小净距隧道爆破振动危害的主动控制研究

为了研究小净距下复线隧道的施工爆破对既有隧道的影响并采取合理的主动控制,采用LS-DYNA动力有限元软件建立了不同净间距时新建隧道和既有隧道的数值模型。将测点峰值振速作为判据,得到了小净距下新建隧道爆破施工时既有隧道的振速测点布置方案及相应的爆破药量优选方案:既有隧道振速测点应布置在迎爆侧边墙距地面1.2m处;随两隧道净间距L的不断减小,应分别在L为9m、8m、7m时合理降低爆破装药量,相应的爆破炸药量建议值分别为48kg、30kg、24kg。数值试验和实测数据对比分析结果表明:在两隧道净间距L从11.9m逐渐减小为6.6m的过程中,既有线实测质点峰值振速与数值分析结果的变化趋势基本一致;合理有效地控制爆破药量,是降低既有隧道爆破振动响应、保证其安全运营的关键。研究所得结论可用于指导小净距条件下新建隧道的爆破施工,实现爆破振动效应危害的主动控制。     

基于Matlab和BP神经网络的爆破振动预测系统

爆破振动预测是一个复杂的非线性问题,可应用非线性功能强大的BP神经网络技术来解决,但由于其数值计算量大、可操作性不强等特点,在实际工程中应用困难。为了解决该问题,本文中将Matlab程序的强大计算能力与VB的友好界面相结合,利用ActiveX自动化技术和BP神经网络算法,开发得到爆破振速峰值预测系统。该预测系统可根据各工程实际情况选取影响爆破振动的主要因素作为输入参数,以预测爆破振速峰值。通过在北京市昌平线暗挖区间隧道工程中的应用表明:该预测系统在实际工程中使用方便,操作简单,预测精度高,人机交互界面友好。     

小净距下穿铁路隧道爆破震动的响应研究

新建翠华山隧道与既有线小峪隧道垂直净间距仅为8m,复线隧道钻爆施工将影响既有隧道的结构安全。为保证既有线的安全运营,本文采用 ANSYS/LS-DYNA 软件建立了隧道的有限元模型,数值分析了下穿铁路隧道爆破施工时隧道间水平距离 L 为-6m～19m 时既有线的动力响应。结合既有线振动速度的实测数据,采用质点振速判据评估了下穿隧道爆破施工时既有线结构的安全性,保障了下穿隧道施工时既有隧道的运营安全。数值模拟结果分析表明：未出现新的自由面之前、爆破炸药量不变的情况下,两隧道水平间距 L 从19m 减小到10m 时,数值模拟所得峰值振速由10.5cm/s 增大到12.0cm/s;出现新的自由面之后、爆破炸药量不变的情况下,两隧道水平间距 L 从10m 变为5m 时,数值模拟所得峰值振速由12.0cm/s 减小到10.2cm/s,其后迅速衰减。因此,隧道爆破施工中可人为地创造自由面以降低爆破震动效应的危害。同时,既有线隧道迎爆面测点竖向振动速度较大,是爆破震动效应控制的薄弱部位,施工过程中应加强该部位的监控量测。     

小净距下穿铁路隧道爆破震动的响应研究

新建翠华山隧道与既有线小峪隧道垂直净间距仅为8m,复线隧道钻爆施工将影响既有隧道的结构安全。为保证既有线的安全运营,本文采用ANSYS/LS-DYNA软件建立了隧道的有限元模型,数值分析了下穿铁路隧道爆破施工时隧道间水平距离L为-6m～19m时既有线的动力响应。结合既有线振动速度的实测数据,采用质点振速判据评估了下穿隧道爆破施工时既有线结构的安全性,保障了下穿隧道施工时既有隧道的运营安全。数值模拟结果分析表明:未出现新的自由面之前、爆破炸药量不变的情况下,两隧道水平间距L从19m减小到10m时,数值模拟所得峰值振速由10.5cm/s增大到12.0cm/s;出现新的自由面之后、爆破炸药量不变的情况下,两隧道水平间距L从10m变为5m时,数值模拟所得峰值振速由12.0cm/s减小到10.2cm/s,其后迅速衰减。因此,隧道爆破施工中可人为地创造自由面以降低爆破震动效应的危害。同时,既有线隧道迎爆面测点竖向振动速度较大,是爆破震动效应控制的薄弱部位,施工过程中应加强该部位的监控量测。     

