Search

A new analytical approach to the nonlinear buckling and postbuckling analyses of functionally graded graphene-reinforced composite laminated cylindrical shells stiffened by functionally graded graphene-reinforced composite laminated stiffeners under external pressure taking into account the elastic foundation effect in a uniformly distributed thermal environment is presented in this paper. An improved smeared stiffener technique is developed for anisotropic stiffeners, and a special design for ring and stringer functionally graded graphene-reinforced composite laminated stiffeners is presented and successfully applied in this paper. The governing equations for the cylindrical shells are established by using the Donnell shell theory with the geometrical nonlinearity term in the von Karman sense with the shell-foundation interaction formulated by the Pasternak elastic foundation model. A three-term solution form is chosen for the deflection, the stress function is introduced, and the Galerkin method is used to establish the nonlinear postbuckling relation. The numerical results validate the effects of the stiffeners, volume fraction of graphene, type of graphene distribution of the shell skin and stiffeners with different geometrical parameters, elastic foundation moduli, and uniformly distributed temperature changes on the nonlinear buckling and postbuckling behaviors of stiffened cylindrical shells.

In this paper, a new design of sandwich cylindrical panels is proposed with two functionally graded carbon nanotube reinforced composite (FG-CNTRC) face sheets and lattice core. The lattice core layer is modeled by improving the novel smeared technique for stiffener according to the first-order shear deformation theory (FSDT). Nonlinear vibration behavior of first-order shear deformable cylindrical panels with the geometric nonlinearities is analyzed in present paper. The stress function is considered and the Galerkin method is used to formulate the nonlinear motion equation system. Nonlinear dynamic responses of panels can be achieved by using the fourth order Runge-Kutta method. Numerical investigations can show the very large effects of lattice core layer, volume fraction of carbon nanotube, type of carbon nanotube distribution on the nonlinear vibration behavior of sandwich FG-CNTRC cylindrical panels.

A semi-analytical approach of nonlinear vibration of functionally graded carbon nanotubes reinforced composite (FG-CNTRC) plates and cylindrical panels stiffened by longitudinal or transversal FG-CNTRC stiffeners by using the first-order shear deformation theory (FSDT) with the geometrical nonlinearities in von Karman sense is reported in this paper. The novel smeared stiffener technique is improved for FG-CNTRC stiffeners according to the FSDT. The stress function is considered and the Galerkin method is used to formulate the nonlinear motion equation system, and dynamic responses of panels are obtained by using the fourth order Runge-Kutta method. Numerical investigations can show the very large effects of FG-CNTRC stiffeners, volume fraction of carbon nanotube, type of carbon nanotube distribution of panels and stiffeners with different geometrical parameters on the nonlinear vibration behaviors of stiffened FG-CNTRC plates and cylindrical panels.

This paper presents a semi-analytical approach to investigate the nonlinear dynamic response and vibration of eccentrically oblique stiffened functionally graded plate resting on elastic foundation. The Lekhnitskii's smeared stiffener technique is improved by using a transformation technique for oblique stiffeners. Governing equations are solved by classical shell theory, Galerkin method, stress function with temperature-dependent material effects. The results show the influences of geometrical parameters, material properties, imperfection, the elastic foundations, eccentrically oblique stiffeners, mechanical loads and temperature on the nonlinear dynamic response and nonlinear vibration of plates. The numerical results in this paper are compared with the results reported in other reports.

The nonlinear buckling and postbuckling behavior of Multilayer functionally graded (FGM) cylindrical shells reinforced by ring, stringer and/or spiral stiffeners made of isotropic material under torsional loads and thermal load is proposed by an analytical approach. The thin shell is composed of three layers: isotropic layer – FGM layer – isotropic layer and surrounded by Pasternark type elastic foundation. The governing equations are based on the Donnell shell theory with von Karman-Donnell-type geometrical nonlinearity, combining the improvability of Lekhnitskii's smeared stiffeners technique for spiral stiffeners. The effects of mechanical and thermal loads are considered in this paper. The number of spiral stiffeners, angle stiffeners, temperature change, and volume fraction index of shells, foundation and stiffeners are numerically investigated. A very large effect of spiral stiffeners on buckling behavior of shell in comparison with orthogonal stiffeners is approved in numerical results.

In the industrial revolution 4.0, the Internet of Things (IoT) system is being seen everywhere. The data is constantly exchanged between divices in the IoT system and Edge or Cloud server with different protocols. Data, that is exchanged between IoT gateway and IoT server, usually uses 2 protocols: MQTT and AMQP. The selection of a good protocol is foundation for the entire IoT system works effectively. In this paper, we present the results of research and evaluation of the effectiveness in using the above two protocols based on experiments, simulating data transmission environment with different latency and packet loss rate. The condition is simulated with the real condition in IoT system, which is using in the Internet Radio system. Finally, a protocol is recommended for different environment’s conditions.

