Large Longitudinal Displacement Research Articles

Dynamic Simulation Analysis and Research of Overhang Cold Launching System

In order to study the structural dynamic response and the separation rule of launch tube and missile of the overhang cold launching system during launching, and provide a basis for the design of new overhang launching system, a dynamic model of the overhang cold launching system was established by using the rigid-flexible coupling method and multi-body dynamics according to the structural characteristics and ejection physical process of the overhang cold launching system. The accuracy and rationality of the modeling method proposed by this paper were validated against the test. Based on this, the dynamic response of ejection and outlet attitude were analysed. The results show that the dynamic model of overhang cold launching system can accurately reflect the vibration characteristics of the system. A large longitudinal displacement of the center of launch tube will occur during the ejection process. The oscillation frequency is relatively small, but the structural vibration caused by the ejection impact will have a great influence on the pitching attitude of the missile. The vibration response of the adjacent launch tube is small, which is beneficial for the continuous launching of the overhang launching system. The research results can provide a basis for the subsequent design of vibration reduction.

Research on vibration reduction of long span cable stayed bridge under fuzzy control of two kinds of membership function

In order to control the collision of long-span cable-stayed bridges with floating systems caused by large longitudinal displacement of beam ends under earthquake action, based on the engineering background of a long-span dual-purpose double-tower cable-stayed bridge, the collision problem of the main approach bridge under earthquake action is proposed. Two kinds of intelligent fuzzy control strategies based on different membership functions are presented, using MR Damper as a control device and modeled by SIMULINK. In this paper, the damping control effect of the proposed fuzzy control strategy on the collision problem of the main approach bridge of the cable-stayed bridge is studied. The results show that changing the range of the membership function will change the size of the control current, and the longitudinal displacement and acceleration of the structure will decrease with the increase in the control current. However, when the control current is too large, the acceleration response will be amplified and oscillated. Both fuzzy controls can reduce collision times, and the peak value of collision force between the main approach bridges and the energy consumption of the MR damper are roughly similar. Based on the control effect of longitudinal displacement response, acceleration response, and collision force response of the main approach bridge and the energy consumption of the damper, fuzzy control A is better than fuzzy control B.

Dynamic analysis of a multi-span simply supported prestressed concrete bridge with restrainers and seismic isolation devices

The Nonlinear F.E. code Structural Analysis Program (SAP) in which the primary nonlinear characteristics of bearings, impact elements and steel restrainer cables considered herein in order to investigate the dynamic analysis of a multi-span simply supported MSSS prestressed concrete bridge, equipped with steel restrainer cables and Lead Rubber Bearings LRB devices including Soil Structure Interaction (SSI) effects. A MSSS bridge with restrainer cables and lead rubber bearings at the two abutments and intermediate bents located in North Algeria is selected according to RPOA for seismic design category 1 is considered in this study. A detailed 3D nonlinear analytical model of study bridge subjected to three components identical seismic excitation including pounding elements, restrainer cables and bearing devices at expansion joints is developed. The nonlinear characteristics of theses boundary elements are represented by bilinear hysteretic models. Under strong seismic excitations, the large longitudinal displacements result the collision between bridge decks or even unseating of these decks at expansion joints of MSSS bridge. Finally, the study reveals among others that in order to prevent deck unseating resulting from restrainer failures and subsequent bridge collapse, particular attention should also be given to proper design of nonlinear characteristics of restrainers and bearing devices.

Nonlinear Pounding Analysis of Multispan and Simply Supported Beam Bridges Subjected to Strong Ground Motions

To investigate the nonlinear impact effect of multispan simply supported beam bridges under strong earthquakes, firstly, the dynamic motion equation, the algorithm of its solution, and some pounding modelling methods are presented and the finite element model of a considered multispan simply supported railway beam bridge is established in the nonlinear finite element software of SAP2000 in which the primary nonlinear characteristics of the bearing and the impact element are considered herein. Secondly, the natural vibration characteristic of the considered railway bridge is analyzed to prepare for the subsequent parameter analysis. Finally, the influence of three nonlinear parameters, i.e., stiffness of impact element, separation gap width of expansion joint, and bearing stiffness, on impact responses of bridge structures is studied. The results show that the first several modes of multispan simply supported beam bridges are mainly longitudinal and vertical vibrations. Under longitudinal seismic excitations, the large longitudinal displacement response is induced possibly and results in the collision or even unseating of superstructures at the expansion joints and abutments. The influence of separation gap width between adjacent decks on the pounding effect of bridges is greater than that of collision stiffness originated from the pounding modelling element. The impact force and pounding number run up to the maximum conditional on the collision stiffness of 9.9 × 109 (N/m) and the separation gap width of 0.14 (m). The bearing stiffness affects significantly the displacement of the pier top and the cross-sectional internal force at the bottom of piers but has little effect on the collision force and number.

