Developing tropical cyclone simulation in Oman

Hydrodynamic

Effects of acute pre-treatment with ethanolamine on isoprenalineinduced myocardial infarction in adult Wistar rats

Ethanolamine (Etn), a biogenic amine, protects isolated hearts against MI, but its effects in vivo are unknown. In this study, we investigated the effects of Etn pretreatment on isoprenaline (ISO)-induced MI in vivo. Wistar rats were treated with either Etn (10mg.kg-1, i.p.) or saline, prior to either ISO (67mg.kg-1, s.c.) or saline. Haemodynamic- and electrocardiographic parameters were recorded under anaesthesia, 24 hours post-treatment with ISO. Infarct sizes were determined by triphenyltetrazolium chloride staining. Oxidative stress plasma parameters, conjugated dienes (CD) and thio-barbituric acid reactive substances (TBARS), were measured by spectrophotometric analysis. Etn decreased ISO-induced pathological Q-waves, but had no effect on ISO-induced low-voltage electrocardiogram. In addition, Etn decreased overall mortality induced by ISO treatment. However, Etn did not prevent ISO-induced infarction or the systolic- and diastolic hypotensive effects. Etn also enhanced the ISO-induced increase in heart-to-body weight ratio, and reversed the decrease in lungs-to-body weight ratio. Neither ISO nor Etn altered CD or TBARS. These results suggest that, despite a tendency to modulate cardiac electrical activity, Etn did not prevent ISO-induced MI or myocardial dysfunction in vivo

Lag effects in morphodynamic modelling of engineering impacts

This paper details the extension of the sediment transport and morphology model SISYPHE to include a lag term within the bed exchange source term of the, depth-averaged, continuity of sediment concentration equation. This lag term represents the time it takes for a sediment concentration profile to adapt to spatial or temporal changes in the flow. The inclusion of a lag term means that the settling velocity is no longer the only scaling factor for the exchange of sediment between the water and the bed. The modified sediment transport and morphodynamics model is tested against field data from the Thames estuary (UK) and on the morphodynamic development of a dredged trench in flume experiments. It is illustrated that the lag factor introduced is essential to model the sediment transport and morphodynamics, especially when considering engineered situations, where the bed is out of equilibrium with the flow conditions. Moreover, with this lag factor included, there is evidence that SISYPHE can be used for morphodynamic modeling of engineered situations

Range Vegetation Response to Burning Thicketized Live Oak Savannah.

16 p

Modelling sediment transport with hysteresis effects

This paper details the extension of the sediment transport and morphology model SISYPHE 2D to include a lag term within the bed exchange source term of the, depthaveraged, continuity of sediment concentration equation. This lag term represents the time it takes for a sediment concentration profile to adapt to spatial or temporal changes in the flow. The inclusion of a lag term means that the settling velocity is no longer the only scaling factor for the exchange of sediment between the water and the bed. The newly modified SISYPHE 2D is tested against field data from the Thames estuary (UK), flume experiments on a dredged trench and a hypothetical channel widening. It is illustrated that the lag factor introduced into SISYPHE 2D is essential to model the sediment transport and morphodynamics, especially when considering engineered situations, where the bed is out of equilibrium with the flow conditions. Moreover, with this lag factor included, there is evidence that SISYPHE 2D can be used for (short term)morphodynamic modeling of engineered situations

The effective bandwidth problem revisited

The paper studies a single-server queueing system with autonomous service and $\ell$ priority classes. Arrival and departure processes are governed by marked point processes. There are $\ell$ buffers corresponding to priority classes, and upon arrival a unit of the $k$th priority class occupies a place in the $k$th buffer. Let $N^{(k)}$, $k=1,2,...,\ell$ denote the quota for the total $k$th buffer content. The values $N^{(k)}$ are assumed to be large, and queueing systems both with finite and infinite buffers are studied. In the case of a system with finite buffers, the values $N^{(k)}$ characterize buffer capacities. The paper discusses a circle of problems related to optimization of performance measures associated with overflowing the quota of buffer contents in particular buffers models. Our approach to this problem is new, and the presentation of our results is simple and clear for real applications.Comment: 29 pages, 11pt, Final version, that will be published as is in Stochastic Model

A study on torsional vibration attenuation in automotive drivetrains using absorbers with smooth and non-smooth nonlinearities

