Study on the Influence of Aspect Ratio on the Seismic Response and Overturning Resistance of a New Staggered Story Isolated Structure

The aspect ratio of the structure has a significant impact on the overall stability of the ultra high-rise building. A large aspect ratio of the structure increases the risk of overturning and reduces the lateral stiffness of the structure, leading to significant tensile and compressive stresses in the isolated bearings. To study the effect of aspect ratio on the seismic response and overturning resistance of a new staggered story isolated structure, three models with different aspect ratios were established. Nonlinear time-history analysis of the three models was conducted using ETABS finite element software. The results indicate that the overturning moment and overturning resistance moment of the superstructure in the new staggered story isolated structure increase with an increasing aspect ratio. However, the increase in the overturning moment of the superstructure is much greater than the increase in the overturning resistance moment, resulting in a decrease in the overturning resistance ratio of the superstructure with an increasing aspect ratio. The overturning moment and overturning resistance moment of the substructure in the new staggered story isolated structure decrease with an increasing aspect ratio. However, the decrease in the overturning moment of the substructure is greater than the decrease in the overturning resistance moment, leading to an increase in the overturning resistance ratio of the substructure with an increasing aspect ratio. The decrease in the overturning resistance ratio of the superstructure in the new staggered story isolated structure is much greater than the increase in the overturning resistance ratio of the substructure. Therefore, as the aspect ratio of the overall structure increases, the overturning resistance ratio of the superstructure and the entire structure decreases.

Progressive Collapse Resistance of a New Staggered Story Isolated System

A new staggered isolated system developed from the mid-story isolated system is the new staggered story isolated system. There are not many studies on this structure currently. In this study, an 18-story new staggered story isolated system model is established using SAP2000. The dynamic nonlinear dynamic alternate method is used to analyze the structure against progressive collapse. Results show that the structure has good resistance to progressive collapse, and there is no progressive collapse under each working condition. The progressive collapse does not occur for the case of removing only one vertical structural member of the new staggered of isolated system. The side column has big influence on this isolated structures’ progressive collapse;the removal of vertical structural member of the isolation layer has less impact on the structure than the removal of the bottom vertical structural member. After the removing of the member, the internal force of the structure will be redistributed, and the axial force of the adjacent columns will change obviously, showing a trend of “near large and far small”.

Improved Staggered Algorithm for Phase-Field Brittle Fracture with the Local Arc-Length Method

The local arc-length method is employed to control the incremental loading procedure for phase-field brittle fracture modeling.An improved staggered algorithm with energy and damage iterative tolerance convergence criteria is developed based on the residuals of displacement and phase-field.The improved staggered solution scheme is implemented in the commercial software ABAQUS with user-defined element subroutines.The layered system of finite elements is utilized to solve the coupled elastic displacement and phase-field fracture problem.A one-element benchmark test compared with the analytical solution was conducted to validate the feasibility and accuracy of the developed method.Our study shows that the result calculated with the developed method does not depend on the selected size of loading increments.The results of several numerical experiments show that the improved staggered algorithm is efficient for solving the more complex brittle fracture problems.

Buckling morphology of glassy nematic films with staggered director field

The photo-induced buckling of axially periodic glassy nematic films with alternating stripped director domains is explored by the F¨oppl-von K′arm′an plate theory along with a modified kinetics approach.The effects of domain widths on the critical light intensity as well as the buckling morphology are examined numerically.It is found that in most cases the buckled film forms regularly aligned dimples and protrusions,but shows large scale bending perpendicular to the periodic axis if the widths of the stripes are nearly the same.In addition,change in light intensity is shown to alter the wavenumber of the buckling pattern.These results are expected helpful to the design of shape-shifting structures with glassy nematic films.

