Search results

This study aims to simulate and test the performance of a transmitting and receiving capacitive micro-machined ultrasonic transducer (CMUT). Aimed at detecting demand of the CMUT, a matched integrated adjustment circuit was designed through analyzing processing methods of transducer’s weak echo signal.

Based on the analysis of CMUT array structure and work principle, the CMUT units are designed and the dynamic performance analysis of SIMULINK is given according to the demand of underwater detecting. A transceiver isolation circuit is used to make transmission mode and receiving mode separate. A detection circuit is designed based on the transimpedance amplifier to achieve extraction of high-frequency and weak signal.

Through experimentation, the effectiveness of the CMUT performance simulation and the transceiver integrated adjustment circuit were verified. In addition, the test showed that CMUT with 400 kHz frequency has wider bandwidth and better dynamic characteristics than other similar transducers.

This paper provides a theoretical basis and design reference for the development and application of CMUT technology.

The Ferritector model 1581 features a magneto resistor transducer and the active elements comprise a single integrated‐circuit amplifier mounted with other units on a printed circuit board. It measures the ferrite content of stainless steel with particular reference to the control of weld quality and possible degradation of neighbouring regions. It is check calibrated with plastic films interposed between the probe tip and a mild steel reference plate.

The purpose of this computational fluid dynamics (CFD) study is to give insight about the influence of the piston bowl geometry and the fuel ignition features on the resonance of direct injection diesel engines combustion chambers in order to provide support to the experimental findings on combustion noise.

The resonance due to the burned gases oscillations in a diesel combustion chamber is caused by the sudden rise in pressure due to the initial ignition of the air‐fuel mixture, and leads to the resonance noise. In the CFD study presented here the excitation source is represented by imposing locally in a small area (excitation zone) the pressure and temperature gradients of the start of combustion. The CFD approach is first validated against the acoustic modal theory. A parametric study representing different ignition conditions is then performed with a real bowl geometry.

The solutions obtained are analysed in terms of the energy of resonance (ER) and the response in the frequency domain. It was found that the response in frequency only varies with the diameter of the bowl, while the ER varies significantly in function of the injection conditions.

These first conclusions need to be verified on the one hand by taking into account the piston motion, and, on the other hand, by modelling in a more realistic way the combustion excitation.

This CFD study has brought some insight into the flow phenomena that affect the resonance modes of a combustion chamber.

This CFD study uses a novel methodology to model the effect of the combustion excitation on the resonance modes of a combustion chamber.

Meyer Waxman and William Chen, staff research scientists of the Institute for Basic Standards, US National Bureau of Standards, have recently developed a new pressure transducer that enables the accurate measurement of the pressure of corrosive gases over wide temperature and pressure ranges. The research was supported in part by the US Atomic Energy Commission.

This study aims to compare cavitation shapes between the simulating test rig and the engines to strengthen the findings that were first observed in the simplified experiments. Different forms of cavitation were identified, and their shape and size (length and width) were dictated from reciprocating speed and viscosity of the lubricant. Cavitation degrades performance in engineering applications and its effect is that it alters the oil film pressure.

Lubricant formulations were used for parametric study as well as different operating testing parameters in a simulating test rig and single cylinder engines with visualisation windows. An algorithm was used for extracting cavitation data from imaging, and comparison was made.

Similar phenomena at the simulating test rig and the engine were investigated and compared. The effect of different operating conditions was assessed along with the variations produced from the parametric lubricant study.

Engine results are limited due to manufacturing difficulties of visualisation windows and oil starvation. Firing tests are another difficult challenge as the modified section pressure is under more pressure and the window view is affected by combustion process. Limited pictures can be captured before cleaning is required. A lubricant manufacturer has to provide data regarding the chemistry of the lubricants.

The effect of cavitation in piston ring lubrication along with variable operating and lubricant parameters is further studied with quantification of cavitation results through image processing. These forms of cavities are affected by lubricant properties and operating conditions. A link between viscosity, cavitation, shear thinning properties, oil film thickness (OFT) and friction is given.

