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Research status and application of artificial intelligence large models in the oil and gas industry
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作者 LIU He REN Yili +6 位作者 LI Xin DENG Yue WANG Yongtao CAO Qianwen DU Jinyang LIN Zhiwei WANG Wenjie 《Petroleum Exploration and Development》 SCIE 2024年第4期1049-1065,共17页
This article elucidates the concept of large model technology,summarizes the research status of large model technology both domestically and internationally,provides an overview of the application status of large mode... This article elucidates the concept of large model technology,summarizes the research status of large model technology both domestically and internationally,provides an overview of the application status of large models in vertical industries,outlines the challenges and issues confronted in applying large models in the oil and gas sector,and offers prospects for the application of large models in the oil and gas industry.The existing large models can be briefly divided into three categories:large language models,visual large models,and multimodal large models.The application of large models in the oil and gas industry is still in its infancy.Based on open-source large language models,some oil and gas enterprises have released large language model products using methods like fine-tuning and retrieval augmented generation.Scholars have attempted to develop scenario-specific models for oil and gas operations by using visual/multimodal foundation models.A few researchers have constructed pre-trained foundation models for seismic data processing and interpretation,as well as core analysis.The application of large models in the oil and gas industry faces challenges such as current data quantity and quality being difficult to support the training of large models,high research and development costs,and poor algorithm autonomy and control.The application of large models should be guided by the needs of oil and gas business,taking the application of large models as an opportunity to improve data lifecycle management,enhance data governance capabilities,promote the construction of computing power,strengthen the construction of“artificial intelligence+energy”composite teams,and boost the autonomy and control of large model technology. 展开更多
关键词 foundation model large language mode visual large model multimodal large model large model of oil and gas industry pre-training fine-tuning
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Calculation mode of side friction for large open caisson 被引量:2
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作者 欧阳效勇 赵文光 +1 位作者 李进 李松 《Journal of Southeast University(English Edition)》 EI CAS 2015年第1期130-136,共7页
To overcome the problems in design methodologies and construction control measures for the large open caisson, systematic research was conducted on the side friction calculation mode of the large open caisson. Based o... To overcome the problems in design methodologies and construction control measures for the large open caisson, systematic research was conducted on the side friction calculation mode of the large open caisson. Based on the field monitoring data of lateral soil pressure on the side wall of the open caisson for the southern anchorage of the Maanshan Yangtze River Highway Bridge, the statistical result of the side friction under different buried depths of the cutting edge of the open caisson was back-analyzed; and the side friction distribution of the large open caisson was underlined. The analysis results indicate that when the buried depth of the cutting edge is smaller than a certain depth H0, the side friction linearly increases with the increase in the buffed depth. However, as the buffed depth of the cutting edge is larger than H0, the side friction shows a distribution with small at both ends and large in the middle. The top of the distribution can be regarded as a linear curve, while the bottom as a hyperbolic curve. As the buffed depth of cutting edge increases continuously, the peak value of the side friction linearly increases and the location of the peak value gradually moves down. Based on the aforementioned conclusions, a revised calculation mode of the large open caisson is presented. Then, the calculated results are compared with the field monitoring data, which verifies the feasibility of the proposed revised calculation mode. 展开更多
关键词 large open caisson side friction distributiondiagram calculation mode
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A Comparison Study on Flesh Quality of Large Yellow Croaker (Larimichthys croceus) Cultured with Three Different Modes 被引量:3
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作者 LI Xiaoqin LI Baian +3 位作者 CHEN Naisong HUANG Xuxiong HUA Xuemin LENG Xiangjun 《Journal of Ocean University of China》 SCIE CAS CSCD 2017年第6期1187-1194,共8页
