Numerical simulation and optimization of aerodynamic uplift force of a high-speed pantograph

Aiming at the problem that aerodynamic uplift forces of the pantograph running in the knuckle-downstream and knuckle-upstream conditions are inconsistent,and their magnitudes do not satisfy the corresponding standard, the aerodynamic uplift forces of pantographs with baffles are numerically investigated, and an optimization method to determine the baffle angle is proposed. First, the error between the aerodynamic resistances of the pantograph obtained by numerical simulation and wind tunnel test is less than 5%, which indicates the accuracy of the numerical simulation method. Second, the original pantograph and pantographs equipped with three different baffles are numerically simulated to obtain the aerodynamic forces and moments of the pantograph components.Three different angles for the baffles are-17°, 0° and 17°.Then the multibody simulation is used to calculate the aerodynamic uplift force of the pantograph, and the optimal range for the baffle angle is determined. Results show that the lift force of the baffle increases with the increment of the angle in the knuckle-downstream condition, whereas the lift force of the baffle decreases with the increment of the angle in the knuckle-upstream condition. According to the results of the aerodynamic uplift force, the optimal angle of the baffle is determined to be 4.75° when the running speed is 350 km/h, and pantograph–catenary contact forces are 128.89 N and 129.15 N under the knuckledownstream and knuckle-upstream operating conditions,respectively, which are almost equal and both meet the requirements of the standard EN50367:2012.

Experimental Investigation of Irregular Wave Uplift Force on Deck of Exposed High-Pile Jetties

A laboratory setup was developed to investigate irregular wave uplift loads on exposed high-pile jetties. It is shown that the dimensionless uplift load increases to the maximum with an increasing relative clearance and then decreases. The relative clearance corresponding to the peak force is linked to a range from 0.4 to 0.8. When the relative clearance exceeds a certain value, the wave can not reach the underside of the deck and the force becomes zero. Distinct trends of dimensionless force with a relative width of deck show that the force tends to decrease as the relative deck width increases, and then the decrease slows down after the relative deck width increases or decreases to a certain value. The pressure distribution length associated with the maximum uplift force is equivalent to the wave contact width x. When x is larger than the width of deck B, it is taken as B. The statistical distribution of loads obeys the Weibull distribution. The results from the analyses of the real data suggest a new dimensionless prediction model on wave-in-deck uplift loads and the conversion ratio between wave loads at different exceedance probabilities. A comparison is made between the new prediction model and the existing widely used three prediction models. These results are used as useful references for structural design of the jetty.

Mechanism of Geogrid Reinforced Soil at Bridge Approach

Using Geogrid-Reinforced Soil （GRS） we studied the working mechanism and design method of GRS at bridge approach with high backfill by field experiment. In a highway section where the height of backfill is 13.5 meters, geogrids were used at two bridge approaches to address the bumping problems. Some soil pressure cells were used to measure the normal and lateral soil pressure at different locations in the roadbed. The experimental results indicate that geogrids in geogrid-reinforced soil （GRS） could produce an uplift force, the closer the location to the abutment, the larger the uplift force, and the reduction of measured soil pressures compared with theoretical values was the largest at the bottom of roadbed, less at the top than at the bottom, and the least in the mid-height of roadbed than at the bottom. These findings are different from those of the traditional greogrid-reinforced subgrade design method,

Wave Uplift Forces on the Bottom of a Circular Cylinder

The analysis of the data of model tests of two large deep wharves and monographic experimental studies show that two aspects are to be improved so as to predict the wave uplift forces on the bottom of a circular cylinder. The first aspect is the uplift pressure distribution on the bottom, and the second is the correct determination of the phase for maximum horizontal wave forces. The second problem has been solved. Synthesizing the results of theoretical analysis and experiments, we suggest a diagram for the determination of the phase when the maximum horizontal wave force appears. On the basis-ef the diagram the simultaneous wave uplift forces can be obtained for the structural stability analysis.

Study on the Impact of Filter Layer Permeability on Revetment Top Layer Stability under Wave Action

In the design of revetment engineering under wave action, to resist the wave action, the pattern of top layer-filter layer-core （subsoil） is often adopted. In general, the structure of top layer is usually single discrete blocks, typically accropode blocks, four-leg square hollow blocks and barrier boards, and also acropode, riprap, paved rock blocks or concrete slabs with smaller waves. Such top layer has been provided with many research findings on its stability and is widely used in engineering. Setting a filter layer between the top layer and the lower dike core mainly has two functions： （1） giving certain permeability, to minimize the hydrodynamic load directly acting on the lower foundation soil; （2） giving certain hydraulic tightness, to prevent fine sediment of the lower foundation soil from being washed out. This paper is focused on a special filter layer with geotextile as its upper structure and coarse aggregate as its lower structure. By simulating geotextile with different permeability and coarse aggregate with different size, the pressure of top of cover layer and the down side of the geotextile is tested under wave actions, and compared with theoretical analysis, in this way, how the permeability of geotextile impacts the stability of top layer is studied. The research shows that when the filter layer under the geotextile has high permeability and the geotextile＇s permeability gets poorer, the uplift force to geotextile and the top layer will be increased under wave action, which will cause damage to the top layer when it is greater than the vertical component of the underwater gravity along the slope surface.

