Cascaded ELM-Based Joint Frame Synchronization and Channel Estimation over Rician Fading Channel with Hardware Imperfections

Due to the interdependency of frame synchronization(FS)and channel estimation(CE),joint FS and CE(JFSCE)schemes are proposed to enhance their functionalities and therefore boost the overall performance of wireless communication systems.Although traditional JFSCE schemes alleviate the influence between FS and CE,they show deficiencies in dealing with hardware imperfection(HI)and deterministic line-of-sight(LOS)path.To tackle this challenge,we proposed a cascaded ELM-based JFSCE to alleviate the influence of HI in the scenario of the Rician fading channel.Specifically,the conventional JFSCE method is first employed to extract the initial features,and thus forms the non-Neural Network(NN)solutions for FS and CE,respectively.Then,the ELMbased networks,named FS-NET and CE-NET,are cascaded to capture the NN solutions of FS and CE.Simulation and analysis results show that,compared with the conventional JFSCE methods,the proposed cascaded ELM-based JFSCE significantly reduces the error probability of FS and the normalized mean square error(NMSE)of CE,even against the impacts of parameter variations.

RESEARCH ON IMPERFECTION SENSITIVE REGION OF SINGLE-LAYER LATTICED DOMES

The concept of the imperfection sensitive region is given. The advanced stochastic imperfection method is used to research the imperfection sensitive region of single-layer latticed domes. Taking a K6 single-layer latticed dome with a diameter of 50 m as an example, its imperfection sensitive region is made up of the first 12 kinds of joints. The influence of the imperfections of support joints on the stability of the K6 single-layer latticed dome is negligible. Influences of the joint imperfections of the main rib and the secondary rib on the structural stability are similar. The initial deviations of these joints all greatly lower the critical load of the dome. Results show that the method can analyze the structural imperfection sensitive region quantitatively and accurately.

Optimum design of hierarchical stiffened shells for low imperfection sensitivity

A concept of hierarchical stiffened shell is proposed in this study, aiming at reducing the imperfection sen- sitivity without adding additional weight. Hierarchical stiffened shell is composed of major stiffeners and minor stiff- eners, and the minor stiffeners are generally distributed between adjacent major stiffeners. For various types of geo- metric imperfections, e.g., eigenmode-shape imperfections, hierarchical stiffened shell shows significantly low imper- fection sensitivity compared to traditional stiffened shell. Furthermore, a surrogate-based optimization framework is proposed to search for the hierarchical optimum design. Then, two optimum designs based on two different opti- mization objectives （including the critical buckling load and the weighted sum of collapse loads of geometrically imperfect shells with small- and large-amplitude imperfections） are compared and discussed in detail. The illustrative example demonstrates the inherent superiority of hierarchical stiffened shells in resisting imperfections and the effectiveness of the proposed framework. Moreover, the decrease of imperfection sensitivity can finally be converted into a decrease of structural weight, which is particularly important in the development of large-diameter launch vehicles.

RELIABILITY ANALYSIS OF FRP LAMINATED PLATES WITH CONSIDERATION OF BOTH INITIAL IMPERFECTION AND FAILURE SEQUENCE

A probabilistic progressive failure analyzing method is applied to estimating the reliability of a simply supported laminated composite plate with an initial imperfection under bi-axial compression load. The initial imperfection and the strength parameters are considered as random variables. Ply-level failure probability is evaluated by the first order reliability method (FORM) together with the Tsai-Wu strength criterion and Tan criterion. Current stresses in the laminated structure are calculated by the classical lamination theory with the stiffness modified based on the last step ply failure. Probabilistically dominant ply-level failure sequences leading to overall system failure are identified, based on which the system failure probability is estimated. A numerical example is presented to demonstrate the methodology proposed. Through parameter studies it is shown that the deviation of the initial imperfection and some of the strength parameters largely influence the system reliability.