To compare the flesh quality of large yellow croaker cultured with three different modes, enclosure culture(EC), cage culture with feeding trash fish(CCF) and cage culture with feeding formula diet(CCD), thirty six fi... To compare the flesh quality of large yellow croaker cultured with three different modes, enclosure culture(EC), cage culture with feeding trash fish(CCF) and cage culture with feeding formula diet(CCD), thirty six fish individuals of EC(484.6 ± 79.8 g), CCF(432.7 ± 87.9 g) and CCD(416.9 ± 49.5 g) were sampled to measure body color, flesh water holding capacity, flesh proximate composition, amino acids and fatty acids composition, and collagen and inosinic acid contents. The analysis showed that there was no significant difference in the yellowness of skin and the contents of crude protein and inosinic acid between CCD and EC(P > 0.05), and the two modes showed higher values than CCF(P < 0.05). Most of the amino acids(AA) in flesh were higher in EC than in CCF(P < 0.05), but CCD showed no difference in AA composition from the other two modes(P > 0.05). EC and CCD had higher contents of collagen, free AA and lower drip loss than CC(P < 0.05). In polyunsaturated fatty acids, EC showed significantly higher levels of C20:5 n-3 and C22:6 n-3 than CCF and CCD(P < 0.05), but CCD had significantly higher C18:2 n-6 than CCF and EC(P < 0.05). In conclusion, the flesh quality of CCD fish is similar to EC fish, and these two modes have better flesh quality than CCF. 展开更多
关键词 large YELLOW CROAKER FLESH quality BODY color culture mode
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Three-Dimensional Multi-Phase Microscopic Simulation of Service Life of Recycled Large Aggregate Self-Compacting Concrete
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作者 Jing Li Lina Gao +3 位作者 Libo Liu Liao Zhang Jianhua Zheng Jing Gao 《Journal of Materials Science and Chemical Engineering》 2024年第4期126-135,共10页
Recycled large aggregate self-compacting concrete (RLA-SCC) within multiple weak areas. These weak areas have poor resistance to chloride ion erosion, which affects the service life of RLA-SCC in the marine environmen... Recycled large aggregate self-compacting concrete (RLA-SCC) within multiple weak areas. These weak areas have poor resistance to chloride ion erosion, which affects the service life of RLA-SCC in the marine environment. A three-dimensional multi-phase mesoscopic numerical model of RLA-SCC was established to simulate the chloride ions transportation in concrete. Experiments of RLA-SCC immersing in chloride solution were carried out to verify the simulation results. The effects of recycled large aggregate (RLA) content and RLA particle size on the service life of concrete were explored. The results indicate that the mesoscopic numerical simulation results are in good agreement with the experimental results. At the same depth, the closer to the surface of the RLA, the greater the chloride ion concentration. The service life of RLA-SCC in marine environment decreases with the increase of RLA content. Compared with the service life of 20% content, the service life of 25% and 30% content decreased by 20% and 42% respectively. Increasing the particle size of RLA can effectively improve the service life of RLA-SCC in chloride environment. Compared with the service life of 50 mm particle size, the service life of 70 mm and 90 mm increased by 61% and 163%, respectively. . 展开更多
关键词 Recycled large Aggregate Self-Compacting Concrete Mesoscopic mode Chloride Ion Diffusion Numerical Analysis
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On the Symbiotic Modes of SMEs and Large Enterprises Based on Symbiotic Energy and Medium
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作者 Feng Delian 《学术界》 CSSCI 北大核心 2017年第6期282-287,共6页
There are three varieties of symbiotic modes of SMEs and large enterprises based on symbiosis energy,including commensalisms,asymmetry mutualism and symmetry mutualism.The symbiotic mediums(such as stock ownership,con... There are three varieties of symbiotic modes of SMEs and large enterprises based on symbiosis energy,including commensalisms,asymmetry mutualism and symmetry mutualism.The symbiotic mediums(such as stock ownership,contract,trust,etc.) have an important influence on symbiotic modes.From the angle of symbiotic medium view,there are some measures that promote symbiotic modes toward symmetry mutualism,such as optimizing stock ownership structure of subsidiary company,promoting mid-system organization growth,building good faith cultural atmosphere. 展开更多
关键词 SME large ENTERPRISE SYMBIOSIS mode
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A novel method of evaluating large mode area fiber design by brightness factor
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作者 张海涛 陈丹 +2 位作者 任海翠 闫平 巩马理 《Chinese Physics B》 SCIE EI CAS CSCD 2015年第2期170-175,共6页
