Numerical simulations of a tanker collision with a bergy bit incorporating hydrodynamics,a validated ice model and damage to the vessel

Numerical simulations of a collision between a loaded tanker and a bergy bit have been conducted using LS-Dyna™ software. The simulations incorporated hydrodynamics, via LS-Dyna's ALE formulation, and a validated crushable foam ice model. The major portion of the vessel was treated as a rigid body and a section of the hull, located on the starboard side of the forward bow where the ice contact occurred, was modeled as typical ship grillage that could deform and sustain damage as a result of the collision. Strategies for dealing with the highly varying mesh densities needed for the simulations are discussed as well as load and pressure distribution on the grillage throughout the course of the collision. Realistic movement of the bergy bit due to the vessel's bow wave prior to contact with the ice was observed and the damage to the grillage resembled published results from actual grillage damage tests in the lab. A load measurement from the lab tests compared reasonably well with a rough estimate from the simulation. The collision eventually ruptured the hull in a ripping fashion resembling documented incidents of vessel impacts with ice masses.     

上海大剧院观众厅使用效果评析

上海率先在我国建成第一座具有国际水平的现代大剧院,作对该剧及单位进行了多次访问调研,章扼要地介绍该剧院观众厅的视线设计,噪声控制,音质设计,声学参数的实测结果以及所采用的可移动音罩,可调混响装置等技术措施,产引用了国内外戏剧界,音乐界名专家观演出后的声学评价以及观众对观众厅使用效果所给出的评分结果。     

On the bit security of the Diffie-Hellman key

Let _p be a finite field of p elements, where p is prime. The bit security of the Diffie-Hellman function over subgroups of ^*_p and of an elliptic curve over _p, is considered. It is shown that if the Decision Diffie-Hellman problem is hard in these groups, then the two most significant bits of the Diffie-Hellman function are secure. Under the weaker assumption of the computational (rather than decisional) hardness of the Diffie-Hellman problems, only about (log p)^1/2 bits are known to be secure.     

Calculations of external bit fields

The amplitude and distribution of the external fields emanating from recorded transitions are of great interest to technologists in the field of information storage and retrieval and, more particularly, to those studying alternate readout techniques to the conventional inductive readout method. Such areas include the magnetic transfer process, Hall probe techniques, and the magneto-optic and Lorentz beam readout techniques. In this paper we used a harmonic analysis simulation of the non-linear digital recording process, and calculated the amplitude and distribution of external bit fields for a wide range of media magnetic properties and thicknesses, and as a function of bit density and spacing above the surface of the media. Justification for using the harmonic analysis model is based upon the good agreement obtained with the reported spatial behavior of the external bit fields measured directly by a scanning electron microscope. In addition, calculations based on simpler models of a line, step, and linear transition show that the harmonic model is a superior first-order approximation of the nonlinear nature of digital magnetic recording.     

Diagnosing ADC nonlinearity at the bit level

Two methods for identifying analog-to-digital converter (ADC) nonlinearity at the bit level are discussed. The integral nonlinearity (INL) is analyzed in the frequency domain using both DFT and Walsh transforms to determine which ADC bit is responsible for which harmonic or bin. It is shown that the effects of different bits on the outputs of either transform are separable. A 5-bit ADC example is investigated using both transforms to illustrate the implementation of the techniques     

Modified signed-digit arithmetic based on redundant bit representation

Fully parallel modified signed-digit arithmetic operations are realized based on redundant bit representation of the digits proposed. A new truth-table minimizing technique is presented based on redundant-bitrepresentation coding. It is shown that only 34 minterms are enough for implementing one-step modified signed-digit addition and subtraction with this new representation. Two optical implementation schemes, correlation and matrix multiplication, are described. Experimental demonstrations of the correlation architecture are presented. Both architectures use fixed minterm masks for arbitrary-length operands, taking full advantage of the parallelism of the modified signed-digit number system and optics.     

Design of half-million bit wire memory

A high volumetric density wire memory stack of 12 000 bits/in³was designed. The high bit density was obtained by the introduction of a novel and continuous digit line printed circuit which is also used to separate and support the plated wires. The printed circuit is also used for interconnecting the planes of the memory stack. Analysis of digit current and signal coupling is given. The advantages of the proposed memory stack configuration are apparent. These include low digit current and digit signal coupling along with good word and digit noise cancellations and high bit density.     