PERTURBATION ANALYSIS FOR MAGNETO-PLASTIC INSTABILITY OF FERROMAGNETIC BEAM-PLATES WITH GEOMETRIC IMPERFECTION

The magneto-plastic instability of a ferromagnetic beam-type plate with simple supports and small initial imperfection is analytically investigated in this paper for that the plastic deformation of the plate with a linear-strain hardening relation is considered when the plate is located in a strong uniformly distributed magnetic ?eld. After the distribution of magnetic ?elds related to the de?ected con?guration of plate is imaginably divided into two parts, i.e., one is related to the ?at plate and the other dependent on the perturbation of magnetic ?elds for which the plate con?guration changes from the ?at into the deformed state, the perturbation technique is employed to analyze the distribution of the perturbation magnetic ?elds in and out-of the magnetic medium of the ferromagnetic structure in a transverse magnetic ?eld, which leads to some analytical formulae/solutions for the magnetic ?elds and the resulting magnetic force exerted on the plate. Based on them, the magneto-plastic buckling and snapping of the plate in a transverse magnetic ?eld is discussed, and the critical magnetic ?eld is analytically formulated in terms of the parameters of geometry and material of the plate employed by solving the governing equation of the magneto-plastic plate in the applied magnetic ?eld. Further, the sensitivity of the initial imperfection on the magneto-plastic instability, expressed by an ampli?cation function, is obtained by solving the dynamic equation of de?ection of the plate after the inertial force in the transverse direction is taken into account. The results obtained show that the critical magnetic ?eld is sensitive to the plastic characteristic, e.g., hardening coe?cient, and the instability mode and de?ection of the plate are dependent on the geometrical imperfection as well.

New insight into the stability and dynamics of fluid-conveying supported pipes with small geometric imperfections

In several previous studies,it was reported that a supported pipe with small geometric imperfections would lose stability when the internal flow velocity became sufficiently high.Recently,however,it has become clear that this conclusion may be at best incomplete.A reevaluation of the problem is undertaken here by essentially considering the flow-induced static deformation of a pipe.With the aid of the absolute nodal coordinate formulation(ANCF)and the extended Lagrange equations for dynamical systems containing non-material volumes,the nonlinear governing equations of a pipe with three different geometric imperfections are introduced and formulated.Based on extensive numerical calculations,the static equilibrium configuration,the stability,and the nonlinear dynamics of the considered pipe system are determined and analyzed.The results show that for a supported pipe with the geometric imperfection of a half sinusoidal wave,the dynamical system could not lose stability even if the flow velocity reaches an extremely high value of 40.However,for a supported pipe with the geometric imperfection of one or one and a half sinusoidal waves,the first-mode buckling instability would take place at high flow velocity.Moreover,based on a further parametric analysis,the effects of the amplitude of the geometric imperfection and the aspect ratio of the pipe on the static deformation,the critical flow velocity for buckling instability,and the nonlinear responses of the supported pipes with geometric imperfections are analyzed.

Vertical Upheaval Buckling of Submarine Buried Heated Pipelines with Initial Imperfection

In this paper,a theoretical solution of vertical buckling is proposed with regard to the typical initial imperfection cases of submarine pipelines.Analytical tools are applied to predicting the occurrence and consequence of inservice buckling of a buried heated pipeline in Bohai Gulf.An evaluation is performed to ensure the pipeline structural integrity during operation under loading conditions.Different protection measures are proposed and their validities are analyzed.Analyses show that for the same magnitude of initial imperfection,the upheaval buckling of pipeline with isolated prop model is the most likely to occur.The empathetic model represents a special sub-case of continuous prop model,and the calculated buckle temperature is between the first stage and the second stage of post-upheaval buckling of continuous prop model.And the larger the initial imperfection,the less the axial force required for the upheaval buckling.Meanwhile,it can be seen that a peak point appears on the curves of temperature difference against buckling amplitude for small initial imperfection.Besides,trenching-burial is one kind of protection measures preventing the pipeline from thermal upheaval.The covered depth-to-diameter ratio depends on the design conditions and subsoil properties.For the given pipeline in this paper,the covered depth-to-diameter ratio is recommended to be 5.