下穿隧道爆破荷载激励下边坡振动预测及能量分析

为解决边坡与下穿近接隧道协同爆破施工安全难题,结合某石油储备基地扩建项目,运用量纲推导、现场实验与信号分析相结合的方法,构建考虑高程影响的振动峰值速度公式,研究隧道爆破振动能量沿坡面的衰减机制。结果显示,边坡同台阶边沿处质点振速峰值大于坡脚处,坡面局部存在振动速度高程放大效应;引入相对坡度H/D的爆破振动模型对坡面质点振速预测精度高,可反映边坡角对高程放大效应的影响;振动速度及能量沿坡面均呈现出近区衰减快、远区衰减慢的传播特性,同时隧道爆破振动能量集中分布在0～300 Hz范围的多个子振频带,且高频能量沿坡面衰减更快,能量卓越频带中值以指数形式衰减,能量最终向低频带集中。     

毫秒延时爆破等效单响药量计算及振速预测

毫秒延时爆破存在同段雷管离散及分段振波叠加效应,对单响药量取值及质点峰值振速的预报带来极大困扰。设计开展毫秒延时爆破试验,建立群孔齐发爆破振速的计算模型,研究并构建炮孔数目对齐发爆破等效药量影响及其取值方法;并基于单孔爆破回归分析结果,提出修正的质点峰值振速与比例距离关系公式。结果表明,群孔齐发爆破等效药量比名义单响药量小,可利用缩比系数和折算炮孔数目进行计算,缩比系数随炮孔数目增加呈指数形式衰减;修正的质点峰值振速与比例距离公式引入的振波叠加因子可反映振波叠加对速度的影响,依据该公式计算得到的质点峰值振速预测值与实测值间平均绝对误差、平均相对误差及均方根误差分别为0.05 cm/s、9.52%、0.059 cm/s,用于现场爆破振动预测切实可行。     

爆破开挖振动下既有大型储油罐的动力响应

针对既有大型储油罐近区基础爆破开挖中的安全问题,采用ANSYS/LS-DYNA的隐式-显式顺序求解方法,结合流固耦合算法,研究了爆破振动下大型储油罐的动力响应规律。分析了罐壁不同位置的质点振速,由于质点振速分布情况较为复杂,不宜用局部质点振速判断罐壁危险点;总结了罐壁上应力的分布规律,结果显示爆破振动对储油罐的影响主要集中在迎爆侧下部,且在罐壁迎爆侧高度为3 m左右的位置最易发生象足屈曲;分析了不同频率爆破振动作用下满载储罐罐壁的质点振速,结果表明在爆破振动主频范围内,载荷频率远大于储罐固有频率条件下,罐壁上质点振速随着爆破振动频率的降低呈减小趋势;建立了储油罐罐壁质点振速与罐内液面高度的关系,结果表明降低液面高度可以有效提高储油罐的爆破振动安全阈值,爆破施工中邻近储罐储液高度不宜高于10 m。     

密集建筑物下隧道开挖微振控制爆破方法与振动分析

为适应城市密集建筑物下隧道爆破对振动的高安全要求, 研究用普通爆破器材进行振速精确控制的爆破技术和参数确定方法。以渝中隧道为研究背景, 在开发准确延时非电雷管的基础上, 利用傅立叶函数和MATLAB软件拟合了不同药量单孔爆破振动波形, 分析了1~50 ms不同间隔下振动叠加的量化数据; 讨论了各微差间隔时间的降振效果; 在指定振速的情况下, 确定单孔药量和微差起爆时间; 实测并分析了现场使用雷管各段微差间隔特点, 据此进行针对性的爆破设计和采用逐孔掏槽爆破进行振速控制。现场应用表明:隧道爆破振速始终小于1.00 cm/s, 在此振速下避免振动叠加的最优单孔药量为1.2 kg, 爆破振速峰值位于主掏槽的第1段或第2段雷管起爆后, 且与理论分析结果吻合较好; 逐孔起爆60 ms后振速下降50%以上。研究表明:在高安全指标下, 以非电雷管实施精确控制爆破是可以实现的。     