A novel evaluation term and a more reasonable criterion,which is described by a new parameter of brightness factor for active large mode area fiber design,are presented.The brightness factor evaluation method is based... A novel evaluation term and a more reasonable criterion,which is described by a new parameter of brightness factor for active large mode area fiber design,are presented.The brightness factor evaluation method is based on the transverse mode competition mechanism in fiber lasers and amplifiers.The brightness factor can be seen as a description of fiber general property since it can represent the output laser brightness of the fiber laser system and because of its ability to resist the nonlinear effect.A core-doped active large pitch fiber with a core diameter of 190 μm and a mode-field diameter of180 μm is designed by this method,and the designed fiber allows effective single-mode operation. 展开更多
关键词 brightness factor large pitch fiber mode competition
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Theoretical analysis of the mode coupling induced by heat of large-pitch micro-structured fibers
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作者 张海涛 陈丹 +2 位作者 郝杰 闫平 巩马理 《Chinese Physics B》 SCIE EI CAS CSCD 2015年第2期176-180,共5页
In this paper,a theoretical model to analyze the mode coupling induced by heat,when the fiber amplifier works at high power configuration,is proposed.The model mainly takes into consideration the mode field change due... In this paper,a theoretical model to analyze the mode coupling induced by heat,when the fiber amplifier works at high power configuration,is proposed.The model mainly takes into consideration the mode field change due to the thermally induced refractive index change and the coupling between modes.A method to predict the largest average output power of fiber is also proposed according to the mode coupling theory.The largest average output power of a large pitch fiber with a core diameter of 190 μm and an available pulse energy of 100 mJ is predicted to be 540 W,which is the highest in large mode field fibers. 展开更多
关键词 fiber amplifier large pitch fiber mode coupling
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Characteristics and advantages of energy performance contracting mode for energy saving transformation of existing large public building
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作者 GUO Han-ding ZHANG Hai-yun +1 位作者 XU Zhen-yan ZHANG Yin-xian 《Ecological Economy》 2016年第1期79-85,共7页
Existing large-scale public building energy saving renovation is the inherent requirement of sustainable development, it has been proved that implementing the energy performance contracting mode in the Existing large ... Existing large-scale public building energy saving renovation is the inherent requirement of sustainable development, it has been proved that implementing the energy performance contracting mode in the Existing large public buildings energy-saving is an effective way both at home and abroad. EPC mode has obvious characteristics for the ESCO and the customers, it can meet the basic requirements of large public buildings energy-saving, such as the width of funding sources, program specifi cation, advanced technology, information fl ow and management level higher, etc. Under the condition of market economy, it also provides a broad platform for the ESCO implements building energy saving transformation, which is conducive to the realization of the win-win cooperation between the parties, and to promote the healthy development of the existing large public building energy saving reconstruction. 展开更多
关键词 existing large PUBLIC building ENERGY SAVING transformation ENERGY performance CONTRACTING mode CHARACTERISTICS advantages
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Large User Direct Transaction: Mechanism and Mode Proposed
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作者 Research Group of Large User Direct Transaction ,Jia Yulu 《Electricity》 2008年第4期30-32,46,共4页
Bilateral Transaction between large users and power generation enterprises is not a simple reform. It is an important stage in power market restructuring and will grant the electricity users the right of service selec... Bilateral Transaction between large users and power generation enterprises is not a simple reform. It is an important stage in power market restructuring and will grant the electricity users the right of service selection. The implementation of bilateral transactions will help to establish the multiple buyers' market structure, reasonable price mechanism and market trading mechanism. It is also an important approach to enhance the competition in the market and improve the efficiency of energy resource allocation. 展开更多
关键词 large User Direct Transaction Mechanism and mode Proposed
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An Adaptive Sliding Mode Tracking Controller Using BP Neural Networks for a Class of Large-scale Nonlinear Systems
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作者 刘子龙 田方 张伟军 《Journal of Shanghai Jiaotong university(Science)》 EI 2007年第6期753-758,共6页
