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This study aimed at evaluating spatiotemporal parameters (STP) and symmetry index (SI), commonly used for evaluating amputee gait for routine clinical use, in individuals with unilateral transtibial amputations wearing energy storage and return (ESAR) feet with fixed ankles, prosthetic feet with adaptive ankles (PFAA) and prosthetic feet with microcontrolled adaptive ankles (PFAA-MC) in ramp ascent and descent. Thirteen individuals with transtibial amputations walked up and down a ramp. The STPs were measured in the amputated and intact legs and the relationship between them was quantified using the SI. The results showed that the use of PFAA-MC decreases walking speed in ramp descent (P < 0.018). However, this was the only parameter that showed a significant change. Hence, the differences in the amputees’ gait pattern when using the above-mentioned prostheses may not be reflected by STP and their SI.

Continuous Scanning Laser Doppler Vibrometry (CSLDV) methods first appeared in the literature in the early 1990s and over the past three decades they have undergone an evolution in terms of procedures and applications which constitute a new state-of-the-art now described in this review paper. The advances in vibration measurement performed by Scanning Laser Doppler Vibrometers augmented the capability of measuring vibration data from a grid of a few hundred measurement points to a single scan which traverses and measures at many thousands of points on the same structure. The deflection shapes of vibration modes can be created by assembling two pieces of information from a scanning measurement - temporal and spatial - and the more measurement ‘points’, the better the spatial density and resolution of the deflection shape(s). The introduction of Continuous Scanning techniques challenged the traditional principle that the number of measurement points defines the spatial definition of the deflection shape. Thereafter, high definition deflection shapes could be achieved by measuring a single time series from a continuously sweeping trajectory covering the same surface area that would traditionally be covered by a set of fixed-point measurements, each of which spans a range of frequencies. The CSLDV approach compresses both the temporal oscillation and the spatial distribution of the deflection shape into one LDV output-modulated signal, whereby the harmonic oscillation and the spatial distribution across a swept area were now defined by a central response harmonic and its sidebands. This change of perspective in vibration measurements from the conventional stepped-scan method to the continuous-scan approach allowed several researchers to exploit and expand the potential of the scanning vibrometer further than its initial design specifications. This paper starts with the raison d’etre, with a brief historical account of how vibration measurements have developed over the past decades, and then moves to the theoretical background and applications of the CSLDV approach. Finally, the paper presents a philosophical and technical account of the research work carried out by several colleagues over the past thirty years and aims to provide a chronological order to the various advancements that CSLDV techniques offer in engineering structural dynamics.

The dual roles of Test and Analysis (experimentation and simulation) in Structural Dynamics have become increasingly inter-dependent for several years, and we are now approaching a level of interaction referred to as Fusion. Today, analysis and test can serve to minimise the effects of the inevitable uncertainties which arise in real engineering circumstances where assumptions, approximations and selections must be made. Here we review the status of this development and identify some specific situations where further enhancements can still be made.

Background Stair-related falls of older people cause a substantial financial and social burden. Deterioration of the visual system amongst other factors put older people at a high risk of falling. Improved lighting is often recommended. The aim of this study was to investigate the effect of lighting illuminance on stair negotiation performance in older individuals with visual impairment. Methods Eleven participants aged 60 or over with a vision of 6/18 or worse ascended and descended a staircase under: 50 lx, 100 lx, 200 lx, 300 lx and distributed 200 lx lighting. A motion capture system was used to measure movements of the lower limb. Clearance, clearance variability, temporal and spatial parameters and joint/segment kinematics were computed. Findings There was no effect on clearance or clearance variability. Participants had lower speed, cadence, increased cycle time and stance time in the 50 lx compared to 300 lx and distributed 200 lx lighting in descent. The minimum hip angle in ascent was increased in the 200 lx lighting. Clearance was found to be moderately correlated with balance scores. Interpretation Individuals with visual impairment adopt precautionary gait in dim lighting conditions. This does not always result in improvements in the parameters associated with risk of falling (e.g. clearance).Background Stair-related falls of older people cause a substantial financial and social burden. Deterioration of the visual system amongst other factors put older people at a high risk of falling. Improved lighting is often recommended. The aim of this study was to investigate the effect of lighting illuminance on stair negotiation performance in older individuals with visual impairment. Methods Eleven participants aged 60 or over with a vision of 6/18 or worse ascended and descended a staircase under: 50 lx, 100 lx, 200 lx, 300 lx and distributed 200 lx lighting. A motion capture system was used to measure movements of the lower limb. Clearance, clearance variability, temporal and spatial parameters and joint/segment kinematics were computed. Findings There was no effect on clearance or clearance variability. Participants had lower speed, cadence, increased cycle time and stance time in the 50 lx compared to 300 lx and distributed 200 lx lighting in descent. The minimum hip angle in ascent was increased in the 200 lx lighting. Clearance was found to be moderately correlated with balance scores. Interpretation Individuals with visual impairment adopt precautionary gait in dim lighting conditions. This does not always result in improvements in the parameters associated with risk of falling (e.g. clearance). Thomas Pocklington Trust.

The Finite Element Method (FEM), Experimental modal analysis (EMA) and other linear analysis techniques have been established as reliable tools for the dynamic analysis of engineering structures. They are often used to provide solutions to small and large structures and other variety of cases in structural dynamics, even those exhibiting a certain degree of nonlinearity. Unfortunately, when the nonlinear effects are substantial or the accuracy of the predicted response is of vital importance, a linear finite element model will generally prove to be unsatisfactory. As a result, the validated linear FE model requires further enhancement so that it can represent and predict the nonlinear behaviour exhibited by the structure. In this paper, a pragmatic approach to integrating test-based system identification and FE modelling of a nonlinear structure is presented. This integration is based on three different phases: the first phase involves the derivation of an Underlying Linear Model (ULM) of the structure, the second phase includes experiment-based nonlinear identification using measured time series and the third phase covers augmenting the linear FE model and experimental validation of the nonlinear FE model. The proposed case study is demonstrated on a twin cantilever beam assembly coupled with a flexible arch shaped beam. In this case, polynomial-type nonlinearities are identified and validated with force-controlled stepped-sine test data at several excitation levels.

