Frequency Domain Fatigue Evaluation on SCR Girth-Weld Based on Structural Stress

The Steel Catenary Riser(SCR)is a vital component for transporting oil and gas from the seabed to the floating platform.The harsh environmental conditions and complex platform motion make the SCR’s girth-weld prone to fatigue failure.The structural stress fatigue theory and Master S-N curve method provide accurate predictions for the fatigue damage on the welded joints,which demonstrate significant potential and compatibility in multi-axial and random fatigue evaluation.Here,we propose a new frequency fatigue model subjected to welded joints of SCR under multiaxial stress,which fully integrates the mesh-insensitive structural stress and frequency domain random process and transforms the conventional welding fatigue technique of SCR into a spectrum analysis technique utilizing structural stress.Besides,a full-scale FE model of SCR with welds is established to obtain the modal structural stress of the girth weld and the frequency response function(FRF)of modal coordinate,and a biaxial fatigue evaluation about the girth weld of the SCR can be achieved by taking the effects of multi-load correlation and pipe-soil interaction into account.The research results indicate that the frequency-domain fatigue results are aligned with the time-domain results,meeting the fatigue evaluation requirements of the SCR.

基于双序列反序的(4,L)规则girth-8 QC-LDPC短码

围长较大的短码长准循环(QC)低密度奇偶校验(LDPC)码的显式构造对于QC-LDPC短码的理论研究与工程应用具有重要意义。首先提出一种基于成对策略的贪婪搜索算法,并根据此算法在列重J为4时的经验结果,归纳总结出一种具有双序列反序特征的指数矩阵。随后证明了该指数矩阵对于任意行重L均对应于围长为8的QC-LDPC码。与现有的典型显式构造方法即最大公约数(GCD)方法相比,新QC-LDPC码提供的码长显著降低。最后,将指数矩阵的拆分拼接和掩膜处理技巧与新QC-LDPC码结合起来,设计出了译码性能在高信噪比区超过5G NR LDPC码的合成码。

低密度奇偶校验码的girth集及其性能分析

girth性质研究已经成为当前LDPC码的研究重点之一,本文在找到一种基于递归的LDPC码girth搜索方法的基础上,提出LDPC码的girth长度与纠错性能之间没有必然关系,并通过IEEE Std 802.16e格式的LDPC码进行了仿真验证;此外.本文指出,girth集影响LDPC码的纠错性能,在girth长度、码长等其他参数相同的情况下,纠错能力随girth集的变小而增强。

一种优化Girth分布的准循环LDPC码设计方法研究

在准循环LDPC码的构造中,校验矩阵拥有尽可能好的girth分布对于改善码的性能有着重要的意义。该文提出了构造准循环LDPC码的GirthOpt-DE算法,优化设计以获得具有好girth分布的移位参数矩阵为目标。仿真结果表明,该文方法得到的准循环LDPC码在BER性能和最小距离上均要优于固定生成函数的准循环LDPC码,Arrary码和Tanner码,并且使用上更为灵活,可以指定码长,码率及尽可能好的girth分布。

大girth多进制阵列准循环LDPC码

Tanner图中girth的大小和分布影响着码字的误码性能,通过适当地增加girth值可进一步提升多进制准循环LDPC(Low-Density Parity-Check)码性能。采用直接构造法确定短环线性约束方程,构造出满足大girth的指数矩阵,提出了基于不同域的广义二维扩展方法,进而与大girth阵列码结合构造出了大girth多进制阵列码。仿真结果表明,在高斯白噪声信道中构造出的码字具有较强的纠错性能,且在一定范围内更大的girth可取得更大的编码增益,利于有效快速的编译码,保证信息的可靠传输,满足高频带利用率。

Girth-8(3,L)-规则QC-LDPC码的一种确定性构造方法

对于围长(girth)至少为8的低密度奇偶校验(LDPC)码,目前的绝大多数构造方法都需要借助于计算机搜索。受贪婪构造算法启发,该文利用完全确定的方式构造出一类围长为8的(3,L)-规则QC-LDPC码。这类QC-LDPC码的校验矩阵由3×L个P×P的循环置换矩阵构成。对于任意整数P≥3L2/4,这类校验矩阵的围长均为8。

Girth weldability and welding process of Baosteel X80 UOE linepipes

An analysis of the girth weldability of Baosteel X80 UOE （U-ing-O-ing-Expanding） linepipes was conducted using manual shielded metal arc welding （SMAW） and semiautomatic self-shielded flux cored wire arc welding （FCAW）. A technical specification for the optimum quality of a girth welding joint was obtained through a large amount of testing. According to the requirements of America Petroleum Institute（API） standard 1104 and the standards of the 2nd West-East natural gas transmission pipeline project,the mechanical properties of a girth welding joint were estimated. In addition,the effect of the girth welding procedure specifications and the consumable＇ s suitability on the impact toughness of the girth welding joint was discussed.

