Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2000.
Includes bibliographical references (leaves 100-101).
The reciprocating motion of the piston of an ...internal combustion engine in the vertical plane is referred to as its primary motion, and it is this primary motion that produces power in the engine. Due to the fact that there is a clearance between the piston and the liner, and that certain forces on the piston have components in the horizontal direction, there exists some lateral motion of the piston and also some rotational motion about the wrist pin axis. This motion is referred to as secondary motion. Secondary motion has significant implications for oil transport past the piston ring-pack, engine friction and engine noise. For these reasons a comprehensive numerical model of secondary motion is a valuable tool for engine designers and development engineers. This work involves the development of a comprehensive and robust computer model of piston secondary motion, which can be easily run on a desktop computer. The model is applicable to both conventional mono-piston assemblies and also to articulated piston assemblies. The modeling approach involves treating the piston assembly as a set of independent rigid bodies, and formulating and solving the equations of motion for each body. The hydrodynamic skirt-liner interaction force is computed by solving the Reynolds equation for the oil film and integrating the computed pressure. This essentially one dimensional calculation is performed at several circumferential locations on the piston, and the results are integrated to yield a single force in the main thrust-anti thrust direction. The model is first developed with a basic form of this hydrodynamic calculation, which is later improved to include a solution for the wetted region and a complete pressure distribution on the piston. Results using both forms of the model are compared and analyzed, and the final model is used to perform several parametric studies involving various engine operating parameters.
by Conor P. McNally.
S.M.
Synopsis
The novel use of an Ellick bladder evacuator for tissue retrieval after operative hysteroscopy by electrosurgical resectoscope can reduce operative time, multiple additional scope ...reinsertions and possible complications.
Lower extremity landing asymmetries are common and associated with strength deficits after anterior cruciate ligament reconstruction. However, less is known regarding trunk control during landing. ...This study's hypotheses were that frontal plane trunk excursion during single-leg landing would be greater in young athletes after anterior cruciate ligament reconstruction compared to controls and would be associated with strength deficits.
Participants included 130 young athletes recently cleared for return-to-sport following anterior cruciate ligament reconstruction and 56 uninjured young athletes. Frontal plane trunk excursion was quantified using three-dimensional motion analysis during a single-leg landing task. Quadriceps and hip abduction strength were measured using an isokinetic dynamometer. Frontal plane trunk excursion was compared between the anterior cruciate ligament reconstruction and control groups and among quadriceps strength subgroups using independent t-tests and one-way analysis of variance. Linear regression examined the association between frontal plane trunk excursion and strength measures in the anterior cruciate ligament reconstruction group.
The anterior cruciate ligament reconstruction group demonstrated greater frontal plane trunk excursion compared to controls. The low-quadriceps group demonstrated greater frontal plane trunk excursion compared to both the high-quadriceps and control groups. Additionally, the high-quadriceps group demonstrated greater frontal plane trunk excursion compared to controls. In the anterior cruciate ligament reconstruction group, lower quadriceps and hip abduction strength were weakly associated with greater frontal plane trunk excursion.
Young athletes at time of return-to-sport after anterior cruciate ligament reconstruction demonstrated increased frontal plane trunk excursion during single-leg landing. Additionally, increased frontal plane trunk excursion was weakly associated with strength deficits.
•Landing trunk control was evaluated in athletes with anterior cruciate ligament reconstruction.•Those with anterior cruciate ligament reconstruction had greater frontal plane trunk excursion.•Greater frontal plane trunk excursion was weakly associated with muscle strength deficits.•A low-quadriceps strength group demonstrated greater frontal plane trunk excursion.
Using detailed musculoskeletal models in computer simulations of human movement can provide insights into individual muscle and joint loading; however, these muscle models increase problem ...dimensionality and require difficult-to-fit parameters. Here, we provide a brief overview of a muscle model alternative, muscle torque generators (MTGs), and highlight how MTG functions have been used by researchers to generate accurate dynamic simulations of optimal sports performance. Multibody dynamic models of a golf drive, track cycling, and wheelchair propulsion were designed and actuated using MTGs. Each MTG was effectively a rotational, single muscle equivalent that contained joint angle/velocity scaling and passive elements to mimic Hill-type muscle model behaviour. Optimal control algorithms were used to predict how each model would execute their respective sports task; these results were compared against experimental data collected from elite athletes. Good agreement between simulated and experimental movement trajectories was observed, with relatively low computational times required for convergence of the MTG-driven multibody simulations.
Purpose
Effective information management can help real estate operators improve asset performance during use, reducing environmental impact. The purpose of this exploratory study is to identify and ...prioritise key drivers, challenges and opportunities relating to information management, from the point of view of a diverse cohort of facilities practitioners, with the aim of guiding future research direction and contributing to a comprehensive domain understanding.
Design/methodology/approach
Nine interviews are conducted across a broad sample of real estate sectors, the respondents including six facility managers and three data managers. A thematic analysis results in the identification and ranking in terms of importance of 44 emergent themes. These themes are then grouped into abstracted categories for analysis and synthesis.
Findings
This study indicates that systemic rather than technical issues are the greatest barrier to effective information management for facilities practitioners, the interviews providing examples of practical measures which address these challenges, promoting lifecycle thinking. Alignment is also found between the facilities and data management cohorts regarding lifecycle thinking towards both physical assets and information.
Practical implications
This study provides direction for future developments in the facilities sector, suggesting the pursuit to address systemic issues as being both worthwhile and feasible.
Originality/value
The novelty of this study is the ranking and synthesis of practitioner priorities with regard to high-level information management issues which is lacking in the literature, with a focus to-date on case-specific technical integration.
Abstract Objective To compare the characteristics of women who select elective repeat cesarean rather than trial of labor after cesarean (TOLAC) for delivery, and to determine individual predictors ...for success and failure within a TOLAC group and observe differences in maternal and neonatal morbidity. Methods The present descriptive, retrospective, observational study was performed in a regional obstetric unit in the United Kingdom. Data were collected from the Northern Ireland Maternity System database on all women who gave birth between April 2010 and April 2012, and had a previous cesarean delivery, and statistical analysis was performed. Results In total, 893 patients were included in the study: 385 underwent TOLAC and 493 underwent elective repeat cesarean. On comparison, women in the elective repeat cesarean group had a shorter inter-delivery interval and fewer had had a previous vaginal delivery ( P < 0.005). Predictors for success in the TOLAC group included previous vaginal delivery and a longer inter-delivery interval ( P < 0.05). Successful vaginal birth after cesarean (VBAC) did not have higher rates of maternal morbidity. Conclusion The majority of patients (56%) chose elective repeat cesarean rather than TOLAC, which has long-term implications both clinically and financially. A validated prediction model might improve patient counseling and identify women with a high likelihood of successful VBAC.
PDF