Background Minimum Toe Clearance (MTC) is defined as the minimum vertical distance between the lowest point under the front part of the foot and the ground, during mid-swing. Low values of MTC and walking on inclines are both related to higher probability of tripping and falling in lower limb amputees. New prosthetic designs aim at improving MTC, especially on ramps, however the real effect on MTC still needs investigation. The objective of this study was then to evaluate the effect of different prosthetic designs on MTC in inclined walking. Methods Thirteen transtibial amputees walked on a ramp using three different prostheses: non articulating ankle (NAA), articulating hydraulic ankle (AHA), and articulating hydraulic ankle with microprocessor (AHA-MP). Median MTC, coefficient of variation (CV), and tripping probability (TP) for obstacles of 10 and 15 mm were compared across ankle type in ascent and descent. Findings When using AHA-MP, larger MTC median values for ascending (P ≤ 0.001, W = 0.58) and descending the ramp (P = 0.003, W = 0.47) were found in the prosthetic limb. Also significantly lower CV was found on the prosthetic limb for both types of AHA feet when compared to NAA for descending the ramp (P = 0.014, W = 0.45). AHA-MP showed the lowest TP for the prosthetic leg in three conditions evaluated. On the sound limb results showed the median MTC was significantly larger (P = 0.009, W = 0.43) and CV significantly lower (P = 0.005, W = 0.41) when using an AHA in ascent. Interpretation Both AHA prosthetic designs help reduce the risk of tripping of the prosthetic limb by increasing the median MTC, lowering its variability and reducing TP for both legs when ascending and descending the ramp. For most of the conditions, AHA-MP showed the lowest TP values. Findings suggest that AHA prostheses, especially AHA-MP could reduce the risk of tripping on ramps in amputees.

This study measured spatio temporal parameters (STP) and their symmetry index (SI) in order to evaluate the differential effect on the gait pattern of individuals with unilateral transtibial amputations when using two different prostheses. Twelve individuals with transtibial amputations walked on level ground using an Energy Storage and Return (ESAR) prosthesis with fixed ankle and a prosthetic foot with adaptive ankle (PFAA). The STP were measured in the prosthetic and sound limbs and the symmetry index for each parameter was calculated afterwards. The results showed no statistically significant differences between the prostheses for the STP measured, and this was the case both for the prosthetic and sound limbs. Similarly, the SI did not reflect statistically significant differences when the different prostheses were used. Thus, the results suggest that the STP studied and their SI may not reflect differences when evaluating ESAR versus PFAA prostheses in the conditions proposed in this study.

Modal testing is widely used today as a means of validating theoretical (Finite Element) models for the dynamic analysis of engineering structures, prior to these models being used for optimisation of product design. Current model validation methodology is confined to linear models and is primarily concerned with (i) correcting inaccurate model parameters and (ii) ensuring that sufficient elements are included for these cases, using measured data. Basic experience is that this works quite well, largely because the weaknesses in the models are relatively sparse and, as a result, are usually identifiable and correctable. The current state-of-the-art in linear model validation has contributed to an awareness that residual errors in FE models are increasingly the consequence of some unrepresented nonlinearity in the structure. In these cases, additional, higher order parameters are required to improve the model so that it can represent the nonlinear behaviour. This is opposed to the current practice of simply refining the mesh. Again, these nonlinear features are generally localised, and are often associated with joints. We seek to provide a procedure for extending existing modal testing to enable these nonlinear elements to be addressed using current nonlinear identification methods directed at detection, characterisation, location and then quantification – in order to enhance the elements in an FE model as necessary to describe nonlinear dynamic behaviour. Emphasis is placed on the outcome of these extended methods to relate specifically to the physical behaviour of the relevant components of the structure, rather than to the nonlinear response characteristics that are the result of their presence.

Missile vibration testing has undergone significant advances in the past decade. This has been the result of improvements in signal processing and test specification development, but more recently due to the implementation of Multi-Input Multi-Output (MIMO) testing. To date, much of the focus of MIMO testing has been on either a twin-shaker, single-axis configuration or multi-axis testing on a 3 or 6 Degree of Freedom (DOF) shaker system. There has been little attention to replication of the 3-dimensional operating deflection shapes that a missile system experiences during its carriage or operation. This paper presents a systematic approach to 3-axis vibration testing, using current MIMO rectangular controller technology, and demonstrates through an experimental setup a near-3 fold improvement in matching the vibration response of the item under test over the more traditional single axis SISO and MIMO test methods.

Continuous scan laser Doppler vibrometry (CSLDV) is a technique which has been described and explored in the literature for over two decades, but remains niche compared to SLDV inspection by a series of discrete-point measurements. This is in part because of the unavoidable phenomenon of laser speckle, which deteriorates signal quality when velocity data is captured from a moving spot measurement. Further, applicability of CSLDV has typically been limited to line scans and rectangular areas by the application of sine, step, or ramp functions to the scanning mirrors which control the location of the measurement laser spot. In this paper it is shown that arbitrary functions to scan any area can easily be derived from a basic calibration routine, equivalent to the calibration performed in conventional discrete-point laser vibrometry. This is extended by performing the same scan path upon a test surface from three independent locations of the laser head, and decomposing the three sets of one-dimensional deflection shapes into a single set of three-dimensional deflection shapes. The test was performed with multi-sine excitation, yielding 34 operating deflection shapes from each scan.

Substantial improvements have been perceived in surgical results following major lower limb amputation, but there remains observed variation in amputation quality for patients referred for prosthetic rehabilitation from different hospitals.To assess various elements that influence residual limb quality and evaluate their impact on progress through initial prosthetic rehabilitation and mobility outcome after rehabilitation.Clinical survey.A revised 10-item residual limb scoring system was used to survey a succession of 95 primary amputees with transtibial and transfemoral amputations (100 residual limbs) presenting for rehabilitation.The majority of residual limbs scored highly, supporting the perception of generally good amputation quality. There were significant differences in average residual limb scores between some hospitals. The overall scores showed weak or minimal correlation to progress through rehabilitation and mobility outcome but residual limbs scoring higher in seven of the items of the score showed significant advantages in key aspects of progress or mobility at discharge.There is need for continued collaboration between surgeons and rehabilitation centres to ensure consistent high standards. The revised residual limb score used in this survey needs further refinement for future use. Clinical relevance Residual limb quality is an important component influencing prosthetic rehabilitation. This survey of residual limbs at one Rehabilitation Centre suggests encouragingly good surgical results but highlights differences between hospitals. A particular issue is the need for effective collaboration between surgeons and prosthetic rehabilitation professionals to optimise residual limb preparation.

