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Gait analysis (GA) is often defined as the study of human walking; typically involving computerized and instrumented measurement of the movement patterns that make up walking. GA can reveal the timing and pattern of activation of muscles and joints, of body segment motions, and the forces that act on them. It can facilitate objective comparison of pathological versus normal gait and monitoring of progress in rehabilitation. However, although raw results can be printed in minutes, the clinical team may spend hours in interpreting the data. The success of this approach is limited mainly by the ability of clinicians to handle large sets of data, their expertise with respect to the biomechanics of gait, and their individual experience with the characteristics of a particular population. In addition, it is recognized that the interpretation of data varies from clinician to clinician and institution to institution which have its impact on clinical decision-making. Also, the techniques used in the interpretation of gait data often do not provide information about possible causes for gait abnormalities. Improving the efficiency of patient testing will greatly enhance the productivity of gait laboratories and improve patient care. For this reason, the focus in this project is on developing a technique for the analysis of gait data to aid clinical interpretation. A software package, also called expert system, is developed based on automating the Rancho Observational Gait Analysis Approach used to denote gait deviations. Causes related to deviations are listed and the result of additional tests that may help prove or refute any cause is also included. A report is then generated that includes all the above. The software is tested with data from a group of cerebral palsy patients to check its efficiency. Results showed that the expert system was capable in denoting deviations and overcoming a number of major challenges in gait data interpretation. However, many limitations are still present such as the need to test it on other pathologies and consider more parameters, e.g. kinetics and EMG data.

In recent years, a number of studies have addressed the possibility of replacing the conventional rigid mirrors that are used in space-based telescopes with optical membranes. Weight reduction, reduced cost of transportation and ability to provide a continuous surface for the attenuation of wave front aberrations are some of the benefits given by optical membranes. Given the harsh environmental loading conditions represented by thermal radiation, debris impact and slewing maneuvers, the ability to characterise fully the dynamics of such low-density thin-film membranes is essential. Nevertheless, the testing of membrane-like structures has proven to be a non-trivial process, and requires a considerable amount of work to achieve accurate results, as well as validating experiments against numerical models. Despite typical testing, the inherent low-density feature of membranes requires the use of non-invasive, non-contact sensors and excitation capability. The work presented here, investigates the possibility of using Operational Modal Analysis (OMA) techniques to extract modal parameters from an acoustically-exited membrane, where responses are collected by using a Scanning Laser Doppler Vibrometer (SLDV) as a non-contact velocity transducer. Results from this experiment are validated against an impedance-based numerical model.

Experimental vibration measurement of mechanical components are very important for studying the dynamic properties. Electromagnetic (EM) shakers are the most widely used exciters in mechanical testing because of both the broadband dynamic range of excitation and the excitation power. However, there are applications where these exciters can work inefficiently, and so underperform. This can be caused by an impedance mismatch between the shaker armature and test rig, which causes dissipation of the generated power into heating the armature rather than moving the test structure. Clearly, mechanical components presenting a high level of structural damping will require higher level of power to obtain high levels of vibration. Hence, it is important to minimize as much as possible any unwanted power dissipation due to both the test rig design and the connection between the shaker and/or the test rig. This paper demonstrates that a bladed disc type of structure can be used as a high impedance connector for a test rig in order to increase the excitation force level. This is possible thanks to otherwise an undesirably dynamic characteristic of bladed discs, which is represented by mistuning of the blades. When this mistuning characteristic is enhanced, it is possible to produce several resonances each with a high impedance match between the shaker and the test rig and this can increase the force applied to the specimen and thus its displacement amplitude. Also, the test rig proposed here can be used of several resonance frequencies depending on the number of blades. Hence the proposed test rig can improve both the performance of a shaker and increase the amplitude of vibration of the test structure. Further to this the application of the amplification process can be used for fatigue trials of composite material component. This has been an application which has caused some considerable difficulty: few cases have been successful and the results in this paper show evidence of how to proceed for future trials.

Underplatform friction dampers are commonly used to control the vibration level of turbine blades in order to prevent high-cycle fatigue failures. Experimental validation of highly non-linear response predictions obtained from FEM bladed disk models incorporating underplatform dampers models has proved to be very difficult so as the assessment of the performance of a chosen design. In this paper, the effect of wedge-shaped underplatform dampers on the dynamics of a simple bladed disk under rotating conditions is measured and the effect of the excitation level on the UPDs performances is investigated at different number of the engine order excitation nearby resonance frequencies of the 1st blade bending modes of the system. The measurements are performed with an improved configuration of a rotating test rig, designed with a non-contact magnetic excitation and a non-contact rotating SLDV measurement system.

