827 research outputs found
Synthesis of Sine-on-Random vibration profiles for accelerated life tests based on fatigue damage spectrum equivalence
No full textIn many real life environments, mechanical and electronic systems are subjected to vibrations that may induce dynamic loads and potentially lead to an early failure due to fatigue damage. Thus, qualification tests by means of shakers are advisable for the most critical components in order to verify their durability throughout the entire life cycle. Nowadays the trend is to tailor the qualification tests according to the specific application of the tested component, considering the measured field data as reference to set up the experimental campaign, for example through the so called “Mission Synthesis” methodology. One of the main issues is to define the excitation profiles for the tests, that must have, besides the (potentially scaled) frequency content, also the same damage potential of the field data despite being applied for a limited duration. With this target, the current procedures generally provide the test profile as a stationary random vibration specified by a Power Spectral Density (PSD). In certain applications this output may prove inadequate to represent the nature of the reference signal, and the procedure could result in an unrealistic qualification test. For instance when a rotating part is present in the system the component under analysis may be subjected to Sine-on-Random (SoR) vibrations, namely excitations composed of sinusoidal contributions superimposed to random vibrations. In this case, the synthesized test profile should preserve not only the induced fatigue damage but also the deterministic components of the environmental vibration. In this work, the potential advantages of a novel procedure to synthesize SoR profiles instead of PSDs for qualification tests are presented and supported by the results of an experimental campaign
Fatigue Damage Spectrum calculation in a Mission Synthesis procedure for Sine-on-Random excitations
Get PDFIn many real-life environments, certain mechanical and electronic components may be subjected to Sine-on-Random vibrations, i.e. excitations composed of random vibrations superimposed on deterministic (sinusoidal) contributions, in particular sine tones due to some rotating parts of the system (e.g. helicopters, engine-mounted components,...). These components must be designed to withstand the fatigue damage induced by the "composed" vibration environment, and qualification tests are advisable for the most critical ones. In the case of an accelerated qualification test, a proper test tailoring which starts from the real environment (measured vibration signals) and which preserves not only the accumulated fatigue damage but also the "nature" of the excitation (i.e. sinusoidal components plus random process) is important to obtain reliable results. In this paper, the classic time domain approach is taken as a reference for the comparison of different methods for the Fatigue Damage Spectrum (FDS) calculation in case of Sine-on-Random vibration environments. Then, a methodology to compute a Sine-on-Random specification based on a mission FDS is proposed
Smart localization of microphones inside an automotive cabin
No full textInterior sound measurements play an important role in vehicle development and refinement. Sometimes hundreds of microphones are installed in an automotive cabin. During test preparation and execution, a lot of time is spent in determining the microphone positions and in tracking cables to the data acquisition channel. A smart acoustic localization approach is presented to automate this process and to realize considerable time gains. It is based on estimating the distance between a microphone and (at least 4) sources by acoustic time-of-arrival measurements, combined with novel algorithms that cope with reflections and non-line-of-sight issues. The method will be illustrated using in-vehicle measurements
Smart localization of microphones inside an automotive cabin
No full textInterior sound measurements play an important role in vehicle development and refinement. Sometimes hundreds of microphones are installed in an automotive cabin. During test preparation and execution, a lot of time is spent in determining the microphone positions and in tracking cables to the data acquisition channel. A smart acoustic localization approach is presented to automate this process and to realize considerable time gains. It is based on estimating the distance between a microphone and (at least 4) sources by acoustic time-of-arrival measurements, combined with novel algorithms that cope with reflections and non-line-of-sight issues. The method will be illustrated using in-vehicle measurements
Book Review: Die Bram Fischer Wals
No full textBook Title: Die Bram Fischer WalsBook Author: Harry Kalmer Johannesburg: Wits University Press, 2016. 67pp. ISBN 978-1-77614-005-3
Shaker testing simulation of non-gaussian random excitations with the fatigue damage spectrum as a criterion of mission signal synthesis.