Slope ambulation is a challenge for trans-femoral amputees due to a relative lack of knee function. The assessment of prosthetic ankles on slopes is required for supporting the design, optimisation, and selection of prostheses. This study assessed two hydraulic ankle-foot devices (one of the hydraulic ankles is controlled by a micro-processor that allows real-time adjustment in ankle resistance and range of motion) used by trans-femoral amputees in ascending and descending a 5-degree slope walking, against a rigid ankle-foot device. Five experienced and active unilateral trans-femoral amputees performed ascending and descending slope tests with their usual prosthetic knee and socket fitted with a rigid ankle-foot, a hydraulic ankle-foot without a micro-processor, and a hydraulic ankle-foot with a micro-processor optimised for ascending and descending slopes. Peak values in hip, knee and ankle joint angles and moments were collected and the normalcy Trend Symmetry Index of the prosthetic ankle moments (as an indication of bio-mimicry) were calculated and assessment. Particular benefits of the hydraulic ankle-foot devices were better bio-mimicry of ankle resistance moment, greater range of motion, and improved passive prosthetic knee stability according to the greater mid-stance external knee extensor moment (especially in descending slope) compared to the rigid design. The micro-processor controlled device demonstrated optimised ankle angle and moment patterns for ascending and descending slope respectively, and was found to potentially further improve the ankle moment bio-minicry and prosthetic knee stability compared to the hydraulic device without a micro-processor. However the difference between the micro-processor controlled device and the one without a micro-processor does not reach a statistically significant level.

In 1964, just a few years after the invention of the laser, a fluid velocity measurement based on the frequency shift of scattered light was made and the laser Doppler technique was born. This comprehensive review paper charts advances in the development and applications of laser Doppler vibrometry (LDV) since those first pioneering experiments. Consideration is first given to the challenges that continue to be posed by laser speckle. Scanning LDV is introduced and its significant influence in the field of experimental modal analysis described. Applications in structural health monitoring and MEMS serve to demonstrate LDV's applicability on structures of all sizes. Rotor vibrations and hearing are explored as examples of the classic applications. Applications in acoustics recognise the versatility of LDV as demonstrated by visualisation of sound fields. The paper concludes with thoughts on future developments, using examples of new multi-component and multi-channel instruments.

One of the limiting factors in our capability to predict the dynamics of structures formed by the assembly of several components has been the difficulty of including suitable models for the joints and interfaces that are an integral part of such structural assemblies. These interfaces often contain surfaces that have a degree of slipping, even if only microslipping, and this influences both the stiffness and the damping properties of the structure. Attempts have been made to include a simple representation of these interface phenomena, encouraged by the empirical observation that often inclusion of an extra stiffness and damping parameter can result in much improved predictions compared with those which assume a perfectly rigid connection at the interface. A common basis for such preliminary models is the presumption that the underlying physics of many interfaces can be represented to a reasonable degree by a cyclic load-deflection curve, referred to throughout this chapter as a “hysteresis characteristic.” In gas turbine applications, hysteresis data are required for different materials, and different material combinations, over a wide range of temperatures, normal loading, amplitudes of slipping regimes, and running time considerations of wear and other time-dependent properties. In all these applications, it was decided to develop rigs on which to measure the hysteresis properties of a nominal contact zone or area that could then be incorporated into a finite element type modeling of specific applications, or joints. This chapter summarizes the developments of hysteresis measurement rigs in four research groups over the past 15 years. These groups are based at Imperial College London, the University of Oxford, Politecnico di Torino, and the University of Cambridge, listed here in chronological sequence of an in-service capability.

The economics of designing structures with and without joints is an issue central to not only the direction of research for interfacial mechanics, but also for the design and development of complex structures. The fundamental tenet of the economics of jointed structures is: “When designing a component, is it better to have a monolithic structure, or a jointed assembly?” Only once joints have been determined to be necessary is it germane to further ask: “How does the joint affect the dynamic performance of the structure that it is within?” These two fundamental questions lie at the center of the economics of jointed structures, but they are unable to be answered directly by the current state of joints research. In order to motivate properly the central tenet of the economics of jointed structures, a cost benefit of joints is needed. In the challenge on the economics of jointed structures, several methods are proposed to estimate what the potential financial savings from a better understanding of joint mechanics. In order to realize fully the potential financial savings of joints contribution, though, further research is needed to develop predictive models of interfacial energy dissipation in jointed structures. With an improved understanding of the energy dissipation in frictional interfaces, joints can be used as a design tool that conditions the response of a structure, instead of a design limitation that introduces nonlinearities that are difficult to model accurately.

All structures for which dynamic behaviour is a primary consideration require application of advanced methods of both theoretical and experimental structural dynamics. Specifically, advances in predictive methods of simulation (especially in the numerical analysis aspects) can demand matching advances in testing to provide commensurate accuracy and coverage of the validation of their output. Acquisition of an improved prediction capability is usually accompanied by an increase in expectations and demands for greater reliability in the predicted behaviour. As a direct result, progress in testing and simulation must advance in step and improvements in testing can often be achieved by smarter implementation of contemporary test procedures based on interpretation of the more advanced models used for their design. This lecture presents an integrated test-analysis strategy for ensuring that next-generation structures of all types exhibit much improved reliability in their structural performance.

