This research aims at deepening the knowledge of the hydrodynamics developing within some specific mixing system configurations. In particular, a standard geometry stirred vessel, an unbaffled stirred vessel of unconventional geometry and a shaken bioreactor are studied. Optical techniques (LDA, PIV) are employed in order to obtain detailed information on the mean and turbulent characteristics of the flow developing within the different lab-scale reactors, while subsequent data analysis addresses the comprehension of the principal macro and micro phenomena occurring in the flow. When studying the standard geometry stirred reactor, the evolution of trailing vortices on the wake of a PBT turbine is investigated for the first time under laminar regime. A three-dimensional characterization of the vortical structures is carried out in terms of vorticity levels and locus. The second case study regards an unbaffled stirred tank of low liquid height-to-tank diameter ratio. Due to the unconventional geometry of the system, peculiar interactions arise between the strong tangential motion of the flow, the impeller discharge stream and the flow free surface. Big efforts are devoted to the characterization of this phenomenon which strongly influences the flow, and a mathematical model able to predict it is sought for. In the last part of this research, the operation of shaken bioreactors is explored. Particularly, the suspension dynamics occurring in the presence of solids within a flat-bottomed cylindrical system are investigated, and the associated two-phase flow is assessed by means of 2D-PIV. Also, the influence of a conical bottom on the single-phase flow is examined. A comparative study of the different bioreactors typologies allowed to identify interesting affinities never detected before in the fluid dynamic behaviour of unbaffled stirred tanks and shaken bioreactors, revealing that these two types of reactors can induce very similar flows, although being technologically very different.

Questo lavoro di dottorato, svolto prevalentemente presso i laboratori hangar della Facoltà di Ing. Aerospaziale di Forlì, in collaborazione con AVIO S.P.A (Colleferro), ha come scopo quello di ricostruire alcune grandezze tipiche di un motore per razzi a propellente solido. In particolare è stato sviluppato un algoritmo in MatLab, successivamente "tradotto" in C++ per evidenti motivi di velocità computazionale, capace di prevedere la frazione volumetrica di un propellente bi-modale. Successivamente, sulla base di questo parametro, e utilizzando informazioni relative alla composizione completa del propellente stesso, si è andati a defnire un "Margine di Colabilità",capace di legare la viscosità cinematica del composto alla sua stessa composizione granulometrica. Infne si è cercato di fruttare queste informazioni per vedere come questi parametri, insieme all'orientazione e concentrazione delle particelle stesse, possono influenzare il proflo di pressione durante la fase di lancio, e cercare quindi di spiegare il così detto effetto HUMP (disuniformità della velocità di combustione internamente al grain) / This doctoral dissertation has been carried out in the laboratories based in the hangar of the Engineering Faculty of Forlì, University of Bolonia, in cooperation with AVIO S.P.A. (Colleferro). The aim of the thesis is to reconstruct some typical characteristics of a solid rocket motor. The work is particularly focused on the development of an algorithm - using MatLab - that has later been "translated" into C++ in order to reduce the computational load and to be able to predict the volume fraction of a bi-modal propellant. Later, using this parameter, as well as some informations concerning the full composition of the propellant, the "castability margin" has been defined, in order to link its cinematic viscosity to the related propellant formulation. Lastly, the informations collected has been exploited to figure out how these parameters, together with the particles' orientation and concentration, may influence the pressure profile during the launch phase. This data tries to explain the so-called HUMP effect (inhomogeneity of the combustion speed inside the grain)

