Pitch-Heave Dynamics of a Segmented Skirt Air Cushion

2002 ◽  
Vol 46 (02) ◽  
pp. 121-137
Author(s):  
T.A. Graham ◽  
P.A. Sullivan
Keyword(s):  
Nonlinear Response ◽  
Experimental Validation ◽  
Basic Structure ◽  
Quantitative Agreement ◽  
Contact Forces ◽  
Test Model ◽  
Air Supply ◽  
Surface Contact ◽  
Air Cushion ◽  
Heave Motion

The formulation and experimental validation of a mathematical model of the nonlinear pitch-heave dynamics of an uncompartmented, segmented skirt cushion system for an air cushion vehicle are described. This system relies on surface contact to attain static stiffness in pitch and roll. The formulation includes a dynamic model of the lift air system, the effect of segment flexibility on effective cushion capacitance and on hovergap, and hysteretic skirt-surface contact forces. Predictions of linear stability and of nonlinear response to pitch disturbances are made for two skirt materials, the first generating considerable hysteresis in pitch stiffness, and the second having much greater extensibility but negligible hysteresis. These predictions are compared with experimental results obtained from a 900 kg test model. The basic structure of the system's stability characteristics are correctly predicted; this includes a nonlinear pitch-heave instability associated with coupling between pitch and heave motion, and with the modulation of the cushion volume by pitch motion. However, there remain unaccounted sources of cushion damping. This and other factors, such as sensitivity of the predicted results to the flexure of the panels that form the model air supply plenum, make close quantitative agreement between theory and experiment difficult to achieve.

scholarly journals Design and Calibration of a Force/Tactile Sensor for Dexterous Manipulation

Sensors ◽  
2019 ◽  
Vol 19 (4) ◽  
pp. 966 ◽  
Author(s):  
Marco Costanzo ◽  
Giuseppe De Maria ◽  
Ciro Natale ◽  
Salvatore Pirozzi
Keyword(s):  
Experimental Validation ◽  
Sensory System ◽  
Tactile Sensor ◽  
Contact Forces ◽  
Dexterous Manipulation ◽  
Soft Contact ◽  
Grasping Force ◽  
Sense Of Touch ◽  
Human Sense ◽  
Robotic Applications

This paper presents the design and calibration of a new force/tactile sensor for robotic applications. The sensor is suitably designed to provide the robotic grasping device with a sensory system mimicking the human sense of touch, namely, a device sensitive to contact forces, object slip and object geometry. This type of perception information is of paramount importance not only in dexterous manipulation but even in simple grasping tasks, especially when objects are fragile, such that only a minimum amount of grasping force can be applied to hold the object without damaging it. Moreover, sensing only forces and not moments can be very limiting to securely grasp an object when it is grasped far from its center of gravity. Therefore, the perception of torsional moments is a key requirement of the designed sensor. Furthermore, the sensor is also the mechanical interface between the gripper and the manipulated object, therefore its design should consider also the requirements for a correct holding of the object. The most relevant of such requirements is the necessity to hold a torsional moment, therefore a soft distributed contact is necessary. The presence of a soft contact poses a number of challenges in the calibration of the sensor, and that is another contribution of this work. Experimental validation is provided in real grasping tasks with two sensors mounted on an industrial gripper.

Dynamic Analysis and Configuration Design of a Two-Component Wave-Energy Absorber

2012 ◽  
Author(s):  
Christophe Cochet ◽  
Ronald W. Yeung
Keyword(s):  
Wave Energy ◽  
Degrees Of Freedom ◽  
Outer Cylinder ◽  
Rigid Body Dynamics ◽  
Contact Forces ◽  
Energy Extraction ◽  
Energy Absorber ◽  
Compound Cylinder ◽  
Motion Study ◽  
Heave Motion