Typical methods of replicating aerodynamic environments in the laboratory are generally poor. A structure which flies “freely” in its normal operating environment, excited over its entire external surface by aerodynamic forces and in all directions simultaneously, is then subjected to a vibration test in the laboratory whilst rigidly attached to a high impedance shaker and excited by forces applied through a few attachment points and in one direction only. The two environments could hardly be more different. The majority of vibration testing is carried out at commercial establishments and it is understandable that little has been published which demonstrates the limitations with the status quo. The primary objective of this research is to do just that with a view to identifying significant improvements in vibration testing in light of modern technology. In this paper, case studies are presented which highlight some of the limitations with typical vibration tests showing that they can lead to significant overtests, sometimes by many orders of magnitude, with the level of overtest varying considerably across a wide range of frequencies. This research shows that substantial benefits can be gained by “freely” suspending the structure in the laboratory and exciting it with a relatively small number of electrodynamic shakers using Multi-Input–Multi-Output (MIMO) control technology. The shaker configuration can be designed to excite the modes within the bandwidth utilising the inherent amplification of the resonances to achieve the desired response levels. This free-free MIMO vibration test approach is shown to result in substantial benefits that include extremely good replication of the aerodynamic environment and significant savings in time as all axes are excited simultaneously instead of the sequential X, Y and Z testing required with traditional vibration tests. In addition, substantial cost savings can be achieved by replacing some expensive large shaker systems with a few relatively small shaker systems.

Purpose: A variety of methods have been proposed for detection of initial contact (IC) and foot off (FO) and some comparative analysis is reported in the literature. Pressure measurement insoles and kinematic systems are often part of footwear analysis. Although gait event detection algorithms using these systems have been proposed and evaluated against kinetic data (KN) from force platforms (typically used as a ‘gold standard’), they have not been compared directly. The objective of this work was to undertake this comparison using the same volunteer dataset and test conditions. Methods: Data from 10 healthy adults walking at self-selected normal speed were collected. Two kinematic algorithms (one using a fixed threshold, KM, and the other using high pass-filtering, HPA) and one algorithm using pressure measurement data from an insole (Contact Area Detection, AD) were tested and compared with the detection provided by KN. All data were synchronised and sampled at 200 Hz. Six basic spatio-temporal parameters were also calculated. Results: The absolute mean difference (AMD) in event detection between the three methods and KN was below 25 ms. However, the methods presented tendencies to detect events earlier or later than KN and this influenced the AMD between the methods, which increased to 47 ms for IC detection between HPA and AD. The spatio-temporal parameters showed no statistically significant differences between AD and KM, but differences reached statistical significance between AD and HPA. Conclusion: It is possible to compare gait events and basic spatio-temporal parameters detected using data from pressure measurement insoles and kinematic algorithms; however the kinematic algorithm used will influence the results. Hence the comparison of findings from alternative detection methods is an important issue for which information about the behaviour of the method used is required. Fil: Catalfamo Formento, Paola Andrea Lucia. Universidad Nacional de Entre Ríos. Facultad de Ingeniería; Argentina. University of Surrey; Reino Unido. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Acevedo, Ruben. Universidad Nacional de Entre Ríos. Facultad de Ingeniería; Argentina Fil: Ghoussayni, Salim. University Of Surrey; Reino Unido Fil: Ewins, David. University of Surrey; Reino Unido

The dynamic response of a structure can consist of up to six degrees of freedom (DOF). Not all of them may be present at all times in a structure, but for a detailed finite element model validation it is important to provide as much information as possible. Current contact transducers can pick up a combination of some of the mentioned DOFs, but are not able to provide all six DOFs from a single transducer. Several contact-less transducers, such as a Scanning Laser Doppler Vibrometer (SLDV), can be combined to a single measurement system that allows the determination of up to three translational degrees of freedom at a point, but they are still not providing rotational information as the laser beam is fixed to a point. Continuously Scanning Laser Doppler Vibrometer (CSLDV) methods can partly overcome this issue by travelling in small circles around the measurement location and thus also sensing the rotation around the three axes at a point. An introduction of CSLDV methods for measuring DOFs at a point is given, focussing on a method for capturing up to 5 DOFs using a lens. However, the lens can make the measurement of the in-plane rotation very difficult and impractical. This paper presents a new type of scanning device which allows measuring all six degrees of freedom at a measurement location with a single setup and a single point LDV, by combining variable small circle scans. Experimental validation of the scanning head is presented and the measurement of the last DOF, the in-plane rotation, is demonstrated.

Complex shaped aerodynamic structures such missiles are prone to exhibit some level of nonlinear phenomena due to their aerodynamically tailored design and application. Aside from the aerodynamic and aeroelastic challenges experienced by a missile, an important but fundamental challenge encountered by a deployable missile is the inevitable concentrated structural nonlinearities which are observed around the hinge of its fins. Due to the current design and manufacturing process, the hinge of the fin of a missile often consist of complex configurations, joints and other nonlinear features that leads to concentrated structural nonlinearities. Some of the nonlinearities encountered includes off sets, piecewise linear, bilinear nonlinearity, hysteresis, coulomb friction and damping nonlinearities. These nonlinearities are frequently triggered at large vibration amplitudes caused by high pressure loads during operational flight. Activation of these nonlinearities often affect the dynamic response of the missile and in some cases lead to structural failures in the air vehicle. In this context, identifying and predicting the vibration response of aerodynamic structures with nonlinearities will be of great advantage to the present aerospace industries. In this paper the nonlinear dynamic behaviour of a prototype missile is examined using established nonlinear identification methods applied to measured data obtained from experimental test. The nonlinear identification is achieved using the acceleration surface method and the Hilbert transform FORCEVIB method, these methods are applied to sine-sweep excitation and stepped sine excitation measurements to obtain nonlinear parametric coefficients. The nonlinear experimental model was developed using the white box identification process (Detection, Characterisation and Parameter Estimation). In addition, Force controlled stepped sine experiments at several excitation levels were conducted to gain useful insight into the amplitude dependant behaviour of the missile in the existence of structural nonlinearities.

Improved walking comfort has been linked with better bio-mimicking of the prosthetic ankle. This study investigated if a hydraulic ankle/foot can provide enough motion in both the sagittal and frontal planes during level and camber walking and if the hydraulic ankle/foot better mimics the biological ankle moment pattern compared with a fixed ankle/foot device. Five active male unilateral trans-femoral amputees performed level ground walking at normal and fast speeds and 2.5E camber walking in both directions using their own prostheses fitted with an aEchelono hydraulic ankle/foot and an aEsprito fixed ankle/foot. Ankle angles and the Trend Symmetry Index of the ankle moments were compared between prostheses and walking conditions. Significant differences between prostheses were found in the stance plantarflexion and dorsiflexion peaks with a greater range of motion being reached with the Echelon foot. The Echelon foot also showed significantly improved bio-mimicry of the ankle resistance moment in all walking conditions, either compared with the intact side of the same subject or with the anormalo mean curve from non-amputees. During camber walking, both types of ankle/foot devices showed similar changes in the frontal plane ankle angles. Results from a questionnaire showed the subjects were more satisfied with Echelon foot.

