Time Domain Calculation of Connector Loads of a Very Large Floating Structure

Loads generated after an air crash, ship collision, and other accidents may destroy very large floating structures （VLFSs） and create additional connector loads. In this study, the combined effects of ship collision and wave loads are considered to establish motion differential equations for a multi-body VLFS. A time domain calculation method is proposed to calculate the connector load of the VLFS in waves. The Longuet-Higgins model is employed to simulate the stochastic wave load. Fluid force and hydrodynamic coefficient are obtained with DNV Sesam software. The motion differential equation is calculated by applying the time domain method when the frequency domain hydrodynamic coefficient is converted into the memory function of the motion differential equation of the time domain. As a result of the combined action of wave and impact loads, high-frequency oscillation is observed in the time history curve of the connector load. At wave directions of 0° and 75°, the regularities of the time history curves of the connector loads in different directions are similar and the connector loads of C1 and C2 in the X direction are the largest. The oscillation load is observed in the connector in the Y direction at a wave direction of 75° and not at 0° This paper presents a time domain calculation method of connector load to provide a certain reference function for the future development of Chinese VLFS

Fault Tree Analysis of Fire and Explosion Accidents for Dual Fuel （Diesel/Natural Gas） Ship Engine Rooms

In recent years, China's increased interest in environmental protection has led to a promotion of energy-efficient dual fuel(diesel/natural gas) ships in Chinese inland rivers. A natural gas as ship fuel may pose dangers of fire and explosion if a gas leak occurs. If explosions or fires occur in the engine rooms of a ship, heavy damage and losses will be incurred. In this paper, a fault tree model is presented that considers both fires and explosions in a dual fuel ship; in this model, dual fuel engine rooms are the top events. All the basic events along with the minimum cut sets are obtained through the analysis.The primary factors that affect accidents involving fires and explosions are determined by calculating the degree of structure importance of the basic events.According to these results, corresponding measures are proposed to ensure and improve the safety and reliability of Chinese inland dual fuel ships.

Guidance Navigation and Control for Chang’E-5 Powered Descent

To achieve the goal of collecting lunar samples and return to the Earth for the Chang’E-5 spacecraft,the lander and ascender module(LAM)of the Chang’E-5 spacecraft successfully landed on the lunar surface on 1 Dec.,2020.The guidance,navigation,and control(GNC)system is one of the critical systems to perform this task.The GNC system of previous missions,Chang’E-3 and Chang’E-4,provides the baseline design for the Chang’E-5 LAM,and the new characteristics of the LAM,like larger mass and liquid sloshing,also bring new challenges for the GNC design.The GNC design for the descent and landing is presented in this paper.The guidance methods implemented in the powered descent are presented in detail for each phase.Propellant consumption and hazard avoidance should be particularly considered in the design.A reconfigurable attitude control is adopted which consists of the quaternion partition control,phase and gain stabilization filter,and dual observer.This controller could provide fast attitude maneuver and better system robustness.For the navigation,an intelligent heterogeneous sensor data fusion method is presented,and it is applied for the inertial measurement unit and velocimeter data.Finally,the flight results of the LAM are shown.Navigation sensors were able to provide valid measurement data during descent,and the thrusters and the main engine operated well as expected.Therefore,a successful soft lunar landing was achieved by the LAM.

Knowledge graph quality control:A survey

A knowledge graph(KG),a special form of semantic network,integrates fragmentary data into a graph to support knowledge processing and reasoning.KG quality control is important to the utility of KGs.It is essential to investigate KG quality and the parameters influencing KG quality to better understand its quality control.Although many works have been conducted to evaluate the dimensions of KG quality,quality control of the construction process,and enhancement methods for quality,a comprehensive literature review has not been presented on this topic.This paper intends to fill this research gap by presenting a comprehensive survey on the quality control of KGs.First,this paper defines six main evaluation dimensions of KG quality and investigates their correlations and differences.Second,quality control treatments during KG construction are introduced from the perspective of these dimensions of KG quality.Third,the quality enhancement of a constructed KG is described from various dimensions.This paper ultimately aims to promote the research and applications of KGs.