Improvement and validation of a flow model for conical vortices

Ye, Jihong,Dong, Xin Techno-Press 2014 Wind and Structures, An International Journal (WAS Vol.19 No.2

Separation bubble and conical vortices on a large-span flat roof were observed in this study through the use of flow visualization. The results indicated that separation bubble occurred when the flow was normal to the leading edge of the flat roof. Conical vortices that occur under the cornering flow were observed near the leading edge, and their appearance was influenced by the wind angle. When the wind changed from along the diagonal to deviating from the diagonal of the roof, the conical vortex close to the approaching flow changed from circular to be more oblong shaped. Based on the measured velocities in the conical vortices by flow visualization, a proposed two-dimensional vortex model was improved and validated by simplifying the velocity profile between the vortex and the potential flow region. Through measured velocities and parameters of vortices, the intensities of conical vortices and separation bubble on a large-span flat roof under different wind directions were provided. The quasi-steady theory was corrected by including the effect of vortices. With this improved two-dimensional vortex model and the corrected quasi-steady theory, the mean and peak suction beneath the cores of the conical vortices and separation bubble can be predicted, and these were verified by measured pressures on a larger-scale model of the flat roof.

Optimization of domes against instability

Jihong Ye,Mingfei Lu 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.28 No.4

Static stability is a decisive factor in the design of domes. Stability-related external factors, such as load and supports, are incorporated into structural vulnerability theory by the definition of a relative rate of joint well-formedness (<i>r_r</i>). Hence, the instability mechanism of domes can be revealed. To improve stability, an optimization model against instability, which takes the maximization of the lowest <i>r_r</i> (<i>r</i>_<i>r</i>,min) as the objective and the discrete member sections as the variables, is established with constraints on the design requirements and steel consumption. Optimizations are performed on two real-life Kiewitt-6 model domes with a span of 23.4 m and rise of 11.7 m, which are initially constructed for shaking table collapse test. Well-formedness analyses and stability calculation (via arc-length method) of the models throughout the optimization history demonstrate that this proposed method can effectively enhance <i>r</i><sub><i>r</i>,min</sub and optimize the static stability of shell-like structures. Additionally, seismic performance of the optimum models subjected to the same earthquake as in the shaking table test is checked. The supplemental simulations prove that the optimum models are superior to the original models under earthquake load as well.

The Modified Force-Density Method for Form-Finding of Membrane Structures

Jihong Ye,Ruo-qiang Feng,Shulu Zhou,Jun Tian 한국강구조학회 2012 International Journal of Steel Structures Vol.12 No.3

In the force-density method, the value of force-density can only be determined after several trial calculations by now, which often depend on the experience of the researcher. This makes the process of form-finding inefficient and sometimes even invalid. In this manuscript, the disadvantage of the above-mentioned method was overcome through the following two modifications: membrane stress and cable tension were used as initial conditions instead of assuming the value of force-density (i.e. the quantitative relationships between the membrane stress, the cable tension and the force-density are established), and the unbalanced force of each node was used to control the error. This significantly reduced the number of trial calculations required. Several complex cases showing the validity and efficiency of the algorithm. A form-finding experiment of the membrane structure using Fluotop T2 was conducted in order to verify the modified force-density method. The experimental model was a saddle-shaped tensile membrane with 4 cable boundaries, 4 supports and a plane size of 4 m×4 m. The following three parameters were selected for measurement: (a) cable strains, (b) membrane strains and (c) coordinates of several testing points on the membrane surface in two states of the model, one called the unrestrained state and the other called the equilibrium state. These three parameters were compared among the results of the experiment, numerical simulation and analytical methods. We concluded that the modified force-density method was valid and can be used in the form-finding analysis for membrane structure engineering applications.

