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- Title
- Motion and Attention.
- Creator
- Fuller, Nicholas Ward, Kersten, Alan, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Psychology
- Abstract/Description
-
The present study examined whether differential motion could influence the spread of attention across an object. In particular, we examined whether the type of motion exhibited by an object would impact the reaction time in which a participant made a judgement on the location of a target or the accuracy of their judgment. We did not find significant effects of motion type upon reaction time. We did find that accuracy was significantly greater for validly cued targets than for invalidly cued...
Show moreThe present study examined whether differential motion could influence the spread of attention across an object. In particular, we examined whether the type of motion exhibited by an object would impact the reaction time in which a participant made a judgement on the location of a target or the accuracy of their judgment. We did not find significant effects of motion type upon reaction time. We did find that accuracy was significantly greater for validly cued targets than for invalidly cued targets. Further investigation may be needed to demonstrate the impact of motion upon the spread of attention across an object.
Show less - Date Issued
- 2018
- PURL
- http://purl.flvc.org/fau/fd/FA00013172
- Subject Headings
- Motion, Attention, Motion--Experiments
- Format
- Document (PDF)
- Title
- On the Drainage Vortices of Liquid in a Container with Two Outlets.
- Creator
- Stankovic, Radivoje, Su, Tsung-Chow, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
-
When a liquid drains through a hole in a container, a vortex may form between the surface and the drainage hole. An interesting phenomenon occurs in the presence of two drainage holes. Only one vortex forms, while the other hole will mostly drain as sink flow. In addition, the vortex can switch between one hole and the other with regular periodicity. The primary goal of this study is to measure this periodicity under varying conditions (height of water in the container, diameter of the...
Show moreWhen a liquid drains through a hole in a container, a vortex may form between the surface and the drainage hole. An interesting phenomenon occurs in the presence of two drainage holes. Only one vortex forms, while the other hole will mostly drain as sink flow. In addition, the vortex can switch between one hole and the other with regular periodicity. The primary goal of this study is to measure this periodicity under varying conditions (height of water in the container, diameter of the drainage holes, and distance between drainage holes). Additionally, a study concerning the volume flow rates of vortical vs. sink flow out of the drainage holes was conducted. In the case of two drainage holes, when the height of the water was decreased in the container, the diameter of drainage holes decreased, or the distance between drainage holes was increased, the switching period was shown to decrease.
Show less - Date Issued
- 2020
- PURL
- http://purl.flvc.org/fau/fd/FA00013572
- Subject Headings
- Drainage, Vortex-motion
- Format
- Document (PDF)
- Title
- TOP-DOWN EFFECTS OF PERCEPTUAL GROUPING ON THE PERCEPTION OF MOTION.
- Creator
- Datta, Debarshi, Hock, Howard S., Florida Atlantic University, Department of Psychology, Charles E. Schmidt College of Science
- Abstract/Description
-
Ullman (1979) has proposed a measurement metric, which he termed “affinity." He described affinity as a certain similarity measure between successively presented surfaces as it affects the perception of apparent motion between the surfaces. Later, the concept of “affinity” has been extended; it entails that how the perception of motion within a surface is affected by its grouping strength with adjacent surfaces (Hock and Nichols, 2012). It has been found that the more attributes, that are...
