Nonlinear analysis of laminated shells with alternating stiff/soft lay-up

This paper proposes a multi-layer formulation for the nonlinear analysis of laminated shells with an alternating stiff/soft lay-up. The zigzag variation of planar displacements is taken into account by adding to the Reissner–Mindlin formulation a specific set of zigzag function which is effective for the considered lay-up. Furthermore, a piecewise linear through-thickness distribution of the material transverse shear strain is assumed, which agrees well with the real distribution. The proposed lamination model with a low-order nonlinear strain–displacement relationship is incorporated within a co-rotational framework for geometric nonlinear analysis, thus upgrading the low-order local element formulation to large displacement analysis with relative ease. In addition, a local shell system is employed for direct definition of the additional zigzag displacement fields and associated parameters, which are thus excluded from the large displacement co-rotational transformations. The application of the proposed laminated shell modelling approach is illustrated in this paper for a 9-noded co-rotational shell element, which utilises the Mixed Interpolation of Tensorial Components (MITC) method in the local system for overcoming locking effects. Several linear and nonlinear numerical examples of multi-layer shell structures with alternating stiff/soft lay-ups are used to illustrate the effectiveness and efficiency of the proposed modelling approach

A hierarchic optimisation approach towards locking-free shell finite elements

A hierarchic optimisation approach is presented for relieving inaccuracies in conforming shell elements arising from locking phenomena. This approach introduces two sets of strain modes: (i) objective strain modes, defined in the physical coordinate system, and (ii) corrective strain modes, representing conforming strains enhanced with hierarchic strain modes. This leads to two alternative families of element, objective and corrective, both arising from minimising the difference between objective and corrective strains. Importantly, the proposed approach not only alleviates shear and membrane locking, but it also addresses locking arising from element distortion. The application of the proposed optimisation approach is demonstrated for a 9-noded quadrilateral Lagrangian shell element, where the membrane, bending and transverse shear strains are separately optimised, all within a local co-rotational framework that extends the element application to geometric nonlinear analysis. Several numerical examples, including cases with geometric and material nonlinearity, are finally presented to illustrate the effectiveness of the optimised 9-noded shell element in relieving the various sources of locking

Distributed Power Allocation Algorithm for General Authorised Access in Spectrum Access System

© 2019 IEEE. To meet the capacity needs of the next generation wireless communications, U.S. Federal Communications Commission has recently introduced Spectrum Access System. Spectrum is shared between three tiers - Incumbents, Priority Access Licensees (PAL) and General Authorised Access (GAA) Licensees. When the incumbents are absent, PAL and GAA share the spectrum under the constraint that GAA ensure the aggregate interference to PAL is no more than -80 dBm within the PAL protection area. Currently GAA users are required to report their geolocations. However, geolocation is private information that GAA may not be willing to share. We propose a distributed GAA power allocation algorithm that does not require centralised coordination on sharing locations with other GAA users via SAS. We analytically proved the critical point of the interference along the PAL protection area to avoid calculating the interference on every points of the area. We proposed exclusion zone, transitional zone and open zone for GAA users to calculate the self-determined transmit power. Simulation results show that our method meets the interference requirement and achieve more than 90% of capacity approximation to the optimal centralised method, while completely masking the GAA locations

A comparison of wettability measurements on a synthesised water repellent sand

Controlling the wettability of granular materials such as soil offers the opportunity to generate new materials. Such materials can completely prevent or partially restrict infiltration depending on their wettability. In this study, the wettability of a synthesised water repellent sand, isolated into four different sieve fractions was investigated by means of 2 different methods: the sessile drop method (SDM) and the Wilhelmy plate method (WPM). Both methods were shown to be effective in the measurement of contact angles (CAs) despite considerable differences in their absolute values. These differences were primarily attributed to the different methodologies which relied on different principles to measure CAs. The CAs measured with both the SDM and WPM showed a decrease in magnitude as particle size increases. The maximum differences in CAs recorded with the SDM and WPM between the particle sizes were respectively 13.3° and 26.1°. In addition to adequately describing the methodology adopted for the measurement of CAs, it is recommended to use the SDM over the WPM for soil samples with considerable clay content

Engineering water repellency in granular solids

The use of water repellent granular solids such as soils is an innovative technology for use in applications such as water tight barriers. Synthesising such solids generally necessitate the exclusive use of chemical treatments with little consideration given to the physical characteristics of the solids. This paper summarises the theoretical framework of surface wettability and contact angle by illustrating the classic models developed. The wettability of 3 isolated sieve fractions of a sand was investigated after treatment with dimethyldichlorosilane (DMDCS). The largest contact angle (measured by the sessile drop method) was achieved with the finest fraction (63-212 μm). Comparison between a flat microscope slide treated with DMDCS and the 63-212 μm fraction showed that the sand had a significantly larger contact angle (a maximum difference of 20°). This difference was attributed to the particle characteristics which includes particle size, particle shape and surface roughness. The results of the study hint at the possible usage of the physical characteristics of soils in an engineering context to control water repellency

