Magnetic Flux Leakage Course of Inner Defects and Its Detectable Depth

As a promising non-destructive testing(NDT)method,magnetic flux leakage(MFL)testing has been widely used for steel structure inspection.However,MFL testing still faces a great challenge to detect inner defects.Existing MFL course researches mainly focus on surface-breaking defects while that of inner defects is overlooked.In the paper,MFL course of inner defects is investigated by building magnetic circuit models,performing numerical simulations,and conducting MFL experiments.It is found that the near-surface wall has an enhancing effect on the MFL course due to higher permeability of steel than that of air.Further,a high-sensitivity MFL testing method consisting of Helmholtz coil magnetization and induction coil with a high permeability core is proposed to increase the detectable depth of inner defects.Experimental results show that inner defects with buried depth up to 80.0 mm can be detected,suggesting that the proposed MFL method has the potential to detect deeply-buried defects and has a promising future in the field of NDT.

Seismic ground amplification induced by box-shaped tunnels

The growing use of underground structures,specifically to facilitate urban transportation,highlights the need to scrutinize the effects of such spaces on the seismic ground response as well as the surrounding buildings.In this regard,the seismic ground amplification variations in the vicinity of single and twin box-shaped tunnels subjected to SV waves have been investigated by the finite difference method.To evaluate the effects,generalizable dimensionless diagrams based on the results of parametric numerical analysis considering factors such as variations in the tunnels′depth,the distances between the tunnels,tunnel lining flexibility,and input wave frequency,have been presented.In addition,to assess the effects of underground box-shaped tunnels on the response spectrum of the ground surface,seven selected accelerograms have been matched based on a specific design spectrum for the stiff soil condition of Eurocode 8(CEN,2006).The results underline the significant amplification effect of the box-shaped tunnels on the ground motions,specifically in the case of horizontal twin tunnels,which should be given more attention in current seismic design practices for surface structures.

Ground surface response induced by shallow buried explosions

Based on the spherical cavity expansion theory in the elastic half space,the ground surface movement characteristics of shallowly buried explosions are analyzed.The results show that the induced seismic wave is a longitudinal wave in the near zone and a Rayleigh wave in the far zone.The maximum displacement(velocity) of the longitudinal wave and the Rayleigh wave are inversely proportional to the scaled distance,and can be described by exponential function with exponents equal to 1.4 and 0.5,respectively.The vibration frequencies of the waves have almost no change.The vibration frequency of the longitudinal wave approximates the natural vibration frequency of the cavity in the broken area,and the vibration frequency of the Rayleigh wave is about half that of the longitudinal wave.On the same reduced buried depth and reduced distance,the particle displacement is directly proportional to the product of the boundary loading and cavity radius,and is inversely proportional to the transversal wave velocity.Meanwhile,the particle velocity is directly proportional to the boundary loading and inversely proportional to the wave velocity ratio.In the far zone,the buried depth of the explosive only has a slight effect on the longitudinal wave,but has a larger effect on the Rayleigh wave.

Preliminary Study on Optimized Conditions for Dry-cultivated Rice Seedling Planting

The effects of soil moisture content, pot seedling buried depth, and pot seedling height on the survival rate and growth of dry planted seedlings were researched by field experiment. The results showed that the seedling survival rate and growth were enhanced with the increase of soil moisture content after pot seedling transplanting, but there was no significant difference in the survival rate and growth of seedlings with 85% and 100% of soil moisture content. Pot seedling buried depth was one of the important factors affecting the survival rate, and when the pot seedlings were buried 2 cm deep, the seedlings showed high survival rate and excellent growth. Under the same condition of soil moisture content and buried depth, seedlings with pot seedling height of 15 cm had the best survival rate and growth. Therefore, the optimized conditions for dry-cultivated rice seedling planting were soil moisture content of 85%, pot seedling buried depth of 2 cm, and pot seedling height of 15 cm.

Analysis of influence of the length of ground heat exchangers on the operation characteristics and economy of ground source heat pumps

A three-dimensional finite element dynamic simulation platform of the ground source heat pump system(GSHPS)is established.According to the outlet temperature of ground heat exchangers(GHEs)required by the code in summer and winter,the calculated minimum buried depth of GHEs meeting the requirements is 60 m,when the number of borehole is 9.By using the established platform,the annual operation performance and cost of the GSHPS under different buried pipe depths are studied.The results show that the deeper the buried depth of GHEs is,the better the heat exchange effect of GHEs is.Compared with the GHEs with 60 m buried depth,when the buried depth of GHEs is 65 m,70 m,75 m and 80 m,the average coefficient of performance(COP)of the unit increases by 4.1%,6.3%,7.7%and 8.2%in cooling period and 1.0%,1.6%,1.8%and 1.9%in heating period,respectively.Considering the performance and initial investment of the GHSPS comprehensively,the optimal buried depth of GHEs is 60 m.However,considering the performance the system and the total cost of the system running for 20 years comprehensively,the optimal buried depth of GHEs is 70 m.