A comparison of regression models for the ice loads measured during the ice tank test

To evaluate the time-domain positioning performance of arctic marine structures, it is necessary to generate an ice load appropriate for the current position and heading of the structure. The position and orientation angle of a floating body continuously change with time. Therefore, an ice load is required for any attitude in the time-domain simulation. In this study, we present a fundamental technique for analyzing ice loads in the frequency domain based on data measured at various angles in the ice-water tank experiment. We perform spectral analysis instead of general FFT to analyze the ice load, which has the characteristics of a random signal. To generate the necessary ice load in the time domain, we must first interpolate the measured data in the frequency domain. Using the Blackman-Tukey method, we estimate the spectrum for the measured data, then process the data to generate the training set required for machine learning. Based on the results, we perform regression analysis by applying four representative techniques, including linear regression, random forest, or neural network, and compare the results with MSE. The deep neural network method performed best, but we provide further discussion for each model

Automatic generation of equations of motion for multibody system in discrete event simulation framework

AbstractIn this paper, the development of a simulation program that can automatically generate equations of motion for mutibody systems in the discrete event simulation framework is presented. The need to analyze the dynamic response of mechanical systems that are under event triggered conditions is increasing. General mechanical systems can be defined as multibody systems that are collections of interconnected rigid bodies, consistent with various types of joints that limit the relative motion of pairs of bodies. For complex multibody systems, a systematic approach is required to efficiently set up the mathematical models. Therefore, a dynamics kernel was developed to automatically generate the equations of motion for multibody systems based on multibody dynamics. The developed dynamics kernel also provides the numerical solver for the dynamic analysis of multibody systems. The general multibody dynamics kernel cannot deal with discontinuous state variables, event triggered conditions, and state triggered conditions, though. To enable it to deal with multibody systems in discontinuous environments, the multibody dynamics kernel was integrated into a discrete event simulation framework, which was developed based on the discrete event system specification (DEVS) formalism. DEVS formalism is a modular and hierarchical formalism for modeling and analyzing systems under event triggered conditions, which are described by discontinuous state variables. To verify the developed program, it was applied to an block-lifting and transport simulation, and dynamic analysis of the system is carried out

Heave Compensation Dynamics for Offshore Drilling Operation

In this study, dynamic response analysis of a heave compensation system for offshore drilling operations was conducted based on multibody dynamics. The efficiency of the heave compensation system was computed using simulation techniques and virtually confirmed before being applied to drilling operations. The heave compensation system was installed on a semi-submersible and comprises several interconnected bodies with various joints. Therefore, a dynamics kernel based on multibody dynamics was developed to perform dynamic response analysis. The recursive Newton–Euler formulation was adopted to construct the equations of motion for the multibody system. Functions of the developed dynamics kernel were verified by comparing them with those from other studies. Hydrostatic force, linearized hydrodynamic force, and pneumatic and hydraulic control forces were considered the external forces acting on the platform of the semi-submersible rig and the heave compensation system. The dynamic simulation was performed for the heave compensation system of the semi-submersible rig for drilling operations up to 3600 m water depth. From the results of the simulation, the efficiency of the heave compensation system was evaluated to be approximately 96.7%

Real-time ship stability evaluation program through deterministic method based on second-generation intact stability

IMO suggests Second-Generation Intact Stability Criterion (SGISC), which consists of five failure modes, because of continuous accidents due to a lack of ship stability. In this study, Level 1 and Level 2 stability of SGISC were evaluated for three stability failure modes (Dead Ship Condition, Surf-riding, and Excessive Acceleration). Level 1 was calculated in the same way as the second-generation intact stability calculation method, and Level 2 was calculated in a deterministic manner by using a real-time maritime environment rather than a probabilistic approach for all maritime environments. Based on this, a program was developed to visualize dangerous and safe areas on a map. Using the developed program, it is expected that SGISC can be used not only in the design stage, but also in the operation stage of ships, such as route planning or selection of operating locations in the ocean

Design of controller for mobile robot in welding process of shipbuilding engineering

