title: Damage identification in skeletal structures: A dynamic stiffness approach

authors: De Los Rios Giraldo, Julian Octavio

subjects: Damage identification

abstract: The present work is devoted to investigate ways of identifying cracks in skeletal structures by frequency monitoring. This is a challenging problem as the number of cracks, their severity and location all need to be found. It has been shown that roving bodies with rotary inertia could be used to find the total number of cracks and their locations without any knowledge of their severity. The Dynamic Stiffness Method was chosen due to its capabilities in enabling an exact solution while facilitating addition of new elements such as springs and masses to the structure in the same way as in the approximate Finite Element Method (FEM). Using the Dynamic Stiffness Matrices (DSM), it was possible to derive an interesting and useful relationship between the determinants of the DSM of the following: the original undamaged structure, the cracked structure and the structure with a hinge at the potential crack location. This relationship is a simple equation which gives the determinant of the cracked structure as the sum of the determinant of the undamaged structure multiplied by the rotational stiffness of the beam at the crack and the determinant of a structure with a hinge at the same crack location.

Experimental results from literature are used to validate the application of the found features in beam structures and frameworks to identify damages or dynamic properties. A semi-experimental methodology is proposed to treat multi-cracked structures where, as a first step, the roving inertia method is used to identify the number and location of the cracks in a simple way without the need to perform any calculations or theoretical analysis. The theoretical basis of this method is explained using the DSM. Experimental work was carried out on a cantilever beam to verify the applicability of the roving inertia method but no conclusive results were obtained. Further experimental investigations are needed to study the practical feasibility of the method. It is hoped that once the locations of all cracks are identified, the severity of the cracks can be found using the frequency measurements as the determinants of the DSM are linear functions of crack severity.

text: Damage identification in skeletal structures: A dynamic stiffness approach The present work is devoted to investigate ways of identifying cracks in skeletal structures by frequency monitoring. This is a challenging problem as the number of cracks, their severity and location all need to be found. It has been shown that roving bodies with rotary inertia could be used to find the total number of cracks and their locations without any knowledge of their severity. The Dynamic Stiffness Method was chosen due to its capabilities in enabling an exact solution while facilitating addition of new elements such as springs and masses to the structure in the same way as in the approximate Finite Element Method (FEM). Using the Dynamic Stiffness Matrices (DSM), it was possible to derive an interesting and useful relationship between the determinants of the DSM of the following: the original undamaged structure, the cracked structure and the structure with a hinge at the potential crack location. This relationship is a simple equation which gives the determinant of the cracked structure as the sum of the determinant of the undamaged structure multiplied by the rotational stiffness of the beam at the crack and the determinant of a structure with a hinge at the same crack location.

Experimental results from literature are used to validate the application of the found features in beam structures and frameworks to identify damages or dynamic properties. A semi-experimental methodology is proposed to treat multi-cracked structures where, as a first step, the roving inertia method is used to identify the number and location of the cracks in a simple way without the need to perform any calculations or theoretical analysis. The theoretical basis of this method is explained using the DSM. Experimental work was carried out on a cantilever beam to verify the applicability of the roving inertia method but no conclusive results were obtained. Further experimental investigations are needed to study the practical feasibility of the method. It is hoped that once the locations of all cracks are identified, the severity of the cracks can be found using the frequency measurements as the determinants of the DSM are linear functions of crack severity.

year: 2017

title: Signal processing approaches for Jitter extraction in time-of-flight range imaging cameras

authors: Anthonys, Gehan

subjects: Science & Technology

abstract: The precision and accuracy of time-of-flight full-field range cameras are important for many applications, however there are a number of noise sources that degrade both precision and accuracy. Many of the noise sources such as nonlinearity, multipath inferences and harmonic cancellation are well investigated. Barely investigated is jitter on the camera light and shutter signals. Here we measure periodic and random jitter on the light signal of a camera. We use signal processing techniques to construct a reference signal, hence find the jitter. The performance of the proposed method is examined using the MESA Imaging SwissRanger 4000. We found periodic jitter of two frequencies at 0.12 and 5.04 MHz and the random jitter of 164 ± 4 ps, on the light signal of the camera.