Show moreUllman (1979) has proposed a measurement metric, which he termed “affinity." He described affinity as a certain similarity measure between successively presented surfaces as it affects the perception of apparent motion between the surfaces. Later, the concept of “affinity” has been extended; it entails that how the perception of motion within a surface is affected by its grouping strength with adjacent surfaces (Hock and Nichols, 2012). It has been found that the more attributes, that are shared by the adjacent surfaces, the greater the likelihood of their being grouped together. However, Ullman (1979) suggested that the relative affinities of pairs of surfaces could determine the solutions for the motion correspondence problem (when more than one motion path is possible). However, it has remained unknown whether the effects of affinity on solutions to the correspondence problem are due to its effects on a single surface apparent motion strength or pre-selection biases; i.e., the top-down effects of perceptual grouping favoring the perception of motion in one direction as opposed to other competing directions. In the current study, it has been confirmed that motion within a surface is affected by its affinity with adjacent surfaces. The current study also confirmed that affinity has a small, but significant effect on motion strength when motion surfaces are presented in a single surface apparent motion configuration, evidence for top-down effects in which motion strength can be affected by affinity. In motion correspondence problem, affinity affects the perceived motion direction due to competition is consistent with the solution to the motion correspondence problem being affected by the relative affinity-determined strength of competing motion signals. But it is seen that there is strong affinity is due to preselection identity biases. To conclude, in motion correspondence problem, stronger motion is perceived between the two similar surfaces is due to pre-selection biases resulting from the perceptual grouping of surfaces with the greatest affinity; i.e., the top-down effects favoring the perception of motion in one direction as opposed to other competing directions.
Show less - Date Issued
- 2020
- PURL
- http://purl.flvc.org/fau/fd/FA00013567
- Subject Headings
- Motion Perception, Perceptual grouping
- Format
- Document (PDF)
- Title
- Effects of adaptation on the perception of motion: The influence of competing mechanisms.
- Creator
- Espinoza, Jessica K., Florida Atlantic University, Hock, Howard S.
- Abstract/Description
-
The effects of adaptation on motion were investigated using a modified apparent motion display. Unlike the classical apparent motion display, a BRLC (background relative luminance contrast) apparent motion display consists of two visible dots, each of a different luminance, which remain in the same position but exchange luminances on successive frames. This forms a bistable stimulus; stationarity-flicker or motion may be perceived, depending on the value of the BRLC. There was a significant...
Show moreThe effects of adaptation on motion were investigated using a modified apparent motion display. Unlike the classical apparent motion display, a BRLC (background relative luminance contrast) apparent motion display consists of two visible dots, each of a different luminance, which remain in the same position but exchange luminances on successive frames. This forms a bistable stimulus; stationarity-flicker or motion may be perceived, depending on the value of the BRLC. There was a significant interaction between condition (baseline or adaptation) and BRLC when testing motion perception following adaptation to a moving stimulus, a flickering stimulus and a static stimulus. Additionally, adaptation to flicker decreased motion perception at high BRLC values and increased it at low BRLC values. Our results reflected the presence of strong inhibitory competition between the mechanisms concerned with the perception of motion and stationarity which restricted adaptation effects to certain values of BRLC.
Show less - Date Issued
- 1998
- PURL
- http://purl.flvc.org/fcla/dt/15574
- Subject Headings
- Luminescence, Motion perception (Vision)
- Format
- Document (PDF)
- Title
- On the perception of relational motion.
- Creator
- Field, Linda C., Florida Atlantic University, Hock, Howard S.
- Abstract/Description
-
Six experiments were performed to examine the adequacy of detection/computation models for understanding the perception of relational motion, and in particular, the perception of three-dimensional motion in two-dimensional displays. The stimuli were a pair of dots which moved relationally (i.e., the relative location of the dots changed). Three-dimensional motion was seen when a contraction of the stimulus preceded an expansion (i.e., the dot separation first decreased, then increased), the...
Show moreSix experiments were performed to examine the adequacy of detection/computation models for understanding the perception of relational motion, and in particular, the perception of three-dimensional motion in two-dimensional displays. The stimuli were a pair of dots which moved relationally (i.e., the relative location of the dots changed). Three-dimensional motion was seen when a contraction of the stimulus preceded an expansion (i.e., the dot separation first decreased, then increased), the angular difference between the pattern orientation and the direction of movement was small, and the spatial separation between dots was small. Neither the activation of higher-order, relational feature detectors, nor the construction/computation of relational motion from the detected motion of individual dots, can adequately explain the perception of three-dimensional motion.
Show less - Date Issued
- 1990
- PURL
- http://purl.flvc.org/fcla/dt/14630
- Subject Headings
- Motion perception (Vision)
- Format
- Document (PDF)
- Title
- MULTIDIMENSIONAL FORMULATION OF THE GENERAL RELATIVISTIC EQUATIONS OF MOTION.