Analysis of human movement provides systematic and quantitative information of movement. A number of tools and methods have been proposed to detect events that occur during walking. The events are then used to calculate spatiotemporal parameters (STP), commonly used for the characterization of gait. Conventional video cameras were proposed as an alternative for gait event detection. However, the accuracy in the calculation of STP has not been evaluated yet. The aim of this study is to evaluate the accuracy of a fully visual method using these cameras in the calculation of STP.

The modelling of nonlinear friction contact interfaces in structural dynamics currently attracts large research interest since the accurate characteristics of the friction interfaces are required in the nonlinear dynamic analysis of assembled structures. For an accurate representation of friction contact interfaces it is important to ensure that a sufficient number of parameters are provided to characterise all aspects of the friction contacts that the measured values are accurate and reliable, and that the contact parameters are interpreted and used correctly in the numerical modelling of the contact interfaces. This investigation focused on three major parameters used in the nonlinear friction contact analysis: (i) the friction coefficient, (ii) the tangential contact stiffness, and (iii) the normal load distribution in the contact. The accuracy of the measured friction input parameters is evaluated and possibilities to obtain reliable normal load distributions for a successful prediction of the measured frequency response function are investigated. Average friction input parameters, based on a large set of experimental data, are introduced, and their effect on the nonlinear resonance response is discussed. (C) 2011 Elsevier Ltd. All rights reserved.

The study of dynamic properties of rotating structures, such as bladed discs, can be conveniently done using simple bladed discs where the blades do not have staggering angles. Simplified design, although not truly representative of real structures, can be easy and economic to manufacture and, still, very helpful for studying specific dynamic properties. An example of this can be called as mass mistune blisk study. Experimental measurements of vibrations of bladed discs under rotating conditions can be performed using Scanning Laser Doppler Vibrometer (SLDV) systems. However, in the aerospace industry, the vibrations of complex bladed discs must be measured under operating conditions which are more hostile than laboratory simulations. The Blade Tip Timing (BTT) measurement method is a measurement technique, which can be used to measure vibrations of bladed discs of an engine aircraft under operating conditions. However, the BTT technique is ineffective when used with a flat bladed disc whose blade vibrations cannot be measured. This can be detrimental when the use of controlled dynamic parameters, such as those obtained from a simple bladed disc design, can improve the confidence for the validation of post-processing software. This paper presents a work about experimental measurements of a simple bladed disc design whose vibrations were measured synchronously by Scanning LDV and BTT measurement systems. A rotating test rig and its mechanical modifications for the installation of the BTT probes are introduced. Implications of rotating a specimen inconsistently are presented so as solutions to obtained constant revolving speed. The experimental comparisons of forced response vibrations measured synchronously at one blade are presented and explained.

This paper presents the first part of a work about modal testing using meaningful measurement parameters. Scanning Laser Doppler Vibrometer (SLDV) systems are becoming largely used both in industry and university for performing vibration measurements. A reason for the success of SLDV systems can be found in their capability of measuring vibration remotely and under different environmental conditions which, when hostile, can inhibit other transducers to work correctly. Hence, SLDV system can be very practical and useful in many engineering applications. SLDV systems are being used as a contactless transducer measuring vibrations from a discrete number of measurement positions marked on the specimen whenever an optical access to it is available. Hence, the advantage of a modal test carried out using accelerometers and one carried out using a SLDV system can be: (i) the automation of the measurements and (ii) the increase of the spatial resolution of the measured modes. This suggests that SLDV systems can be used as a practical replacement of accelerometers operating the same measurement method. Continuous Scanning method is a novel approach of using contactless transducers for measuring vibrations. The most important difference between a discrete and a continuous approach is the method of measuring a vibration pattern. A discrete method measures the level of vibrations at discrete positions on a structure whereas a continuous method captures the modulation of the vibrations produced by the excited modes. This is possible when a transducer can travel across a vibrating surface. This first part of the work presents a new approach of continuous scanning measurement method using a multi-tonal excitation waveform. The paper starts from a comparison between a step and continuous scan mode to introduce a novel approach of continuous scan and multi-tonal excitation waveform. The objective of this first part of work is to present and understand that measurement parameters, such as measurement positions, and can be carefully chosen to improve the measurement technique. A laboratory test piece and a helicopter tail cone are used as examples for the application of this new measurement method approach.

Background Femoral osseointegrated implants represent a new development in amputee rehabilitation, eliminating socket pressure discomfort, improving hip range of movement and facilitating prosthetic limb attachment. A clinical aspect that has not previously been reported on is the function of muscles in the residuum with implications concerning energy expenditure, hip-hiking and viability of the electrogram as a myoprocessor. Typically, amputees fitted with osseointegrated fixation have shorter residuums and weaker attachment of cleaved muscles. Function of muscle can be assessed by surface electromyography through changes in amplitude and median frequency of the signal. Methods Five male transfemoral amputees with osseointegrated fixations participated together with a control group comprised of ten adult males. Electrodes recorded surface electromyographic activity of five residual limb muscles or left lower limb muscles of control subjects. Isometric contractions were performed against resistance. The increase in mean rectified amplitude from resting to maximally contracting was calculated and median frequencies estimated. Findings The amputees were unable to maintain a maximum voluntary contraction of constant amplitude. Amplitude increase was lowest for rectus femoris and adductor magnus. The median frequency of adductor magnus was significantly greater (P = 0.02) for the amputees than intact subjects and there was a significant difference (P Interpretation High electromyographic amplitude variability suggests that using residuum muscles singly as a myoprocessor might be challenging. Adductor magnus displayed a different sEMG profile compared to intact subjects indicating decreased function and neuromuscular changes. Further work into optimal muscle anchorage is required to ensure maximal mechanical performance.

