Numerical Derivation of Hydrodynamic Forces and Invention of a New Diving Technique for the Batoid Underwater Robot

2016 ◽  
Vol 50 (5) ◽  
pp. 59-73 ◽  
Author(s):  
Farhood Azarsina ◽  
Mohammad Shahabadi ◽  
Arash Shadlaghani
Keyword(s):  
Thrust Force ◽  
Center Of Mass ◽  
Symmetry Plane ◽  
Vertical Plane ◽  
Hydrodynamic Forces ◽  
Underwater Robot ◽  
Ansys Cfx ◽  
Constant Pitch ◽  
Out Of Plane ◽  
A New Technique

AbstractAs part of a design project for a batoid-inspired underwater robot, its dive to a predetermined depth is questioned here. Previously, the vehicle was designed with a streamlined hull shape that resembles a Dasyatis batoid fish, and the fish locomotion was imitated using undulating fins at each side. We did not, however, provide a buoyancy engine or any fins to turn the vessel in the vertical plane and conduct diving maneuvers. We expect to leave the vessel on the water surface, and it dives to a desired depth and then maintains a constant pitch angle and a constant forward speed. A new technique is invented here: the thrust forces of the two fins are shifted off the central top-bottom symmetry plane of the hull, therefore producing a pitching moment on the vessel. An initial trim is also introduced by shifting the center of mass forward the center of buoyancy. Therefore, the vessel is initially bowed down and, by its out-of-plane thrust force, adjusts its pitch attitude. The question is whether a final balance between the thrust force and the hydrodynamic forces will be feasible. The hydrodynamic forces at such forward speeds and attack angles were numerically derived using the computational fluid dynamics powerful software ANSYS-CFX.

Experimental Investigation of the Submarine Crashback Maneuver

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
David H. Bridges ◽  
Martin J. Donnelly ◽  
Joel T. Park
Keyword(s):  
Vortex Structure ◽  
Thrust Force ◽  
Ring Vortex ◽  
Forward Motion ◽  
Compact Structure ◽  
Moment Coefficient ◽  
Different Types ◽  
Out Of Plane ◽  
Direction Opposite ◽  
Relative Flow

In order to decelerate a forward-moving submarine rapidly, often the propeller of the submarine is placed abruptly into reverse rotation, causing the propeller to generate a thrust force in the direction opposite to the submarine’s motion. This maneuver is known as the “crashback” maneuver. During crashback, the relative flow velocities in the vicinity of the propeller lead to the creation of a ring vortex around the propeller. This vortex has an unsteady asymmetry, which produces off-axis forces and moments on the propeller that are transmitted to the submarine. Tests were conducted in the William B. Morgan Large Cavitation Channel using an existing submarine model and propeller. A range of steady crashback conditions with fixed tunnel and propeller speeds was investigated. The dimensionless force and moment data were found to collapse well when plotted against the parameter η, which is defined as the ratio of the actual propeller speed to the propeller speed required for self-propulsion in forward motion. Unsteady crashback maneuvers were also investigated with two different types of simulations in which propeller and tunnel speeds were allowed to vary. It was noted during these simulations that the peak out-of-plane force and moment coefficient magnitudes in some cases exceeded those observed during the steady crashback measurements. Flow visualization and LDV studies showed that the ring vortex structure varied from an elongated vortex structure centered downstream of the propeller to a more compact structure that was located nearer the propeller as η became more negative, up to η=−0.8. For more negative values of η, the vortex core appeared to move out toward the propeller tip.

Many-legged maneuverability: dynamics of turning in hexapods

1999 ◽  
Vol 202 (12) ◽  
pp. 1603-1623 ◽  
Author(s):  
D.L. Jindrich ◽  
R.J. Full
Keyword(s):  
Horizontal Plane ◽  
Center Of Mass ◽  
Vertical Plane ◽  
Force Production ◽  
The Body ◽  
Mean Velocity ◽  
Blaberus Discoidalis ◽  
Body Design ◽  
Reaction Forces ◽  
Straight Ahead

