Detection of internal crack growth in polyethylene pipe using guided wave ultrasonic testing

Despite the success of guided wave ultrasonic inspection for internal defect detection in steel pipes,its application on polyethylene(PE)pipe remains relatively unexplored.The growth of internal cracks in PE pipe severely affects its pressure-holding capacity,hence the early detection of internal cracks is crucial for effective pipeline maintenance strategies.This study extends the scope of guided wave-based ultrasonic testing to detect the growth of internal cracks in a natural gas distribution PE pipe.Laboratory experiments and a finite element model were planned to study the wave-crack interaction at different stages of axially oriented internal crack growth with a piezoceramic transducer-based setup arranged in a pitch-catch configuration.Mode dispersion analysis supplemented with preliminary experiments was performed to isolate the optimal inspection frequency,leading to the selection of the T(0,1)mode at 50-kHz for the investigation.A transmission index based on the energy of the T(0,1)mode was developed to trace the extent of simulated crack growth.The findings revealed an inverse linear correlation between the transmission index and the crack depth for crack growth beyond 20%crack depth.

Model Test and Design of the Wave Energy System on "Central Fairway No. 1" Light Ship

This paper presents the test of a ship model for the design of a backward-bent duct oscillating water column type wave energy conversion system, to supply electric power for a light ship. This system suggests a new way to produce electric power automatically for large light ships.

Wave Motion Compensation Scheme and Its Model Tests for the Salvage of An Ancient Sunken Boat

The application of the vertical hoisting jack and wave motion compensation techniques to the salvage of an ancient sunken boat is introduced. The boat is wooden, loaded with cultural relics. It has been immersed at the bottom of the South China Sea for more than 800 years. In order to protect the structure of the boat and the cultural relics inside to the largest extent, an open caisson is used to hold the sunken beat and the silts around before they are raised from the seabed all together as a whole. In the paper, first, the seakeeping model test of the system of the salvage barge and the open caisson is done to determine some important wave response parameters. And then a further experimental study of the ap- plication of the vertical hoisting jack and wave motion compensation scheme to the salvage of the sunken boat is carried out. In the model tests, the techniques of the integrative mechanic-electronic-hydraulic control, wave motion forecast and wave motion compensation are used to minimize the heave motion of the open caisson. The results of the model tests show that the heave motion of the open caisson can be reduced effectively by the use of the present method.

Numerical Simulations and Model Tests of the Mooring Characteristic of A Tension Leg Platform Under Random Waves

Analyzing the dynamic response and calculating the tendon tension of the mooring system are necessary for the structural design of a tension leg platform （TLP）. The six-degree-of-freedom dynamic coupling responses and the mooring characteristics of TLP under random waves are studied by using a self-developed program. Results are verified by the 1：40 scaling factor model test conducted in the State Key Laboratory of Ocean Engineering at Shanghai JiaoTong University. The mean, range, and standard deviation of the numerical simulation and model test are compared. The influences of different sea states and wave approach angles on the dynamic response and tendon tension of the mooring system are investigated. The acceleration in the center and corner of the deck is forecasted.

Three-Dimensional Model Test for Port Engineering with Multi-Directional Waves

-The necessity of using irregular waves, especially multi- directional waves to conduct three-dimensional model tests for port engineering and the test method are described in this paper through an example of model test for a port. The test results show that a deep navigation channel has a large effect on the waves in front of the breakwater near the port entrance and on the wave condition in the port.

RESEARCH ON MICROWAVE HUMIDITY TESTING OF CERAMIC PRODUCTS

This paper analyses the principle of microwave humidity testing. According to the problems in the production procedure of ceramic products, a microwave humidity testing system is designed and analyzed for its advantages. Furthermore, the system has been applied to the production line that produces ceramic products and the testing results are also satisfying.