PurposeThe EPOC neuroheadset is a commercially available device that allows game players to control a computer using their facial expressions or their thoughts. This paper aims to examine whether it has the potential to be used as an input for assistive technology (AT) devices.Design/methodology/approachTwo experiments were conducted. In the first, 12 non‐impaired subjects used the neuroheadset to control a computer with their facial expressions. They also used a simple system of two head switches for comparison. In the second experiment, three non‐impaired subjects were trained to use the neuroheadset to control a computer with their thoughts.FindingsIn the first experiment, the neuroheadset was slower and less accurate than the head switches (pResearch limitations/implicationsAll subjects were non‐impaired, and the sample size in the second experiment was small. Further research should concentrate on the second experiment, using larger sample sizes and impaired subjects.Practical implicationsThe EPOC neuroheadset is substantially cheaper than similar specialist devices, and has the potential to allow those with no voluntary muscle control to access AT with their thoughts.Originality/valueThe results of these two experiments show that the Emotiv EPOC neuroheadset can be used as an interface for non‐impaired users to transfer information to a computer, which could in turn be used to control AT.

Engineering structures seldom behave linearly and, as a result, linearity checks are common practice in the testing of critical structures exposed to dynamic loading to define the boundary of validity of the linear regime. However, in large scale industrial applications, there is no 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, a simple method based on the information contained in the frequency response function (FRF) properties of a structure is studied. This technique falls within the category of single-degree-of-freedom (SDOF) modal analysis methods. The principle upon which it is based is effectively a linearisation whereby it is assumed that at given amplitude of displacement response the system responds at the same frequency as the excitation and that stiffness and damping are constants. In so doing, by extracting this information at different amplitudes of vibration response, it is possible to estimate the amplitude-dependent ‘natural’ frequency and modal loss factor. Because of its mathematical simplicity and practical implementation during standard vibration testing, this method is particularly suitable for practical applications. In this paper, the method is illustrated and new analyses are carried out to validate its performance on numerical simulations before applying it to data measured on a complex aerospace test structure as well as a full-scale helicopter.

An angle of 10° to 12° incline between the anterior border of the tibia (shank) and the vertical (SAV) at mid-midstance has been recommended as a starting point from which the “moment arm” at the knee can be optimized (tuned) in children wearing fixed ankle-foot orthoses. The aim of this study was to document the SAV and “moment arm” at the knee throughout stance in normally developing children. Data were collected from 11 healthy children aged 5 to 16 years, and SAV and “moment arm” at the knee plotted throughout stance, both barefoot and shod. The mean (standard deviation) SAV at mid-midstance was 11.4° (3.4°) barefoot and 10.5° (3.6°) shod. The mean (standard deviation) “moment arm” at the knee (normalized to leg length) at mid-midstance was 2.5% (1.7%) barefoot and 1.3% (2.4%) shod. The study provides preliminary evidence for current tuning techniques.

This paper presents the development of an instrumented-treadmill, designed for use in the evaluation of prosthetic limbs during amputee running. The motorised treadmill was chosen for this study because of its advantages over conventional ground mounted force platforms, e.g. decreased time required for the data- collection, laboratory space required, repeatability, control of speed, and improved statistical power through collection of a high number of successive foot contacts. The long-term aim of this work is to investigate amputee running and thus identify prosthetic limb/wearer characteristics, which may improve the training process and subsequent running experience. An existing treadmill was modified to measure the ground reaction force underneath the belt. A new treadmill bed was designed using finite element analysis techniques. Four biaxial strain gauge transducers were designed and fabricated in-house to measure the applied loads. The instrumented-treadmill has been statically and dynamically tested and calibrated, showing a maximum error of ± 3% and crosstalk of ± 4% to the horizontal force components, a hysteresis up to 8 N, and a 250 Hz natural frequency. Associated software has been developed to capture, process and display information related to gait data in a format suitable for left and right limb comparison. A pilot study was conducted to examine the force-measuring treadmill for evaluating amputee running.

This paper presents the latest developments of the continuous-scanning laser Doppler vibrometry (C-SLDV) measurement methods applied to rotating axially symmetric structures such as bladed discs. Measurement of vibrations of rotating structures are still difficult to perform. The main reason is due to the limitations of conventional transducers used for capturing the vibrations, these are often unable to measure and/or transfer a good quality signal remotely. The LDV became an ideal candidate to replace/aid such transducers, but only the introduction of two scanning mirrors in front of a laser head produced a step forward in measurements of vibrations of rotating targets; SLDV systems are now widely used both in industry and academic communities. This work shows how a commercial SLDV system can be used for measurement of vibrations of bladed discs under rotating conditions. The features of the scanning head, which was not modified for this study, were exploited up to the limit to achieve the synchronization between the scanner and a rotating target. The simplest tracking technique is performed when a circle-line scan pattern is synchronized with the rotating bladed disc so as to produce the point tracking measurement method. The extension of such a discrete measurement method to a full-field one is made when the laser beam is capable of tracing continuously either a line (LineScan tracking) or an area (AreaScan tracking) over the surface of the rotating structure. The development of tracking C-SLDV measurement techniques is achieved by the use of the traditional excitation methods and the development of a new excitation system, which will bring the excitation and the measurement to be in the same rotating frame of reference. Several experimental results are provided to illustrate the use of such techniques in turbomachinery industries.

The mistuning pattern on a bladed disc is controlled in Part 2 of the two-part article either by (i) imposing a small maximum allowable mistune according to the small mistuning approach or (ii) incorporating non-identical blades of specific patterns, known as the intentional mistuning approach. These approaches resemble the tolerance design stage of the Taguchi method of robust design. The first-order maximum amplification factor sensitivity in a single-degree-of-freedom (DOF)-per-sector system is derived to support a new definition of the interblade coupling ratio and to illustrate the dependence of the maximum amplification factor sensitivity on design parameters of a bladed disc. It is found that the variability of the forced vibration response levels in flexible bladed discs can be reduced by controlling the degree of mistune within realistic levels. The potential of a “linear” mistuning pattern to become an effective intentional mistuning pattern is evaluated by observing the amplification factors of bladed discs with combined intentional mistuning and additional random mistuning. A tool based on the importance sampling method is used to reduce the computational effort in determining the magnitude of intentional mistuning. Guidelines of designing bladed discs with a lower variability of forced vibration response levels are given according to the findings in casting the blade mistuning problem as a robust design problem.

