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Engineering Mechanics: Dynamics
Abstract
Vyd. 1. Na obálce nad názvem: Univerzita obrany, Fakulta vojenských technologií Na obálce označení: S-2703/2 50 výt.
... A fully elastic impact is defined as the impact in which both kinetic energy and momentum are conserved. In reality, all collisions are inelastic because permanent deformation on the microscopic scale will happen [61], but this solution will provide a bound on the actual behavior. The two beams will not remain in contact after impact and they will behave independently. ...
... Impact of a failed member in a precast concrete structure According to Boresi and Schmidt[61], a collision, or impact between two bodies is defined as "a strong interaction between the bodies, either by direct contact or by the nature of their proximity, that lasts a relatively short time". In general, when two bodies collide many questions arise such as: For given velocities of two bodies before they collide, what are their velocities after the collision? ...
... How much damage occurs in the collision? How far do the two bodies travel after they collide?[61]. In general, collisions between two bodies result in a loss of some kinetic energy and in this case the collision is called an inelastic collision. ...
Presented in this work are the possible collapse mechanisms initiated by a precast flexural member dropping on a lower member. The ultimate goal of this research is to develop design guidelines and advice to prevent progressive collapse in such cases. The problem is complicated due to the dynamic analyses involved in the dropping, the impact, and the resulting vibration. Analytical solutions and numerical solutions were developed to solve three possible collapse scenarios: perfectly plastic, inelastic, and elastic. These impact scenarios should provide a reasonable understanding of the dynamic behaviour for the member after impact. The analytical solution involves using Fourier series and the numerical solution involves a developed method of converting an initial velocity profile to an impulse load using SAP2000. The members are from typical parking garages. The first solutions developed were for the perfectly plastic and elastic impact scenarios based on assumed initial velocity profiles. The resulting reactions from the impact were evaluated against ACI provisions. It has been found that a shear failure can be prevented by providing some shear reinforcement. However, the resulting bending moment is high and the member is prone to fail under flexure. The second solutions developed were for perfectly plastic impact based on the pre-impact velocity profile of the top beam. The post-impact velocity profiles were not assumed. SAP2000 was used to calculate the post-impact velocity profiles for the upper and lower beams. The resulting shear and bending moment for the perfectly plastic scenario were extremely high and caused the member to fail. However, the resulting shear and bending moment for the case of inelastic impact did not cause failure. Finally, a simulation of the impact using the finite element analysis COMSOL Multiphysics program was performed. When simulating impact, the COMSOL documents caution the user to check conservation of momentum and energy to ensure that the results are reasonable. Conservation of momentum has been checked and found not to be satisfied. Therefore, COMSOL Multiphysics is not recommended for this type of analysis.
... The dynamic rollover metrics are based on the Newton's second law of motion, and these include, for instance, the Dynamic Stability Index (DSI) [7]. Examples of energybased metrics include the Critical Sliding Velocity (CSV) [8], [9], [10], [5], which is a minimum lateral velocity required to tip a vehicle over when the vehicle is sliding laterally and hitting a curb, and the Rollover Prevention Energy Reserve (RPER) [7], which is defined as the difference between the potential energy required to bring a vehicle to its tipover position and the sum of the instantaneous linear and rotational kinetic energy. One issue with the previous metrics is that they do not provide a situation-dependent warning. ...
... Considering a kinematic chain in Fig. 1 and using general equations of motion [28], [29], [26] and D'Alembert's principle [10], the moment equation about point A in Fig. 1 induced by inertial forces and gravity is: ...
Rollover accidents are one of the leading causes of death in highway accidents due to their very high fatality rate. A key challenge in preventing rollover via chassis control is that the prediction of the onset of rollover can be quite difficult, especially in the presence of terrain features typical of roadway environments. These road features include superelevation of the road (e.g road bank), the median slope, and the shoulder down-slope. This work develops a vehicle rollover prediction algorithm that is based on a kinematic analysis of vehicle motion, a method that allows explicit inclusion of terrain effects. The solution approach utilizes the concept of zero-moment point (ZMP) that is typically applied to walking robot dynamics. This concept is introduced in terms of a lower-order model of vehicle roll dynamics to measure the vehicle rollover propensity, and the resulting ZMP prediction allows a direct measure of a vehicle rollover threat index. Simulation results using a complex multi-body vehicle simulation show the effectiveness of the proposed algorithm during different road geometry scenarios and driver excitations.
