Research on stability of laminated composite plate under nonlinear aerodynamic load

In this paper,we propose an finite element approach based on classical plate theory to investigate the dynamic stability of a layered composite plate subject to nonlinear aerodynamic load.This study considers the influence of temperature,nonlinear geometry,and nonlinear aerodynamic load on composite plate structures simultaneously.Specifically,the present work conduct comparison the results of the critical pressure value between the nonlinear aerodynamic load and the linear aerodynamic load,thereby pointing out some necessary cases which must consider the nonlinearity of aerodynamic load for calculating the aerospace structures.We determine the critical pressure value and vibrational amplitude response of the plate by means of calculation.The outcomes of our calculations can be useful in designing and repairing body shells and wings of aircraft equipment.

Secure transmission in backhaul NOMA systems:A physical layer security design with untrusted user and eavesdropper

In order to improve the Physical Layer Security(PLS)perspective,this paper aims to empower function of PLS by considering a backhaul Non-Orthogonal Multiple Access(NOMA)system in two practical situations.In the proposed schemes,the untrusted user intercepts information transmitted to the far user,or the external eavesdropper overhears confidential information sent to the far user in the context of NOMA technique.Unlike the conventional NOMA systems,this paper emphasizes the actual situations of the existence of actual illegal users and legitimate users,especially the reasonable use of relay selection architecture to improve the confidentiality performance.To evaluate the security properties of the proposed scheme,a comprehensive analysis of the Security Outage Probability(SOP)performance is first performed,and then the corresponding SOP asymptotic expressions are derived for real scenarios related to eavesdroppers and untrusted users.Numerical results are performed to verify the analysis in terms of the secure performance metric.

Effects of Material and Dimension on TCF,Frequency,and Q of Radial Contour Mode AlN-on-Si MEMS Resonators

This paper investigates the effects of material and dimension parameters on the frequency splitting,frequency drift,and quality factor(Q)of aluminium nitride(AlN)-on-n-doped/pure silicon(Si)microelectromechanical systems(MEMS)disk resonators through analysis and simulation.These parameters include the crystallographic orientation,dopant,substrate thickness,and temperature.The resonators operate in the elliptical,higher order,and flexural modes.The simulation results show that i)the turnover points of the resonators exist at 55°C,-50°C,40°C,and-10°C for n-doped silicon with the doping concentration of 2×1019 cm-3 and the Si thickness of 3.5μm,and these points are shifted with the substrate thickness and mode variations;ii)compared with pure Si,the modal-frequency splitting for n-doped Si is higher and increases from 5%to 10%for all studied modes;iii)Q of the resonators depends on the temperature and dopant.Therefore,the turnover,modal-frequency splitting,and Q of the resonators depend on the thickness and material of the substrate and the temperature.This work offers an analysis and design platform for high-performance MEMS gyroscopes as well as oscillators in terms of the temperature compensation by n-doped Si.

Effects of urbanization on groundwater level in aquifers of Binh Duong Province,Vietnam

The purpose of this paper was to assess the impact of urbanization on the groundwater level(GWL)in aquifers of Binh Duong(BD)Province.The research method is to analyze the trend of GWL,the recharge capacity of surface over time and the relationship between them.The data of the GWL used in the study are the average values in the dry and rainy seasons of 35 observation wells from 2011 to 2018,which are in Pleistocene and Pliocene aquifers.The ability to recharge groundwater from the surface in this study was represented by the curve number(CN),a parameter used in hydrology for calculating direct runoff or infiltration from rainfall.The land use data to identify the CN was analyzed from the Landsat images.The results show that besides over-exploitation,the change of surface characteristic due to the urbanization development process is also the cause of the GWL decline.The analysis of seasonal GWL data shows that the increase in impervious surface area is the cause of GWL decline in the Pleistocene aquifer,which is more evident in the rainy season than in the dry season.The statistical results also show that in the rainy season and in shallow aquifers,a higher CN change can be found with the wells that had a remarkable GWL decline compared to the remaining wells.

