scholarly journals Mechanical models in computational form finding of bending-active structures

2018 ◽  
Vol 33 (2) ◽  
pp. 86-97 ◽  
Author(s):  
Carlos Lázaro ◽  
Juan Bessini ◽  
Salvador Monleón
Keyword(s):  
Three Dimensional ◽  
Beam Theory ◽  
Task Type ◽  
Degree Of Freedom ◽  
Complex Nature ◽  
Dynamic Relaxation ◽  
Form Finding ◽  
Beam Elements ◽  
Active Structures ◽  
Computational Form

This article reviews the different aspects involved in computational form finding of bending-active structures based on the dynamic relaxation technique. Dynamic relaxation has been applied to form-finding problems of bending-active structures in a number of references. Due to the complex nature of large spatial deformations of flexible beams, the implementation of suitable mechanical beam models in the dynamic relaxation algorithm is a non-trivial task. Type of discretization and underlying beam theory have been identified as key aspects for numerical implementations. References can be classified into two groups depending on the selected discretization: finite-difference-like and finite-element-like. The first group includes 3- and 4-degree-of-freedom implementations based on increasingly complex beam models. The second gathers 6-degree-of-freedom discretizations based on co-rotational three-dimensional Kirchhoff–Love beam elements and geometrically exact Reissner–Simo beam elements. After reviewing and comparing implementation details, the advantages and drawbacks of each group have been discussed, and open aspects for future work have been pointed out.

scholarly journals A fast and accurate dynamic relaxation approach for form-finding and analysis of bending-active structures

2019 ◽  
Vol 34 (1-2) ◽  
pp. 40-53
Author(s):  
Jef Rombouts ◽  
Geert Lombaert ◽  
Lars De Laet ◽  
Mattias Schevenels
Keyword(s):  
Computation Time ◽  
High Accuracy ◽  
Dynamic Relaxation ◽  
Time Step ◽  
Form Finding ◽  
Form Complex ◽  
Beam Elements ◽  
Active Structures ◽  
Newton Raphson ◽  
Raphson Method

Active bending is an increasingly popular construction technique that uses elastically bent structural members to form complex curved shapes. The design and analysis of bending-active structures requires an accurate simulation of the bending process, which is often complicated by the occurrence of large displacements. In this article, we propose to combine a previously developed implicit dynamic relaxation method with co-rotational beam elements to obtain a fast and accurate method for form-finding and analysis of bending-active structures. This approach is applied to four test cases. Implicit dynamic relaxation is compared to the classic Newton–Raphson method and conventional dynamic relaxation. The results show that the proposed implicit dynamic relaxation approach can be stabilized intuitively by changing the time step and damping ratio, making it more stable than the classic Newton–Raphson method. Moreover, the proposed approach converges fast compared to the conventional dynamic relaxation: the total computation time is considerably lower, even though the computation time per iteration is higher. Finally, a high accuracy is achieved due to the use of co-rotational beam elements. The combination of high accuracy and low computation time makes this approach well-suited for both form-finding and analysis of bending-active structures.

Three-Dimensional reconstruction of isolated centrosomes by automated electron tomography

1994 ◽  
Vol 52 ◽  
pp. 310-311
Author(s):  
M.B. Braunfeld ◽  
M. Moritz ◽  
B.M. Alberts ◽  
J.W. Sedat ◽  
D.A. Agard
Keyword(s):  
Electron Tomography ◽  
Three Dimensional ◽  
Vital Role ◽  
Complex Nature ◽  
Animal Cells ◽  
Microtubule Organizing Center ◽  
Nucleation Sites ◽  
Dimensional Reconstruction ◽  
Organizing Center ◽  
Resolution Model