Test particle simulations of resonant interactions between energetic electrons and discrete, multi-frequency artificial whistler waves in the plasmasphere

Modulated high frequency （HF） heating of the ionosphere provides a feasible means of artificially generating ex- tremely low frequency （ELF）/very low frequency （VLF） whistler waves, which can leak into the inner magnetosphere and contribute to resonant interactions with high energy electrons. Combining the ray tracing method and test particle simulations, we evaluate the effects of energetic electron resonant scattering driven by the discrete, multi-frequency arti- ficially generated ELF/VLF waves. The simulation results indicate a stochastic behavior of electrons and a linear profile of pitch angle and kinetic energy variations averaged over all test electrons. These features are similar to those associated with single-frequency waves. The computed local diffusion coefficients show that, although the momentum diffusion of relativistic electrons due to artificial ELF/VLF whistlers with a nominal amplitude of ~ 1 pT is minor, the pitch angle scattering can be notably efficient at low pitch angles near the loss cone, which supports the feasibility of artificial triggering of multi-frequency ELF/VLF whistler waves for the removal of high energy electrons from the magnetosphere. We also investigate the dependences of diffusion coefficients on the frequency interval （△f） of the discrete, multi-frequency waves. We find that there is a threshold value of Af for which the net diffusion coefficient of multi-frequency whistlers is inversely proportional to △f （proportional to the frequency components Nw） when △f is below the threshold value but it remains unchanged with increasing Af when △f is larger than the threshold value. This is explained as being due to the fact that the resonant scattering effect of broadband waves is the sum of the effects of each frequency in the ＇effective frequency band＇. Our results suggest that the modulation frequency of HF heating of the ionosphere can be appropriately selected with reasonable frequency intervals so that better performance of controlled precipitation of high energy electrons in the plasmasphere by artificial ELF/VLF whistler waves can be achieved.

Excitation and Detection of Shear Horizontal Waves with Electromagnetic Acoustic Transducers for Nondestructive Testing of Plates

The fundamental shear horizontal（SH0） wave has several unique features that are attractive for long-range nondestructive testing（NDT）. By a careful design of the geometric configuration, electromagnetic acoustic transducers（EMATs） have the capability to generate a wide range of guided wave modes, such as Lamb waves and shear-horizontal（SH） waves in plates. However, the performance of EMATs is influenced by their parameters. To evaluate the performance of periodic permanent magnet（PPM） EMATs, a distributed-line-source model is developed to calculate the angular acoustic field cross-section in the far-field. Numerical analysis is conducted to investigate the performance of such EMATs with different geometric parameters, such as period and number of magnet arrays, and inner and outer coil widths. Such parameters have a great influence on the directivity of the generated SH0 waves that arises mainly in the amplitude and width of both main and side lobes. According to the numerical analysis, these parameters are optimized to obtain better directivity. Optimized PPM EMATs are designed and used for NDT of strip plates. Experimental results show that the lateral boundary of the strip plate has no perceivable influence on SHO-wave propagation, thus validating their used in NDT. The proposed model predicts the radiation pattern ofPPM EMATs, and can be used for their parameter optimization.

Laboratory Research on Effective Test Area of Short-Crested Waves Generated by Two-Sided Segmented Wavemakers

The size and shape of the effective test area are crucial to consider when short-crested waves are created by segmented wavemakers. The range of the effective test area of short-crested waves simulated by two-sided segmented wavemakers is analyzed in this paper. The experimental investigation on the wave field distribution of short-crested waves generated by two-sided segmented wavemakers is conducted by using an array of wave gauges. Wave spectra and directional spreading function are analyzed and the results show that when the main direction is at a certain angle with the normal line of wave generators, the wave field of 3D short-crested waves generated by two-sided segmented wavemakers has good spatial uniformity within the model test area. The effective test area can provide good wave environments for seakeeping model tests of various ocean engineering structures in the deep ocean engineering basin.

Evaluation of Treadmill Exercise Test Induced U-wave Inversion in Diagnosis of Coronary Artery Disease

U-wave changes during treadmill exercise test were compared between 34 patientswith CAD and 33 normal controls.All of them were confirmed by coronary angiographv.Tenpatients with CAD and 1 normal subject in this study showed U-wave inversion during exercisetest.Of the 10 patients,4 had significant stenosis in one-vessel and 6 in multi-vessel of the ma-jor coronary arteries.The sensitivity,specificity and predictive value of exercise-inducedU-wave inversion were 29％, 97％ and 91％,respectively.It is proposed that exercise inducedU-wave inversion is a reliable predictive index of CAD.