Design of good QC-LDPC codes without small girth in the p-plane

A construction method based on the p-plane to design high-girth quasi-cyclic low-density parity-check （QC-LDPC） codes is proposed. Firstly the good points in every line of the p-plane can be ascertained through filtering the bad points, because the designed parity-check matrixes using these points have the short cycles in Tanner graph of codes. Then one of the best points from the residual good points of every line in the p-plane will be found, respectively. The optimal point is also singled out according to the bit error rate （BER） performance of the QC-LDPC codes at last. Explicit necessary and sufficient conditions for the QC-LDPC codes to have no short cycles are presented which are in favor of removing the bad points in the p-plane. Since preventing the short cycles also prevents the small stopping sets, the proposed construction method also leads to QC-LDPC codes with a higher stopping distance.

Girth weldability evaluation for submarine pipeline laying

Based on the offshore standard DNV-OS-F101-2010,girth welding tests and girth weldability evaluations were carried out for the X65 and X70 UOE submarine pipelines of 3 wall thickness gauges,in which semi-automatic gas metal arc welding （GMAW） was adopted matched with metal powder flux cored wire. The girth welding procedure specification （WPS） was optimized to obtain good quality and cold-crack-free girth weld joint without preheating and post-weld heat treatment. At the same time, porosities, inclusions and incomplete fusion defects were avoided. Girth weld joints were evaluated for tensile strength, bending, Vickers hardness, charpy impact toughness and crack tip opening displacement （CTOD） fracture toughness. Results show that all the girth weld joints have good mechanical performances,indicating that the irth weldabilitv of Baosteel＇ s UOE submarine pipelines is excellent in the case of semi-automatic GMAW.

Investigation of the impact toughness of self- shielded flux- cored wire girth welds for X80 pipelines

Self-shielded flux-cored wire is a convenient and efficient consumable for pipeline field girth welding because of its self-protection characteristic and high deposition rate, especially for remote construction sites in rugged terrain. From the perspective of pipeline safety, the impact toughness of the girth welds is an important factor in pipeline integrity ,which determines the crack arrest behavior in the girth welds. Therefore, improving the girth weld impact toughness is of primary importance in the field of pipeline girth welding. Three self-shielded flux-cored wires comprising different chemical composition systems have been applied to large diameter X80 UOE （U-ing-O- ing-Expanding） pipeline semi-automatic girth welding,and the impact toughness of the welds has been evaluated by girth weld chemical composition analysis and microstructural analysis using scanning electron microscopy （SEM） and energy dispersive spectrometry （EDS） to investigate pipeline girth weld impact toughness and find ways to improve it. This helps in determining the main factors that influence girth weld impact toughness. Pipeline girth weld impact toughness is mainly determined by the final microstructure produced in the solid-state phase transition. In the as-weld state,acicular ferrite （AF） and fine bainite （FB） are a benefit to the impact toughness. For multilayer semiautomatic self-shielded flux-cored wire welding, the normalizing and tempering function of the latter beads to the initial beads plays an important role in the transition of girth weld microstructure, which affects the impact toughness. The original AF and FB and the corresponding heat treatment microstructure of the fine and uniform block ferrite and pearlite result in very good impact toughness. The following two mechanisms are found to promote the production of AF and FB in the girth weld. First, elements promoting the broadening of the austenitic region, such as Ni, C, Cu, and Mn, induce low temperature phase transitions and restrain the opposing function of Al, which is a benefit to the production of AF and FB. Second, dispersed high-melting-point inclusions, especially Al2O3 ,induce the nucleated production of AF. The advantageous function of inclusions is determined by their shape, distribution, and dimension. Dispersed spherical inclusions of small dimension are a benefit to the production of AF, and result in good impact toughness.