In recent years, a number of different methods have been developed in order to update an analytical structural dynamics model using the limited data which can be obtained from vibration tests. The majority of these methods are based on correlation between the analytical and measured modal data and, in most cases, spatial completeness of the measured co-ordinates is critical. In this paper, a new method is presented which tackles the model updating problem by using an incomplete set of measured FRF data directly. It is shown that model updating methods based on modal data are, essentially, particular cases of the present generalised method in which FRF data at resonance frequencies only are employed. The advantages of using FRF data (over modal data) to update an analytical model are demonstrated. Special attention is given to the application of the method to the case where both measured modes and co-ordinates are incomplete. The practical applicability of the method is assessed based on the GARTEUR structure which has been used in a Europe-wide correlation exercise.

In this work the distortions in the receptance plots of forced non-linear mechanical systems are examined. Weak non-linearities of stiffness and damping are considered, and approximate harmonic steady-state responses are evaluated using the method of equivalent linearisation. It is found that in the case of pure damping non-linearities, the frequency of maximum frequency separation in the receptance Nyquist plot is approximately equal to the natural frequency of the corresponding linearised system. However, when stiffness non-linearities are encountered, the maximum frequency separation is influenced by two non-linear terms: one accounting for the dependence of the equivalent natural frequency on the stiffness non-linearity, and the other accounting for the asymmetry of the Bode diagram. Based on the results of the analysis presented in this paper, a method for identifying and quantifying weak non-linearities in the frequency responses of practical systems is suggested. The applicability of the proposed technique is then tested with theoretical and experimental data.

Integral bladed disks (also known as blisks) are more widely used in modern aeroengine compressor designs because of the potential weight savings, but there are challenges in controlling the extreme vibration response levels in mistuned blisks, which are blisks with blades slightly different from each other. As blisks lack the uncertainty and variability of friction properties related to joints, the maximum vibration response level of a blisk test piece in operation can be predicted prior to installation. A previously proposed response-level prediction procedure for mistuned blisks is outlined, and its robustness is studied. A method of improving the results, given noisy experimental data, is proposed. Some of the issues discussed are validated by using experimental data.

It is known that small differences between nominally identical turbomachine blades, known as mistuning, can lead to significant variation in their vibration response levels. A commonly used term in mistuning studies called the “amplification factor” is clearly defined in this paper, and the high sensitivity of high-cycle-fatigue-related fatigue life to the level of vibration response levels is presented. Computer simulations are run to study the distribution of the amplification factor in three situations, namely, (i) bladed disks with damping mistuning, (ii) EO excitation of bladed disk modes in the veering region, and (iii) apparently tuned bladed disks. In addition to running simulations, the upper bound of the adjusted amplification factor in damping-mistuned bladed disks is derived theoretically.

Continuous-Scanning LDV (CSLDV) methods are now available as alternative approaches to the conventional Stepping mode for Operational Deflection Shape (ODS) measurements. CSLDV techniques were initially used with sinusoidal excitation where the LDV time history could be also used to extract modal parameters by post-processing the data using modal analysis software. The latest extension of CSLDV is the use of a pseudo random signal to excite the tested structure for this work, a cantilever steel beam was used. Analytical models of the structure, the LDV output signal and excitation waveform were produced to simulate several responses which could be studied to identify the relationship between three fundamental parameters: (i) LDV scan rate, (ii) sampling frequency and (iii) frequency resolution of the pseudo random signal. This paper produces a theoretical background of the study presenting simulations and validations of both LDV output time signals and ODSs, respectively.

Engineering structures seldom behave linearly and linearity checks are common practice in the development of critical structures exposed to dynamic loading to define the boundary of validity of the linear regime. However, and especially in large scale industrial applications, there is not a general methodology for dynamicists to extract nonlinear parameters from measured vibration data so that these can be then included in the associated numerical models. In this paper, it is proposed a simple method based on the information contained in the frequency response function (FRF) of a structure. The technique falls within the category of Single-Degree-of-Freedom (SDOF) methods. The basic principle is that, at a fixed amplitude of response, it is possible to extract the dynamic properties of the underlying linear system. Repeating this linearisation for different response amplitudes allows to extract the stiffness and damping as functions of the amplitude vibration. Furthermore, because of its mathematical simplicity and practical implementation during standard vibration test, is particularly suitable for the engineering community. Results of numerical simulations as well as measured data demonstrate the potential benefit offered by this approach.

The design of high cycle fatigue resistant bladed disks requires the ability to predict the expected damping of the structure in order to evaluate the dynamic behaviour and ensure structural integrity. Highly sophisticated software codes are available today for this nonlinear analysis but their correct use requires a good understanding of the correct model generation and the input parameters involved to ensure a reliable prediction of the blade behaviour. The aim of the work described in this paper is to determine the suitability of current modelling approaches and to enhance the quality of the nonlinear modelling of turbine blades with underplatform dampers. This includes an investigation of a choice of the required input parameters, an evaluation of their best use in nonlinear friction analysis, and an assessment of the sensitivity of the response to variations in these parameters. Part of the problem is that the input parameters come with varying degrees of uncertainty, since some are experimentally determined, others are derived from analysis and a final set are often based on estimates from previous experience. In this investigation the model of a commercial turbine bladed disc with an underplatform damper is studied and its first flap, first torsion and first edgewise modes are considered for 6EO and 36EO excitation. The influence of different contact interface meshes on the results is investigated, together with several distributions of the static normal contact loads to enhance the model setup and hence increase accuracy in the response predictions of the blade with an underplatform damper. A parametric analysis is carried out on the friction contact parameters and the correct setup of the nonlinear contact model to determine their influence on the dynamic response and to define the required accuracy of the input parameters.

