一种基于模态强度筛选的水面干扰抑制方法

在浅海环境中,水面离散强干扰严重影响水下目标的远程预警探测。理论上,浅海常见的负梯度声速剖面下,水面声源和水下声源激发的简正波模态具有明显差异性。基于模波束形成方法,通过对声源激发简正波模态强度的筛选,对水面干扰进行抑制。仿真表明:模态强度筛选能够通过对水面干扰激发的模态强度的剔除,抑制水面干扰,但定位精度不高;快拍数的增加和声源激发模态数的增多均有利于提高水下目标定位精度,且快拍数增加对于提高分辨率效果更为显著。

基于强度和模态分析的CDV副车架优化设计

以CDV副车架为研究对象,对其进行了强度和模态分析。CAE分析与台架测试、道路耐久试验表明,优化后,该车架的结构强度得到提升,本体质量降低了8.16%,其固有频率更是远离了悬架系统的共振频率,性能得到了提升。

基于Workbench的重型货车驾驶室强度分析

货车驾驶室的强度与模态特性对货车乘员的安全以及乘坐舒适至关重要。为了更好地对货车驾驶室的强度进行分析,对其优化提出建议,本文建立了某重型货车驾驶室的有限元模型,对弯曲、扭转工况进行静强度分析,并对其进行自由模态分析,在保证力学特性的同时,对驾驶室应力集中和变形较大的部分提出了改进意见。

Influence of technical parameters on strength and ductility of AlSi9Cu3 alloys in squeeze casting

An orthogonal test was conducted to investigate the influence of technical parameters of squeeze casting on the strength and ductility of AISigCu3 alloys. The experimental results showed that when the forming pressure was higher than 65 MPa, the strength （ab） of A1Si9Cu3 alloys decreased with the forming pressure and pouring temperature increasing, whereas ab increased with the increase of filling velocity and mould preheating temperature. The ductility （6） by alloy was improved by increasing the forming pressure and filling velocity, but decreased with pouring temperature increasing. When the mould preheating temperature increased, the ductility increased first, and then decreased. Under the optimized parameters of pouring temperature 730 ℃, forming pressure 75 MPa, filling velocity 0.50 m/s, and mould preheating temperature 220 ℃, the tensile strength, elongation, and hardness of A1Si9Cu3 alloys obtained in squeeze casting were improved by 16.7%, 9.1%, and 10.1%, respectively, as compared with those of sand castings.

基于Hypermesh的重卡传动轴有限元分析

传动轴作为重型卡车传动系统中的重要部分,起着传递发动机功率的重要作用,但其强度不足会引发失效和结构笨重等问题。针对这些问题,文章基于HYPERMESH有限元软件对某商用车的传动轴强度、模态与吊挂模态强度进行分析,检验此商用车的传动轴设计是否存在缺陷。根据强度分析结果与满足结构安全的要求,提出结构改进方案,对传动轴设计的进一步优化具有参考意义。

L2 Syntactic Alignment in the Reading-Writing Integrated Continuation Task: Evidence From Chinese EFL Learners’ Description of Motion Events

This study investigated how the mode in which the reading-writing integrated continuation task was conducted modulates the effects of second language(L2) syntactic alignment, through the English motion event construction with manner verbs. Ninety Chinese students were assigned to either of the two experimental groups or a control group, and they all experienced a pretest, an alignment phase and a posttest. In the alignment phase, the two experimental groups completed a reading-writing integrated continuation task but in different modes. For the multi-turn mode,participants reconstructed a picture story by continuing the episodes extracted from the story with one episode presented and continued at a time;for the single-turn mode, the first half of the same picture story was presented as a chunk, and then participants read and continued it. Results show that L2 learners aligned with the target structure in completing the story, and the alignment effect was retained in the posttest conducted after a delay of two weeks. Moreover, syntactic alignment was modulated by task mode with the multi-turn group exhibiting stronger immediate and longterm alignment effects. We conclude that the continuation task is a fruitful context for L2 structural alignment, and the magnitude of alignment effect hinges on interactive intensity.

Influential Intensity of Urban Agglomeration on Evolution of Ecoenvironmental Pressure:A Case Study of Changchun,China

In this paper,we study the interactive relationship between the agglomeration of urban elements and the evolution of eco-environmental pressure.We build an index system for evaluating the agglomeration of urban elements and eco-environmental pressure.Using the entropy method and response intensity model,we analyze how urban elements agglomeration influenced eco-environmental pressure in Changchun from 1990 to 2012,eliciting the changing features and influential factors.Ultimately,we conclude there is a significant interactive relationship between the agglomeration of urban elements and the evolution of eco-environmental pressure in Changchun.This is inferred from the degree of this agglomeration in Changchun having increased since 1990,with the degree of eco-environmental pressure first decreasing and then increasing.Alongside this,the impact of urban elements agglomeration on eco-environmental pressure has changed from negative to positive.The main reasons behind this shift are arguably the rapid growth of urban investment and ongoing urbanization.

