Experimental study and numerical analysis on bearing behaviors of super-long rock-socketed bored pile groups

A centrifuge modeling test and a three-dimensional finite element analysis（FEA）of super-long rock-socketed bored pile groups of the Tianxingzhou Bridge are proposed.Based on the similarity theory,different prototypical materials are simulated using different indicators in the centrifuge model.The silver sand,the shaft and the pile cap are simulated according to the natural density,the compressive stiffness and the bending stiffness,respectively.The finite element method（FEM）is implemented and analyzed in ANSYS,in which the stress field during the undisturbed soil stage,the boring stage,the concrete-casting stage and the curing stage are discussed in detail.Comparisons in terms of load-settlement,shaft axial force distribution and lateral friction between the numerical results and the test data are carried out to investigate the bearing behaviors of super-long rock-socketed bored pile groups under loading and unloading conditions.Results show that there is a good agreement between the centrifuge modeling tests and the FEM.In addition,the load distribution at the pile top is complicated,which is related to the stiffness of the cap,the corresponding assumptions and the analysis method.The shaft axial force first increases slightly with depth then decreases sharply,and the rate of decrease in rock is greater than that in sand and soil.

Collapse mechanism of deep tunnels with three-centered arch cross section

The possible collapse of different circumstances is derived with the help of the limit analysis theory.Analytical equations related to collapsing mechanisms in deep tunnel with smooth three-centered arc cross sections are derived on the basis of Hoek-Brown failure criterion and upper bound limit analysis.The pore water pressure is considered in the analysis,as a work rate of external force.Numerical results about the shape of detaching curve and the weight of collapsing block per unit length corresponding to different parameters are obtained with the help of mathematical software.The shapes of collapsing block are drawn with respected to different parameters.Furthermore,the effects of different parameters on the shape of detaching curve and the weight of the collapsing block are discussed.

The study on the Psychological motivation of Costs Stickiness --Empirical Evidence from China

This paper studies Whether the managerial overconfidence have any impact on the Cost management （Characterized by the degree of the Costs Stickiness ） .Using the ample of the A-share listed companies between 2007-2011 in China, We document that SG＆A cost stickiness decreases in the degree of overconfidence. The further studies show the negative relation is more significant in the state-owned listed companies,which proved our speculation that the manager will cut expenses avoiding significant decline in performance when the sales decline in the state-owned listed company.

Short- and Long-term Therapeutic Efficacies of Intravenous Transplantation of Bone Marrow Stem Cells on Cardiac Function in Rats with Acute Myocardial Infarction:A Meta-analysis of Randomized Controlled Trials

Objective To investigate the short- and long-term therapeutic efficacies of intravenous transplantation of bone marrow stem cells(MSCs) in rats with experimental myocardial infarction by metaanalysis.Methods Randomized controlled trials were systematically searched from Pub Med,Science Citation Index(SCI),Chinese journal full-text database(CJFD) up to December 2014.While the experimental groups(MSCs groups) were injected MSCs intravenously,the control groups were injected Delubecco's minimum essential medium(DMEM) or phosphate buffered saline(PBS).Subgroup analysis for each outcome measure was performed for the observing time point after the transplantation of MSCs.Weighted mean differences(WMD) and 95% confidence intervals(CI) were calculated for outcome parameters including ejection fraction(EF) and fractional shortening(FS),which were measured by echocardiogram after intravenous injection and analyzed by Rev Man 5.2 and STATA 12.0.Results Data from 9 studies(190 rats) were included in the meta-analysis.As compared to the control groups,the cardiac function of the experimental groups were not improved at day 7(EF:WMD=0.08,95%CI-1.32 to 1.16,P>0.01; FS:WMD=-0.12,95%CI-0.90 to 0.65,P>0.01) until at day 14 after MSCs' transplantation(EF:WMD=10.79,95%CI 9.16 to 12.42,P<0.01; FS:WMD=11.34,95%CI 10.44 to 12.23,P<0.01),and it lasted 4 weeks or more after transplantation of MSCs(EF:WMD=13.94,95%CI 12.24 to 15.64,P<0.01; FS:WMD=9.64,95%CI 7.98 to 11.31,P<0.01).Conclusion The therapeutic efficacies of MSCs in rats with myocardid infarction become increasing apparent as time advances since 2 weeks after injection.

The Incentive Mechanism Research of Knowledge Workers

＂Knowledge workers＂ is the carrier of enterprise knowledge and technology and is undoubtedly the most important resource and core competence. How to effectively motivate such people create greater wealth for the enterprise has become the key problem of the era of knowledge economy. Based on the concept and characteristics of knowledge workers, this paper uses classical analysis framework of incentive theory; through quantitative and qualitative analysis, it points out the existing problems and puts forward solutions on the basis of full analysis of the present incentive situation.

Performance analysis and improvement of a high flow coefficient centrifugal compressor

Very high flow coefficient centrifugal compressor stages are mostly performance of this type of stages is critical to the entire centrifugal applied as the first stages of multistage compressors. The compressors, but surprisingly little related information is available in the open literature. A centrifugal compressor with high inlet flow coefficient of 0.2, presenting a narrow operating range and unstable running situation even at design speed during the test, is investigated here. To reveal flow details in this centrifugal compressor, numerical simulations have been carried out and indicate that excessive impeller flow diffusion results in the poor performance of this centrifugal compressor. With the same inlet flow coefficient, six redesign cases coming from an in-house one-dimensional analysis program are proposed together with impeller trimming and equal flow area design method for corresponding vaneless diffuser. Performance comparison among these redesign centrifugal compressors is presented and the most suitable one is recommended for test in the future. In addition, three redesign cases with lower inlet flow coefficient developed by means of flow trimming are shown in the end to satisfy potential application areas. Finally, the results in this study can provide valuable reference information for multistage centrifugal compressor design.

