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Finding buckling points for nonlinear structures by dynamic relaxation scheme

Mohammad REZAIEE-PAJAND, Hossein ESTIRI

《结构与土木工程前沿（英文）》 2020年 第14卷 第1期   页码 23-61 doi: 10.1007/s11709-019-0549-z

摘要： Dynamic Relaxation Method (DRM) is an explicit approach for solving the simultaneous systems of equations. In this tactic, the fictitious mass and damping are added to the static governing equations, and an artificial dynamic system is constructed. By using DRM for nonlinear analysis, the structural static equilibrium path is obtained. This outcome is extremely valuable, since it leads to the behavior of structures. Among the finding related to the structural static path are the critical and buckling points for nonlinear structures. In this paper, a new way for calculating the load factor is proposed by setting the external work zero. Mixing the dynamic relaxation scheme with external work technique has not been formulated so far. In all incremental-iterative methods, the load factor increment sign should be determinated by extra calculations. This sign leads to increase or decrease of the load increment. It is worth emphasizing that sign of the load factor increment changes at the load limit points. Therefore, the sign determinations are required in the common work control methods. These disadvantages are eliminated in the proposed algorithm. In fact, the suggested load factor depends only on the Dynamic Relaxation (DR) fictitious parameters. Besides, all DR calculations are performed via vector operation. Moreover, the load factor is calculated only by one formula, and it has the same relation in the all solution processes. In contrast to the arc length techniques, which requires the sign determined, the proposed scheme does not need any sign finding. It is shown that author’s technique is quicker than the other dynamic relaxation strategies. To prove the capability and efficiency of the presented scheme, several numerical tests are performed. The results indicate that the suggested approach can trace the complex structural static paths, even in the snap-back and snap-through parts.

关键词： load factor     external work     dynamic relaxation     static equilibrium path     large displacement    

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Design and modeling of a novel soft parallel robot driven by endoskeleton pneumatic artificial muscles

《机械工程前沿（英文）》 2022年 第17卷 第2期 doi: 10.1007/s11465-022-0678-2

摘要： Owing to their inherent great flexibility, good compliance, excellent adaptability, and safe interactivity, soft robots have shown great application potential. The advantages of light weight, high efficiency, non-polluting characteristic, and environmental adaptability provide pneumatic soft robots an important position in the field of soft robots. In this paper, a soft robot with 10 soft modules, comprising three uniformly distributed endoskeleton pneumatic artificial muscles, was developed. The robot can achieve flexible motion in 3D space. A novel kinematic modeling method for variable-curvature soft robots based on the minimum energy method was investigated, which can accurately and efficiently analyze forward and inverse kinematics. Experiments show that the robot can be controlled to move to the desired position based on the proposed model. The prototype and modeling method can provide a new perspective for soft robot design, modeling, and control.

关键词： pneumatic artificial muscles     soft robot     modeling approach     principle of virtual work     external load    

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nitride enabled benzimidazoles production from furyl/aryl bio-alcohols and -nitroanilines without an external

《化学科学与工程前沿（英文）》 2023年 第17卷 第1期   页码 68-81 doi: 10.1007/s11705-022-2174-y

摘要： Benzimidazole derivatives have wide-spectrum biological activities and pharmacological effects, but remain challenging to be produced from biomass feedstocks. Here, we report a green hydrogen transfer strategy for the efficient one-pot production of benzimidazoles from a wide range of bio-alcohols and o-nitroanilines enabled by cobalt nitride species on hierarchically porous and recyclable nitrogen-doped carbon catalysts (Co/CNx-T, T denotes the pyrolysis temperature) without using an external hydrogen source and base additive. Among the tested catalysts, Co/CNx-700 exhibited superior catalytic performance, furnishing 2-substituted benzimidazoles in 65%–92% yields. Detailed mechanistic studies manifest that the coordination between Co2+ and N with appropriate electronic state on the porous nitrogen-doped carbon having structural defects, as well as the remarkable synergetic effect of Co/N dual sites contribute to the pronounced activity of Co/CNx-700, while too high pyrolysis temperature may cause the breakage of the catalyst Co–N bond to lower down its activity. Also, it is revealed that the initial dehydrogenation of bio-alcohol and the subsequent cyclodehydrogenation are closely correlated with the hydrogenation of nitro groups. The catalytic hydrogen transfer-coupling protocol opens a new avenue for the synthesis of N-heterocyclic compounds from biomass.

