Ziqiang Zhu

Photoacoustic endoscopy with hollow structured lens-focused polyvinylidine fluoride transducer.

Currently, most transducers in photoacoustic endoscopy (PAE) are ceramic based, which are complicated to fabricate and are expensive. In this work, we have for the first time presented a hollow structured epoxy lens-focused transducer that was based on a 52 μm thick polyvinylidine fluoride (PVDF) film for the purpose of PAE imaging. Intensive field characteristic tests were performed on transducers with different lens curvatures, and results show that with the 6 mm fixed aperture, a lateral resolution less than 0.5 mm can be obtained with a focal length around 19 mm, which is close to the theoretical calculations. The PAE application of the built transducer was also demonstrated with phantom experiments. Compared with the commonly used ceramic-based transducers, the proposed method has greatly reduced the design and fabrication cost of the hollow structured focused transducer as required in PAE, and facilitated the development of the PAE system in lab conditions. The built transducer may play an important role in the PAE imaging of some relatively large human structures and organs, such as the gastrointestinal tract and the cervical canal.

The FDTD Modeling of GPR for Tunnel Inspection

Xianqi-He, Ziqiang-Zhu , Guangyin-Lu*,Qunyi-Lu info-physics and geomatics school central south university, changsha, cina 13975894898@139.com Abstract-Ground-penetrating radar is an important tool nondestructive testing for buildings and transportation systems. However, ground-penetrating radar signals is extremely complex and is easily influenced by many factors ,which lead the interpretation of radar data to be very complex and often with a certain error. The accurately interpretation of radar data need workers have some special experience, such experience is often get through the acquisition of a large number of data and their predecessor’s scholarly papers. Based on the finite-difference timedomain method, the forward modeling of GPR signal provides the reference for the interpretation of ground penetrating radar data in tunnel lining inspection , so that the reliability of detection can be improved.

Tunnel Liner Quality Management with GPR

Ground penetrating radar (GPR) is regularly applied to examine tunnel liners, roads,railways and runways. Many applications have been pioneering proof-of-concept tests to define the benefits and limitations of GPR. For the quality of tunnel liners major include three parts:1the thickness of the liner 2 the Defects of the liner such as the voids 、 non-compacting area and crack 3 the number、diameter of the rebar and rebar corrosion. There are many situations where GPR signals do contain quantitative information useful for developing data needed for engineering decision making.

Numerical simulation for tunnel excavation in stratified rock mass by FLAC3D

Stratified rock mass has been widely existing in geotechnical engineering, especially in tunnel engineering. When tunnel excavated in stratified rock mass, the stress and deformation characteristic of the surrounding rock mass are very different from that in the normal rock mass. In order to study the stress and deformation response tunnel excavation, numerical model is built by the commercial package ANASYS, then the model is transferred based on the self-compiled program to the to the FLAC3D for calculation, then the excavation of tunnel is simulated to find out the effect of the excavation disturbance on the tunnel surrounding rock mass. During simulation procedure, different insitu-stress is set to the model to obtain effect of different horizontal stress on the calculation results, such as the unbalance force of the tunnel surrounding rock mass, the maximum displacement of the tunnel, the horizontal displacement contour and the vertical displacement contour. The calculation result can give some guidance for the real practice.

Optimal design on digital filter algorithm of Hankel transform

This study investigates the influence of the parameter c of Hankel transform pairs and sampling interval s on the digital filter of Hankel transform based on the idea of Hankel digital filtering algorithm proposed by Kong. The results show that the selection of the parameter c highly influence the precision of digital filter algorithm, i.e., an inappropriate c can induce algorithm errors. Upon the optimal selection of the parameter c and the constant length of the digital filter, it is found that an optimal sampling interval s also exists to achieve the best precision of digital filter algorithm. Finally, this study proposes six groups of 0-, 1-order Hankel transform digital filters with different length and promote its application.