On the Usage of Geolocation-Aware Spectrum Measurements for Incumbent Location and Transmit Power Detection

© 2017 IEEE. Determining the geographical area that needs to be excluded due to incumbent activity is critical to realize high spectral utilization in spectrum sharing networks. This can be achieved by estimating the incumbent location and transmit power. However, keeping the hardware complexity of sensing nodes to a minimum and scalability are critical for spectrum sharing applications with commercial intent. We present a discrete-space l1-norm minimization solution based on geolocation-aware energy detection measurements. In practice, the accuracy of geolocation tagging is limited. We capture the impact as a basis mismatch and derive the necessary condition that needs to be satisfied for successful detection of multiple incumbents' location and transmit power. We find the upper bound for the probability of eliminating the impact of limited geolocation tagging accuracy in a lognormal shadow fading environment, which is applicable to all generic I1-norm minimization techniques. We propose an algorithm based on orthogonal matching pursuit that decreases the residual in each iteration by allowing a selected set of basis vectors to rotate in a controlled manner. Numerical evaluation of the proposed algorithm in a Licensed Shared Access (LSA) network shows a significant improvement in the probability of missed detection and false alarm

Utility of Lamb Waves for Near Surface Crack Detection

Ultrasonic waves have a long history in detection of surface breaking cracks. Attempts are being made to use guided waves as a defect detection tool in aging skin structures in aircrafts and in the power generation industries as these waves offer a great advantage over conventional bulks waves. Guided waves can be excited at one position and allowed to propagate considerable distances before attenuating. Depending on the configuration employed for defect detection, reflected or received waveforms give information regarding the integrity of the structure along the line of sight. This description makes the technique look rather simple. Particularly, NDT utilizing Lamb waves is more complex due to the existence of two or more modes at any given frequency. Success was reported by several authors on defect detection using Lamb waves. Brief or no explanation was given on the reasons behind the choice of specific excitation frequencies and incident angles. The emphasis was solely on the defect detection aspects

Effect of Variety, Seed Rate and Row Spacing on the Growth and Yield of Rice in Bauchi, Nigeria

Field experiments were conducted at Abubakar Tafawa Balewa University, Fadama Farm Bauchi, during the rainy seasons of 2006 and 2007 to study the effects of variety, seeding rate and row spacing on growth and yield of rice. Two varieties of rice; Ex – China (Indigenous and upland/lowland) and NERICA-1 (improved and upland), three seeding rates (32, 54 and 75 kg/ha) and four row spacings (15, 20, 25 and broadcast) were used during the study. The treatments were combined and laid in a split – split plot design with three replications. Variety was placed in the main plot, seeding rate in the sub plot while row spacing was placed in sub –sub plot. Data were collected on parameters such as plant height, number of tillers per plant, spikes per hill, spikelets per spike and number of seeds per spike, seed weight per hill, 1000 grain weight and yield kg ha-1 and analyzed using analysis of variance procedure for split – split plot and significant differences among the treatment means were separated using the Duncan multiple range test (DMRT). Variety Ex-China produced significantly (P<0.05) higher numbers of tillers per plant and spikes per hill. However, NERICA-1 produced significantly (P<0.05) higher numbers of spikelets per spike, seeds per spike, weight of seed per spike, weight of seed per hill, 1000 grain weight and yield in kg ha-1 than Ex-China. Row spacings of 15, 20 and 25cm also had significant effects on the number of tillers per plant, number of spikes per hill, number of spikelets per spike, number of seeds per spike, weight of seed per spike, weight of seed per hill, 1000 grain weight and yield kg ha-1 over the control. From the factors studied, seeding rate did not show any significant difference during the two years of investigation. Interactions were also observed among the factors studied. Therefore, row spacings irrespective of the method used, or hole planting of rice could be more appropriate for optimum grain yield.Key words: Seed rate, Row spacing, Spike

An Adaptive UAV Network for Increased User Coverage and Spectral Efficiency

© 2019 IEEE. Unmanned Aerial Vehicles (UAVs) are fast becoming a popular choice in a variety of applications in wireless communication systems. UAV-mounted base stations (UAV-BSs) are an effective and cost-efficient solution for providing wireless connectivity where fixed infrastructure is not available or destroyed. We present a method of using UAV-BSs to provide coverage to mobile users in a fixed area. We propose an algorithm for predicting the user locations based on their mobility data and clustering the predicted locations, so that one UAV-BS would provide coverage to one user cluster. The proposed method, hence is similar to the UAV-BSs following the users to keep them under the coverage region. Simulation results show that the proposed method increases the user coverage by 47%-72% and increases the spectral efficiency by 43%-55% depending on the scenario and in addition, reduces the number of UAV-BSs required to provide coverage