基于等效路径的爆破地震波衰减规律

针对露天矿山台阶爆破地形和地质条件的复杂性, 分析了地形对爆破地震波传播路径的影响, 提出了等效路径及等效距离两个概念。同时考虑岩石波阻抗和岩体的完整性系数及最大一段装药量与炸药的定容爆热等因素的影响, 构建了露天台阶爆破地震波地表质点振速峰值随等效距离衰减的表达式。通过矿山爆破震动监测检验, 发现用该公式预测地表质点振速峰值, 能够适应实际地形和地质条件的变化, 预测结果的准确性显著高于萨氏公式, 表明该公式较好地反映了质点振速峰值沿等效路径衰减的基本规律, 为台阶爆破地震波质点振速峰值预测提供了一种新方法。     

既有裂缝、空洞病害隧道爆破振动安全控制标准

爆破荷载作用下,既有隧道衬砌的振动安全振速控制标准制定,大多以既有隧道完好为前提条件,不考虑病害因子对结构动力响应的影响,与实际不相符。为此,以既有新岭隧道旁拟建新隧道为工程背景,基于既有隧道衬砌裂缝和背后空洞的实际分布特征与规律,建立带裂缝与空洞的二维、三维结构模型,分析裂缝、空洞对衬砌动力响应的影响,提出以振速为指标的标准管理体系。结果表明:裂缝的最不利分布位置为迎爆侧边墙处,裂缝的存在增强了既有衬砌对S₁应力(拉应力)的响应,振速控制标准的制定应以S₁应力和裂缝径向深度为控制指标;当裂缝径向深度为(0～1/8)h、(1/8～1/2)h和＞(1/2)h（h为衬砌厚度）时,控制标准分别为12、10和8 cm/s。空洞的最不利分布位置为拱顶,空洞的存在增强了既有衬砌对S₁应力和振速的双重响应,以增强振速响应为主,振速控制标准的制定应以振速、空洞面积及纵向长度为控制指标,空洞工况下,控制标准为12 cm/s;空洞沿隧道纵向长度小于7 m时,监控范围为3～4倍纵长;空洞沿隧道纵向长度大于7 m时,监控范围为1～1.5倍纵长;纵向长度小时,倍数取大值。     

Optically sliced measurement of velocity and pH distribution in microchannel

A simultaneous measurement technique for the velocity and pH distribution was developed by using a confocal microscope and a 3CCD color camera for investigations of a chemical reacting flow field in a microchannel. Micron-resolution particle image velocimetry and laser induced fluorescence were utilized for the velocity and pH measurement, respectively. The present study employed fluorescent particles with 1 μm diameter and Fluorescein sodium salt whose fluorescent intensity increases with an increase in pH value over the range of pH 5.0–9.0. The advantages of the present system are to separate the fluorescence of particles from that of dye by using the 3CCD color camera and to provide the depth resolution of 5.0 μm by the confocal microscope. The measurement uncertainties of the velocity and pH measurements were estimated to be 5.5 μm/s and pH 0.23, respectively. Two aqueous solutions at different pH values were introduced into a T-shaped microchannel. The mixing process in the junction area was investigated by the present technique, and the effect of the chemical reaction on the pH gradient was discussed by a comparison between the proton concentration profiles obtained from the experimental pH distribution and those calculated from the measured velocity data. For the chemical reacting flow with the buffering action, the profiles from the numerical simulation showed smaller gradients compared with those from the experiments, because the production or extinction of protons was yielded by the chemical reaction. Furthermore, the convection of protons was evaluated from the velocity and pH distribution and compared with the diffusion. It is found that the ratio between the diffusion and convection is an important factor to investigate the mixing process in the microfluidic device with chemical reactions.     

Ag2S纳米粒子原位合成以增强PAI涂层机械和摩擦学性能

借助单源前驱体热分解在聚酰胺酰亚胺(PAI)涂层中原位合成了硫化银(Ag₂S)纳米粒子,并通过调节单源前驱体的含量进一步调控纳米粒子尺寸. 采用X射线衍射仪和高分辨场发射扫描电镜对原位合成Ag₂S纳米粒子的物相结构、形貌、尺寸和尺寸分布进行了表征和分析;详细研究了Ag₂S纳米粒子对PAI涂层机械性能和摩擦学性能的影响;对其增强机制进行了探讨. 结果表明:PAI涂层中原位合成的Ag₂S纳米粒子粒径较小而且分散均匀,且调节单源前驱体能有效调控Ag₂S纳米粒子的尺寸和尺寸分布. Ag₂S纳米粒子的原位引入(优化质量分数为5.0%)有效改善了PAI涂层的机械性能和摩擦学性能,其摩擦学性能的增强归因于机械强度的提高和诱导转移膜的形成.      