基于L_(1)&TV正则化的低过采样Staggered SAR成像方法

高分辨率宽测绘带(high-resolution and wide-swath,HRWS)成像是星载合成孔径雷达(synthetic aperture radar,SAR)发展的重要趋势。Staggered SAR通过改变脉冲重复频率(pulse repetition frequency,PRF)将盲区分散在整个成像带内,可以将距离向幅宽扩展为传统体制的数倍。针对变PRF模式存在的非均匀采样和回波数据丢失问题,提出了一种基于L_(1)&TV正则化的低过采样Staggered SAR成像方法。所提方法可以在不恢复丢失数据的情况下实现方位模糊抑制,并且在稀疏重构模型中引入TV正则化项,从而实现分布式目标的精确重构。仿真和实际数据实验验证了所提方法的有效性。

Numerical simulation of seismic wavefields in TTI media using the rotated staggered-grid compact finite-difference scheme

Numerical simulation in transverse isotropic media with tilted symmetry axis（TTI） using the standard staggered-grid finite-difference scheme（SSG）results in errors caused by averaging or interpolation. In order to eliminate the errors, a method of rotated staggered-grid finite-difference scheme（RSG） is proposed. However, the RSG brings serious numerical dispersion. The compact staggered-grid finite-difference scheme（CSG） is an implicit difference scheme, which use fewer grid points to suppress dispersion more effectively than the SSG. This paper combines the CSG with the RSG to derive a rotated staggered-grid compact finite-difference scheme（RSGC）. The numerical experiments indicate that the RSGC has weaker numerical dispersion and better accuracy than the RSG.

Cosine-modulated window function-based staggered-grid finite-difference forward modeling

The numerical dispersion and computational cost are high for conventional Taylor series expansion staggered-grid finite-difference forward modeling owing to the high frequency of the wavelets and the large grid intervals. In this study, the cosine-modulated binomial window function （CMBWF）-based staggered-grid finite-difference method is proposed. Two new parameters, the modulated time and modulated range are used in the new window function and by adjusting these two parameters we obtain different characteristics of the main and side lobes of the amplitude response. Numerical dispersion analysis and elastic wavefield forward modeling suggests that the CMBWF method is more precise and less computationally costly than the conventional Taylor series expansion staggered-grid finite-difference method.

Variable-order rotated staggered-grid method for elastic-wave forward modeling

Numerical simulations of a seismic wavefield are important to analyze seismic wave propagation. Elastic-wave equations are used in data simulation for modeling migration and imaging. In elastic wavefield numerical modeling, the rotated staggered-grid method （RSM） is a modification of the standard staggered-grid method （SSM）. The variable-order method is based on the method of variable-length spatial operators and wavefield propagation, and it calculates the real dispersion error by adapting different finite-difference orders to different velocities. In this study, the variable-order rotated staggered-grid method （VRSM） is developed after applying the variable-order method to RSM to solve the numerical dispersion problem of RSM in low-velocity regions and reduce the computation cost. Moreover, based on theoretical dispersion and the real dispersion error of wave propagation calculated with the wave separation method, the application of the original method is extended from acoustic to shear waves, and the calculation is modified from theoretical to time-varying values. A layered model and an overthrust model are used to demonstrate the applicability of VRSM. We also evaluate the order distribution, wave propagation, and computation time. The results suggest that the VRSM order distribution is reasonable and VRSM produces high-precision results with a minimal computation cost.

Impact of Impeller Stagger Angles on Pressure Fluctuation for a Double-Suction Centrifugal Pump

Pressure fluctuation may cause high amplitude of vibration of double-suction centrifugal pumps, but the impact of impeller stagger angles is still not well understood. In this paper, pressure fluctuation experiments are carried out for five impeller configurations with different stagger angles by using the same test rig system. Results show that the stagger angles exert negligible effects on the characteristics of head and efficiency. The distributions of pressure fluctuations are relatively uniform along the suction chamber wall, and the maximum pressure fluctuation amplitude is reached near the suction inlet tongue region. The pressure fluctuation characteristics are affected largely by impeller rotation, whose dominant frequencies include impeller rotation frequency and its harmonic frequencies, and half blade passage frequency. The stagger angle exerts a small effect on the pressure fluctuations in the suction chamber while a great effect on the pressure fluctuation in volute casing, especially on the aspect of decreasing the amplitude on blade passage frequency. Among the tested cases, the distribution of pressure fluctuations in the volute becomes more uniform than the other impeller configurations and the level of pressure fluctuation may be reduced by up to 50% when the impeller stagger angle is close to 24° or 360°.The impeller structure pattern needs to be taken into consideration during the design period, and the halfway staggered impeller is strongly recommended.

