Langevin dynamic simulations of fast remagnetization processes in ferrofluids with internal magnetic degrees of freedom

2006 ◽  
Vol 18 (38) ◽  
pp. S2595-S2621 ◽  
Author(s):  
D V Berkov ◽  
N L Gorn ◽  
R Schmitz ◽  
D Stock
Keyword(s):  
Degrees Of Freedom ◽  
Dynamic Simulations ◽  
Langevin Dynamic

scholarly journals Jumping in frogs: assessing the design of the skeletal system by anatomically realistic modeling and forward dynamic simulation

2002 ◽  
Vol 205 (12) ◽  
pp. 1683-1702 ◽  
Author(s):  
William J. Kargo ◽  
Frank Nelson ◽  
Lawrence C. Rome
Keyword(s):  
Degrees Of Freedom ◽  
The Body ◽  
Joint Torque ◽  
Rotational Degree ◽  
Skeletal System ◽  
Dynamic Simulations ◽  
Inverse Dynamic ◽  
Maximal Distance ◽  
Out Of Plane ◽  
Rotational Degrees Of Freedom

SUMMARY Comparative musculoskeletal modeling represents a tool to understand better how motor system parameters are fine-tuned for specific behaviors. Frog jumping is a behavior in which the physical properties of the body and musculotendon actuators may have evolved specifically to extend the limits of performance. Little is known about how the joints of the frog contribute to and limit jumping performance. To address these issues, we developed a skeletal model of the frog Rana pipiens that contained realistic bones, joints and body-segment properties. We performed forward dynamic simulations of jumping to determine the minimal number of joint degrees of freedom required to produce maximal-distance jumps and to produce jumps of varied take-off angles. The forward dynamics of the models was driven with joint torque patterns determined from inverse dynamic analysis of jumping in experimental frogs. When the joints were constrained to rotate in the extension—flexion plane, the simulations produced short jumps with a fixed angle of take-off. We found that, to produce maximal-distance jumping,the skeletal system of the frog must minimally include a gimbal joint at the hip (three rotational degrees of freedom), a universal Hooke's joint at the knee (two rotational degrees of freedom) and pin joints at the ankle,tarsometatarsal, metatarsophalangeal and iliosacral joints (one rotational degree of freedom). One of the knee degrees of freedom represented a unique kinematic mechanism (internal rotation about the long axis of the tibiofibula)and played a crucial role in bringing the feet under the body so that maximal jump distances could be attained. Finally, the out-of-plane degrees of freedom were found to be essential to enable the frog to alter the angle of take-off and thereby permit flexible neuromotor control. The results of this study form a foundation upon which additional model subsystems (e.g. musculotendon and neural) can be added to test the integrative action of the neuromusculoskeletal system during frog jumping.

Using a Redundant Planar Hip Exoskeleton to Reduce Human-Device Interface Forces

2017 ◽  
Author(s):  
David Schmitthenner ◽  
Samuel H. Shoemaker ◽  
Anne E. Martin
Keyword(s):  
Soft Tissue ◽  
Hip Joint ◽  
Degrees Of Freedom ◽  
Shear Forces ◽  
Dynamic Simulations ◽  
Lower Shear ◽  
Human Soft Tissue ◽  
Priority Method ◽  
Joint Center ◽  
Human Device

Robotic exoskeletons have the potential to improve gait rehabilitation. Currently, most exoskeletons use revolute joints that must be exactly aligned with the user’s joints to prevent uncomfortable shear forces at the human-device interface. This paper presents an alternative design for a planar hip exoskeleton based on a planar Stewart platform. In theory, this mechanism does not require exact knowledge of the human hip joint center of rotation to prevent large shear forces. The total human-device system has four degrees of freedom if the human soft tissue is neglected, which does complicate the control of the system compared to a rotational exoskeleton. To find a mapping between the desired human hip angle and the four actuated joints, the task priority method is used. To determine how well the proposed device can guide the hip through a step, dynamic simulations were conducted and compared to the results for a rotational exoskeleton. The compliance in the human soft tissue was included in the simulations because it can play a significant role in both the motion of the system and the human-device forces. Both the ideal case of exact hip joint alignment and the more likely case of hip joint misalignment were considered. In addition, the effects of differing levels of human effort were compared. In all cases, both exoskeletons were well able to guide the human hip in the desired motion. In addition, the novel exoskeleton has significantly lower shear forces at the thigh human-device connection point.