Improvement and validation of a flow model for conical vortices

Jihong Ye,Xin Dong 한국풍공학회 2014 Wind and Structures, An International Journal (WAS Vol.19 No.2

Separation bubble and conical vortices on a large-span flat roof were observed in this study through the use of flow visualization. The results indicated that separation bubble occurred when the flow was normal to the leading edge of the flat roof. Conical vortices that occur under the cornering flow were observed near the leading edge, and their appearance was influenced by the wind angle. When the wind changed from along the diagonal to deviating from the diagonal of the roof, the conical vortex close to the approaching flow changed from circular to be more oblong shaped. Based on the measured velocities in the conical vortices by flow visualization, a proposed two-dimensional vortex model was improved and validated by simplifying the velocity profile between the vortex and the potential flow region. Through measured velocities and parameters of vortices, the intensities of conical vortices and separation bubble on a large-span flat roof under different wind directions were provided. The quasi-steady theory was corrected by including the effect of vortices. With this improved two-dimensional vortex model and the correctedquasi-steady theory, the mean and peak suction beneath the cores of the conical vortices and separation bubble can be predicted, and these were verified by measured pressures on a larger-scale model of the flat roof.

Combination of DEM/FEM for Progressive Collapse Simulation of Domes Under Earthquake Action

Ye Jihong,Qi Nian 한국강구조학회 2018 International Journal of Steel Structures Vol.18 No.1

In this paper, a coupled DEM/FEM model is presented to overcome the disadvantages generated by individually using discrete element method (DEM) or finite element method (FEM). The model divides the domain into two independent parts: the DEM sub-domain and the FEM sub-domain. First, the governing equations of the coupled model are established according to the virtual work equation and variational principle, the formula of interface-coupled force is derived based on the penalty function method, and the corresponding program is coded. Second, the key problems involved in the coupled model are investigated, which are the selection of the penalty parameter, the determination of the time-step, and the formulation of the governing equations of the system in the DEM and FEM domains. Finally, the coupled model is applied to progressive collapse simulation of single-layer reticulated domes subjected to severe earthquakes. Both the collapse process and failure mechanism of the numerical results are consistent with the shaking table test phenomena, thereby verifying the validity of the coupled model proposed. The method proposed realizes the balance between computational efficiency and accuracy, that is, the small deformation region is simulated by FEM, while the DEM is applied to discretize the large deformation or failure region. Additionally, it is of high computational efficiency and of reliable precision.

A Form-Finding Method of Beam String Structures - Offload by Steps Method

Jihong Ye,Ruo-qiang Feng,Xianbo Zhao,Bin Liu 한국강구조학회 2012 International Journal of Steel Structures Vol.12 No.2

The problem of form-finding of beam string structures was studied, and the method named offload by steps was put forward in accordance with the properties of the mechanical status of the structures. This method was used to find the form of the unstrained state on the basis of the pre-stressed state without the need to assume the unstrained form first. Numerical simulations and experimental research on the form-finding of beam string structures were carried out to verify the offload by steps method and, more importantly, to study the application of the method in engineering practice. The scale of the experimental model was 1/20, and the stretching pattern was the same as that in practical engineering. Comparisons of internal forces and deformations corresponding to unstrained and pre-stressed states of the model were made between experimental and calculation results. The following conclusions were drawn. First, the offload by steps method can be applied to the engineering practice without assuming the form of the unstrained state, and the form of the unstrained state corresponding to that of the pre-stressed state can be obtained directly. Second, the internal forces of the beam string structures in their pre-stressed states can be obtained easily by using the statically-determinate calculation model in the offload by steps method, which can guide design effectively. Third, the method for estimating the cable tension by balancing the deadweight of the beam string truss can be applied to engineering practice.