Irregular surface seismic forward modeling by a body-fitted rotated–staggered-grid finite-difference method

Finite-difference(FD) methods are widely used in seismic forward modeling owing to their computational efficiency but are not readily applicable to irregular topographies. Thus, several FD methods based on the transformation to curvilinear coordinates using body-fitted grids have been proposed, e.g., stand staggered grid(SSG) with interpolation, nonstaggered grid, rotated staggered grid(RSG), and fully staggered. The FD based on the RSG is somewhat superior to others because it satisfies the spatial distribution of the wave equation without additional memory and computational requirements; furthermore, it is simpler to implement. We use the RSG FD method to transform the firstorder stress–velocity equation in the curvilinear coordinates system and introduce the highprecision adaptive, unilateral mimetic finite-difference(UMFD) method to process the freeboundary conditions of an irregular surface. The numerical results suggest that the precision of the solution is higher than that of the vacuum formalism. When the minimum wavelength is low, UMFD avoids the surface wave dispersion. We compare FD methods based on RSG, SEM, and nonstaggered grid and infer that all simulation results are consistent but the computational efficiency of the RSG FD method is higher than the rest.

A method of solving the stiffness problem in Biot＇s poroelastic equations using a staggered high-order finite-difference

In modelling elastic wave propagation in a porous medium, when the ratio between the fluid viscosity and the medium permeability is comparatively large, the stiffness problem of Blot＇s poroelastic equations will be encountered. In the paper, a partition method is developed to solve the stiffness problem with a staggered high-order finite-difference. The method splits the Biot equations into two systems. One is stiff, and solved analytically, the other is nonstiff, and solved numerically by using a high-order staggered-grid finite-difference scheme. The time step is determined by the staggered finite-difference algorithm in solving the nonstiff equations, thus a coarse time step may be employed. Therefore, the computation efficiency and computational stability are improved greatly. Also a perfect by matched layer technology is used in the split method as absorbing boundary conditions. The numerical results are compared with the analytical results and those obtained from the conventional staggered-grid finite-difference method in a homogeneous model, respectively. They are in good agreement with each other. Finally, a slightly more complex model is investigated and compared with related equivalent model to illustrate the good performance of the staggered-grid finite-difference scheme in the partition method.

Effect of extrusion ratio on the microstructure and texture evolution of AZ31 magnesium alloy by the staggered extrusion(SE)

There are many problems with the conventional processes of magnesium alloy bending products,such as long processes and difficulty in controlling the product shape.This paper provides a staggered extrusion(SE)process to solve the above manufacturing bottlenecks.The effects of different extrusion ratios(λ)on the AZ31 magnesium alloy bending products prepared by the SE process was investigated in this paper.The results show that the bending radii of the AZ31 Mg bending products increase with the increase ofλat the same staggered distance(h=16 mm).When A is in creased from 11.11 to 44.44,the average bending radius of bending products is decreased from 14.7 mm to 9 mm,and the average grain size is decreased by 59.43%.After the SE process,the extruded fiber texture of the AZ31 Mg bending products is obvious,and the deformed texture is a mixed texture of{0001}(10-10)deformation texture and{10-11}(11-20)recrystallization texture.The results of XRD and EBSD showed that pyramidal slip is an important mode of crystal slip systems in AZ31 magnesium alloys during the SE process.It provided a scientific basis for forming AZ31 Mg alloy bending products with excellent microstructure by the SE process.