Design and locomotion analysis of a novel deformable mobile robot with two spatial reconfigurable platforms and three kinematic chains

2016 ◽  
Vol 231 (8) ◽  
pp. 1481-1499 ◽  
Author(s):  
Wan Ding ◽  
Qiang Ruan ◽  
Yan-an Yao
Keyword(s):  
Mobile Robot ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Three Dimensional Model ◽  
Dynamic Simulations ◽  
Gait Planning ◽  
Plane Symmetric ◽  
Kinematic Chains ◽  
Reconfigurable Platforms ◽  
Actuation Systems

A novel five degrees of freedom deformable mobile robot composed of two spatial reconfigurable platforms and three revolute–prismatic–spherical kinematic chains acting in parallel to link the two platforms is proposed to realize large deformation capabilities and multiple locomotion modes. Each platform is an improved deployable single degrees of freedom three-plane-symmetric Bricard linkage. By taking advantage of locomotion collaborating among platforms and kinematic chains, the mobile robot can fold into stick-like shape and possess omnidirectional rolling and worm-like motions. The mechanism design, kinematics, and locomotion feasibility are the main focus. Through kinematics and gait planning, the robot is analyzed to have the capabilities of rolling and turning. Based on its deformation, the worm-like motion performs the ability to overcome narrow passages (such as pipes, holes, gaps, etc.) with large range of variable size. Dynamic simulations with detailed three-dimensional model are carried out to verify the gait planning and provide the variations of essential motion and dynamic parameters in each mode. An experimental robotic system with servo and pneumatic actuation systems is built, experiments are carried out to verify the validity of the theoretical analysis and the feasibility of the different locomotion functions, and its motion performances are compared and analyzed with collected data.

Research of Trajectory Planning of a High-Altitude Long-Range Gliding Unmanned Underwater Vehicle

2014 ◽  
Vol 519-520 ◽  
pp. 1313-1320
Author(s):  
Guang Pan ◽  
Huan Huan Liu
Keyword(s):  
High Altitude ◽  
Long Range ◽  
Degrees Of Freedom ◽  
Underwater Vehicle ◽  
Water Entry ◽  
Dynamic Simulations ◽  
Six Degrees Of Freedom ◽  
Unmanned Underwater Vehicle ◽  
The One ◽  
Air Trajectory

The air trajectory planned studied of the high-altitude long-range gliding unmanned underwater vehicle (HALRG-UUV) based on segmented control strategy is proposed. The aim of this research is twofold. On the one hand, specifying an altitude penetration strategy at the end of the gliding stage was presented with the aim of improving the vehicle glide ratio and achieving penetration. On the other hand, a rocket deceleration strategy was applied to adjust the speed and attitude of the vehicle in order to meet the water entry requirement. Besides, six-degrees-of-freedom mathematical model of the HALRG-UUV was developed based on the Newton’s law. Dynamic simulations of the vehicle under various conditions were performed with the aid of the MATLAB/Simulink codes. The result shows that the vehicle has a glide ratio of 1/9 in the air trajectory and meets the water entry requirement above water. This study lays the foundation for the further research of maneuverability and water impact of the vehicle.

ON THE POSSIBILITY OF THE POSTTRANSITION STATE CLASSICAL TRAJECTORY PREDICTIONS OF ENERGY DEPOSITION IN THE REACTION PRODUCTS' DEGREES OF FREEDOM

2020 ◽  
Author(s):  
B. I. Loukhovitski ◽  
◽  
A. S. Sharipov ◽  
Keyword(s):  
Energy Distribution ◽  
Degrees Of Freedom ◽  
Energy Deposition ◽  
Classical Trajectory ◽  
Reaction Products ◽  
Dynamic Simulations ◽  
Bimolecular Reactions

The possibility of applying the method of posttransition state classical trajectory dynamic simulations to study the nascent energy distribution among the molecular degrees of freedom of the reaction products on the example of a number of bimolecular reactions is considered.

Semiactive Control of Multiple Degree of Freedom Systems

1997 ◽  
Author(s):  
Mehdi Ahmadian
Keyword(s):  
Degrees Of Freedom ◽  
Hybrid Control ◽  
Control Policy ◽  
The Body ◽  
Semiactive Control ◽  
Dynamic Simulations ◽  
Passive Dampers ◽  
Suspension Model ◽  
The Cost ◽  
Resonance Control

Abstract Semiactive control of systems with multiple degrees of freedom is addressed. Two systems representing a pitch-plane model of a vehicle and a single suspension are used to illustrate the results. The dynamic simulations show the well-known compromise between resonance control and isolation, due to passive dampers. It is shown that semiactive dampers also compromise between controlling different bodies. For skyhook and groundhook control policies, the control of one body is achieved at the cost of less control on the other bodies. For instance, in a single suspension model, skyhook semiactive dampers better control the body resonance, but significantly increase the axle resonance (wheelhop). The groundhook dampers provide a better control of wheelhop at the expense of increasing body resonance. A hybrid control policy that combines the effect of skyhook and groundhook policies is introduced. This policy can be used to provide the proper control on all bodies, while using the hardware common to existing semiactive dampers.