关键词： biomass conversion     furanic compounds     benzimidazoles     hydrogen transfer     bifunctional catalysis    

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Unified solution of limit loads of thick wall cylinder subject to external pressure considering strain

CHEN Changfu, XIAO Shujun, YANG Yu

《结构与土木工程前沿（英文）》 2007年 第1卷 第3期   页码 329-333 doi: 10.1007/s11709-007-0043-x

摘要： Based on the unified strength theory [1], a unified strength criterion for strain softening materials, such as concrete or rock, was derived, and the elastic and plastic limit loads of a thick-walled cylinder made of these materials subject to external pressure were also given. In addition, the influence of some factors on the limit loads of such cylinders as the ratio of the external radius to internal radius,/, the coefficient , which reflects the effect of medium principal stress and the normal stress of the relevant surface on the material destroy degree, the ratio of tensile strength to compressed strength of the material, , and the damage variable
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monitoring of the strengthening construction of a segmental box girder bridge and field testing of external

Ali Fadhil NASER, Zonglin WANG

《结构与土木工程前沿（英文）》 2012年 第6卷 第3期   页码 308-320 doi: 10.1007/s11709-012-0140-3

摘要： Prestressed concrete segmental box girder bridges are composed of short concrete segments that are either precast or cast in situ and then joined together by longitudinally post-tensioning internal, external, or mixed tendons. The objectives of this study are to monitor the construction process of the external prestressing tendons to strengthen the bridge structure and perform a field load test to measure the strain and the deflection of the anchorage devices of the external prestressing tendons to determine the state of these devices after tension forces are applied. The monitoring process of the external prestressing tendons construction includes inspecting the cracks in the diaphragm anchorage and the deviation block devices before the tension forces are applied to the external tendons; measuring the deformation of the steel deviation cross beam during the tension process; measuring the deformation of the box girder after different levels of tension forces are applied; measuring the elongation of the external tendons in each level of the tension; and measuring the natural frequency of the external tendons after the tension process is complete. The results of the monitoring process show that the measured values of the deformation, the elongation, and the natural frequency meet the requirements. Therefore, there is no damage during the construction and the tensioning of the external prestressing tendons. A field load test is performed to the anchorage beam, the steel deviation block devices, and the steel deviation cross beam. The field load test results of the anchorage devices show that the values of the strains, the stresses, and the deflection are less than the respective allowable limit values in the requirements. Therefore, the anchorage devices have sufficient strength, and the working state is good after the tension forces are applied to the external prestressing tendons.

关键词： prestressed concrete     box girder     monitoring     external tendons     strain     deflection    

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Shear behavior of ultra-high-performance concrete beams prestressed with external carbon fiber-reinforced

《结构与土木工程前沿（英文）》 2021年 第15卷 第6期   页码 1426-1440 doi: 10.1007/s11709-021-0783-z

摘要： The ultra-high-performance concrete (UHPC) and fiber-reinforced polymer (FRP) are well-accepted high-performance materials in the field of civil engineering. The combination of these advanced materials could contribute to improvement of structural performance and corrosion resistance. Unfortunately, only limited studies are available for shear behavior of UHPC beams reinforced with FRP bars, and few suggestions exist for prediction methods for shear capacity. This paper presents an experimental investigation on the shear behavior of UHPC beams reinforced with glass FRP (GFRP) and prestressed with external carbon FRP (CFRP) tendons. The failure mode of all specimens with various shear span to depth ratios from 1.7 to 4.5 was diagonal tension failure. The shear span to depth ratio had a significant influence on the shear capacity, and the effective prestressing stress affected the crack propagation. The experimental results were then applied to evaluate the equations given in different codes/recommendations for FRP-reinforced concrete structures or UHPC structures. The comparison results indicate that NF P 18-710 and JSCE CES82 could appropriately estimate shear capacity of the slender specimens with a shear span to depth ratio of 4.5. Further, a new shear design equation was proposed to take into account the effect of the shear span to depth ratio and the steel fiber content on shear capacity.