EXPERIMENTAL STUDY ON TOTAL UPLIFT FORCES OF WAVES ON HORIZONTAL PLATES

The total uplift forces of waves acting on horizontal plates are theimportant basis for the design of maritime hollow-trussed structures. In this paper, an experimentalstudy on the total uplift forces of waves on horizontal plates was conducted by a series of modeltests. The results show that the maximum total uplift forces do not necessarily occur with themaximum impact pressure intensity synchronously. On the basis of the test results, formationmechanism of the total uplift forces of waves as well as its influencing factors were analyzed indetail, and an equation for calculation of the maximum total uplift forces of waves on plates wasput forward. Lots of test data shows the present equation is in good agreement with the testresults.

SPECTRAL ANALYSIS OF RANDOM WAVE UPLIFT FORCE ON A HORIZONTAL DECK

This article presents a spectral analysis of wave uplift loads on a horizontal deck.The wave uplift force spectrum on the underside of the deck is obtained.It is shown that the wave uplift force spectral density decreases with the increase of the relative clearance1/3Δh /H.The influences of different incident wave parameters,including the relative wave height1/3H /d,the relativedeck width/sB L and the relative clearance1/3Δh /Hon the dimensionless zeroth spectral moment of the uplift forces arediscussed.It is found that the zeroth spectral moment of the uplift forces increases with the increase of the relative wave height1/3H /d,and decreases with the increase of the relative clearance1/3Δh /H.A new dimensionless prediction model for the zerothspectral moment of wave uplift loads on the deck is proposed and the relationship between the wave uplift forces and the zerothspectral moment of the uplift force are obtained.

AN EXPERIMENTAL STUDY ON VERTICAL HYDRODYNAMIC FORCE ON A CIRCULAR SLAB NEAR FREE SURFACE BY WATER WAVES

An experimental study has been carried out to investigate the vertical force on a slab of sea-crossing bridge piers in the cases of different hydrodynamic conditions. The experimental study is divided into two parts in terms of regular waves and irregular waves. The hydrodynamic loads acting on the slab are measured by a six component balance and pressures on the bottom of the slab are measured by pressure transducers. It turns out that the vertical lbrce patterns can be considered as impact type and bouyant uplili type. For these two different patterns, time series of the vertical hydrodynamic forcc are measured and analyzed. The influences of wave height, wave period, clearance height of slab on the vertical force arc discussed in detail.

ANALYTICAL SOLUTION OF WAVE-INDUCED SEEPAGE PRESSURE ACTING ON THE BASE OF BREAKWATER

The wave loads acting on a breakwater resting on seabed include not only the wave force from the wave field around the structure but also the wave-induced seepage pressure acting on the base of breakwater.The latter is also a circumstance load which can not be neglected in engineering design.This paper presents a closed-form analytical solution of wave-induced seep- age pressure acting on the base of breakwater resting on an infinite-depth porous elastic seabed. Based on the Biot's consolidation theory,the soil deformation and the compressibility of pore wa- ter are considered.The water wave pressure on sea bottom is determined by the linear water wave theory.The numerical results of uplifting force and moment caused by the wave-induced seepage pressure are given and the influences of soil deformation and pore water compressibility on the calculation results are discussed.

Mechanism of Reservoir Water in the Deformation of Hefeng Landslide

The trial impoundment was carried on in Three Gorges Reservoir from September 27, 2008. There were strong deformation and failure in Hefeng （鹤峰） landslide when the reservoir water level descended from the altitude of 173 m. It indicates that the deformation is closely related to reservoir water fluctuation. For this reason, the effect of reservoir water in the deformation was studied, taking Hefeng landslide as an example in this article. First, the geological characteristics and deformation situation of strong deformation region are analyzed to disclose the intrinsic factors and the pattern of the deformation under the condition of water level fluctuation. Second, the stabilities of the landslide are calculated during the rising and descending processes, and the corresponding relationship between reservoir water level fluctuation and landslide deformation is further identified. At last, the seepage fields and the force condition of landslide body below the phreatie line are analyzed to reveal the effect of reservoir water. Moreover, it can be concluded that for better permeable reservoir landslide, during reservoir water rising, the favorable effect of seepage force weakens the unfavorable effect of uplift force, so the rising of reservoir water has little effect on the stability, and no deformation is caused; but during the descending of reservoir water, the unfavorable effect of seepage force is superimposed on the unfavorable effect of the uplift force, which causes the stability to dramatically decrease and leads to the failure of the accumulation body in front of the landslide.