Evaluation of natural gas hydrate resources in the South China Sea using a new genetic analogy method

Natural gas hydrate(NGH)has attracted much attention as a new alternative energy globally.However,evaluations of global NGH resources in the past few decades have casted a decreasing trend,where the estimate as of today is less than one ten-thousandth of the estimate forty years ago.The NGH researches in China started relatively late,but achievements have been made in the South China Sea(SCS)in the past two decades.Thirty-five studies had been carried out to evaluate NGH resource,and results showed a flat trend,ranging from 60 to 90 billion tons of oil equivalent,which was 2-3 times of the evaluation results of technical recoverable oil and gas resources in the SCS.The big difference is that the previous 35 group of NGH resource evaluations for the SCS only refers to the prospective gas resource with low grade level and high uncertainty,which cannot be used to guide exploration or researches on development strategies.Based on the analogy with the genetic mechanism of conventional oil and gas resources,this study adopts the newly proposed genetic method and geological analogy method to evaluate the NGH resource.Results show that the conventional oil and gas resources are 346.29×10^(8)t,the volume of NGH and free dynamic field are 25.19×10^(4)km^(3) and(2.05-2.48)×10^(6)km^(3),and the total amount of in-situ NGH resources in the SCS is about(4.47-6.02)×10^(12)m^(3).It is considered that the resource of hydrate should not exceed that of conventional oil and gas,so it is 30 times lower than the previous estimate.This study provides a more reliable geological basis for further NGH exploration and development.

The Continuous Analogy of Newton’s Method for Solving a System of Linear Algebraic Equations

We propose a continuous analogy of Newton’s method with inner iteration for solving a system of linear algebraic equations. Implementation of inner iterations is carried out in two ways. The former is to fix the number of inner iterations in advance. The latter is to use the inexact Newton method for solution of the linear system of equations that arises at each stage of outer iterations. We give some new choices of iteration parameter and of forcing term, that ensure the convergence of iterations. The performance and efficiency of the proposed iteration is illustrated by numerical examples that represent a wide range of typical systems.

A CONCISE M-METRIC LEAST SQUARE FORMULA FOR POLYNOMIAL ANALOGY

An M-metric least square method for polynomial analogy is presented. The relative normal eqUation is of diagonal form, such that the concise solution formula is explicit, and it is suitable to Parallel computation. On the other hand, by error analysis of a typical example, we can see that the presented method is reliable.

Hierarchical Symbolic Analysis of Large Analog Circuits with Totally Coded Method

Symbolic analysis has many applications in the design of analog circuits. Existing approaches rely on two forms of symbolic-expression representation: expanded sum-of-product form and arbitrarily nested form. Expanded form suffers the problem that the number of product terms grows exponentially with the size of a circuit. Nested form is neither canonical nor amenable to symbolic manipulation. In this paper, we present a new approach to exact and canonical symbolic analysis by exploiting the sparsity and sharing of product terms. This algorithm, called totally coded method (TCM), consists of representing the symbolic determinant of a circuit matrix by code series and performing symbolic analysis by code manipulation. We describe an efficient code-ordering heuristic and prove that it is optimum for ladder-structured circuits. For practical analog circuits, TCM not only covers all advantages of the algorithm via determinant decision diagrams (DDD) but is more simple and efficient than DDD method.

SOME PROBLEMS WITH THE METHOD OF FUNDAMENTAL SOLUTION USING RADIAL BASIS FUNCTIONS

The present work describes the application of the method of fundamental solutions （MFS） along with the analog equation method （AEM） and radial basis function （RBF） approximation for solving the 2D isotropic and anisotropic Helmholtz problems with different wave numbers. The AEM is used to convert the original governing equation into the classical Poisson＇s equation, and the MFS and RBF approximations are used to derive the homogeneous and particular solutions, respectively. Finally, the satisfaction of the solution consisting of the homogeneous and particular parts to the related governing equation and boundary conditions can produce a system of linear equations, which can be solved with the singular value decomposition （SVD） technique. In the computation, such crucial factors related to the MFS-RBF as the location of the virtual boundary, the differential and integrating strategies, and the variation of shape parameters in multi-quadric （MQ） are fully analyzed to provide useful reference.

