. The results indicate that the proposed method can eliminate the temperature and humidity effect on frequency precisely and effectively. With the effect of temperature and humidity on frequency eliminated, the bridge condition assessment can be evaluated accurately through the reliability analysis based on SHM and the dynamic Bayesian network.

The final authenticated version is available online at https://doi.org/10.1007/978-3-030-91877-4_22. Monitoring structural damage is widely used for sustaining and preserving the service life in civil structures, especially in bridges. The influence of environmental variability like temperature affects the dynamic behavior, which can mask subtler structural changes caused by damage. The direct application of vibration-based damage detection methods to measured responses without a prior treatment of the ambient data may lead to false condition assessments. In this article, the main objective is to separate the structural damage conditions from the changes caused by the environmental effects in a numerical benchmark bridge. The Principal Component Analysis (PCA) is applied to decide if the change in vibration characteristics is due to environmental effects or structural damages. The proposed approach in the use of PCA not only allows to detect the damage without the requirement of the baseline to consist of damage sensitivity features obtained from a wide range of environmental conditions, but also serves as a measure for its quantification. The effectiveness and robustness of the proposed methodology is applied to a benchmark bridge structure generated as part of COST Action TU1402 on quantifying the value of information (VoI) in SHM. The benchmark model consisted of a two-span steel bridge under environmental effects, in which two levels of damage were introduced.

Vision-based techniques are frequently used to compute the dynamic deflections of bridges but they are rather computationally complicated and require demanding instrumentation. In this article, we show that it is possible to reconstruct the 2-D kinematics of flexible bridges using a simplified algorithm to analyze common video imagery. The only requirements are that the movement of the control points is clearly visible on the images and that next to each control point, there exist vertical and horizontal bridge elements defining the image scale. We applied this technique during controlled, forced excitations of a timber bridge that was stiff in the vertical but very flexible in the lateral axis because of cumulated damage. We used videos from low-cost cameras, in which the changes of the pixel coordinates of several control points during excitation events and their attenuation were clear. These videos were obtained during two annual structural health monitoring surveys using numerous sensors (Global Navigation Satellite Systems (GNSS), robotic total station (RTS), accelerometers), and hence the output of the video analysis was fully controlled. Because of various errors, the transformation of the video image coordinates into bridge coordinates yielded spurious deflections along the main axis of the bridge, which were used to control the uncertainty of our results. We found that the computed lateral deflections (i) were statistically significant, (ii) satisfied structural constraints, and (iii) were consistent with structural estimates derived from other sensors. Additionally, they provided accurate estimates of the natural frequency and the damping factor of the bridge. This approach can be applied in other cases of monitoring of flexible structures if the requirements for planar deformation, pixel resolution and scale definition are satisfied.

The modal frequencies of a structure are affected by continuous changes in ambient factors, such as temperature, wind speed etc. This study incorporates nonlinear principal component analysis (NLPCA) with support vector regression (SVR) to build a mathematical model to reflect the correlation between ambient factors and modal frequencies. NLPCA is first used to eliminate the high correlation among different ambient factors and extract the nonlinear principal components. The extracted nonlinear principal components are input into the SVR model for training and predicting. The proposed method is verified by the measured data provided in the Guangzhou New TV Tower (GNTVT) Benchmark. The grid search method (GSM), genetic algorithm (GA) and fruit fly optimization algorithm (FOA) are applied to determine the optimal hyperparameters for the SVR model. The optimized result of FOA is most suitable for the NLPCA-SVR model. As evaluated by the hypothesis test and goodness-of-fit test, the results show that the proposed method has a high generalization performance and the correlation between the ambient factor and modal frequency can be strongly reflected. The proposed method can effectively eliminate the effects of ambient factors on modal frequencies.