The research aim of the present thesis was to investigate the in vitro biomechanical properties of human thoraco-lumbar natural and treated vertebral body, undergo prophylactic augmentation. To overcome some limitation of the current in vitro test methods, an anatomical reference frame for human vertebrae was formally defined and validated and the effects of in vitro boundary conditions on the strain experienced by vertebral body investigated. Moreover an integrated approach, which incorporated different measurement methods (strain gauges and digital volume correlation) at different dimensional scales was adopted to investigate natural and augmented vertebrae during non-destructive and destructive testing. The effects of prophylactic augmentation were investigated for the first time through digital volume correlation, which allowed to measure the state of strain inside the vertebral body, in the injected cement, and in the bone-cement interdigitated region of vertebrae, including the elastic regime, but also the internal micro-failure mechanisms. Findings showed that augmentation is not associated to a modification of the strain magnitude but rather to a re-arrangement of the higher strain due to an alteration of the load sharing between the trabecular core and the cement region. The most critical region was the interdigitated area, where the initial microdamage gradually spread across the surrounded trabecular bone. Prophylactic augmentation increased in some vertebrae the failure force required to damage the vertebrae, conversely in other case the failure force was lower than in the controls (not-augmented). This variability of the weakening/strengthening effect of prophylactic augmentation seems to support that the effect of augmentation depends on the quality of augmentation itself (amount, localization and distribution of the injected material). It is therefore reasonable to assume that to improve the outcomes of prophylactic augmentation, more attention should be dedicated to the quality of augmentation itself. / L'obiettivo principale della tesi è la caratterizzazione biomeccanica di vertebre umani toraco-lombari naturali e sottoposte alla vertebroplastica profilattica. Per superare alcune limitazioni dei test in vitro, è stato per la prima volta definito e validato un sistema di riferimento in vitro per l'allineamento delle vertebre, ed è stato effettuato uno studio sugli effetti sulla distribuzione delle sollecitazioni al variare delle condizioni al contorno più comunemente utilizzate in letteratura. Questo studio si basa su un'approccio integrato che incorpora differenti metodi di misura delle sollecitazioni (estensimetri e digital volume correlation), utilizzati durante i test in campo elastico e a rottura. L'efficacia della vertebroplastica profilattica è stata investigata per la prima volta grazie alla Digital Volume Correlation, che permette di misurare lo stato di deformazione all'interno del corpo vertebrale a livello dell'osso trabecolare, nel cemento iniettato e all'interfaccia osso-cemento, sia in campo elastico che a rottura. Rispetto alle vertebre naturali i risultati mostrano che il trattamento non altera l'entità delle deformazioni bensì le zone di massimo stress, ciò è dovuto ad un'alterazione nella condivizione del carico tra il tessuto trabecolare e il cemento. la zona più critica si ha all'interfaccia osso-cemento, dove ha origine la frattura. In certi casi il trattamento aumenta la resistenza delle vertebre in altri casi la forza di rottura è inferiore a quella del controllo. Questa variabilità nelle prestazioni meccaniche delle vertebre aumentate dipende dalla qualità del trattamento stesso (quantità cemento, posizionamento e distribuzione).

In recent years numerical simulations are becoming fundamental for the design of many engineering components. For this reason many multiphysical and multiscale problems are investigated by coupling different existent software created specifically for solving each single problem. However, because of the intrinsic differences among these codes, such coupling is very challenging. In this thesis we develop a computational platform that can be used to integrate different computing tools into the common framework of the SALOME platform. Inside this platform various codes are coupled through numerical libraries with the purpose of exchanging data and melting intrinsic differences. After a description of the generic code integration procedure into the numerical platform, we introduce three classes of problems where different codes have been coupled and complex computational problems are studied. In the irst problem class, the computational platform is used to study a nuclear reactor system. We study the dynamics of a multiscale primary loop of a liquid metal reactor by coupling a mono-dimensional system code with the high resolution three-dimensional full scale core components models. Also we investigate a thermal-hydraulic-neutron multiphysics problem. The heat energy production in the reactor core, obtained by solving the neutron code DRAGON-DONJON, is coupled with the solution of the thermal-hydraulics conservative equations implemented in a in-house code. In the second problem class, we consider multiscale multiphysics Fluid Structure Interaction problems implemented in different modules of the FEMUs code. The mechanics of a three-dimensional particular component of the cardiovascular system is coupled with a mono-dimensional model that takes into account the remaining parts of a simplified circulatory system. Finally, in the last class of problems, Multiphase Fluid tructure Interaction problems are investigated by coupling the solution of a multiphase fluid interface advection VOF module with a FSI solver.

Large Eddy Simulation (LES) represents nowadays one of the most promising techniques for the evaluation of the dynamics and evolution of turbulent structures characterizing Internal Combustion Engines (ICE). The demand for a high level of resolution accuracy as well as the need to evaluate different scenarios and system configurations lead to considerable computational and economic costs for both the hardware infrastructure and the licensing fees of commercial codes. In such context, the present Doctoral project has the objective to define the most suitable numerical methodology to perform LES analysis of ICE flows and to implement such methodology in an efficient, accurate and robust CFD code, based on open-source components. An evaluation of freely available CFD codes has led to the choice of the open-source CFD package OpenFOAM as the most suited code for the project’s objective. The LES modeling of interest for ICE applications has been then studied and three Sub-grid scale models particularly suited for such flows have been implemented and assessed into OpenFOAM. Moreover, Python scripts have been developed in order to automate and speed-up both pre-processing and post-processing phases. The CFD methodology has been then applied to a real world ICE systems such as a stationary flow bench, for which prior RANS simulations had shown some predictive deficiencies. The quality of the analyses has been assessed through specific LES quality estimators and the computational results have been validated against measurements, showing pretty good agreement. Finally, LES simulations have allowed the accurate investigation of the flow bench fluid-dynamic behavior and, thanks to the insights gained, an alternative RANS approach based on the Reynolds Stress Tensor Modeling has been proposed and tested in order to alleviate the aforementioned predictive deficiencies.