Aircraft engine components, such as bladed discs, are subjected to high levels of vibration due to their service conditions and vibratory stresses can reduce the expected operational life. High Cycle Fatigue (HCF) is the most common cause of component failure in gas turbine engines. Laboratory testing is important for understanding the fatigue properties of materials and for producing a database eventually used during the design of new components. HCF test can be performed in the laboratory using a test rig on which is installed a test structure, connected to an electromagnetic shaker supplying the excitation. A simple test rig can be made comprising a holding block connected by push rod to the armature of a shaker so as to produce a base excitation. Such a test rig can be specifically designed to increase the test piece vibration levels by tuning it to one resonance of the structure. However, in doing so, a test rig of this type can present an impedance which is mismatched with the shaker, thereby causing dissipation of the excitation force. Any power loss can be a problem, exacerbated by components presenting high levels of structural damping, because of the higher force levels required to achieve high levels of vibration. Hence, any HCF test can be ineffective because of the diversion of shaker power from the test component to other parts of the test setup. The aim of this paper is to study the impedance mismatch between test rig and shaker by modelling a simple test rig, using a lumped-parameter model, for designing and measuring vibrations of the test rig to identify its weakness for HCF.

The blade mistuning vibration problem refers to the often-dramatic scatter - and thus increase - in vibration response levels when the nominally-identical blades on a bladed disc are slightly different to each other. For example, when a set of blades have eigenfrequencies varying randomly with a 0.5% scatter about the design value, the vibration response of the individual blades can vary dramatically, with individual blades displaying increases of as much as 100-500% as compared with the level which would be observed on every blade in a perfect (i.e. “tuned”) bladed disc. As both the vibration response levels and variations of blades are physical in nature, the variation is called aleatory uncertainty or simply variability. Although the problem became a research topic over 40 years ago with more than 400 papers already published, industry still faces shortened fatigue lives due to these extreme vibration responses, with high levels of scatter and uncertainty as to the likely incidence of extreme response levels. In the paper, the blade mistuning problem is viewed as a robust design problem, where the maximum blade response on the bladed disc is the robustness. The dependence of robustness on selected design parameters is discussed, and a procedure for managing the consequences of blade mistuning on manufactured bladed discs, rather than trying to eliminate the problem, is presented.

Detailed numerical and experimental studies are presented on the chaotic dynamic behaviour of non-linear mechanical systems with backlash. Such systems arise in engineering structures in which components make intermittent contact due to the existence of clearances. Chaotic vibration behaviour of the system is illustrated in the time, frequency and state-space domains. Poincare maps of the motion reveal a fractal-like structure of the attractor and the related positive Lyapunov exponents give further indication of chaotic vibration. The forcing parameter field for the existence of chaos and the influence of damping on the chaotic behaviour have been investigated. It is found that periodic as well as chaotic solutions exist under different forcing conditions. The fact that such a simple non-linear mechanical system can lead to chaotic vibration means that care must be taken in the design of mechanical control systems and that statistical stress/fatigue analysis is recommended when such systems are considered. Also, from a condition monitoring point of view, it is quite possible for a broad band response to be caused by a pure sinusoidal excitation when such non-linear mechanisms as backlash stiffness exist.

Studies of the consequences of mistuning on bladed disc vibration levels have been undertaken for over 40 years and yet mistuning is still an unresolved problem for turbomachinery designers. Why is this? How have we failed to solve this problem? And what can we do now? This paper proposes a different approach which seeks to manage, rather than solve, the blade mistuning problem.

The modelling of friction contact interfaces in structural dynamics attracts much interest in the gas turbine industry. In order to obtain reliable predictions of typical friction interfaces, such as encountered in under platform dampers or blade roots, accurate characteristics of friction interfaces must be provided to the analysis. It must be ensured that a sufficient number of parameters are provided, characterising all aspects of the friction contact, that the values are measured accurately, and that the contact parameters are interpreted and used correctly in the numerical modelling of the contact interfaces. This investigation demonstrates that measured friction coefficient and tangential contact stiffness are sufficient to reproduce the experimental friction interface behaviour and that these two parameters can be measured reliably in the available test rig. In combination with fine nonlinear interface meshes and accurate contact pressure representations, the measured interface behaviour of stick, micro- and macroslip is reproduced with good accuracy. The capability of modelling the microslip behaviour for the contact interface by a multitude of friction contact elements is explored and the effect of the normal stress distribution over the contact area on the microslip is studied.