The automotive industry is predominantly driven by legislations on stringent emissions. This has led to the introduction of downsized engines, incorporating turbocharging to maintain output power. As downsized engines have higher combustion pressures, the resulting torsional oscillations (engine order vibrations) are of broadband nature with an increasing severity, which affect noise and vibration response of drive train system. Palliative devices, such as clutch pre-dampers and dual mass flywheel have been used to mitigate the effect of transmitted engine torsional oscillations. Nevertheless, the effectiveness of these palliative measures is confined to a narrow band of response frequencies. Studying nonlinear targeted energy transfers is a promising approach to study vibration mitigation within a broader range of frequencies, using nonlinear vibration absorbers (or nonlinear energy sinks – NESs). These devices would either redistribute vibration energy within the modal space of the primary structure thus dissipating the vibrational energy more efficiently through structural damping, or passively absorb and locally dissipate a part of this energy (in a nearly irreversible manner) from the primary structure . The absence of a linear resonance frequency of an NES, enables its broadband operation (in contrast to the narrowband operation of current linear tuned mass dampers). Parametric studies are reported to determine the effectiveness of various smooth or non-smooth nonlinear stiffness characteristics of such absorbers. A reduced drivetrain model, incorporating single and multiple absorber attachments is used and comparison of the predictions to numerical integrations proves its efficacy

Damping Effects Introduced by a Nonlinear Vibration Absorber in Automotive Drivelines at Idle Engine Speeds

Legislation on vehicle emissions and the requirements for fuel efficiency are currently the key development driving factors in the automotive industry. Research activities to comply with these targets point to engine downsizing and new boosting technologies, which have adverse effects on the NVH performance, durability and component life. As a consequence of engine downsizing, substantial torsional oscillations are generated due to high combustion pressures. Meanwhile, to attenuate torsional vibrations, the manufacturers have implemented absorbers that are tuned to certain frequency ranges, including clutch dampers, Dual Mass Flywheel (DMF) and centrifugal pendulum dampers. These devices add mass/inertia to the system, potentially introducing negative effects on other vehicle attributes, such as weight, driving performance and gear shiftability. This paper provides a study of torsional damping effects of nonlinear vibration absorbers on drivetrain NVH refinement by attenuating torsional oscillations at the idling engine speeds. The nonlinear absorber concept presented operates on the principle of Targeted Energy Transfer (TET), whereby the energy excess (vibration) from a donor (primary powertrain system) is transferred to a receiver (nonlinear absorber) in a nearly irreversible manner. Thereafter, the received energy can be absorbed, dissipated, or redistributed. This potentially allows the absorber to operate over a broadband frequency range, whilst being light and compact, which is ideal for automotive powertrains. In the present work, simulations are performed using an automotive drivetrain (subsystem) model with a nonlinear absorber. The damping content of the absorber is varied to study its effect on the attenuation of torsional oscillations

On the effect of multiple parallel nonlinear absorbers in palliation of torsional response of automotive drivetrain

Torsional vibrations transmitted from the engine to the drivetrain system induce a plethora of noise, vibration and harshness (NVH) concerns, such a transmission gear rattle and clutch in-cycle vibration, to name but a few. The main elements of these oscillations are variations in the inertial imbalance and the constituents of combustion power torque, collectively referred to as engine order vibration. To attenuate the effect of these transmitted vibrations and their oscillatory effects in the drive train system, a host of palliative measures are employed in practice, such as clutch pre-dampers, slipping discs, dual mass flywheel and others, all of which operate effectively over a narrow band of frequencies and have various unintended repercussions. These include increased powertrain inertia, installation package space and cost. This paper presents a numerical study of the use of multiple Nonlinear Energy Sinks (NES) as a means of attenuating the torsional oscillations for an extended frequency range and under transient vehicle manoeuvres. Frequency–Energy Plots (FEP) are used to obtain the nonlinear absorber parameters for multiple NES coupled in parallel to the clutch disc of a typical drivetrain configuration. The results obtained show significant reduction in the oscillations of the transmission input shaft, effective over a broad range of response frequencies. It is also noted that the targeted reduction of the acceleration amplitude of the input shaft requires significantly lower NES inertia, compared with the existing palliative measures