The purpose of the first part of the research activity was to develop an aerobic cometabolic process in packed bed reactors (PBR) to treat real groundwater contaminated by trichloroethylene (TCE) and 1,1,2,2-tetrachloroethane (TeCA). In an initial screening conducted in batch bioreactors, different groundwater samples from 5 wells of the contaminated site were fed with 5 growth substrates. The work led to the selection of butane as the best growth substrate, and to the development and characterization from the site’s indigenous biomass of a suspended-cell consortium capable to degrade TCE with a 90 % mineralization of the organic chlorine. A kinetic study conducted in batch and continuous flow PBRs and led to the identification of the best carrier. A kinetic study of butane and TCE biodegradation indicated that the attached-cell consortium is characterized by a lower TCE specific degredation rates and by a lower level of mutual butane-TCE inhibition. A 31 L bioreactor was designed and set up for upscaling the experiment. The second part of the research focused on the biodegradation of 4 polymers, with and with-out chemical pre-treatments: linear low density polyethylene (LLDPE), polyethylene (PP), polystyrene (PS) and polyvinyl chloride (PVC). Initially, the 4 polymers were subjected to different chemical pre-treatments: ozonation and UV/ozonation, in gaseous and aqueous phase. It was found that, for LLDPE and PP, the coupling UV and ozone in gas phase is the most effective way to oxidize the polymers and to generate carbonyl groups on the polymer surface. In further tests, the effect of chemical pretreatment on polyner biodegrability was studied. Gas-phase ozonated and virgin polymers were incubated aerobically with: (a) a pure strain, (b) a mixed culture of bacteria; and (c) a fungal culture, together with saccharose as a co-substrate.

No description available.