关键词： beam     external prestressing     ultra-high-performance concrete     fiber-reinforced polymers     shear behavior     design equation    

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Estimation of composite load model with aggregate induction motor dynamic load for an isolated hybrid

Nitin Kumar SAXENA,Ashwani Kumar SHARMA

《能源前沿（英文）》 2015年 第9卷 第4期   页码 472-485 doi: 10.1007/s11708-015-0373-7

摘要： It is well recognized that the voltage stability of a power system is affected by the load model and hence, to effectively analyze the reactive power compensation of an isolated hybrid wind-diesel based power system, the loads need to be considered along with the generators in a transient analysis. This paper gives a detailed mathematical modeling to compute the reactive power response with small voltage perturbation for composite load. The composite load is a combination of the static and dynamic load model. To develop this composite load model, the exponential load is used as a static load model and induction motors (IMs) are used as a dynamic load model. To analyze the dynamics of IM load, the fifth, third and first order model of IM are formulated and compared using differential equations solver in Matlab coding. Since the decentralized areas have many small consumers which may consist large numbers of IMs of small rating, it is not realistic to model either a single large rating unit or all small rating IMs together that are placed in the system. In place of using a single large rating IM, a group of motors are considered and then the aggregate model of IM is developed using the law of energy conservation. This aggregate model is used as a dynamic load model. For different simulation studies, especially in the area of voltage stability with reactive power compensation of an isolated hybrid power system, the transfer function of the composite load is required. The transfer function of the composite load is derived in this paper by successive derivation for the exponential model of static load and for the fifth and third order IM dynamic load model using state space model.

关键词： isolated hybrid power system (IHPS)     composite load model     static load     dynamic load     induction motor load model     aggregate load    

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Ductile extension of 3-D external circumferential cracks in pipe structures

Wuchao YANG, Xudong QIAN

《结构与土木工程前沿（英文）》 2011年 第5卷 第3期   页码 294-303 doi: 10.1007/s11709-011-0115-9

摘要： This study investigates the ductile fracture resistance of 3-D external circumferential cracks in the wall of a steel pipe under remote tension, using a damage-mechanism model originally proposed by Gurson and Tvergaard. The ductile crack extension utilizes an element extinction technique implemented in the computational cell framework. The key parameter for the computational cell method, i.e., the initial porosity ratio , is calibrated using both the fracture resistance and the load-deformation responses obtained from fracture tests of multiple single-edge bend [SE(B)] specimens made of high-strength steel, HY80, which has a yield strength of 630 MPa. The fracture resistance along the 3-D semi-elliptical crack front is computed from the calibrated cell model. Based on the similarity concept in the near-tip stress-strain fields, this study demonstrates that an equivalent 2-D axi-symmetric model provides conservative estimations of the fracture resistance for 3-D circumferential cracks in pipes.

关键词： ductile fracture     computational cell method     G-T model     J-R curve    

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Mesh relationship modeling and dynamic characteristic analysis of external spur gears with gear wear

《机械工程前沿（英文）》 2022年 第17卷 第1期   页码 9-9 doi: 10.1007/s11465-021-0665-z

摘要： Gear wear is one of the most common gear failures, which changes the mesh relationship of normal gear. A new mesh relationship caused by gear wear affects meshing excitations, such as mesh stiffness and transmission error, and further increases vibration and noise level. This paper aims to establish the model of mesh relationship and reveal the vibration characteristics of external spur gears with gear wear. A geometric model for a new mesh relationship with gear wear is proposed, which is utilized to evaluate the influence of gear wear on mesh stiffness and unloaded static transmission error (USTE). Based on the mesh stiffness and USTE considering gear wear, a gear dynamic model is established, and the vibration characteristics of gear wear are numerically studied. Comparison with the experimental results verifies the proposed dynamic model based on the new mesh relationship. The numerical and experimental results indicate that gear wear does not change the structure of the spectrum, but it alters the amplitude of the meshing frequencies and their sidebands. Several condition indicators, such as root-mean-square, kurtosis, and first-order meshing frequency amplitude, can be regarded as important bases for judging gear wear state.

关键词： gear wear     mesh relationship     mesh stiffness     transmission error     vibration characteristics    

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单向离合器外环应力计算的有限元方法研究

罗一新,吴波

《中国工程科学》 2004年 第6卷 第9期   页码 56-59

摘要：

单向离合器是一种常见的机械传动部件，其外环应力计算尚无理想的方法。文章以五滚柱式单向离合器为研究对象，根据外环的特点，采用有限元分析方法，分析了影响其计算精度的各种因素，计算出其外环的应力，并且将计算结果与曲梁计算法进行了比较。研究表明，有限元分析方法对于外环类零件的应力计算确是一种理想的方法。

关键词： 离合器     外环     应力     有限元    

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patients with advanced malignant obstructive jaundice treated by percutaneous transhepatic biliary external