Turbulent-Induced Noise around a Circular Cylinder Using Permeable FW-H Method

Varieties of research on turbulent-induced noise are conducted with combinations of acoustic analogy methods and computational fluid dynamic methods to analyse efficiently and accurately. Application of FW-H acoustic analogy without turbulent noise is the most popular method due to its calculation cost. In this paper, turbulent-induced noise is predicted using RANS turbulence model and permeable FW-H method. For simplicity, noise from 2D cylinder is examined using three different methods: direct method of RANS, FW-H method without turbulent noise and permeable FW-H method which can take into account of turbulent-induced noise. Turbulent noise was well predicted using permeable FW-H method with same computational cost of original FW-H method. Also, ability of permeable FW-H method to predict highly accurate turbulent-induced noise by applying adequate permeable surface is presented. The procedure to predict turbulent- induced noise using permeable FW-H is established and its usability is shown.

METHOD OF MOMENT EXCITATION IN TESTING OF STRUCTURES

The method of the moment excitation in the studies of the structure-borne sound using a moment actuator is introduced. Some design considerations for the moment actuator are presented. A standard mechanical system is established to calibrate the performance of the moment actuator. The frequency and mechanical power performances of the actuator are discussed.

Application of A Fully Nonlinear Higher-Order Element Method for Modelling Three-Dimensional Wave Entry of A Cone

Fully nonlinear water entry of a cone into waves with gravity effect has been analyzed based on a three-dimensional(3D)higher-order boundary method(HOBEM).The total velocity potential at the initial time is divided into the incident and scattering components.In the subsequent time steps,the solution of the velocity potential is defined as a whole through instantaneous boundary conditions.Based on the image theory,a modified Green function is applied to establish the integral equations so that only half of the calculation domain is considered and the seabed can be excluded.The free surface elevation is tracked along a given azimuth plane in the polar coordinate system,while the horizontal motion of the water particle is updated by using a segment-spring analogy method,which redistributes nodes and maintains mesh connectivity according to linear stiffness.An auxiliary function is applied to solve the pressure distribution,instead of directly calculating time derivative of the velocity potential.The high accuracy of the present numerical method is achieved through a detailed convergence study and comparison with results in the literature.Simulations are emphatically performed to examine the effects of gravity,wave nonlinearity,entry location,and oblique entry.

一流课程建设背景下勘探地震学课程教学改革探索与实践

高等教育是支撑、推动和引领国家现代化发展的重要力量,课程建设是高等教育发展的源泉,在以落实立德树人为根本任务,全面开展一流本科课程建设的背景下,开展教育教学改革是优化课程的重要驱动力。勘探地震学课程,从分析传统教学的局限性出发,提出“一引领,三结合,主体性,一体化”的教学改革理念,建设优质丰富的课程资源,实施“四维、六化、全程性评价”的创新改革举措,进行系统的教学模式改革,打造优质课程,培养复合型、高素质、创新性专门人才。该文为相关专业课程进行教学改革提供参考,对进行高质量课程建设具有一定的指导意义。

基于系统结构图的模拟电子技术课程教学探索

掌握知识是教学目标的核心要素,对基本元件和基本电路的深入探索是领悟模拟电子技术课程知识的关键。为此,该文提出以系统结构图为工具开展课程教学,首先分析教学内容与系统结构图的关联关系,然后通过两个知识点的分析过程,阐述系统结构图在课程教授中的具体应用,最后运用案例分析、仿真实践、翻转教学等教学方法,实现启发学生融会贯通、注重创新培养、强化学生自主探究的目标。

问题驱动的类比法、互动型、研究性教学模式——以电磁学课程建设为例

充分考虑一流课程应具备的高阶性、创新性和挑战度的特点与要求,作者以北京航空航天大学(北航)电磁学课程建设为例,经过近四年在应用物理专业强基计划、物理学专业拔尖计划学生的教学实践中,提出并实施了问题驱动的类比法、互动型、研究性的教学模式,使电磁学课程的教学质量、学生综合素质和创新能力得到持续提升。