Comparisons between centrifuge and numerical modeling results for slope toppling failure

This paper presents series studies on the toppling mechanism by centrifuge tests and numerical simulations. Two different discrete element methods, i.e., the continuum-based discrete element method(CDEM) and the discontinuous deformation analysis(DDA), are adopted. The modeling results show that both the methods can accurately capture the failure modes of the centrifuge tests, including three distinct zones and two failure surfaces. Comparisons are made between the physical test and numerical simulation results. The critical inclination angle of the tilting table where the slope models are fixed on can be moderately predicted by the two methods, with different degrees of precision. The error between the test results and the simulated results is within 1% for the slope models without rock-bridges by both CDEM and DDA. However, it is amplified for the staggered-joint models that simulate the rock-bridges. With DDA, the average error is about 5%, and the maximum error is up to 17%. While with CDEM, the errors for the aligned-joint models are ranged from 1% to 6%, and it is from 10% to 29% for the staggered-joint models. The two numerical methods show the capability in simulating toppling failure of blocky rock mass with and without rock-bridges. The model with rock-bridges which provides a certain bending resistance is more stable than the one without any rock-bridge. In addition, the two failure surfaces were observed, which is different from the common understanding that only one failure surface appears.

Performance of a centrifugal compressor with holed casing treatment in the large flowrate condition

As demonstrated by former work,the holed casing treatment can be used to expand the stall margin of a centrifugal compressor with unshrouded impeller.In addition,the choked margin can also be expanded as experimental results indicated.Moreover,the compressor performance,especially the efficiency,on the whole working range is improved.As shown by experiments,the stall margin and choked margin of the compressor are extended,and the maximum efficiency improvement is 14%at the large flowrate of 1.386.Numerical simulations were carried out to analyze the flow in the impeller and in the holes in the case of large flowrate.The results indicate that in large flowrate conditions,there is a low-pressure region on the throat part of the impeller passage,leading to the bypass flows appearing in the holes,which means the flow area at the inlet of the impeller is increased.The bypass flow can also contribute to the decrease of the Mach number at the throat part near the shroud end-wall which implies that the choked margin is expanded.Besides,as the bypass flow would inhibit the development of the vertexes in the tip clearance and suppress the flow recirculation in the shroud end-wall region,both the pressure ratio and efficiency of the compressor are improved,which agrees well with the experiments.

An Analysis of Flow in a Centrifugal Impeller by FEM with k-ε Model

In this study, we attempt the analysis of the passage flow in the centrifugal impeller using FEM with/without the turbulence model, and compare this result with the experimental result. The turbulence model is the low Reynolds k-ε model proposed by Chien. We use the GSMAC method for the Reynolds averaged Navier-Stokes equstions, the Euler explicit method for the transport equations of the turbulent kinetic energy and the dissipation rate. All equations are discretized by the Galerkin’s method. At the midpassage of the centrifugal impeller the passagewise velocity component tends to increase in the pressure-to-suction direction, and the other component toward the pressure surface tends to be large in the region of the middle blade-to-blade to the hub side. The tip leakages appear around the region of the middle blade-to-blade near the casing together with the secondary flow toward the suction surface. These phenomena correspond with the experimental result, qualitatively.

Dynamical System Analysis of Unsteady Phenomena inCentrifugal Compressor

Surge and rotating stall occurring in a centrifugal compressor system are investigated by using a phaseportrait reconstruction method. From experimentally measured time series of data, the method clari-fied the cyclic behavior of surge. For rotating stall, there still remain problems in the phase portraitdue to the chaotic behavior. However, the results obtained by the present method are able to providenew insights to the modelings for surge and rotating stall. Surge and rotating stall occurring in acentrifugal compressor system are investigated by using a phase portrait reconstruction method. Fromexperimentally measured time series of data, the method clarified the cyclic behavior of surge. Forrotating stall, there still remain problems in the phase portrait due to the chaotic behavior. However,the results obtained by the present method are able to provide new insights to the modelings for surgeand rotating stall.

Simulation Analysis of Factors Influencing Chiller EER

This study constructed a mathematic model of a variable frequency centrifugal chiller using Simulink software. By running the simulation, it was discovered that when the other factors are constant, the EER(Energy Efficiency Ratio) of the chiller increases with decreases in the temperature of the cooling water and increases in the temperature of the chilled water. The effect of changes in the cooling water temperature on the EER of the chiller is stronger than that of changes in the chilled water temperature. In addition, as the chiller load decreases, the EER increases until reaching a maximum, after which it decreases. Furthermore, the EER of chillers working under a constant flow rate is slightly higher than that of those working under varying flow rates.

Numerical Analysis of Flow in Ultra Micro Centrifugal Compressor -Influence of Meridional Configuration

A single stage ultra micro centrifugal compressor constituting ultra micro gas turbine is required to operate at high rotational speed in order to achieve the pressure ratio which establishes the gas turbine cycle. As a conse- quence, the aerodynamic losses can be increased by the interaction of a shock wave with the boundary layer on the blade surface. Moreover, the centrifugal force which exceeds the allowable s^ress of the impeller material can act on the root of blades. On the other hand, the restrictions of processing technology for the downsizing of im- peller not only relatively enlarge the size of tip clearance but also make it difficult to shape the impeller with the i three-dimensional blade. Therefore, it is important to establish the design technology for the impeller with the two-dimensional blade which possesses the sufficient aerodynamic performance and enough strength to bear the centrifugal force caused by the high rotational speed. In this study, the flow in two types of impeller with the two-dimensional blade which have different meridional configuration was analyzed numerically, The computed results clarified the influence of the meridional configuration on the loss generations in the impeller passage.