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INTRODUCTION Most packing problems (Dowsland and Dow-sland, 1992) are NP-hard (Garey and Johnson, 1979); among which are bin-packing, floorplan, rectangle packing, packing a set of circles into a large circle or square, non-rectangular packing problems and so on (Li and Milenkovic, 1995; Liang et al., 2002; Lip-nitskii, 2002; Milenkovic and Daniels, 1996; Milenk-ovic et al., 1991; Osogami and Okano, 2003; Wang, 2002). Some of these such as bin-packing problem and rectangle packing p… 相似文献
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针对普通摇椅自身不能动的情况,进行了电动摇椅的机械创新设计,运用UG等CAD软件虚拟设计与传统机械设计理论及经验结合,将一些常用机构有机组合为一个整体,建立了结构合理且能够实现自动摆动的电动摇椅虚拟模型。结果表明:电动摇椅结构设计合理,可有效消除疲惫、放松身心,提高生活质量。通过电动摇椅设计,在实际应用中对机构的创新设计具有一定的参考价值。 相似文献
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INTRODUCTION An important problem in foundation engineeringis the determination of the rate of settlement of a raftfoundation placed on a deep clay layer. Gibson andMcNamee (1957), and McNamee and Gibson (1960a;1960b) considered the problem of normal uniformloading applied to the surface of a half-space andshowed that one-dimensional theory gives a markedunderestimate of the rate of settlement. This theorycorresponds to the case of a perfectly flexible footing.However, it is often… 相似文献
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风暴潮极值状态下珠江河网白坭水道内的不稳定流动 总被引：1，自引：0，他引：1
利用1999年洪季和9316号台风风暴潮的实测资料,通过ECOMSED数学模型对珠江河网广州区域进行数值模拟计算.计算结果显示,在99年洪季时,河网内白坭水道流动为通常的往复流动;但在风暴潮极值状态下,由于受极值流速及地形的影响,流动在白坭水道中弯曲扭摆,呈现出流动不稳定现象. 相似文献
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以某沿海城市地铁车站结构为例,通过室内单桩竖向抗压静载试验,计算单桩极限侧阻力,理论验算和MIDAS 有限元软件数值模拟相结合,对比分析不同抗浮措施下车站结构底板位移、变形大小。 结果表明:围护结构法抗浮,车站底板竖向位移得到控制,但结构底板变形较大,底板水头高度为17.4 m 时,底板最大变形5.75 mm;抗浮锚杆和抗浮桩可有效减小结构底板变形,底板水头高度为17.4m 时,两种抗浮措施下底板最大变形分别为2.37 和2.04 mm;抗浮组合措施能够发挥各自优势,抗浮效果明显,对结构变形控制较好;排水减压法基于减小结构水浮力原理抗浮,抗浮效果显著。 相似文献
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3-D scattering of obliquely incident plane p waves by alluvial valley embedded in layered half-space
The indirect boundary element method(IBEM) was established to solve the problem of 3-D seismic responses of 2-D topographies,by calculating the free-field responses with the direct-stiffness method and simulating the scattering wave fields with the dynamic Green’s functions of moving distributed loads.The proposed method yields accurate results,because the 3-D dynamic stiffness matrixes used are exact and the fictitious moving distributed loads can be acted directly on the interface between the alluvial valley and the layered half-space without singularity.The comparison with the published methods verifies the validity of the proposed method.And the numerical analyses are performed to give some beneficial conclusions.The study shows that 3-D scattering by an alluvial valley is essentially different from the 2-D case,and that the presence of soil layer affects not only the amplitude value of surface displacements but also the distribution of surface displacements. 相似文献
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The averaging analysis was carried out to study the motion of a quasi-axisymmetrical gyrostat under a small-magnitude self-excited control troque.The common approach to investigating the problem of rigid body rotatyion under the action of a small torque known in the body frame was described.Using this approach,the problem(Grammel‘s problem for the case of small torque) that is maintaining the angular velocity of a quasi-axisymmetrical gyrostat using a control torque quadratic in the angular velocity was solved.Maintaining the angular velocity of a quasi-axisymmetrical gryostat using a control torque quadratic in the angular velocity was solved. 相似文献