- Creator
- BEYL, LAWRENCE MICHAEL., Florida Atlantic University, McGuire, James B.
- Abstract/Description
-
A 4N-dimensional formalism is developed and a corresponding space is found. The necessity of coupling the particle's proper times to one parameter is discussed. The appropriate conditions and constraints which relate this space to the ordinary 4-space are found. The transformation properties which are consistent with general 4-space transformations are determined. These transformation properties are used to determine the form of the 4x4 matrices making up the 4N-dimensional metric tensor. The...
Show moreA 4N-dimensional formalism is developed and a corresponding space is found. The necessity of coupling the particle's proper times to one parameter is discussed. The appropriate conditions and constraints which relate this space to the ordinary 4-space are found. The transformation properties which are consistent with general 4-space transformations are determined. These transformation properties are used to determine the form of the 4x4 matrices making up the 4N-dimensional metric tensor. The form of these matrices indicates they represent interactions between particles. The diagonal matrices are shown to represent gravitational interaction and the off-diagonal matrices to represent other interparticle interactions. A metric theory to cover all interparticle interactions is then proposed. The equations of motion for one particle in this 4N-dimensional space are found. These equations are then related to the motion of N interacting particles in 4- space . Finally, an approximation procedure is applied to determine the first order equations of motion.
Show less - Date Issued
- 1974
- PURL
- http://purl.flvc.org/fcla/dt/13659
- Subject Headings
- General relativity (Physics), Motion
- Format
- Document (PDF)
- Title
- Estimation of motion parameters of a planar body using binocular camera configuration.
- Creator
- Haliyur, Padma., Florida Atlantic University, Sudhakar, Raghavan
- Abstract/Description
-
This thesis is concerned with the estimation of motion parameters of planar-object surfaces viewed with a binocular camera configuration. Possible application of this method includes autonomous guidance of a moving platform (AGVS) via imaging, and segmentation of moving objects by the use of the information concerning the motion and the structure. The brightness constraint equation is obtained by assuming the brightness of a moving patch as almost invariant. This equation is solved for single...
Show moreThis thesis is concerned with the estimation of motion parameters of planar-object surfaces viewed with a binocular camera configuration. Possible application of this method includes autonomous guidance of a moving platform (AGVS) via imaging, and segmentation of moving objects by the use of the information concerning the motion and the structure. The brightness constraint equation is obtained by assuming the brightness of a moving patch as almost invariant. This equation is solved for single camera case as well as binocular camera case by knowing values of the surface normal or by iteratively determining it using the estimates of motion parameters. For this value of the surface normal, rotational and translational motion components are determined over the entire image using a least squares algorithm. This algorithm is tested for simulated images as well as real images pertaining to a single camera as well as binocular camera situations. (Abstract shortened with permission of author.)
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/14692
- Subject Headings
- Motion, Image processing
- Format
- Document (PDF)
- Title
- SHIP MOTION PREDICTION USING AUTO REGRESSIVE MOVING AVERAGE METHOD (NAVAL ARCHITECTURE, OFFSHORE TECHNOLOGY, DYNAMIC POSITIONING).
- Creator
- CHANDRASEKHARAN, CHANDRAMOHAN., Florida Atlantic University, Lin, Newman K.
- Abstract/Description
-
The time series method of Auto Regressive Moving Average (ARMA) is applied to the problem of real time ship motion prediction. The theory of Scalar input Scalar output ARMA (n, n-1) model and the same extended to multiple series as vector, ARMAV model have been concisely presented. The field experimental procedure for roll measurement of vessel at sea and barge model test procedure for heave and pitch measurements are discussed. The time series data of roll is analysed as a scalar ARMA (n, n...