Based on the Donnell shell theory and smeared stiffeners technique, the governing equations of functionally graded annular spherical segments with functionally graded eccentrically stiffeners are d...

A new nonlinear approach on the buckling and postbuckling of functionally graded orthogonal and/or spiral-stiffened circular cylindrical shells subjected to torsional loads is proposed in this paper. The shells skin are stiffened by eccentrically rings, stringers, and/or spiral stiffeners at the surface of shells assuming that the material distribution laws of shell skin and stiffeners are graded by two distribution models. Lekhnitskii’s smeared stiffeners technique is improved for spiral stiffeners with effect of thermal terms. This is the significant novelty and scientific contribution of this paper. Theoretical formulations were established by using the Donnell shell theory taking into account the geometrical nonlinearity of von Kármán. The obtained results investigated in numerical forms show effects of volume fraction exponent of shell skin and stiffeners, geometrical parameter and stiffeners on the torsional buckling, and postbuckling behavior of functionally graded cylindrical shells. Especially, very large effects of spiral stiffeners on torsional stability behavior are obtained in comparison with same quantity material of orthogonal stiffeners.

A two-layer (connected by stubs) partial composite plate is a structure with outstanding advantages which can be widely applied in many fields of engineering such as construction, transportation, and mechanical. However, studies are scarce in the past to investigate this type of structure. This paper is based on the new modified first-order shear deformation plate theory and finite element method to develop a new four-node plate element with nine degrees of freedom per node for static bending and vibration analysis of the two-layer composite plate. The numerical results are compared to published data for some special cases. The effects of some parameters such as the boundary condition, stiffness of the connector stub, height-to-width ratio, thickness-to-thickness ratio between two layers, and aspect ratio are also performed to investigate new numerical results of static bending and free vibration responses of this structure.

There are many beam models to simulate the variable thickness functionally graded material (FGM) beam, each model has advantages and disadvantages in computer aided engineering of the mechanical behavior of this beam. In this work, a new model of beam is presented to study the mechanical static bending, free vibration, and buckling behavior of the variable thickness functionally graded material beams. The formulations are based on modified first order shear deformation theory and interpolating polynomials. This new beam model is free of shear-locking for both thick and thin beams, is easy to apply in computation, and has efficiency in simulating the variable thickness beams. The effects of some parameters, such as the power-law material index, degree of non-uniformity index, and the length-to-height ratio, on the mechanical behavior of the variable thickness FGM beam are considered.

Based on the classical thin shell theory with the geometrical nonlinearity in von Karman-Donnell sense, the smeared stiffener technique, Galerkin method and an approximate three-term solution of deflection taking into account the nonlinear buckling shape is chosen, the governing nonlinear dynamic equations of eccentrically stiffened functionally graded circular cylindrical shells subjected to time dependent axial compression and external pressure is established in part 1. In this study, the nonlinear dynamic responses are obtained by fourth order Runge-Kutta method and the nonlinear dynamic buckling behavior of stiffened functionally graded shells under linear-time loading is determined by according to Budiansky-Roth criterion. Numerical results are investigated to reveal effects of stiffener, input factors on the vibration and nonlinear dynamic buckling loads of stiffened functionally graded circular cylindrical shells.

Based on the classical thin shell theory with the geometrical nonlinearity in von Karman-Donnell sense, the smeared stiffener technique and Galerkin method, this paper deals with the nonlinear dynamic problem of eccentrically stiffened functionally graded circular cylindrical shells subjected to time dependent axial compression and external pressure by analytical approach. The present novelty is that an approximate three-term solution of deflection taking into account the nonlinear buckling shape is chosen, the nonlinear dynamic second-order differential three equations system is established and the frequency-amplitude relation of nonlinear vibration is obtained in explicit form.

A semi-analytical approach eccentrically stiffened functionally graded circular cylindrical shells surrounded by an elastic medium subjected to external pressure is presented The elastic medium is assumed as two-parameter elastic foundation model proposed by Pasternak. Based on the classical thin shell theory with the geometrical nonlinearity in von Karman–Donnell sense, the smeared stiffeners technique and Galerkin method, this paper deals the nonlinear dynamic problem. The approximate three-term solution of deflection shape is chosen and the frequency–amplitude relation of nonlinear vibration is obtained in explicit form. The nonlinear dynamic responses are analyzed by using fourth order Runge–Kutta method and the nonlinear dynamic buckling behavior of stiffened functionally graded shells is investigated according to Budiansky–Roth criterion. Results are given to evaluate effects of stiffener, elastic foundation and input factors on the frequency–amplitude curves, natural frequencies, nonlinear responses and nonlinear dynamic buckling loads of functionally graded cylindrical shells.