... In this case, a portion of the tool swept volume penetrates itself so that it becomes difficult to get a topologically consistent SV without extra geometrical treatment, which leads to a higher time complexity. Due to the geometric and computational complexity the theme 1 Any point on a rigid body or on its extension that has zero velocity is called the instantaneous center of velocity or instantaneous axis of rotation (IAR) of the body [11]. ''self-penetration (SP) or self-intersection (SI) in SV generation'' has been neglected, skipped or reported very restrictively in most scientific research [2][3][4][5][6][7]. ...
... Peternell et al. [20] generate SV from a solid Φ with a piecewise smooth boundary by eliminating local self-intersection. Using the tangency condition f (=v(X) · n(X) = 0, X ∈ ∂Φ(t)) [11], grazing points plus surface normals are gathered into a set Q at each adaptive time interval which is determined by considering the evolution speed of the trajectory. Then with a marching cube (MC) algorithm the points which lie on the boundary of the SV are extracted. ...
In this paper the swept volume with self-penetration (or self-intersection) of the cutter is presented. The complete swept volume (SV), which describes the side and bottom shape of a milling cutter undergoing self-penetration, is generated by using the Gauss map method proposed in the authors’ previous paper [Lee SW, Nestler A. Complete swept volume generation—part I: swept volume of a piecewise C1-continuous cutter at five-axis milling via Gauss map. Computer-Aided Design 2011; 43(4): 427–41]. Based on the Gauss map method, the comprehensive analysis of envelope profiles of the tool is accomplished. Through the analysis the necessary condition of the self-penetration of the cutter at five-axis movement is identified. After having classified movement types of the milling cutter in an in-depth manner, the topologically consistent boundary of SV is generated by trimming the invalid facets interior to the SV. To demonstrate the validity of the proposed method, a cutting simulation kernel for five-axis machining has been implemented and applied to cavity machining examples such as intake ports of automobile engines and so forth where the self-penetration occurs. The proposed method is proved to be robust and amenable for the practical purpose of the NC simulation.
... In a second dynamics textbook, [2], the chapters are as follows: The above-mentioned three textbooks cases establish the consistency of the current organization of topics. This is based on deriving equations for a single particle then extending the derivations to a system of particles and in the second half of the course applying the system of particle equations to rigid bodies. ...
... We developed an "Influence Factor" to measure the difference in student performance between students taught by the first author ("Author") and students taught by another instructor ("Other") [2,3]. The rationale for distinguishing student performance on this basis is that, because the targeted issues are central and highly emphasized in courses taught by the Author, performance of the Author's students is possibly correlated with the effectiveness of the targeted methods. ...
... The vast majority of dynamics textbooks (Hibbeler (2016), Boresi and Schmidt (2000), Beer and Johnston (2015), Meriam and Kraige (2015), Shames (1996), Bedford and Fowler (2007), Soutas-Little and Inman (1999), Tongue (2009), and Gray, Costanso, and Plesha (2012)) are organized with an almost identical ordering of topics [1]- [9]. This ordering is generally particle kinematics, particle kinetics, rigid body kinematics, rigid body kinetics, 3-D kinematics and kinetics, and finally vibrations. ...
... Determine the speed V G of it's mass center G so that it rolls without slipping completely around the loop of radius R + r without leaving the track. I G = (2/5)mr 2 . Express your answer in terms of radius R and the acceleration of gravity g. ...
... Imani, and Braga-Neto [7] gave an estimation of state and parameters of Partially Observed Boolean Dynamical Systems. We have taken the help from other references including [8][9][10][11][12][13][14][15][16][17][18] in the field of friction and lifting machine to complete the work. The bell crank lever is an apparatus shown in Figure-1 which is used to verify the law of moments. ...
... The second relevant impact equation is obtained from the coefficient of restitution [26] ...
We consider a two-degree-of-freedom model where the focus is on
analyzing the vibrations of a fixed but flexible structure that is struck repeatedly by a
second object. The repetitive impacts due to the second mass are driven by a flowing
fluid. Morison’s equation is used to model the effect of the fluid on the properties of
the structure. The model is developed based on both linearized and quadratic fluid
drag forces, both of which are analyzed analytically and simulated numerically. Conservation
of linear momentum and the coefficient of restitution are used to characterize
the nature of the impacts between the two masses. A resonance condition of the model
is analyzed with a Fourier transform. This model is proposed to explain the nature
of ice-induced vibrations, without the need for a model of the ice-failure mechanism.