Show moreThe time series method of Auto Regressive Moving Average (ARMA) is applied to the problem of real time ship motion prediction. The theory of Scalar input Scalar output ARMA (n, n-1) model and the same extended to multiple series as vector, ARMAV model have been concisely presented. The field experimental procedure for roll measurement of vessel at sea and barge model test procedure for heave and pitch measurements are discussed. The time series data of roll is analysed as a scalar ARMA (n, n-1) model and the results of prediction are presented. The model test data of heave, pitch and wave were analysed as ARMAV (n,n-1) vector model and the results are presented. The model test and experimental results demonstrate the feasibility of ARMA modeling procedure as a valuable tool in the area of real time ship motion prediction.
Show less - Date Issued
- 1985
- PURL
- http://purl.flvc.org/fcla/dt/14246
- Subject Headings
- Motion study, Marine engineering
- Format
- Document (PDF)
- Title
- Nine multiply separated precision point synthesis of coplanar four bar linkages.
- Creator
- Smith, Donn Alan., Florida Atlantic University, Case, Robert O., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
This study presents the equations of motion for nine multiply separated precision point synthesis of coplanar four bar linkages. A computer program called NINEPT is introduced which employs the equations of motion to solve the problem of nine finitely separated precision point synthesis. The algorithms of NINEPT are described in detail and a program listing is provided.
- Date Issued
- 1990
- PURL
- http://purl.flvc.org/fcla/dt/14601
- Subject Headings
- Links and link-motion
- Format
- Document (PDF)
- Title
- Separation flow around airfoil with upstream disturbance by discrete vortex method.
- Creator
- Li, Feng., Florida Atlantic University, Su, Tsung-Chow, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The discrete vortex method was applied to the calculation of separation flow past NACA 4412 airfoil: Vortex panel was used to represent the body surface and discrete vortices were used to model the wake. Generally the uniform upstream condition is used in the calculation of separation flow. But actually an airfoil could move in wake of other airfoils or disturbed fluid. In this thesis, discrete vortices were used to model the upstream disturbance to investigate the effect of upstream...
Show moreThe discrete vortex method was applied to the calculation of separation flow past NACA 4412 airfoil: Vortex panel was used to represent the body surface and discrete vortices were used to model the wake. Generally the uniform upstream condition is used in the calculation of separation flow. But actually an airfoil could move in wake of other airfoils or disturbed fluid. In this thesis, discrete vortices were used to model the upstream disturbance to investigate the effect of upstream disturbance to the pressure, lift and drag coefficients around the airfoil. Also the animation of separation flow was made on HP workstation using "Starbase" computer graphic package to study the separation process.
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/14739
- Subject Headings
- Vortex-motion, Fluid dynamics
- Format
- Document (PDF)
- Title
- Resisting the others: Gender, multiculturalism, and social identity in "Alien Resurrection".
- Creator
- Sowers, Joseph W., Florida Atlantic University, Budd, Michael N.
- Abstract/Description
-
Despite increasing racial diversity, the growth of multicultural awareness, and constantly changing ideas regarding gender roles in the United States, some Hollywood films still, directly and indirectly, stereotype "others" via images. Through methods of ideological film criticism, genre analysis of the science fiction film, some feminist theory and psychoanalysis, and the theory of the cyborg, this thesis argues that the Hollywood film Alien Resurrection is a cultural text which promotes...
Show moreDespite increasing racial diversity, the growth of multicultural awareness, and constantly changing ideas regarding gender roles in the United States, some Hollywood films still, directly and indirectly, stereotype "others" via images. Through methods of ideological film criticism, genre analysis of the science fiction film, some feminist theory and psychoanalysis, and the theory of the cyborg, this thesis argues that the Hollywood film Alien Resurrection is a cultural text which promotes racism, sexism, and Eurocentrism. Various film techniques, narrative elements, characters along with their development, and other aspects of the film serve to stereotype and confine those with multiple social identities.
Show less - Date Issued
- 1999
- PURL
- http://purl.flvc.org/fcla/dt/15641
- Subject Headings
- Racism in motion pictures, Sexism in motion pictures, Alien resurrection (Motion picture: 1997)
- Format
- Document (PDF)
- Title
- Design and evaluation of a swirling flow combustion system.
