Numerical Simulation of a Floater in a Broken-Ice Field: Part I — Model Description

2012 ◽  
Author(s):  
Ivan Metrikin ◽  
Wenjun Lu ◽  
Raed Lubbad ◽  
Sveinung Løset ◽  
Marat Kashafutdinov
Keyword(s):  
Dimensional Space ◽  
Rigid Bodies ◽  
Interaction Process ◽  
Contact Forces ◽  
Model Description ◽  
Physics Engine ◽  
Broken Ice ◽  
Ice Floes ◽  
Rigid Multibody ◽  
Ice Model

This paper presents a novel concept for simulating the ice-floater interaction process. The concept is based on a mathematical model which emphasizes the station-keeping scenario, i.e. when the relative velocity between the floater and the ice is comparatively small. This means that the model is geared towards such applications as dynamic positioning in ice and ice management. The concept is based on coupling the rigid multibody simulations with the Finite Element Method (FEM) simulations. The rigid multibody simulation is implemented through a physics engine which is used to model the dynamic behaviour of rigid bodies which undergo large translational and rotational displacements (the floater and the ice floes). The FEM is used to simulate the material behaviour of the ice and the fluid, i.e. the ice breaking and the hydrodynamics of the ice floes. Within this framework, the physics engine is responsible for dynamically detecting the contacts between the objects in the calculation domain, and the FEM software is responsible for calculating the contact forces. The concept is applicable for simulations in a three-dimensional space (3D). The model described in this paper is divided into two main parts: the mathematical ice model and the mathematical floater model. The mathematical ice model allows modelling both intact level ice and discontinuous ice within a single framework. However, the primary focus of this paper is placed on modelling the broken ice conditions. A floater is modelled as a rigid body with 6 degrees of freedom, i.e. no deformations of the floater’s hull are allowed. Nevertheless, the hydrodynamics of the floater and the ice is considered within the outlined model. The presented approach allows implementing realistic, high fidelity 3D simulations of the ice-fluid-structure interaction process.

Numerical Simulation of a Floater in a Broken-Ice Field: Part II — Comparative Study of Physics Engines

2012 ◽  
Author(s):  
Ivan Metrikin ◽  
Andrey Borzov ◽  
Raed Lubbad ◽  
Sveinung Løset
Keyword(s):  
Numerical Simulation ◽  
Dimensional Space ◽  
Three Dimensional ◽  
Contact Forces ◽  
Limited Attention ◽  
Detection Accuracy ◽  
Documentation Quality ◽  
Physics Engine ◽  
Broken Ice ◽  
Ice Floes

Numerical simulation of a floater in ice-infested waters can be performed using a physics engine. This software can dynamically detect contacts and calculate the contact forces in a three-dimensional space among various irregularly shaped bodies, e.g. the floater and the ice floes. Previously, various physics engines were successfully applied to simulate floaters in ice. However, limited attention was paid to the criteria for selecting a particular engine for the simulation of a floater in broken-ice conditions. In this paper, four publicly available physics engines (AgX Multiphysics, Open Dynamics Engine, PhysX and Vortex) are compared in terms of integration performance and contact detection accuracy. These two aspects are assumed to be the most important for simulating a floater in broken ice. Furthermore, the access to code, documentation quality and the level of technical support are evaluated and discussed. The main conclusion is that each physics engine has its own strength and weaknesses and none of the engines is perfect. These strength and weaknesses are revealed and discussed in the paper.

scholarly journals The GFDL Global Ocean and Sea Ice Model OM4.0: Model Description and Simulation Features

2019 ◽  
Vol 11 (10) ◽  
pp. 3167-3211 ◽  
Author(s):  
Alistair Adcroft ◽  
Whit Anderson ◽  
V. Balaji ◽  
Chris Blanton ◽  
Mitchell Bushuk ◽  
...  
Keyword(s):  
Sea Ice ◽  
Global Ocean ◽  
Model Description ◽  
Ice Model

Choosing the Optimal Contact Force Distribution for Multi-Limbed Mobile Robots With Three Feet Contact

2003 ◽  
Author(s):  
Dennis W. Hong ◽  
Raymond J. Cipra
Keyword(s):  
Contact Force ◽  
Dimensional Space ◽  
Contact Point ◽  
Optimal Solution ◽  
Solution Space ◽  
Contact Forces ◽  
Force Distribution ◽  
Normal Vector ◽  
Optimization Criteria ◽  
Contact Force Distribution

