A new technique that couples modal analysis and wavelet transforms for detection of multiple damage in structures is introduced. Structural damage may cause local changes in one or more of the following parameters; stiffness, mass and damping that affect the dynamic behavior of the structure. For example, a crack reduces the stiffness of the structure in a localized sense, and thus reducing its natural frequency, and causes changes in both modal damping and mode shapes. In this research, two different structures have been analyzed: beams and plates. First, uniform beams with a single damage (notch) of different sizes at different locations were considered. Then, a beam with multiple damages was analyzed. Secondly, a uniform plate with a single square damage was considered. For all structures considered, the responses were obtained experimentally (using experimental modal analysis) and numerically (using finite element analysis), then wavelet transform was used to detect and characterize these defects. Most vibration-based methods require knowledge of the undamaged state of the structure, which is unavailable in most cases. However, using wavelet transformation has the advantage of not requiring knowledge of the undamaged state. In addition, wavelet transform has the characteristics that make the visualization of the signal discontinuities clear. Here it has been found that some wavelets were able to detect the damage location for all cases. Also it was observed that the magnitude of the wavelet coefficient increased linearly with the increase in the amount of damage.

The transmission line is an underappreciated style of loudspeaker enclosure characterized by an acoustic labyrinth stemming from the rear of the speaker driver. In practice, the transmission line enclosure produces airy sound uncharacteristic of other styles, at the cost of more pronounced resonant peaks. The most important practical drawback of this loudspeaker enclosure design is the difficulty of properly applying damping to these enclosures. Ideally, this difficulty can be mitigated using an analytical model that accurately predicts the SPL frequency response of a transmission line loudspeaker system for a given geometry and mass of damping material. This research takes the first step towards establishing such a model by developing a limited model for a simple enclosure geometry. Through the application of a modal analysis, this research predicts the frequency response of the enclosure for the first five modes, discusses the effect damping has on this response, and experimentally verifies the produced outputs. For the simplified transmission line enclosure, the developed model successfully predicts the target portion of the frequency response. The model produces accurate results for a range of damping levels using experimentally derived damping ratios for the first five modes. The resulting curves for each modal damping ratio allow for a set of novel damping ratios to be produced from an input mass of damping material. Through this process, an input mass of damping material produces the predicted frequency response for a straight, non-tapered transmission line enclosure. This prediction can make damping a transmission line enclosure much more efficient, allowing for transmission line loudspeakers to be more widely available.

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Approved for public release, distribution is unlimited / Ensign, United States Navy

Findings from a project involving rotating equipment defect detection using the Algorithm of Mode Isolation (AMI) are presented. The prototypical system evaluated is a rotating shaft, supported by hydrodynamic bearings at both ends, with one disk mounted to the shaft. Shaft cracks and bearing wear are the two equipment defects considered. An existing model of the prototypical system from the literature, termed the simplified model. is modified to simulate the presence of a transverse shaft crack at mid-span. This modified model is termed the standard model. Ritz series analysis, in conjunction with a previously published description of the compliance related to the presence of a transverse shaft crack, is used to describe the decrease in shaft stiffness associated with the crack. The directional frequency response function (dFRF) is shown in the literature to provide benefits over the standard frequency response function (FRF) in both system identification and shaft crack detection for rotating equipment. The existing version of AMI is modified to process dFRFs and termed Two-Sided AMI. The performance of Two-Sided AMI is verified through system identification work using both the simplified model and a rigid rotor model from the literature. The results confirm the benefits of using the dFRF for system identification of isotropic systems. AMI and Two-Sided AMI are experimental modal analysis (EMA) routines, which estimate modal properties based on a frequency domain expression of system response. Eigenvalues and associated modal residues are the modal properties considered in the present work. Three defect detection studies are fully described. In the first, the simplified model is used to investigate bearing wear detection. Various damage metrics related to the eigenvalue and the residue are evaluated. The results show that residue-based metrics are sensitive to bearing wear. Next, the standard model is used in an in-depth investigation of shaft crack detection. When a shaft crack is present, the standard model is time-varying in both the fixed and moving coordinate systems. Therefore, this analysis is also used to evaluate performing EMA on non-modal data. In addition to continuing the evaluation of various xiv damage metrics, the shaft crack study also investigates the effects of noise and coordinate system choice (fixed or moving) on shaft crack detection. Crack detection through EMA processing of noisy, non-modal data is found to be feasible. The eigenvalue-based damage metrics show promise. Finally, the standard model is used in a dual-defect study. The system is configured with both a shaft crack and a worn bearing. One defect is held constant while the magnitude of the other is increased. The results suggest that AMI is usable for defect detection of rotating machinery in the presence of multiple system defects, even though the response data is not that of a time-invariant system. The relative merits of both input data types, the FRF and the dFRF, are evaluated in each study.

Modal parameter identification of a structure is done through modal testing and modal analysis using various system identification methods. These methods employ linear input-output relationships to extract the modes of a structure. There are cases where laboratory testing of a structure is not possible or information about the structure under operating conditions is seeked. A set of techniques called Operational Modal Analysis have been developed for modal parameter identification in operating conditions of a structure. These techniques use only response measurements to extract the modes. The aim of this study is to investigate the applicability and use of three selected time-domain methods adapted to operational modal analysis. The algorithms are programmed in Matlab&copy / environment, and various cases are evaluated using computer simulations for each method. Two of the selected methods are evaluated on a laboratory scale test setup.

The aim of this work is to determine the influence of noise on determination of own frequen-cies for machine tool by operational modal analysis. For the assigned machine tool operation-al analysis is performed using Data-Driven and Covariance-Driven method for multiple exci-tation variants. Based on the results are created stabilization diagrams used to determine ma-chine tool own frequencies. The results for each excitation variant are compared to each oth-er and the effect of noise influence on the results is determined.

CubeSat or Cubic Satellite is an effective method to study the space aroundthe Earth thanks to its low cost, easy maintenance and short lead time. However, a great challenge of small satellites lies in achieving technicaland scientific requirements during the design stage. In the present workprimary focus is given to dynamic characterization of the deployable tapespringboom in order to verify and study the boom deployment dynamiceffects on the satellite. The deployed boom dynamic characteristics werestudied through simulations and experimental testing. The gravity offloadingsystem was used to simulate weightlessness environment in theexperimental testing and simulations showed that the deployment of thesystem influence the results in a different way depending on the vibrationmode shape. / En CubeSat eller kubisk satellit är effektivt för att studera rymden runtjorden på grund av dess låga kostnad, enkla underhåll och korta ledtid. Enstor utmaningen i utformningen av små satelliter är att uppnå de tekniskaoch vetenskapliga kraven. Detta arbete har analyserat de dynamiska egenskapernahos en utfällbar band-fjäder bom i syfte att verifera och för attstudera bommens utfällningsdynamiska effekter på satellitens bana och attityd.Den utfällda bommens dynamiska egenskaper har studerats genomsimuleringar och experimentella tester. Ett tyngdkraftskompenserande systemhar använts för att simulera tyngdlöshet i de experimentella testernaoch simuleringar visar att utformningen av detta system påverkar resultatenolika beroende på svängingsmodens form.

The diploma thesis deals with determination of modal parameters for machine tool manage-ment. Experimental modal analysis is performed and a new method for determining the damping and stiffness of the machine tool guidance is proposed. A mathematical model for the calculation of signals using state equations was created and the damping stiffness was determined using hysteresis curves.