Short-term results of incremental penile girth enhancement using liquid injectable silicone： words of praise for a change

Aim： To report our experience with penile girth augmentation using liquid injectable silicone. Methods： Between August 2003 and July 2006, 324 men （mean age 35 years, range 19-65 years） received a series of liquid silicone subcutaneous injections between the penile skin and the corpora cavernosa on the dorsal and lateral aspects of the penile shaft, under local anesthesia. Digital photographs taken pre- and post-procedure （n = 324）, and penile contour measurements （n = 30） yielded objective results. Subjective results were derived from patient and partner testimony of satisfaction. Follow-up averaged 20 months （range 1-36 months）. Results： Three hundred and twenty-four procedures were primary augmentations. Most men （61%） were married, 7% were accompanied by their partners, and 93% were circumcised. The mean measured penile circumference was 9.5 cm （7.5-11.5 cm） pretreatment and 12.1 cm （10.3-15.3 cm） post-treatment （mean increase of 27% in circumference and 0.84 cm in diameter）. Patient and partner satisfaction was already expressed after the first two treatments. Sexual activity could be resumed after 8 h. Complications （mild bruising） were easily resolved. Conclusion： Penile girth augmentation using liquid injectable silicone yields very satisfactory short-term results with no immediate or short-term complications.

Ruling out small stopping sets and small girth in Tanner graph of QC-LDPC code

The existing constructions of quasi-cyclic low-density parity-check （QC-LDPC） codes do not consider the problems of small stopping sets and small girth together in the Tanner graph, while their existences will lead to the bit error rate （BER） performance of QC-LDPC codes being much poorer than that of randomly constructed LDPC codes even decoding failure. To solve the problem, some theorems of the specific chosen parity-check matrix of QC-LDPC codes without small stopping sets and small girth are proposed. A novel construction for QC-LDPC codes with long block lengths is presented by multiplying mmin or the multiple of mmin, which is the minimum order of the identity matrix for the chosen parity-check matrix. The simulation results show that the specific chosen parity-check matrix of QC-LDPC codes can effectively avoid specified stopping sets and small girth and exhibit excellent BER performance than random LDPC codes with the same longer codes length.

Combinatorial design-based quasi-cyclic LDPC codes with girth eight

This paper presents a novel regular Quasi-Cyclic (QC)Low Density Parity Check (LDPC)codes with columnweight three and girth at least eight.These are designed on the basis of combinatorial design in which subsets applied for the construction of circulant matrices are determined by a particular subset.Considering the nonexistence of cycles four and six in the structure of the parity check matrix,a bound for their minimum weight is proposed.The simtdations conducted confirm that without applying a masking technique,the newly implemented codes have a performance similar to or better than other well-known codes.This is evident in the waterfall region, while their error floor at very low Bit Error Rate (BER)is expected.

Fatigue life evaluation of girth butt weld within welded cast steel joints based on the extrapolation notch stress method

The fatigue life evaluation of the girth butt weld within the welded cast steel joint was studied based on the extrapolation notch stress method.Firstly,the mesh sensitivity of the finite element model of the welded cast steel joint was analyzed to determine the optimal mesh size.Based on the stress field analysis of the finite element model of the welded cast steel joint at the weld toe and weld root,the sharp model of the extrapolation notch stress method was applied to derive the effective notch stress of the rounded model belonging to the effective notch stress method,in which the key problem is to calculate the extrapolation point C,and the extrapolation point C has an exponential function relationship with the geometric parameters of the welded cast steel joint.By setting different values of geometric parameters,the corresponding value of parameter C is calculated,and then the functional relationship between the extrapolation point C and the geometric parameters can be obtained by the multiple linear regression analysis.Meanwhile,the fatigue life evaluation of the girth butt weld within welded cast steel joints based on the effective notch stress was performed according to the guideline recommended by the IIW(International Institute of Welding).The results indicate that the extrapolation notch stress method can effectively simplify the process of calculating the effective notch stress and accurately evaluate the fatigue life of the girth butt weld within welded cast steel joints.