One of the inherent problems of multi-limbed mobile robotic systems is the problem of multi-contact force distribution; the contact forces and moments at the feet required to support it and those required by its tasks are indeterminate. A new strategy for choosing an optimal solution for the contact force distribution of multi-limbed robots with three feet in contact with the environment in three-dimensional space is presented. The optimal solution is found using a two-step approach: first finding the description of the entire solution space for the contact force distribution for a statically stable stance under friction constraints, and then choosing an optimal solution in this solution space which maximizes the objectives given by the chosen optimization criteria. An incremental strategy of opening up the friction cones is developed to produce the optimal solution which is defined as the one whose foot contact force vector is closest to the surface normal vector for robustness against slipping. The procedure is aided by using the “force space graph” which indicates where this solution is positioned in the solution space to give insight into the quality of the chosen solution and to provide robustness against disturbances. The “margin against slip with contact point priority” approach is also presented which finds an optimal solution with different priorities given to each foot contact point for the case when one foot is more critical than the other. Examples are presented to illustrate certain aspects of the method and ideas for other optimization criteria are discussed.

Guidance Model Representing an Ice Field for Path-Planning in Ice Management

2020 ◽  
Author(s):  
Jon Bjørnø ◽  
Mathias Marley ◽  
Roger Skjetne
Keyword(s):  
Path Planning ◽  
Breaking Effect ◽  
B Splines ◽  
Planning Algorithm ◽  
Broken Ice ◽  
Ice Field ◽  
Ice Floes ◽  
Path Planning Algorithm ◽  
Guidance Information ◽  
Guidance Model

Abstract In the work presented in this paper, the problem on how to represent a simplified ice field in a guidance model, enabling path and maneuver planning for IM operation, has been studied. The use of B-splines and other basis functions are considered to represent relevant guidance information over the 2D drifting ice field. A weight value is computed and updated at locations that represents broken ice (visited by an icebreaker) versus unbroken ice. The guidance model will ensure that there is a continuous representation of the state of the ice field during the operations. The drifting behavior of the ice field is incorporated into the guidance model. The model will be updated with new (solid) ice that is formed at the beginning of the ice field, and it will continuously be updated in the path where the icebreaker moves. To simulate the maneuvers of the icebreaker, a dynamic model is used, and the ice breaking effect where the ice field is continuously broken into smaller ice floes is included in the model. This representation of an ice field can be used in a path-planning algorithm to determine the icebreaker path in a moving ice environment in order to reduce the ice field into small enough ice floes and reduce the load on the protected structure.

Multi-Body Modeling of Human Musculoskeletal System for an Exercise Therapy Method and its Verification

2013 ◽  
Author(s):  
Munehiro Michael Kayo ◽  
Yoshiaki Ohkami
Keyword(s):  
Exercise Therapy ◽  
Musculoskeletal System ◽  
Human Body ◽  
Structural Model ◽  
Force Plate ◽  
Rigid Bodies ◽  
Contact Forces ◽  
Estimation Of Parameters ◽  
Human Body Model ◽  
Multi Body

The objective of this paper is to establish a concise structural model of the human musculoskeletal system (HMS) that can be applied to an exercise therapy that treats malfunctions or distortions of the human body. There exist a number of traditional exercise therapy methods in Japan and China, but any systematic approaches for learning, coaching or training are not found to the best of the author’s knowledge. Among such approaches, we deal with an exercise therapy called Somatic Balance Restoring Therapy (SBRT) in which a patient executes a series of non-invasive and painless motions in face-up/down laid posture. Although thousands of results have been piled up in a fixed-format data base, justification for the SBRT has not been provided in bio/mechanical engineering sense. The purpose of modeling is a first step for this holistic approach. For such reasons, the model must be useful and uncomplicated for therapists to identify the problematic areas of the human body with adequate visualization while maintaining a theoretical thoroughness in mechanics or dynamics. To bridge multi-body dynamics and the SBRT, we have utilized a human body model with a collection of joint connected 15 rigid bodies in a topological tree configuration as used for humanoid robot with 80 Degrees-of-Freedom (DOF). In order to achieve the purpose stated above, we have developed a static force/torque balance equation for each body element. In addition, we will describe modeling processes, derivation of static equations, and estimation of parameters/states and verification based on the analysis of the FPS experimental data, and contact forces are parameterized with quantitative values to be given by the Force Plate System (FPS), installed at CARIS at the University of British Columbia (UBC).