Analysis on column-bracing forces considering random initial imperfections

A large number of column-bracing systems were modeled and analyzed by second-order analysis using finite element program ANSYS,in which the random combination of the initial imperfections between columns and horizontal braces was well considered by Monte Carlo Method.According to the analysis results,four kinds of instability modes of column-bracing systems were found,the probability density function of the mid-height horizontal bracing forces was established based on probability statistics,and the design bracing forces were also obtained.The results indicated that the above design bracing forces are smaller than that proposed by the "Code for design of steel structures"(GB50017-2003) when the top axial compressions on the braced columns are equal,and much smaller than the latter when the top axial compressions on the braced columns are unequal.The results also indicated that the random combination of the initial imperfections between columns and horizontal braces leads to the randomness of the mid-height horizontal bracing forces in compression or in tension,so that the design bracing forces can be reduced.

INFLUENCE OF INITIAL IMPERFECTION AND COUPLING BETWEEN BENDING AND EXTENSION ON VIBRATION, BUCKLING AND NONLINEAR DYNAMIC STABILITY OF LAMINATED PLATES

In this paper, the influence of init ial imperfection and coupling between bending and extension on vibration, buckling and nonlinear dynamic stability of laminated plates is studied. The governing e quation is derived. It is a nonlinear modified Mathieu Equation. Numerical solut ions of 5 typical composite materials namely, Glass_epoxy Scotch_1002, Aramid_ep oxy Kevlar_49, Boron_epoxy B4_5505, Graphite_epoxy T300_5208 and AS_3501 are co mputed. Results reveal that the existence of initial imperfection, and also coup ling effect,make the plates much more sensitive to entering parametric resonance with amplitude greater than that of perfect plates. Coupl ing effect for different composite laminates, especially, for that with few laye rs, is different. If coupling effect is neglected, the design of plate structure s for buckling and dynamic stability would unconservatively be for more than 10% .

Evaluation of the Residual Capacity of a Submarine for Different Limit States with Various Initial Imperfection Models

The current design philosophy for submarine hulls,in the preliminary design stage,generally considers as governing limit states material yielding along with various buckling modes.It is common belief that,beyond the design pressure,material yielding of the shell plating should occur first,eventually followed by local buckling,while global buckling currently retains the highest safety factor.On the other hand,in the aeronautical field,in some cases structural components are designed in such a way that local instability may occur within the design loads,being the phenomena inside the material elastic range and not leading to a significant drop in term of stiffness.This paper is aimed at investigating the structural response beyond a set of selected limit states,using nonlinear FE method adopting different initial imperfection models,to provide the designers with new information useful for calibrating safety factors.It was found that both local and global buckling can be considered as ultimate limit states,with a significant sensitivity towards initial imperfection,while material yielding and tripping buckling of frames show a residual structural capacity.In conclusion,it was found that the occurrence of local buckling leads to similar sudden catastrophic consequences as global buckling,with the ultimate strength capacity highly affected by the initial imperfection shape and amplitude.

2D hierarchical lattices' imperfection sensitivity to missing bars defect

Commercially available lattices contain various kinds of morphological imperfections which result in great degradation in lattices＇ mechanical properties, therefore, to obtain imperfection insensitive lattice structure is obviously a practical research subject. Hierarchical structure materials were found to be a class of promising anti-defect materials, This paper builds hierarchical lattice by adding soft adhesion to lattice＇s cell edges and numerical results show that its imperfection sensitivity to missing bars is minor compared with the classic lattice. Soft adhesion with appropriate properties reinforce cell edge＇s bending stiffness and thus reduce the bending deformation in lattice caused by missing bars defect, which is confirmed by statistical analysis of normalized node displacements of imperfect lattices under hydrostatic compression and shear loads.

Structural Imperfections Associated with Supersaturated Vacancies in an HPHT-Grown Diamond Single Crystal

A diamond single crystal, which was synthesized at a high temperature of 1570 K and a high pressure of 5.5 GPa in a Fe-Ni-C system, was directly and systematically examined by transmission electron microscopy (TEM). It is proposed that there exists a variety of imperfections such as dislocation loops, stacking faults, twins and stacking-fault tetrahedral in the diamond, which may be derived from the supersaturated vacancies generated during rapid cooling from high temperature. The formation process of the imperfections is discussed briefly.