Field girth weldability evaluation of X70 UOE pipeline

Based on API STD 1104-2005 and CSA Z662-2007, field girth welding tests and girth weldability evaluations were executed for three types of wall thickness X70 UOE pipeline, in which the most popular main line girth welding method, single-wire automatic gas metal arc welding （GMAW）, was used. The welding procedure specification was optimized to achieve a good quality and cold-crack-free girth weld joint without preheating or post-weld heat treatment. In addition ,porosities ,inclusions ,and incomplete fusion defects were avoided. The tensile strength,bending ,Vickers hardness,Charpy V-notch impact toughness, and crack tip opening displacement fracture toughness of the girth weld joint were evaluated, and the field girth weldability of Baosteel＇ s X70 UOE pipeline is joint exhibited good mechanical performance. Thus, the excellent for automatic GMAW.

Girth welding system for vortex type refrigeration compressor of air conditioner

According to the requirements of welding process for vortex type compressor of air conditioner manufactured in product line, a special girth welding machine with PLC as control core was developed, which had both upright and 45 ° incline service positions. And some key technologies were researched, such as structural design of machine body, reliable conduction of rotary weldments and quality control of welding process and so on. The experimental results showed that this machine could satisfy the requirements of welding quality and girth welding technology, results also proved the machine was a high-effwiency and low-cost automatic welding device.

Low net primary productivity of dominant tree species in a karst forest, southwestern China： first evidences from tree ring width and girth increment

Aboveground net primary productivity(ANPP)of two dominant species, one deciduous tree(Platycarya strobilacea) and one evergreen tree(Machilus cavaleriei),was estimated based on the tree-ring width and the girth increment as well as allometric functions in a karst evergreen and deciduous broadleaved mixed forest in central Guizhou Province, southwestern China. Results showed that the ANPP increased from 1961 to 2015, especially during the last 20–30 years, but with strong variations. The deciduous tree had higher ANPP than the evergreen tree according to two kinds of estimates by the tree ring and girth increment. The averaged ANPP for these two mature trees was 2.27 kg/individual/year, ca. 8 t/ha/year considering the normal stand density. Such karst forest productivity was lower than the natural subtropical forests in China and in the world.

3-restricted connectivity of graphs with given girth

Let G = （V, E） be a connected graph. X belong to V（G） is a vertex set. X is a 3-restricted cut of G, if G- X is not connected and every component of G- X has at least three vertices. The 3-restricted connectivity κ3（G） （in short κ3） of G is the cardinality of a minimum 3-restricted cut of G. X is called κ3-cut, if ｜X｜ = κ3. A graph G is κ3-connected, if a 3-restricted cut exists. Let G be a graph girth g ≥ 4, κ3（G） is min{d（x） ＋ d（y） ＋ d（z） - 4 ： xyz is a 2-path of G}. It will be shown that κ3（G） = ξ3（G） under the condition of girth.

一类girth-8QC-LDPC码构造方法的简化和扩展

围长(girth)较大的QC-LDPC码,由于译码性能优良而且便于硬件实现,因此目前已经成为国际信道编码领域的一个研究热点。最近,J-W Zhang在第四届多媒体信息网络与安全国际会议上提出了一种构造girth-8(3,L)QC-LDPC码的新方案,但是没有对围长特性和分块矩阵尺寸取值进行理论分析和论证。利用等价变换和最大公约数体系,本文得到了该方案的围长特性和分块矩阵尺寸取值的精确理论结果。此外,还利用最大公约数体系对该方案进行了扩展,得到一种新的围长为8的QC-LDPC码。新码的参数选取范围包含很多原方案不适用的参数选择范围。仿真结果说明,新码在和积译码算法下具有较优良的译码性能。

基于模拟退火算法构造girth-12(3,5)和(3,6)-规则QC-LDPC码

文章提出了一种基于模拟退火算法的准循环校验矩阵设计方法。首先,建立了一类具有特殊结构的准循环校验矩阵的设计步骤与模拟退火算法中迭代初始解、目标函数和邻域结构之间的联系,然后利用有记忆的模拟退火算法设计出了两个准循环校验矩阵。利用这两个矩阵,文章对于任意P 217构造出了girth-12(3,5)规则QC-LDPC码;对于任意P 449构造出了girth-12(3,6)规则QC-LDPC码。与已知的最好结果相比,该文将girth-12(3,5)和(3,6)规则QC-LDPC码连续存在的码长下限分别降低了420比特和492比特。