To obtain some basic laws for bird-strike resistance of composite materials in aeronautical application, the high-velocity impact behaviors of composite laminates with different materials were studied by numerical methods. The smoothed particle hydrodynamics (SPH) and finite element method (FEM) coupling models were validated from various perspectives, and the numerical results were comparatively investigated. Results show that the different composite materials have relatively little effect on projectile deformations during the bird impact. However, the impact-damage distributions can be significantly different for different composite materials. The strength parameters and fracture energy parameters play different roles in different damage modes. Lastly, modal frequency was tentatively used to explain the damage behavior of the composite laminates, for it can manifest the mass and stiffness characteristics of a dynamic structure. The dynamic properties and strength properties jointly determine the impact-damage resistance of composite laminates under bird strike. Future optimization study can be considered from these two aspects.

[Objectives] In order to improve the overall bending mode frequency of the structure and reduce the acceleration level at the end of the stiffened cone in the low frequency range, a mathematical model of a multi-objective optimization design for the vibration characteristics of a stiffened conical shell is established. [Methods] Finite element software ANSYS is used to model a vertical and horizontal stiffened conical shell. The vibration modal frequency and structural response under the vertical downward unit concentrated force at the end of the stiffened conical shell are analyzed. Based on Matlab, the vibration characteristics of the stiffened conical shell are optimized by a genetic algorithm and the tolerance sorting method. [Results] The results show that with the increase of tolerance and target weight, the acceleration level of the optimal structural scheme decreases. With single objective optimization for the same target value, there can be multiple schemes. [Conclusions] The research results of this paper can provide useful references for the acoustic design of reinforced conical shell structures.

Finite Element Analysis of Thin Circular Cylindrical Shells

The structural health monitoring of power transmission towers (PTTs) has drawn increasing attention from researchers in recent years, however, no long-term monitoring of the dynamic parameters of PTTs has previously been reported in the literature. This study performed the long-term monitoring of an instrumented PTT. An automated subspace identification technique was used to extract the dynamic parameters of the PTT from ambient vibration measurements taken over approximately ten months in 2017. Ten target modal frequencies were selected to explore the effects of environmental factors, such as temperature and wind speed, as well as the root-mean-square (RMS) acceleration response of the PTT. Variations in the modal frequencies of approximately 2% to 8% were observed during the study period. In general, among the environmental factors, the temperature was found to be the primary cause of decreases in the modal frequencies, except in the case of some of the higher modes. Typhoon Nesat, which affected the PTT on July 29th, 2017, seems to have decreased the modal frequencies of the PTT, especially for the higher modes. This reduction in the modal frequencies seems to have lasted for approximately two and a half months, after which they recovered to their normal state, probably due to a seasonal cool down in temperature. The reduction percentages in the modal frequencies due to Typhoon Nesat were quantified as approximately &minus, 0.89% to &minus, 1.34% for the higher modes, but only &minus, 0.07% to &minus, 0.46% for the remaining lower modes. Although the unusual reductions in the modal frequencies are reported in this study, the reason for this phenomenon is not clear yet. Further studies would be required in the future in order to find the cause.

International audience; The paper deals with the results of an experimental campaign carried out on a post tensioned concrete beam with the aim of investigating the possibility to detect early warning signs of deterioration based on static and/or dynamic tests. The beam was tested in several configurations aimed to reproduce 5 different phases of the ‘life‘ of the beam: in the original undamaged state, un-der increasing loss of tension in the post tensioning cables, during and after the formation of cracks at mid span, after a strengthening intervention carried out by means of a second tension cable, dur-ing and after the formation of further cracks on the strengthened beam. Responses of the beam were measured by an extensive set of instruments consisting of accelerometers, inclinometers, displace-ment transducers, strain gauges and optical fibers. In this paper data from accelerometers and dis-placement transducers have been exploited. The paper presents the test program and the dynamic characterization of the beam in the different damage scenarios in terms of the first modal frequency, identified from dynamic tests and of the bending stiffness monitored during static tests.

