基于有限元法的含凹陷油气管道应变分析

为对含凹陷的油气管道进行更合理的完整性评价,采用有限元法模拟管道在承受外部岩石挤压时的应变分布,讨论凹陷深度、管道壁厚和挤压体大小等参数对应变的影响.结果表明：在相同条件下,最大等效应变随凹陷深度增大而增大;在同样深度条件下,管壁较厚处的凹陷最大等效应变较大;挤压体半径越大,凹陷的轮廓越光滑,应变集中程度越小;管材等级对等效应变的影响很小.该方法和结论可用于改进凹陷评价方法和风险排序.     

某轻型客车翼子板抗凹性分析和优化

抗凹性是反映汽车外覆盖件使用性能的一项重要指标。研究某轻型客车翼子板抗凹性分析理论以及评价标准,同时针对该款车型翼子板采用Abaqus软件进行抗凹性数值模拟分析。通过有限元分析结果确定其性能,并通过优化使其达到抗凹性能的要求。     

某越野车外覆盖件抗凹分析自动化流程开发

针对越野车外覆盖件抗凹分析流程中考察点多、加载工况复杂、工作效率低的现状,采用TCL/TK语言和基于HyperMesh前处理平台,开发一套简单、高效、便捷的可视化CAE抗凹分析自动化流程。该流程主界面简单,可以按照需求自动完成网格细化、压头创建和工况分析,操作简便。以某越野车发动机盖抗凹分析为例,验证该抗凹分析自动化流程的高效率和分析结果的准确性。 关键词： 发动机盖; 抗凹分析; 自动化; TCL/TK; HyperMesh     

Use of RADARSAT‐1 data and a digital elevation model to assess flood damage and improve rice production in the lower part of the Chi River Basin,Thailand

In Thailand, flooding due to seasonal monsoon conditions frequently destroys a substantial amount of rice production, the most important agricultural activity of the country. Taking the 2001 monsoon flooding that hit the Lower Chi River Basin as an example, we developed a new method for accurately assessing damage to flood‐affected paddies. A RADARSAT‐1 image acquired during peak flooding was combined with a 30‐m digital elevation model (DEM) to develop a ‘flood‐level‐determination’ algorithm for estimating floodwater depth. Based on the elongation capability of the rice varieties, a water depth of 80 cm was used to separate ‘non‐damaged’ from ‘damaged’ paddy areas, indicating that about 60% of the paddy fields in the flooded areas were non‐damaged paddies. To minimize the loss of rice and maximize farmers' incomes, a map of rice varieties appropriate for the damaged paddy areas was produced, combining the flood‐affected paddy map with the flood frequency map. Our results demonstrate the potential of using single‐date RADARSAT‐1 data and a DEM to provide accurate and economic means of assessing flood damage to rice fields that can be used to improve rice production.     

Fatigue crack in large-scale tubular joints for offshore structures

Tubular members have been used for constructing offshore structures. Large-scale fatigue tests of welded tubular K-joints under the balanced in-plane bending brace were carried out to investigate the fatigue behavior of API 2W Gr.50 steel produced by POSCO. The experimental results were verified by numerical approaches and compared with the IIW, DnV RP-C203 and API RP 2A-WSD design curves. The test results based on the hot spot stress were in agreement with the design curves. The SCF factor for tubular K-jo...     

A comparative simulation study on the power–performance of multi-core architecture

Nowadays, multi-core processor is the main technology used in desktop PCs, laptop computers and mobile hardware platforms. As the number of cores on a chip keeps increasing, it adds up the complexity and impacts more on both power and performance of a processor. In multi-processors, the number of cores and various parameters, such as issue-width, number of instructions and execution time, are key design factors to balance the amount of thread-level parallelism and instruction-level parallelism. In this paper, we perform a comprehensive simulation study that aims to find the optimum number of processor cores in desktop/laptop computing processor models with shallow pipeline depth. This paper also explores the trade-off between the number of cores and different parameters used in multi-processors in terms of power–performance gains and analyzes the impact of 3D stacking on the design of simultaneous multi-threading and chip multiprocessing. Our analysis shows that the optimum number of cores varies with different classes of workloads, namely: SPEC2000, SPEC2006 and MiBench. Simulation study is presented using architectures with shorter pipeline depth, showing that (1) the optimum number of cores for power–performance is 8, (2) the optimum number of threads in the range [2, 4], and (3) for beyond 32 cores, multi-core processors are no longer efficient in terms of performance benefits and overall power consumption.     