3-D characteristics of conical vortex around large-span flat roof by PIV technique

Sun, Huyue,Ye, Jihong Techno-Press 2016 Wind and Structures, An International Journal (WAS Vol.22 No.6

Conical vortices generated at the corner regions of large-span flat roofs have been investigated by using the Particle Image Velocimetry (PIV) technique. Mean and instantaneous vector fields for velocity, vorticity, and streamlines were measured at three visual planes and for two different flow angles of $15^{\circ}$. The results indicated that conical vortices occur when the wind is not perpendicular to the front edge. The location of the leading edge corresponding to the negative peak vorticity and maximum turbulent kinetic energy was found at the center of the conical vortex. The wind pressure reaches the maximum near the leading edge roof corner, and a triangle of severe suctions zone appears downstream. The mean pressure in uniform flow is greater than that under turbulent flow condition, while a significant increase in the fluctuating wind pressure occurs in turbulent streams. From its emergence to stability, the shape of the vortex cross-section is nearly elliptical, with increasing area. The angle that forms between the vortex axis and the leading edge is much smaller in turbulent streams. The detailed flow structures and characteristics obtained through FLUENT simulation are in agreement with the experimental results. The three dimensional (3-D) structure of the conical vortices is clearly observed from the comprehensive arrangement of several visual planes, and the inner link was established between the vortex evolution process, vortex core position and pressure distribution.

The application of BEM in the Membrane structures interaction with simplified wind

Xu Wen,Ye Jihong,Shan Jian 국제구조공학회 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.31 No.3

Membrane structures are quite sensitive to wind and therefore the fluid-solid interaction can not be neglected in dynamic analysis. A boundary element method (BEM) for 3D simulation of windstructure interaction in tensile membrane structures is presented in this paper. The flow is treated as incompressible and potential. The flow field is solved with boundary element method codes and structural simulation is performed by finite element method software ANSYS. The nonlinear equations system is solved iteratively, with segregated treatment of the fluid and structure equations. Furthermore this method has been demonstrated to be effective by typical examples. Besides, the influence of several parameters on the wind-structure interaction, such as rise-span ratio, prestress and the wind velocity are investigated according to this method. The results provide experience in wind resistant researches and engineering.

Modeling and Parameter Estimation of Particle Swarm Optimization Algorithm for Smart Power Grid

He Tao,Liang Zhidong,Ye Xinquan,Sun Shufeng,Pang Jihong 보안공학연구지원센터 2015 International Journal of Grid and Distributed Comp Vol.8 No.6

This paper analysis the electric power communication network structure and performance requirements. To investigate the power communication backbone network and network power substation general way, and in electric power communication network delay, error rate, network bandwidth demand were analyzed. The for prevalent in electric power communication network is not a fully meshed network, explore artificially cobweb logic change principle and system method, artificial transform sheet mesh to the standard web, and making use of the cobweb, based on the characteristics of network fast routing. In order to better in the smart grid communication network using artificially cobweb routing algorithm, for the smart grid in the presence of irregular mesh network, this paper presents a kind of the mesh network into logical artificially cobweb network general standardization method. The principle of combination of label switching, this paper presents artificially cobweb source routing algorithm, expounds the artificially cobweb routing algorithm of label switching and label update mechanism, and artificially cobweb routing algorithm balancing routing method and routing method is described in detail.

Research on Exploration and Analysis of Supply Chain Flexibility Measure Index

He Tao,Liang Zhidong,Ye Xinquan,Pang Jihong 보안공학연구지원센터 2016 International Journal of u- and e- Service, Scienc Vol.9 No.11

The supply chain risk assessment and management system has been developed, people still do not determine the way to overcome all these risks, especially for high impact, low probability events, such as SARS and the outbreak of foot-and-mouth disease, or a centralized terrorist attacks. This is because the lack of historical data to make all kinds of prediction and statistical tools fail. The modern supply chain were more vulnerable to risk, supply chain risk mainly comes from many aspects of the internal and external environment, the supply chain industry products background, upstream and downstream supply chain relationship, decision support. In this paper, the establishment of a complete supply chain model with variable structure, through the simulation method for quantitative observation of supply chain flexibility curve, and abstract to describe the elastic curve of a set of parameters; after the design of simulation experiment to observe the different supply chain structure parameters (inventory level, supply chain, supplier selection for number of sources) influence supply chain resilience curve.