The present study describes the development of control hardware and software for a mobile welding robot. This robot is able to move and perform welding tasks in a double hull structure. The control hardware consists of a main controller and a welding machine controller. Control software consists of four layers. Each layer consists of modules. Suitable combinations of modules enable the control software to perform the required tasks. Control software is developed using C programming under QNX operating system. For the modularizing architecture of control software, we designed control software with four layers: Task Manager, Task Planner, Actions for Task, and Task Executer. The embedded controller and control software was applied to the mobile welding robot for successful execution of the required tasks. For evaluate this imbedded controller and control software, the field tests are conducted, it is confirmed that the developed imbedded controller of mobile welding robot for shipyard is well designed and implemented

Event-based scenario manager for multibody dynamics simulation of heavy load lifting operations in shipyards

This paper suggests an event-based scenario manager capable of creating and editing a scenario for shipbuilding process simulation based on multibody dynamics. To configure various situation in shipyards and easily connect with multibody dynamics, the proposed method has two main concepts: an Actor and an Action List. The Actor represents the anatomic unit of action in the multibody dynamics and can be connected to a specific component of the dynamics kernel such as the body and joint. The user can make a scenario up by combining the actors. The Action List contains information for arranging and executing the actors. Since the shipbuilding process is a kind of event-based sequence, all simulation models were configured using Discrete EVent System Specification (DEVS) formalism. The proposed method was applied to simulations of various operations in shipyards such as lifting and erection of a block and heavy load lifting operation using multiple cranes

Experimental Study on Development of Mooring Simulator for Multi Floating Cranes

In this study, the coupled motion of a mooring system and multifloating cranes were analyzed. For the motion analysis, the combined equations of motions of the mooring line and multifloating cranes were introduced. The multibody equations for floating cranes were derived from the equations of motion. The finite element method (FEM) was used to derive equations to solve the stretchable catenary problem of the mooring line. To verify the function of mooring simulator, calculation results were compared with commercial mooring software. To validate the analysis results, we conducted an experimental test for offshore operation using two floating crane models scaled to 1:40. Two floating crane models and a pile model were established for operation of uprighting flare towers. During the model test, the motion of the floating cranes and tensions of the mooring lines were measured. Through the model test, the accuracy of the mooring analysis program developed in this study was verified. Therefore, if this mooring analysis program is used, it will be possible to perform a mooring analysis simulation at the same time as a maritime work simulation

A Kinematic Collision Box Algorithm Applied for the Anti-Collision System of Offshore Drilling Vessels

With the advances in technology and the automation of drilling platforms, the Anti-Collision System (ACS) has appeared as an affordable technology, which is intended to keep equipment on the drilling floor working harmoniously and to prevent the potential hazards associated with accidents. However, the specialty of the machinery on the drilling floor requires a distinguished structure for the ACS and a reliable collision-avoidance algorithm, which is not similar to any algorithm in other applications, such as automobiles and robotics. The aim of this paper is to provide a comprehension of the configuration of an ACS in an Integrated Drilling System and to develop a practical anti-collision algorithm that can be applied to the machine arrangement for an offshore drilling operation. By analyzing the motions and using kinematic parameters, such as the speed and deceleration information of drilling equipment, a kinematic collision box algorithm is developed to eliminate the limitation of conventional algorithms. While the conventional collision-avoidance algorithm uses a collision box with fixed size, the kinematic collision box algorithm uses a collision box with a flexible scale that can be correspond to the velocity and deceleration rate of the equipment. Several operating scenarios are simulated by a visual model of ACS to authenticate the functionality of the proposed algorithm. The operation of the top drive is an outstanding scenario. Only 2.25 s are required to stop the top drive from its maximum velocity, and a conventional algorithm uses this number to create a fixed bounding box. Also, the kinematic collision box algorithm uses the real-time data of velocity and acceleration to adjust the scale of the bounding box when the speed of the top drive increases from 0 to its maximum value. The simulation result illustrates the reliability and advances of the kinematic collision box algorithm in performing the collision-avoidance function in ACS compared to the conventional algorithm