This paper presents an overview of the vibration problems which are experienced in running gas turbines, and other high-speed machinery. The primary problem is that of resonance, where response levels under dynamic loading can be 100 or 1000 times greater than the levels resulting from static loading of the same magnitude. These resonances can be caused by steady, non-oscillatory, forces being applied to a rotating disc and their prediction and observation from measurement under running conditions are essential capabilities for the machinery dynamics engineer. Additional problems can arise if instabilities are encountered, either from aerodynamic sources (flutter) or from rotor dynamics. In all cases where severe vibrations are encountered, they must be controlled by the introduction of extra damping to the critical components, usually by incorporating friction devices. The use of visual displays to illuminate and help to understand the complexities of vibration in rotating machinery structures is presented.

The reliance of the aerospace industry on finite element models during the design of new products requires the best possible models for the prediction of the dynamic behaviour and so it is usually necessary to validate an original model using some additional reference data as the basis—usually data measured on a test structure. Finite element model updating can lead to the required accuracy, and while attempts are under way to minimise the required experimental testing involved in the process, measurements still are an integral part of the procedure. To improve the validation process, a major aim of current experimental research is to provide a more complete set of data from a single experiment in a shorter amount of time, so as to increase the overall efficiency of the updating routine. To this end, a new continuously scanning laser Doppler vibrometery measurement technique is presented for application to cylindrical structures. It allows the measurement of the dynamic behaviour of a cylindrical structure with a previously unachievable spatial resolution in a much shorter time than conventional measurement methods. The introduced method is evaluated through a detailed simulation in order to investigate its robustness and to ensure data quality, and the results from a proof-of-concept test rig are presented.

Vibrations in rotating machinery cause many problems such as fatigue of the rotating components, excessive noise, or transmission of vibration to the supporting structure. A major source of this vibration is out-of-balance forces and this paper proposes that the rotor response is reduced by suspending the machine on nonlinear springs. In the field of vibration isolation, nonlinear mounts have been proposed which have the same static stiffness as an equivalent linear support, i.e. load bearing capability, but at the same time offer a low dynamic stiffness, i.e. a lower natural frequency. Thus the isolator is effective over an increased frequency range. These mounts are known in the literature as high-static-low-dynamic-stiffness (HSLDS) mechanisms. In this paper, the rotor is suspended on a hardening HSLDS spring to considerably reduce the critical speeds to values far away from the operating speed. The advantages of the nonlinear supports are demonstrated using a simple two degree of freedom rotating machine model consisting of a rigid disk, and shafts, bearings and supports that are flexible but have negligible mass. Following a linear analysis to highlight the benefits of a low dynamic stiffness, an approximate analytical solution of the nonlinear equation of motion is presented. A comparison between the linear and nonlinear response shows the effectiveness of the nonlinear supports. Finally, the problems that occur if the nonlinearity is too strong are highlighted.

A model validation technique in structural dynamics and its application in aero-engine development is introduced. The concept and the approaches of model validation based on reference data supplied from experimental tests or from supermodel simulation are discussed in detail. An aero-engine component is used as an example to demonstrate the validation using the experimental test and supermodel information, respectively. A satisfactory agreement with both approaches is achieved, and finally, a strategy of model validation for the whole engine model is introduced.

A portable system capable of accurate detection of initial contact (IC) and foot off (FO) without adding encumbrance to the subject would be extremely useful in many gait analysis applications. Force platforms represent the gold standard method for determining these events and other methods including foot switches and kinematic data have also been proposed. These approaches, however, present limitations in terms of the number of steps that can be analysed per trial, the portability for outdoor measurements or the information needed beforehand. The purpose of this study was to evaluate the F-Scan® Mobile pressure measurement system when detecting IC and FO. Two methods were used, one was the force detection (FD) in-built algorithm used by F-Scan software and a new area detection (AD) method using the loaded area during the gait cycle. Both methods were tested in ten healthy adults and compared with the detection provided by a kinetic detection (KT) algorithm. The absolute mean differences between KT and FD were (mean ± standard deviation) 42 ± 11 ms for IC and 37 ± 11 ms for FO. The absolute mean differences between KT and AD were 22 ± 9 ms for IC and 10 ± 4 ms for FO. The AD method remained closer to KT detection for all subjects providing sufficiently accurate detection of both events and presenting advantages in terms of portability, number of steps analysed per trial and practicality as to make it a system of choice for gait event detection.

The validation of mathematical models constructed for the dynamic analysis of critical structures is a very important, but complex, process. The essential requirement is to provide confirmation, using independent and more reliable data than that presented by the model in question, that the subject model is capable of describing the essential physics of the structure’s behaviour within the required accuracy. In this paper, the procedures of model validation using experimental data on a structure are summarised and applied to a structural dynamics validation problem developed by Sandia National Laboratories. One of the essential issues is to separate out any non-linear features of the system and to construct an appropriate linear model that is as accurate as possible to cope with variability of the subsystem structures. The linear model, which is constructed using simulated test data from an assembly of sample subsystems, is expressed as a mean model with a standard deviation. It is further used in the system response prediction for system accreditation and target application under specified excitation loads. The influence of the weak non-linearity features are neglected in the system response prediction because the experimental method used to derive the test data obscured the non-linear effects and precluded their identification. Further consideration of identification and modelling of the non-linear element for the Sandia 3DOF calibration system is discussed to evaluate its influence on the accuracy of the spatial model.

The value of gait analysis for research and product development/evaluation in prosthetics is well understood. However, in the rehabilitation of amputees, the application of gait analysis beyond observation in the clinical setting is not routinely practiced, largely due to the cost and time taken to complete a fully instrumented data collection and analysis. To address the time issue, a weekly clinical gait service for primary amputees, based around a reduced data set from video and video vector technology, has been developed. In this clinic primary amputees are seen twice in the Gait Laboratory during their rehabilitation period, with the clinic time for each patient being no more than 15 minutes, which covers both data collection and review. A questionnaire was developed to evaluate the patients' perceptions of the clinic. The questionnaire was completed anonymously by 48 primary amputees over a 6-month period. The results from the questionnaire demonstrate that the clinic was perceived positively by the patients, and suggested areas of future development, e.g. the education of junior staff, and the need to include the patient's physiotherapist in the data collection and review process.