In animal cells, the centrosome functions as the primary microtubule organizing center (MTOC). As such the centrosome plays a vital role in determining a cell's shape, migration, and perhaps most importantly, its division. Despite the obvious importance of this organelle little is known about centrosomal regulation, duplication, or how it nucleates microtubules. Furthermore, no high resolution model for centrosomal structure exists.We have used automated electron tomography, and reconstruction techniques in an attempt to better understand the complex nature of the centrosome. Additionally we hope to identify nucleation sites for microtubule growth.Centrosomes were isolated from early Drosophila embryos. Briefly, after large organelles and debris from homogenized embryos were pelleted, the resulting supernatant was separated on a sucrose velocity gradient. Fractions were collected and assayed for centrosome-mediated microtubule -nucleating activity by incubating with fluorescently-labeled tubulin subunits. The resulting microtubule asters were then spun onto coverslips and viewed by fluorescence microscopy.

scholarly journals Compressive behaviours of octet-truss lattices

2020 ◽  
Vol 234 (16) ◽  
pp. 3257-3269 ◽  
Author(s):  
Yifan Li ◽  
Huaiyuan Gu ◽  
Martyn Pavier ◽  
Harry Coules
Keyword(s):  
Failure Modes ◽  
Density Ratio ◽  
Three Dimensional ◽  
Compressive Load ◽  
High Strength ◽  
Detailed Comparison ◽  
Compressive Response ◽  
Beam Elements ◽  
Structural Applications ◽  
Octet Truss

Octet-truss lattice structures can be used for lightweight structural applications due to their high strength-to-density ratio. In this research, octet-truss lattice specimens were fabricated by stereolithography additive manufacturing with a photopolymer resin. The mechanical properties of this structure have been examined in three orthogonal orientations under the compressive load. Detailed comparison and description were carried out on deformation mechanisms and failure modes in different lattice orientations. Finite element models using both beam elements and three-dimensional solid elements were used to simulate the compressive response of this structure. Both the load reaction and collapse modes obtained in simulations were compared with test results. Our results indicate that three-dimensional continuum element models are required to accurately capture the behaviour of real trusses, taking into account the effects of finite-sized beams and joints.

New Type of Two Degree of Freedom Motor Three-Dimensional Tooth Layer Field Application and Solution

2013 ◽  
Vol 391 ◽  
pp. 232-236
Author(s):  
Wen Huan Yang ◽  
Hai Xu Chen ◽  
Shuang Xie ◽  
Chun Ren Fang
Keyword(s):  
Linear Equations ◽  
Three Dimensional ◽  
Field Application ◽  
Degree Of Freedom ◽  
Refined Method ◽  
New Type ◽  
Type Motor ◽  
Quasi Newton ◽  
Two Degree Of Freedom ◽  
Non Linear Equations

A new Multi-degree of freedom motor and its establishing of teeth layer parameters have been introduced in the paper, also including application method of database, namely using Quasi-Newton methods to solve the non-linear equations of the new motors magnetic circuit net, formed a refined method for designing and analyzing of motor. The establishment of 3d tooth layer parameters database, is provided for the calculation in the design of the new type motor conveniently.

Modeling of a One-Sided Bonded and Rigid Constraint Using Beam Theory

2008 ◽  
Vol 75 (3) ◽  
Author(s):  
Peter J. Ryan ◽  
George G. Adams ◽  
Nicol E. McGruer
Keyword(s):  
Boundary Conditions ◽  
Microelectromechanical Systems ◽  
Three Dimensional ◽  
Beam Theory ◽  
Rotational Stiffness ◽  
Element Analysis ◽  
Transverse Loads ◽  
Rigid Constraint ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

In beam theory, constraints can be classified as fixed/pinned depending on whether the rotational stiffness of the support is much greater/less than the rotational stiffness of the freestanding portion. For intermediate values of the rotational stiffness of the support, the boundary conditions must account for the finite rotational stiffness of the constraint. In many applications, particularly in microelectromechanical systems and nanomechanics, the constraints exist only on one side of the beam. In such cases, it may appear at first that the same conditions on the constraint stiffness hold. However, it is the purpose of this paper to demonstrate that even if the beam is perfectly bonded on one side only to a completely rigid constraining surface, the proper model for the boundary conditions for the beam still needs to account for beam deformation in the bonded region. The use of a modified beam theory, which accounts for bending, shear, and extensional deformation in the bonded region, is required in order to model this behavior. Examples are given for cantilever, bridge, and guided structures subjected to either transverse loads or residual stresses. The results show significant differences from the ideal bond case. Comparisons made to a three-dimensional finite element analysis show a good agreement.

