Mechanical Engineering - Research Publications
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ItemModel Reduction of Turbocharged (TC) Spark Ignition (SI) Engines(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2011-03-01)This paper proposes a new procedure to reduce the order of control oriented turbocharged (TC) spark ignition (SI) engine models. The starting point of this work is a higher dimensional, fully validated model defined which is not appropriate for control design. The model reduction technique is based on the identification of time scale separation within the dynamics of various engine state variables with pertinent use of perturbation theory. The model reduction is accomplished in two steps and exploits the dynamic and physical characteristics of engine design and operation. In the first step, regular and singular perturbation theories are collectively employed to eliminate temperature dynamics and replace them with their quasi-steady state values. This is followed by the elimination of fast pressures. As a result, a library of engine models is obtained which are associated with each other on a sound theoretical basis and at the same time allow sufficient flexibility in terms of the reduced order modeling. Different assumptions under which this model reduction is justified are presented and their implications are discussed. The approximating properties of the proposed engine models with respect to the original higher dimensional model are quantitatively assessed through comprehensive simulations.
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ItemOn Extremum Seeking in Bioprocesses with Multivalued Cost Functions(WILEY, 2009)Finding optimal operating modes for bioprocesses has been, for a long time, a relevant issue in bioengineering. The problem is of special interest when it implies the simultaneous optimization of competing objectives. In this paper, we address the problem of finding optimal steady states that achieve the best tradeoff between yield and productivity by using nonmodel-based extremum-seeking control with semiglobal practical stability and convergence properties. A special attention is paid to processes with multiple steady states and multivalued cost functions.
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ItemOn global extremum seeking in the presence of local extrema(PERGAMON-ELSEVIER SCIENCE LTD, 2009-01-01)We propose a global extremum seeking scheme which can seek the global optimal value in the presence of local extrema. It is shown that the proposed global extremum seeking scheme can converge to an arbitrarily small neighborhood of the global extremum from an arbitrarily large set of initial conditions if sufficient conditions are satisfied. A simple example illustrates the effectiveness of the proposed scheme.
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ItemOn the choice of dither in extremum seeking systems: A case study(PERGAMON-ELSEVIER SCIENCE LTD, 2008-05-01)We discuss how the choice of dither (excitation signal) affects the performance of extremum seeking using a benchmark situation: a static scalar map; and a simple scalar extremum seeking scheme. Our comparisons are based on the performance of the system with different dithers in terms of three performance indicators: the speed of convergence, domain of attraction and accuracy (i.e. the ultimate bound on trajectories). Our analysis explicitly shows how the dither shape affects each of these performance indicators. Our study suggests that the practitioners using extremum seeking control should consider the dither shape as an important design parameter. Computer simulations support our theoretical findings.
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ItemOn non-local stability properties of extrernum seeking control(PERGAMON-ELSEVIER SCIENCE LTD, 2006-06-01)In this paper, we consider several extremum seeking schemes and show under appropriate conditions that these schemes achieve extremum seeking from an arbitrarily large domain of initial conditions if the parameters in the controller are appropriately adjusted. This non-local stability result is proved by showing semi-global practical stability of the closed-loop system with respect to the design parameters. We show that reducing the size of the parameters typically slows down the convergence rate of the extremum seeking controllers and enlarges the domain of the attraction. Our results provide guidelines on how to tune the controller parameters in order to achieve extremum seeking. Simulation examples illustrate our results.
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ItemNo Preview AvailableInfluence of muscle-tendon wrapping on calculations of joint reaction forces in the equine distal forelimb(HINDAWI PUBLISHING CORPORATION, 2008)The equine distal forelimb is a common location of injuries related to mechanical overload. In this study, a two-dimensional model of the musculoskeletal system of the region was developed and applied to kinematic and kinetic data from walking and trotting horses. The forces in major tendons and joint reaction forces were calculated. The components of the joint reaction forces caused by wrapping of tendons around sesamoid bones were found to be of similar magnitude to the reaction forces between the long bones at each joint. This finding highlighted the importance of taking into account muscle-tendon wrapping when evaluating joint loading in the equine distal forelimb.
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ItemReliability and normative values for the foot mobility magnitude: a composite measure of vertical and medial-lateral mobility of the midfoot(BMC, 2009)BACKGROUND: A study was conducted to determine the reliability and minimal detectable change for a new composite measure of the vertical and medial-lateral mobility of the midfoot called the foot mobility magnitude. METHODS: Three hundred and forty-five healthy participants volunteered to take part in the study. The change in dorsal arch height between weight bearing and non-weight bearing as well as the change in midfoot width between weight bearing and non-weight bearing were measured at 50% of total foot length and used to calculate the foot mobility magnitude. The reliability and minimal detectable change for the measurements were then determined based on the assessment of the measurements by three raters with different levels of clinical experience. RESULTS: The change in dorsal arch height between weight bearing and non-weight bearing, midfoot width between weight bearing and non-weight bearing, and the foot mobility magnitude were shown to have high levels of intra-rater and inter-rater reliability. Normative data are provided for the left and right feet of both the female (n = 211) and male (n = 134) subjects. CONCLUSION: While the measurements of navicular drop and drift have been used as a clinical method to assess both the vertical and medial-lateral mobility of the midfoot, poor to fair levels of inter-rater reliability have been reported. The results of the current study suggest that the foot mobility magnitude provides the clinician and researcher with a highly reliable measure of vertical and medial-lateral midfoot mobility.
