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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Experimental and CFD Study of Wind-Induced Response for Bridge Cables with Ice accretion

Songyu, Cao January 2015 (has links)
Cable-stayed bridges are massive structures which rely on their structural elements such as deck girder, towers and stay-cables for their stability. The bridge stay-cables can be considered as the most flexible elements of the cable-stayed bridges, and thus their structural stability integrity is verified for several phenomena which might affect them. Wind and wind/rain induced vibrations for bridge stay-cables were comprehensively studied by researchers worldwide; however recent projects have identified a new type of cable vibrations caused by ice accretion formed around the cable circumference. The current research proposed two ice accretion profiles for inclined bridge cables and has experimentally investigated the wind-induced vibrations of the two models for the bridge stay-cables with ice accretion, under different vertical (inclination) and horizontal (yaw) angles, and for different wind speeds. Initially, three models of the bridge cable with 1.0 cm and 2.0 cm ice profile were tested in the wind tunnel of cross-section 61 cm × 90 cm, and a maximum wind speed of 30 m/s. In total 6 cases with 1.0 cm ice thickness and 3 cases with 2.0 cm ice thickness were investigated and the vertical and torsional oscillatory displacements were recorded for wind speeds from 1.5 m/s to 15 m/s at intervals of 1.5 m/s. The wind-induced vibrations were analyzed and were compared with the response reported for cables without ice and with the rain-induced response for stay-cables. Computational Fluid Dynamics (CFD) simulations were performed to observe the drag, lift and pressure coefficients around the surface of the accreted cable models yawed and inclined at α = 0°, β = 0° and α = 60°, β = 15° under the effect of 10 m/s and 15 m/s wind speed applied for both cases. A verification for galloping divergent instability was conducted based on the Den Hartog formulation and the vertical vibrations obtained from the wind tunnel experiment.
2

Evolving dynamic maneuvers in a quadruped robot

Krasny, Darren P., January 2005 (has links)
Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Includes bibliographical references (p. 246-254).
3

Wind tunnel studies on rotational effects in lightly-iced transmission line galloping

Fleming, Patrick Hugh 30 June 2010 (has links)
Overhead transmission lines are prone to undergo large amplitude, low frequency vibrations when exposed to freezing rain and steady side winds. These vibrations are referred to as galloping. They involve a dominant vertical motion in addition to twisting and horizontal swaying. Field reports indicate that the majority of galloping cases are associated with lightly-iced lines with thin ice accretions. Previous studies have failed to explain this trend satisfactorily. The present thesis involves a series of wind tunnel experiments to understand the rotational effects in lightly-iced transmission line galloping. The work to restore and upgrade the wind tunnel used for the experiments are also reported. Aerodynamic loads are measured first on a stationary model of a short, representative section of a lightly-iced conductor. Subsequently, automated controls force the model to undergo rotational oscillations, and the aerodynamic loads measured from these dynamic tests are compared to the stationary results. The airflow in both sets of experiments is visualised by using a laser-based system. The stationary test shows that the well-established den Hartog criterion for predicting vertical galloping does not explain why lightly-iced lines gallop. The dynamic experiments however confirm the presence of rotation-induced lift, unaccounted for by quasi-steady theory and the den Hartog criterion. This additional lift force increases the coupling between the rotational and vertical directions and may promote coupled aerodynamic instability. Visualisations indicate that the surface irregularities of the ice and the rotational motion are jointly responsible for the rotation-induced lift forces observed in the aerodynamic measurements.
4

Wind tunnel studies on rotational effects in lightly-iced transmission line galloping

