Methods and Models for Accelerating Dynamic Simulation of Fluid Power Circuits

The objective of this dissertation is to improve the dynamic simulation of fluid power circuits. A fluid power circuit is a typical way to implement power transmission in mobile working machines, e.g. cranes, excavators etc. Dynamic simulation is an essential tool in developing controllability and energy-efficient solutions for mobile machines. Efficient dynamic simulation is the basic requirement for the real-time simulation. In the real-time simulation of fluid power circuits there exist numerical problems due to the software and methods used for modelling and integration. A simulation model of a fluid power circuit is typically created using differential and algebraic equations. Efficient numerical methods are required since differential equations must be solved in real time. Unfortunately, simulation software packages offer only a limited selection of numerical solvers. Numerical problems cause noise to the results, which in many cases leads the simulation run to fail. Mathematically the fluid power circuit models are stiff systems of ordinary differential equations. Numerical solution of the stiff systems can be improved by two alternative approaches. The first is to develop numerical solvers suitable for solving stiff systems. The second is to decrease the model stiffness itself by introducing models and algorithms that either decrease the highest eigenvalues or neglect them by introducing steady-state solutions of the stiff parts of the models. The thesis proposes novel methods using the latter approach. The study aims to develop practical methods usable in dynamic simulation of fluid power circuits using explicit fixed-step integration algorithms. In this thesis, twomechanisms whichmake the systemstiff are studied. These are the pressure drop approaching zero in the turbulent orifice model and the volume approaching zero in the equation of pressure build-up. These are the critical areas to which alternative methods for modelling and numerical simulation are proposed. Generally, in hydraulic power transmission systems the orifice flow is clearly in the turbulent area. The flow becomes laminar as the pressure drop over the orifice approaches zero only in rare situations. These are e.g. when a valve is closed, or an actuator is driven against an end stopper, or external force makes actuator to switch its direction during operation. This means that in terms of accuracy, the description of laminar flow is not necessary. But, unfortunately, when a purely turbulent description of the orifice is used, numerical problems occur when the pressure drop comes close to zero since the first derivative of flow with respect to the pressure drop approaches infinity when the pressure drop approaches zero. Furthermore, the second derivative becomes discontinuous, which causes numerical noise and an infinitely small integration step when a variable step integrator is used. A numerically efficient model for the orifice flow is proposed using a cubic spline function to describe the flow in the laminar and transition areas. Parameters for the cubic spline function are selected such that its first derivative is equal to the first derivative of the pure turbulent orifice flow model in the boundary condition. In the dynamic simulation of fluid power circuits, a tradeoff exists between accuracy and calculation speed. This investigation is made for the two-regime flow orifice model. Especially inside of many types of valves, as well as between them, there exist very small volumes. The integration of pressures in small fluid volumes causes numerical problems in fluid power circuit simulation. Particularly in realtime simulation, these numerical problems are a great weakness. The system stiffness approaches infinity as the fluid volume approaches zero. If fixed step explicit algorithms for solving ordinary differential equations (ODE) are used, the system stability would easily be lost when integrating pressures in small volumes. To solve the problem caused by small fluid volumes, a pseudo-dynamic solver is proposed. Instead of integration of the pressure in a small volume, the pressure is solved as a steady-state pressure created in a separate cascade loop by numerical integration. The hydraulic capacitance V/Be of the parts of the circuit whose pressures are solved by the pseudo-dynamic method should be orders of magnitude smaller than that of those partswhose pressures are integrated. The key advantage of this novel method is that the numerical problems caused by the small volumes are completely avoided. Also, the method is freely applicable regardless of the integration routine applied. The superiority of both above-mentioned methods is that they are suited for use together with the semi-empirical modelling method which necessarily does not require any geometrical data of the valves and actuators to be modelled. In this modelling method, most of the needed component information can be taken from the manufacturer’s nominal graphs. This thesis introduces the methods and shows several numerical examples to demonstrate how the proposed methods improve the dynamic simulation of various hydraulic circuits.