Effect of Poly-Alkylene-Glycol Quenchant on the Distortion, Hardness, and Microstructure of 65Mn Steel

Currently,the 65Mn steel is quenched mainly by oil media.Even though the lower cooling rate of oil compared to water reduces the hardness of steel post quenching,the deforming and cracking of parts are often minimized.On the other hand,the oil media also has the disadvantage of being ammable,creating smoke that adversely affects the media.The poly alkylene glycol(PAG)polymer quenchant is commonly used for quenching a variety of steels based on its advantages such as non-ammability and exible cooling rate subjected to varying concentration and stirring speed.This article examines the effect of PAG polymer quenching solution(with concentrations of 10%and 20%)on deformation,hardness,and microstructure of C-ring samples made of 65Mn steel.Furthermore,the performance of PAG polymer quenchant is also compared with those of two common quenching solutions:Water and oil.When cooling in water,the C-ring samples had the largest deformation and 2 times higher than the results obtained when a 10%PAG solution was used.In particular,similar levels of deformation on the C-ring samples were observed in both cases of 20%PAG solution and oil as the primary quenching media.Furthermore,the hardness level measured between the sampled parts quenched in the 20%PAG solution appeared to be more uniform than that obtained from the oil-quenched sample.The study of the microscopic structure of steel by optical microscopy combined with X-ray diffraction showed that the water hardened sample exhibited cracks and comprised of two phases,martensite and retained austenite.According to the results of Electron Back Scattering Diffraction(EBSD)analysis and backscattering electronic image(BSE),the content of austenite residue in the sample when the sample was cooled in PAG 10 and 20%solution was 3.21%and 4.73%,respectively and smaller than the measurements obtained from oil quenching solution.Thus,the 65Mn steel is cooled in 20%PAG solution for high hardness and more evenly distributed than when it is quenched in oil while still ensuring a small level of deformation.Therefore,the PAG 20%solution can completely replace oil as the main media used to quench the 65Mn steel.

Green Synthesis of Silver Nanoparticles Using Plectranthus Amboinicus Leaf Extract for Preparation of CMC/PVA Nanocomposite Film

In the present study,the biogenic silver nanoparticles have been synthesized using aqueous leaf extract of Plectranthus amboinicus(PA),which acted as both reducing and stabilizing agents.The PA synthesized silver nanoparticles were blended with carboxymethyl cellulose/polyvinyl alcohol(CMC/PVA)biocomposite.The prepared AgNPs as well as the biogenic AgNPs incorporated CMC/PVA films were investigated using UV-visible spectrophotometry,Fourier-transform infrared spectroscopy(FT-IR),dynamic light scattering(DLS),scanning electron microscope(SEM),and X–ray diffraction(XRD).The DLS results showed that biogenic AgNPs had the average particle size of 65.70 nm with polydispersity index of 0.44.The surface plasmon resonance of AgNPs,which was determined by UV-vis spectrophotometry,showed the value of 410.00 nm.These results therefore confirmed the reduction Ag+into Ag°and the formation of AgNPs in the medium.The SEM imaging showed that AgNPs was quasi-spherical and monodisperse.The XRD peaks at 33.07°,44.19°,64.58°and 77.47°confirmed the crystalline nature and presence of AgNPs.The CMC/PVA films that incorporated with AgNPs displayed best mechanical strength and morphological properties than the pure CMC/PVA film.The film of CMC/PVA-AgNPs exhibited significant antibacterial activities against Bacillus spizizenii,Staphylococcus aureus,Salmonella typhi and Escherichia Coli.

Chemical constituents and biological activities of essential oils of Amomum genus(Zingiberaceae)

Amomum Roxb.includes the aromatic and medicinal plants native to tropical and subtropical Asia belonging to the family Zingiberaceae.Members of Amomum genus have been used for a long time in traditional medicine for the treatment of throat trouble,congestion of lungs,inflammation of eyelids,and digestive disorders,etc.Amomum essential oils have been studied for their chemical profiles in which limonene,allo-aromadendrene,1,8-cineole,camphor,farnesyl acetate,α-pinene,β-pinene,caryophyllene,camphene,D-camphor,santolina triene,methyl chavicol,bornyl acetate,β-elemene,δ-3-carene,etc.were the major compounds.Furthermore,the oils extracted from Amomum plants have been reported to possess antimicrobial,antioxidant,insecticidal,larvicidal,cytotoxic,anti-scabies,and anti-inflammatory activities.This review focuses on the chemical constituents and biological activities of the essential oils isolated from the different plant parts of Amomum plants.The objective of the present review is to highlight therapeutic potentials and provide evidence for future medicinal applications of these species of genus Amomum.