Combined support mechanism of rock bolts and anchor cables for adjacent roadways in the external staggered split-level panel layout

Using the spatial structure of the external staggered split-level panel layout,a combined support technology for adjacent roadways was developed and analyzed for a rock bolt and anchor cable mechanism.The influence of the side rock bolt and anchor cable parameters on the mechanical properties of the anchorage body and the support stress distribution of the lateral coal body were revealed using the FLAC3D software.The optimal support parameters of the side rock bolts and anchor cables were subsequently determined,and the support effect of gob-side entry in a mining scenario was verified.The results show that the support of the side rock bolts and anchor cables improves the mechanical properties and stress state of the anchorage body,producing a good protective effect on the coal body of the air-intake entry roof and side wall.This is beneficial to the stability of the side wall and the realization of the suspension effect for roof rock bolts and anchor cables,which in turn makes the surrounding rock maintenance of the gob-side entry to a thick coal seam more favorable.

Microstructure evolution and corrosion resistance of AZ31 magnesium alloy tube by stagger spinning

This study fabricates an AZ31 magnesium alloy tube by spinning technology-power stagger forward spinning.The microstructure evolution of the tube is investigated by combining electron backscatter diffraction and transmission electron microscopy analysis,and the corrosion resistance is measured by an electrochemical corrosion test.Results show that the grains are obviously more uniform and finer along the wall thickness’s direction of the AZ31 alloy tube after the third spinning pass.The number of twins ascends first and then descends,while the varying trend of low-angle grain boundaries(LAGBs)is opposite to that of the twins as the spinning pass increases.With the increase of the total spinning deformation,the deformation texture initially increases and the c-axis of the{0001}crystal plane gradually rotates to the axial direction of the tube;the deformation texture then decreases and the orientation of grains becomes more random.The main mechanism of grain refinement is dynamic recrystallization by the twin-induced way and bowing out of the nucleation at grain boundaries during the first and second pass.However,the dominant mechanism of the refined grain is the high-temperature dynamic recovery in the third pass,and the microstructure mainly consists of substructured grains.After the spinning deformation,the corrosion resistance of the AZ31 alloy tube decreases due to the combined effect of twins and high density-dislocations.

Effect of cyclotron resonance on ‘hot’ dispersion in a staggered double metallic grating sheet beam travelling wave tube

Based on the beam wave synchronous interaction in transverse and longitudinal directions at the same time and starting from Maxwell’s equation and linear Vlasov equation, the beam–wave interaction ‘hot’ dispersion equation considering both cyclotron resonance and Cherenkov resonance in a staggered double metallic grating traveling wave tube is deduced.Through the reasonable selection for geometric and electrical parameters, the numerical calculation and analysis of the ‘hot’ dispersion equation shows that the beam–wave interaction gain and frequency band with the cyclotron resonance enhancement effect are higher than those with only Cherenkov resonance radiation.

Fluid Flow Past a Circular Cylinder with Tandem Rod and Staggered Rod at Low Reynolds Number

The flow past a primary cylinder with one tandem control rod and one staggered control rod is simulated in this paper through solving the Navier-Stokes equations. Two examples are simulated to validate the model, and the results matched well with those of previous researches. The Reynolds number based on the diameter of the primary cylinder is 500. The diameter ratio between the control rod and the primary cylinder （d/D） is 0.25. It was found that the effect of the combination of one upstream tandem control rod and one staggered control rod on the hydrodynamics of the primary cylinder is a linear superposition of the effect of a corresponding single control rod, and the effect of the upstream tandem control rod is dominant at larger spacing ratios such as G/D=2. For the combination of a downstream tandem control rod and a staggered control rod, the effect of the control rods is different from that of the corresponding single control rod in the region of 0.2〈G/D〈0.5 ＆ 30°〈a〈120° and 0.9〈G/D〈1.4 ＆ 30°〈a〈50°, where the additional effect is obvious. In this case, the effect of the downstream tandem control rod is dominant at small spacing ratios （such as G/D=0.1）. At moderate spacing ratios such as G/D=0.4, the effects of the tandem control rod and the staggered control rod are comparable in both cases.