This study aimed to provide a description of the continuous recording of the true load regime experienced during daily living by the abutment of a trans-femoral amputee fitted with an osseointegrated fixation. The specific objectives: (i) To present an apparatus and a procedure allowing recording of the load regime, and (ii) an example of the raw data and six performance indicators of the usage of the prosthesis obtained with this method. A subject was monitored for a period of 5 hours as he went about his daily activities. The load regime was directly measured and recorded using a commercial transducer and data logger. The overall load profile presented alternative periods of variable length of inactivity (64%) and activity (36%), respectively. The maximum load applied on the mediolateral, anteroposterior and the long axes represented 21%, 21% and 120% of the body weight, respectively. The anteroposterior, mediolateral and long components of the impulse were 395 kN.s, 359 kN.s and 2,323 kN.s, respectively. The amputee generated a total of 2312 gait cycles of the prosthetic leg, giving an approximate overall cadence of 8 stride/min. Preliminary outcomes indicated that the proposed method was an improvement on the current techniques as it provided the true loading and actual usage of the prosthesis during daily living. This study is a stepping stone in the development of future affordable, on-board and user-friendly load recording systems that can be used in evidence-based practice.

Osseointegration trans-femoral implants are a new orthopaedic anchoring method to attach prosthetic limbs. The clinical success of this promising technique depends on the effectiveness of osseointegration achieved after implantation. The aim of this study is to use the resonant characteristics of the implant system to determine the changes in stability as a reflection of boundary condition of the implant. With a small mechanical excitation, Vibration responses of the trans-femoral implant to a small mechanical excitation were measured using an accelerometer and the vibration signal was analyzed using Fast Fourier Transform (FFT) software to obtain the fundamental natural frequency (NF) of the implant system. In-vitro study was conducted using different silicone rubbers to simulate the interface condition. The result showed that a high NF corresponded to a high elastic modulus of the interface material between the implant and bone. A preliminary in-vivo study with one osseointegration trans-femoral implant patient showed that there was a decrease of NF after initial weight bearing rehabilitation. After continued weight bearing, the NF gradually returned to the pre-loading level at around day 24 and the general trend of the NF reached a stable state 38 days after the first weight bearing exercise.

The dynamic forced response of a two-degrees-of-freedom model of an unbalanced overhung rotor with clearance and symmetric piecewise-linear stiffness is examined in the time domain. The stiffness nonlinearity is representative of the contact between the rotor and a concentric stator ring. This rubbing interaction comes as a result of the rotor transient motion initiated by the sudden application of a static unbalance, such as in a blade loss scenario. The focus of this study is on the range of rotor speeds above resonance, where the contact between rotor and stator is characterised by a “bouncing” or intermittent type of behaviour. Brute-force numerical bifurcation analysis on the long-term forced response revealed ranges of rotation frequency for which there is bi-stability between non-impacting synchronous equilibrium and impacting sub-synchronous motion. It is found that, for sufficiently high levels of transient energy in the rotor, there exists the possibility for the solution to jump into a stable limit cycle characterised by three non-harmonically related frequencies, namely the synchronous response frequency and the forward and backward whirl frequencies. A simple relationship defining the point of synchronisation between these three components is proposed as an explanation to the region of bi-stability detected. The stiffening effect induced by the contact non-linearity enables this synchronisation to be maintained over a range of forcing frequencies rather than just at the single condition determined from the nominal whirl mode frequencies.Copyright © 2014 by Rolls-Royce plc

In this paper a comprehensive analysis of steady-state forced response is performed for the case of a system with snap-through nonlinear springs. Stiffness characteristics of these springs include cubic and linear terms and the linear stiffness term is negative. There are a very restricted number of solutions found in literature for such type of nonlinearity. Because of that, the primary goal of the study is to obtain a full set of possible solutions providing stable and unstable periodic forced response regimes. The solutions sought include three major groups of the periodic response: (i) vibrations having a period coinciding with the excitation; (ii) subharmonic vibrations; and (iii) superharmonic vibrations. A multi-harmonic balance method is applied for highly efficient and accurate frequency-domain analysis of steady-state forced responses in a wide range of excitation frequency variation. Time-marching integration methods are used for validation and further analysis, including assessment of stability for the solutions found by the multi-harmonic balance method. The numerical studies performed reveal a wide variety of periodic regimes which are inherent for structures with snap-through springs

The problem of estimating the mutual interaction of the effects of Coriolis forces and of blade mistuning on the vibration characteristics of bladed disks is addressed in this paper. The influence of different degrees of mistuning on forced response and amplification factors are studied in the presence of Coriolis forces and then compared to their non-Coriolis counterparts using a computationally inexpensive, yet representative, model of a bladed disk. The primary objective of the study reported in this paper is to establish whether current mistuned bladed disk analyses should incorporate Coriolis effects in order to represent accurately all the significant factors that affect the forced response levels.

The osseointegration trans-femoral implant is a new orthopedic anchoring method to attach prosthetic limb. The success of this technique depends on how healthy the osseointegration between implant and bone can be achieved and how the post-surgical rehabilitation is progressed. The current clinical practice is based on patient fitness feeling. To achieve a high success rate of osseointegration and an optimal rehabilitation process, a quantitative measurement of the degree of osseointegration is required. In this paper, the authors present a non-invasive method to determine the stability of an osseointegration trans-femoral implant system. It uses resonant frequency of implant system to observe the integration between the implant and bone. The vibration signals of a trans-femoral implant system were collected using an accelerometer attached to the implant abutment and analyzed using Fast Fourier Transform (FFT). The results of in vitro tests are presented to demonstrate that the developed instrument system can be used in future in vivo clinical research.

An approach is developed to analyze the multiharmonic forced response of large-scale finite element models of bladed disks taking account of the nonlinear forces acting at the contact interfaces of blade roots. Area contact interaction is modeled by area friction contact elements which allow for friction stresses under variable normal load, unilateral contacts, clearances, and interferences. Examples of application of the new approach to the analysis of root damping and forced response levels are given and numerical investigations of effects of contact conditions at root joints and excitation levels are explored for practical bladed disks.

The use of a single implantable microprobe to detect multiple, bi-directional action potential velocities is demonstrated. By using multiple electrode sites along the direction of propagation to record the same action potentials, the velocities of action potentials from both sensory and motor neurons can be determined.

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