The predictions of the model are compared to ice-induced vibrations data that are
available in the open literature and found to be in good agreement. Therefore, the use
of a repetitive impact model that does not require modeling the ice-failure mechanism
can be used to explain some of the observed behavior of ice-induced vibrations.
... The a max –l curve in expected, a max decreases monotonically as l increases. The smallest possible a max as l approaches infinity (a cable) can be found to be 0.37 through a simple statics analysis (Boresi and Schmidt, 2000). On the other hand, as l approaches 0, a max approaches 1. ...
In this paper, we study the deformation and stability of a heavy elastica resting symmetrically on two frictionless point supports on the same horizontal level. The static analysis finds multiple equilibria when the distance of the two point supports is smaller than a certain value. In order to determine whether these equilibria are stable, a dynamic analysis is conducted to calculate their natural frequencies. In order to take into account the sliding between the elastica and the smooth point supports during vibration, a dynamic analysis based on an Eulerian description is adopted. It is found that stable equilibrium can exist only when the half support span a is between two limits amin(s)andamax(s). This range depends on a dimensionless ratio between the weight density and the flexural rigidity of the elastica. When an a between amin(s)andamax(s) decreases and approaches amin(s), the elastica will slip away from the side. On the other hand, when an a between amin(s)andamax(s) increases and approaches amax(s), the elastica will slip through between the two supports.
... Dynamics involves the analysis of time-dependent motion, and represents textbook knowledge in most physical science and engineering curricula (e.g., see Sandor, 1983). One area of Dynamics called Kinematics offers potential to inform dynamic organizational performance, fit and change. ...
... During the pre-collision phase, vehicle speed, V t , decreases due to sliding friction force applied on tires (Hibbeler, 1986). ...
The study aims at developing analysis approaches of vehicle-accident reconstruction in an attempt to recreate the initial impact configuration and clarify accident responsibility. One purpose is to conclude a straightforward and confident recon- struction module as a base of dealing with vehicle impact accidents. Both forward and backward deriving methods have been applied as the means of accident reconstruction. The initial impact configuration can be resulted from dynamic equations of pre-impact, impact and post-impact phases. The obtained formulated relations have been further schemed to be an interactive human-machine environment. The initial impact configuration can thus be yielded, as some necessary data are input to the developed program.
... The sum of the kinetic energy K and potential energy P of an upright pendulum consisting of a slender bar with mass m and length l is [11] ...
Among rigid-body dynamics parameters, the inertia
is more difficult to identify or verify. In fact, some robot manufacturers
provide information on masses and centers of masses,
but not on inertias. This work will propose an experimental
procedure in identifying inertia parameters through natural
oscillation. The experiment proceeds by letting the rigid-body
system achieve a linear second-order system response and its
oscillation is measured. A well-defined value of the desired
natural oscillation transforms the identification experiment into
an optimization problem. A theorem is presented to justify the
validity of the experimental approach, and experimental results
are shown.
... The sum of the kinetic energy K and potential energy P of an upright pendulum, as shown in Fig. 1, consisting of a slender bar with mass m and length l is [18] ...
This work presents a new method of dynamics
identification for rigid-body manipulators under the influence
of gravity. It is assumed that each link has an actuated joint
where the axis of rotation is different from the center of mass,
such that the driving torque is influenced by gravitational force.
The dynamics model compensation together with the force of
gravity are utilized to achieve natural oscillation for each link.
The natural oscillation allows the system to be converted into
an optimization problem where the frequency of oscillation
is minimized. The correct dynamics parameters are already
found when the minimum frequency of oscillation is achieved.
The proposed method is analyzed and a theorem is presented
to support the claims presented in this work, together with
implementation results.
... In this work, they adopt the method of moving frame introduced by [13], as well as the method of explicit closed-form representation, introduced by [17], to formulate envelope profile for five-axis tool motions. The partial extension is dedicated to solution analysis and special case analysis of generalized cutters for five-axis tool motions by using rigid body motion theory [24] and envelope theory [25]. SV is modeled in the framework of an open source [26]. ...
