A Loosely-Coupled Passive Dynamics and Finite Element based Model for Minimising Biomechanically Driven Unhealthy Joint Loads during Walking in Transtibial Amputees

The primary objective of a prosthetic foot is to improve the quality of life for amputees by enabling them to walk in a similar way to healthy individuals. Amputees su˙er from health risks including joint pain, back pain and joint inflammation. The aim of this thesis is to develop a new computational approach to reduce the likelihood of biomechanically driven joint pain in transtibial amputees resulting from sustained exposure to Unhealthy Loads (ULs) during walking. This is achieved by developing a computational methodology to achieve a customisable sti˙ness design solution for prosthetic feet so that the occurrence of unhealthy joint loads during walking is minimised.It is assumed that the healthy population is able to spend energy most optimally during walking at all walking speeds. During walking, the force exerted by the body on the ground is measured by the ground reaction force (GRF). The GRF value is normalised with the body weight defining a dimensionless parameter . The values are similar for both legs in healthy populations but are di˙erent for the sound and a˙ected leg for amputees. A new hypothesis has been proposed in this thesis that walking is comfortable for an amputee when the di˙erence between values is minimal between the amputee and an equivalent healthy population. The values for healthy adults, as well as amputees, follow a finite number of patterns. The pattern of the values (or the GRF curve) depends on the walking speed of an individual, categorised as slow, fast or free walking. However, it is observed in the literature that free walking speed (FWS) varies over a wide range for healthy individuals (e.g. 1.1 m/s to 1.5 m/s). As a result, it was diÿcult to establish a relationship between walking speed and GRF pattern. A novel parametrised description of GRF curves for a healthy population and amputees is proposed so that a new dimensionless velocity ratio parameter and the corresponding value of the FWS can be predicted by observing the GRF pattern of a healthy adult or an amputee. A new classification approach based on the parametrised description of GRF curves, along with the dimensionless velocity ratio parameter, has been recommended for categorising very slow, slow, free, fast and very fast walking. The GRF result predictions are validated on healthy adults in an experiment conducted in a gait lab. A group of candidates who walk a lot in their daily life were specially selected for this experiment. This classification approach is used to develop a new measure of ULs based on the parametrised GRF description for healthy population and amputees. An innovative computational methodology is proposed to design an optimal sti˙ness response of a prosthetic foot that minimises the occurrence of ULs. This is achieved by transferring the roll-over shape (ROS) information of the prosthetic foot and the corresponding information for a given velocity ratio across a passive walking dynamic (PWD) and a finite element model via a newly defined form of loose coupling. A theoretical case study is presented in which an amputee walks in a gait lab with a representative C-shaped prosthetic foot. The thesis explains how the proposed novel computational methodology is able to redesign the prosthetic foot in a way that is better suited to minimising ULs. The redesign process of the prosthetic foot has led to the development of an innovative 3D printable double keel and double heel design. With the advancement of carbon reinforced polymers and additive manufacturing technology, the sti˙ness customisation methodology proposed in this thesis has the potential to create a new generation of energy-eÿcient prosthetic feet

The Luminous Starburst Ring in NGC 7771: Sequential Star Formation?

Only two of the twenty highly luminous starburst galaxies analyzed by Smith et al. exhibit circumnuclear rings of star formation. These galaxies provide a link between 10^11 L_sun systems and classical, less-luminous ringed systems. We report the discovery of a near-infrared counterpart to the nuclear ring of radio emission in NGC 7771. A displacement between the ~10 radio bright clumps and the ~10 near-infrared bright clumps indicates the presence of multiple generations of star formation. The estimated thermal emission from each radio source is equivalent to that of ~35000 O6 stars. Each near-infrared bright knot contains ~5000 red supergiants, on average. The stellar mass of each knot is estimated to be ~10^7 M_sun. The implied time-averaged star formation rate is \~40 M_sun per yr. Several similarities are found between the properties of this system and other ringed and non-ringed starbursts. Morphological differences between NGC 7771 and the starburst + Seyfert 1 galaxy NGC 7469 suggest that NGC 7771 may not be old enough to fuel an AGN, or may not be capable of fueling an AGN. Alternatively, the differences may be unrelated to the presence or absence of an AGN and may simply reflect the possibility that star formation in rings is episodic.Comment: accepted for publication in The Astrophysical Journal (10 January 1999); 48 pages including 13 figures; AAS LaTe