Experimental and Numerical Investigation on the Ultimate Strength of Stiffened Plates with Scanned Initial Geometrical Imperfection

The study of the ultimate strength of stiffened plates is a hot topic in ocean engineering. The ultimate strength and behavior of collapse of stiffened plates were investigated using experimental and numerical methods. Two stiffened plates, with one and two half-bays in both longitudinal and transverse directions, were tested under the uniaxial compression. There were clamped boundaries at both ends of the stiffened panels and a restrained boundary on the transverse frames. The novel three-dimensional laser scanning technology was used to measure the initial geometric imperfections and the ultimate deformation of the stiffened panels after the test. The initial geometric deformation was imported into the finite element model, and the ultimate strength and behavior of collapse of the stiffened plates were calculated using the finite element analysis. FE analysis results based on the measured initial geometric imperfections were compared with the test results. It is concluded that structural deformation can be well measured by three-dimensional laser scanning technology, and can be conveniently imported into the finite element analysis. With the measured initial geometric imperfections considered, the FE analysis results agree well with the experimental results in ultimate strength, behavior of collapse, and the ultimate displacement distribution of the stiffened panels.

Simulation of the influence of imperfections on dynamical decoupling of a superconducting qubit

Dynamical decoupling is widely used in many quantum computing systems to combat decoherence. In a practical superconducting quantum system, imperfections can plague decoupling performance. In this work, imperfections in a superconducting qubit and its control system are modeled via modified Hamiltonian and collapse operator. A master equation simulation is carried out on the qubit under 1/f environment noise spectrum. The average dephasing rate of qubit is extracted to characterize the impact of different imperfections on the decoupling from dephasing. We find that the precision of pulse position, on–off ratio, and filtering effect are most critical. Bounded pulses have weaker impact,while variation in pulse width and qubit relaxation are insignificant. Consequently, alternative decoupling protocols, jitter mitigation, cascaded mixers, and pulse shaping can be conducive to the performance of decoupling. This work may assist the analysis and optimization of dynamical decoupling on noisy superconducting quantum systems.

Sensitivity analysis of composite laminated plates with bonding imperfection in Hamilton system

Sensitivity analysis of composite laminated plates with bonding imperfection is carried out based on the radial point interpolation method （RPIM） in a Hamilton system. A set of hybrid governing equations of response and sensitivity quantities is reduced using the spring-layer model and the modified Hellinger-Reissner （H-R） variational principle. The analytical method （AM）, the semi-analytical method （SAM）, and the finite difference method （FDM） are used for sensitivity analysis based on the reduced set of hybrid governing equations. A major advantage of the hybrid governing equations is that the convolution algorithm is avoided in sensitivity analysis. In addition, sensitivity analysis using this set of hybrid governing equations can obtain response values and sensitivity coefficients simultaneously, and accounts for bonding imperfection of composite laminated plates.

Postbuckling of Marine Stifened Composite Plates with Initial Geometric Imperfections Using Progressive Failure Analysis

This work explores the postbuckling behavior of a marine stifened composite plate in the presence of initial imperfections.The imperfection shapes are derived from buckling mode shapes and their combinations.Thereafter,these imperfection shapes are applied to the model,and nonlinear large defection fnite element and progressive failure analyses are performed in ANSYS 18.2 software.The Hashin failure criterion is employed to model the progressive failure in the stifened composite plate.The efect of the initial geometric imperfection on the stifened composite plate is investigated by considering various imperfection patterns and magnitudes.Results show that when the magnitude of the imperfection is 20 mm,the ultimate strength of the stifened composite plate decreases by 31%.Moreover,global imperfection shapes are found to be fundamental in determining the ultimate strength of stifened composite plates and their postbuckling.

THE IMPACT TORSIONAL BUCKLING OF ELASTIC CYLINDRICAL SHELLS WITH ARBITRARY FORM IMPERFECTION

A perturbation analysis for the impact torsional buckling of imperfective elastic cylindrical shells subjected to a step torque is given The imperfection is supposed to be small and has arbitrary form. It is shown that only the imperfection which has the shape of static torsional buckling mode could influence the critical step torque. Finally a formula is presented for the critical step torque.