邮轮开敞区域典型杆件风致噪声特性数值研究

[目的]旨在研究邮轮开敞区域典型杆件产生的风致噪声。[方法]基于计算流体动力学(CFD)联合声类比法、声振耦合法开展气动噪声与风致振动噪声的数值模拟,探究上述两种噪声产生机理及特性。[结果]结果显示,在不同风速下,圆杆、方杆、椭圆杆的气动噪声最大值频率由脱涡频率主导,风致振动噪声最大值频率由结构固有频率主导。3种不同截面形状杆件产生的气动噪声总体上大于风致振动噪声,且方杆的气动噪声最大。当杆件脉动压力频率接近固有频率时,在大柔度下风致振动噪声会接近甚至超过气动噪声。[结论]设计邮轮开敞区域典型杆件时应选择圆形杆件而避免使用方形杆件,且合理选择杆件尺寸,尽量避免杆件脱涡频率与固有频率接近,以此降低风致噪声。

“电磁场与传输理论”中亥姆霍兹定理的类比教学法

亥姆霍兹定理是“电磁场与传输理论”中的一个重要定理,其数学表述抽象、物理意义深刻的特性使得学生在学习中普遍存在理解难度大的问题。我们通过优化教学方法,用类比教学法替代纯数学推导的传统教学方法,从电学谐振系统和力学的类比出发,可直观揭示亥姆霍兹定理所蕴含的数理意义。教学实践表明,通过类比教学法讲授亥姆霍兹定理具有很好的教学效果。

基于量子电压的模数转换器性能评估

相比于用传统半导体器件研制的信号源,约瑟夫森任意波形发生器合成信号的幅值可溯源至自然常数,其输出波形具有超低噪声、超低失真的优点。使用约瑟夫森任意波形发生器评估了National Instruments公司24位数字采集卡PXI 5922的性能。其中,采用零补偿波形合成方法简化系统硬件结构,并且使用高精度、多比例的感应分压器提升评估效率。首先,在10 kHz的带宽内标定了PXI 5922单通道的增益及其稳定性、信噪比、无杂散动态范围、总谐波失真、信纳比和有效位数;其次,标定了PXI 5922两通道不同相位下的相位差;最后,结合电网的谐波情况,以60 Hz的基波频率为例,标定了PXI 5922在12阶谐波以内各谐波的幅度与相位响应。约瑟夫森任意波形发生器的超高精度和宽带输出能力在评估高精度模数转换器的性能方面具有广阔的应用前景。

螺旋桨水动力噪声数值计算方法研究

为了确立水动力噪声量化计算规程,对基于FW-H方程的声类比计算方法进行系统性研究。采用螺旋桨水动力性能EFD及CFD标模DTMB 4 119螺旋桨为研究对象,基于大涡模拟方法系统探讨了声类比计算收敛性相关问题,包括声学计算时间的影响分析、单个叶片声压与叶片总声压的关系、声压与流动压力比较等。研究表明,声学计算时间的长短对频率谱的分布有影响,但平均声压级几乎不受影响,误差不到1%;单个叶片的SPL几乎相等但声压存在相位差,总体SPL相比单个叶片有所降低;螺旋桨远场声压一般低于流动压力,近场螺旋桨域内则例外,呈现不收敛趋势。由此可见,将流动与声传播解耦的声类比方法对于近场声压求解有一定局限性。

基于声电类比的低频消音结构优化设计

基于声电类比,设计了与电滤波器性能相似的低频消音结构,并结合传递矩阵法和模拟退火法,构造了声学结构的优化设计策略。首先,采用归一化方法,以四阶切比雪夫高通电滤波器为基准,设计了电学带阻滤波器;然后,基于声电类比,将电路中的电感电容转换为声学结构中的细管和圆柱腔,构造了消音结构原型,并利用传递矩阵法,建立其数学模型,推导声波传递损失表达式;最后,结合声学结构的数学模型和模拟退火法,以有效衰减带宽最大为目标,以消音结构的尺寸参数为变量,对原型结构进行优化设计。结果表明:基于声电类比,能获得合理的消音结构原型,克服了仅依靠经典消音结构进行设计的局限;结合推导的传递损失数学模型和模拟退火法,对消音结构原型进行参数优化,能显著提高其消音效果,表现在传递损失超过20 dB的带宽拓宽至410~2 165 Hz,是优化前带宽的202%,特别是优化后的结构克服了原型结构在466~537 Hz频率内不能实现有效消音的缺陷,获得了连续的大跨度有效带宽,且传递损失曲线平均增幅达22.8%。