Tunneling-stabilized magnetic force microscopy of bit tracks on ahard disk

A scanning tunneling microscope (STM) for surface magnetic force measurements on thin-film longitudinal magnetic storage media is described. The usual rigid PtIr tip of the STM was replaced by a flexible Fe-film tip and the tip position was stabilized near the surface of the sample using the STM feedback system as tunneling occurs between the tip and sample surface. Images of a CoCrTa thin-film hard disk showing 5 μm×3 μm bit tracks written by the ferrite head of a computer disk drive are presented. The images shown are comparable to images of the bit tracks on textured surfaces using either ferrofluid decoration or other magnetic force microscopy (MFM) imaging techniques. The sensitivity of the Fe-film tip was such that the influence on the image due to magnetic forces was larger than the influence due to sample surface topography     

Cone bit bearing seal failure analysis based on the finite element analysis

Failure analysis of cone bit bearing seals is important in reducing production cost and preventing in-service component failure. However, a generally accepted criterion for their failure has not yet been established because of complexities in both their material properties and the environment. In this study, a two-dimensional axisymmetric finite element analysis (FEA) numerical model was established. FEA software was developed based on the Mooney–Rivlin constitutive model of the rubber material, and the penalty function contact algorithm. The distributions of stress, strain and contact pressure were analyzed to establish their effect on failure. The locations and causes of the failure and preventive measures were determined by comparison with an actual failure case. It was found that stress concentration and uneven pressure distribution occur at the seal. Rubber rings are highly and unequally compressed. Metal ring structure mainly determines sealing performance. To reduce the occurrence of failure, the structure must be improved by: designing an appropriate angle-tapered metal ring end face structure instead of a plane to change the trend in pressure distribution, increasing the contact area of the metal ring end face to reduce contact pressure and make the contact pressure distribution more uniform to reduce sealing surface wear, reducing the radial thickness to reduce the compression of the rubber ring, and improving back support structures to reduce the stress concentration. Results from the study can prevent and minimize risk for future failures to increase bit life and reduce drilling costs.     

混合式单牙轮钻头破岩性能研究

在石油钻探过程中,优质的钻头对于降低钻井成本和提高钻井效率至关重要。通过设计,将牙掌结构与牙轮结构相连接,并且分别在牙轮和牙掌上安装锥形齿和PDC齿,从而设计出一种新型的混合式单牙轮钻头。该混合式单牙轮钻头较一般单牙轮钻头多了PDC齿,利用冲击和剪切原理破岩。牙轮大端通过井底中心,所有齿圈与井壁接触,在破岩的同时可以起到保径作用。建立了混合式单牙轮钻头与岩石相互作用的有限元模型,并对钻头井底模型、牙齿主切削力和破岩体积进行了仿真分析。通过台架实验对数值模拟得到的钻压和进尺量进行验证。研究结果表明,数值模拟得到的钻压和进尺量与台架测试结果相符,破岩载荷规律与钻头结构设计特点一致。混合式单牙轮钻头与球形单牙轮钻头相比,侧向力减小39.6%,破岩效率提高37%。使用该混合式单牙轮钻头钻井时稳定性更高,可以减小井斜发生的概率。根据结果可知,数值模拟在研究该混合式单牙轮钻头破岩规律中是有效的,该方法为钻头进一步设计及其工作特性的评估提供了依据。     

基于双混沌系统伪随机比特发生器的研究

研究了基于双混沌系统伪随机比特发生器（CCS-PRBG）生成序列的密码学性质,证明了此二进制序列是i.i.d.序列。理论分析表明,CCS-PRBG可生成具有理想保密性的二进制混沌密码序列。     

基于银行服务系统的不耐烦行为

针对已有的顾客排队行为决策模型未考虑服务机构对顾客不耐烦行为的干预,从服务机构提供的额外服务增加顾客收益的角度出发,提出了新的决策模型。进一步研究了在该模型条件下的M/M/1排队系统的服务能力补充策略,构建基于服务台利用率的评价函数,计算得出开启备用服务台的最优策略。仿真结果表明,开启备用服务台后,顾客的止步概率降低,排队人数维持在较低且稳健的水平。     