- Creator
- Li, Ceji., Florida Atlantic University, Moslemian, Davood, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A swirling flow combustion system has been designed and constructed. An integral laser Doppler velocimeter is constructed for the investigations of fluid mechanics aspects of a swirling flow combustor. The combustor consists of one fuel flow and two swirled air flows. The inner air flow has a fixed swirling strength and the outer air flow has an adjustable swirler. Both counterswirl and coswirl flows with variable swirl strength can be generated. Premixed or non-premixed combustion can be...
Show moreA swirling flow combustion system has been designed and constructed. An integral laser Doppler velocimeter is constructed for the investigations of fluid mechanics aspects of a swirling flow combustor. The combustor consists of one fuel flow and two swirled air flows. The inner air flow has a fixed swirling strength and the outer air flow has an adjustable swirler. Both counterswirl and coswirl flows with variable swirl strength can be generated. Premixed or non-premixed combustion can be investigated on this system. Evaluation of the swirling combustion system and performance check of the velocity measurement system are conducted. Detailed time mean and fluctuating flow measurements are obtained for coswirl and counterswirl conditions with the LDV system. A central recirculation zone is observed in both swirl conditions, but the size in counterswirl is much smaller. The reasons for the difference are discussed.
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/14767
- Subject Headings
- Fluid dynamics, Vortex-motion, Combustion chambers
- Format
- Document (PDF)
- Title
- Impact forces at the knee joint: A comparative study on running styles.
- Creator
- Sol, Constanza., Florida Atlantic University, Torok, Don
- Abstract/Description
-
The focus of this study was to quantify changes in impact forces at the knee when changing footstrike. The subjects included 17 heelstrikers (trained = 8, controls = 9). The 12-week training consisted of drills that focused on landing on the midfoot as per the Pose Method of running. The kinematics variables quantified were stride rate, stride length, stance phase, and knee flexion angle at footstrike. The kinetics measured were maximum vertical ground reaction forces at the ground and at the...
Show moreThe focus of this study was to quantify changes in impact forces at the knee when changing footstrike. The subjects included 17 heelstrikers (trained = 8, controls = 9). The 12-week training consisted of drills that focused on landing on the midfoot as per the Pose Method of running. The kinematics variables quantified were stride rate, stride length, stance phase, and knee flexion angle at footstrike. The kinetics measured were maximum vertical ground reaction forces at the ground and at the knee joint during initial impact, and maximum loading rate. The data were analyzed with a repeated measures ANOVA with (P < 0.05). Significant decreases was found in stride rate, stance phase and in all kinetic variables. These preliminary results are encouraging because they demonstrate that changing the footstrike can result in a reduction in impact forces at the knee joint.
Show less - Date Issued
- 2001
- PURL
- http://purl.flvc.org/fcla/dt/12776
- Subject Headings
- Knee, Running, Joints--Range of motion
- Format
- Document (PDF)
- Title
- Optimal coordination of robotic systems with redundancy.
- Creator
- Varma, K. R. Hareendra., Florida Atlantic University, Huang, Ming Z., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The research work described in this dissertation is primarily aimed at developing efficient algorithms for the rate allocation problem in redundant serial chain manipulators. While the problem of redundancy resolution in the context of robot manipulators, had been a well researched one, search for optimality in computational efficiency has caught the attention only recently. Further, the idea of modifying the already developed performance criteria to improve computational efficiency, had...