This paper gives a bibliographical review of the finite element methods (FEMs) applied to the analysis of ceramics and glass materials. The bibliography at the end of the paper contains references to papers, conference proceedings and theses/dissertations on the subject that were published between 1977‐1998. The following topics are included: ceramics – material and mechanical properties in general, ceramic coatings and joining problems, ceramic composites, ferrites, piezoceramics, ceramic tools and machining, material processing simulations, fracture mechanics and damage, applications of ceramic/composites in engineering; glass – material and mechanical properties in general, glass fiber composites, material processing simulations, fracture mechanics and damage, and applications of glasses in engineering.

NOT perhaps the most vintage of Farnboroughs from the point of view of new aircraft and new technology, but undoubtedly one of the most successful in relation to the business done. Some fifteen major orders worth over £32½ million were announced, bringing the total order book for the industry this year to more than £782 million already. This exceeds by a handsome margin the new business won by the industry in any nine‐month period in the past, and it is expected that by the end of the year orders worth well over £800 million will have been received. Highlights of the new British hardware on show were the Hawker Siddeley Nimrod and production Harriers on the military side; the B.A.C. One‐Eleven 500, the Handley Page Jetstream, the Garrett‐engined Short Skyvan, and the Beagle Pups showed the resurgence of the industry's civil interests. The number of foreign aircraft that appeared, sponsored in the main by Rolls‐Royce, bore witness to the strength of Britain's aero engine and aircraft equipment industry, and further evidence of this was found in the exhibition proper with many examples of major items of equipment having been adopted for overseas markets. The overall impression at Farnborough was a new‐found confidence in the future of the industry exemplified by a more aggressive and effective export sales policy that has already proved our ability to deliver the goods. It is not possible to cover all the exhibits shown at Farnborough, but the report following describes many of the interesting items.

The purpose of this paper is to provide a new computational method based on the polynomial chaos (PC) expansion to identify the uncertain parameters of load sensing proportional valve (LSPV), which is commonly used to improve the efficiency of brake system in heavy truck.

For this investigation, the mathematic model of LSPV is constructed in the form of state space equation. Then the estimation process is implemented relying on the experimental measurements. With the coefficients of the PC expansion obtained by the numerical implementation, the output observation function can be transformed into a linear and time-invariant form. The uncertain parameter recursively update functions based on Newton method can therefore be derived fit for computer calculation. To improve the estimation accuracy and stability, the Newton method is modified by employing the acceptance probability to escape from the local minima during the estimation process.

The accuracy and effectiveness of the proposed parameter estimation method are confirmed by model validation compared with other estimation methods. Meanwhile, the influence of measurement noise on the robustness of the estimation methods is taken into consideration, and it is shown that the estimation approach developed in this paper could achieve impressive stability without compromising the convergence speed and accuracy too much.

The model of LSPV is originally developed in this paper, and then the authors propose a novel effective strategy for recursively estimating uncertain parameters of complicate pneumatic system based on the PC theory.

The test procedure for characterizing the tribological behavior of lubricants and materials for the system “piston ring/cylinder liner” outside of engines is now operational and validated. The test parameters presented in this paper (F_N=50 N; v=0.3 m/s, s=24 km) may act only as an indicator and should be used to the tasks regarded. It allows the check prior expensive engine testing, if a tribomaterial, tribocouple or new lubricant will reach a satisfactory engine performance. The introduction of piston ring segments and cylinder liner as specimen into the test rig as well as the volumetric wear determined by means of stylus profilometry represented a big step forward in order to increase the transferability of “tribotests” to engine tests on an acceptable level.

Ducted Propulsors have been designed and developed specifically for piston engine powered General Aviation aircraft. This class of aircraft is defined as having a gross weight of less than 12 500 lbs. The main purpose of the development is to reduce the noise level. General Aviation aircraft were excluded from the original plans to control aircraft noise, but about four years ago legislation was proposed and subsequently introduced to control noise of small aircraft.