ZHU Lidong, CHEN Xiaoping

《医学前沿（英文）》 2007年 第1卷 第4期   页码 364-368 doi: 10.1007/s11684-007-0070-y

摘要： The aim of this article was to study the influence of immunity function of advanced malignant obstructive jaundice (MOJ) treated by percutaneous transhepatic biliary external and internal drainage. Ninety-six cases of MOJ were divided into two groups according to the different ways of biliary drainage. Fifty-two external drainage tubes were placed in 41 cases of percutaneous transhepatic biliary external drainage group and 66 metal stents were placed in 55 cases of percutaneous transhepatic biliary internal drainage group. Liver function, serum TNF- and cellular function were examined one day before operation and one week after operation and liver function was re-examined two weeks after operation, in order to observe the change and analyze the asso ciation among them and compare with the control group. All patients conditions were improved after operation. In the percutaneous transhepatic biliary external and internal drainage groups, the total level of bilirubin decreased from (343.54±105.56) μ mol/L and (321.19±110.50) μ mol/L to (290.56±103.46) μ mol/L and (283.72±104.95) μ mol/L after operation respectively, which were significantly lower than pre-operation (<0.05), but there was no significant difference between the two groups (>0.05). Serum alanine aminotransferase (ALT) of all patients one week after operation was significantly lower than that before operation. TNF- in percutaneous transhepatic biliary external and internal groups decreased from (108.58±19.95) pg/mL, (109.98±16.24) pg/mL of pre-operation to (104.32±19.59) pg/mL, (83.92±13.43) pg/mL of post-operation respectively, there was notable improvement (<0.01) in internal drainage group after operation. Patients serum CD4, CD3 and CD4/CD8 were notably increased, but CD8 was notably decreased (<0.05). There was no difference in external drainage group (>0.05). There was a significant difference between the two groups. Serum TNF- and ALT had positive correlation. Percutaneous transhepatic biliary internal or external drainage was an effective and important method to treat MOJ. Patients immune function was weak when they suffered MOJ, but body s cellular immune function can be notably improved after internal biliary drainage.
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Intrinsic kinetics and external diffusion of catalytic steam gasification of fine coal char particles

Xuantao Wu, Jie Wang

《化学科学与工程前沿（英文）》 2019年 第13卷 第2期   页码 415-426 doi: 10.1007/s11705-018-1725-8

摘要： Catalytic steam gasification of fine coal char particles was carried out using a self-made laboratory reactor to determine the intrinsic kinetics and external diffusion under varying pressures (0.1–0.5 MPa) and superficial gas flow velocities (GFVs) of 13.8–68.8 cm?s . In order to estimate the gas release rate at a low GFV, the transported effect of effluent gas on the temporal gasification rate pattern was simulated by the Fluent computation and verified experimentally. The external mass transfer coefficients ( ) and the effectiveness factors were determined at lower GFVs, based on the intrinsic gasification rate obtained at a high GFV of 55.0 cm?s . The was found to be almost invariable in a wider carbon conversion of 0.2–0.7. The variations of at a median carbon conversion with GFV, temperature and pressure were found to follow a modified Chilton-Colburn correlation: (0.04< <0.19), where is total pressure and is atmospheric pressure. An intrinsic kinetics/external diffusion integrating model could well describe the gasification rate as a function of GFV, temperature and pressure over a whole gasification process.

关键词： coal char     catalytic steam gasification     pressure     kinetics     diffusion    

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Calculation method of load distribution on pipe threaded connections under tension load

Shoujun CHEN, Lianxin GAO, Qi AN

《机械工程前沿（英文）》 2011年 第6卷 第2期   页码 241-248 doi: 10.1007/s11465-011-0219-x

摘要：

This paper presents a new calculation method that can calculate the load distribution on pipe threaded connections under tension load. On the basis of elastic mechanics, the new method was developed by analyzing each thread tooth, and a new deformation and covariant equation by making a mechanics analysis on each thread tooth was obtained. Compared with the traditional method proposed by the previous references, the new deformation and covariant equation could be used to describe the relation between the previous and the next thread tooth. By applying the new method on the sample of P-110S pipe threaded connection, the obtained results show that the load on thread tooth mainly concentrates on the four or five threads engaged and the middle teeth were not utilized well to bear the loads. The model offers a new way to calculate the loads carried on the thread teeth under tension load.