Damage threshold influenced by polishing imperfection distribution under 355-nm laser irradiation

A systematic interpretation of laser-induced damage in the nanosecond regime is realized with a defect distribution buried inside the redeposited layer arising from a polishing process. Under the 355-nm laser irradiation, the size dependence of the defect embedded in the fused silica can be illustrated through the thermal conduction model. Considering CeO2 as the major initiator, the size distribution with the power law model is determined from the damage probability statistics. To verify the accuracy of the size distribution, the ion output scaling with depth for the inclusion element is obtained with the secondary ion mass spectrometer. For CeO2 particulates in size of the depth interval with ion output satisfied in the negative exponential form, the corresponding density is consistent with that of the identical size in the calculated size distribution. This coincidence implies an alternative method for the density analysis of photoactive imperfections within optical components at the semi-quantitative level based on the laser damage tests.

Research on Strengthening Method of Concave Cone-toroid-cylinder Combined Shell with Initial Imperfection

As a new joint structure,the impact of initial imperfection to stress of Concave cone-toroid-cylinder combined shell was analyzed. Firstly the location and shape of combined shell's initial imperfection caused by welding was studied. Secondly dominated stress was chosen after comparing varioustypical stress. Then it was analyzed that the influence of imperfection to dominated stress via changing the shape of frame's deflection and shell's concave-convex. At last the strengthening case for combined shell with imperfection was pointed out. The conclusions are:(1) Stress of frame 9 is more sensitive to initial imperfection than circumferential stress of toroidmidsurface,which is a new concern;(2) To strength the frames in the sides of toroid not only can decrease the stress of frame,but also can reduce the circumference stress of toroid's midsurface.

First-principles study of the structural, electronic, and magnetic properties of double perovskite Sr2FeReO6 containing various imperfections

The structural, electronic, and magnetic properties of double perovskite Sr_2FeReO_6 containing eight different imperfections of FeReor ReFeantisites, Fe1–Re1 or Fe1–Re4 interchanges, V_（Fe）, V_（Re）, VOor V_（Sr） vacancies have been studied by using the first-principles projector augmented wave（PAW） within generalized gradient approximation as well as taking into account the on-site Coulomb repulsive interaction（GGA＋U）. No obvious structural changes are observed for the imperfect Sr_2FeReO_6 containing FeReor ReFeantisites, Fe1–Re1 or Fe1–Re4 interchanges, or VSrvacancy defects. However, the six（eight） nearest oxygen neighbors of the vacancy move away from（close to） VFeor V_（Re）（VO） vacancies. The half-metallic（HM） character is maintained for the imperfect Sr_2FeReO_6 containing FeReor ReFeantisites, Fe1–Re4 interchange, V_（Fe）,VO or V_（Sr） vacancies, while it vanishes when the Fe1–Re1 interchange or VRevacancy is presented. So the Fe1–Re1 interchange and the VRevacancy defects should be avoided to preserve the HM character of Sr_2FeReO_6 and thus usage in spintronic devices. In the FeReor ReFeantisites, Fe1–Re1 or Fe1–Re4 interchanges cases, the spin moments of the Fe（Re）cations situated on Re（Fe） antisites are in an antiferromagnetic coupling with those of the Fe（Re） cations on the regular sites. In the V_（Fe）, V_（Re）, VO, or V_（Sr） vacancies cases, a ferromagnetic coupling is obtained within each cation sublattice,while the two cation sublattices are coupled antiferromagnetically. The total magnetic moments μtot（μB/f.u.） of the imperfect Sr_2FeReO_6 containing eight different defects decrease in the sequence of VSrvacancy（3.50）, VRevacancy（3.43）,FeReantisite（2.74）, VOvacancy（2.64）, VFevacancy（2.51）, ReFeantisite（2.29）, Fe1–Re4 interchange（1.96）, Fe1–Re1interchange（1.87）, and the mechanisms of the saturation magnetization reduction have been analyzed.