Show moreThe research work described in this dissertation is primarily aimed at developing efficient algorithms for the rate allocation problem in redundant serial chain manipulators. While the problem of redundancy resolution in the context of robot manipulators, had been a well researched one, search for optimality in computational efficiency has caught the attention only recently. Further, the idea of modifying the already developed performance criteria to improve computational efficiency, had rarely been treated with the importance it deserves. The present work in fact, provides many alternative formulations to the existing performance criteria. As a result of the present investigation, we developed a mathematical tool for the minimum norm solution for underdetermined systems of linear equations, using the orthogonal null space. Closed form equations were provided for cases with two or three degrees of redundancy. Detailed study of computational efficiency showed substantial reduction in the arithmetic operations necessary for such a solution. The above concept was later generalized to utilize the self motion characteristics of redundant manipulators, to provide alternate solutions. The duality concept between the Jacobian and the null space, established in this work, enabled the authors to develop a highly efficient formulation as an alternative to the commonly used pseudoinverse-based solution. In addition, by providing the example of a 7R anthropomorphic arm, the feasibility of obtaining analytical formulation of null space coefficient matrix and the transformed end effector velocity vector for any geometry has been demonstrated. By utilizing the duality between the Jacobian and its null space, different performance criteria commonly used in the redundancy resolution problem have been modified, increasing the computational efficiency. Various simulations performed as part of the present work, utilizing the analytical null space coefficient matrix and the transformed end effector velocity vector for 3R planar case and 7R spatial anthropomorphic arm corroborates the theories. Another practical application has been demonstrated by the example of a Titan 7F arm mounted on a mobile base. The work is consolidated by reiterating the insight obtained to the physical aspects of the redundancy resolution problem and providing a direction for future work. Suggestions are given for extending the work for high d.o.r. systems, with relevant mathematical foundations. Future work in the area of dynamic modelling, is delineated which also includes an example of modified dynamic manipulability measure.
Show less - Date Issued
- 1992
- PURL
- http://purl.flvc.org/fcla/dt/12292
- Subject Headings
- Algorithms, Redundancy (Engineering), Robotics, Robots--Motion
- Format
- Document (PDF)
- Title
- Robot singularities under small perturbations in the kinematic parameters.
- Creator
- Mohile, Ajey Avinash., Florida Atlantic University, Roth, Zvi S., College of Engineering and Computer Science, Department of Computer and Electrical Engineering and Computer Science
- Abstract/Description
-
When small perturbations in the kinematic parameters of a robot are taken into consideration, the model of a robot no longer contains perfect parallelism and perpendicularity that makes the nominal inverse kinematics so simple. In particular, the effect of joint axis misalignments and small perturbations in the kinematic parameters on the robot singularities is of interest. This aspect is particularly important when planning the workspace of a robot that must undergo calibration. To utilize...
Show moreWhen small perturbations in the kinematic parameters of a robot are taken into consideration, the model of a robot no longer contains perfect parallelism and perpendicularity that makes the nominal inverse kinematics so simple. In particular, the effect of joint axis misalignments and small perturbations in the kinematic parameters on the robot singularities is of interest. This aspect is particularly important when planning the workspace of a robot that must undergo calibration. To utilize the work volume most efficiently, one must know exactly what points are permissible as taught points. In other words, reachable workspace must be clearly defined to avoid the robot from entering the singularity zones not only of the nominal robot but also of all future actual robots. Once singularity zones for the actual robot are correctly identified, workspace planning becomes a simple task. In this thesis the relationship between small perturbations in kinematic parameters and singularities of a simple three-revolute articulated arm are studied. It is shown that singularities in such a robot do shift to new locations.
Show less - Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/14476
- Subject Headings
- Robots--Dynamics, Robots--Motion
- Format
- Document (PDF)
- Title
- Vortex street wakes downstream of truncated and full cylinders in a rotating fluid.
- Creator
- Leader, Bram., Florida Atlantic University, Marshall, Jeffrey S., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
An experimental study has been conducted to examine the flow field about and the wake behind truncated cylindrical obstacles of varying height, which are towed through a fluid with a free surface in a rotating system. The results show the development of a vortex street-type wake downstream of the obstacle for retrograde (westward) flows, even for very small ratios of obstacle height to water layer depth. For short obstacles, a pronounced backward flowing jet is observed, which impinges on the...
