1,721,181 research outputs found
Homo Sapiens und Homo Faber. Epistemische und technische Rationalität in Antike und Gegenwart; Festschrift für Jürgen Mittelstraß
No full textCarrier M, Wolters G, eds. Homo Sapiens und Homo Faber. Epistemische und technische Rationalität in Antike und Gegenwart; Festschrift für Jürgen Mittelstraß. Berlin: de Gruyter; 2005
The propagation of wave impact induced pressures into cracks and fissures
No full textRock cliffs and blockwork coastal structures often suffer a peculiar type of damage, whereby individual blocks are removed out of their location towards the sea. The location of damage suggests that breaking wave action is the main cause. It has been suggested that wave impact pressures travel into the water or air filled cracks and fissures of the structures, leading to large pressures acting inside of the structure or cliff and to the removal of blocks. This assumption was only recently confirmed for water filled cracks with a series of model tests at Queen's University Belfast. Real cracks in rock cliffs are, however, often only partially filled with water. A new experimental study, also conducted at Queen's University Belfast, revealed that wave impact generated pressures can ravel into both fully or partially water filled cracks or joints. In partially submerged cracks the pressure pulse was found to travel in the air, propagating fast and with little attenuation deep into the structure, signifying that partially filled cracks are potentially more dangerous for the integrity of the structure than completely water filled cracks. These pressure pulses may be the main cause for the seaward removal of blockwork in coastal engineering structures or of rock cliff material
Pressure transients and energy dissipation in liquid-liquid impacts
No full textIn or near some engineering structures, such as sea walls, breakwater caissons or stilling basins, a moving water mass can strike another water mass at rest close to the structure. Very little is known about the pressures generated by such water-water impacts, although it has recently been realized that such impacts may affect the stability or integrity of these structures. A series of model tests was conducted at Queen's University Belfast in order to establish whether or not fluid-fluid impact can generate high transient pressure pulses, and to investigate the characteristics of such pressures. It was found that fluid-fluid impacts can generate high impulsive pressures, and that these pressures propagate away from the impact zone. Larger water masses appeared to lose their compact shape while falling, and generated smaller (but longer lasting) impact pressures than the smaller masses. The experiments also showed that the water, even when at rest, retains a small amount of air in the form of microbubbles which reduces the speed of propagation of the compression wave dramatically. The energy contained in the pressure pulses was found to be small when compared with the total energy contained in the impacting masses
Knowledge and Control: On the Bearing of Epistemic Values in Applied Science
Full text linkCarrier M. Knowledge and Control: On the Bearing of Epistemic Values in Applied Science. In: Machamer P, Wolters G, eds. Science, Values and Objectivity. Pittsburgh-Konstanz series in the history and philosophy of science. Pittsburgh, Pa.: Univ. of Pittsburgh Pr. [u.a.]; 2004: 275-293
Wave effects on blockwork structures: numerical models
No full textTransient or fluctuating pressures, generated for example by a wave impact on a sea wall or a water jet plunging into a pool, have been shown to propagate into water filled cracks or fissures of structures and rock. Model studies revealed the characteristics of impact generated pressure pulses, which were observed to travel at very low speeds of 60–160 m/s and to attenuate, whereby higher frequencies were preferentially damped out. Other effects, such as reflection and dynamic amplification also indicated that the pulses constituted waves propagating through an elastic 2-phase medium consisting of water and a small amount of air. Based on these observations, concepts for a numerical model of pressure pulse propagation in water were developed and implemented. It was found that the numerical model approximates the physical model test results well, both in the linear and the non-linear range and including the transition from an initial steep pressure pulse to wave-like forms. The damping coefficient was found to be a constant, independent of the degree of aeration. The results from the numerical studies imply that, within very short time frames, water behaves like a visco-elastic solid rather than as a fluid
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