Fleming, Patrick Hugh 30 June 2010 (has links)
Overhead transmission lines are prone to undergo large amplitude, low frequency vibrations when exposed to freezing rain and steady side winds. These vibrations are referred to as galloping. They involve a dominant vertical motion in addition to twisting and horizontal swaying. Field reports indicate that the majority of galloping cases are associated with lightly-iced lines with thin ice accretions. Previous studies have failed to explain this trend satisfactorily. The present thesis involves a series of wind tunnel experiments to understand the rotational effects in lightly-iced transmission line galloping. The work to restore and upgrade the wind tunnel used for the experiments are also reported. Aerodynamic loads are measured first on a stationary model of a short, representative section of a lightly-iced conductor. Subsequently, automated controls force the model to undergo rotational oscillations, and the aerodynamic loads measured from these dynamic tests are compared to the stationary results. The airflow in both sets of experiments is visualised by using a laser-based system. The stationary test shows that the well-established den Hartog criterion for predicting vertical galloping does not explain why lightly-iced lines gallop. The dynamic experiments however confirm the presence of rotation-induced lift, unaccounted for by quasi-steady theory and the den Hartog criterion. This additional lift force increases the coupling between the rotational and vertical directions and may promote coupled aerodynamic instability. Visualisations indicate that the surface irregularities of the ice and the rotational motion are jointly responsible for the rotation-induced lift forces observed in the aerodynamic measurements.
5

Evaluación técnico económica sobre uso de dispositivos de mitigación climática en líneas de alta tensión para Codelco División El Teniente

Larrea Moraga, Julián Eduardo January 2015 (has links)
Ingeniero Civil Eléctrico / La gran minería de Chile se encuentra localizada, en su mayoría, en la alta montaña lo que hace vulnerable al sistema eléctrico a distintas condiciones climáticas como nieve y viento. El presente trabajo de título pretende caracterizar los distintos efectos asociados a estos fenómenos naturales. Asimismo se mostrarán las opciones de mitigación existentes en el mercado para evaluar desde el punto de vista técnico y económico si resulta pertinente comprar e instalar dichas opciones. En este caso en particular se estudiará el complejo minero de El Teniente perteneciente a la Corporación Nacional del Cobre. Los dos grandes fenómenos que afectan a las líneas de alta tensión producto de nieve y viento son el efecto galloping y el ice jumping. Ambos, de características similares, tienen las mismas soluciones desde el punto de vista técnico, a través del uso de separadores. Se encontró durante el curso de la investigación, que los contrapesos también resultan útiles para evitar fallas por ice jumping. Consecuentemente se consideraron ambos dispositivos para el análisis. La metodología propuesta consiste en identificar las líneas que presentan fallas debido a estos fenómenos y luego calcular el costo de la eventual falla producida. Posteriormente este valor se contrasta con el precio de compra de los dispositivos, entregados por empresas proveedoras. Se concluye que los dispositivos evaluados resultan atractivos de instalar siempre y cuando se tenga bien identificado dónde ocurre el problema y los costos que los disturbios traen. En particular para la división El Teniente se considera que la instalación de separadores para la línea Sauzal Minero mitigaría de manera importante las fallas que se producen en invierno.. En el caso de la línea Coya Colina no resulta conveniente la instalación de dispositivos de mitigación por diversos factores. En primer lugar la antigüedad de la misma hace difícil cualquier tipo de trabajo de implementación Otro motivo es que no se tiene identificado de manera satisfactoria los vanos en los cuales se registran con mayor frecuencia las fallas y finalmente se tiene un sistema eficiente de mitigación para la acumulación de nieve en los conductores, que es la condición de derretidor de nieve.
6

Estudio experimental de un sistema tipo Wake Galloping para distintas geometrías generadoras de vórtices