Asymptotic properties of steep solutions in shells

Summary Analogies in formulation and discrepancies in admissibile simplifications in application, between theories for stress states in shallow shells and for steep solutions in non-shallow shells, are noticed.Distributions of external forces or dislocations along the normals to the midsurface for which particular solutions can be constructed by means of the differential system under consideration, are defined in asymptotic form.

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Sommario La teoria del guscio piatto presenta analogia con quella degli stati con distribuzione ripida nel guscio curvo: tuttavia le semplificazioni ammissibili nelle due accezioni presentano differenze che l'analisi asintotica mette in rilievo.Si indicano le distribuzioni di forze esterne o dislocazioni lungo le normali alla superficie media per le quali soluzioni particolari sono costruibili mediante il sistema differenziale in esame.

     

Limiting conditions of yielding for anisotropic materials

Summary The known Limiting Conditions of Yielding presuppose homogeneity andisotropy of the material. Formulas for anisotropic materials have been proposed: but they cannot be applied to all practical applications. The Limiting Condition of Yielding already proposed by the A. for isotropic materials can easily be extended to materials with different mechanical properties in different directions: the formulas obtained confirm the particular cases and the particular formulas already known for isotropic materials. The various solutions proposed by the A. for anisotropic bodies are usually represented by paraboloids whose characteristics obviously depend on the experimental parameters.

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Sommario Le condizioni di plastificazione che si conoscono presuppongono omogeneità eisotropia del materiale. Per corpi anisotropi sono state proposte espressioni che non possono essere applicate in casi riguardanti le pratiche applicazioni. La condizione di plastificazione proposta dall'A. per i corpi isotropi può essere con opportune trasformazioni adattata a materiali presentanti differenti proprietà meccaniche nelle tre direzioni principali: le formule che se ne ottengono confermano i casi particolari e le formule già note per i corpi isotropi. Le soluzioni proposte dall'A. per i corpi anisotropi sono rappresentate in genere da paraboloidi le cui caratteristiche dipendono ovviamente dai parametri sperimentali.

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Expected fatigue life of bridges under traffic load

Summary Random vibrations theory is applied to study the response characteristics of elastic damped multi-degrees-of-freedom structures subjected to traffic loads. Four kinds of randomness are included in the non stationary process modeling the crossings: the weight of the vehicles, the excentricity of the passing lane, the initial dynamic conditions and disturbances due to road surface uneveness. Modal analysis and impulse response functions are employied to derive the non stationary probability density function of stresses and displacements of the structure.Assuming Vöhler type curves and cumulative damage hypothesis to describe the fatigue strength of the structure, its expected life is calculated as a function of traffic volume.

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Sommario La risposta di strutture elastiche smorzate a molti gradi di libertà sotto l'azione del traffico è studiata in termini di dinamica aleatoria. Il carico che transita sul ponte è simulato mediante un processo aleatorio a quattro componenti: esse descrivono le aleatorietà insite nel peso dei veicoli, la loro eccentricità di marcia, le condizioni dinamiche di ingresso, le irregolarità del transito. Per mezzo dell'analisi modale ed usando le funzioni di risposta ad impulso si ottengono le caratteristiche aleatorie della risposta, in particolare la funzione densità di probabilità delle sollecitazioni e degli spostamenti, variabile nel tempo.Caratterizzando la resistenza a fatica della struttura mediante curve di Vöhler ed accettando l'ipotesi del danno cumulato di Palmgren-Miner, si determina la vita media attesa della struttura.

     

Minimum theorems for displacement and plastic strain rate histories in structural elastoplasticity

Summary The finite element method approach is used to obtain formulations of analysis problems relative to elastic-plastic structures when subjected to prescribed programmes of loads, and under the restrictive hypotheses:a) the yielding surfaces are piecewise linearized, andb) the plastic flow-laws are supposed to be of holonomic type within a single “finite” time interval. For mulations are given as linear complementarity problems and quadratic programming problems: one pair of formulations in terms of velocity and plastic multiplier rate histories, and another pair in terms of plastic multiplier rate histories only. The solutions are shown to be characterized by two minimum principles for displacement and plastic strain rate histories. After some general remarks about computational procedures, the paper is concluded with some suggestions for future developments.