Comprehensive Evaluation of Safety for Bored Pile Construction of Chishi Bridge

Chishi Bridge is seated on Carboniferous limestone and Carbon limestone in which karst is strongly developed. Based on analysis the characteristics of the construction of bored Pile an geology, a scientific safety assessment system is the established and Fuzzy AHP(Analytic Hierarchy Process) is used to conduct a comprehensive safety assessment. The results are accordant with the actual and good results can be achieved. But in practice same new situation may be meted, the evaluation system suit be improved and supplement constantly to make the system more perfect.

Three dimensional computer modeling for the stress and deformation interaction of rock slope and tunnel

The interaction between the rock slope and tunnel is very important in geotechnical engineering for they will affect each other. In some cases, tunnel is first excavated long time ago, then with the time passed on, the stress in the rock mass reaches its equilibrium state, and the deformation of the rock mass becomes unchanged. In the following, the surface rock mass is excavated to form a slope, but due to the excavation of the tunnel had disturbed the stress and deformation of rock mass, the slope stability and excavation response will be different from the cases where there does not exist the tunnel excavation in the rock mass. So the interaction between the slope and tunnel need to be considered. In the past, the simplified engineering method is chosen to solve these problems. Recently, due to the rapid advances in computer technology and sustained development, the numerical modeling method has been pushed to the forefront of geotechnical practice, which explores a new way for geotechnical designing. So in the present paper, one slope of rock mass with tunnel in it is chosen as the engineering background, the numerical model is built to realize the modeling for the interaction between the slope and tunnel; two situations are set to study the differences of stress and deformation characteristic between the slope in rock mass with tunnel and without tunnel, whose results can give some guidance for the real practice.

Three Dimensional Numerical Modeling for the Stratified Rock Slope and the Parametric Analysis

Stratified rock mass has been widely existing in geotechnical engineering. With obvious transversely isotropic characteristic, stability of stratified rock mass is not only related to strength of intact rock but also to the inclination and characteristic of structure plane. The parameters of the structure plane have great impact on the stability of stratified rock mass. For the stratified rock mass is no homogenous, the homogenous model is not suitable to describe the characteristic of stratified rock mass. Then building an appropriate becomes necessary. In the present paper, Ubiquitous-joint model is introduced to describe the characteristic of rock mass, and the strength reduction method based on the Ubiquitous-joint model is proposed, which then is used to calculate the safety factor of slope, while the relationships between safety factor, strength properties of structure plane are analyzed, whose results can give guidance for the real practice.

Numerical Simulation for the Interaction between Soil and Cable in Deep Foundation Pit

Simplified mechanical model can not reflect the real situation of the interaction between foundation and cables. Then numerical software FLAC3D is used to simulate the procedure of foundation excavation and cable reinforcement. Deformation responses of foundation are analyzed as well as the mechanical response of cables. The results show that, (1) the procedure of excavation leads to the deformation of soil mass in foundation, which is the reasons of tensile failure and shear failure; for tensile failure areas, the length of soil nailing should be set surpass the slip plane; for shear failure areas, the density of cables should be set larger at the place of shear opening. (2) after excavation, the axial stress distributes different along the cable shaft, location of maximum axial stress along cable can indicate the location of potential slip plane. FLAC3D can simulate the excavation and reinforcement of foundation reasonably, whose result can give guidance for design and construction.

Numerical simulation for the interaction of soil and cable during pull-out test

Pull-out test of cable is an important test to obtain some useful parameters for geotechnical engineering. In order to numerical simulate the pull-out tests of cable to study the mechanical deformation characteristic of soil and cable, the numerical software FLAC3D is used to simulate the procedure of cable being pulled out. After calculation, the mechanical characteristic of cable, response of soil are analyzed, which show that, (1) the axial stress of cable reduces along shaft; (2) the soil mass tends to be pulled out by cable with the friction force between cable and soil mass; (3) with the increase of surrounding stress, the curve of loading-displacement before failure phase becomes more obviously characteristic in linear way, while the failure load of cable becomes larger and larger, whose relationship between failure load of cable and surrounding stress can be fitted by exponential equation with high coefficient; (4) the increase of surrounding stress can lead to the increase of cohesion between cable and surrounding soil mass, but with a limit magnitude; so when surrounding stress increases to some degree, it can not increase the anchor force of cable.