Non-Contact Stress Measurement during Tensile Testing Using an Emat for SH₀-Plate Wave and Lamb Wave

The stress on a test specimen during tensile testing is generally measured by a strain gauge. This method has some problems in that it would influence the measurement conditions of the tensile test and can evaluate only the position at which the strain gauge is attached. The acoustoelastic method is proposed as a method replacing the strain gauge method. However, an ultrasonic sensor with a piezoelectric oscillator requires a coupling medium to inject an ultrasonic wave into a solid material. This condition, due to the error factor of the stress measurement, makes it difficult for the ultrasonic sensor to move on the specimen. We then tried to develop a non-contact stress measurement system during tensile testing using an electromagnetic acoustic transducer (EMAT) with an SH0-plate wave and S0-Lamb wave. The EMAT can measure the propagation time in which the ultrasonic wave travels between a receiver and a transmitter without a coupling medium during the tensile testing and can move easily. The interval between the transmitter and the receiver is 10mm and can be moved along the parallel direction or the vertical direction of the tensile load. The transit time was measured by a cross-correlation method and converted into the stress on the test specimen using the acoustoelastic method. We confirmed that the stress measurement using an SH0-plate wave was superior to that with an S0-Lamb wave.

Relationship between Star-Wave Test and Visual/Motor Maturity in Young Children

The developmental maturity (M) scale using the Star-Wave Test that was independently developed by Yalon and Zion indicates poor learning abilities if the M-scale score is low, which may be caused by developmental delays, such as intellectual disability and learning disorder or organic mental disorder. Furthermore, the distress (D) scale is thought to be influenced by mild neurological disorders, hand coordination problems, and environmental factors. In this study, we conducted a Star-Wave Test on 44 nursery school children in Japan and examined the M scale, the D scale, as well as the level of stress induced by coordination problems and the environment. The t-test was conducted on the M scale and D scale of the group without coordination problems and that with coordination problems, and we found a significant difference at 1% level. From this result, we can confirm the relationship of the M scale and the D scale with Visual and motor maturity.

Modeling of Electromagnetic Wave Propagation and Its Applicationin Virtual Test

With the development of virtual test,the computation of the effect of different weather conditions on electromagnetic wave propagation is required in many simulation systems. Firstly,this paper presents a unique point of view for computing the electromagnetic wave attenuation ratio under different weather conditions by means of an independent electromagnetic wave propagation component that can be directly implemented in virtual test, and is easy to configure and easy to reuse. We present an analysis of the principles of electromagnetic wave propagation and the algorithms designed for realization of various propagation models within the electromagnetic wave propagation component. Secondly,this paper presents a use-case analysis and outlines the design of the component,verifies the developed models under various weather conditions,and obtains equivalent values as those obtained theoretically. Finally,we build a virtual test system,verify the system in different weather conditions,and again obtain equivalent values to those obtained theoretically. The algorithms in the electromagnetic wave propagation component are developed in the C language, which substantially improves the computational speed,and meets the real-time requirements of the virtual testing platform.

箱型浮式防波堤的波浪消减性能分析研究

为了综合比选现有箱型浮式防波堤、分析其截面的改进设计方向,本文总结了目前提出的箱型浮式防波堤的截面型式,并收集对应的物理模型试验结果对其波浪消减性能进行了分析。通过引入无量纲参数β,对各类浮堤的消波特性进行讨论,得到了不同截面型式浮式防波堤的消浪性能边界。结果表明:当入射波周期小于9 s时,各类浮堤的透射系数可达到0.5以下;当大于9 s时,浮堤的消浪能力大幅下降,透射系数集中在0.8~1.0。在此基础上,总结了3种改进浮式防波堤截面的途径,建议优选组合异形截面并添设消波模块。

基于故障相关性的随钻方位电磁波测井仪器可靠性失效建模研究

随钻方位电磁波测井仪器作为石油勘探开发的高端装备,对于实时钻井地质导向、井眼轨迹优化及提高储层钻遇率具有十分重要的意义.但因井下复杂环境应力的影响,导致仪器故障率不断升高同时测井响应出现畸变、极值甚至重合,不仅对实时地质导向造成极大影响并且难以给出合理准确的解释.因此,本文以AziExpress随钻方位电磁波测井仪器为研究实体,通过环境应力可靠性试验对仪器内部天线系统失效模式进行分析.同时对天线系统主要部件的失效时间进行统计并结合历史故障及维修统计数据拟合可靠性失效分布模型,再利用K-S检验法对天线系统各主要部件失效分布模型进行检验.最后依据失效分布模型计算各主要部件的可靠性性能指标,结合失效概率密度函数、失效率、累积失效分布函数对天线系统的可靠性进行分析与评价.研究结果表明,威布尔失效分布模型对于随钻方位电磁波测井仪器天线系统主要部件的最小拟合优度检验值D_(n)为0.131,基于故障相关性的可靠性建模方法能够对仪器天线系统可靠性仿真分析与预测提供依据.