Remarkable similarities in the vertical plane of forward motion exist among diverse legged runners. The effect of differences in posture may be reflected instead in maneuverability occurring in the horizontal plane. The maneuver we selected was turning during rapid running by the cockroach Blaberus discoidalis, a sprawled-postured arthropod. Executing a turn successfully involves at least two requirements. The animal's mean heading (the direction of the mean velocity vector of the center of mass) must be deflected, and the animal's body must rotate to keep the body axis aligned with the heading. We used two-dimensional kinematics to estimate net forces and rotational torques, and a photoelastic technique to estimate single-leg ground-reaction forces during turning. Stride frequencies and duty factors did not differ among legs during turning. The inside legs ended their steps closer to the body than during straight-ahead running, suggesting that they contributed to turning the body. However, the inside legs did not contribute forces or torques to turning the body, but actively pushed against the turn. Legs farther from the center of rotation on the outside of the turn contributed the majority of force and torque impulse which caused the body to turn. The dynamics of turning could not be predicted from kinematic measurements alone. To interpret the single-leg forces observed during turning, we have developed a general model that relates leg force production and leg position to turning performance. The model predicts that all legs could turn the body. Front legs can contribute most effectively to turning by producing forces nearly perpendicular to the heading, whereas middle and hind legs must produce additional force parallel to the heading. The force production necessary to turn required only minor alterations in the force hexapods generate during dynamically stable, straight-ahead locomotion. A consideration of maneuverability in the horizontal plane revealed that a sprawled-postured, hexapodal body design may provide exceptional performance with simplified control.

Comparison of Electronic Component Durability Under Uniaxial and Multiaxial Random Vibrations

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Matthew Ernst ◽  
Ed Habtour ◽  
Abhijit Dasgupta ◽  
Michael Pohland ◽  
Mark Robeson ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Failure Modes ◽  
Accumulation Rate ◽  
Center Of Mass ◽  
Dynamic Environment ◽  
Test Method ◽  
Printed Wiring Board ◽  
Uniaxial Testing ◽  
Out Of Plane ◽  
Wiring Board

Multiaxial and uniaxial vibration experiments were conducted in order to study the differences in failure modes and fatigue life for the two types of excitation. An electrodynamic (ED) shaker capable of controlled vibration in six degrees of freedom (DOF) was employed for the experiments. The test specimen consisted of six large inductors insertion mounted on a printed wiring board (PWB). Average damage accumulation rate (DAR) in the inductor leads was measured for random excitations in-plane, out-of-plane, and both directions simultaneously. Under simultaneous multiaxial excitation, the average DAR was found to be 2.2 times greater than the sum of the in-plane and out-of-plane DARs. The conclusion was that multiple-step sequential uniaxial testing may significantly overestimate the durability of large/heavy structures with high center of mass in a multiaxial dynamic environment. Additionally, a test method utilizing uniaxial vibration along a direction other than the principal directions of the structure was examined. This method was found to have significant limitations, but showed better agreement with simultaneous multiaxial vibration experiments.

Calculating Cutoff Speeds of a Multistage Pump Rotor Taking into Account Lomakin Effect in the Front Seal of the Impeller

2020 ◽  
pp. 59-67
Author(s):  
D.G. Svoboda ◽  
A.A. Zharkovskii ◽  
E.A. Ivanov ◽  
I.O. Borshchev
Keyword(s):  
Hydrodynamic Forces ◽  
Centrifugal Pumps ◽  
Pump Rotor ◽  
Operating Modes ◽  
Flow Parameters ◽  
Ansys Cfx ◽  
Vibrational Characteristics ◽  
Shaft Deflection ◽  
Multistage Pump ◽  
Quantitative Impact

Studies of dynamic frequencies are an important stage in designing multistage vane pumps. This research aimed to confirm the rigidity and vibrational reliability of the pump rotor. Based on the recommendations of J.F. Gülich, the nominal rotational speed of the rotor shaft should differ from the cutoff speed by no less than 25 %. The Lomakin effect supposes taking into consideration the hydrodynamic forces acting in the gap seals and having a damping effect on the pump rotor. This research solved the problem of developing and verifying a numerical method of calculating hydrodynamic forces, which arise in seals of vane pumps at critical speeds. The studies were conducted on a ‘dry’ model of the rotor using ANSYS Mechanical software package. During computational modeling of bearings and seals, the COMBIT214 ele¬ment was used where the stiffness coefficient values were set. These values were determined by calculating the flow parameters in the gap seal using ANSYS CFX. The proposed method was verified using the experimental data obtained. The seal rigidity was calculated for different operating modes of the pump. It was shown that the hydrodynamic forces which arose in the gap seals had a significant influence on the rotor’s critical speed. Accounting for these forces increased the main own frequency of the rotor by approximately 44 %. This fact had a significant qualitative and quantitative impact on the vibrational characteristics of the pump. This study showed that the value of the hydrodynamic force was influenced by several factors: shaft deflection, differential pressure and geometry of the gap seal. The proposed method is recommended for use for multistage centrifugal pumps.