Show moreAn experimental study has been conducted to examine the flow field about and the wake behind truncated cylindrical obstacles of varying height, which are towed through a fluid with a free surface in a rotating system. The results show the development of a vortex street-type wake downstream of the obstacle for retrograde (westward) flows, even for very small ratios of obstacle height to water layer depth. For short obstacles, a pronounced backward flowing jet is observed, which impinges on the Taylor column from downstream. Prograde (eastward) flows are found to have a meandering wake that extends farther than eight obstacle diameters downstream and do not exhibit backjetting or vortex street formation. Upwelling is believed to occur within the side boundary layers of the Taylor column, which could play a significant role in deep water production in the ocean.
Show less - Date Issued
- 1992
- PURL
- http://purl.flvc.org/fcla/dt/14827
- Subject Headings
- Taylor vortices, Fluid dynamics, Vortex-motion
- Format
- Document (PDF)
- Title
- A numerical study of bluff body aerodynamics by vortex method.
- Creator
- He, Fusen., Florida Atlantic University, Su, Tsung-Chow, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Vortex methods are grid-free; therefore, their use avoids a number of shortcomings of Eulerian, grid-based numerical methods for solving high Reynolds number flow problems. These include such problems as poor resolution and numerical diffusion. In vortex methods, the continuous vorticity field is discretized into a collection of Lagrangian elements, known as vortex elements. Vortex elements are free to move in the flow field which they create. The velocity field induced by these vortex...
Show moreVortex methods are grid-free; therefore, their use avoids a number of shortcomings of Eulerian, grid-based numerical methods for solving high Reynolds number flow problems. These include such problems as poor resolution and numerical diffusion. In vortex methods, the continuous vorticity field is discretized into a collection of Lagrangian elements, known as vortex elements. Vortex elements are free to move in the flow field which they create. The velocity field induced by these vortex elements is a solution to the Navier-Stokes equation, and in principle the method is suitable for high Reynolds number flows. In this dissertation, viscous vortex element methods are studied. Some modifications are developed. Discrete vortex element methods have been used to solve the Navier-Stokes equations in high Reynolds number flows. Globally satisfactory results have been obtained. However, computed pressure fields are often inaccurate due to the significant errors in the surface vorticity distribution. In addition, different ad hoc assumptions are often used in different proposed algorithms. In the present study, improvements are made to better represent the near-wall vorticity when obtaining numerical solutions for the Navier-Stokes equations. In particular, we split the boundary vortex sheet into two parts at each time step. One part remains a vortex sheet lying on the boundary of the solid body, and the other enters into the flow field as a free vortex element with a uniformly distributed vorticity. A set of kinematic relationships are used to determine the two appropriate portions of the split, and the position of the vortex element to be freed at the time of release. Another improvement is to include the nonlinear acceleration terms in the governing equations near the solid boundary when evaluating the surface pressure distribution. The aerodynamic force coefficients can then be obtained by summing up the pressure forces. By comparing the computed surface vorticities, surface pressures and aerodynamics force coefficients with existing numerical/experimental data in the cases of viscous flow around a circular cylinder, an aerofoil, and a bridge deck section, it is shown that the present approach is more accurate in modelling the flow features and force coefficients without making different ad hoc assumptions for different geometries. The computation is efficient. It can be useful in the study of the unsteady fluid flow phenomenon in practical engineering problems.
Show less - Date Issued
- 1998
- PURL
- http://purl.flvc.org/fcla/dt/12574
- Subject Headings
- Vortex-motion, Fluid mechanics, Viscous flow
- Format
- Document (PDF)
- Title
- Interaction of vortex sheet with a finite vortex.
- Creator
- Viswanathan, K. S., Florida Atlantic University, Dhanak, Manhar R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The rollup of a vortex sheet of elliptic span loading in the presence of a vortex of finite core size is studied in the Trefftz plane. The vorticity in the finite vortex is taken to be uniform and sign opposite to that of the sheet and the flow is assumed to be inviscid and incompressible. A numerical scheme is developed to determine the evolution of (a) the finite vortex using the Contour Dynamics technique, (b) the vortex sheet using an algorithm developed by Krasny. The interaction is...