No full textExperimental simulations of random excitations are nowadays performed digitally by applying the Inverse Fast Fourier Transform (IFFT) to the desired Power Spectral Density (PSD) profile, in combination with randomized IFFT phases. However, the excitations generated in this way will always have a Gaussian probability distribution, whereas real-life random excitations are typically non-Gaussian. For example, in the case of land transportation some distinctive peaks will occur which exceed the average level of vehicle vibration. The sta-tistical parameter known as kurtosis can characterize this feature and could be controlled in experimental simulations in addition to the PSD. The so-called “kurtosis control” can be achieved by special phase manipulation instead of selecting the phases randomly. By increasing the kurtosis, it is furthermore also possible to obtain an accelerated qualification test, whereby the time-to-failure (TTF) is decreased in a controlled manner. It is known that the response of a lightly-damped linear system is closer to Gaussian than the applied excitation. Therefore, in order to increase the response kurtosis in an accelerated test, the kurtosis control method must be able to effectively generate extra kurtosis. In this work a method was used which indeed achieves a high excitation kurtosis, which moreover passes into the re-sponse of the structure. According to the Fatigue Damage Spectrum (FDS) model, a single-degree-of-freedom system was hereby considered in order to calculate the structural response. Furthermore, the rainflow counting procedure and the Miner damage accumulation rule were employed to predict relative TTFs for operational excitation and accelerated test mission. Finally, the considered method of non-Gaussian shaker testing simulation was also advanced from kurtosis control to direct application of the FDS as a criterion for mission signal synthesis. An extensive experimental campaign was carried out, where an example of a real-life vibration excitation measured on the cabin floor of a car was considered. Shaker testing was performed for a cantilevered test specimen subjected to various simulated Gaussian, non-Gaussian, accelerated non-Gaussian, and real road excitations
Bram Stoker and the stage: reviews, reminiscences, essays and fiction
No full textThough best known as the author of Dracula (1897) Bram Stoker had a successful career in the theatre. This collection brings together all Stoker’s theatrical reviews from Dublin’s Evening Mail, his published essays and interviews on the theatre, selections from Reminiscences of Henry Irving (1906) and a fictional work on the theatre
Postcolonial rewritings of Bram Stoker´s Dracula: Mudrooro's vampire trilogy
No full textIndigenous-Australian fiction has experimented with subgenres of the Fantastic in various ways to secure an empowering location from which to address post/colonial dispossession. In the mid-1990s, the Australian writer and critic Mudrooroo, formerly known as Colin Johnson, proposed Maban Reality as a genre denomination for fiction which introduces the reader to the powerful and empowering universe of the Aboriginal maban or shaman, also known as the Dreaming. Mudrooroo's coining of Maban Reality was a way of establishing an Australian variant of Magic Realism which defied a European epistemology of the universe, engaging and enabling Dreamtime spirituality as a solid pillar of Aboriginal reality. Mudrooroo had already experimented with a postcolonial reversal of the Gothic, a dark version of the Fantastic, in the first of his Tasmanian quintet, Dr Wooreddy's Prescription for Enduring the Ending of the World (1983), but left its gloomy resignation to a dire Indigenous fate under colonial rule behind for the upbeat Master of the Ghost Dreaming (1993). Yet, as the result of a deep personal crisis¿believed not to have an Aboriginal bloodline, in the mid-1990s he was barred from the tribal affiliation he had long claimed¿Mudrooroo resorted to the gloominess of the postcolonial Gothic again in a vampire trilogy to reflect on the devastating impact of colonisation on Australian identity at large. This essay comments on the ways in which he has reflected on the present state of Australianness by rewriting Bram Stoker's Dracula
Postcolonial Rewritings of Bram Stoker´s Dracula: Mudrooroo’s Vampire Trilogy
Get PDFIndigenous-Australian fiction has experimented with subgenres of the Fantastic in various ways to secure an empowering location from which to address post/colonial dispossession. In the mid-1990s, the Australian writer and critic Mudrooroo, formerly known as Colin Johnson, proposed Maban Reality as a genre denomination for fiction which introduces the reader to the powerful and empowering universe of the Aboriginal maban or shaman, also known as the Dreaming. Mudrooroo’s coining of Maban Reality was a way of establishing an Australian variant of Magic Realism which defied a European epistemology of the universe, engaging and enabling Dreamtime spirituality as a solid pillar of Aboriginal reality. Mudrooroo had already experimented with a postcolonial reversal of the Gothic, a dark version of the Fantastic, in the first of his Tasmanian quintet, Dr Wooreddy’s Prescription for Enduring the Ending of the World (1983), but left its gloomy resignation to a dire Indigenous fate under colonial rule behind for the upbeat Master of the Ghost Dreaming (1993). Yet, as the result of a deep personal crisis—believed not to have an Aboriginal bloodline, in the mid-1990s he was barred from the tribal affiliation he had long claimed—Mudrooroo resorted to the gloominess of the postcolonial Gothic again in a vampire trilogy to reflect on the devastating impact of colonisation on Australian identity at large. This essay comments on the ways in which he has reflected on the present state of Australianness by rewriting Bram Stoker’s Dracula
Postcolonial rewritings of Bram Stoker´s Dracula: Mudrooro's vampire trilogy
No full textIndigenous-Australian fiction has experimented with subgenres of the Fantastic in various ways to secure an empowering location from which to address post/colonial dispossession. In the mid-1990s, the Australian writer and critic Mudrooroo, formerly known as Colin Johnson, proposed Maban Reality as a genre denomination for fiction which introduces the reader to the powerful and empowering universe of the Aboriginal maban or shaman, also known as the Dreaming. Mudrooroo's coining of Maban Reality was a way of establishing an Australian variant of Magic Realism which defied a European epistemology of the universe, engaging and enabling Dreamtime spirituality as a solid pillar of Aboriginal reality. Mudrooroo had already experimented with a postcolonial reversal of the Gothic, a dark version of the Fantastic, in the first of his Tasmanian quintet, Dr Wooreddy's Prescription for Enduring the Ending of the World (1983), but left its gloomy resignation to a dire Indigenous fate under colonial rule behind for the upbeat Master of the Ghost Dreaming (1993). Yet, as the result of a deep personal crisis¿believed not to have an Aboriginal bloodline, in the mid-1990s he was barred from the tribal affiliation he had long claimed¿Mudrooroo resorted to the gloominess of the postcolonial Gothic again in a vampire trilogy to reflect on the devastating impact of colonisation on Australian identity at large. This essay comments on the ways in which he has reflected on the present state of Australianness by rewriting Bram Stoker's Dracula
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