Performance evaluation of a two-way relay network with energy harvesting^and hardware noises

In this paper,we propose a Two-Way Cognitive Relay Network(TWCRN)where the secondary users operate on an underlay mode to access the licensed bands.In the proposed protocols,two secondary sources transmit their data to a relay in the first time slot,and then the relay would forward the received information to both sources in the remaining time.Moreover,the relay is self-powered by harvesting energy from ambient Radio Frequency(RF)signals,using the Time Switching(TS)and the Power Switching(PS)method.This paper concentrates on eval-uating the performance of the secondary networks under the impact of hardware impairments and co-channel interference from the primary networks.In particular,based on the secondary transmitters'constraint power,we derive the closed-form expressions of the outage probability and the throughput over Rayleigh fading channels in two cases:TS and PS.We also investigate the energy efficiency issue and the locally optimal position of the relay to maximize the system throughput,which provides much information to install the relay location.Finally,our derivations are verified by Monte Carlo simulation.

Test Case Generation from UML-Diagrams Using Genetic Algorithm

Software testing has been attracting a lot of attention for effective software development.In model driven approach,Unified Modelling Language(UML)is a conceptual modelling approach for obligations and other features of the system in a model-driven methodology.Specialized tools interpret these models into other software artifacts such as code,test data and documentation.The generation of test cases permits the appropriate test data to be determined that have the aptitude to ascertain the requirements.This paper focuses on optimizing the test data obtained from UML activity and state chart diagrams by using Basic Genetic Algorithm(BGA).For generating the test cases,both diagrams were converted into their corresponding intermediate graphical forms namely,Activity Diagram Graph(ADG)and State Chart Diagram Graph(SCDG).Then both graphs will be combined to form a single graph called,Activity State Chart Diagram Graph(ASCDG).Both graphs were then joined to create a single graph known as the Activity State Chart Diagram Graph(ASCDG).Next,the ASCDG will be optimized using BGA to generate the test data.A case study involving a withdrawal from the automated teller machine(ATM)of a bank was employed to demonstrate the approach.The approach successfully identified defects in various ATM functions such as messaging and operation.

Comparison of Layer-stacking and Dempster-Shafer Theory-based Methods Using Sentinel-1 and Sentinel-2 Data Fusion in Urban Land Cover Mapping

Data fusion has shown potential to improve the accuracy of land cover mapping,and selection of the optimal fusion technique remains a challenge.This study investigated the performance of fusing Sentinel-1(S-1)and Sentinel-2(S-2)data,using layer-stacking method at the pixel level and Dempster-Shafer(D-S)theory-based approach at the decision level,for mapping six land cover classes in Thu Dau Mot City,Vietnam.At the pixel level,S-1 and S-2 bands and their extracted textures and indices were stacked into the different single-sensor and multi-sensor datasets(i.e.fused datasets).The datasets were categorized into two groups.One group included the datasets containing only spectral and backscattering bands,and the other group included the datasets consisting of these bands and their extracted features.The random forest(RF)classifier was then applied to the datasets within each group.At the decision level,the RF classification outputs of the single-sensor datasets within each group were fused together based on D-S theory.Finally,the accuracy of the mapping results at both levels within each group was compared.The results showed that fusion at the decision level provided the best mapping accuracy compared to the results from other products within each group.The highest overall accuracy(OA)and Kappa coefficient of the map using D-S theory were 92.67%and 0.91,respectively.The decision-level fusion helped increase the OA of the map by 0.75%to 2.07%compared to that of corresponding S-2 products in the groups.Meanwhile,the data fusion at the pixel level delivered the mapping results,which yielded an OA of 4.88%to 6.58%lower than that of corresponding S-2 products in the groups.