A global non-destructive damage assessment methodology for civil engineering structures

This paper describes a potential methodology to continuously assess the safety of civil engineering structures, e.g. bridges, frames and offshore platforms. The proposed damage assessment methodology not only detects and sizes damage, but also evaluates the impact of the damage on the performance of the structure. The proposed methodology deals with two broad activities: (i) periodic non-destructive damage localization and severity estimation; and (ii) the assessment of structural safety based on the results of the non-destructive damage detection. To accomplish these activities, first an established methodology which yields information on the changes in localized sectional stiffness properties (e.g. axial, bending and torsion) from changes in dynamic properties (i.e. mode shapes and frequencies) of the pre-damaged and post-damaged structures is reviewed. Next, an efficient technique to directly assess the reliability of a structural system using reliabilities of the components of the structure is developed. The efficacy of the combination of the non-destructive damage detection and the structural reliability evaluation is demonstrated using pre-damage and post-damage modal data obtained from numerical simulations of a rigid frame.     

发动机盖舷窗角部表面凹陷分析

为从根本上解释和解决汽车覆盖件局部表面凹陷的形成,以上海通用汽车公司的某车型为例,借助CAE仿真软件分析发动机盖舷窗区域在成型过程中的主次应力的演变过程;分析该类局部凹陷产生的力学机理,并提出调整拉延筋阻力和施加局部强压的工程解决办法.实际零件的验证表明该方法能很好地消除表面凹陷.     

Knowledge sharing in online health communities: A social exchange theory perspective

Online health communities (OHC) are becoming valuable platforms for patients to communicate and find support. These communities are different from general online communities. The knowledge shared in an OHC can be categorized as either general (public) or specific (private), and each category is shared in vastly different ways. Using the social exchange theory, we propose a benefit vs. cost knowledge sharing model for OHCs. The benefits are mainly based on Maslow's hierarchy of needs, and the cost includes cognitive and executional costs. We use this benefit vs. cost model to examine how OHC members share general and specific knowledge. Data were collected from 323 users of two well-known OHCs in China and were analyzed using the structural equation model. The results demonstrate that three factors positively impact the sharing of both general and specific knowledge: a sense of self-worth, members’ perceived social support, and reputation enhancement. Another factor, face concern, has a negative influence on specific knowledge sharing and a positive influence on general knowledge sharing. Executional cost only negatively impacts general knowledge sharing, and cognitive cost only negatively impacts specific knowledge sharing. This study of OHCs reveals that personal benefits promote knowledge sharing and costs prohibit it. These impacts vary between general knowledge and specific knowledge sharing.     

Mapping the underside of an iceberg with a modified underwater glider

Icebergs pose many challenges to offshore operations in the Arctic Ocean and sub‐arctic regions. They could damage underwater infrastructure such as pipelines, and disrupt marine transportation. The below‐water shape of an iceberg is a key factor for iceberg management in the North Atlantic Ocean because it affects the iceberg towing plans and iceberg drift patterns. In recent years, unmanned platforms have been proposed as potential candidates for underwater iceberg mapping. Compared to a conventional ship‐based iceberg survey, using unmanned platforms is more efficient and safer. In this paper, we present research using a hybrid underwater glider to measure the underwater shape of an iceberg. The vehicle is equipped with a mechanical scanning sonar for range sensing and iceberg mapping, and a guidance system is designed to use the sonar measurements for guiding the vehicle to circumnavigate an iceberg at the desired standoff distance. Several field experiments have been conducted on an iceberg to evaluate the system performance. With repeated observations, the underside of the target iceberg was successfully reconstructed, and iceberg shape comparisons are presented.     

基于PVDF传感器和工作曲率变形实现裂纹梁裂纹检测

提出通过压电高分子薄膜PVDF(Polyvinylidene Fluoride)作为传感器直接测量结构的工作曲率变形(Curvature Operating Shape)实现结构裂纹检测.以悬臂裂纹梁为例,首先探讨基于PVDF传感器测量工作曲率变形,并用于结构损伤检测的可行性,然后介绍工作曲率变形用于损伤检测的理论基础,并以PVDF压电薄膜作为传感器,提出只通过损伤后结构的频率响应函数,直接得到工作曲率变形和损伤指标.最后通过对一条裂纹和两条裂纹悬臂梁的损伤检测实验,证明该方法在梁结构损伤识别和健康监测中的有效性,并且识别过程不需要健康结构的振动信息.     