A new type controller, BP neural-networks-based sliding mode controller is developed for a class of large-scale nonlinear systems with unknown bounds of high-order interconnections in this paper. It is shown that dece... A new type controller, BP neural-networks-based sliding mode controller is developed for a class of large-scale nonlinear systems with unknown bounds of high-order interconnections in this paper. It is shown that decentralized BP neural networks are used to adaptively learn the uncertainty bounds of interconnected subsystems in the Lyapunov sense, and the outputs of the decentralized BP neural networks are then used as the parameters of the sliding mode controller to compensate for the effects of subsystems uncertainties. Using this scheme, not only strong robustness with respect to uncertainty dynamics and nonlinearities can be obtained, but also the output tracking error between the actual output of each subsystem and the corresponding desired reference output can asymptotically converge to zero. A simulation example is presented to support the validity of the proposed BP neural-networks-based sliding mode controller. 展开更多
关键词 BP NEURAL networks SLIDING mode control large-SCALE nonlinear systems uncertainty dynamics
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Attitude tracking control of flexible spacecraft with large amplitude slosh 被引量:4
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作者 Mingle Deng Baozeng Yue 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2017年第6期1095-1102,共8页
This paper is focused on attitude tracking control of a spacecraft that is equipped with flexible appendage and partially filled liquid propellant tank. The large amplitude liquid slosh is included by using a moving p... This paper is focused on attitude tracking control of a spacecraft that is equipped with flexible appendage and partially filled liquid propellant tank. The large amplitude liquid slosh is included by using a moving pulsating ball model that is further improved to estimate the settling location of liquid in microgravity or a zero-g environment. The flexible appendage is modelled as a three-dimensional Bernoulli–Euler beam, and the assumed modal method is employed.A hybrid controller that combines sliding mode control with an adaptive algorithm is designed for spacecraft to perform attitude tracking. The proposed controller has proved to be asymptotically stable. A nonlinear model for the overall coupled system including spacecraft attitude dynamics,liquid slosh, structural vibration and control action is established. Numerical simulation results are presented to show the dynamic behaviors of the coupled system and to verify the effectiveness of the control approach when the spacecraft undergoes the disturbance produced by large amplitude slosh and appendage vibration. Lastly, the designed adaptive algorithm is found to be effective to improve the precision of attitude tracking. 展开更多
关键词 Attitude tracking large amplitude liquid slosh Flexible spacecraft Dynamic coupling Adaptive sliding mode control
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Impacts of Coastal Reclamation on Natural Wetlands in Large River Deltas in China 被引量:3
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作者 MA Tiantian LI Xiaowen +1 位作者 BAI Junhong CUI Baoshan 《Chinese Geographical Science》 SCIE CSCD 2019年第4期640-651,共12页
Little information is available on the impacts of coastal reclamation on wetland loss in large-river deltas at a regional scale.Using remote sensing data of coastal wetland and reclamation in four deltas in China from... Little information is available on the impacts of coastal reclamation on wetland loss in large-river deltas at a regional scale.Using remote sensing data of coastal wetland and reclamation in four deltas in China from 1978 to 2014, we tracked their continuous area changes in four periods: 1978–1990, 1990–2000, 2000–2008, and 2008–2014. The areal relation between wetland loss and reclamation was quantified and used to identify coastal reclamation mode intensity coupled with another three indicators: reclamation rate,accretion rate and land-use intensity of coastal reclamation. The results showed that coastal reclamation driven by economic development reduced, or even reverse the original growth of delta which was determined by the offset between wetland acceleration rate and wetland loss rate. Generally, the area of reclamation showed a positive linear correlation with the area of wetland loss. The findings imply that human activities should control reclamation rate and intensity to alleviate total wetland loss and maintain wetland ’net gain’.Inappropriate coastal reclamation modes can magnify total wetland loss;therefore, coastal reclamation with a slow increment rate and low impervious surface percent is of great importance for sustainable development in future coastal management. 展开更多
关键词 COASTAL RECLAMATION WETLAND loss COASTAL RECLAMATION mode multi-case comparison large river DELTA COASTAL management
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Experimental analysis of crack tip fields in rubber materials under large deformation 被引量:5
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作者 Xia Xiao Hai-Peng Song +3 位作者 Yi-Lan Kang Xiao-Lei Li Xiao-Hua Tan Hao-Yun Tan 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2012年第2期432-437,共6页
