INVESTIGATION OF AUTOMOTIVE CREEP GROAN NOISE WITH A DISTRIBUTED-SOURCE EXCITATION TECHNIQUE

Creep groan is a high-intensity, low-frequency noise and vibration problem that affects road vehicles at very low speeds. It usually persists for short periods of time, but a “skilled” driver can deliberately make it last several seconds by tuning the force exerted on the brake pedal. The original cause is considered to be a self-induced vibration of the brake components, due to the friction material characteristics that make the system prone to a stick-slip behaviour. No clear evidence upon the creep groan and how it is perceived inside the passenger cockpit has yet been analyzed in the literature and no formal methods are yet available for its analysis. The present study focuses on the transmission of the vibration from the brake component regions to the ears of the vehicle occupants. Characterization of the calliper acceleration and noise inside the cockpit are described for a test vehicle. Distributed-source noise excitation via the standard vehicle hi-fi system is proposed as a practical but less rigorous particular application of the exact reciprocity method. Virtual groan (in which sound power is delivered by means of a loudspeaker) dismisses the airbone path and shows that the phenomenon is structure-borne. On the examined vehicle, front brakes contribute more strongly than rear. Groan frequency close to cavity acoustic resonance constitutes the worst case scenario, and has to be avoided.     

MRCISD calculations of the six lowest valence states of I2 −

Potential curves for the four Hund's case (a) basis electronic states (²Σ, ²Π_g, ²Π_u, and ²Σ⁺) correlating with the I(²P_u) + I^?(¹S_g) dissociation limit have been calculated at the MRCISD level of theory using an all-electron double-zeta basis set augmented with an extensive set of polarization and diffuse functions complete through i angular momentum functions. Transition moments for the dipole allowed transitions between these states are determined as a function of internuclear separation. The four Hund's case (a) curves are used to determine the six Hund's case (c) potential curves which arise when spin-orbit coupling is considered. The rovibrational eigenvalues for each of these six states are determined numerically, and standard spectroscopic constants are determined by fitting the energy of these levels to a Duham series. The results are compared with available experimental and theoretical information.     

Modelling maintenance practice of production plant using the delay-time concept

In this paper we present a study carried out for a copper productsmanufacturing company, developing and applying the delay-timemodelling technique to model and thus optimize preventive maintenance(PM) of the plant. A key machine in the plant is used to illustratethe modelling process and management reaction. The parameter values of the process by which faults arise andof the delay-time distribution are estimated from maintenancerecord data of failures and faults found at PM, using the methodof maximum likelihood. A test of the model fit to data is carriedout. Based upon the estimated model parameters and the failuredelay time, an inspection model is proposed to describe therelationship between the total downtime and the PM interval.     

Collisionless Flow in Vacuum Traps

Molecules stream in collisionless flow out of a reservoir intoan axially symmetric tube consisting of two equal and oppositelyinclined conical frustra—a shape used in industrial vacuumtraps. In the general case there is a baffle in the centre ofthe tube. Some of the molecules strike the wall of the tube,some the baffle, and are reflected; eventually they either flyback into the reservoir or escape out of the tube into the vacuumbeyond. Other particles stream directly from the reservoir intothe vacuum without any collisions with a surface. The impact density of molecules along the wall in the steadystate is determined by a system of integral equations, fourin all when the baffle is present, otherwise two. These numberscan be reduced by half by utilizing certain combinations ofthe equations, suggested by the physical system, that yieldanalytical relations between the impact densities. The remainingintegral equations are solved numerically. One of the kernelshas an indeterminacy corresponding to the kink in the longitudinalcross-section of the tube, but the existence and uniquenessof the solution is established by analytical means. The resultsof calculations of the molecular impact density on the surfacesand the conductance of the tube with baffle for a number oftypical systems are given in graphical form.     

Two-stage and Three-stage Diagonally Implicit Runge-Kutta Nystrom Methods of Orders Three and Four

We investigate the existence of two-stage and three-stage R-stable,P-stable, RL-stable, and dispersively enhanced diagonally implicitRunge-Kutta Nyström methods of orders three and four. Wefirst show that a one-parameter family of two-stage third-orderR-stable diagonally implicit methods exists, and that theirdispersive order is at most four. From this we show that two-stagefourth-order R-stable, and third-order P-stable and RL-stablediagonally implicit methods do not exist. Next we show a two-parameterfamily of three-stage fourth-order R-stable diagonally implicitmethods exists with dispersive order at most four, and thatthis family contains a one-parameter family of P-stable methodsand a unique RL-stable. We also show that a one-parameter familyof fourth-order diagonally implicit methods with dispersiveorder at least six exists, and that they are not R-stable. Wepresent third- and fourth-order R-stable and P-stable methodswith small principal truncation coefficients and discuss howthese methods might be implemented in an efficient integrator.     

The delay-time modelling of preventive maintenance of plant given limited PM data and Selective repair at PM

This paper presents a maintenance-modelling case study of aplant manufacturing brake linings. A delay–time modelis developed and applied to model and optimize preventive maintenance(PM). A key subsystem in the plant is used to illustrate themodelling process and management reaction. Defects identifiedat PM may not all be removed. This incomplete response to PMis a feature which has not been modelled before. The parametervalues of the delay-time process are estimated from objectivedata from maintenance records of failures, using the methodof maximum likelihood. This is aided by a theorem extendingresults on the NHPP arival rate of failures in a perfect-inspectioncase to the non-perfect-inspection case. Problems of parameterestimation given inadequate data collected at PMs are discussed,and the necessity to augment objective data with subjectiveassessments highlighted. Based upon the estimated model parametersand delay-time distribution, an inspection model is constructedto describe the relationship between the total unit downtimeand the PM interval. The response of management is discussed.