It is well known that it is very difficult to manufacture perfect thin cylindrical shell. Initial GEOMETRICAL IMPERFECTIONS existing in the shell structure is one of the main determining factor for load bearing capacity of thin cylindrical shell under uniform lateral pressure. As these IMPERFECTIONS are random, the strength of same size cylindrical shell will also random and a statistical method can be preferred to find the allowable load of these shell structures and therefore a In this work the cylindrical shell of size R/t = 228, L/R = 2 and t=1mm is taken for study. The random GEOMETRICAL IMPERFECTIONS are modeled by linearly adding the first 10 eigen mode shapes using 2k full factorial design matrix of DoE. By adopting this method 1024 FE random imperfect cylindrical shell models are generated with tolerance limit of ± 1 mm. Nonlinear static FE analysis of ANSYS is used to find the buckling strength of these 1024 models. FE results of 1024 models are used to predict the reliability based on MVFOSM method.

One of the common failure modes of thin cylindrical shell subjected external pressure is buckling. The buckling pressure of these shell structures are dominantly affected by the GEOMETRICAL IMPERFECTIONS present in the cylindrical shell which are very difficult to alleviate during manufacturing process. In this work, only three types of GEOMETRICAL imperfection patterns are considered namely (a) eigen affine mode imperfection pattern, (b) inward half lobe axisymmetric imperfection pattern extended throughout the height of the cylindrical shell and (c) local GEOMETRICAL imperfection patterns such as inward dimple with varying wave lengths located at the mid-height of the cylindrical shell. ANSYS FE non-linear buckling analysis including both material and GEOMETRICAL non-linearities is used to determine the critical buckling pressure. From the analysis it is found that when the maximum amplitude of IMPERFECTIONS is 1t, the eigen affine imperfection pattern gives out the lowest critical buckling pressure when compared to the other imperfection patterns considered When the amplitude of IMPERFECTIONS is above 1t, the inner half lobe axisymmetric imperfection pattern gives out the lowest critical buckling pressure when compared to the other imperfection patterns considered.

Some studies point out, under the assumption of the particular combination of market IMPERFECTIONS in both the goods and asset markets not only explain the short-run behavior of exchange rates but are also the driving force behind it. Indeed, they constitute the key element to its understanding. This paper shows that a combination of local currency pricing, heterogeneity in goods distribution, and noise trader expectation, as imperfect market, may combine to produce very high exchange rate volatility. The data in this article are related to the fixed prices in the year 2004 and run annually from 1966 to 2013 in a per capita basis. Having logarithms taken, the variables are de-traded through Hodrick-Prescott filter. The final model equations are linearized around the steady state and using Uhlig (1999) approach accidental equations are also linearized and are specified as space state pattern in Matlab software. Finally, the calibration of parameters is assessed, variables are simulated and compared with real data. The results show that the introduced model can simulate the impact of shocks on macroeconomic variables. It also shows that a money supply shock in local currency pricing, increases of the domestic consumption and thus causing a depreciation temporary of the home currency. Also, with increase in inverse of elasticity of money demand parameter, the exchange rate's response will be more to the domestic supply money shock. We find that the change in noise trader expectation can increase the nominal and real exchange rates volatility. This model shows that there is relationship between exchange rates and any macroeconomic aggregates, then "disconnect exchange rate puzzle" does not establish for economic Iran. We suggest that the government with the increase of "Tobin tax" can reduce the exchange rate volatility, of course the effect of a Tobin tax on exchange rate volatility depends crucially on the structure of the foreign exchange market and the interaction of the Tobin tax with other trading costs.

It is impossible to estimate and ensure the safety of a double-layer space structure without consideration of the influences of uncertainties. In fact, precise manufacturing and assembling of such structure with hundreds or thousands of members is almost impossible and the existence of several IMPERFECTIONS such as non-rectilinearity of geometric axis of members, material and connection defects, initial lack of fit and residual stresses, which inherently has random nature, is inevitable. Consequently, the response of a real-life structure has also random nature. So this paper investigates the effects of these random IMPERFECTIONS on reliability of double-layer space structures by using Monte Carlo simulation method. OpenSees finite element software package is used to perform the numerical analysis. It is demonstrated that these random IMPERFECTIONS have significant influences on reliability assessment of double-layer space structures.

This paper presents a novel event-triggered predictive control (ETPC) approach for the stabilization of discrete-time output-feedback networked control systems (NCSs). The studied NCS is considered to be subject to both random external input and output disturbances, and network IMPERFECTIONS including random communication delay, random packet dropout, packet disorder, limitation of network bandwidth, and network resources. In the proposed algorithm, an observer-based event detector is designed for reducing the number of sent packets through the communication network using the estimated system states by the Luenberger observer. In this way, the system’s energy resources are saved and network-induced effects are skipped. A switched predictive controller with multiple gains are used to compensate for network-induced effects. Controller gains are designed compatible with different possible values of delays and packet dropouts. A novel augmented representation of the state-space equations of the system is derived to design observer gain and controller gains. The asymptotic stability of the system is guaranteed by designing the observer and controller based on the Lyapunov function through solving linear matrix inequalities (LMIs). Putting all the aforementioned points together has made the whole framework presented in this paper a comprehensive one. The effectiveness of the proposed approach is demonstrated by comparative simulation results.

This study aims to investigate the effects of geometric IMPERFECTIONS on buckling of thin cylindrical shells due to global shear. To this end, more than 320 finite element models of cylindrical shells with different diameter to thickness ratios were prepared. Random IMPERFECTIONS with different amplitudes were applied to numerical models. The results revealed that global buckling of cylindrical shells are susceptible to imperfection patterns. It was also shown that Yamaki’s expression can be considered as upper band for plastic shear buckling of thin cylindrical shells.

Although many researchers investigated the effect of GEOMETRICAL imperfection on the buckling load of unstiffened shells, the stiffened shells have not been studied yet. In this paper, the effects of GEOMETRICAL imperfection the buckling load of unstiffened and stiffened composite shell with and without cutout are investigated. For this goal, several specimens are manufactured and tested. The mechanical properties of fibers and resin matrix and volume fraction of fibers in the shell and the stiffeners are determined based on the standard tests. Finally, the mechanical properties of each component are calculated by micromechanical relations. These properties are used for finite element modeling by ABAQUS package. Linear eigenvalue analysis and nonlinear RIKS method -which can consider the GEOMETRICAL imperfection- are used. FE results are validated in comparison with experimental tests. Using FE model, the effects of imperfection amplitude on the buckling behavior of unstiffened and stiffened shell with and without cutout are studied. The results show that GEOMETRICAL IMPERFECTIONS have more effect on the buckling load of unstiffened shells in comparison with stiffened ones. Nevertheless, ignoring these IMPERFECTIONS and using eigenvalue analysis overestimates the buckling load. This fact is further evidence for shells without an opening. In perforated shells, the cutout itself represents an imperfection that is much more significant than geometric IMPERFECTIONS.

This study aimed to investigate the effects of stiffeners on buckling of thin cylindrical shells under uniform axial compression. To this end, more than 300 finite element models of stiffened cylindrical shells were prepared. The variables considered are shell thickness, number, dimension and the location of the vertical and horizontal stiffeners as well as circular symmetrical IMPERFECTIONS. Results show that the stiffeners can increase buckling of the stiffened cylindrical shells under axial compression. It is also shown that buckling of the cylindrical shells is susceptible to some circular imperfection patterns. In this context, buckling graph of the models are compared with each other; obviously, the stiffened shells with more stiffeners have upper buckling graph in force - displacement curves.