Assessment of Livelihood Vulnerability to Drought: A Case Study in Dak Nong Province, Vietnam

In recent years,droughts have strongly affected the Central Highlands of Vietnam and have resulted in crop damage,yield decline,and serious water shortage.This study investigated the livelihood vulnerability of five communities of farmers who are exposed to droughts in one of the more vulnerable regions of Vietnam—Dak Nong Province.A survey of 250 households was conducted in the five communities to collect data on the region’s sociodemographic profile,livelihood systems,social networks,health status,food and water security,drought conditions,and climate variability.Data were aggregated using a livelihood vulnerability index and the IPCC vulnerability index.The survey results indicate that Quang Phu community is the most vulnerable of the study’s communities,followed by Nam N’dir,Dak Nang,Duc Xuyen,and Dak D’ro in descending order of vulnerability.Water availability and livelihood strategies are the most important variables in determining the vulnerability of the five surveyed communities.In order to reduce vulnerability to droughts,water management practices and livelihood diversification in farming and nonfarming activities are recommended for the study area.

Minimizing Warpage for Macro-Size Fused Deposition Modeling Parts

In this study,we investigated warpage and corner lifting minimization for three-dimensional printed parts generated by macro-size fused deposition modeling(FDM).First,the reasons for warpage were theoretically elucidated.This approach revealed that the thermal deformation and differential volumetric shrinkage of the extruded molten plastic resulted in warpage of FDM parts.In addition,low adhesion between the deposited model and the heated or non-heated printing bed may intensify warpage further.As a next step,initial small-size and medium-size models were used to identify parameters to manage and minimize warpage in a way that would reduce material consumption and running time.Finally,a macro-size model was built to experimentally investigate and verify the technical solutions to minimize the warpage of FDM parts.In conclusion,an improved part with reduced warpage was efficiently produced after detailed consideration of thermal effects and adhesion force.Potential exists to widen the application scope of FDM technology in manufacturing for processes like thermoforming that involve mold core fabrication with heating.This technology,which has applications not only in mechanical engineering but also in related engineering fields,is convenient and could readily be applied to practical manufacturing industries.

Thermodynamic Simulation on the Change in Phase for Carburizing Process

The type of technology used to strengthen the surface structure of machine parts,typically by carbon-permeation,has made a great contribution to the mechanical engineering industry because of its outstanding advantages in corrosion resistance and enhanced mechanical and physical properties.Furthermore,carbon permeation is considered as an optimal method of heat treatment through the diffusion of carbon atoms into the surface of alloy steel.This study presented research results on the thermodynamic calculation and simulation of the carbon permeability process.Applying Fick’s law,the paper calculated the distribution of carbon concentration in the alloy steel after it is absorbed from the surface into the internal of the sample.Using the SYSWELD software,an analysis was performed on the carbon permeability process to determine the distribution of carbon concentrations in 20CrMo steel that was then followed by a detailed analysis of the microstructure of the sample post the carburizing process.According to the calculation results,the surface carbon content was 0.9%and steadily decreased into the core.After 3 hours,the depth of the absorbent layer was measured at 0.5 mm for both the cylindrical and cubic samples.By analyzing the phase,the distribution of martensite phases such as ferrite/pearlite and residual austenite was also determined after the carburizing process.

Optimum Design for the Magnification Mechanisms Employing Fuzzy Logic-ANFIS

To achieve high work performance for compliant mechanisms of motion scope,continuous work condition,and high frequency,we propose a new hybrid algorithm that could be applied to multi-objective optimum design.In this investigation,we use the tools of finite element analysis(FEA)for a magnificationmechanism to find out the effects of design variables on the magnification ratio of the mechanism and then select an optimal mechanism that could meet design requirements.A poly-algorithm including the Grey-Taguchi method,fuzzy logic system,and adaptive neuro-fuzzy inference system(ANFIS)algorithm,was utilized mainly in this study.The FEA outcomes indicated that design variables have significantly affected on magnification ratio of the mechanism and verified by analysis of variance and analysis of the signal to noise of grey relational grade.The results are also predicted by employing the tool of ANFIS in MATLAB.In conclusion,the optimal findings obtained:Its magnification is larger than 40 times in comparison with the initial design,the maximum principal stress is 127.89MPa,and the first modal shape frequency obtained 397.45 Hz.Moreover,we found that the outcomes obtained deviation error compared with predicted results of displacement,stress,and frequency are 8.76%,3.6%,and 6.92%,respectively.