Dynamic compressive strength and failure mechanisms of microwave damaged sandstone subjected to intermediate loading rate

To investigate the influence of microwave heating on the dynamic behavior and failure mechanisms of rock,dynamic compression tests were conducted on microwave-irradiated sandstone specimens using a modified split Hopkinson pressure bar(SHPB)system.Experimental results show that microwave radiation can effectively weaken the compressive strength of sandstone.Rock specimens show three different failure modes under impact load:tensile failure,tensile−shear composite failure and compressive−shear failure.The dynamic Poisson’s ratio,calculated using the measured P-and S-wave velocities,is introduced to describe the deformation characteristics of sandstone.With the increase in microwave power and heating time,the Poisson’s ratio declines first and then increases slightly,and the turning point occurs at 244.6℃.Moreover,the microstructural characteristics reveal that microwave radiation produces dehydration,pore expansion,and cracking of the rock.The damage mechanisms caused by microwave radiation are discussed based on thermal stress and steam pressure inside the rock,which provides a reasonable explanation for the experimental results.

Statistical analysis of pressure fluctuations during unsteady flow for low-specific-speed centrifugal pumps

A three-dimensional transient numerical simulation was conducted to study the pressure fluctuations in low-specific-speed centrifugal pumps. The characteristics of the inner flow were investigated using the SST k-ω turbulence model. The distributions of pressure fluctuations in the impeller and the volute were recorded, and the pressure fluctuation intensity was analyzed comprehensively, at the design condition, using statistical methods. The results show that the pressure fluctuation intensity increases along the impeller streamline from the leading edge to the trailing edge. In the impeller passage, the intensity near the shroud is much higher than that near the hub at thc inlet. However, the intensity at the middle passage is almost equal to the intensity at the outlet. The pressure fluctuation intensity is the highest at the trailing edge on the pressure side and near the tongue because of the rotor-stator interaction. The distribution of pressure fluctuation intensity is symmetrical in the axial cross sections of the volute channel. However, this intensity decreases with increasing radial distance. Hence, the pressure fluctuation intensity can be reduced by modifying the geometry of the leading edge in the impeller and the tongue in the volute.

Fast and Slow Responses of the North Pacific Mode Water and Subtropical Countercurrent to Global Warming

Six coupled general circulation models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) are em-ployed for examining the full evolution of the North Pacific mode water and Subtropical Countercurrent (STCC) under global warming over 400 years following the Representative Concentration Pathways (RCP) 4.5. The mode water and STCC first show a sharp weakening trend when the radiative forcing increases, but then reverse to a slow strengthening trend of smaller magnitude after the radiative forcing is stablized. As the radiative forcing increases during the 21st century, the ocean warming is surface-intensified and decreases with depth, strengthening the upper ocean's stratification and becoming unfavorable for the mode water formation. Moving southward in the subtropical gyre, the shrinking mode water decelerates the STCC to the south. After the radiative forcing is stabilized in the 2070s, the subsequent warming is greater at the subsurface than at the sea surface, destabilizing the upper ocean and becoming favorable for the mode water formation. As a result, the mode water and STCC recover gradually after the radiative forc-ing is stabilized.

Wing crack propagation model under high hydraulic pressure in compressive-shear stress state

A new wing crack model subjected to hydraulic pressure and far-field stresses was proposed considering the effect of hydraulic pressure in wing crack and the connected part of the main crack on the stress intensity factor at the wing crack tip. With the equivalent crack length Ieq of the wing crack introduced, the stress intensity factor Kl at the wing crack tip was as- sumed to the sum of two terms： on one hand a component K1^（1） for a single isolated straight wing crack of length 21, and subjected to hydraulic pressure in the wing crack and far-field stresses; on the other hand a component K1（2） due to the effective shear stress induced by the presence of the equivalent main crack. The lateral tensile stress and hydraulic high pressure are the key factors that induce crack propagation unsteadily. The new wing crack theoretical model proposed can supply references for the study on hydraulic fracture in fractured masses, hydraulic fracturing in rock masses.

多模态视角下二语语用道歉行为研究

二语语用能力是二语学习者在社会环境中进行恰当交流的能力,而交流则涉及不同模态的相互作用。在道歉言语行为研究中引入多模态分析,是以新的研究范式重新审视语用学经典研究课题,可拓宽其研究视角并更加清晰地揭示语言以及其他模态在话语意义构建过程中所扮演的角色。本研究采用多模态互动分析方法,通过角色扮演任务对两名中国英语学习者与两名津巴布韦英语学习者在面对面互动交流中的道歉行为表现进行多模态分析,并绘制雷达图直观展现两组参与者的手势、头部动作、凝视、面部表情、姿势与口语六种不同模态资源的模态密度异同情况。研究发现,四名参与者在交际互动过程中凝视模态强度较高,口语模态并不完全占据所有道歉序列结构的中心地位。中国英语学习者与津巴布韦英语学习者各模态强度分别在解释策略与转移话题策略中达到最高值,表明他们对不同道歉策略的重视。相比之下中国英语学习者模态复杂度略低,表明他们未进行较复杂的行动,但仍协同使用言语与非言语模态共建会话。

