Rigid multibody systems have been studied extensivley due to its direct application in design and analysis of various mechanical systems such as robots and spacecraft structures. The dynamics of multibody system is governed by its equations of motion and various terms associated with it, such as the mass matrix, the generalized force vector, are well known..Forward dynamics algorithms play an important role in the simulation of multibody systems and the recursive forward dynamics algorithm for branched multibody systems is very popular. The recursive forward dynamic algorithm is highly efficient algorithm with O(n) computational complexity and scores over other algorithms when number of rigid bodies n in the system is very large. The algorithm involves finding an important mass matrix, which has been popularly termed as articulated body inertia (AB inertia). To find ijth term of any general mass matrix, we separately give virtual change to ith and jth generalized coordinates. At each point of the multibody system, the dot product of the resulting virtual displacements are taken with each other and eventually integrated over the entire multibody system, weighted by the mass. This quantity divided by the virtual changes in ith and jth coordinates gives the ijth element of the mass matrix. This is one of the fundamental ways of looking at the mass matrix. However, in literature, the AB inertia is obtained as a result of mathematical manipulation and its physical or geometrical significance from the above view point is not clear. In this thesis we present a more geometric and physical explanation for the AB inertia. The main step is to obtain a new set of generalized coordinates which relate directly to the AB inertia. We have also shown the equivalence of our method with existing methods. A comprehensive treatement on change of generalized coordinates and its effect on equations of motion has also been presented as preliminaries. The second part of the thesis deals with closed loop multibody systems.A few years ago an iterative algorithm called the sequential regularization method (SRM) was proposed for simulation of closed loop multibody systems with attractive claims on its efficiency. In literature we find that this algorithm has been implemented and studied only for planar multibody systems. As a part of the thesis work, we have developed a C-programming language code which can simulate 3-dimensional spatial multibody systems using the SRM algorithm. The programme can also perform simulation using a relatively efficient Conventional algorithm having O(n+m3) complexity, where m denotes number of closed loop constraints. Simulation studies have been carried out on a few multibody systems using the two algorithms. Some of the results have been also been validated using the commercial simulation package -ADAMS. As a result of our simulation studies, we have detected certain points, after which the solution from SRM loses it convergence. More study is required to understand this lack of convergence.

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Over one million amputees are living in the United States with major lower limb loss (Ziegler-Graham et al. 2008). Lower limb amputation leads to the functional loss of the ankle plantar flexor muscles, which are important contributors to body support, forward propulsion, and leg swing initiation during walking (Neptune et al. 2001; Liu et al. 2006). Effective prosthetic component design is essential for successful rehabilitation of amputees to return to an active lifestyle by partially replacing the functional role of the ankle muscles. The series of experimental and computer simulation studies presented in this research showed that design characteristics of energy storage and return prosthetic ankles, specifically the elastic stiffness, significantly influence residual and intact leg ground reaction forces, knee joint moments, and muscle activity, thus affecting muscle output. These findings highlight the importance of proper prosthetic foot stiffness prescription for amputees to assure effective rehabilitation outcomes. The research also showed that the ankle muscles serve to stabilize the body during turning the center of mass. When amputees turn while supported by their prosthetic components, they rely more on gravity to redirect the center of mass than active muscle generation. This mechanism increases the risks of falling and identifies a need for prosthetic components and rehabilitation focused on increasing amputee stability during turning. A proper understanding of the effects of prosthetic components on amputee walking mechanics is critical to decreasing complications and risks that are prevalent among lower-limb amputees. The presented research is an important step towards reaching this goal. / text

Αντικείμενο της παρούσας διπλωματικής εργασίας είναι αρχικά η καταγραφή της ανθρώπινης κίνησης με κάποια συσκευή παρακολούθησης και κατόπιν η δημιουργία ενός αντιπροσωπευτικού μοντέλου, ώστε να μπορεί να μελετηθεί η δυναμική του συμπεριφορά. Ως συσκευή καταγραφής χρησιμοποιήθηκε ο αισθητήρας Kinect της Microsoft. Το μοντέλο που αναπτύχθηκε αφορά κυρίως τα κάτω άκρα του ανθρώπου και επιπλέον διαθέτει μυοσκελετική δομή με 86 μύες. Στα πλαίσια των αναλύσεων χρησιμοποιήθηκαν διάφορες τεχνικές για την εξαγωγή των αποτελεσμάτων, όπως είναι η αντίστροφη κινηματική, αντίστροφη δυναμική, υπολογισμός μυϊκών διεγέρσεων και ορθή δυναμική και προτείνουμε μια στρατηγική για την ανάλυση και την εξαγωγή αποτελεσμάτων. / The research developed in this thesis first deal with the problem of capturing the human body motion and then concentrates on the creation of musculoskeletal models, which can capture and accurately study its dynamical behavior. The Microsoft's Kinect sensor was utilized to capture the human motion. The model used for the simulations is the human lower extremity with 86 attached muscles. For the analysis phase we used some common methods such as inverse kinematics, inverse dynamics, computed muscle control and forward dynamics and we showed a general pipeline strategy for generating correct results.