A new procedure is developed to find the probabilities of extremely high amplification factors in mistuned bladed disk vibration levels, typical of events which occur rarely. While a rough estimate can be made by curve-fitting the distribution function generated in a Monte Carlo simulation, the procedure presented here can determine a much more accurate upper bound and the probabilities of amplification factors near to that bound. The procedure comprises an optimization analysis based on the conjugate gradient method and a stochastic simulation using the importance sampling method. Two examples are provided to illustrate the efficiency of the procedure, which can be 2 or 3 orders of magnitude more efficient than Monte Carlo simulations.

The SNL/AWE joint mechanics workshop, held in Dartington Hall, Totnes, Devon, UK 26-29 April 2009 was a follow up to another international joints workshop held in Arlington, Virginia, in October 2006. The preceding workshop focused on identifying what length scales and interactions would be necessary to provide a scientific basis for analyzing and understanding joint mechanics from the atomistic scale on upward. In contrast, the workshop discussed in this report, focused much more on identification and development of methods at longer length scales that can have a nearer term impact on engineering analysis, design, and prediction of the dynamics of jointed structures. Also, the 2009 meeting employed less technical presentation and more break out sessions for developing focused strategies than was the case with the early workshop. Several 'challenges' were identified and assignments were made to teams to develop approaches to address those challenges.

Gyroscopes have been proposed as sensors for ambulatory gait analysis and functional electrical stimulation systems. Accurate determination of the Initial Contact of the foot with the floor (IC) and the final contact or Foot Off (FO) on different terrains is important. This paper describes the evaluation of a gyroscope placed on the shank for determination of IC and FO in subjects walking outdoors on level ground, and up and down an incline. Performance was compared with a reference pressure measurement system. The mean difference between the gyroscope and the reference was less than –25 ms for IC and less than 75 ms for FO for all terrains. Detection success was over 98%. These results provide preliminary evidence supporting the use of the gyroscope for gait event detection on inclines as well as level walking.

The traditional form of a frequency response function (FRF) measurement for a single-shaker modal testing (also for multi-shaker modal testing) using random excitation is an open-loop system. However, inevitable physical constraints cause such FRF measurements to be inherently of a closed-loop form. This paper presents the effect of hidden feedback paths on some current FRF estimators. Attention has been drawn to the effects of noise and leakage on these estimators. The closed-loop model is generalised to explore the effect of shaker-structure interaction in two-shaker modal testing. The complexity of multi-shaker modal testing is illustrated by using a multi-input multi-output model from which a frequency domain technique is developed to give noise-free estimates of the FRFs. The applicability of the closed-loop model in a two-shaker sine dwell test is validated using results from experiments carried out on a circular disk.

Basically, there are two approaches to resolve this incompatibility: condensing the analytical model to those coordinates that are or that can be identified experimentally, and expanding the measured vibration modes to the full set of coordinates using the existing analytical model.

This paper presents a new procedure for determining the revised modal properties (eigenvalues and mass-normalized eigenvectors) in a structural modification analysis. The procedure is based on expressing the eigenvectors of the modified structure as a linear combination of the eigenvectors of the original structure and employs the stationary property of the Rayleigh quotient to determine the modified structure's eigenvalues. It has the same theoretical basis as first- and second-order sensitivity analysis, but here the non-linear effects contributed by all high-order terms [generally assumed to be small relative to the effect contributed by first- and second-order terms (1–6)] are preserved in full. Hence, the usual shortcoming of sensitivity analysis—that it is limited to small modifications—is overcome. A special feature of this procedure is that the exact modal properties of the modified structure are determined without solving the generalized eigenvalue problem for the modified structure. Thus, this procedure can greatly reduce the computation cost and increase the efficiency of structural modification analysis (or reanalysis) during a structural optimization process. Numerical examples demonstrate the superconvergence characteristic of the technique. The limitations caused by modal and coordinate incompleteness, and the sensitivity of this technique with respect to simulated measurement errors, are investigated by using a finite element model of a steel frame structure and a ten-degrees-of-freedom mass-spring model.

In recent years a number of studies have employed long pulse biphasic stimulation as a treatment for denervated muscle to improve tissue quality and in some cases to improve contractile capability sufficient to restore function. However, in the U.K., this treatment is yet to be widely adopted clinically. A 5 subject, case based pilot study of long pulse biphasic direct stimulation of peripheral limb denervated muscle is being conducted and its effect on the tissue evaluated by measurement of muscle bulk, limb blood flow, and skin temperature. In cases of partial denervation. trapezoidal shaped pulses are used to minimize sensory and motor nerve fiber recruitment.