Explicit analytic expression for normal moveout from horizontal and dipping reflectors in weakly anisotropic media of arbitrary symmetry type

Geophysics ◽  
2000 ◽  
Vol 65 (4) ◽  
pp. 1294-1304 ◽  
Author(s):  
P. N. J. Rasolofosaon
Keyword(s):  
Wave Velocity ◽  
Symmetry Plane ◽  
Vertical Plane ◽  
Anisotropic Media ◽  
P Wave ◽  
Symmetry Type ◽  
Seismic Reflection Data ◽  
General Symmetry ◽  
P Wave Velocity ◽  
Analytic Expression

When processing and inverting seismic reflection data, the NMO velocity must be correctly described, taking into account realistic situations such as the presence of anisotropy and dipping reflectors. Some dip‐moveout (DMO) algorithms have been developed, such as Tsvankin’s analytic formula. It describes the anisotropy‐induced distortions in the classical isotropic cosine of dip dependence of the NMO velocity. However, it is restricted to the vertical symmetry planes of anisotropic media, so the technique is unsuitable for the azimuthal inspection of sedimentary rocks, either with horizontal bedding and vertical fractures or with dipping bedding but no fractures. However, under the weak anisotropy approximation the deviations of the rays from a vertical plane can be neglected for the traveltimes computation, and the equation can still be applicable. Based on this approach, an explicit analytic expression for the P-wave NMO velocity in the presence of horizontal or dipping reflectors in media exhibiting the most general symmetry type (triclinic) is obtained in this work. If the medium exhibits a horizontal symmetry plane, the concise DMO equations are formally identical to Tsvankin’s except that the parameters δ and ε are not constant but depend on the azimuth ψ Physically, δ(ψ) is the deviation from the vertical P-wave velocity of the P-wave NMO velocity for a horizontal reflector normalized by the vertical P-wave velocity for the azimuth ψ. The function ε(ψ) has the same definition as δ(ψ) except that the P-wave NMO velocity is replaced by the horizontal P-wave velocity. Both depend linearly on (1) new dimensionless anisotropy parameters and (2) generalizing to arbitrary symmetry the transversely isotropic parameters δ and ε. In the most general symmetry case (triclinic), an additional term to the DMO formula is necessary. The numerical examples, based on experimental data in rocks, show two things. First, the magnitude of the DMO errors induced by anisotropy depends primarily on the absolute value of ε(ψ) − δ(ψ) and not on the individual values of ε(ψ) and δ(ψ), which is a direct consequence of the similarity between Tsvankin’s equation and the equation presented here. Second, the anisotropy‐induced DMO correction can be significant even in the presence of moderate anisotropy and can exhibit complex azimuthal dependence.

2D Contractile Water Jet Thruster Characterization for Bio-Inspired Underwater Robot Locomotion

2014 ◽  
Vol 490-491 ◽  
pp. 1099-1104 ◽  
Author(s):  
M.F. Shaari ◽  
Z. Samad
Keyword(s):  
Thrust Force ◽  
Fluid Velocity ◽  
Water Jet ◽  
Underwater Robot ◽  
Two Dimensional ◽  
Contraction Force ◽  
Robot Locomotion ◽  
Major Parameter ◽  
Pneumatic Cylinders ◽  
Thrust Performance

This research was conducted to analyze the thrust performance generated from a two dimensional contractile water jet thruster (CWJT). The main aim of this research is to investigate the relation and reaction between the input parameters of the contractile water jet thruster. The major parameter of this study is the actuating force as the input and the thrust force as the output. In addition to these parameters, nozzle area and fluid velocity influence were also considered in the investigation. Two pneumatic cylinders were applied to actuate the contraction. Thrust force was measured by both experimentally and theoretically. Generally the increment of the contraction force increases the thrust force. However, generated thrust at different contraction force depends on the size of the nozzle.