高原环境爆炸冲击波传播规律及计算模型研究

为研究高原地区的低温低压环境对冲击波传播特性的影响,在海拔1500,3000,4500 m环境下开展了TNT爆炸试验,并使用有限元软件对高原环境TNT的爆炸冲击波进行数值仿真计算,分析了不同海拔对冲击波传播特性的影响规律。对比了Sadovskyi,Kinney-Graham和Sachs修正公式的超压峰值和比冲量计算结果与试验结果,并采用Sachs修正中的温度修正项对Sadovskyi高原超压峰值公式进行了修正。研究结果表明:随着海拔的升高,冲击波的波阵面速度加快,到达时间提前,每升高1 km,冲击波超压峰值下降约2%~4%,比冲量下降约4%;对超压峰值进行修正时,3种修正公式均具有一定的准确性;对比冲量进行修正时,Kinney-Graham修正的比冲量值随比例距离增加呈线性降低,与试验结果吻合较差,庞春桥与Sachs的修正结果随比例距离增加呈指数降低;基于温度项修正的Sadovskyi高原冲击波超压峰值经验公式的平均误差减小了3.1%。该研究结果对于高海拔地区的弹药毁伤效能评估有参考意义。

应用Test.Lab进行高速车体线路模态试验

针对高速列车的振动问题,通过线路模态试验进行车体结构模态参数研究,采用LMS test.lab振动噪声测试系统进行数据采集和分析后处理。基于环境激励模态试验方法及模态参数识别理论,运用PolyMax模态提取法,获取了车体的前三阶弹性模态参数和对应的模态振型,为车体结构优化设计提供依据。

车辆段运用库上盖建筑减振措施效果分析

以某车辆段为研究对象,实测运用库行车引起的源强、盖板及上盖建筑的垂向振动,对比不同断面振动规律的变化;建立轨道-大地-车辆段-上盖建筑三维有限元模型,结合车辆轨道动力学模型计算加载所需轮轨力,将轮轨力加载至有限元模型钢轨上求解振动响应,再用实测数据加以验证,在此基础上研究不同扣件刚度及不同楼板厚度工况下上盖建筑的振动变化,研究结果表明:加减速状态下,源强各处振动主频带较匀速状态下更宽;盖板上各测点主频为31.5 Hz,上盖建筑主频为63 Hz;减振扣件在20~125 Hz内有较好的减振效果;同一楼层板厚每增加20 mm,上盖建筑Z振级对应衰减0.84~1.46 dB。

铝合金薄板焊缝根部缺陷高阶半跨模式波定量检测

铝合金薄板焊接时会产生接近垂直的根部缺陷,且表面余高制约超声检测探头与楔块布置。结合常规半跨模式波的全聚焦方法有助于实现根部垂直缺陷轮廓表征与定量,但受余高影响,相控阵探头声场仍难以有效覆盖焊缝区域。该文考虑了薄板内的超声波多次反射,提出利用声束路径更长、声场覆盖范围更广的高阶半跨模式波进行缺陷轮廓重建。对存在和不存在余高的厚度6.0 mm铝合金板中端点深度3.0 mm、高度3.0 mm的根部裂纹,采用32阵元、中心频率5 MHz相控阵探头配合55◦横波楔块实施全矩阵捕捉和高阶半跨模式波成像。仿真和实验结果表明,缺陷轮廓可以被完整呈现,且缺陷高度定量相对误差均不超过5.0%。此外,需依据板材厚度合理选择半跨模式波阶数,板厚越薄,适用的半跨模式波阶数越高。

跨海桥梁基础多因素影响下的波流耦合试验及工程应用研究

跨海大桥所在工程海域面临强台风及其引起的大浪、急流等恶劣海洋环境威胁,且桥梁结构采用大尺度高桩承台群桩基础,涉及结构安全校核时,无法利用规范或经验公式计算其受到的波流力。因此采用了比尺为1颐40的整体物理模型试验方法,通过波高、周期、水位、冲刷深度等多因素影响的试验组合,论证桥梁基础(承台和群桩)受波流力的影响,揭示了多因素影响与结构受波流力之间的变化规律。同时为了便于工程应用,利用本次成果,以及类似工程——深中通道岛桥结合部桥梁基础受力试验成果,进一步拟合了基础结构受波流力的经验公式,成果不仅解决工程实际问题,也可为类似工程设计提供基础数据和参考。