Kinematic gait analysis is limited by simplified marker sets and related models. The majority of sets in clinical use were developed with low resolution imaging systems so required various assumptions about body behaviour. Further major limitations include soft tissue artefact and ambiguity in landmark identification. An alternative is the use of sets based on six degrees-of-freedom (DOF) principles, primarily using marker clusters for tracking. This study evaluates performance of a 6DOF set, based largely on CAST/ISB recommendations, through comparison with a conventional set and assessment of repeatability. Ten healthy subjects were assessed in treadmill walking, with both sets applied simultaneously on two occasions. Data were analysed using repeatability coefficients, correlation of key features, and comparison of joint angle curves and difference curves with confidence bands. Apart from pelvic tilt all segment and joint angles from both sets showed high within and between session repeatability (CMC > 0.80). Hip rotations showed clear differences between the two sets with indications in support of the 6DOF set. Knee coronal angles showed evidence of cross-talk in the conventional set, highlighting difficulties with anatomical identification despite control measures such as a foot alignment template. Knee transverse angles showed inconsistent patterns for both sets. At the ankle the conventional set only allowed true measurement in two planes so with high repeatability the 6DOF set is preferable. The 6DOF set showed comparable performance to the conventional set and overcomes a number of theoretical limitations, however further development is needed prior to clinical implementation.

In the past decade, Continuous Scanning Laser Doppler Velocimetry (CSLDV) has been successfully used inexperimental modal analysis and vibration tests. Essentially, this technique consists in the use of a LaserScanning Velocimeter (LDV) moving continuously across a vibrating surface rather than stepping in a point-by-point fashion. If the structure is undergoing harmonic vibration, its Operating De”ection Shape (ODS) canbe recovered in a very short time and without the limitations in spatial resolution typical of discrete pointmeasurements. Recently, this technique has been extended to transient excitation -i.e. the object is swept by thelaser transducer during a period of transient free response caused by an impact. The combination of a broadbandexcitation with a full-“eld measurement results in a highly complex signal, modulated both by the mode shapesof the structure and by the exponential decays due to damping eects. Thus, the signal contains in its spectruma mixture of temporal information (the eigenvalues of the structure) and spatial information (the eigenvectors),all in a single time history. This paper presents a mathematical model of this new concept, “rst applied to asimple one-dimensional scan and then to a rectangular 2-D area scan. The numerically-simulated signals of the1-D case are compared with actual measurements, both in time and frequency domains. Finally, an analysis ofthe measurement parameters involved in this method is provided.Keywords: Impact Testing, CSLDV, Continuous Scanning, LDV

Laser techniques are commonly used to measure structural vibration responses with high spatial resolution over an extended area. Forced mode shapes will generally be similar to natural mode shapes and undamped mode shapes, if the damping is not too great nor the modal spacing too close. When this is not the case, the real components of forced mode shapes of close modes, and of the response at an off-resonant frequency, can be combined to reveal the corresponding natural mode shapes. These components are combined in proportions calculated to fit natural mode shape data extracted from frequency responses, measured at a relatively small number of suitable points within the scanned area. Procedures may be varied to suit different measurement techniques; continuous-scan LDV techniques offer the possibility of fitting to line-scan polynomial coefficients instead of the amplitudes at specific points thus reducing the time needed for the data acquisition. All the techniques promise considerable economies in test measurement timescales.

In this paper, we present a methodology and results from an experimental investigation of forced vibration response for a bladed disk with fitted underplatform “cottage-roof” friction dampers, together with the corresponding numerical predictions. A carefully designed and constructed rotating test rig is used to make precise measurements, which involve only the phenomena of interest. For this purpose, the measurement rig is operated under vacuum to eliminate aerodynamic effects on the rotating blisk and noncontact excitation and measurement techniques are employed so as not to modify the bladed disk dynamics. The experimental data measured are used for validation of multiharmonic balance-based prediction tools developed at the Imperial College. Predictions are carried out both with and without taking inherent mechanical mistuning into account, which is identified from measured data. Measured and predicted response curves are compared with each other and the degree of correlation is discussed.

In this paper, robust maximum forced response reduction strategies based on a “large mistuning” concept are introduced, including both (i) random and (ii) deterministic approaches. An industrial bladed fan disk serves as an application example for a reliability assessment of the aforementioned strategies using two well-established tools for uncertainty analysis: (i) statistics and (ii) sensitivity and robustness. The feasibility and other practical aspects of implementing large mistuning as a means of preventing excessive forced response levels caused by random mistuning and ensuring the predictability of the response are discussed.