Primary stability of stems in cementless total hip replacements is recognized to play a critical role for long-term survival and thus for the success of the overall surgical procedure. In Literature, several studies addressed this important issue. Different approaches have been explored aiming to evaluate the extent of stability achieved during surgery. Some of these are in-vitro protocols while other tools are coinceived for the post-operative assessment of prosthesis migration relative to the host bone. In vitro protocols reported in the literature are not exportable to the operating room. Anyway most of them show a good overall accuracy. The RSA, EBRA and the radiographic analysis are currently used to check the healing process of the implanted femur at different follow-ups, evaluating implant migration, occurance of bone resorption or osteolysis at the interface. These methods are important for follow up and clinical study but do not assist the surgeon during implantation. At the time I started my Ph.D Study in Bioengineering, only one study had been undertaken to measure stability intra-operatively. No follow-up was presented to describe further results obtained with that device. In this scenario, it was believed that an instrument that could measure intra-operatively the stability achieved by an implanted stem would consistently improve the rate of success. This instrument should be accurate and should give to the surgeon during implantation a quick answer concerning the stability of the implanted stem. With this aim, an intra-operative device was designed, developed and validated. The device is meant to help the surgeon to decide how much to press-fit the implant. It is essentially made of a torsional load cell, able to measure the extent of torque applied by the surgeon to test primary stability, an angular sensor that measure the relative angular displacement between stem and femur, a rigid connector that enable connecting the device to the stem, and all the electronics for signals conditioning. The device was successfully validated in-vitro, showing a good overall accuracy in discriminating stable from unstable implants. Repeatability tests showed that the device was reliable. A calibration procedure was then performed in order to convert the angular readout into a linear displacement measurement, which is an information clinically relevant and simple to read in real-time by the surgeon. The second study reported in my thesis, concerns the evaluation of the possibility to have predictive information regarding the primary stability of a cementless stem, by measuring the micromotion of the last rasp used by the surgeon to prepare the femoral canal. This information would be really useful to the surgeon, who could check prior to the implantation process if the planned stem size can achieve a sufficient degree of primary stability, under optimal press fitting conditions. An intra-operative tool was developed to this aim. It was derived from a previously validated device, which was adapted for the specific purpose. The device is able to measure the relative micromotion between the femur and the rasp, when a torsional load is applied. An in-vitro protocol was developed and validated on both composite and cadaveric specimens. High correlation was observed between one of the parameters extracted form the acquisitions made on the rasp and the stability of the corresponding stem, when optimally press-fitted by the surgeon. After tuning in-vitro the protocol as in a closed loop, verification was made on two hip patients, confirming the results obtained in-vitro and highlighting the independence of the rasp indicator from the bone quality, anatomy and preserving conditions of the tested specimens, and from the sharpening of the rasp blades. The third study is related to an approach that have been recently explored in the orthopaedic community, but that was already in use in other scientific fields. It is based on the vibration analysis technique. This method has been successfully used to investigate the mechanical properties of the bone and its application to evaluate the extent of fixation of dental implants has been explored, even if its validity in this field is still under discussion. Several studies have been published recently on the stability assessment of hip implants by vibration analysis. The aim of the reported study was to develop and validate a prototype device based on the vibration analysis technique to measure intra-operatively the extent of implant stability. The expected advantages of a vibration-based device are easier clinical use, smaller dimensions and minor overall cost with respect to other devices based on direct micromotion measurement. The prototype developed consists of a piezoelectric exciter connected to the stem and an accelerometer attached to the femur. Preliminary tests were performed on four composite femurs implanted with a conventional stem. The results showed that the input signal was repeatable and the output could be recorded accurately. The fourth study concerns the application of the device based on the vibration analysis technique to several cases, considering both composite and cadaveric specimens. Different degrees of bone quality were tested, as well as different femur anatomies and several levels of press-fitting were considered. The aim of the study was to verify if it is possible to discriminate between stable and quasi-stable implants, because this is the most challenging detection for the surgeon in the operation room. Moreover, it was possible to validate the measurement protocol by comparing the results of the acquisitions made with the vibration-based tool to two reference measurements made by means of a validated technique, and a validated device. The results highlighted that the most sensitive parameter to stability is the shift in resonance frequency of the stem-bone system, showing high correlation with residual micromotion on all the tested specimens. Thus, it seems possible to discriminate between many levels of stability, from the grossly loosened implant, through the quasi-stable implants, to the definitely stable one. Finally, an additional study was performed on a different type of hip prosthesis, which has recently gained great interest thus becoming fairly popular in some countries in the last few years: the hip resurfacing prosthesis. The study was motivated by the following rationale: although bone-prosthesis micromotion is known to influence the stability of total hip replacement, its effect on the outcome of resurfacing implants has not been investigated in-vitro yet, but only clinically. Thus the work was aimed at verifying if it was possible to apply to the resurfacing prosthesis one of the intraoperative devices just validated for the measurement of the micromotion in the resurfacing implants. To do that, a preliminary study was performed in order to evaluate the extent of migration and the typical elastic movement for an epiphyseal prosthesis. An in-vitro procedure was developed to measure micromotions of resurfacing implants. This included a set of in-vitro loading scenarios that covers the range of directions covered by hip resultant forces in the most typical motor-tasks. The applicability of the protocol was assessed on two different commercial designs and on different head sizes. The repeatability and reproducibility were excellent (comparable to the best previously published protocols for standard cemented hip stems). Results showed that the procedure is accurate enough to detect micromotions of the order of few microns. The protocol proposed was thus completely validated. The results of the study demonstrated that the application of an intra-operative device to the resurfacing implants is not necessary, as the typical micromovement associated to this type of prosthesis could be considered negligible and thus not critical for the stabilization process. Concluding, four intra-operative tools have been developed and fully validated during these three years of research activity. The use in the clinical setting was tested for one of the devices, which could be used right now by the surgeon to evaluate the degree of stability achieved through the press-fitting procedure. The tool adapted to be used on the rasp was a good predictor of the stability of the stem. Thus it could be useful for the surgeon while checking if the pre-operative planning was correct. The device based on the vibration technique showed great accuracy, small dimensions, and thus has a great potential to become an instrument appreciated by the surgeon. It still need a clinical evaluation, and must be industrialized as well. The in-vitro tool worked very well, and can be applied for assessing resurfacing implants pre-clinically.