Covalently linked perylenetetracarboxylic diimide dimers and trimers with rigid "J-type" aggregation structure.

Covalently linked perylenetetracarboxylic diimide (PDI) dimers (D1 and D2) and trimers (T1 and T2) with slipped “face-to-face” stacked structure are prepared and their molecular structures are characterized by 1H NMR, MALDI-TOF mass spectroscopy and elemental analysis. The rigid molecular structures of these compounds make it easier to establish a direct correlation between the aggregate structure and the photophysical properties. The minimized molecular structures of these compounds reveal that they are all “face-to-face” stacked aggregates with large longitudinal displacement. Their absorption spectra show red-shifted bands, suggesting the presence of “J” type excitonic coupling between the PDI subunits in these compounds. However, their steady state and time resolved fluorescence spectra revealed that the emission from the “excimer-like” states dominates the fluorescence of these compounds, this is similar to that of “H-type” aggregates and may be ascribed to the “face-to-face” stacked structure. In the fluorescence spectra of these compounds, a minor “J-type” emission can be identified for the compounds with a relatively large longitudinal displacement. An increase in the number of subunits in one aggregate from 2 to 3 also brings about distinctive changes in their photophysical properties, which can be ascribed to the changes in the stacking structure caused by the steric hindrance.

Longitudinal Vibration Control of Long-Span Railway Cable-Stayed Bridge

As the floating type cable-stayed bridge has no longitudinal constraint between the main girder and the pylon, it may cause the main girder a large longitudinal displacement and the root of tower a large longitudinal bending moment, and affect the normal use and safety of the bridge under the earthquake or the train braking. It is an important part of the design to select an appropriate vibration control scheme. Taking a long-span railway bridge for example, this paper build the finite element model and analyses the damping effect in the view of train braking, moreover, the present study also examines the dynamic behavior with focus on two parameters of damping coefficient C and damping exponent αof the viscous dampers through dynamic time-history analysis. The results show that setting viscous dampers with the reasonable parameters can reduce the vibration and the response of the bridge by train braking and have a good energy dissipation effect.

Investigation Concerning Vibration Reduction of Self-Anchored Suspension Bridge under Vehicle Braking Forces

Large longitudinal displacement would be generated by vehicle braking force in the girder of self-anchored suspension bridge, just as the floating system of cable-stayed bridge. In this paper, taking Pingsheng bridge as an engineering example, the vehicle braking force models are established according to traffic survey, furthermore dynamic response and vibration reduction of the bridge under vehicle braking force are investigated by finite element analysis. The results show that the longitudinal displacement of the girder is relatively large, and it can effectively be controlled by viscous dampers with optimal parameters.

Comparison between Shape Memory Alloy Seismic Restrainers and Other Bridge Retrofit Devices

Strong earthquakes can result in large longitudinal displacements in multiple-frame bridges. This could lead to excessive displacements/openings at the intermediate joints. Bridges with small seat widths are vulnerable to the unseating of their superstructure. Seismic steel restrainers are currently used to limit joint openings in bridges. However, past earthquakes have shown that restrainer cables have limitations in regards to preventing unseating in bridges. Other devices have been proposed to limit joint displacements, including metallic dampers, viscoelastic dampers, and shape memory alloys (SMAs), which are known for their ability to recover their original shape after being deformed. A sensitivity and a case study are conducted using computer simulations to compare the effectiveness of SMA retrofit devices with other devices. Results show that the effectiveness of the devices is a function of characteristics of the bridge frames and the ground motion characteristics. In all cases, the steel restrainer cables were the least effective in limiting joint displacements. The SMA devices have the additional benefit of significantly limiting the residual joint displacement in bridges.