Subsurface Ice Transport at a Transversally Towed Ship Model

2017 ◽  
Author(s):  
Li Zhou ◽  
Rüdiger U. Franz von Bock und Polach ◽  
Xu Bai
Keyword(s):  
Froude Number ◽  
Densimetric Froude Number ◽  
Ship Model ◽  
Drift Speed ◽  
Ice Accumulation ◽  
Underwater Cameras ◽  
Low Froude Number ◽  
Broken Ice ◽  
Level Ice ◽  
Ice Floes

The subsurface transport of ice along the underwater body of a ship hull or a structure may cause damages to appendages. In order to investigate the conditions under which the ice accumulation occurs, a series of model tests was carried out in the ice basin of Aalto University. The used ship model was towed laterally against the ice with one side breaking level ice. The transport of broken ice floes broken off from the intact ice sheet has been has been monitored with underwater cameras. Both the model drift speed, respectively the ice drift speed, and the ice thickness are found to affect ice accumulation process. The Densimetric Froude number is introduced as measured to determine whether ice floes will accumulate on the upstream of the hull. It is found that ice accumulation is triggered at relatively low Froude number.

Rigid Body Collisions

1989 ◽  
Vol 56 (1) ◽  
pp. 133-138 ◽  
Author(s):  
Raymond M. Brach
Keyword(s):  
Energy Loss ◽  
Classical Problem ◽  
Negative Energy ◽  
Coefficient Of Restitution ◽  
Rigid Bodies ◽  
Interaction Process ◽  
Energy Losses ◽  
Conservation Of Energy ◽  
Special Case ◽  
Two Bodies

A general approach is presented for solving the problem of the collision of two rigid bodies at a point. The approach overcomes the difficulties encountered by others on the treatment of contact velocity reversals and negative energy losses. A classical problem is solved; the initial velocities are presumed known and the final velocities unknown. The interaction process between the two bodies is modeled using two coefficients. These are the classical coefficient of restitution, e, and the ratio, μ, of tangential to normal impulses. The latter quantity can be a coefficient of friction as a special case. The paper reveals that these coefficients have a much broader intepretation than previously recognized in the solution of collision problems. The appropriate choice of values for μ is related to the energy loss of the collision. It is shown that μ is bounded by values which correspond to no sliding at separation and conservation of energy. Another bound on μ combined with limits on the coefficient e, provides an overall bound on the energy loss of a collision. Examples from existing mechanics literature are solved to illustrate the significance of the coefficients and their relationship to the energy loss of collisions.

Robust contact force estimation for robot manipulators in three-dimensional space

2006 ◽  
Vol 220 (9) ◽  
pp. 1317-1327 ◽  
Author(s):  
J Jung ◽  
J Lee ◽  
K Huh
Keyword(s):  
Contact Force ◽  
Robot Manipulator ◽  
Robot Manipulators ◽  
Dimensional Space ◽  
Three Dimensional ◽  
Contact Forces ◽  
Robust Estimator ◽  
Force Sensors ◽  
Force Estimation ◽  
Estimation Algorithms

Information on contact forces in robot manipulators is indispensable for fast and accurate force control. Instead of expensive force sensors, estimation algorithms for contact forces have been widely developed. However, it is not easy to obtain the accurate values due to uncertainties. In this article, a new robust estimator is proposed to estimate three-dimensional contact forces acting on a three-link robot manipulator. The estimator is based on the extended Kalman filter (EKF) structure combined with a Lyapunov-based adaptation law for estimating the contact force. In contrast to the conventional EKF the new estimator is designed such that it is robust to the deterministic uncertainties such as the modelling error and the sensing bias. The performance of the proposed estimator is evaluated through simulations of a robot manipulator and demonstrates robustness in estimating the contact force. The estimation results show that it can be potentially used to replace the expensive force sensors in robot applications.

Contact Force Analysis in Static Two-Fingered Robot Grasping

2013 ◽  
Author(s):  
I Cheng ◽  
C. H. Liu ◽  
Yin-Tien Wang
Keyword(s):  
Rigid Bodies ◽  
The Body ◽  
Contact Forces ◽  
Contact Theory ◽  
Force Analysis ◽  
Equilibrium Solutions ◽  
Spherical Object ◽  
Closed Form Solutions ◽  
Robot Grasping ◽  
Force Displacement

Static grasping of a spherical object by two robot fingers is studied in this paper. The fingers may be rigid bodies or elastic beams, they may grasp the body with various orientation angles, and the tightening displacements may be linear or angular. Closed-form solutions for normal and tangential contact forces due to tightening displacements are obtained by solving compatibility equations, force-displacement relations based on Hertz contact theory, and equations of equilibrium. Solutions show that relations between contact forces and tightening displacements depend upon the orientation of the fingers, the elastic constants of the materials, and area moments of inertia of the beams.

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