The knee joint is a key structure of the human locomotor system. The knowledge of how each single anatomical structure of the knee contributes to determine the physiological function of the knee, is of fundamental importance for the development of new prostheses and novel clinical, surgical, and rehabilitative procedures. In this context, a modelling approach is necessary to estimate the biomechanic function of each anatomical structure during daily living activities. The main aim of this study was to obtain a subject-specific model of the knee joint of a selected healthy subject. In particular, 3D models of the cruciate ligaments and of the tibio-femoral articular contact were proposed and developed using accurate bony geometries and kinematics reliably recorded by means of nuclear magnetic resonance and 3D video-fluoroscopy from the selected subject. Regarding the model of the cruciate ligaments, each ligament was modelled with 25 linear-elastic elements paying particular attention to the anatomical twisting of the fibres. The devised model was as subject-specific as possible. The geometrical parameters were directly estimated from the experimental measurements, whereas the only mechanical parameter of the model, the elastic modulus, had to be considered from the literature because of the invasiveness of the needed measurements. Thus, the developed model was employed for simulations of stability tests and during living activities. Physiologically meaningful results were always obtained. Nevertheless, the lack of subject-specific mechanical characterization induced to design and partially develop a novel experimental method to characterize the mechanics of the human cruciate ligaments in living healthy subjects. Moreover, using the same subject-specific data, the tibio-femoral articular interaction was modelled investigating the location of the contact point during the execution of daily motor tasks and the contact area at the full extension with and without the whole body weight of the subject. Two different approaches were implemented and their efficiency was evaluated. Thus, pros and cons of each approach were discussed in order to suggest future improvements of this methodologies. The final results of this study will contribute to produce useful methodologies for the investigation of the in-vivo function and pathology of the knee joint during the execution of daily living activities. Thus, the developed methodologies will be useful tools for the development of new prostheses, tools and procedures both in research field and in diagnostic, surgical and rehabilitative fields.

Background. The surgical treatment of dysfunctional hips is a severe condition for the patient and a costly therapy for the public health. Hip resurfacing techniques seem to hold the promise of various advantages over traditional THR, with particular attention to young and active patients. Although the lesson provided in the past by many branches of engineering is that success in designing competitive products can be achieved only by predicting the possible scenario of failure, to date the understanding of the implant quality is poorly pre-clinically addressed. Thus revision is the only delayed and reliable end point for assessment. The aim of the present work was to model the musculoskeletal system so as to develop a protocol for predicting failure of hip resurfacing prosthesis. Methods. Preliminary studies validated the technique for the generation of subject specific finite element (FE) models of long bones from Computed Thomography data. The proposed protocol consisted in the numerical analysis of the prosthesis biomechanics by deterministic and statistic studies so as to assess the risk of biomechanical failure on the different operative conditions the implant might face in a population of interest during various activities of daily living. Physiological conditions were defined including the variability of the anatomy, bone densitometry, surgery uncertainties and published boundary conditions at the hip. The protocol was tested by analysing a successful design on the market and a new prototype of a resurfacing prosthesis. Results. The intrinsic accuracy of models on bone stress predictions (RMSE < 10%) was aligned to the current state of the art in this field. The accuracy of prediction on the bone-prosthesis contact mechanics was also excellent (< 0.001 mm). The sensitivity of models prediction to uncertainties on modelling parameter was found below 8.4%. The analysis of the successful design resulted in a very good agreement with published retrospective studies. The geometry optimisation of the new prototype lead to a final design with a low risk of failure. The statistical analysis confirmed the minimal risk of the optimised design over the entire population of interest. The performances of the optimised design showed a significant improvement with respect to the first prototype (+35%). Limitations. On the authors opinion the major limitation of this study is on boundary conditions. The muscular forces and the hip joint reaction were derived from the few data available in the literature, which can be considered significant but hardly representative of the entire variability of boundary conditions the implant might face over the patients population. This moved the focus of the research on modelling the musculoskeletal system; the ongoing activity is to develop subject-specific musculoskeletal models of the lower limb from medical images. Conclusions. The developed protocol was able to accurately predict known clinical outcomes when applied to a well-established device and, to support the design optimisation phase providing important information on critical characteristics of the patients when applied to a new prosthesis. The presented approach does have a relevant generality that would allow the extension of the protocol to a large set of orthopaedic scenarios with minor changes. Hence, a failure mode analysis criterion can be considered a suitable tool in developing new orthopaedic devices.