The Influence of Hold-Back Vessels on the Operation of a DP Drilling Rig: Control System and Stability Analysis

2017 ◽  
Author(s):  
Alex S. Huang ◽  
Eduardo Aoun Tannuri ◽  
Asdrubal N. Queiroz Filho ◽  
André S. S. Ianagui ◽  
Douglas G. T. Yuba ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Dynamic Instability ◽  
Simplified Model ◽  
Fast Time ◽  
Dynamic Simulations ◽  
Positioning Systems ◽  
Time Dynamic ◽  
Drilling Rig ◽  
The Stability ◽  
Drilling Rigs

Certain maritime operations require the accurate positioning of the vessel, and in order to accomplish that DP (dynamic positioning) systems were developed. It combines the information obtained from sensors with the expected dynamic of the ship to better estimate its actual position and the external forces, and with those information the controller allocates the forces among the available actuators so the vessel keeps a desired position. In situations where drift of the vessel could cause great harm (human, material or environmental losses) it might be necessary to provide additional safeguards. One possible solution is to connect an AHTS (anchor handling tug supply) to the original DP vessel, in order to complement the forces generated by its thrusters. However as shown by Jensen (2008) and IMCA M 185 (2012), this connection could actually degrade the position keeping ability of the vessel, nullifying the purpose of improving the safety of the operation. The objective of the present paper is to confirm the hypothesis that the use of hold-back vessels to support DP drilling rigs may degrade the performance of the DP system, causing dynamic instability, and to determine the boundaries of operation under which this phenomenon occurs: sea state, parameters of the vessels and force transmitted by the hold-back vessel. Firstly, an analytical study of the system was done. It was considered a simplified model of two vessels connected by a cable with two degrees of freedom (one for each vessel), since the force applied by a cable is unidirectional. Using control theory, the limiting stiffness of the cable was determined by analyzing the poles of the system. Considering a catenary model for the connecting cable, it was possible to determine the maximum force that could be transmitted between the vessels without the system becoming unstable. The influence of the Kalman Filter in the stability of the system was also studied. Those results were then compared and confirmed with fast time dynamic simulations of the system, in which the influence of different environmental conditions were also added to the analysis. To complete the study, real time simulations were done on a full mission simulator, equipped with the original Kongsberg DP system for the drilling rig. The simplified model showed consistent results, validated by the simulations, demonstrating it can be a useful tool when analyzing the stability of two connected vessels.

Two-Temperature Thermodynamics for Metal Viscoplasticity: Continuum Modeling and Numerical Experiments

2016 ◽  
Vol 84 (1) ◽  
Author(s):  
Shubhankar Roy Chowdhury ◽  
Gurudas Kar ◽  
Debasish Roy ◽  
J. N. Reddy
Keyword(s):  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Internal Variable ◽  
Thermodynamic System ◽  
Internal Variables ◽  
Face Centered Cubic ◽  
Dynamic Simulations ◽  
Face Centered ◽  
Atomic Lattices ◽  
Two Temperature

A physics-based model for dislocation mediated thermoviscoplastic deformation in metals is proposed. The modeling is posited in the framework of internal-variables theory of thermodynamics, wherein an effective dislocation density, which assumes the role of the internal variable, tracks permanent changes in the internal structure of metals undergoing plastic deformation. The thermodynamic formulation involves a two-temperature description of viscoplasticity that appears naturally if one considers the thermodynamic system to be composed of two weakly interacting subsystems, namely, a kinetic-vibrational subsystem of the vibrating atomic lattices and a configurational subsystem of the slower degrees-of-freedom (DOFs) of defect motion. Starting with an idealized homogeneous setup, a full-fledged three-dimensional (3D) continuum formulation is set forth. Numerical exercises, specifically in the context of impact dynamic simulations, are carried out and validated against experimental data. The scope of the present work is, however, limited to face-centered cubic (FCC) metals only.

Dynamic Comparison of a 3-Degrees-of-Freedom Parallel Manipulator With Multiple Dry Clearance Joints and With Lubricated Joints

2018 ◽  
Author(s):  
Haodong Zhang ◽  
Xianmin Zhang ◽  
Xuchong Zhang ◽  
Zhenhui Zhan
Keyword(s):  
Parallel Manipulator ◽  
Degrees Of Freedom ◽  
Dynamic Performance ◽  
Hydrodynamic Forces ◽  
Force Model ◽  
Dynamic Simulations ◽  
Clearance Joints ◽  
Significant Difference ◽  
Prismatic Joints ◽  
Lubricated Joints

This paper compares the dynamic response of a 3-degree-of-freedom (3-DOFs) parallel manipulator with multiple dry clearance joints and with lubricated joints. For this purpose, a methodology developed on Newton–Euler equations is proposed to study lubricated joints in the parallel manipulator, which involves the hydrodynamic forces and impact forces in the constrained equations. Specifically, the hydrodynamic forces are based on the Reynolds’ equation of an infinitely long lubricated joint. Dynamic simulations are presented through the dynamic parameters of a planar parallel manipulator (3-PRR, the underline of the P represents the actuated joint, P and R represents prismatic and revolute pairs respectively), which has six revolute clearance joints and three ideal prismatic joints. The results of the comparison show that the lubricant makes significant difference and greatly improves the dynamic performance of the parallel manipulator with multiple revolute joints. More periodic states are observed from the dynamic behavior of the parallel manipulator with lubricated joints, making the manipulator easier to drive. All results demonstrate the usage of the procedures which contain the hydrodynamic force model of multiple lubricated joints in non-linear DAEs of a 3-DOFs parallel manipulator.

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