Soil-structure interaction and effect of axial force on the dynamics of offshore structures

The offshore structures are flexible systems subjected to various types of loadings. The heavy gravitational loads on the top decks, wind and water wave pressures acting on the platforms are transferred to the soil through the piles or mat foundations. Under the vibration, the variation in the pore pressures induces additional effects on the embedded part of the piles. The effect of the soil-structure interaction on the dynamics of the structure is taken into account as the deformations of the soil caused by the motion of the structure which in turn modify the response of the structure. The effect of the axial forces, within the individual members, on the vibration of the structure is included in the formulation. The dynamic stiffness matrix of the members are developed by considering the actual mass distribution and the effect of the axial force of the members. For the members embedded into soil, the soil reactions and the skin frictions are also considered as continuously varying over the members. Therefore, the equations of motion are satisfied along any infinitesimal element of the members. The new formulation is introduced in the general purpose computer code STDYNL, then the sensitivity of the overall dynamic response of the deep water platforms to the variation of the soil characteristics and to the effect of the axial forces of the members are investigated.     

自适应参数分析结果的航空发动机孔探图像损伤检测

目的 航空发动机孔探图像的损伤检测关系到航空发动机是否要非例行更换,直接影响飞机的飞行安全和利用率。现有的孔探图像损伤检测方法直接使用目标检测方法训练一个多类别损伤检测器,使用相同的参数在不同位置检测损伤。由于没有考虑同类型损伤在发动机不同区域发生概率的不同,导致现有方法的检测准确率较低。为了提高损伤检测的准确率,提出了一种自适应参数的航空发动机孔探图像损伤检测方法。方法 通过识别孔探图像所属的发动机区域,针对不同区域孔探图像设置不同的参数用于检测发动机损伤。同时为了避免单检测器上不同类型损伤之间相互干扰,采用独立检测器检测单一类型的损伤,并对误检率高的损伤进行真假识别。通过合并检测到的不同类型的损伤,得到最终的损伤检测结果。此外,为了改进水平的矩形检测框,使用分割结果产生旋转的检测框,有效地减少了框中的背景区域。结果 在13个航空发动机区域的2 654幅孔探图像上针对烧蚀、裂缝、材料丢失、涂层脱落、刻痕和凹坑等6种典型的发动机损伤进行检测实验。提出的损伤检测方法在准确率和召回率两方面分别达到了90.4%和90.7%,相较于目标检测方法YOLOv5 （you only look once version 5）的准确率和召回率高24.8%和25.1%。实验结果表明,本文方法在航空发动机损伤检测方面优于其他对比方法。结论 本文所提出的自适应参数的航空发动机损伤检测模型通过识别发动机图像所属的部位,针对同种类型的损伤检测器设定不同的参数,有效地提高了检测器的检测性能。同时,针对容易误检的裂缝、刻痕和凹坑增加了真假损伤判别器,有效地减少了误检的情况。     

Underwater inspection of bridge substructures using sonar and deep convolutional network

Bridges are vital structures for worldwide physical infrastructure networks, and efficient inspection methods are needed to reveal and evaluate the health conditions of damaged critical bridges. In contrast to the superstructure inspection, underwater inspection methods are still time-consuming and labor-intensive tasks. As the underwater environment is invisible and hard to access, scouring and damage are easily neglected in traditional human diving. To address this problem, this paper presents a rapid underwater inspection framework using a sonar device and a deep convolutional network to provide quantitative measuring results for scour depth and apparent damage. The side-scan sonar and fixing platform were used to collect underwater images, and a modified semantic segmentation was designed based on the U-Net architecture. The pretrained residual building blocks and a designed feature fusion connection called Respath were utilized to replace the original encoder and skip connection. Comparative experiments showed that this modified architecture achieved the best performance in multiple-class segmentation for sonar images in which the mean intersection over union (mIoU) and IoU for specific apparent damage can reach up to 0.918 and 0.63, respectively. An on-site test was also conducted to validate the applicability of the proposed method, and the scour depth and two points of damage were identified based on the pixelwise segmentation images. Therefore, further structural evaluation can proceed based on these accurate measuring results.     

A swift technique for damage detection of determinate truss structures

In this study, a novel two-stage approach for damage detection of determinate truss structures is proposed. The method lies in the group of vibration-based methods but it just needs the first natural frequency and mode shape vector of these structures for identifying the location and severity of damage. In the first stage, the modal residual force vector for different modes of a structure is introduced and the one associated with the first mode is applied to the structure as an external nodal force vector. Then, the residual local nodal force vector can be computed for all elements of the structure. Next, the elements with non-zero residual internal force are considered as damaged elements. In the second stage, the damage severity of each damaged element is determined using a new relation which can be categorized as a force–displacement relation. To show the efficiency and simplicity of the proposed method, three truss structures including a 13-bar planar truss, a 29-bar planar truss, and a 77-bar planar truss under different damage scenarios are studied; the results of which indicate that the method is innovatively capable of suitably detecting, for determinate truss structures, not only damaged members but also their individual damage severity by carrying solely one analysis.