The transformation of a 30 m long timber pedestrian bridge into a wobbly (laterally swaying) bridge with a dramatically reduced first lateral modal frequency has been monitored by seven annual, multi-sensor surveys. This evidence, in combination with analysis of the wind record, observations of local damage and evidence of wind-induced excitations from other bridges, is used to present a multi-stage scenario of the extraordinary structural weakening of our study bridge in only a few years. Our analysis is constrained by observations of asymmetric damage (longitudinal splitting cracks around metallic connections along the south side of the deck, not explained by ordinary, essentially symmetric lateral oscillations) and over-threshold analysis of strong northerly wind events, including gusts. The proposed scenario is that an unexpected for the area icing event took advantage of construction vicissitudes and produced damage that reduced the lateral stiffness of the bridge, especially of the arch superstructure. In addition, strong winds sharing common direction with gusts produced a combination of semi-static lateral bending and of dynamic oscillations, leading to numerous cycles of asymmetric high amplitude lateral deflections producing tensile stress normal to grain, cracks localized in connections, and fatigue. The vertical stiffness of the bridge was only slightly affected.

Diplomsko delo je namenjeno spoznavanju teorije zvoka in akustike. Poudarek dela je v obnašanju zvočnega valovanja v zaprtih prostorih, kjer se pri predvajanju zvoka pojavljajo zvočni pojavi, ki vplivajo na kvaliteto predvajanega zvoka. Zajeti so podatki, ki omogočajo razumevanje teh pojavov in pripomorejo k zmanjšanju vpliva teh pojavov. Da lahko zmanjšamo vpliv teh pojavov, potrebujemo poleg znanja akustike tudi poznavanje opreme za predvajanje in manipulacijo zvoka. Teoretična dognanja so v določeni meri tudi preizkušena v praktičnem okolju. The thesis is devoted to the theory of sound and acoustics. The emphasis is on the behaviour of sound waves in confined spaces, where acoustic phenomena emerge during playback of sound, that affect the quality of the playback. The captured data allows the understanding of these phenomena and help to reduce the impact of these sounds. To be able to minimize the impact of these phenomena, we not only need the knowledge of acoustics, but also we need to understand the equipment that provides playback and manipulation of sound. The theoretical findings are to some extent also tested in a practical environment.

将来、ロボットが自律的に軌道上での大型柔軟宇宙構造物の組立や不具合検知、修理を行うことが期待される。その際に計画立案や制御を効率よく行うためにはロボット自身と相互作用する構造物の変形や動きを知る必要がある。本稿は非同期ラスタスキャン方式のレンジイメージャを用いて振動するモードシェイプ既知の宇宙構造物の形状や動き、モデルパラメタなどを推定する方法を述べる。本手法は近似的なモードシェイプが既知であると仮定し、その情報と振動モデルを利用し、モーダル係数やモーダル周波数、ダンピング係数などを推定することができる。筆者らは宇宙空間での柔軟構造物の低周波部分の動きを模擬できるシステムを空気浮上式定盤の上に構築し、本手法の有効性を実験により検証した。, Future space missions are expected to use robotic systems to assemble, inspect, and maintain large space structures automatically in orbit. For effective planning and control, robots must know the deformations and motions of the structures with which they interact. This paper presents a method for estimating the shape, motion, and dynamic model parameters of a vibrating space structure using asynchronous raster-scanning range imagers. We mounted a flexible panel, which emulates the motion of the large space structure, on an air table. We then conducted experiments using the representative structure and asynchronous raster-scanning range imagers to evaluate the performance of the estimation algorithm., 資料番号: AA0063480035

Quantifying the uncertainty in the dynamic properties of large-scale complex engineering structures presents significant computational challenges. Monte Carlo simulation (MCS) method is extensively employed to perform uncertainty quantification (UQ) because of its generality, stability, and easy implementation. However, a brute-force MCS approach may be unaffordable and impractical when the target model contains a large number of uncertain parameters. In this circumstance, MCS requires a potentially burdensome (if not computationally intractable) number of model evaluations to obtain a credible estimate of the global statistics. In this study, a general framework for analytical UQ of model outputs using a Gaussian process (GP) metamodel is presented, where case inputs are characterized as normal and/or uniform random variables. A detailed derivation of important low-order statistical moments (mean and variance) is given analytically. This analytical method is adopted to characterize the uncertainty of modal frequencies of two bridges with assumed normally- and uniformly-distributed parameters. Meanwhile, the brute-force MCS approach is used for comparison of GP metamodel-derived statistics. Results show that the GP method outperforms the MCS methodology in terms of computational cost, with consistency in the "true" values obtained by MCS. It demonstrates that this GP method is feasible and reliable for modal frequency UQ of complex structures. © 2014 Elsevier Ltd.