Grand Opening of the Plenary Meeting on Publicity of the 2005 World Standard Day

Organized by the Standard Administration of China (SAC), the plenary meeting on publicity of the 2005 World Standards Day was held on October 14, 2005 at the Great Hall of People. Surrounding the theme of this year's World Standards Day - "Standards for a Safer World", the meeting made publicized the sta-     

Grand Opening of the Plenary Meeting on Publicity of the 2005 World Standard Day

Organized by the Standard Administration of China (SAC), the plenary meeting on publicity of the 2005 World Standards Day was held on October 14, 2005 at the Great Hall of People. Surrounding the theme of this year's World Standards Day - "Standards for a Safer World", the meeting made publicized the status of construction and implementation of the food safety and production safety standard system of our country,the result of clearance on national standards and the announcement of formal operation of the system for online free-of-charge access to the full text of national compulsory standards, and the system for online distribution and service of national standards. Attending the meeting were Li Changjiang, Director of AQSIQ, Li Chuanqing,Party Group Secretary of AQSIQ, Li Zhonghai, Director of SAC, high-ranking officers of relevant departments of the State Council, Chen Xiaohong, Vice-minister of Ministry of Health, Wang Xianzheng, Vice-director of the National General Bureau of Supervision and Administration on Production Safety, and representatives and experts from enterprises of various sectors with a total of over 300 people. The meeting was presided over by Zhang Yanhua, Standing Vice-director of SAC.     

基于供应链金融的银行决策分析

根据需求模型,建立了包含银行在内的供应链决策模型,研究分散决策模型下的收益问题,分别得到供应链各个参与者的期望收益,并通过数值仿真,得到银行在供应链中产生的影响。从供应链金融的角度出发,研究零售商订购量、制造商批发价格、银行利率的关系。并利用Stackelberg博弈的理论,以银行为主导者,制造商和零售商为跟随者,求出均衡最优解。研究发现当市场需求较小时,三者收益函数趋势一致;当市场需求较大时,银行利率对零售商订购量没有影响并且银行的收益最后逐渐平稳达到一个固定值。     

Experimental research on the surface strengthening technology of roller cone bit bearing based on the failure analysis

The roller cone bit is one of the most important rock breaking tools used in the oil–gas drilling industry. Its performance directly influences the drilling quality, efficiency and cost. As the world’s oil–gas resource exploration continuously developed, the drilling speed accelerated, accelerating the failure speed of the bearing. The roller cone bit’s service life was almost directly dependent on that of the bearing. In this paper, a bearing failure analysis, and an experimental research on the surface strengthening technology of the bearing with field applications etc. were carried out. The results showed that the bearing’s main failure modes included fracture, plastic deformation and wear. The main reasons were overload and uneven distribution of the load; elevated temperature due to friction caused property and structure change in material; wear increased the fit clearance between the bearing and the cone, increasing dynamic impact load etc. The bearing surface strengthening technology, employing plasma-arc surfacing DH-60 wear resistance alloy, could prolong the service life of the bearing. Experimental research and field tests showed that the wear and impact resistance of the enhanced bearing increased by 30% with an increased service life of 12% on average.     

基于运河文化的数字化导向设计动态可变式图形研究

目的基于我国目前对运河文化的重视,深度挖掘运河历史价值及文化内涵,提升运河文化特色与认知度。对运河文化数字化导向设计动态可变式图形进行分析研究,对大运河文化带沿线城镇的导向设计提出具体的优化设计方案。方法以图形符号学原理为基础,对地域文化进行基因梳理与提取,形成运河文化符号;通过构建动态图形分析框架,设计出系列性动态标志图形并应用到沿河城镇景观导向设计中。结论提炼运河地域性文化在导向设计实际需求中的重要性,创造性地提出了"动态可变式图形",使导向设计与运河文化受众需求之间产生互动体验性使设计内涵更加丰富。在传承和保护运河文化遗产,树立文化自信等方面具有较高的现实意义。在新媒体时代背景下必将成为运河文化推广与传播的主流趋势和新途径。     

啤酒商标生产存在的问题及对策

简要介绍了当今国内啤酒商标生产的形势。对目前啤酒商标生产中存在的问题及其成因进行分析与探讨，并提出相应的对策与建议。