Dynamic Response Modeling of High-Speed Planing Craft with Enforced Acceleration

An approach is investigated in this study for structural dynamic analysis of a high-speed planing hull, in which the pointwise acceleration data collected from sea trials are enforced as base excitation. The paper first performed the full boat analysis of an 11-meter high speed craft for a period of one wave impact selected from each of nine seakeeping runs. The sea trial acceleration data collected from 11 accelerometers placed close to the centerline and the keel are enforced as input, while those from 3 accelerometers placed around the pilot cabin are selected for validation. The substructure dynamic analysis of the isolated pilot cabin was then conducted and validated, in which 7 pointwise enforced accelerations are selected from the simulation output of the full boat dynamic analysis. The substructure dynamic analysis enables detailed investigation of local stress concentrations where critical equipment and personnel are located. The proposed approach can be extended to rigid-flexible body coupling analysis of a high-speed craft when it is running with large pitching and yawing motion

A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies

We have completed an optical spectroscopic survey of the nuclear regions (r < 200 pc) of a large sample of nearby galaxies. Although the main objectives of the survey are to search for low-luminosity active galactic nuclei and to quantify their luminosity function, the database can be used for a variety of other purposes. This paper presents measurements of the spectroscopic parameters for the 418 emission-line nuclei, along with a compilation of the global properties of all 486 galaxies in the survey. Stellar absorption generally poses a serious obstacle to obtaining accurate measurement of emission lines in nearby galactic nuclei. We describe a procedure for removing the starlight from the observed spectra in an efficient and objective manner. The main parameters of the emission lines (intensity ratios, fluxes, profile widths, equivalent widths) are measured and tabulated, as are several stellar absorption-line and continuum indices useful for studying the stellar population. Using standard nebular diagnostics, we determine the probable ionization mechanisms of the emission-line objects. The resulting spectral classifications provide extensive information on the demographics of emission-line nuclei in the local universe. This new catalog contains over 200 objects showing spectroscopic evidence for recent star formation and an equally large number of active galactic nuclei, including 46 which show broad H-alpha emission. These samples will serve as the basis of future studies of nuclear activity in nearby galaxies.Comment: To appear in the Astrophysical Journal Supplements. LaTex, 31 pages, plus an additional 23 figures and 5 tables. AASTex macro aaspp4.st