The main goal of this study was to evaluate whether three dimensional musculoskeletal modelling (3D) is effective in assessing the safety and efficacy of resistance training equipment. The focus of the evaluation was on the biomechanical and anthropometric considerations of the end-user. 3D musculoskeletal modelling was used to evaluate four pieces of resistance training equipment, namely the seated biceps curl, abdominal crunch, seated row and chest press. Three anthropometric cases were created; these represented a traditional 5th percentile female as well as a 50th and 95th percentile male based on body mass index (BMI). Resistance on the training machines was set at fifty percent of the functional strength one repetition maximum (1RM), for each anthropometric case and piece of exercise equipment two repetitions were performed except for the abdominal crunch model during which four repetitions were simulated. Each piece of equipment presented unique challenges. In three of the four studies (seated biceps curl, seated row and chest press) the default model created by the modelling software was not adequate to solve the forward dynamics simulations and thus adjustments had to be made to the default model in order to complete the modelling process. 3D musculoskeletal modelling by means of LifeModelerTM software was able to identify some potential risk for musculoskeletal injury as well as highlight the discrepancies between the anthropometric cases, specifically the accommodation of the 5th percentile female and the machines’ engineered adjustability. 3D musculoskeletal modelling has the potential to indicate shortcomings in resistance training equipment design. Therefore it appears as if 3D musculoskeletal modelling can be used to evaluate resistance training equipment design however the limitations as indicated by this study must be taken into consideration especially when using default models.AFRIKAANS: Die doel van die studie was om die effektiwiteit van driedimensionele (3D) muskuloskeletale modellering te evalueer in terme van die tegniek se vermoë om die veiligheid en doeltreffendheid van weerstands oefenapparaat te evalueer. Die fokus van die evaluasie was op die biomeganiese en antropometriese oorwegings van die end-gebruiker. 3D muskuloskeletale modellering was gebruik in die evaluasie van vier weerstands oefenapparate genaamd die sittende biceps krul, abdominale krul, sittende roei en sittende borsstoot. Drie antropometriese gevalle is geskep, die het ‘n tradisionele 5e persentiel vrou, sowel as ‘n 50ste en 95ste persentiel man voorgestel en was gebasseer op liggaamsmassa indeks waardes. Die eksterne weerstand van die apparaat was bepaal teen vyftig persent van die funsionele krag een-repetisie- maksimum vir elk van die antropometriese gevalle en twee repetisies is uitgevoer behalwe vir die abdominale krul waartydens vier repetisies gesimuleer is. Elke apparaat het unieke uitdagings gestel. In drie van die vier studies (sittende biceps krul, sittende roei en sittende borsstoot) was die standaard model van die sagteware onvoldoende om die voorwaards dinamiese simulasie op te los en moes aanpassings aan die modelle gemaak word vir suksesvolle simulasies. Die modellerings proses met die Lifemodeler™ sagteware kon potensiële risiko vir muskuloskeletale besering sowel as verskille tussen die verskeie antropometriese gevalle uitwys. Dit was veral opvallend vir die akkomodasie van die 5e persentiel vrou asook betreffende die apparaat se vervaardigde verstelbaarheid. 3D muskuloskeletale modellering beskik oor die vermoë om voorstelle vir verbetering in die ontwerp van weerstands oefenapparaat uit te wys. Dit blyk dus dat 3D muskuloskeletale modellering beslis gebruik kan word vir die evaluasie van weerstands oefenapparaat ontwerp, die beperkings van die studie moet egter in gedagte gehou word, veral wanneer standaard modelle gebruik word. / Thesis (DPhil)--University of Pretoria, 2011. / Biokinetics, Sport and Leisure Sciences / unrestricted