Abstract: The paper presented focuses on fatigue crack growth observation in the microstructure of magnesium alloy AZ 91D using finite element software ADINA. ADINA offers a wide range of capabilities based on reliable and efficient finite element procedures. For this reason, ADINA is often chosen for applications where reliability and safety is of critical importance in different industries such as biomedical, automotive, nuclear, forming, civil engineering, hi-tech and others, e.g., in the dynamic analysis of bridge structures – earthquake analysis ,in biomedical applications, in the design of nuclear reactors or in studies on safety. This work shows efficiency and good correlation between experimental and numerical results and verifies this program for its utilization in the field of fatigue endurance determination and evaluation.
Keywords: microstructure; modelling and simulation; material fatigue; experiments; cracks and defects; reliability and personnel security
Abstract: Wireless Ad-Hoc networks are collections of nodes that communicate without any fixed infrastructure. A critical problem in Ad-Hoc networks is finding an efficient and correct route between a source and a destination. The need for scalable and efficient protocols, along with the recent availability of small, inexpensive low-power positioning instruments justify adopting position-based routing protocols in mobile Ad-Hoc networks. This paper presents an overview of the existing Ad-Hoc routing protocols that make forwarding decisions based on the geographical position of a packet's destination. We also outline the main problems for this class of routing protocols. We conclude our findings by discussing opportunities for future research.
Keywords: position-based routing; location-aware routing; ad-hoc networks; wireless networks; routing protocols
Abstract: This paper proposes a novel hybrid active power filter (HAPF) topology based on the cascaded connection of the AC-side capacitor and the third-order LCL-filter, which has the advantage of the conventional hybrid filter and the LCL-filter in terms of reduced dclink voltage and better switching ripple attenuation. The robust deadbeat control law is derived for the current loop, with special emphasis on robustness analysis. The stability and robustness analysis under parameter variations are presented for the converter-side current tracking scheme and the grid-side current tracking scheme. It is found that the stability margins obtained from the converter-side current tracking control scheme are generally higher than those obtained from the grid-side current tracking scheme. However, the converter-side current tracking scheme is sensitive to the variation of the damping resistance, and it would impose additional parameter uncertainty on the control system and complicate the problem. Hence the grid-side current tracking scheme is implemented. The simulation results obtained from Matlab/Simulink are presented for verification, where the inductance variation and grid disturbance scenarios are also taken into consideration. The effectiveness of the proposed hybrid APF is substantially confirmed by the simulation and experimental results.
Keywords: power quality; harmonic estimation; active filter; hybrid; robustness analysis; digital signal processor (DSP)
Abstract: The paper deals with testing the coarse alignment algorithm for the inertial measurement unit ADIS16405 using a rotation platform. The ADIS16405 is the new sixdegree of freedom inertial measurement unit which is being produced by Analog Devices. The main goal of the paper is to describe the determination of the initial attitude of the inertial measurement unit with respect to the navigation frame as a referenced frame and to depict appropriate tests using a rotation platform. In this work the attitude is represented by the Euler angles (the roll, pitch and yaw angles). The tests were conducted using the INS/GNSS development kit which had been mounted on the rotation platform. The overall factual results are illustrated and correctness of the algorithm was definitely confirmed.
Keywords: alignment algorithm; attitude; inertial measurement unit; navigation
Abstract: This paper describes a study of the RHEED intensity change against temperature in case of GaAs and InAs surfaces. RHEED as a technique is a widely used monitoring method for observing molecular-beam-epitaxial (MBE) growth. The reconstruction and other changes of the surface can be investigated by observing the RHEED pattern. Both the static and the dynamic RHEED-s are very complex phenomena, but these effects can be used as versatile tools for in-situ monitoring of the growth of the epitaxial layer, in spite of the fact that we do not know much about the details of its nature. Our observations showed that the specular beam intensity of RHEED had changed with the change of the surface temperature. We investigated the changes of the GaAs and InAs (001) surfaces by using this effect. The change in intensity follows the observed surface reconstruction. This change in the RHEED intensity against temperature shows hysteretic properties, with a different character for each material. So far, the explanations for these phenomena were different in both cases. Here, we explain these hysteretic phenomena in general terms with the T(x) hyperbolic model for coupled hysteretic systems, which is applicable to both materials. Experimental results presented in the paper are in good agreement with the model predictions.
Keywords: RHEED; GaAs; InAs; hysteresis; surface reconstruction
Abstract: This paper presents the evaluation as well as the combined analytical and experimental identification (gray box identification) of a servo-valve torque motor as the directional valve applied in a pneumatic actuator. Based on analytical modelling, a simple linear parametric model with transfer function and block diagram is developed. Next, the static and dynamic characteristics of the torque motor are obtained from experimental observations. The characteristics confirm the desired linear behaviour of the torque motor. Hence, linearized coefficients from a best curve fitting of static characteristics can be derived. Classical methods of identification are applied on the frequency and step responses obtained from a set of tests on the torque motor. Obtained tests results based on parsimony principle and model order of analytical investigations are then implemented to derive the best identified transfer function to describe the performance of the servo-valve torque motor. Design parameters are estimated with the comparison of the experimental and analytical models. These parameters can be implemented with acceptable accuracy for servo control studies of pneumatic actuators.
Keywords: pneumatic actuator; servo-valve; limited angle torque motor; gray box modeling
Abstract: The effects of the initial state of the samples and the saturation evaluated in terms of Skempton's pore pressure B on the behavior of Chlef sand were studied in this article. For this purpose, the results of two series of undrained monotonic compression tests on medium dense sand (RD= 50%) are presented. In the first test series, the influence of the specimens’ fabric and confining pressure is studied. Triaxial specimens containing Chlef sand with 0.5% non plastic silt content were isotropically consolidated to 50 kPa, 100 kPa and 200 kPa. The specimens were formed using both dry funnel pluviation and wet deposition. The results indicate that the confining pressure and the method of sample preparation have a significant influence on the liquefaction resistance of the sand. In the second series of tests, the saturation influence on the resistance to the sand liquefaction is realized on samples at an effective stress of 100 kPa for Skempton's pore pressure coefficient varying between 32% and 90%. It was found that an increase in the Skempton' S pore pressure coefficient B reduces the soil dilatancy and amplifies the phase of contractancy.
Keywords: liquefaction; sand; dry funnel pluviation; wet deposition; confining pressure; pore pressure; compression; undrained; saturation
Abstract: For any fuzzy logic application the first and foremost task is to select the optimum number and shape of membership functions such as bell shape, singleton, triangular, etc. for fuzzification; then it is equally essential to select the appropriate defuzzification method, such as COG, COM, MOM, etc. The sampling rate to execute the given command is another important parameter. If these three parameters are optimally selected then the output response of motion controller will have a shorter rise time, less settling time, minimized overshoots/undershoots and negligible steady state error. Hence, the systematic study on selection of number and shape of membership function, selection of defuzzification methods and sampling time for speed control of PMDC micro motor is studied experimentally by applying LabVIEW software. The experimental results reveal that 7 numbers of triangular membership functions, COG defuzzification method and 1 millisecond (msec) sampling rate for labVIEW program execution are the optimum parameters for motion control.
Keywords: fuzzy logic; pmdc motor; labVIEW