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研究目的：建立一种适用于理想膜结构可进行高精度褶皱形变模拟的稳定可靠的数值分析技术及方法。创新要点：根据薄壳理论,在向量式混合质点单元方法（VFPEM）薄膜计算理论的基础上,引入弯曲内力分析模型并与其进行组合,发展了一种能够描述膜材面外变形的新型非线性薄壳计算理论,同时给出了将其应用于褶皱形变模拟的关键求解技术。研究方法：1．针对薄壳计算模型中的弯曲内力,利用移动基础架构和逆向刚体运动的概念扣除刚体转动,在只含有节点独立转动自由度的单元变形坐标系下根据虚功原理和平衡条件进行计算;2．借助于薄壳非线性屈曲模拟方法,引入合理的初始扰动作为诱发理想平面膜材中形成褶皱的有效机制;3．采用拟动力显式数值积分技术求解质点运动方程,通过追踪质点平衡位置来获得稳态的褶皱构形。重要结论：采用本文模型和方法可以模拟薄膜结构在面内荷载作用下褶皱的分布模式、具体构形信息及应力状态,计算过程不存在收敛性困难,结果准确。 相似文献
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INTRODUCTION The dynamic response of foundations resting onthe surface of a half space is of significant importancein soil-foundation interactions and machine founda-tion designs. Observation of earthquake damage in-dicated that the local soil properties, foundation ge-ometries, etc., play a central role in the dynamic be-havior of the soil-foundation system. Ever-increasing research has been devoted to theproblem of an elastic half space indented by a rigidfooting by employi… 相似文献
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The dynamic response of moored crane-ship is studied. Governing equations for the dynamic response of a crane-ship coupled with the pendulum motion of the payload are derived based on Lagrange＇s equations. The boom is modeled based on finite element method, while the payload is modeled as a planar pendulum of point mass. The dynamic response was studied using numerical method. The calculation results show that the large-amplitude responses occur at wave periods near the natural period of the payload. Load swing angle is smaller for crane-ship with flexible boom, in comparison with rigid boom. The ship surge motions have large vibrations for crane-ship with flexible boom, which were not observed for a rigid boom. The analysis identifies the significance of key parameters and reveals how the system design can be adjusted to avoid critical conditions. 相似文献
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宗长江 《石家庄铁路工程职业技术学院学报》2013,(4):37-41
红柳河特大桥48m简支箱梁预应力质量控制的关键是节段箱梁预制过程中的预应力孔道位置控制和节段拼装过程中的湿接缝预应力孔道位置控制。由于48m箱梁节段拼装预应力筋过长、弯曲较多都会加大预应力筋的孔道摩阻损失,因此,后张法在张拉前测试预应力孔道的摩阻力是确保施工质量的有效措施。预应力孔道的摩阻测试有效验证了孔道位置施工质量,给预应力张拉提供准确的施工参数,确保预应力张拉施工质量。 相似文献
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ＩＮＴＲＯＤＵＣＴＩＯＮＩｔｉｓｉｍｐｏｒｔａｎｔｔｏｆｏｒｅｃａｓｔａｎｄｃａｌｃｕｌａｔｅｔｈｅｒｏｌｅｏｆｃｏｎｓｏｌｉｄａｔｉｏｎｉｎｓｔｒｅｎｇｔｈｅｎｉｎｇｓｏｆｔｓｏｉｌｇｒｏｕｎｄ .Ｆｏｒｃｏｎｖｅｎｉｅｎｔｕｓｅｉｎｅｎｇｉｎｅｅｒｉｎｇ ,ｔｈｅｍｏｄｅｌｏｆｃｏｎｓｏｌｉｄａｔｉｏｎｗａｓｒｅｄｕｃｅｄｔｏａｏｎｅ ｄｉ ｍｅｎｓｉｏｎａｌｐｒｏｂｌｅｍｉｎｓｐａｔｉａｌｄｏｍａｉｎ .ＳｉｎｃｅＴｅｒｚａｇｈｉｅｓｔａｂｌｉｓｈｅｄｏｎｅ ｄｉｍｅｎｓｉｏｎａｌｌｉｎｅａｒｃｏ… 相似文献
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The authors give the solution to the problem of one-dimensional consolidation of double-layered ground with the use of the
differential quadrature method. Case studies showed that the computational results for pore-water pressure in soil layer agreed
with those of analytical solution; and that in the computational results for the interface of soil layer also agreed with
those of the analytical solution except for the small discrepancies during shortly after the start of computation. The advantages
of the solution presented in this paper are that compared with the analytical solution, it avoids the cumbersome work in solving
the transcendental equation for eigenvalues, and in the case of the Laplace transform solution, it can resolve the precision
problem in the numerical solution of long time inverse Laplace transform. Because of the matrix form of the solution in this
paper, it is convenient for formulating computational program for engineering practice. The formulas for calculating double-layered
ground consolidation may be easily extended to the case of multi-layered soils.