A three-nested-deformation model is proposed to describe crack-tip fields in rubber-like materials with large deformation. The model is inspired by the distribution of the measured in-plane and out-of-plane deformatio... A three-nested-deformation model is proposed to describe crack-tip fields in rubber-like materials with large deformation. The model is inspired by the distribution of the measured in-plane and out-of-plane deformation. The in- plane displacement of crack-tip fields under both Mode 1 and mixed-mode (Mode I-II) fracture conditions is measured by using the digital Moir6 method. The deformation character- istics and experimental sector division mode are investigated by comparing the measured displacement fields under differ- ent fracture modes. The out-of-plane displacement field near the crack tip is measured using the three-dimensional digital speckle correlation method. 展开更多
关键词 Crack-tip field. large deformation Sector divi- sion mode. Three-nested-deformation model- Digital Moir6 method
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Study of a millimeter-wave squint indirect holographic algorithm suitable for imaging with large field-of-view
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作者 高翔 李超 方广有 《Chinese Physics B》 SCIE EI CAS CSCD 2014年第2期546-551,共6页
In this paper a millimeter-wave (MMW) squint indirect holographic method is presented, which is suitable for imaging with a large field-of-view. The proposed system employs the squint operation mode to remove the ba... In this paper a millimeter-wave (MMW) squint indirect holographic method is presented, which is suitable for imaging with a large field-of-view. The proposed system employs the squint operation mode to remove the background and twin- image interferences, which achieves a similar effect to off-axis holography but leaves out the large-aperture quasi-optical component. The translational scanning manner enables a large field of view and ensures the image uniformity, which is difficult to realize in off-axis holography. In addition, a corresponding imaging algorithm for the presented scheme is developed to reconstruct the image from the recorded hologram. Some imaging results on typical objects, obtained with electromagnetic simulation, demonstrate good performance of the imaging scheme and validate the effectiveness of the image reconstruction algorithm. 展开更多
关键词 millimeter-wave (MMW) indirect holographic scheme squint operation mode translational scan- ning manner large field-of-view image uniformity
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Force-Based Quadrilateral Plate Bending Element for Plate Using Large Increment Method
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作者 贾红学 刘西拉 《Journal of Donghua University(English Edition)》 EI CAS 2015年第3期345-350,共6页
A force-based quadrilateral plate element( 4NQP13) for the analysis of the plate bending problems using large increment method( LIM) was proposed. The LIM, a force-based finite element method( FEM),has been successful... A force-based quadrilateral plate element( 4NQP13) for the analysis of the plate bending problems using large increment method( LIM) was proposed. The LIM, a force-based finite element method( FEM),has been successfully developed for the analysis of truss,beam,frame,and 2D continua problems. In these analyses,LIMcan provide more precise stress results and less computational time consumption compared with displacement-based FEM. The plate element was based on the Mindlin-Reissner plate theory which took into account the transverse shear effects.Numerical examples were presented to study its performance including accuracy and convergence behavior,and the results were compared with the results have been obtained from the displacementbased quadrilateral plate elements and the analytical solutions. The4NQP13 element can analyze the moderately thick plates and the thin plates using LIMand is free from spurious zero energy modes and free from shear locking for thin plate analysis. 展开更多
关键词 large increment method(LIM) displacement-based finite element method(FEM) Mindlin-Reissner plate theory spurious zero energy modes shear locking
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THE SOLUTION OF RECTANGULAR PLATES WITH LARGE DEFLECTION BY SPLINE FUNCTIONS
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作者 潘立宙 陈为众 《Applied Mathematics and Mechanics(English Edition)》 SCIE EI 1990年第5期429-439,共11页
In this paper, Von Karman's set of nonlinear equations for rectangular plates with large deflection is divided into several sets of linear equations by perturbation method, the dimensionless center deflection bein... In this paper, Von Karman's set of nonlinear equations for rectangular plates with large deflection is divided into several sets of linear equations by perturbation method, the dimensionless center deflection being taken as a perturbation parameter. These sets of linear equations are solved by the spline finite-point (SFP) method and by the spline finite element (SFE) method. The solutions for rectangular plates having any length-to-width ratios under a uniformly distributed load and with various boundary conditions are presented, and the analytical formulas for displacements and deflections are given in the paper. The computer programs are worked out by ourselves. Comparison of the results with those in other papers indicates that the results of this paper are satisfactorily better. 展开更多