复合成层地层盾构隧道施工引起土体变形计算研究

为解决盾构上部多层水平覆土且开挖面内上下水平分层的复合地层条件下盾构施工引起的土体变形问题,在统一土体解析解法的基础上对其中土质条件影响参数进行修正,使其可以进行复合地层条件下的土体变形计算,并对土体移动焦点范围进行了重新的划分。将修正后的统一土体解析解法与类随机介质理论相结合,得到可以解决盾构开挖面上存在多种土层情况的计算方法,并且可适用于任意开挖面形状的盾构施工。研究结果表明:经过多组工程案例验算,验证了方法的可行性;开挖面上某一土层厚度等量增加会使土体变形发生非线性变化;由于土体损失比变形传递路径对土体变形的影响更大,相同洞径比下的土体变形可能存在差异。

一种基于全差分环形放大器的高精度两步SAR ADC设计

基于0.18μm CMOS工艺,设计了一款18位、采样率为5 MS/s的高精度逐次逼近型模数转换器(SAR ADC)。整体电路采取两步法的设计思路,利用全差分环形放大器将前级8位电容分裂型ADC的剩余电压放大后,再由后级10位桥接电容型ADC继续采样和量化,以此实现了高精度的模数转换器。采用了全差分环形放大器,该种放大器有高带宽、高增益和较低功耗的特点,在较低的功耗代价下,全差分环形放大器既有效提高了整体电路的精度,又充分验证两步SAR ADC架构在高精度SAR ADC设计上的可行性。仿真结果表明,在3 V电源电压、5 MS/s采样率下,SAR ADC的有效位数(ENOB)为17.03 bits,功耗为5.12 mW,无杂散动态范围(SFDR)为107.5 dB,信噪失真比(SNDR)为104.3 dB。

基于磁导-电容类比法和解析Preisach模型的铁心动态磁滞建模方法

铁磁材料的磁滞、涡流和驰豫效应对电力变压器铁心的非线性特性和功率损耗有显著的影响。为了研究电磁暂态过程中电力变压器的时域响应行为,需要准确计及铁心的动态磁化特性,在电路仿真中对电力变压器铁心进行精细建模。为此,该文首先采用考虑可逆分量的解析Preisach模型表征铁磁材料的静态磁滞效应,通过磁导-电容类比法建立了铁心的回转器-磁导模型,构建铁心静态电磁模型。其次,基于传统损耗统计理论和场分离理论,在静态电磁模型的基础上引入恒定磁阻和受控磁动势源,分别用于表征铁磁材料的涡流效应和弛豫效应对磁滞效应和损耗效应的影响,构建基于传统损耗统计理论的铁心动态电磁模型。最后,运用R-L分数阶导数对涡流损耗表达式进行修正,采用受控磁动势源表示涡流效应,对传统的铁心动态电磁模型进行改进。基于电工钢测量系统测量了硅钢铁心在不同频率、不同磁通密度下的动态磁滞回线,与实验相比改进模型的平均相对误差为6.59%,验证了所提出的改进动态模型的正确性。

一种多通道模数转换器的误差校正方法

介绍了一种模拟数字结合的时分交织模数转换器的校正方法,包括模拟时钟调整电路、频域误差检测电路以及数字误差校正方案等,针对传统时分交织校正算法校正方案复杂、扩展难等缺点,结合模拟电路的粗校正和数字校正方案的细校正,创新性地提出一种综合校正机制,能够有效地完成检测误差分配,实现粗校正和细校正的有效配合,并跟踪误差随频率和温度变化的波动,完成多通道模数转换器的通道误差校正,具有设计结构简单、易于扩展和稳定的特点。