Applying Strip Theory Based Linear Seakeeping Loads to 3D Full Ship Finite Element Models

2013 ◽  
Author(s):  
Chengbi Zhao ◽  
Ming Ma ◽  
Owen Hughes
Keyword(s):  
Finite Element ◽  
Structural Model ◽  
Velocity Potential ◽  
Structural Models ◽  
Vertical Shear ◽  
Finite Element Models ◽  
3D Finite Element ◽  
Hull Girder ◽  
Strip Theory ◽  
Extreme Load

Panel based hydrodynamic analyses are well suited for transferring seakeeping loads to 3D FEM structural models. However, 3D panel based hydrodynamic analyses are computationally expensive. For monohull ships, methods based on strip theory have been successfully used in industry for many years. They are computationally efficient, and they provide good prediction for motions and hull girder loads. However, many strip theory methods provide only hull girder sectional forces and moments, such as vertical bending moment and vertical shear force, which are difficult to apply to 3D finite element structural models. For the few codes which do output panel pressure, transferring the pressure map from a hydrodynamic model to the corresponding 3D finite element model often results in an unbalanced structural model because of the pressure interpolation discrepancy. To obtain equilibrium of an imbalanced structural model, a common practice is to use the “inertia relief” approach to rebalance the model. However, this type of balancing causes a change in the hull girder load distribution, which in turn could cause inaccuracies in an extreme load analysis (ELA) and a spectral fatigue analysis (SFA). This paper presents a method of applying strip theory based linear seakeeping pressure loads to balance 3D finite element models without using inertia relief. The velocity potential of strip sections is first calculated based on hydrodynamic strip theories. The velocity potential of a finite element panel is obtained from the interpolation of the velocity potential of the strip sections. The potential derivative along x-direction is computed using the approach proposed by Salvesen, Tuck and Faltinsen. The hydrodynamic forces and moments are computed using direct panel pressure integration from the finite element structural panel. For forces and moments which cannot be directly converted from pressure, such as hydrostatic restoring force and diffraction force, element nodal forces are generated using Quadratic Programing. The equations of motions are then formulated based on the finite element wetted panels. The method results in a perfectly balanced structural model.

A Hybrid 2.5-Dimensional High-Speed Strip Theory Method and Its Application to Apply Pressure Loads to 3-Dimensional Full Ship Finite Element Models

2016 ◽  
Vol 32 (04) ◽  
pp. 216-225
Author(s):  
Chengbi Zhao ◽  
Ming Ma
Keyword(s):  
Finite Element ◽  
High Speed ◽  
Hybrid Approach ◽  
Structural Models ◽  
Vertical Shear ◽  
Theory Method ◽  
3D Fem ◽  
3D Finite Element ◽  
Hull Girder ◽  
Strip Theory

As the three-dimensional (3D) finite element model (FEM) has become the de facto standard for ship structural design, interest in accurately transferring seakeeping loads to panel-based structural models has increased dramatically in recent years. In today's design practices, panel-based hydrodynamic analyses are often used for mapping seakeeping loads to 3D FEM structural models. However, 3D panel-based hydrodynamic analyses are computationally expensive. For monohull ships, methods based on strip theories have been successfully used in the industry for many years. They are computationally efficient, and provide good predictions for motions and hull girder loads. However, many strip theory methods provide only hull girder sectional forces and moments, such as vertical bending moment and vertical shear force, which are difficult to apply to 3D finite element structural models. Previously, the authors have proposed a hybrid strip theory method to transfer 2D strip theory-based seakeeping loads to 3D FEM. In the hybrid approach, the velocity potentials of strip sections are first calculated based on the ordinary 2D strip theories. The velocity potentials of a finite element panel are obtained from the interpolation of the velocity potentials of the strip sections. The panel pressures are then computed based on Bernoulli's equation. Integration of the pressure over the FEM wetted panels yields the hydrodynamic forces and moments. The equations of motion are then formulated based on the FEM. The method not only produces excellent ship motion results, but also results in a perfectly balanced structural model. In this article, the hybrid approach is extended to the 2.5D high-speed strip theory. The simple Rankine source function is used to compute velocity potentials. The original linearized free surface condition, where the forward speed term is not ignored, is used to formulate boundary integral equations. A model based on the Series-64 hull form was used for validating the proposed hybrid method. The motion response amplitude operators are in good agreement with VERES's 2.5D strip theory and with experimental results. Finally, an example is provided for transferring seakeeping loads obtained by the 2.5D hybrid strip theory to a 3D FEM.