The wave-energy absorber being developed at UC Berkeley is modeled as a moored compound cylinder, with an outer cylinder sliding along a tension-tethered inner cylinder. With rigid-body dynamics, it is first shown that the surge and pitch degrees of freedom are decoupled from the heave motion. The heaving motion of the outer cylinder is analyzed and its geometric proportions (radii and drafts ratios) are optimized for wave-energy extraction. Earlier works of Yeung [1] and Chau and Yeung [2,3] are used in the present heave-motion study. The coupled surge-pitch motion can be solved and can provide the contact forces between the cylinders. The concept of capture width is used to characterize the energy extraction: its maximization leads to optimal energy extraction. The methodology presented provides the optimal geometry in terms of non-dimensional proportions of the device. It is found that a smaller radius and deeper draft for the outer cylinder will lead to a larger capture width and larger resulting motion.

Drill Bit Contact Dynamics Including Side Cutting: Simulation and Validation

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Alfonso Callejo ◽  
Siamak Arbatani ◽  
József Kövecses ◽  
Masoud Kalantari ◽  
Nick R. Marchand
Keyword(s):  
Experimental Validation ◽  
Contact Forces ◽  
Contact Dynamics ◽  
Specific Method ◽  
Directional Drilling ◽  
Simulation Framework ◽  
Finite Segment ◽  
Oil Drilling ◽  
Simulation Techniques ◽  
Drilling Tools

Simulation techniques are increasingly becoming popular in recent years as a way of simulating oil drilling processes. Among them, directional drilling is a specific method that benefits enormously from such numerical techniques, inasmuch as the estimation of the wellbore curvature is crucial and cannot be properly estimated through approximate geometry methods. We present here some of the latest advances in bit contact dynamics, wellbore update algorithms, and experimental validation of side cutting, in the context of a finite element (FE) and finite segment simulation framework. The framework is based on the high-fidelity dynamic simulation of the mechanical system, including detailed geometry, large displacements, and accurate contact forces. The theoretical aspects, along with the experimental results, are thoroughly presented. Overall, this paper constitutes a step toward a more deterministic way of calculating build rates and designing downhole drilling tools.

scholarly journals Numerical and Experimental Validation of the Prototype of A Bio-Inspired Piping Inspection Robot

Robotics ◽  
2019 ◽  
Vol 8 (2) ◽  
pp. 32 ◽  
Author(s):  
Swaminath Venkateswaran ◽  
Damien Chablat ◽  
Frédéric Boyer
Keyword(s):  
Dry Friction ◽  
Experimental Validation ◽  
Closed Loop ◽  
Contact Forces ◽  
Force Model ◽  
Static Force ◽  
Force Analysis ◽  
Inspection Robot ◽  
Dc Motors ◽  
Inspection Robots

Piping inspection robots are of greater importance for industries such as nuclear, chemical and sewage. Mechanisms having closed loop or tree-like structures can be employed in such pipelines owing to their adaptable structures. A bio-inspired caterpillar type piping inspection robot was developed at Laboratoire des Sciences du Numérique de Nantes (LS2N), France. Using DC motors and leg mechanisms, the robot accomplishes the locomotion of a caterpillar in six-steps. With the help of Coulomb’s law of dry friction, a static force model was written and the contact forces between legs of robot and pipeline walls were determined. The actuator forces of the DC motors were then estimated under static phases for horizontal and vertical orientations of the pipeline. Experiments were then conducted on the prototype where the peak results of static force analysis for a given pipe diameter were set as threshold limits to attain static phases inside a test pipeline. The real-time actuator forces were estimated in experiments for similar orientations of the pipeline of static force models and they were found to be higher when compared to the numerical model.

scholarly journals Application and Experimental Validation of a Multibody Model with Weakly Coupled Lateral and Vertical Dynamics to a Scaled Railway Vehicle

Sensors ◽  
2020 ◽  
Vol 20 (13) ◽  
pp. 3700 ◽  
Author(s):  
Pedro Urda ◽  
Sergio Muñoz ◽  
Javier F. Aceituno ◽  
José L. Escalona
Keyword(s):  
Experimental Validation ◽  
Multibody System ◽  
Contact Forces ◽  
Railway Vehicle ◽  
Lateral Dynamics ◽  
Multibody Model ◽  
Weakly Coupled ◽  
Multibody Dynamic ◽  
Angular Velocities ◽  
The University