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Sommario Si usa il metodo degli elementi finiti per formulare problemi di analisi relativi a strutture elasto-plastiche soggette a prescritti programmi di carico, sotto le ipotesi restrittive:a) le superfici di plasticizzazione sono linearizzate a tratti, eb) la legge del flusso plastico è olonoma all'interno del singolo intervallo di tempo “finito”. Si danno formulazioni come problemi di complementarità lineare e come problemi di programmazione quadratica: due formulazioni sono in termini di storia delle velocità e dei coefficienti di attivazione plastica, altre due sono in termini di storia dei coefficienti di attivazione plastica soltanto. Si dimostra che le soluzioni sono caratterizzate da due principi di minimo per la storia delle velocità di deformazione. Dopo alcune osservazioni generali sui procedimenti di calcolo, il lavoro si conclude con dei suggerimenti per futuri sviluppi.

     

Natural convective heat transfer in water enclosed between pairs of differentially heated vertical plates

This paper presents the results of an experimental study of buoyancy-driven convective heat transfer between three parallel vertical plates, symmetrically spaced with water as the intervening medium. The centre plate was electrically heated, while the other side plates were water-cooled forming two successive parallel vertical channels of dimensions 20 cm × 3.5 cm × 35 cm (length W, gap L, height H) each. Top, bottom and sides of the channels were open to water in the chamber which is the novel aspect of this study. Plate surface temperature and bath temperature at different levels of height from the bottom of channel were measured by K-type thermocouples. Experimental data have been correlated as under:

Nonlinear analysis of elastic round rods

Summary The nonlinear theory of elastic round rods is split into a vector equation concerning the properties of finite inextensional flexural deflections and a scalar equation concerning torsional deformations. In particular, the related boundary conditions are examined for the case of a Cardan joint. The buckling configurations of a rod under tension and torsion, constrained at both ends by Cardan joints, are determined by the linearized form of the above theory and compared with previous findings about the rod with cylindrical end hinges.

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Sommario La teoria non lineare della verga elastica rotonda è compendiata in un'equazione vettoriale che esprime le proprietà della deformata flessionale inestensionale: le associate condizioni al contorno includono le proprietà torsionali della verga. In particolare si considerano le condizioni ai limiti per deformazioni finite nel caso di vincolo con giunto cardanico. Per la verga con giunti cardanici ai due estremi, soggetta a trazione e torsione si determinano le configurazioni critiche.

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Post-graduate Student, Department of Structural Engineering, Politecnico di Torino.

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Professor emeritus, Department of Structural Engineering, Politecnico di Torino.     

Stability and synthetic damping of a third order control system affected by backlash viscous and coulomb friction

Summary A Control System for a resonant mechanical loads affected by backlash and Coulomb friction may encounter severe stability problems if load feedback is used.The stability condition for a simple system including the above effects and a pure integration in the forward path is first determined, based upon natural damping only.Some damping augmentation techniques useful for improving the stability conditions are then evaluated both theoretically and by analog simulation means; the need for Coulomb friction to damp small amplitude oscillations is also demonstrated.The study is particularly devoted to accurate positioning control systems where load feedback has to be used to compensate for backlash errors.

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Sommario In un servosistema con carico risonante soggetto a giochi ed attrito Coulombiano possono sorgere notevoli problemi di stabilità nel caso che il segnale di retroazione venga prelevato sul carico.Lo studio determina, nella prima parte, le condizioni di stabilità per un sistema con integrazione semplice sulla catena diretta, soggetto simultaneamente a tutte le condizioni di cui sopra: in tali termini non risulta dalla letteratura (ampiamente esaminata) che il problema sia stato affrontato da altri Autori.Successivamente vengono esaminati taluni metodi, di cui uno originale, che consentono di migliorare le condizioni di stabilità e quindi le prestazioni del sistema: lo studio teorico è confermato da un'ampia serie di simulazioni mediante calcolatore analogico.Viene inoltre dimostrata la necessità di un valore relativamente modesto dell'attrito Coulombiano per lo smorzamento delle piccole oscillazioni.Lo studio è dedicato particolarmente a quei sistemi di posizionamento automatico nei quali si impiega la retroazione sul carico ai fini della compensazione degli errori dovuti ai giochi.