On Full Scale Slamming Testing of High-Speed Boats

This dissertation consists of four articles on the experimental investigation of slamming in high speed craft. The investigation utilizes data from the purpose-built 9 meter high-speed offshore research boat Numerette. The unique hybrid steel/composite construction and high-speed, high channel count instrumentation and data acquisition system have enabled collection of the wealth of experimental data that is analyzed in these articles. In the first article the role of hull bottom panel stiffness in slamming is investigated. Two panels of differing construction are mounted on starboard and port on the Numerette, which is run at relatively high speeds in the Atlantic Ocean. Displacements of the two different panels are compared. The structural response under slamming loading is then compared with the behavior under static loading. It is shown that the static stiffness relationship is not directly reflected in the experimental slamming data; rather the relative response falls somewhere between the case of a static loading and the dynamic response of a simple mass-spring system. In the second article, the structural response of bottom panels to slamming loads is investigated further. Experiments are described and results presented for modal and static analysis of the Numerette bottom panels in free air. Strain data is then presented from slamming experiments, investigating the influence of wave encounter conditions and vessel rigid body motions on response in the time and frequency domains.The third article presents an analysis technique that uses the wavelet transform to provide insight into the behavior of marine structures subjected to slamming loads. Pressure, strain, acceleration and displacement data for an isolated slamming event are presented in the time domain and in the frequency domain with Fourier transforms and wavelet transforms. Two periods of high acceleration are identified and using the wavelet transform are shown to be vibration at the dry and then wet eigenfrequencies. Mode shapes are identified during these two phases using data from an array of accelerometers. The optimal time-frequency resolution of the wavelet transform makes it a powerful tool in analyzing slamming data, revealing non-stationary behavior that the Fourier transform obscures. Identifying such behavior can be critical, in particular in hull structures with reduced stiffness where strong hydroelastic effects are expected.The final article presents the validation of a high fidelity CFD/FE FSI code using data from Numerette. The CFD code CFDShip-Iowa and finite element solver Ansys are used. Hydrodynamic simulations are performed at a range of Froude numbers and sea conditions. Good agreement is shown with experimental data in calm seas. A one-way fluid structure interaction study is performed and strains show a qualitative agreement between numerical and experimental data.These articles give insight to the designer of high speed craft by comparing the response of panels of varying, but relevant constructions to slamming loads. Additionally, the time-frequency analysis tool presented enables evaluation of structural response and identification of behavior that can be critical in slamming. Finally the collected data is used to validate a CFD/FE FSI code that could be used early in the design phase to optimize a structure and hull geometry under realistic conditions

The 20th Aerospace Mechanisms Symposium

Numerous topics related to aerospace mechanisms were discussed. Deployable structures, electromagnetic devices, tribology, hydraulic actuators, positioning mechanisms, electric motors, communication satellite instruments, redundancy, lubricants, bearings, space stations, rotating joints, and teleoperators are among the topics covered

Concept design of a fast sail assisted feeder container ship

A fast sail assisted feeder container ship concept has been developed for the 2020 container market in the South East Asian and Caribbean regions.The design presented has met the requirements of an initial economic study, with a cargo capacity of 1270 twenty-foot equivalent unit containers, meeting the predictions of container throughput derived from historical data. In determining suitable vessel dimensions, account has also been taken for port and berthing restrictions, and considering hydrodynamic performance. The vessel has been designed for a maximum speed of 25 knots, allowing it to meet the demand for trade whilst reducing the number of ships operating on the routes considered.The design development of the fast feeder concept has involved rigorous analyses in a number of areas to improve the robustness of the final design. Model testing has been key to the development of the concept, by increasing confidence in the final result. This is due to the fact that other analysis techniques are not always appropriate or accurate. Two hull forms have been developed to meet requirements whilst utilising different propulsor combinations. This has enabled evaluation of efficiency gains resulting from different hydrodynamic phenomena for each design. This includes an evaluation of the hydrodynamic performance when utilising the sail system. This has been done using a combination of model test results and data from regression analysis. The final propulsor chosen is a contra-rotating podded drive arrangement. Wind tunnel testing has been used to maximise the performance of a Multi-wing sail system by investigating the effects of wing spacing, stagger and sail-container interactions. This has led to an increase in lift coefficient of 32% from initial predictions. The savings in power requirement due to the sail system are lower than initially predicted. However, another benefit of their installation, motion damping, has been identified. Whilst this has not been fully investigated, additional fuel savings are possible as well as improved seakeeping performance.The design is shown to be environmentally sustainable when compared to existing vessels operating on the proposed routes. This is largely due to the use of low-carbon and zero-sulphur fuel (liquefied natural gas) and improvements in efficiency regarding operation. This especially relates to cargo handling and scheduling. Green house gas emissions have been predicted to fall by 42% and 40% in the two regions should the design be adopted. These savings are also due to the use of the Multi-wing sail system, which contributes to reductions in power requirement of up to 6% when the vessel operates at its lower speed of 15 knots. It is demonstrated that the fast feeder is also economically feasible, with predicted daily cost savings of 27% and 33% in the South East Asian and Caribbean regions respectively. Thus the fast feeder container ship concept is a viable solution for the future of container transhipment. <br/