Experimental study of pitch damping in a coaxial model helicopter

Small helicopters are known to have poor rotor damping in pitch and roll and mostly need stabilizers to improve the damping to provide sufficient flying stability. An experimental investigation was carried out to study pitch damping in a model coaxial helicopter fixed with a Bell stabilizer bar to elucidate the effects of the design of a fly-bar. High speed photography was used to observe the motion of the tethered helicopter, subjected to a step change in the shaft angle. The motion of the fly-bar, the upper and lower rotor blades and the shaft were analyzed to obtain the response. The inertia of the fly-bar was varied by replacing the weights made of different materials, namely, aluminum, steel and tungsten carbide. The videos were analyzed to obtain relevant response parameters such as shaft rotation velocity (co) and the relative displacement of rotor tip path plane (8 T). It was found that the lag of the top rotor, to which the fly-bar was connected, systematically increased with the increase of the fly-bar moment of inertia and appeared to follow a parabolic relation. For low fly-bar weights, the value of the parameter 8/co matched with the theoretical expectation given by 16/y £1 The experimental method developed can be used to assess the pitch stability of small helicopters under development such as the Helitrike being developed at NAL

Comparison of Passive Damping based LCL Filter Design Methods for Grid-connected Voltage Source Converters

Distributed generators are typically interfaced to the grid via power electronic converters that are usually operated in pulse width modulation mode. This results in undesirable higher-order harmonics in currents and voltages that deteriorate the power quality. In order to mitigate these harmonics, a filter is usually connected at the output of the converter before it is interfaced to the grid. The most commonly adopted filter is the LCL filter. This paper analyses the performance of different methods proposed in the literature to design passive LCL filters for a 3- f grid-connected voltage source converter. Various filter design techniques are tested for their compliance with the standards IEEE 519-2014 and IEEE 1547-2018. Further, comparison is carried out in terms of essential system metrics such as reactive power requirement, power factor, and the voltage drop across the filter. The performance of various filter design approaches is analyzed using simulation studies on different distributed generator configurations. © 2020 IEEE

Analytical and experimental studies on ballistic impact behavior of 2D woven fabric composites

A generalized analytical formulation is presented for the prediction of ballistic impact behavior of 2D woven fabric composite laminates impacted with a rigid cylindrical projectile. The formulation is valid for a wide range of laminate thicknesses. The formulation is based on stress wave propagation and energy balance between the projectile and the composite target. During the ballistic impact event, the energy lost by the projectile is absorbed by the target through various damage and energy absorbing mechanisms such as compression of the target directly below the projectile, compression in the region surrounding the impacted zone, shear plugging, stretching and tensile failure of yarns/layers in the region consisting of primary yarns, tensile deformation of yarns/layers in the region consisting of secondary yarns, conical deformation on the back face of the target, delamination, matrix cracking, and friction between the projectile and the target. The formulation presented considers both shear plugging and tensile failure during conical deformation. Solution procedure for the evaluation of ballistic impact performance is presented. Experimental validation is performed on the ballistic impact behavior of two types of composite specimens: 2D plain weave E-glass/epoxy and 2D 8H satin weave T300 carbon/epoxy. Typical results on ballistic limit velocity and energy absorbed by various mechanisms are presented

Design and Development of Vedic Mathematics based BCD Adder

In a conventional Binary Coded Decimal (BCD) representation is used in the scientific and computing calculation. Now they are also started to have impact in the processing unit. The only overhead in the converting the value from decimal to binary, processing and converting back to decimal. The direct reproduction of decimal value in computation produces the significant improvement in conversion and processing time. This paper is the extended version of Alp Arslan Bayracci and Ahmet Akkas et al of reduced delay Binary Coded Decimal (BCD) adder. When the design is simulated for the corner cases, the design was not responding as expected and we have proposed the modified design

Reaction mechanisms in the

Reactions induced by the weakly bound 6Li projectile interacting with the intermediate mass target 52Cr are investigated. The choice of this particular reaction in our study is because it is proposed as a surrogate reaction [6Li(52Cr, d)56Fe*] for the measurement of 55Fe(n,p) reaction cross-section, which has been found to be very important in fusion reactor studies. All the conditions which have to be satisfied for using the surrogate method have been checked. The energy of 6Li beam is selected in a way so as to get equivalent neutron energy in the region of 9-14 MeV, which is of primary interest in fusion reactor application. In the present work, statistical model calculations PACE (Projection-Angular-Momentum-Coupled-Evaporation), ALICE and Continuum-Discretized–Coupled-Channel (CDCC: FRESCO) have been used to provide information for the 6Li + 52Cr system and the respective contributions of different reaction mechanisms. The present theoretical work is an important step in the direction towards studying the cross-section of the 55Fe(n, p)55Mn reaction by surrogate method

Characterisation of sweet stem sorghum genotypes for bio-ethanol production

In an effort to characterise and select promising sweet stem sorghum genotypes with enhanced biofuel productivity, the present study investigated phenotypic variability present among diverse sweet stem sorghum genotypes based on ethanol production and related agronomic traits. One hundred and ninety genotypes were evaluated. Data were subjected to variance, cluster, correlation, path coefficient and principal component analyses. Significant differences (P < 0.01) were detected among tested genotypes for all measured traits. Days to flowering varied from 62 to 152 with a mean of 93. Plant height varied from 90 to 420 cm with a mean of 236 cm. Stem diameter ranged from 7 to 31 mm with a mean of 16 mm. Biomass yield varied from 6.668 to 111.2 t ha−1 with a mean of 30 t ha−1. Stalk dry matter content ranged from 17.2% to 44.2% with a mean of 29.8%, while fibre content varied from 8.92% to 34.8% with a mean of 17.2%. The stalk brix yield varied from 3.3% to 18.9% with a mean of 12.1%. Ethanol productivity ranged from 240.9 to 5500 l ha−1 with a mean of 1886 l ha−1. The best ethanol producing genotypes were AS203, AS391, AS205, AS251 and AS448. Days to flowering, plant height, stalk brix and stem diameter exerted the greatest indirect effects on ethanol production through higher biomass production. Biomass yield had the greatest direct effect on ethanol production. Therefore, the above traits should be considered during breeding sorghum for bio-ethanol production. Also, the traits had high heritability values, hence selection should provide for good genetic gains. Overall, the above sweet stem sorghum genotypes are useful genetic resources for breeding of sorghum with enhanced bio-ethanol production