An analysis of 2D and 3D multiple attenuation for a canonical example

Geophysics ◽  
2005 ◽  
Vol 70 (6) ◽  
pp. A13-A28 ◽  
Author(s):  
Luc T. Ikelle
Keyword(s):  
Free Surface ◽  
Inverse Scattering ◽  
Three Dimensional ◽  
Homogeneous Medium ◽  
Vertical Plane ◽  
Multiple Attenuation ◽  
Out Of Plane ◽  
Seismic Acquisition ◽  
2D And 3D ◽  
The Relationship

Three-dimensional formulations of free-surface multiple attenuation for multioffset seismic data are well known. They are not yet used in practice because they require very dense source-receiver coverage, which is still out of reach with existing seismic-acquisition systems. The development of alternative solutions based on 2D algorithms depends on our understanding of the relationship between 2D and 3D free-surface multiple-attenuation methods. This paper attempts to enhance this understanding by establishing the relationship between 2D and 3D inverse scattering free-surface multiple attenuation. A 3D model consisting of three scattering points (one scattered point located in the vertical plane containing the shooting line and the other two points outside this plane) in a homogeneous medium (for which the exact pressure field is analytically known) is used to show that the 2D inverse scattering multiple-attenuation algorithm predicts all free-surface multiples as does its 3D counterpart but with some traveltime and amplitude errors. One implication of this result is that the current 2D inverse scattering multiple-attenuation algorithm, with an appropriate 2D-to-3D correction, can be used to predict the free-surface multiples for data containing out-of-plane scattering.

Design and Testing of a Thin-Flexure Bistable Mechanism Suitable for Stamping From Metal Sheets

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Benjamin Todd ◽  
Brian D. Jensen ◽  
Stephen M. Schultz ◽  
Aaron R. Hawkins
Keyword(s):  
Compliant Mechanisms ◽  
Elliptic Integral ◽  
Plane Motion ◽  
Acceleration Threshold ◽  
Metal Sheets ◽  
Out Of Plane ◽  
A New Technique ◽  
Bistable Mechanism ◽  
Force Displacement ◽  
Design And Testing

We present a new technique for fabricating compliant mechanisms from stamped metal sheets. The concept works by providing thinned segments to allow rotation of flexural beams 90 deg about their long axis, effectively providing a flexure as wide as the sheet’s thickness. The method is demonstrated with the design and fabrication of a metal bistable mechanism for use as a threshold accelerometer. A new model based on elliptic integral solutions is presented for bistable mechanisms incorporating long, thin flexures. The resulting metal bistable mechanisms are tested for acceleration threshold sensing using a drop test and a vibration test. The mechanisms demonstrate very little variation due to stress relaxation or temperature effects. The force-displacement behavior of a mechanism is also measured. The mechanisms’ switching force is less than the designed value because of out-of-plane motion and dynamic effects.

scholarly journals Identification of a simplified mathematical model of an unmanned aerial vehicle

2020 ◽  
pp. 26-33
Author(s):  
A. A. Lobaty ◽  
Y. F. Yatsyna ◽  
S. S. Prohorovith ◽  
Y. A. Hvitko
Keyword(s):  
Mathematical Model ◽  
Transfer Function ◽  
Unmanned Aerial Vehicle ◽  
Center Of Mass ◽  
Experimental Studies ◽  
Vertical Plane ◽  
Parametric Identification ◽  
Ease Of Use ◽  
Aerial Vehicle ◽  
Discrete Values

The problem of determining the shape and parameters of a mathematical model in the form of a transfer function for the movement of an unmanned aerial vehicle (UAV) in the vertical plane of space is solved. The angle of deviation of the Elevator is considered as the input signal, and the pitch angle of the UAV is considered as the output signal. We use the results of experimental studies of UAV flight, which are considered as known values of input and output signals under specified flight conditions. The measured discrete values of the experimental results are approximated by a fourth-order polynomial based on regression analysis for ease of use in identification. The analytical substantiation of the need to apply the methods of linearization of the mathematical model of UAV movement and the accepted assumptions for obtaining differential equations of UAV movement relative to the center of mass, allowing to synthesize the required transfer function of the corresponding element of the UAV control system. The results of computer modeling confirmed the validity of the synthesized mathematical model obtained on the basis of structural and parametric identification. This approach can be used to obtain simplified mathematical models that are used to solve problems of synthesis and optimization of control systems not only for UAVS, but also for other dynamic objects.

Inverted Pendulum Stabilization of Submarines in Free Positive Buoyancy Ascent

1994 ◽  
Vol 38 (01) ◽  
pp. 71-82
Author(s):  
Fotis A. Papoulias ◽  
Brian D. McKinley
Keyword(s):  
Steady State ◽  
Inverted Pendulum ◽  
Initial Conditions ◽  
Vertical Plane ◽  
Out Of Plane

The problem of steady-state vertical ascent of a submarine with excess buoyancy is analyzed. All possible vertical plane solutions are computed and their stability is established in both in-plane and out-of-plane perturbations. Divergence of trajectories, sensitivity of solutions to initial conditions, and stable inverted pendulum configurations are shown to exist for certain ranges of parameters.

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