It is well known that friction is really important to reduce amplitudes of vibration of rotor blades. Underplatform dampers are a common solution for introducing friction damping, but there are also other friction damping sources on blades that are produced in places with high normal loads and small relative displacements (e.g. lockplates and blade-disc joints). Several approaches based on the classical Coulomb friction law have been used in order to model the friction damping at those interfaces, but their results are not accurate enough for those cases with small displacements where high normal loads appear. This paper presents simulations of typical cases of friction on rotor blades (underplatform dampers, lockplates and blade root) using a method based on macroslip and the method developed by ‘Industria de TurboPropulsores’ (ITP) based on microslip (InTerPart MIcroslip COntact method), and their comparison with experimental results obtained with several tests performed at Imperial College London (IC). The comparison shows that, for cases with high normal loads and small displacements, the ITPMICO method obtains further more accurate results than based-on-macroslip one.Copyright © 2008 by ASME

This paper highlights the application to structural dynamics of the sensitivity analysis methods developed by numerical analysts and presents a historical development of first- and higher-order eigenvalue and eigenvector sensitivities. Different formulae for an eigenvalue sensitivity are presented and it is shown that all of these are implicitly the same. A condition number is presented to give the limited bound of application for the first-order eigenvalue and eigenvector sensitivities. An alternative structural modification method based on Rayleigh Quotient Iteration is presented. A lumped spring-mass system with 7 degrees-of-freedom (7DoF) is used to show the applicability of the Rayleigh quotient iteration method.

The NSF/SNL joint mechanics workshop, held in Arlington, Virginia, 16-18 October, 2006, attempted to assess the current state of the art for modeling joint mechanics for the purpose of structural dynamics calculation, to identify the underlying physics issues that must be addressed to advance the field, and to propose a path forward. Distinguished participants from several countries representing research communities that focus on very different length and time scales identified multiple challenges in bridging those scales. Additionally, two complementary points of view were developed for addressing those challenges. The first approach - the 'bottom-up' perspective - attempts to bridge scales by starting from the smallest length scale and working up. The other approach starts at the length scale of application and attempts to deduce mechanics at smaller length scales through reconciliation with laboratory observation. Because interface physics is a limiting element of predictive simulation in defense and transportation, this issue will be of continuing importance for the foreseeable future.

In this paper, robust maximum forced response reduction strategies based on a “large mistuning” concept are introduced, including both (i) probabilistic and (ii) deterministic approaches. An industrial bladed fan disc serves as an application example for a reliability assessment of the aforementioned strategies using two well-established tools for uncertainty analysis: (i) statistics and (ii) sensitivity and robustness. The feasibility and other practical aspects of implementing large mistuning as a means of preventing excessive forced response levels caused by random mistuning and ensuring the predictability of the response are discussed.Copyright © 2007 by ASME

One major problem facing finite element model updating is the spatial incompatibility between the measurement of mode shapes through a limited set of physical sensors and the corresponding analytical predictions at a large number of finite element DOFs. Expansion of the measured mode shape data or reduction of the size of the initial FE model to the measured degrees of freedom is normally used to match the requirement. However, both techniques bring some erroneous information into the process. With the Continuous Scanning Laser Doppler Vibrometry (CSLDV) technique, a large number of degrees of freedom (DOFs) can be measured and accurate mode shapes can be achieved in a relatively short testing time. Such features provide great potential for dealing with the problem of the spatial incompatibility in FE model updating. In this paper, an application of finite element model updating using the continuous scanning laser Doppler vibrometry measurement is discussed. A real test piece of a square steel plate and its FE model were built. The first 20 natural frequencies and the corresponding mode shapes expressed by a large number of DOFs were measured using the CSLDV technique and further used for FE model updating. The initial FE model was assumed that random errors up to 20% of the theoretical values of Young's modulus were distributed among 25 areas of the plate due to uncertainties on the physical parameters. Model updating was undertaken to minimise the discrepancy between the FE model predicted and the experiment measured modal parameters and satisfactory results were obtained.

A method of measuring vibration response on rotating components using an LDV and its application on bladed disks are presented. Understanding and controlling of vibration amplitudes of bladed disks has been a primary concern for aero-engine manufacturers for many years. The vibration amplitudes of these components are known to be significantly affected by break down of symmetry due to variations in dimensional or material properties. A bladed disk exhibiting these variations is said to be mistuned and considerable research effort is put into acquisition of prediction tools to calculate the effects of these variations. However, the validation of these tools against real measurements is often ignored because of the difficulties involved in application of appropriate excitation and measurement techniques in rotating conditions. In this paper we present successful use of non-intrusive measurement and excitation techniques towards achievement of this goal. These techniques are independent of rotational speed. The so-called self-tracking LDV measurement method used in this paper was introduced in a previous paper by the authors. Here the use of method for acquisition of high quality reference response data for validation of mistuned bladed disks and those fitted with under-platform friction dampers are given.