A Hybrid 2.5D High Speed Strip Theory Method and its Application to Apply Pressure Loads to 3D Full Ship Finite Element Models

2014 ◽  
Author(s):  
Chengbi Zhao ◽  
Ming Ma
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
High Speed ◽  
Hybrid Approach ◽  
Structural Models ◽  
Element Model ◽  
3D Finite Element ◽  
Hull Girder ◽  
Strip Theory ◽  
The Finite Element Model

As the three-dimensional finite element model has become the de facto standard for ship structural design, interest in accurately transferring seakeeping loads to panel based structural models has increased dramatically in recent years. In today’s design practices, panel based hydrodynamic analyses are often used for mapping seakeeping loads to 3D FEM structural models. However, 3D panel based hydrodynamic analyses are computationally expensive. For monohull ships, methods based on strip theories have been successfully used in the industry for many years. They are computationally efficient, and provide good predictions for motions and hull girder loads. However, many strip theory methods provide only hull girder sectional forces and moments, such as vertical bending moment and vertical shear force, which are difficult to apply to 3D finite element structural models. Previously, the authors have proposed a hybrid strip theory method to transfer 2D strip theory based seakeeping loads to 3D finite element models. In the hybrid approach, the velocity potentials of strip sections are first calculated based on the ordinary 2D strip theories. The velocity potentials of a finite element panel are obtained from the interpolation of the velocity potentials of the strip sections. The panel pressures are then computed based on Bernoulli’s equation. Integration of the pressure over the finite element model wetted panels yields the hydrodynamic forces and moments. The equations of motion are then formulated based on the finite element model. The method not only produces excellent ship motion results, but also results in a perfectly balanced structural model. In this paper, the hybrid approach is extended to the 2.5D high speed strip theory. The simple Rankine source function is used to compute velocity potentials. The original linearized free surface condition, where the forward speed term is not ignored, is used to formulate boundary integral equations. A model based on the Series-64 hull form was used for validating the proposed hybrid method. The motion RAOs are in good agreement with VERES’s 2.5D strip theory and with experimental results. Finally, an example is provided for transferring seakeeping loads obtained by the 2.5D hybrid strip theory to a 3D finite element model.

The Collagen Fiber Kinematics in the Anteroinferior Glenohumeral Capsule Are Not Affine-Predicted

2011 ◽  
Author(s):  
Carrie A. Voycheck ◽  
Patrick J. McMahon ◽  
Richard E. Debski
Keyword(s):  
Finite Element ◽  
Structural Model ◽  
Glenohumeral Joint ◽  
Structural Models ◽  
Clinical Problem ◽  
Collagen Fibers ◽  
Material Behavior ◽  
Finite Element Models ◽  
Glenohumeral Ligament ◽  
Glenohumeral Capsule

Glenohumeral dislocation is a significant clinical problem and often results in injury to the anteroinferior (anterior band of the inferior glenohumeral ligament (AB-IGHL) and axillary pouch) glenohumeral capsule. [1] However, clinical exams to diagnose capsular injuries are not reliable [2] and poor patient outcome still exists following repair procedures. [3] Validated finite element models of the glenohumeral capsule may be able to improve diagnostic and repair techniques; however, improving the accuracy of these models requires adequate constitutive models to describe capsule behavior. The collagen fibers in the anteroinferior capsule are randomly oriented [4], thus the material behavior of the glenohumeral capsule has been described using isotropic models. [5,6] A structural model consisting of an isotropic matrix embedded with randomly aligned collagen fibers proved to better predict the complex capsule behavior than an isotropic phenomenological model [7] indicating that structural models may improve the accuracy of finite element models of the glenohumeral joint. Many structural models make the affine assumption (local fiber kinematics follow global tissue deformation) however an approach to account for non-affine fiber kinematics in structural models has been recently developed [8]. Evaluating the affine assumption for the capsule would aid in developing an adequate constitutive model. Therefore, the objective of this work was to assess the affine assumption of fiber kinematics in the anteroinferior glenohumeral capsule by comparing experimentally measured preferred fiber directions to the affine-predicted fiber directions.

EFFECT OF FACE COOLING ON WORKPIECE TEMPERATURES USING 2D AND 3D FINITE ELEMENT ANALYSIS OF CREEP-FEED GRINDING

2008 ◽  
Vol 32 (3-4) ◽  
pp. 439-452 ◽  
Author(s):  
David Anderson ◽  
Andrew Warkentin ◽  
Robert Bauer
Keyword(s):  
Finite Element ◽  
Steady State ◽  
Contact Temperature ◽  
Grinding Wheel ◽  
Finite Element Models ◽  
3D Finite Element ◽  
Creep Feed ◽  
2D And 3D ◽  
Maximum Contact ◽  
Face Cooling

This work uses validated 2D and 3D finite element models of the creep-feed grinding operation to study the effects of face cooling on the workpiece temperatures. The results show that as the intensity of the face cooling is increased the maximum contact temperature decreases and the location of the maximum contact temperature shifts away from the finished workpiece material and towards the uncut workpiece surface. The finite element models are also used to study the maximum temperatures along the workpiece during a complete grinding pass. The temperature profiles show that there are four important temperature features on the workpiece, which are the cut-in, steady-state, temperature spike, and cut-out zones. Cut-in occurs when the grinding wheel initially engages the workpiece, steady-state occurs in the middle of the workpiece, the temperature spike occurs at the beginning of cut-out, and cut-out occurs as the grinding wheel disengages from the workpiece. Finally, the results show that face cooling need only be applied to the area immediately adjacent to the contact zone to be effective and that there is very little benefit to applying coolant to the entire front and back workpiece faces.

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