The purpose of this paper is to perform a multidisciplinary design and analysis (MDA) of honeycomb panels used in the satellites structural design. All the analysis is based on clamped-free boundary conditions. In the present work, detailed finite element models for honeycomb panels are developed and analysed. Experimental tests were carried out on a honeycomb specimen of which the goal is to compare the previous modal analysis made by the finite element method as well as the existing equivalent approaches. The obtained results show a good agreement between the finite element analysis, equivalent and tests results; the difference in the first two frequencies is less than 4% and less than 10% for the third frequency. The results of the equivalent model presented in this analysis are obtained with a good accuracy. Moreover, investigations carried out in this research relate to the honeycomb plate modal analysis under several aspects including the structural geometrical variation by studying the various influences of the dimension parameters on the modal frequency, the variation of core and skin material of the honeycomb. The various results obtained in this paper are promising and show that the geometry parameters and the type of material have an effect on the value of the honeycomb plate modal frequency., {"references":["Thimas P. Sarafin and Wiley J. Larson, spacecraft structures and\nmechanisms-from concept to launch, Microcosm, Inc. 1995.","Wiley J. Larson and James R. Wertz, Space mission analysis and design,\nsecond edition, Microcosm, Inc. ISBN 0-7923-1998-2, 1992.","Meifeng He, Wenbin Hu, A study on composite honeycomb sandwich\npanel structure, Materials and Design, 29 (2008) 709-713.","A. Boudjemai, M. Bekhti, , M.H. Bouanane, A.M. Si Mohammed, G.\nCooper and G. Richardson, Small satellite Computer-Aided Design and\nManufacturing, pp.181-188, SP-581, August 2005, Proceedings of the\nEuropean conference on Spacecraft Structures, Materials & Mechanical\nTesting, 10-12 May 2005, ISSN: 1609-042X","A. Boudjemai, M.H. Bouanane and, M.A. Si Mohammed, Structural\nModelling and Small Satellite Optimisation, page 51, Second\nInternational Congress Design and Modelling of Mechanical Systems,\nCMSM-07, proceeding, 12-21 march 2007, Monastir Tunisia.","A. Boudjemai, M.H. Bouanane, L. Merad and M.A. Si Mohammed,\nSmall Satellite Structural Optimisation Using Genetic Algorithm\nApproach, 3rd International Conference on Recent Advances in Space\nTechnologies, RAST '07, pp. 398-406, Istanbul, Turkey, ISBN: 1-4244-\n1057-6, ┬® IEEE 2007.","Jeom Kee Paik, Anil K. Thayamballi, Gyu Sung Kim, The strength\ncharacteristics of aluminium honeycomb sandwich panels, Thin-Walled\nStructures 35 (1999) 205-231, ┬® Elsevier Science Ltd.","Noor, A., Burton, W., and Bert, C. 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Roggero, M.Cerocchi, A.Rauschert, M. Sepulveda, A Analysis and\ndesign of a new alternative for satellite platforms, 10th Annual\nAIAA/USU Conference on Small Satellites, 1996.\n[15] Burton, W.S., Noor, A.K. (1997), Assessment of continuum models for\nsandwich panel honeycomb cores, Computer Methods in Applied\nMechanics and Engineering, 145(3-4), 341-360.\n[16] S.D. Yu, W.L. Cleghorn, Free flexural vibration analysis of symmetric\nhoneycomb panels, Journal of Sound and Vibration 284 (2005) 189-\n204.\n[17] P. Gri┼íkevi─ìius, D. Zeleniakiene, V. Lei┼íis, M. Ostrowski, Experimental\nand Numerical Study of Impact Energy Absorption of Safety Important\nHoneycomb Core Sandwich Structures, pp. 119-123, Materials Science\n(Medžiagotyra). Vol. 16, No. 2. 2010, ISSN 1392-1320.\n[18] S. Debruyne , L. Mehrez, D. Vandepitte , E. 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The modal frequency response problem is solved in many vibration analyses of large structures. Commercial programs that are currently available solve this problem by factoring the coefficient matrix at hundreds or thousands of frequencies, which can take many hours. Recently, new algorithms have been developed at the University of Texas that solve the modal frequency response problem much more economically than by performing a direct factorization at every frequency. These fast frequency response analysis algorithms can be used to solve various extensions to the modal frequency response problem that accommodate fluid-structure interaction, enforced motion, and structural optimization using the modal correction approach. These algorithms had previously been implemented in a research program designed for use with shared memory parallel computers. The research discussed in this thesis is focused on creating a new implementation of these fast frequency response analysis algorithms in a maintainable, object-oriented program for distributed memory parallel computers using the Message Passing Interface standard. This program has been shown to produce accurate results much more quickly than commercial programs that solve the modal frequency response problem by factoring the coefficient matrix at every frequency and has achieved significant parallel speedup when run on multiprocessor computers