Relieved after Doctor's Consultation? Primary Health Care Patients' Complaint-related Worries

Worry is one of the central factors in primary health care patients’ experience with their current complaint. Worry is associated with, e.g., patients’ expectations and the outcomes of doctor’s consultations. The aim of this study was to explore primary health care patients’ complaint-related worry and its changes, as well as contributing factors. Furthermore, the reasons behind patients’ pre-consultation worry and possible relief were examined. The study was conducted in a public primary health care centre in Forssa in Southern Finland. Patients, aged 18–39 years, with a current complaint were interviewed before and after a doctor’s consultation. The patients’ characteristics, perceptions of their complaint and their expectations and experiences concerning the consultation were obtained through interviews. In addition, two questionnaires were administered to measure general tendency to illness worry (IWS) and psychiatric symptoms (SCL-90). The patients’ ratings of the intensity of worry and the severity of their complaint were measured with a visual analogue scale (VAS 0–100). Changes in worry were measured by comparing pre- and post-consultation VAS ratings and asking the patients to compare their worry after the consultation with the worry they felt before it. In connection with these ratings the patients also gave reasons for their experiences in their own words. The patients’ doctors assessed the medical severity of the complaints and whether they had found a medical explanation for the complaints. Many patients were very worried before the consultation (65 % scored over 50 points on the VAS). Worry and severity ratings were associated with the duration and course of the complaint, with a general tendency to illness worry and hostility. On average, the patients were less worried after the consultation than before it. Persistent worry was associated with the patients’ uncertainty about their complaint, their perceiving it as severe, expectations for examinations and reporting symptoms of anxiety. Patients were most often worried about the nature of their complaint (e.g. duration or intensity), not knowing what was wrong, the possible harmful effects of the complaint on body functions, the complaint’s prognosis, e.g. will it get better, and their ability to function. Patients were relieved by getting an explanation or treatment or by having a positive view of the complaint’s prognosis. Patients who reported uncertainty (lack of an explanation, worry about the nature of the complaint) or worry about the complaint’s possible bodily harmfulness were relieved by getting an explanation, often accompanied with getting treatment. On the other hand, worries about the ability to function tended to persist. Doctors should bring up patients’ worries for discussion in order to be able to respond to them appropriately. Because it tends to persist, worry about the ability to function should be addressed. Uncertain patients with concerns about their complaint’s bodily harmfulness or psychological consequences need special attention from their doctor.

Primary and Revision Hip Replacement. A University Hospital Database and Registry Study

Large-headed total hip arthroplasty (THA) and hip resurfacing arthroplasty (HRA) with metal-on-metal (MoM) bearings became popular during the last decade. Recently, it has become evident that the large-head MoM hip implants are associated with increased revision rates despite their theoretical advantages. The purpose of this study was to evaluate the early results of primary MoM hip replacements and of acetabular revisions. I analyzed retrospectively the results of four MoM implant designs and the survival rate of acetabular revisions with impaction bone grafting, as documented in the Turku University Hospital database. Further, I evaluated the correlation between femoral head size and dislocation rate, and used the Finnish Arthroplasty Register data to compare the survival of three large-head MoM THAs to analogous HRAs. The early results for the Magnum M2A–ReCap THA were good. A larger head size decreased the risk of dislocation. Articular surface replacement (ASR) THA yielded inferior results compared to analogous HRA. For two other designs the results were similar. The R3–Synergy THA yielded inferior results compared to the reference implants. The survival of acetabular reconstructions with impaction bone grafting was inferior compared to previous reports. In conclusion, the early results of the Biomet ReCap–Magnum design were promising, and large head sizes decreased the dislocation rate. The survival of different MoM hip implant designs varied. The survival of new designs and techniques may be inferior to those reported by the clinics where implants are developed. An important caveat is that early promising results of new devices may rapidly worsen. New implants need to be introduced in a controlled fashion to the market; here, arthroplasty registers are a valuable tool that needs to be used.

Experiences among primary school teachers in Tanzania

The overall aim of the study was to explore primary school teachers’ experiences of constraints to their work, and actions taken for improvement after undergoing in-service courses in the Education Quality Improvement through Pedagogy program. The research interest was thus to deepen the understanding of teachers’ experiences of constraints to their work and experiences of actions taken to improve classroom actions. In order to achieve this ambition, the study was conducted with primary school teachers in Shinyanga district-Tanzania. Two research questions guided the study: What do teachers experience as constraints to their work? The second: How have teachers improved their classroom actions after undergoing professional development courses? The theoretical framework of the study is centred on limiting and enabling frames on teachers’ work and professional development. In order to understand the classroom situations, qualitative research was designed applying a phenomenological approach with semi-structured interview, observation and videotaping to collect data. Forty experienced primary school teachers from ten primary schools participated in the study. The results of the first research question indicate that teachers face many constraints in their work. Three categories identified as interactional, environmental and professional role constraints. The most critical experienced by all teachers is teaching in large classes and inadequate teaching and learning materials. The results of the second research question show that teachers’ actions taken for improving their work were influenced by professional development activities. Three main categories including expanded interaction, expanded use of environment and expanded professional roles were identified. Generally, the knowledge generated is relevant for viewing teachers’ experiences of the challenges they encounter in teaching and the importance of professional development beyond the sampled respondents. The results suggest that constant provision of teachers’ professional development could improve teaching performance.