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ItemCan foot anthropometric measurements predict dynamic plantar surface contact area?(BIOMED CENTRAL LTD, 2009)BACKGROUND: Previous studies have suggested that increased plantar surface area, associated with pes planus, is a risk factor for the development of lower extremity overuse injuries. The intent of this study was to determine if a single or combination of foot anthropometric measures could be used to predict plantar surface area. METHODS: Six foot measurements were collected on 155 subjects (97 females, 58 males, mean age 24.5 +/- 3.5 years). The measurements as well as one ratio were entered into a stepwise regression analysis to determine the optimal set of measurements associated with total plantar contact area either including or excluding the toe region. The predicted values were used to calculate plantar surface area and were compared to the actual values obtained dynamically using a pressure sensor platform. RESULTS: A three variable model was found to describe the relationship between the foot measures/ratio and total plantar contact area (R2 = 0.77, p < 0.0001)). A three variable model was also found to describe the relationship between the foot measures/ratio and plantar contact area minus the toe region (R2 = 0.76, p < 0.0001). CONCLUSION: The results of this study indicate that the clinician can use a combination of simple, reliable, and time efficient foot anthropometric measurements to explain over 75% of the plantar surface contact area, either including or excluding the toe region.
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ItemPredictors of short and long term outcome in patellofemoral pain syndrome: a prospective longitudinal study(BMC, 2010-01-19)BACKGROUND: Patellofemoral pain syndrome (PFP) is a common musculoskeletal condition that has a tendency to become chronic and problematic in a proportion of affected individuals. The objective of this study was to identify prognostic factors that may have clinical utility in predicting poor outcome on measures of pain and function in individuals with PFP. METHODS: A prospective follow-up study was conducted of 179 participants in a randomised clinical trial. Nine baseline factors (age, gender, body mass index, arch height, duration of knee pain, worst pain visual analogue scale, Kujala Patellofemoral Score (KPS), functional index questionnaire (FIQ), step down repetitions) were investigated for their prognostic ability on outcome assessed at six, 12 and 52 weeks (worst pain, KPS and FIQ). Factors with significant univariate associations were entered into multivariate linear regression models to identify a group of factors independently associated with poor outcome. RESULTS: Long symptom duration was the most consistent predictor of poor outcome over 52 weeks rated on the KPS and the FIQ (beta-0.07, 95% confidence interval -0.1 to -0.03, p < 0.000; and -0.02, -0.03 to -0.01, p < 0.000, respectively). Worse KPS at baseline was predictive of outcome at six, 12 and 52 weeks. Gender, body mass index and arch height were generally not associated with outcome (univariate analysis), while age, worst pain, FIQ and step downs were excluded during multivariate analyses. CONCLUSIONS: Patients presenting with PFP of long duration who score worse on the KPS have a poorer prognosis, irrespective of age, gender and morphometry. These results suggest that strategies aimed at preventing chronicity of more severe PFP may optimise prognosis.
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ItemFoot orthoses and physiotherapy in the treatment of patellofemoral pain syndrome: A randomised clinical trial(BIOMED CENTRAL LTD, 2008-02-27)BACKGROUND: Patellofemoral pain syndrome is a highly prevalent musculoskeletal overuse condition that has a significant impact on participation in daily and physical activities. A recent systematic review highlighted the lack of high quality evidence from randomised controlled trials for the conservative management of patellofemoral pain syndrome. Although foot orthoses are a commonly used intervention for patellofemoral pain syndrome, only two pilot studies with short term follow up have been conducted into their clinical efficacy. METHODS/DESIGN: A randomised single-blinded clinical trial will be conducted to investigate the clinical efficacy and cost effectiveness of foot orthoses in the management of patellofemoral pain syndrome. One hundred and seventy-six participants aged 18-40 with anterior or retropatellar knee pain of non-traumatic origin and at least six weeks duration will be recruited from the greater Brisbane area in Queensland, Australia through print, radio and television advertising. Suitable participants will be randomly allocated to receive either foot orthoses, flat insoles, physiotherapy or a combined intervention of foot orthoses and physiotherapy, and will attend six visits with a physiotherapist over a 6 week period. Outcome will be measured at 6, 12 and 52 weeks using primary outcome measures of usual and worst pain visual analogue scale, patient perceived treatment effect, perceived global effect, the Functional Index Questionnaire, and the Anterior Knee Pain Scale. Secondary outcome measures will include the Lower Extremity Functional Scale, McGill Pain Questionnaire, 36-Item Short-Form Health Survey, Hospital Anxiety and Depression Scale, Patient-Specific Functional Scale, Physical Activity Level in the Previous Week, pressure pain threshold and physical measures of step and squat tests. Cost-effectiveness analysis will be based on treatment effectiveness against resource usage recorded in treatment logs and self-reported diaries. DISCUSSION: The randomised clinical trial will utilise high-quality methodologies in accordance with CONSORT guidelines, in order to contribute to the limited knowledge base regarding the clinical efficacy of foot orthoses in the management of patellofemoral pain syndrome, and provide practitioners with high-quality evidence upon which to base clinical decisions. TRIAL REGISTRATION: Australian Clinical Trials Registry ACTRN012605000463673ClinicalTrials.gov NCT00118521.