A scheme to treat the singularity in global seismic wavefield simulation using pseudospectral method with staggered grids

The pseudospectral method has been applied to the simulation of seismic wave propagation in 2-D global Earth model. When a whole Earth model is considered, the center of the Earth is included in the model and then singularity arises at the center of the Earth where r=0 since the 1/r term appears in the wave equations. In this paper, we extended the global seismic wavefield simulation algorithm for regular grid mesh to staggered grid configuration and developed a scheme to solve the numerical problems associated with the above singularity for a 2-D global Earth model defined on staggered grid using pseudospectral method. This scheme uses a coordinate transformation at the center of the model, in which the field variables at the center are calculated in Cartesian coordinates from the values on the grids around the center. It allows wave propagation through the center and hence the wavefield at the center can be stably calculated. Validity and accuracy of the scheme was tested by compared with the discrete wavenumber method. This scheme could also be suitable for other numerical methods or models parameterized in cylindrical or spherical coordinates when singularity arises at the center of the model.

A staggered double vane circuit for a W-band traveling-wave tube amplifier

Based on the combination of a staggered double vane slow wave structure （SWS） and round electron beam, a 200-W W-band traveling-wave tube （TWT） amplifier is studied in this paper. The main advantages of round beam operation over the sheet beam is that the round beam can be formed more easily and the focus requirement can be dramatically reduced. It operates in the fundamental mode at the first spatial harmonic. The geometric parameters are optimized and a transition structure for the slow wave circuit is designed which can well match the signal that enters into and goes out from the tube. Then a TWT model is established and the particle-in-cell （PIC） simulation results show that the tube can provide over 200-W output power in a frequency range of 88 GHz-103 GHz with a maximum power of 289 W at 95 GHz, on the assumption that the input power is 0.1 W and the beam power is 5.155 kW. The corresponding conversion efficiency and gain at 95 GHz are expected to be 5.6% and 34.6 dB, respectively. Such amplifiers can potentially be used in high power microwave-power-modules （MPM） and for other portable applications.

Quantum Monte Carlo study on the phase transition for a generalized two-dimensional staggered dimerized Heisenberg model

In order to gain a deeper understanding of the quantum criticality in the explicitly staggered dimerized Heisenberg models, we study a generalized staggered dimer model named the J0 J1 J2 model, which corresponds to the staggered j-j′ model on a square lattice and a honeycomb lattice when J1/J0 equals 1 and O, respectively. Using the quantum Monte Carlo method, we investigate all the quantum critical points of these models with J1/J0 changing from 0 to 1 as a function of coupling ratio a = J2/J0. We extract all the critical values of the coupling ratio ac for these models, and we also obtain the critical exponents v,β/ν, and η using different finite-size scaling ansatz,. All these exponents are not consistent with the three-dimensional Heisenberg universality class, indicating some unconventional quantum ciriteial points in these models.

Source wavefield reconstruction based on an implicit staggered-grid finite-difference operator for seismic imaging

Reverse time migration and full waveform inversion involve the crosscorrelation of two wavefields,propagated in the forward-and reverse-time directions,respectively.As a result,the forward-propagated wavefield needs to be stored,and then accessed to compute the correlation with the backward-propagated wavefield.Boundary-value methods reconstruct the source wavefield using saved boundary wavefields and can significantly reduce the storage requirements.However,the existing boundary-value methods are based on the explicit finite-difference(FD)approximations of the spatial derivatives.Implicit FD methods exhibit greater accuracy and thus allow for a smaller operator length.We develop two(an accuracy-preserving and a memory-efficient)wavefield reconstruction schemes based on an implicit staggered-grid FD(SFD)operator.The former uses boundary wavefields at M layers of grid points and the spatial derivatives of wavefields at one layer of grid points to reconstruct the source wavefield for a(2M+2)th-order implicit SFD operator.The latter applies boundary wavefields at N layers of grid points,a linear combination of wavefields at M–N layers of grid points,and the spatial derivatives of wavefields at one layer of grid points to reconstruct the source wavefield(0≤N<M).The required memory of accuracy-preserving and memory-efficient schemes is(M+1)/M and(N+2)/M times,respectively,that of the explicit reconstruction scheme.Numerical results reveal that the accuracy-preserving scheme can achieve accurate reconstruction at the cost of storage.The memory-efficient scheme with N=2 can obtain plausible reconstructed wavefields and images,and the storage amount is 4/(M+1)of the accuracy-preserving scheme.