关键词 LI THE SOLUTION OF RECTANGULAR PLATES WITH large DEFLECTION BY SPLINE FUNCTIONS CHEN mode
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Multi-parameter Fault ProbabilityEvaluation Method of Large Generator 被引量:1
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作者 HE Yingchun WANG Youyuan CHEN Weigen 《高电压技术》 EI CAS CSCD 北大核心 2012年第8期1995-2000,共6页
关键词 局部放电 射频信号 放电量 高电压技术
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Free-Interface Dual-Compatibility Modal Synthesis Substructure Method in Large-Scale Structures
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作者 彭桂瀚 林伟 +1 位作者 陈尚鸿 余洁歆 《Transactions of Tianjin University》 EI CAS 2015年第4期347-355,共9页
Free-interface dual-compatibility modal synthesis method(compatibility of both force and displacement on interfaces)is introduced to large-scale civil engineering structure to enhance computation efficiency. The basic... Free-interface dual-compatibility modal synthesis method(compatibility of both force and displacement on interfaces)is introduced to large-scale civil engineering structure to enhance computation efficiency. The basic equations of the method are first set up, and then the mode cut-off principle and the dividing principle are proposed. MATLAB is used for simulation in different frame structures. The simulation results demonstrate the applicability of this substructure method to civil engineering structures and the correctness of the proposed mode cut-off principle. Studies are also conducted on how to divide the whole structure for better computation efficiency while maintaining better precision. It is observed that the geometry and material properties should be considered, and the synthesis results would be more precise when the inflection points of the mode shapes are taken into consideration. Furthermore, the simulation performed on a large-scale high-rise connected structure further proves the feasibility and efficiency of this modal synthesis method compared with the traditional global method. It is also concluded from the simulation results that the fewer number of DOFs in each substructure will result in better computation efficiency, but too many substructures will be time-consuming due to the tedious synthesis procedures. Moreover, the substructures with free interface will introduce errors and reduce the precision dramatically, which should be avoided. 展开更多
关键词 SUBSTRUCTURE method dynamic SUBSTRUCTURE analysis free-interface dual-compatibility MODAL synthesismethod large-scale CIVIL engineering structure mode CUT-OFF principle
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一种大模场面积抗弯曲的环芯侧孔少模光纤的研究
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作者 蒲俊宇 刘凯 +4 位作者 李长江 孙宏森 闫煜鹏 宋锡策 余先伦 《光学技术》 北大核心 2025年第1期36-42,共7页
为了降低少模光纤的模间耦合和弯曲损耗,增大有效模场面积,设计了一种环芯和侧孔辅助结构的少模光纤。理论分析了这种光纤的有效折射率分布、弯曲损耗和有效模场面积,采用有限元法计算光纤参数对相邻LP模式间最小有效折射率差、有效模... 为了降低少模光纤的模间耦合和弯曲损耗,增大有效模场面积,设计了一种环芯和侧孔辅助结构的少模光纤。理论分析了这种光纤的有效折射率分布、弯曲损耗和有效模场面积,采用有限元法计算光纤参数对相邻LP模式间最小有效折射率差、有效模场面积和弯曲损耗的影响,各模式之间的最小有效折射率差可达1.7×10^(-3),所有模式的有效模场面积均大于106μm^(2),当弯曲半径为28mm时,各模式弯曲损耗最大仅为10^(-11)dB/m。该结构具有大模场面积,低模间串扰以及更好的抗弯曲性能,延伸了空分复用的研究思路。 展开更多
关键词 少模光纤 环芯侧孔 有效折射率 大模场面积 弯曲损耗
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Forward modeling for “earth-ionosphere” mode electromagnetic field 被引量:2
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作者 LI Di-quan 《Journal of Central South University》 SCIE EI CAS CSCD 2016年第9期2305-2313,共9页
A fixed artificial source(greater than 200 kW) was used and the source location was selected at a high resistivity region to ensure high emission efficiency. Some publications used the "earth-ionosphere" mod... A fixed artificial source(greater than 200 kW) was used and the source location was selected at a high resistivity region to ensure high emission efficiency. Some publications used the "earth-ionosphere" mode in modeling the electromagnetic(EM) fields with the offset up to a thousand kilometer, and such EM fields still have a signal/noise ratio of 10-20 dB. This means that a new EM method with fixed source is feasible, but in their calculation, the displacement in air was neglected. In this work, some three-layer modeling results were presented to illustrate the basic EM fields' characteristics in the near, far and waveguide areas under "earth-ionosphere" mode, and a standard is given to distinguish the boundary of near, far and waveguide areas. Due to the influence of the ionosphere and displacement current in the air, the "earth-ionosphere" mode EM fields have an extra waveguide zone, where the fields' behavior is very different from that of the far field zone. 展开更多
关键词 earth-ionosphere mode large power large offset electromagnetic field forward modeling
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