Show moreThe rollup of a vortex sheet of elliptic span loading in the presence of a vortex of finite core size is studied in the Trefftz plane. The vorticity in the finite vortex is taken to be uniform and sign opposite to that of the sheet and the flow is assumed to be inviscid and incompressible. A numerical scheme is developed to determine the evolution of (a) the finite vortex using the Contour Dynamics technique, (b) the vortex sheet using an algorithm developed by Krasny. The interaction is shown to substantially affect the development of the vortex sheet rollup. The vortex sheet undergoes significant deformation at the rolling up tip region due to its devouring the vortex patch as well as due to the formation of secondary rollup features on the sheet. These features are believed to be important in inhibiting rollup considerably. The interaction is quantified by using a criterion developed to measure the extent of the tip vortex rollup and its characteristics are studied for a range of flow parameters. The strength of the rolling up tip region of the vortex sheet is found to be highly dependent on the location and the vorticity in the finite vortex.
Show less - Date Issued
- 1994
- PURL
- http://purl.flvc.org/fcla/dt/15048
- Subject Headings
- Turbulence, Whirlwinds, Vortex-motion, Wakes (Aerodynamics)
- Format
- Document (PDF)
- Title
- Cooperative self-organization in the perception of coherent motion.
- Creator
- Balz, Gunther William, Florida Atlantic University, Hock, Howard S.
- Abstract/Description
-
A row of dots is presented in a series of alternating frames; dots in each frame are located at the midpoints between dots of the preceding frame. Although the perceived frame-to-frame direction of motion could vary randomly, cooperativity is indicated by the emergence of two coherent motion patterns, one unidirectional, the other oscillatory. Small increases in the time between frames are sufficient for the bias, which maintains the previously established motion direction (unidirectional...
Show moreA row of dots is presented in a series of alternating frames; dots in each frame are located at the midpoints between dots of the preceding frame. Although the perceived frame-to-frame direction of motion could vary randomly, cooperativity is indicated by the emergence of two coherent motion patterns, one unidirectional, the other oscillatory. Small increases in the time between frames are sufficient for the bias, which maintains the previously established motion direction (unidirectional motion), to be reversed, becoming a bias which inhibits that direction (oscillatory motion). Unidirectional motion, which predominates for small dot separations, and oscillatory motion, which predominates for large separations, are associated with short-range and long-range motion (Braddick, 1974) by manipulating the shape of the dots, their luminance, and the luminance of the inter-frame blank field. Pulsing/flicker emerges as a third perceptual state that competes with unidirectional motion for very small dot separations.
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/14712
- Subject Headings
- Motion perception (Vision), Perceptual-motor learning
- Format
- Document (PDF)
- Title
- A visual rotation invariant in fixated motion.
- Creator
- Ozery, Nissim Jossef., Florida Atlantic University, Raviv, Daniel, College of Engineering and Computer Science, Department of Computer and Electrical Engineering and Computer Science
- Abstract/Description
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This thesis studies the 2-D-based visual invariant that exists during relative motion between a camera and a 3-D object. We show that during fixation there is a measurable nonlinear function of optical flow that produces the same value for all points of a stationary environment regardless of the 3-D shape of the environment. During fixated camera motion relative to a rigid object, e.g., a stationary environment, the projection of the fixated point remains (by definition) at the same location...
Show moreThis thesis studies the 2-D-based visual invariant that exists during relative motion between a camera and a 3-D object. We show that during fixation there is a measurable nonlinear function of optical flow that produces the same value for all points of a stationary environment regardless of the 3-D shape of the environment. During fixated camera motion relative to a rigid object, e.g., a stationary environment, the projection of the fixated point remains (by definition) at the same location in the image, and all other points located on the 3-D rigid object can only rotate relative to that 3-D fixation point. This rotation rate of the points is invariant for all points that lie on the particular environment, and it is measurable from a sequence of images. This new invariant is obtained from a set of monocular images and is expressed explicitly as a closed form solution.
Show less - Date Issued
- 1994
- PURL
- http://purl.flvc.org/fcla/dt/15095
- Subject Headings
- Invariants, Visual perception, Motion perception (Vision)
- Format
- Document (PDF)