     

The use of multi‐temporal Landsat images for the change detection of the coastal zone near Hurghada,Egypt

A Landsat 5 Thematic Mapper (TM) image of 1987 and a Landsat 7 Enhanced Thematic Mapper Plus (ETM+) image of 2000 were used to examine changes in land use/land cover (LULC) around Hurghada, Egypt, and changes in the composition of coral reefs offshore. Prior to coral reef bottom‐type classification, the radiance values were transformed to depth‐invariant bottom indices to reduce the effect of the water column. Subsequently, a multi‐component change detection procedure was applied to these indices to define changes. Preliminary results showed significant changes in LULC during the period 1987–2000 as well as changes in coral reef composition. Direct impacts along the coastline were clearly shown, but it was more difficult to link offshore changes in coral reef composition to indirect impacts of the changing LULC. Further research is needed to explore the effects of the different image‐processing steps, and to discover possible links between indirect impacts of LULC changes and changes in the coral reef composition.     

一种用于管道检测的磁致伸缩式周向超声导波传感器

传感器由磁化器、激励线圈、接收线圈和聚磁器等组成.实验结果表明,利用周向超声导波传感器可以在大直径管道中激励和接收周向超声导波并可对管道中的缺陷进行长范围、全覆盖的非接触无损检测.     

Performance Impacts of Web-Enabled Retail Services: An Empirical Study

Prior studies suggest that the growth in online retail is attributed to the effective implementation of media-rich and interactive services and functionalities that help overcome the para-social distance between customers and online retail stores. However, few studies have offered empirical evidence that demonstrates the specific impacts these interactive services and functionalities have on the financial performance of online retailers. Using data on the operations and financial performance of the top 500 online retailers in the U.S., this study investigates the impact that website features and functionalities have on sales performance and other intermediate performance measures. Our findings suggest that website features and functionalities have a significant direct impact on sales as well as an indirect impact through intermediate performance measures. Furthermore, our model identifies the specific performance measures that each website feature targets to improve.     

Getting the control across: Control transmission in information systems offshoring projects

Offshoring of information systems (IS) projects has become a widespread global practice. While prior research suggests that controlling, and communicating with, offshore vendors represent key managerial challenges, the topic of how control is communicated, or transmitted, from client to vendor has been widely neglected. Our study focuses on control transmission in the critical relationship between client and offshore vendor managers, and its impact on the performance of IS offshoring projects. Drawing on a matched‐pair survey with 172 client and vendor managers from 86 projects, our results provide several new insights to the IS literature: First, we find that both behaviour and outcome control have the capacity to be transmitted consistently in lateral IS offshore project relationships. Second, our results show that consistent transmission translates into a performance effect only for outcome control. Third, we find that high‐performing offshore projects are characterized by both greater control transmission consistency and greater use of outcome control compared to low‐performing projects. In sum, our study extends theory on IS project control by highlighting that effective control of IS offshoring projects is not only about selecting proper controls but also about ensuring that, as a controller, you get the control across to the controllee.     

Simulating analogue film damage to analyse and improve artefact restoration on high-resolution scans

Digital scans of analogue photographic film typically contain artefacts such as dust and scratches. Automated removal of these is an important part of preservation and dissemination of photographs of historical and cultural importance. While state-of-the-art deep learning models have shown impressive results in general image inpainting and denoising, film artefact removal is an understudied problem. It has particularly challenging requirements, due to the complex nature of analogue damage, the high resolution of film scans, and potential ambiguities in the restoration. There are no publicly available high-quality datasets of real-world analogue film damage for training and evaluation, making quantitative studies impossible. We address the lack of ground-truth data for evaluation by collecting a dataset of 4K damaged analogue film scans paired with manually-restored versions produced by a human expert, allowing quantitative evaluation of restoration performance. We have made the dataset available at https://doi.org/10.6084/m9.figshare.21803304. We construct a larger synthetic dataset of damaged images with paired clean versions using a statistical model of artefact shape and occurrence learnt from real, heavily-damaged images. We carefully validate the realism of the simulated damage via a human perceptual study, showing that even expert users find our synthetic damage indistinguishable from real. In addition, we demonstrate that training with our synthetically damaged dataset leads to improved artefact segmentation performance when compared to previously proposed synthetic analogue damage overlays. The synthetically damaged dataset can be found at https://doi.org/10.6084/m9.figshare.21815844, and the annotated authentic artefacts along with the resulting statistical damage model at https://github.com/daniela997/FilmDamageSimulator. Finally, we use these datasets to train and analyse the performance of eight state-of-the-art image restoration methods on high-resolution scans. We compare both methods which directly perform the restoration task on scans with artefacts, and methods which require a damage mask to be provided for the inpainting of artefacts. We modify the methods to process the inputs in a patch-wise fashion to operate on original high resolution film scans.