In this paper, a multibody dynamic model of a railway vehicle that assumes that vertical and lateral dynamics are weakly coupled, has been experimentally validated using an instrumented scaled vehicle running on a 5-inch-wide experimental track. The proposed linearised model treats the vertical and lateral dynamics of the multibody system almost independently, being coupled exclusively by the suspension forces. Several experiments have been carried out at the scaled railroad facilities at the University of Seville in order to test and validate the simulation model under different working conditions. The scaled vehicle used in the experiments is a bogie instrumented with various sensors that register the accelerations and angular velocities of the vehicle, its forward velocity, its position along the track, and the wheel–rail contact forces in the front wheelset. The obtained results demonstrate how the proposed computational model correctly reproduces the dynamics of the real mechanical system in an efficient computational manner.

Heave and Pitch Response of an Offshore Platform With Air Cushion Support in Shallow Water

2004 ◽  
Author(s):  
K. P. Thiagarajan ◽  
M. T. Morris-Thomas ◽  
A. Spargo
Keyword(s):  
Linear Wave ◽  
Test Results ◽  
Regular Waves ◽  
Long Wavelength ◽  
Air Cushion ◽  
Decay Tests ◽  
Heave Motion ◽  
The University ◽  
Scaled Models ◽  
Water Depths

Model tests were conducted on two 1:100 scaled models of a typical concrete gravity substructure at the University of Western Australia. The two models had dimensions 0.5m length × 0.5m width with the first model being a sealed closed bottom box of height 0.1m and the second model being an open bottom box with skirt length of 0.1m. The open bottom model had the capacity to hold an air cushion with dimensions 0.49m width × 0.49m length × 0.08m height. Each model was floated at a constant draft of 0.1m and tested in water depths ranging between 0.03m (shallow) and 0.8m (deep). The environment comprised of regular waves with periods ranging between 0.6s and 3.5s and amplitude of 0.08m–0.02m. To quantify the dynamic response the heave and pitch motion of each model were measured. The model test results were compared with a theoretical solution based on long wavelength, linear wave assumptions applied to a box shaped floating vessel without an internal free surface. Results show that experimental trends compare reasonably well with analytical solution. Added mass values were predicted from heave and pitch decay tests. The results show that introducing air cushion support into a CGS increases the pitch response, while having little effect of the heave motion. The theory is also used to delineate regions of safe and unsafe tow-out operations of the air cushion structure.

scholarly journals Simultaneous Kinematic and Contact Force Modeling of a Human Finger Tendon System Using Bond Graphs and Robotic Validation

2019 ◽  
Vol 142 (3) ◽  
Author(s):  
James A. Tigue ◽  
Raymond J. King ◽  
Stephen A. Mascaro
Keyword(s):  
Bond Graph ◽  
Contact Forces ◽  
Free Motion ◽  
Force Transmission ◽  
Bond Graphs ◽  
Moment Arms ◽  
Static Contact ◽  
Surface Contact ◽  
Bond Graph Modeling ◽  
Contact Experiments

Abstract This paper aims to use bond graph modeling to create the most comprehensive finger tendon model and simulation to date. Current models are limited to either free motion without external contact or fixed finger force transmission between tendons and fingertip. The forward dynamics model, presented in this work, simultaneously simulates the kinematics of tendon-finger motion and contact forces of a central finger given finger tendon inputs. The model equations derived from bond graphs are accompanied by nonlinear relationships modeling the anatomical complexities of moment arms, tendon slacking, and joint range of motion (ROM). The structure of the model is validated using a robotic testbed, Utah's Anatomically correct Robotic Testbed (UART) finger. Experimental motion of the UART finger during free motion (no external contact) and surface contact are simulated using the bond graph model. The contact forces during the surface contact experiments are also simulated. On average, the model was able to predict the steady-state pose of the finger with joint angle errors less than 6 deg across both free motion and surface contact experiments. The static contact forces were accurately predicted with an average of 11.5% force magnitude error and average direction error of 12 deg.