Flying mirror model for interaction of a super-intense laser pulse with a thin plasma layer: Transparency and shaping of linearly polarized laser pulses

A self-consistent one-dimensional (1D) flying mirror model is developed for description of an interaction of an ultra-intense laser pulse with a thin plasma layer (foil). In this model, electrons of the foil can have large longitudinal displacements and relativistic longitudinal momenta. An approximate analytical solution for a transmitted field is derived. Transmittance of the foil shows not only a nonlinear dependence on the amplitude of the incident laser pulse, but also time dependence and shape dependence in the high-transparency regime. The results are compared with particle-in-cell (PIC) simulations and a good agreement is ascertained. Shaping of incident laser pulses using the flying mirror model is also considered. It can be used either for removing a prepulse or for reducing the length of a short laser pulse. The parameters of the system for effective shaping are specified. Predictions of the flying mirror model for shaping are compared with the 1D PIC simulations, showing good agreement.

Global diagnostics of the ionospheric perturbations related to the seismic activity using the VLF radio signals collected on the DEMETER satellite

Abstract. The analysis of the VLF signals radiated by ground transmitters and received on board of the French DEMETER satellite, reveals a drop of the signals (scattering spot) connected with the occurrence of large earthquakes. The extension of the "scattering spots" zone is large enough (1000–5000 km) and, probably, it increases with the magnitude of the "relative" earthquake. A possible model to explain the phenomenology, based on the acoustic gravity waves and the ionosphere turbulence, is proposed. The method of diagnostics applied to this study has the advantage to be a global one due to the world wide location of the powerful VLF transmitters and of the satellite reception. However, a specific disadvantage exists because the method requires rather a long time period of analysis due to the large longitudinal displacements among the successive satellite orbits. At the moment, at least, one month seems to be necessary.

Distinguishing between the bi-stripe and Wigner-crystal model: A crystallographic study of charge-orderedLa0.33Ca0.67MnO3

In order to resolve discrepancies in the charge-ordered structure between the Wigner-crystal and bi-stripe models, ${\mathrm{La}}_{0.33}{\mathrm{Ca}}_{0.67}{\mathrm{MnO}}_{3}$ was studied using quantitative electron diffraction and high-resolution imaging. Image simulations based on dynamic electron-diffraction theory suggest that the apparent difference in spacing between the ${\mathrm{Mn}}^{3+}{\ensuremath{-}\mathrm{M}\mathrm{n}}^{3+}$ and ${\mathrm{Mn}}^{3+}{\ensuremath{-}\mathrm{M}\mathrm{n}}^{4+}$ stripes, which is the basis of the bi-stripe model, can vary significantly with imaging conditions and may not directly represent the difference in actual spacing of atomic planes. Electron-diffraction study of crystal regions far away from defects, using parallel and convergent beams, reveal the existence of $a[001]$ glide planes and $n[100]$ diagonal glide planes that are incompatible with the large longitudinal displacement of the bi-stripe model. Although our study supports the Wigner-crystal model, detailed analysis suggests that, in our samples, the incommensurate charge modulation in the material has an average wave vector $\mathbf{q}=(0.284,0,\ensuremath{\xi})$ with $|\ensuremath{\xi}|=0.010.$ The symmetry breaking associated with the small component \ensuremath{\xi} along the c axis has not been previously observed by high-resolution x-ray or neutron powder diffraction.

Phase behaviour and structural characterization of poly(1,3-propylene adipate)s with cyanoazobenzene side groups

The phase behaviour and the structure of three poly(1,3-propylene adipate)s containing cyanoazobenzene side groups bonded to the backbone unit through flexible spacers with 6, 8 and 10 methylene groups have been studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD) analysis. The polyadipates behave as enantiotropic side group liquid crystalline polymers. XRD analysis has shown that the organized phase of these polyadipates possesses a crystalline or a tilted structure of the SmF or SmG type. The temperature of fusion of this phase (Tm= 45-48 C) is almost independent of the length of the side group spacers. The crystalline phase can be obtained only by prolonged annealing at room temperature because crystallization from kinetically hindered. The range of thermodynamic stability (Ti- Tm) of the mesophase formed on melting increases with the length of the side group flexible spacers. The structure of the mesophase, determined by XRD, is of the smectic A type, and is characterized by a relatively large longitudinal displacement of the side groups, which is responsible for the unusually weak low angle Bragg reflections.