The main aim of this work is to extract modal parameters of a light aircraft wing. Modal parameters like modal frequency, modal damping and mode shapes characterise the dynamic response of a particular structure and can be used for determining an excess wing flexure as well as the long-term effect of fatigue. For the experimental part the response of the Piper Warrior II was recorded during ground runs. A set of temporarily attached accelerometers was used to record the response of the wing and the signals were recorded. Subsequently a Frequency Response Function was generated in the post-processing stage, which resulted in determining the first and second bending modes as well as the first twisting mode. A Finite Elements Model was applied to validate the results. Due to the limitations of the taxiing speed the method cannot excite higher frequency modes; however the findings can find numerous applications in real time in-flight flexure monitoring., Eleventh Australian International Aerospace Congress; Melbourne, Australia

Random Decrement (RANDEC) Analysis was applied to time histories of roll motion for the Spruance class destroyer. The data was generated from sea trials conducted on a ship in 1987. The RANDEC process was applied to obtain estimates of roll- resonance modal damping and frequencies due to ship motion excitation by random-natured hydrodynamic forces and moments. Prior to applying the RANDEC technique to ship data, a numerical algorithm was developed and validated using reference data sets with known dynamic traits approaching that expected of the ship. http://archive.org/details/shiprollmodeinfo1094528531 Lieutenant, United States Navy Approved for public release; distribution is unlimited.

Vibration measurements were taken to determine the effects of architectural components on the dynamic properties (modal frequency, modal damping ratio, and mode shape) of a long-span floor system. The floor was located above a two-storey gymnasium in a recently constructed three-storey elementary school. The dynamic properties of the bare floor system were measured during the construction phase, immediately after the main structural components and the exterior masonry walls were in place. Six months later, with construction completed and the school ready for occupancy, the properties of the finished floor system, complete with internal partitions, mechanical ducts, furnishings, and carpeting, were again obtained.A comparison of the results of the two test series indicated that the dynamic properties of the floor system were altered by the addition of the architectural components. The fundamental frequency rose by 3% and the frequencies of the higher modes by 23%, even though the static load on the floor increased by about 26%. The substantial stiffening of the floor system necessary to precipitate these increases in frequency was linked to the presence of the internal partitions. A full-span partition was also found to behave as a floor support, creating an additional set of modes which were not previously present. Except for the fundamental mode, damping ratios increased by about 2% of critical, from 1.5% to 3.5% of critical. For the fundamental mode, the negligible increase in damping from 4.1 to 4.2% of critical could not be explained. Key words: floors, composite structures, vibration tests, spectrum analysis, resonant frequency, vibration damping.