Project (No. RC9609) supported by the Zhejiang Provincial Natural Science Foundation of China 相似文献
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选择含氮节镍型QN2109Mo奥氏体不锈钢作为研究对象,采用XRD、TEM、SEM、EDS、摩擦磨损试验机和电化学工作站等检测手段,研究QN2109Mo不锈钢的组织结构、摩擦磨损性能以及耐腐蚀性能,并与316L不锈钢进行对比。实验结果表明:N原子主要以间隙固溶形式存在于QN2109Mo不锈钢中,对QN2109Mo不锈钢组织起到了细化作用,提高了QN2109Mo 不锈钢的硬度。在干摩擦状态下,QN2109Mo不锈钢的耐磨损性能优于316L不锈钢,其磨损机理为氧化磨损和磨粒磨损共同作用。在w(NaCl)为3.5%的溶液中,QN2109Mo不锈钢表现出比316L不锈钢更低的自腐蚀电流密度和更高的点蚀电位,具有更优异的耐NaCl 溶液腐蚀性能。 相似文献
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One of the subjects that undergraduate students learning Object Oriented (OO) design find hard to apply is the construction of class hierarchies in general, and the use of interface classes in particular. The design process requires decomposition and reconstruction of problems in order to model software classes. The common attributes and behaviors are usually modeled using class inheritance except when the common behaviors do not belong to the same class hierarchy; in such case, an interface class is preferred. In order to be able to properly design, the designer has to demonstrate the abstraction abilities on various levels. In this study, we aimed at examining the students' demonstration of abstraction levels during design of class hierarchy in general, and whether or not they use interface classes in particular. The results of the study reveal that a majority of students were able to build a reasonable class hierarchy; however, many of them did not use interface classes as a tool for expressing common behaviors. Nevertheless, all of them could identify and choose the best solution for a particular problem among four different solutions, which included the use of interface class. 相似文献
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谢超凡 《福建师大福清分校学报》2012,(5):37-41
高校异构系统形成的信息孤岛引发的数据集成和共享需求是高校面临的最重要的信息问题之一。如何在资金有限的情况下,最大限度发挥数据的共享能力,已经成为各个高校数据库集成过渡时期的迫切需要,基于这个要求,本文以福建师范大学福清分校为案例,提出了一套解决异构数据源通过设计接口来共享数据的方案,来应对在数字化校园过渡时期存在的信息孤立问题。 相似文献
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The dynamic stress path of a rock and soil mass under seismic action has a crucial influence on its catastrophic behavior. In soil dynamics, earthquakes are commonly simplified as vertically incident shear waves and the seismic stresses in soil are estimated based on rigid foundation models. However, the great effect of P-waves should not be overlooked in strong earthquakes, which have happened frequently in recent years. The characteristics of the dynamic stress path under longitudinal waves with significant oblique incidence are still unclear. Analytical formulas for the seismic stresses at any depth of a semi-infinite elastic space under obliquely incident P-waves are derived, which degenerate into the traditional rigid foundation method in soil dynamics when both the incident angle and Poisson’s ratio are taken as zero. Here, we reveal the fundamental characteristics of a dynamic stress path under obliquely incident P-waves. The stress path is proved mathematically to be an oblique ellipse in the plane of normal stress difference and horizontal shear stress. We identify factors affecting the stress path, including the incident angle, Poisson’s ratio, and depth corresponding to unit wavelength. The possible variation in the range of an oblique elliptic stress path is systematically analyzed, which lays a theoretical foundation for further study of the dynamic response of sites under obliquely incident seismic waves. 相似文献
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INTRODUCTION Pose and structural parameters analysis of 2Dimages sets find application in many areas such asobject recognition, motion estimation, navigationplanning, and structural analysis of 3D objects(Huang and Netravali, 1994), image communica-tion, and image coding (Mitiche and Aggarwal,1986). Normally, given one set of 3D object pointdata and their corresponding 2D projective imagepoint data, the 3D-2D calibration problem is re-ferred to as the estimation of the camera par… 相似文献
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To effectively reduce the damage to people and devices in civil defense engineering subjected to blast shock, a blast shock isolation system with magnetorheological fluid dampers (MRFD) is proposed. MRFD can provide continuously adjustable Coulomb friction and has many advantages for semi-active control. Numerical simulation of this isolation system is finished using Matlab simulink toolbox. General semi-active control algorithms are consided based on instantaneous optimal active control algorithm. And the results indicate that the shock isolation system can work efficiently, decreasing about 93% of the peak acceleration of the isolation floor. 相似文献