An Equivalent 3-D Method for Analyzing Orthogonally Stiffened Plate Structures

1987 ◽  
Vol 31 (02) ◽  
pp. 101-106
Author(s):  
Kyu Nam Cho ◽  
William S. Vorus
Keyword(s):  
Bridge Decks ◽  
Three Dimensional ◽  
Stiffened Plate ◽  
Plate Structures ◽  
Work Related ◽  
Beam Elements ◽  
Proposed Model ◽  
The Relationship

A new three-dimensional method is proposed for analyzing orthogonally stiffened grillage structures. The method is based on earlier work related to bridge decks. The relationship between system displacement and loads is described mathematically, and matrices are developed to examine the shear compatibility between plate and beam elements. The paper concludes with a comparison between deflections obtained by several different procedures and the proposed model.

Force-based delay compensation for hardware-in-the-loop simulation divergence of 6-DOF space contact

2017 ◽  
Vol 233 (1) ◽  
pp. 151-165
Author(s):  
Qian Wang ◽  
Chenkun Qi ◽  
Feng Gao ◽  
Xianchao Zhao ◽  
Anye Ren ◽  
...  
Keyword(s):  
Dynamic Model ◽  
Dynamic Models ◽  
Contact Process ◽  
Three Dimensional ◽  
Compensation Method ◽  
Degree Of Freedom ◽  
Hardware In The Loop ◽  
Delay Compensation ◽  
Measurement Delay ◽  
Six Degree Of Freedom

The contact process of a space docking device needs verification before launching. The verification cannot only rely on the software simulation since the contact dynamic models are not accurate enough yet, especially when the geometric shape of the device is complex. Hardware-in-the-loop simulation is a choice to perform the ground test, where the contact dynamic model is replaced by a real device and the real contact occurs. However, the Hardware-in-the-loop simulation suffers from energy increase and instability since time delay is unavoidable. The existing delay compensation methods are mainly focused on a uniaxial or three-dimensional contact. In this paper, a force-based delay compensation method is proposed for the hardware-in-the-loop simulation of a six degree-of-freedom space contact. A six degree-of-freedom dynamic model of the spacecraft motion is derived, and a six degree-of-freedom delay compensation method is proposed. The delay is divided into track delay and measurement delay, which are compensated individually. Experiment results show that the proposed delay compensation method is effective for the six degree-of-freedom space contact.

Engineering Analysis of Shoulder Dystocia in the Human Birth Process by the Finite Element Method

1992 ◽  
Vol 206 (4) ◽  
pp. 243-250 ◽  
Author(s):  
A Meghdari ◽  
R Davoodi ◽  
F Mesbah
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
Shoulder Dystocia ◽  
Point Of View ◽  
Engineering Analysis ◽  
The Finite Element Method ◽  
Birth Process ◽  
Beam Elements ◽  
Finite Element Package ◽  
Human Birth

This paper presents an engineering analysis of shoulder dystocia (SD) in the human birth process which usually results in damaging the brachial plexus nerves and the humerus and/or clavicle bones of the baby. The goal is to study these injuries from the mechanical engineering point of view. Two separate finite element models of the neonatal neck and the clavicle bone have been simulated using eight-node three-dimensional elements and beam elements respectively. Simulated models have been analysed under suitable boundary conditions using the ‘SAP80’ finite element package. Finally, results obtained have been verified by comparing them with published clinical and experimental observations.

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