In recent years, the CSLDV (Continuing Scanning LDV) technique has been developed to obtain the ODS (Operational Deflection Shape) of a structure within a very short period of time. The ability to predict and to measure the ODS of a vibrating structure suggests its use to increase the potential for structural damage detection, localization and severity assessment. Previous research based on simulation of some simple test cases showed the effect of excitation locations on structural damage detection. Four steel plates were acquired and a FEM model of that structure was produced. Modal analysis, theoretical and experimental, was performed on the plate to obtain eigenvalues and eigenvectors and to update the FEM model. This time, the damage was simulated either using two permanent magnets which could be attached and de-attached easily without compromise the integrity of the structure or reducing the thickness of some elements. Hence, 4 damaged plates were modelled in FE software upon the position of the damage. The simulation and testing of the ODSs and the MSE (Mean Square Error) of the 4 plate structures in the damaged and the undamaged cases were performed based on CSLDV measurement method and compared respectively. Results show effect of vibration excitation location in the damage detection.

Optical techniques are widely used to measure the vibration response patterns (ODSs) of structures over a scanned area, excited at resonance frequencies. The ODSs may be similar to natural mode shapes, but not if there are close modes coupled together by the structural damping. Natural mode shapes are usually extracted by analysis of frequency responses measured at every response point, but this is impracticable with area-scan measurements. The vibration responses at resonance frequencies can be regarded as being a linear combination of just a few natural mode shapes, and these can therefore be separated by combining an equivalent number of area-scan ODSs. For m component modes, measurements of real and imaginary ODS components at m /2 test frequencies and frequency responses at m points on the structure are required. Vibration responses can equally be regarded as being a combination of undamped natural mode shapes and these can be extracted in a similar way, if their amplitudes are known a priori at m points on the structure. Continuous-scan LDV measurements of the ODSs of a damped rectangular plate are used to demonstrate the techniques, and some suggestions are made on the inclusion of split modes and of extraneous resonances.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The aim of this paper is to present an overview of the CAISER MYMESIS software platform that has been developed to simulate and to perform the vibration measurement procedures using Tracking/Continuous Scanning LDV (T/CSLDV) methods, such as area scan on structures under both stationary and rotating conditions. Mathematical models to simulate the LDV output for all CSLDV methods are also included in the software platform as well as the traditional Step-Scanning approach. The software platform can be used in one of two modes: (i) first, to conduct a 'virtual test' to explore various proposed test configurations in order to define an optimum test specification, and (ii) second, to carry out an actual measurement, including driving the scanning mirrors, acquiring data and quickly post-processing data for an immediate inspection of the ODS of the vibrating structures.

Implantable microelectrodes have the potential to become part of neural prostheses to restore lost nerve function after nerve damage. The initial adsorption of proteins to materials for implantable microelectrodes is an important factor in determining the longevity and stability of the implant. Once an implant is in the body, protein adsorption takes place almost instantly before the cells reach the surface of an implant. The aim of this study was to identify an optimum material for electrode recording sites on implantable microelectrodes. Common materials for electrode sites are gold, platinum, iridium, and indium tin oxide. These, along with a reference material (titanium), were investigated. The thickness and the structure of adsorbed proteins on these materials were measured using a combination of atomic force microscopy and ellipsometry. The adsorbed protein layers on gold (after 7 and 28 days of exposure to serum) were the smoothest and the thinnest compared to all the other substrate materials, indicating that gold is the material of choice for electrode recording sites on implantable microelectrodes. However, the results also show that indium tin oxide might also be a good choice for these applications.

Measurement of vibration "operating deflection shapes" (ODSs) on cylindrical or conical surfaces is difficult with optical techniques, because of the restricted angle of view. Point measurement transducers such as accelerometers, on the other hand, can provide extensive coverage, but with poor spatial resolution. This paper proposes two techniques using a continuous-scan LDV which can be used to give full area coverage on such components. In the first technique, the structure is mounted on a stand which is oscillated, typically, at 0.3 Hz, over ±180°, to provide a scan in the circumferential direction, with a straight line scan parallel to the axis of rotation. Analysis is identical to that for a rectangular scan, and gives the ODS as a 2D polynomial series. The second technique uses a fixed-point LDV with a continuously-rotating 45° mirror to provide a circumferential scan, the mirror being simultaneously translated, sinusoidally, along the axis to give a scan on the inside of the structure. Analysis is the same as that for a spiral, circular scan on a vibrating disc, and gives the ODS as a Fourier series in the circumferential direction and a polynomial in the axial direction.

Implantable microelectrodes have the potential to become useful tools for recording from and/or stimulating cells of the nervous system in paralysed individuals, or as part of neural prostheses for amputees. Once implanted into the body, these electrodes are expected to remain functional for many years; therefore the materials must be compatible within their biological environment, in order to minimise complications and implant failure. In this study, the biocompatibility of materials for electrode sites has been investigated using two measures: cytotoxicity and protein adsorption. The cytotoxic effects of materials on cells have been investigated using neutral red assay, and adsorption of proteins onto materials has been investigated using atomic force microscopy and ellipsometry. Materials investigated in this study are gold (Au), platinum (Pt), iridium (Ir), indium tin oxide (ITO) and titanium (Ti). Ti has been chosen as a reference material because it is a long established implant material. After 72 hours of exposure to fibroblast cells, Au, ITO, and Ir show no inhibitory effects on cell growth, whereas Pt and Ti show greater amounts of growth inhibition. The protein adsorption to different materials shows a steady growth following the initial adsorption pattern. After 24 hours of exposure to plasma, Ti had the thickest and ITO had the thinnest layer of adsorbed protein.