Bellei Pardo, Andrés January 2017 (has links)
Ingeniero Civil Mecánico / El cosechamiento de energía, proveniente del inglés energy harvesting, es el proceso a través del cual se captura pequeñas cantidades de energía que de otro modo se perderían como calor, luz, sonido, vibración o movimiento. Esta energía puede ser utilizada en distintas aplicaciones, por ejemplo reinyectándose en sistemas que la estén perdiendo o reemplazando baterías en pequeños equipos electrónicos de baja potencia, tales como sensores de monitoreo remoto. En la presente memoria se estudia un sistema vibratorio del tipo wake galloping, con el objetivo de investigar experimentalmente el efecto de la geometría del generador de vórtices de sección cuadrada y tipo placa plana en la potencia obtenida. Para llevar a cabo dicho objetivo se plantean los siguientes objetivos específicos: implementar modificaciones al montaje experimental existente y validar el procedimiento experimental reproduciendo curva de aceleración y frecuencia versus velocidad del viento para el generador de vórtices cilíndrico de sección circular, estimar la potencia obtenida usando como generador de vórtices un cilindro de sección cuadrada y estimar la potencia obtenida usando como generador de vórtices una placa plana. Este sistema, a escala pequeña, puede aprovecharse por ejemplo en túneles de trenes subterráneos, alimentando sensores de monitoreo remotos, pudiendo clasificarse como un sistema de cosechamiento de energía. Las variables en estudio para cada geometría fueron: la velocidad del viento, y la razón de aspecto en distancia X=L⁄D, donde D es el diámetro del cilindro móvil y L es la distancia entre dicho cilindro y el generador de vórtices. Para el cilindro de sección cuadrada además se varía el ángulo de inclinación del mismo con respecto al flujo incidente. Se midió experimentalmente la aceleración del cuerpo vibratorio por medio de acelerómetros instalados al centro del mismo. A partir de los resultados obtenidos, se encuentra que la potencia máxima alcanzada es de ≈312 [mW], utilizando como generador de vórtices un cilindro cuadrado rotado en 12°, a una razón de distancia X=3 y a una velocidad de viento de 7 [m/s]. Para todos los generadores de vórtices estudiados, la máxima potencia se alcanza a la mayor velocidad de viento utilizada: 7 [m/s]. Aunque no es posible establecer un patrón que determine qué distancia X maximiza las potencias obtenidas, se observa sin embargo una tendencia en que los mayores valores de potencia se agrupan en el rango 5≤X≤7 para todos los generadores de vórtices.
7

Harvesting wind energy using a galloping piezoelectric beam

Mahadik, Rohan Ram 12 July 2011 (has links)
Galloping of structures such as transmission lines and bridges is a classical aeroelastic instability that has been considered as harmful and destructive. However, there exists potential to harness useful energy from this phenomenon. The study presented in this paper focuses on harvesting wind energy that is being transferred to a galloping beam. The beam has a rigid prismatic tip body. Triangular and D-section are the two kinds of cross section of the tip body that are studied, developed and tested. Piezoelectric sheets are bonded on the top and bottom surface of elastic portion of the beam. During galloping, vibrational motion is input to the system due to aerodynamic forces acting on the tip body. This motion is converted into electrical energy by the piezoelectric (PZT) sheets. A potential application for this device is to power wireless sensor networks on outdoor structures such as bridges and buildings. The relative importance of various parameters of the system such as wind speed, material properties of the beam, electrical load, beam natural frequency and aerodynamic geometry of the tip body is discussed. A model is developed to predict the dynamic response, voltage and power results. Experimental investigations are performed on a representative device in order to verify the accuracy of the model as well as to study the feasibility of the device. A maximum output power of 1.14 mW was measured at a wind velocity of 10.5 mph. / text
8