Collective dynamical properties of molten salts: molecular dynamics calculations on sodium chloride

1977 ◽  
Vol 357 (1688) ◽  
pp. 37-57 ◽  
Keyword(s):  
Molecular Dynamics ◽  
Memory Function ◽  
Basic Structure ◽  
Quantitative Agreement ◽  
Small Time ◽  
Static Structure ◽  
Memory Functions ◽  
Structure Factors ◽  
Molecular Dynamics Calculations ◽  
Molecular Dynamics Results

We present the results of molecular dynamics calculations on a system simulating molten NaCl at a temperature of 1090 K. Attention has been focused on the study of the collective modes, as described by the auto-correlation functions of the longitudinal and transverse components of the currents of mass and charge. Explicit expressions are given for the coefficients in the small-time Taylor development of the autocorrelation functions and these, together with data on the static structure factors, are used in analysing the current fluctuations and their spectra in terms of memory functions. The memory function has the same basic structure in all cases, consisting of a short-lived initial decay and a long-lived quasi-exponential tail. Inclusion of the tail is essential in order to achieve quantitative agreement with the measured spectra, particularly at small wavenumbers. To that extent our results are consistent with calculations on simpler systems, suggesting that the dynamical events which contribute to the tail in the memory functions are a feature characteristic of liquids in general. The relation to neutron-scattering experiments is also discussed. It is shown, in particular, that a propagating charge density fluctuation of the type seen in the molecular dynamics results is likely to be undetectable in a neutron experiment, except in particularly favourable circumstances.

Heave motion of air cushion vehicles

1978 ◽  
Vol 12 (2) ◽  
pp. 85-87 ◽  
Author(s):  
M. Robinson Swift ◽  
David Lebel
Keyword(s):  
Air Cushion ◽  
Heave Motion ◽  
Air Cushion Vehicles

scholarly journals A Theoretical Study on the Hydrodynamics of a Zero-Pressurized Air-Cushion-Assisted Barge Platform

2020 ◽  
Vol 8 (9) ◽  
pp. 664
Author(s):  
Fengmei Jing ◽  
Li Xu ◽  
Zhiqun Guo ◽  
Hengxu Liu
Keyword(s):  
Coupling Effect ◽  
Low Cost ◽  
Engineering Application ◽  
Theoretical Method ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
Floating Body ◽  
Motion Response ◽  
Air Cushion ◽  
Heave Motion

Thebarge platform has the advantages of low cost, simple structure, and reliable hydrodynamic performance. In order to further improve the hydrodynamics of the barge platform and to reduce its motion response in waves, a zero-pressurized air cushion is incorporated into the platform in this paper. The pressure of the zero-pressurized air cushion is equal to atmospheric pressure and thus does not provide buoyancy to the platform. As compared to the conventional pressurized air cushion, the zero-pressurized one has advantages of less air leakage risk. However, due to the coupling effect on the interface between water and air cushion, the influence of the gas inside the air cushion on the performance of the floating body has become a difficult problem. Based on the boundary element method, the motion response of the zero-pressurized air-cushion-assisted barge platform under regular and irregular waves is calculated and analyzed in the paper. Compared with the barge platform without air cushion, numerical results from the theoretical method show that in regular waves, the air cushion could significantly reduce the amplitude of heave and pitch (roll) response of the round barge platform in the vicinity of resonance. In irregular waves, the air cushion also observably reduces the pitch (roll) motion, though amplifies the heave motion due to the transfer of heave resonance frequency. Thetheoretical study demonstrates that the zero-pressurized air cushion can reduce the seakeeping motion of barge platforms in high sea states, but might also bring negative effects to heave motion in low sea states. One should carefully design the air cushion for barge platforms according to the operating sea states to achieve satisfactory hydrodynamic performance in engineering application.

Sign in / Sign up

Export Citation Format

Share Document