An implantable micromachined microelectrode (microprobe) for sensing of action potentials in the locust peripheral nervous system is presented. The microprobe has been used to record signals from the locust nervous system to identify the effect of key probe parameters on recording site selectivity.

When making recordings from peripheral nerve with high impedance microelectrodes (>1M/spl Omega/), high impedance, high gain amplifiers are required. In order to analyse the recorded signals from multichannel microelectrode devices, it is desirable that the amplifier and filter channels used match as closely as possible, and that the data be stored by computer for off-line analysis. A five channel system is described for this purpose. The instrumentation was designed with off-the-shelf components, to have a matching between channel gains of better than 3% and the frequency characteristics of the Butterworth filter stages employed to match to 2%. Input resistance was designed to be 100 M/spl Omega/, gain switchable from 5000 to 75000 times, and bandwidth of 10 Hz or 100 Hz to 10 kHz. The system noise (including the electrode) was measured experimentally to be of the order of 15 /spl mu/V rms (r.t.i). Data acquisition was performed by a PC, sampling each channel at up to 40 kHz, with custom software written in LabVIEW.

Thin-film microelectrode probes (microprobes) are being investigated as peripheral nerve neural signal transducers for use in functional electrical stimulation orthoses. Finite element modelling techniques have been used to determine the effects of microprobe substrates on extracellular signals recorded intraneurally from locust peripheral nerve. The models show that probes with widths of the order of one-tenth the longitudinal extent of the action potential can have effects of amplifying signals from nerve fibres in front of the probe, and attenuating signals from fibres behind. The nerve sheath can also contribute to, and modulate, these effects. >

Experiments have been carried out using thin-film multi-microelectrode probes (microprobes) to record from locust peripheral nerve. Selective recordings have been made with 8 /spl mu/m by 8 /spl mu/m gold electrodes spaced 40 /spl mu/m apart. Further improvements are necessary to confirm these findings, and to determine the level of selectivity that can ultimately be achieved. >

The shape (geometry) of planar thin-film microelectrode recording sites may have some influence on neural signal transduction. This was examined numerically for three different geometries; circular, triangular, and square. The results indicated that circular sites were most like ideal point electrodes. Triangular sites appeared to have some directionality in their recording properties. It was also shown that for sources close to the site, smaller sites would be expected to record larger signals.

A significant factor in the optimisation of implantable electrodes for long-term neural recording is the effect electrode size has on the data collected. It is preferable to have as small an electrode as possible for improved selectivity (i.e. the ability to discriminate between different neurons), but reducing electrode size increases electrode impedance and thermal noise. Here, the authors present the results of a study of action potentials recorded from locusts in vivo. Signals recorded from electrodes of dimensions between 4/spl times/4 /spl mu/m and 50/spl times/50 /spl mu/m are presented, with analyses of action potentials and recorded noise. It is observed that there appears to be an optimum electrode size of about 20/spl times/20 /spl mu/m, which presents the best compromise between size and recording characteristics.

The use of biocompatible materials is important in determining the longevity of chronically implantable microelectrodes. Protein adsorption is the initial event that takes place once an implant is in the body. These adsorbed proteins are then a significant influence on the subsequent adsorption of further proteins and cells; they thus dictate the interfacial reactions and ultimately the biocompatibility of the material. Results from protein adsorption studies on materials for sensing electrodes using ellipsometry are presented. The results suggest that among the materials investigated, indium tin oxide (ITO) is the best material in preventing protein adsorption, a characteristic required for electrode recording sites.

Three methods of using an LDV to measure the vibration of a bladed disc in a rotating rig are described. I.e. (i) the response of one blade is monitored continuously by diverting the laser beam via a small mirror on the rotating disc, and a fixed, annular, conical mirror. Any of the blades may be targeted, by indexing the rotating mirror. (ii) circular scans give circumferential response mode shapes directly, or (iii) via spectra, as nodal diameter coefficients. Some natural modes of blisks (integral bladed discs) occur in isolated pairs, with amplitude distributions which are sinusoidal around a circular scan line. The natural frequencies increase with the number of sinusoids around the circumference, asymptotically to the cantilever blade frequency. Forced vibration of these modes, in a rotating situation, produces various combinations of standing and rotating waves. With a mistuned blisk, the close modes couple to create natural mode shapes which are very irregular. Excitation frequencies are at multiples of rotation speed, exciting modes with equivalent numbers of nodal diameters, sometimes aliased with the number of blisk blades. The LDV techniques described can cover all these effects, and some example measurements are included to illustrate their potential.