Effects of ENSO and Climate Change on Reference Evapotranspiration in Southern Vietnam

This study aims to evaluate the effects of climate change and El Nino-Southern Oscillation(ENSO)on reference evapotranspiration(ET_(o))in the climate sub-regions of South Vietnam(SVN)and the role of the related meteorological variables.The trend analysis shows that ET_(o) has been increasing quite clearly,especially during the rainy season.By examining the contribution of meteorological variables to the increase of ET_(o),it is indicated that temperature is the main contributor.Among the meteorological variables that are related to ET_(o),temperature is also the factor that has gained the most significant increase.Analysis of variance reveals that there is no difference in the increase of ET_(o) among the climate sub-regions of SVN.The effect of ENSO on ET_(o) is assessed based on the difference in the mean value of ET_(o) between the El Nino and La Nina phases.The results show that this difference is most obvious from October to May,and the main factor contributing to the increase is not temperature but sunshine hours.The difference in sunshine hours between the warm and cold phases in these months is around one hour per day,contributing about58%-86%to the ET_(o) difference.Further analysis of variance shows that ENSO has different levels of influences on ET_(o) in the climate sub-regions.Compared to the increase in ET_(o) due to climate change over the past 40 years,the ET_(o) difference between El Nino and La Nina phases is many times higher.In addition,since the effect of ENSO on ET_(o) is most obvious in the study area during the dry season,it is much stronger.In order to mitigate the effect of ENSO on drought in this area,monitoring and forecasting meteorological variables that have the main contribution to the variation of ET_(o),including the number of sunshine hours,should be promoted.

Predicted aerodynamic damping of slender single beam structures in across-wind vibrations

The paper presents a generalization of the conventional analytical approach where the quasisteady theory is utilised to evalu-ate the across-wind aerodynamic damping of slender single beam structures.This generalized theory considers the variation of structural and aerodynamic parameters along the structural height,together with the nature of the vertical wind profile and mode shapes.Closed-form solutions for typical uniform and tapered tall buildings are given.A numerical application on a prototype tall building shows that the conventional method may be oversimplified,which results in incorrect predictions of the aerodynamic damping.

Regularization of the Inverse Problem for Time Fractional Pseudo-parabolic Equation with Non-local in Time Conditions

This paper is devoted to identifying an unknown source for a time-fractional diffusion equation in a general bounded domain.First,we prove the problem is non-well posed and the stability of the source function.Second,by using the Modified Fractional Landweber method,we present regularization solutions and show the convergence rate between regularization solutions and sought solution are given under a priori and a posteriori choice rules of the regularization parameter,respectively.Finally,we present an illustrative numerical example to test the results of our theory.

A fully automated framework for helicopter rotor blades design and analysis including aerodynamics,structure, and manufacturing

This study describes an integrated framework in which basic aerospace engineering aspects(performance, aerodynamics, and structure) and practical aspects(configuration visualization and manufacturing) are coupled and considered in one fully automated design optimization of rotor blades. A number of codes are developed to robustly perform estimation of helicopter configuration from sizing, performance analysis, trim analysis, to rotor blades configuration representation. These codes are then integrated with a two-dimensional airfoil analysis tool to fully design rotor blades configuration including rotor planform and airfoil shape for optimal aerodynamics in both hover and forward flights. A modular structure design methodology is developed for realistic composite rotor blades with a sophisticated cross-sectional geometry. A D-spar cross-sectional structure is chosen as a baseline. The framework is able to analyze all realistic inner configurations including thicknesses of D-spar, skin, web, number and ply angles of layers of each composite part,and materials. A number of codes and commercial software(ANSYS, Gridgen, VABS, Pre VABS,etc.) are implemented to automate the structural analysis from aerodynamic data processing to sectional properties and stress analysis. An integrated model for manufacturing cost estimation ofcomposite rotor blades developed at the Aerodynamic Analysis and Design Laboratory(AADL),Aerospace Information Engineering Department, Konkuk University is integrated into the framework to provide a rapid and dynamic feedback to configuration design. The integration of three modules has constructed a framework where the size of a helicopter, aerodynamic performance analysis, structure analysis, and manufacturing cost estimation could be quickly investigated. All aspects of a rotor blade including planform, airfoil shape, and inner structure are considered in a multidisciplinary design optimization without an exception of critical configuration.