Ground-borne vibrations induced by impact pile driving: experimental assessment and mitigation measures

Impact pile driving is an interesting technique for the construction of deep foundations from a practical and economical point of view.However,the generalization of this technique can be restricted due to the excessive vibration levels that can be generated,which can be especially problematic in residential areas.However,different mitigation measures can be applied to prevent excessive vibration levels inside buildings located near construction sites.To compare its efficiency through a numerical prediction tool,two experimental test sites are first presented and characterized.From the results obtained,it was found that the construction of an open trench near the impact source can be used as an efficient mitigation measure to reduce the maximum vibration levels evaluated in this study.

LAND USE AND LAND COVER CHANGE IN CHINA

This paper deals with land use and land cover change in China in the last 500 years. It aims at sensitizing related fields in giving due consideration on integration of environmental change and social economic development process and at proposing a framework for discussion towards further study. Based on historical review,several important changes were summarized as: natural vegetation were replaced by secondary or cultivated Plants, land cover changes differ from time to time and from place to place:and cropping pattern change is a sensitive indicator of land cover change in China. In the history of Cnina, many factors contributed to land use and land cover change either in positive or negative Ways. Four major driving forces were concluded, namely, climatic change, social transformation and turbulence, technology improvement, and international trade competition. In the last Part of tne Paper, a proposal on 'land use/land cover cnange' is framed, so as to calling comments on improving tne study and collaborations from varied authorities and researcn institutions.

A 2-dimensional impact driven precise actuator using piezoelectric bimorphs

A new precise actuator is proposed,which is ac-tuated by the impact force of an end-loaded piezoelectric bimorph cantilever,and bears two degrees of freedom for translation and rotation.The dynamic characteristics of the piezoelectric bimorph were analyzed by FEM,and are fur-ther proved by experimental tests.A new control system for the actuator was put forward and tested,which is called the fixed-frequency with adjustable voltage.In addition,the actuator’s performance of translation and rotation were both measured.The results demonstrate that the actuator is char-acterized by a simple structure,large movement range,strong driving ability and high positioning resolution.Its cost is estimated at only 1%of the traditional impact actuators.

Closed-Loop Control of an XYZ Micro-Stage and Designing of Mechanical Structure for Reduction in Motion Errors

This paper presents a compact XYZ micro-stage driven by an impact driving mechanism.A moving body is translationally actuated along the X-,Y-,and Z-axes in millimeter-scale range and with nanometer-scale resolution.Cr-N thin-film strain sensors are integrated into the micro-stage for closed-loop positioning.Closed-loop control is also carried out.The motion errors in six degrees of freedom are also investigated for this micro-stage.It is clarified by analysis of finite element method that rotational motion errors around the driving axis are caused by torques due to tensions from the elastic hinges of microstage.The mechanical structure of XYZ micro-stage to cancel out the torque generated is proposed and the second prototype is fabricated.Although the rotational motion error is successfully suppressed in the second prototype,a rotational motion error of more than 0.1°remains due to remaining torque and assembly error of the elastic hinges.Then,in order to reduce the rotational motion error,the prototype is designed in which the location of elastic hinges is single-layered.By designing a mechanical structure in which torque is suppressed,all rotational motion errors are successfully reduced to less than 0.05°in the prototype with single-layer hinges.

Micro-simulation insights into the safety and operational benefits of autonomous vehicles

Several past studies showed that Autonomous Vehicles(AVs)can reduce crash risk,stop-and-go traffic,and travel time.To analyze the safety benefits of AVs,most of the researchers proposed algorithms and simulation-based techniques.However,these studies have not assessed the safety benefits of AVs for different vehicle types under heterogeneous conditions.With this opportunity,this study focuses on the benefits of AVs in terms of safety for different penetration rates under heterogeneous conditions.This study considered three driving logics during peak hour conditions to assess the performance of AVs in terms of safety.In VISSIM,default driving behavior models for AVs were adopted to consider cautious and all-knowing driving logic and the third driving logic(Atkins)was modeled in VISSIM using parameters adopted from the previous studies.To this end,using VISSIM,the travel time output results were obtained.Also,using Surrogate Safety Assessment Model(SSAM),conflicts were extracted from output trajectory files(VISSIM).The results suggest that“cautious driving logic”reduced travel time and crash risk significantly when compared to the other two driving logics during peak hour conditions.Furthermore,the statistical analysis clearly demonstrated that“cautious driving logic”differs significantly from the other two driving logics.When Market Penetration Rates(MPR)were 50%or greater,the“cautious driving logic”significantly outperforms the other two driving logics.The results highlight that adopting“cautious driving logic”at an expressway may significantly increase safety at higher AV penetration rates(above 50%).