Gear Rattle during a start-up transient in a driveline equipped with a tuneable torsional Vibration Damper with Magneto-Rheological Elastomers

The paper reports a numerical investigation on the dynamic behaviour of a vehicle driveline, equipped with a Torsional Vibration Damper (TVD) based on Magneto-Rheological Elastomeric (MRE) spring elements, during the start-up transient considering an abrupt manoeuvre of clutch engagement. The TVD device consists of a flywheel and a damper disk, with interposed some elastomeric samples which react for relative angular displacements of the two disks. The dynamical parameters of the TVD can be properly tuned by varying the magnetic field surrounding the MRE springs to mitigate the torsional oscillations of the flywheel, causes of many undesired inconveniences as critical speeds or vibro-acoustic issues. The present study promotes the use of the MRE torsional vibration damper to reduce the annoying vibroacoustic phenomenon of “gear rattle” arising in the unloaded gear pairs of the gear box, during and after the rapid clutch engagement transients in the vehicle start-up phase and is conducted on a simplified automotive driveline equipped with a dry clutch. The possibility of quickly tuning the mechanical properties of the MRE-TVD, makes this device particularly eligible for suppressing the above disturbance, adapting to the various operative conditions of the automotive driveline. Results of the analysis, by the help of a Gear Rattle Index (GRI), demonstrate the effectiveness of the proposed device in reducing the vibroacoustic phenomenon during the transient phases of the vehicle start-up, until the vehicles speed conditions are reached.

Cyclic Behavior in the Fumaroles Output Detected by Direct Measurement of Temperature of the Ground

On the Island of Vulcano (Aeolian Archipelago, Italy) the temperatures of fumarole emissions, have ranged from about 700 °C to the boiling point. Since the end of the last eruption (1890 A.D.), many periods of increased heating of hydrothermal systems, underlying the La Fossa area have been identified, but an eruptive condition has not yet been reached. The time variation of the high temperature fumaroles has been tracked by the network of sensors located at a few discrete sites on the summit area of La Fossa cone. The same continuous monitoring network has been working for more than 30 years. The time series shows that a natural cyclic modulation has repeated after almost 20 years, and its periodicity yet has to be discussed and interpreted. The statistical approach and the spectral analysis could provide an objective evaluation to reveal the timing, intensity, and general significance of the thermodynamic perturbations that occurred in the hydrothermal circuits of La Fossa caldera, during the study period. The continuous monitoring data series avoid unrealistic interpolations and allow promptly recognizing changes, which perturb the hydrothermal circuits, highlighting—possibly in near real time—the transient phases of energy release from the different sources (hydrologic/magmatic).

Dynamic processes in transient phases during self-assembly of organic semiconductor thin films

Crystallization of organic semiconductor small molecules from solution proceeds in multiple steps. This study describes how asymmetric molecules lead to long-lived transient phases and their impact on carrier mobility for electronic devices.

EXTENDING CTF MODELING CAPABILITIES TO SFRs AND VALIDATION AGAINST SHRT TESTS

The utilization of liquid metals as coolants for fast reactors brings several economical and practical advantages that lead to a sustainable future for nuclear energy. Molten sodium is used as a coolant in Sodium Fast Reactors (SFRs). Sodium is relatively cheaper than other metal coolants. It requires lower pumping power, causes less neutron moderation and it is non-corrosive to the fuel cladding. The SFR hexagonal subassemblies are relatively smaller than Light Water Reactors (LWRs) subassemblies. The differences in the geometrical design of SFRs compared to LWRs lead to different physical behavior of the coolant. Several models and correlations particular to sodium were implemented in thermal-hydraulics (TH) computer codes in order to model the coolant behavior accurately. CTF is a subchannel TH code that was designed and validated for LWRs. In this work, the capabilities of the code were extended to SFRs by incorporating sodium coolant properties and correlations for friction factor, flow mixing coefficient and conduction heat transfer. The code was then validated against selected steady state data from the Experimental Breeder Reactor II Shutdown Heat Removal Tests SHRT-17 and SHRT-45R. CTF was used to simulate the instrumented subassemblies XX09 and XX10. The results demonstrate the capability of CTF to model SFRs. Code validation is currently being extended to the transient phases of the SHRT experiments.

Automatic Indexation of Turbofan Data to Identify Anomalous Behaviors

Flight data are now flowing in our databases. The fact is that we cannot analyze every single observation and we need a tool to automatically alert in case of unusual behavior and another tool to find similarities between parts of real aircraft flights. Our proposal is to systematically index the databases replacing each multivariate numerical signal acquired by the aircraft and the engine sensors by a sequence of labels. Each label should characterize a specific part of the signal such as a stationary phase or a transient phase. Stationary phases are summarized by snapshots made of statistics of the distribution parameters the multivariate signal and are easy to characterize. Transient phases are a more complex in a multivariate environment. This work apply a specific fast change detection algorithm to identify transient phases and an adaptive classification neural network to label each temporal behavior. However, as it seems natural to automatically separate standard flight phases like engine start, taxi, take-off, climb, etc. our goal is to identify different behaviors among those main classes. For example, we detect engines with slow thermal stabilization during the take-off and separate them from engines with fast thermal stabilization. We also separate hot engines during the climb phase to cold ones. The same sort of analysis is done on mechanical transfer as we may identify fast or slow crossing of specific vibration modes, etc. At the end of this segmentation and classification process, each multivariate signal is replaced by sequences of classes corresponding to context, rotation speed for example, and any endogenous observation like temperature or vibration. Then working on discrete data, it becomes easier to query the database for rare behaviors, usual behaviors, or to search some similarity with a specific engine observation. For example, looking at a specific temporal interval during a given flight it becomes possible to ask for flights and engines with similar behavior in the historic database.

Experimental and Numerical Analysis of Start-Up of a Capillary Pumped Loop for Terrestrial Applications

A study on the start-up phases of a capillary pumped loop for terrestrial application (CPLTA) is proposed in this paper. Experimental analysis and numerical modeling, using a one-dimensional spatial discretization model, based on thermohydraulic equations and solved by nodal network/electrical analogy, are presented to study the thermal and hydraulic behavior of the loop for methanol and n-pentane as working fluids, during start-up transient phases. The experimental observations are backed up by the numerical model to help the transient and steady analysis of this kind of loop. The precise numerical study allows to have a better understanding of the complicated phenomena happening during the start-up and to have a global view of the behavior of the capillary pumped loop for integrated power (CPLIP) during these phases. In this study, it will be also shown the influence of vapor line solid walls thermal inertia and its impact on the dynamic behavior and on the success of the start-up of the loop.