关键词： load distribution     calculation method     pipe threaded connections     tension load    

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Comparison of optimal capacitor placement methods in radial distribution system with load growth andZIP load model

Veera Venkata Satya Naryana MURTY, Ashwani KUMAR

《能源前沿（英文）》 2013年 第7卷 第2期   页码 197-213 doi: 10.1007/s11708-013-0249-7

摘要： In this paper, a combined power loss sensitivity (PLS) index-based approach is proposed to determine the optimal location of the capacitors in the radial distribution system (RDS) based on the real and reactive combined loss sensitivity index, as capacitor placement not only reduces real power loss with voltage profile improvement but also reduces reactive power loss due to the reactive power compensation in the network. The results have been obtained with the existing methods of power loss index (PLI) and index vector (IV) method for comparison. Besides, the optimal placement has been obtained with the proposed method as well as existing methods and the total kVar support has been obtained. In addition, the results of net cost savings for the 10-, 34-, and 69-bus systems are obtained for comparison. Moreover, the results have been obtained for a large system of 85 buses to validate the results with combined sensitivity based approach. Furthermore, the load growth factor has been considered in the study which is essential for the planning and expansion of the existing systems, whereas the impact of the realistic load model as ZIP load model has been considered for the study of all the systems.

关键词： load growth     load models     reactive power compensation     radial distribution system     power loss index (PLI)     power loss sensitivity (PLS)     index vector (IV)    

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体内-体外混合配束节段预制拼装箱梁足尺模型试验研究

郑开启,卜红旗,刘钊,惠卓,吕志涛

《中国工程科学》 2013年 第15卷 第8期   页码 89-94

摘要：

以南京长江第四大桥引桥为背景，开展了一孔48 m跨径体内-体外混合配束节段预制拼装箱梁的足尺模型试验，以研究该类箱梁在正常使用阶段和施工状态下的结构行为。根据试验箱梁的尺寸参数以及实际约束条件确定了拼装与加载方案。本文重点研究正常使用荷载和梁上运梁两种工况下梁体应力状况与位移变化等结构静力性能，并与试验梁实体有限元模型进行对比分析。研究结果表明：在正常使用阶段，加、卸载后拼装梁体残余变形较小，基本处于弹性工作状态，整体性较好；键齿接缝两侧基本无相对滑移，接缝截面纵向应变沿梁高大致呈线性变化，力学行为基本符合平截面假定；体外预应力束在转向处基本无滑移，体内外预应力增量随跨中弯矩基本呈线性变化；在梁上运梁工况下，实测梁体下缘压应力储备充足，满足运梁安全性要求。

关键词： 节段预制拼装     模型试验     体外预应力     足尺试验    

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标题 作者 时间 类型 操作

Finding buckling points for nonlinear structures by dynamic relaxation scheme

Mohammad REZAIEE-PAJAND, Hossein ESTIRI

期刊论文

Design and modeling of a novel soft parallel robot driven by endoskeleton pneumatic artificial muscles

期刊论文

nitride enabled benzimidazoles production from furyl/aryl bio-alcohols and -nitroanilines without an external

期刊论文

Unified solution of limit loads of thick wall cylinder subject to external pressure considering strain

CHEN Changfu, XIAO Shujun, YANG Yu

期刊论文

monitoring of the strengthening construction of a segmental box girder bridge and field testing of external

Ali Fadhil NASER, Zonglin WANG

期刊论文

Shear behavior of ultra-high-performance concrete beams prestressed with external carbon fiber-reinforced

期刊论文

Estimation of composite load model with aggregate induction motor dynamic load for an isolated hybrid

Nitin Kumar SAXENA,Ashwani Kumar SHARMA

期刊论文

Ductile extension of 3-D external circumferential cracks in pipe structures

Wuchao YANG, Xudong QIAN

期刊论文

Mesh relationship modeling and dynamic characteristic analysis of external spur gears with gear wear

期刊论文

单向离合器外环应力计算的有限元方法研究

罗一新,吴波

期刊论文

patients with advanced malignant obstructive jaundice treated by percutaneous transhepatic biliary external

ZHU Lidong, CHEN Xiaoping

期刊论文

Intrinsic kinetics and external diffusion of catalytic steam gasification of fine coal char particles

Xuantao Wu, Jie Wang

期刊论文

Calculation method of load distribution on pipe threaded connections under tension load

Shoujun CHEN, Lianxin GAO, Qi AN

期刊论文

Comparison of optimal capacitor placement methods in radial distribution system with load growth andZIP load model

Veera Venkata Satya Naryana MURTY, Ashwani KUMAR

期刊论文

体内-体外混合配束节段预制拼装箱梁足尺模型试验研究

郑开启,卜红旗,刘钊,惠卓,吕志涛

期刊论文