text: Signal processing approaches for Jitter extraction in time-of-flight range imaging cameras The precision and accuracy of time-of-flight full-field range cameras are important for many applications, however there are a number of noise sources that degrade both precision and accuracy. Many of the noise sources such as nonlinearity, multipath inferences and harmonic cancellation are well investigated. Barely investigated is jitter on the camera light and shutter signals. Here we measure periodic and random jitter on the light signal of a camera. We use signal processing techniques to construct a reference signal, hence find the jitter. The performance of the proposed method is examined using the MESA Imaging SwissRanger 4000. We found periodic jitter of two frequencies at 0.12 and 5.04 MHz and the random jitter of 164 ± 4 ps, on the light signal of the camera.

year: 2018

title: Culture and collaborative conservation? Inter-cultural difference and the Maungatautari Project

authors: Harms, Matthew

subjects: Inter-cultural navigation

abstract: This thesis situates and examines the role of sociocultural difference and biculturalism in the Maungatautari Sanctuary Mountain project, a multi-stakeholder community-based biodiversity conservation project in the Waikato region of New Zealand’s North Island. In the project, Mana Whenua (local indigenous Māori groups) and Pākehā (New Zealanders of British and European descent) from the area endeavour to interact and partner in the non-profit Maungatautari Ecological Island Trust (MEIT) as its primary stakeholder groups. Utilizing sociocultural anthropology, three years of participant observation, participant interviews, fieldwork data and contextualizing history, the role of culture and issues of biculturalism and partnership are examined in relation to the respective sociocultural backgrounds and identity of project participants. Findings indicate that sociocultural difference in the form of varying beliefs, values, attitudes, practices and protocol, and identity/cultural politics have led to dissonance and strained stakeholder interrelations that negatively affected the project. In some instances, a post-colonial ‘neo-paternalism’ marginalised local Māori cultural input and needs in the project. At other times project participants successfully bridged inter-cultural differences. In these occurrences they created a collaborative, complementary, bicultural partnership which valued, sought to understand, and incorporated differing sociocultural aspects, advancing project goals. Further analysis identified an ongoing risk of future multi-stakeholder dissonance relative to culturally-derived disparate views on such issues as cultural harvesting, species reintroductions and care, ecotourism, development on the mountain, and biodiversity research. Normative solutions are identified which can aid Maungatautari stakeholders and other culturally-heterogeneous multi-stakeholder conservation groups work toward and produce inclusive, inter-cultural partnership.

text: Culture and collaborative conservation? Inter-cultural difference and the Maungatautari Project This thesis situates and examines the role of sociocultural difference and biculturalism in the Maungatautari Sanctuary Mountain project, a multi-stakeholder community-based biodiversity conservation project in the Waikato region of New Zealand’s North Island. In the project, Mana Whenua (local indigenous Māori groups) and Pākehā (New Zealanders of British and European descent) from the area endeavour to interact and partner in the non-profit Maungatautari Ecological Island Trust (MEIT) as its primary stakeholder groups. Utilizing sociocultural anthropology, three years of participant observation, participant interviews, fieldwork data and contextualizing history, the role of culture and issues of biculturalism and partnership are examined in relation to the respective sociocultural backgrounds and identity of project participants. Findings indicate that sociocultural difference in the form of varying beliefs, values, attitudes, practices and protocol, and identity/cultural politics have led to dissonance and strained stakeholder interrelations that negatively affected the project. In some instances, a post-colonial ‘neo-paternalism’ marginalised local Māori cultural input and needs in the project. At other times project participants successfully bridged inter-cultural differences. In these occurrences they created a collaborative, complementary, bicultural partnership which valued, sought to understand, and incorporated differing sociocultural aspects, advancing project goals. Further analysis identified an ongoing risk of future multi-stakeholder dissonance relative to culturally-derived disparate views on such issues as cultural harvesting, species reintroductions and care, ecotourism, development on the mountain, and biodiversity research. Normative solutions are identified which can aid Maungatautari stakeholders and other culturally-heterogeneous multi-stakeholder conservation groups work toward and produce inclusive, inter-cultural partnership.

year: 2018