The biomechanical factors limiting athletic performance in racehorses

Self, Zoe T. January 2012 (has links)
No description available.
9

Conversión de energía eólica mediante vibraciones inducidas

Soto Valle, Rodrigo Andrés January 2016 (has links)
Magíster en Ciencias de la Ingeniería, Mención Mecánica. Ingeniero Civil Mecánico / Energy harvesting es la conversión de energía presente en el entorno a energía eléctrica. Dentro de esta clasificación la energía eólica puede ser capturada desde diferentes fuentes: naturales, como flujo de aire en campos libres; pseudo-artificiales, como corrientes de aire en ambientes urbanos; artificiales, como túneles de transporte, autopistas y ductos de ventilación. Este trabajo de Tesis tiene como objetivo principal estudiar la potencia capturable debido a la interacción fluido-estructura de un arreglo de dos cilindros circulares, rectos y paralelos, enfrentado a un flujo de aire perpendicular a su eje. Se estudian la influencia de separaciones, tamaños y velocidad de ataque en un dispositivo de captación de energía eólica, mediante vibraciones del tipo wake galloping. Se realiza un análisis computacional de vibraciones inducidas por vórtices para régimen laminar, en el programa ANSYS Fluent 14.5 y una implementación numérica de interacción fluido estructura, en el programa FORTRAN con el propósito de caracterizar el flujo y movimientos de un generador de vórtices. Posteriormente se construye un montaje experimental en el túnel de viento del Laboratorio de Procesos del Departamento de Ingeniería Mecánica de la Universidad de Chile para analizar la aceleración y potencia en un arreglo de wake galloping. El dispositivo consta de dos cilindros alineados, de diámetros D1 y D2, a una distancia L entre sus centros. Se estudia la razón de tamaño, Y=D2/D1, y razón de distancia, X=L/D1, para velocidades de viento en el rango 1-7[ms-1]. Los resultados experimentales muestran que la aceleración posee una relación directamente proporcional al cuadrado de la velocidad del viento y una potencia RMS máxima de ~4.5[mW], bajo una configuración de tamaño Y=0.7 y distancia X=3, lograda bajo el acoplamiento de la frecuencia natural y de la frecuencia del desprendimiento de vórtices sobre el cilindro aguas abajo. Frente a frecuencias no coincidentes el mayor desempeño se produce para una relación de tamaño Y=1.5 y distancia X=4 con un rango de potencia RMS de 0.1-0.4[mW]. La potencia generada puede ser fácilmente incrementada considerando para todas las razones de tamaño y distancia, excitar el sistema a su resonancia variando la frecuencia natural del sistema, por ejemplo, al modificar su rigidez.
10

Aerodynamic Testing of Variable Message Signs

Meyer, Debbie 12 November 2014 (has links)
The increasing nationwide interest in intelligent transportation systems (ITS) and the need for more efficient transportation have led to the expanding use of variable message sign (VMS) technology. VMS panels are substantially heavier than flat panel aluminum signs and have a larger depth (dimension parallel to the direction of traffic). The additional weight and depth can have a significant effect on the aerodynamic forces and inertial loads transmitted to the support structure. The wind induced drag forces and the response of VMS structures is not well understood. Minimum design requirements for VMS structures are contained in the American Association of State Highway Transportation Officials Standard Specification for Structural Support for Highway Signs, Luminaires, and Traffic Signals (AASHTO Specification). However the Specification does not take into account the prismatic geometry of VMS and the complex interaction of the applied aerodynamic forces to the support structure. In view of the lack of code guidance and the limited number research performed so far, targeted experimentation and large scale testing was conducted at the Florida International University (FIU) Wall of Wind (WOW) to provide reliable drag coefficients and investigate the aerodynamic instability of VMS. A comprehensive range of VMS geometries was tested in turbulence representative of the high frequency end of the spectrum in a simulated suburban atmospheric boundary layer. The mean normal, lateral and vertical lift force coefficients, in addition to the twisting moment coefficient and eccentricity ratio, were determined using the measured data for each model. Wind tunnel testing confirmed that drag on a prismatic VMS is smaller than the 1.7 suggested value in the current AASHTO Specification (2013). An alternative to the AASHTO Specification code value is presented in the form of a design matrix. Testing and analysis also indicated that vortex shedding oscillations and galloping instability could be significant for VMS signs with a large depth ratio attached to a structure with a low natural frequency. The effect of corner modification was investigated by testing models with chamfered and rounded corners. Results demonstrated an additional decrease in the drag coefficient but a possible Reynolds number dependency for the rounded corner configuration.

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