Finite Element Simulation of Flexible Roll Forming with Supplemented Material Data and the Experimental Verification

Flexible roll forming is a promising manufacturing method for the production of variable cross section products. Considering the large plastic strain in this forming process which is much larger than that of uniform deformation phase of uniaxial tensile test, the widely adopted method of simulating the forming processes with non-supplemented material data from uniaxial tensile test will certainly lead to large error. To reduce this error, the material data is supplemented based on three constitutive models. Then a finite element model of a six passes flexible roll forming process is established based on the supplemented material data and the original material data from the uniaxial tensile test. The flexible roll forming experiment of a B pillar reinforcing plate is carried out to verify the proposed method. Final cross section shapes of the experimental and the simulated results are compared. It is shown that the simulation calculated with supplemented material data based on Swift model agrees well with the experimental results, while the simulation based on original material data could not predict the actual deformation accurately. The results indicate that this material supplement method is reliable and indispensible, and the simulation model can well reflect the real metal forming process. Detailed analysis of the distribution and history of plastic strain at different positions are performed. A new material data supplement method is proposed to tackle the problem which is ignored in other roll forming simulations, and thus the forming process simulation accuracy can be greatly improved.

Water storage changes in North America retrieved from GRACE gravity and GPS data

As global warming continues,the monitoring of changes in terrestrial water storage becomes increasingly important since it plays a critical role in understanding global change and water resource management.In North America as elsewhere in the world,changes in water resources strongly impact agriculture and animal husbandry.From a combination of Gravity Recovery and Climate Experiment（GRACE） gravity and Global Positioning System（GPS） data,it is recently found that water storage from August,2002 to March,2011 recovered after the extreme Canadian Prairies drought between 1999 and 2005.In this paper,we use GRACE monthly gravity data of Release 5 to track the water storage change from August,2002 to June,2014.In Canadian Prairies and the Great Lakes areas,the total water storage is found to have increased during the last decade by a rate of 73.8 ± 14.5 Gt/a,which is larger than that found in the previous study due to the longer time span of GRACE observations used and the reduction of the leakage error.We also find a long term decrease of water storage at a rate of-12.0 ± 4.2 Gt/a in Ungava Peninsula,possibly due to permafrost degradation and less snow accumulation during the winter in the region.In addition,the effect of total mass gain in the surveyed area,on present-day sea level,amounts to-0.18 mm/a,and thus should be taken into account in studies of global sea level change.

Evaluation of Reanalysis Data Based on the Three-dimensional High-density Sounding Data of the Qinghai-Tibet Plateau

Based on the data of the third Qinghai-Tibet Plateau atmospheric science experiment from 2015 to 2017,the applicability of plateau weather systems and meteorological elements of two commonly used reanalysis data(NCEP/NCAR reanalysis data set,and ERA-Interim reanalysis data set)in the plateau was evaluated.Some conclusions are obtained as follows.Compared with EC reanalysis data,NCEP reanalysis data are more consistent with the scientific experimental data.The correlation of geopotential height is above 0.99,followed by temperature;The correlation of specific humidity is the worst.Seen from average deviation,geopotential height and temperature are both lower;for EC,the westerly and southerly winds are both weaker;for NCEP,westerly wind is weaker,while southerly wind is stronger;specific humidity is higher.From the perspective of monthly and seasonal distribution characteristics,the average deviation of geopotential height is larger in spring and summer,and that of temperature is slightly worse in late spring and early summer.In terms of wind field,EC deviation is more obvious in winter,while NCEP deviation is more obvious in late spring and early summer.Seen from spatial distribution,the deviations of geological height and temperature in the north of the plateau are smaller than those in the south of the plateau.For wind field,the westerly wind in the Qaidam Basin is weaker,and the southerly wind in the southern plateau is weaker.In vertical profile,the deviation of geopotential height at high levels is greater than that of low levels.The deviation of temperature and wind field is larger near the ground.The temperature at middle levels and the westerly wind at middle and high levels are smaller,and southerly wind is stronger for NCEP.The establishment of the three sounding stations(Gaize,Shenzha and Shiquanhe)is conducive to the discovery of plateau vortex and plateau shear line in the western plateau.The western plateau vortex and plateau shear line mostly appeared in the flood season.Most plateau weather systems were maintained within 24 h,and mainly appeared and disappeared in situ.The objective recognition rate of EC for plateau weather systems is higher than NCEP,so EC is more conducive to the diagnosis and analysis of evolution characteristics of plateau weather systems.

Evaluation of a Micro-scale Wind Model's Performance over Realistic Building Clusters Using Wind Tunnel Experiments

The simulation performance over complex building clusters of a wind simulation model（Wind Information Field Fast Analysis model, WIFFA） in a micro-scale air pollutant dispersion model system（Urban Microscale Air Pollution dispersion Simulation model, UMAPS） is evaluated using various wind tunnel experimental data including the CEDVAL（Compilation of Experimental Data for Validation of Micro-Scale Dispersion Models） wind tunnel experiment data and the NJU-FZ experiment data（Nanjing University-Fang Zhuang neighborhood wind tunnel experiment data）. The results show that the wind model can reproduce the vortexes triggered by urban buildings well, and the flow patterns in urban street canyons and building clusters can also be represented. Due to the complex shapes of buildings and their distributions, the simulation deviations/discrepancies from the measurements are usually caused by the simplification of the building shapes and the determination of the key zone sizes. The computational efficiencies of different cases are also discussed in this paper. The model has a high computational efficiency compared to traditional numerical models that solve the Navier–Stokes equations, and can produce very high-resolution（1–5 m） wind fields of a complex neighborhood scale urban building canopy（～ 1 km ×1km） in less than 3 min when run on a personal computer.

Monthly gravity field solution from GRACE range measurements using modified short arc approach

In this paper we present a series of monthly gravity field solutions from Gravity Recovery and Climate Experiment（GRACE） range measurements using modified short arc approach,in which the ambiguity of range measurements is eliminated via differentiating two adjacent range measurements.The data used for developing our monthly gravity field model are same as Tongji-GRACEOl model except that the range measurements are used to replace the range rate measurements,and our model is truncated to degree and order 60,spanning Jan.2004 to Dec.2010 also same as Tongji-GRACE01 model.Based on the comparison results of the C_（2,0）,C_（2,1）,S_（2,1）,and C_（15,15）,S_（15,15）,time series and the global mass change signals as well as the mass change time series in Amazon area of our model with those of Tongji-GRACE01 model,we can conclude that our monthly gravity field model is comparable with Tongji-GRACE01 monthly model.

A data readout approach for physics experiments

With increasing physical event rates and the number of electronic channels, traditional readout schemes meet the challenge of improving readout speed caused by the limited bandwidth of the crate backplane. In this paper, a high-speed data readout method based on the Ethernet is presented to make each readout module capable of transmitting data to the DAQ. Features of explicitly parallel data transmitting and distributed network architecture give the readout system the advantage of adapting varying requirements of particle physics experiments. Furthermore,to guarantee the readout performance and flexibility, a standalone embedded CPU system is utilized for network protocol stack processing. To receive the customized data format and protocol from front-end electronics, a field programmable gate array（FPGA） is used for logic reconfiguration. To optimize the interface and to improve the data throughput between CPU and FPGA, a sophisticated method based on SRAM is presented in this paper. For the purpose of evaluating this high-speed readout method, a simplified readout module is designed and implemented.Test results show that this module can support up to 70 Mbps data throughput from the readout module to DAQ.