考虑多振型贡献和弹塑性位移谱的改进地震动强度参数

为减小增量动力分析中结构地震反应的离散程度,提出了改进的地震动强度参数。首先,基于等效模态荷载和模态组合系数,提出并定义模态强度参数。然后,采用推广的模态推覆方法,构造1阶振型的等效单自由度体系,采用非线性时程分析计算该体系的弹塑性位移谱谱值,用于修正1阶模态强度参数。最后,组合各阶模态强度参数,得到改进的地震动强度参数。对不同矢跨比的两个格构钢拱模型进行36条地震波的增量动力分析结果表明,改进参数可有效减小结构反应离散性。相比于其他常用地震动强度参数,该参数对各项需求指标拟合结果的判定系数均处于0.9678~0.9786范围内,拟合标准差均处于0.195~0.239范围内,具有更好的相关性、有效性。同时,该参数拟合斜率较高,具有较好实用性;其拟合残差通过了显著性检验,满足充分性的要求。

城轨地铁齿轮箱吊杆自主化统型设计研究

为了降低城轨地铁齿轮箱吊杆采购成本以及设计质量风险管控,对其进行自主化设计和统型研究,采用CATIA和ANSYS仿真软件对齿轮箱吊杆进行三维设计、静强度、疲劳强度及模态计算,并开展产品试制和试装车验证。试验结果显示:齿轮箱吊杆有限元分析强度满足要求,其静态径向、轴向、扭转、偏转等刚度试验验证合格,结合外观尺寸检查以及其他关键试验验证,该齿轮箱吊杆所有性能均满足列车行驶要求,试装车运行考核达标。研究结果表明:自主化统型设计吊杆,化繁为简,减少吊杆组成种类,逐渐平台化。在效益以及质量管控方面具有较高价值,也为列车大修提供有力的参考与保障。

裂纹参数和筋条布局对共振九宫板动态应力强度因子的影响

由于裂纹的出现会改变振动结构的断裂行为,本文建立了含中心裂纹九宫板结构的有限元模型并采用模态叠加原理快速求解出该结构在共振条件下的裂纹尖端应力强度因子(SIF),然后分析并讨论了裂纹参数(偏转角度和裂纹长度)及筋条布局对应力强度因子的影响。结果表明:随着裂纹偏转角度的增加,Ⅰ、Ⅱ和Ⅲ型应力强度因子最大值分别表现出不同的变化趋势(单调增加、无显著变化、先增加后减小);裂纹长度同时影响应力强度因子最大值和裂纹类型;对于裂纹参数相同的九宫板,筋条布局改变了结构的模态振型,从而导致不同裂纹类型出现;特别地,当九宫板中央区域为正方形时,应力强度因子最大值和裂纹类型对裂纹偏转角度不敏感。

Influence of static pre-loading on the dynamic bending strength of concrete with particle element modeling

Experimental tests show that static pre-loading has a significant effect on the dynamic strength of concrete.Based on meso-scale particle element model,numerical simulations of dynamic bending tests with pre-loading are performed.Complete stress–strain relationships are then obtained.Significant increase in dynamic strength is found when the pre-loadings are imposed within the elastic limit of concrete.However,when the imposition of pre-loadings reaches the plastic or softening range,dynamic strengths may gradually decrease along with the increase in pre-loadings.The distribution of energy components and the failure modes are discussed to explain the mechanisms of the phenomena.

Bending characteristics of dual-hole PM-PCF based on LP_(01) and LP_(11) modal interference

The bending characteristics of dual-hole polarization maintaining photonic crystal fiber(PM-PCF) are demonstrated in this paper. The modal interference is induced by the LP_(01) mode and LP_(11) mode propagating in a single PM-PCF with the same polarization direction. Simulation results demonstrate that the bending radius induces the phase difference between LP_(01) mode and LP_(11) mode, which leads to the change of light interference intensity on the fiber output facet. The relationship between bending radius and normalized interference intensity with three different bending angles is discussed, where the bending angle is defined as the angle between hole axis and the x axis. The bending sensitivity is obtained to be about-188.78/m around the bending radius of 1.5 cm with the bending angle of 90°. The bending characteristics can contribute for online bending detection in widespread areas.

Room-Temperature Steady-State Entanglement in a Four-Mode Optomechanical System

Stationary entanglement in a four-mode optomechanical system,especially under room-temperature,is discussed.In this scheme,when the coupling strengths between the two target modes and the mechanical resonator are equal,the results cannot be explained by the Bogoliubov-mode-based scheme.This is related to the idea of quantummechanics-free subspace,which plays an important role when the thermal noise of the mechanical modes is considered.Significantly prominent steady-state entanglement can be available under room-temperature.