This paper presents an analytical approach to investigate the nonlinear buckling of imperfect eccentrically stiffened functionally graded thin circular cylindrical shells subjected to axial compression and surrounded by an elastic foundation. Based on the classical thin shell theory with the geometrical nonlinearity in von Karman-Donnell sense, initial geometrical imperfection, the smeared stiffeners technique and Pasternak’s two-parameter elastic foundation, the governing equations of eccentrically stiffened functionally graded cylindrical shells are derived. The functionally graded cylindrical shells are reinforced by homogeneous ring and stringer stiffener system on internal and (or) external surface. The resulting equations are solved by the Galerkin method to obtain the explicit expression of static critical buckling load, post-buckling load-deflection curve and nonlinear dynamic motion equation. The nonlinear dynamic responses are found by using fourth order Runge-Kutta method. The dynamic critical buckling loads of shells are considered for step loading of infinite duration and linear-time compression. The obtained results show the effects of foundation, stiffeners and input factors on the nonlinear buckling behavior of these structures.

An analytical approach is presented to investigate the nonlinear static and dynamic buckling of imperfect eccentrically stiffened functionally graded thin circular cylindrical shells subjected to axial compression. Based on the classical thin shell theory with the geometrical nonlinearity in von Karman–Donnell sense, initial geometrical imperfection and the smeared stiffeners technique, the governing equations of motion of eccentrically stiffened functionally graded circular cylindrical shells are derived. The functionally graded cylindrical shells with simply supported edges are reinforced by ring and stringer stiffeners system on internal and (or) external surface. The resulting equations are solved by the Galerkin procedure to obtain the explicit expression of static critical buckling load, post-buckling load–deflection curve and nonlinear dynamic motion equation. The nonlinear dynamic responses are found by using fourth-order Runge–Kutta method. The dynamic critical buckling loads of shells under step loading of infinite duration are found corresponding to the load value of sudden jump in the average deflection and those of shells under linear-time compression are investigated according to Budiansky–Roth criterion. The obtained results show the effects of stiffeners and input factors on the static and dynamic buckling behavior of these structures.

This paper presents a semi-analytical approach to investigate the nonlinear dynamic of imperfect eccentrically stiffened functionally graded shallow shells taking into account the damping subjected to mechanical loads. The functionally graded shallow shells are simply supported at edges and are reinforced by transversal and longitudinal stiffeners on internal or external surface. The formulation is based on the classical thin shell theory with the geometrical nonlinearity in von Karman–Donnell sense and the smeared stiffeners technique. By Galerkin method, the equations of motion of eccentrically stiffened imperfect functionally graded shallow shells are derived. Dynamic responses are obtained by solving the equation of motion by the Runge–Kutta method. The nonlinear critical dynamic buckling loads are found according to the Budiansky–Roth criterion. Results of dynamic analysis show the effect of stiffeners, damping, pre-loaded compressions, material and geometric parameters on the dynamical behavior of these structures.

Based on the classical shell theory with the geometrical nonlinearity in von Karman–Donnell sense and the smeared stiffeners technique, the governing equations of motion of eccentrically stiffened functionally graded cylindrical panels with geometrically imperfections are derived in this paper. The characteristics of free vibration and nonlinear responses are investigated. The nonlinear dynamic buckling of cylindrical panel acted on by axial loading is considered. The nonlinear dynamic critical buckling loads are found according to the criterion suggested by Budiansky–Roth. Some numerical results are given and compared with the ones of other authors.

The paper deals with the formulation of governing equations of eccentrically stiffened functionally graded plates and shallow shells based upon the classical shell theory and the smeared stiffeners technique taking into account geometrical nonlinearity in Von Karman-Donnell sense. Material properties are assumed to be temperature-independent and graded in the thickness direction according to a simple power law distribution in terms of the volume fraction of constituents. The shells are reinforced by eccentrically longitudinal and transversal stiffeners made of full metal or full ceramic depending on situation of stiffeners at metal-rich side or ceramic-rich side of the shell respectively. Obtained governing equations can be used in research on nonlinear postbuckling of mentioned above structures. By use of the Galerkin method an approximated analytical solution to the nonlinear stability problem of reinforced FGM plates and shallow shells is performed. The postbuckling load-deflection curves of the shells are investigated and analytical expressions of the upper and lower buckling loads are presented. A comparison of the effectiveness of stiffeners in enhancing the stability of FGM plates and shallow shells is given.

Obtaining insights on the illicit consumption of endangered wildlife products is challenging, especially when the study objects are the super-rich. This research note draws upon my experience interviewing nearly 1,000 rhino horn consumers in Vietnam. Trust is crucial in such interactions. No interviews could have been conducted without good rapport between interviewers and respondents. Nonetheless, soliciting interviews requires skills that one cannot expect to teach enumerators in the short term. This includes a winning sense of humour, colourful life experience, and true grit. Once good rapport is established, the use of specialised questionning techniques or bias-mitigation tools becomes unnecessary. Instead I suggest a practical approach to study consumers of illegal and luxury wildlife products in an Asian context.