In this paper, we present a methodology to generate swept volume of prevailing cutting tools undergoing multi-axis motion and it is proved to be robust and amenable for practical purposes with the help of a series of tests. The exact and complete SV, which is closed from the tool bottom to the top of the shaft, is generated by stitching up envelope profiles calculated by Gauss map. The novel approach finds the swept volume boundary for five-axis milling by extending the basic idea behind Gauss map. It takes piecewise C^1-continuous tool shape into account. At first, the tool shape is transformed from Euclidean space into Tool map (T-Map) on the unit sphere and the velocity vector of a cutter is transformed into Contact map (C-Map) using Gauss map. Then, closed intersection curve is found between T-Map and C-Map on the Gaussian sphere. At last, the inverse Gauss map is exploited to get envelope profile in Euclidean space from the closed curve in the range. To demonstrate its validity, a cutting simulation kernel for five-axis machining has been implemented and applied to mold and die machining.
... This can be found in basic textbooks on dynamics and fluid mechanics. Examples: Section 17.10 in Engineering Mechanics: Dynamics by Boresi and Schmidt [10], Section 5.6 in Mechanics of Fluids by Shames [11], Section 3.2 in An Introduction to Fluid Dynamics by Batchelor [12], and Section 3.2 in Mechanics of Fluids by Potter and Wiggert [13]. ...
Full understanding of the fluid–object interactions subcomputation technique (FOIST) and the related fundamental concepts in dynamics and fluid mechanics is essential in using this technique in a meaningful way. We explain what constitutes a correct implementation of the FOIST and give a published example of what does not. Copyright © 2009 John Wiley & Sons, Ltd.
... This experiment focuses on one type of collision which can be modeled classically as a direct, central impact of particles. The theory of direct, central impact of particles ± which follows from Newton's laws of motion ± can be found in numerous textbooks (e.g., [2] [3]) that present the fundamentals of dynamics. More advanced treatments of planar and three-dimensional impact for both particles and rigid bodies are developed in specialized textbooks (e.g., [4±6]). ...
This paper describes a simple experiment well suited for an undergraduate course in me-chanical measurements and/or dynamics, in which physical information is extracted from an acoustic emission signature. In the experiment, a ping±pong ball is dropped onto a hard table surface and the audio signal resulting from the ball±table impacts is recorded. The times between successive bounces,ò¯ight times'', are used to determine the height of the initial drop and the coecient of restitution of the impact. The experiment prompts questions about modeling the dynamics of a simple impact problem, including the use of the coecient of restitution and the importance of accounting for aerodynamic eects.
... Newton-Euler method is used for dynamic modeling of CDRPM [10]. According to acceleration of rotating velocity vector [11], [10] ...
This paper is devoted to the control of a cable driven redundant parallel manipulator, which is a challenging problem due the optimal resolution of its inherent redundancy. Additionally to complicated forward kinematics, having a wide workspace makes it difficult to directly measure the pose of the end-effector. The goal of the controller is trajectory tracking in a large and singular free workspace, and to guarantee that the cables are always under tension. A control topology is proposed in this paper which is capable to fulfill the stringent positioning requirements for these type of manipulators. Closed-loop performance of various control topologies are compared by simulation of the closed-loop dynamics of the KNTU CDRPM, while the equations of parallel manipulator dynamics are implicit in structure and only special integration routines can be used for their integration. It is shown that the proposed joint space controller is capable to satisfy the required tracking performance, despite the inherent limitation of task space pose measurement.
The virtual haptics is a crucial aspect of immersive virtual reality, extending the traditional experiences of sight and hearing. The vibration can provide direct normal vibration and friction reduction, making it a promising method to realize virtual haptics. However, the optimum perceptual threshold of skin for vibration is 100 Hz to 500 Hz, resulting in a too low vibrotactile resolution. The conflict between the low perceptual frequency and high resolution still remains challenges. In this paper, a low-frequency envelope wave methodology is proposed to realize the localized vibrotactile feedback. The high-frequency components are modulated into a low-frequency envelope waveform, which provides low-frequency perception and high resolution at the same time. Due to hardware limitations, the modes must be truncated and minimized as much as possible. This requirement conflicts with achieving localized vibration at arbitrary points and further implementing complex vibration patterns. Therefore, a modal optimization algorithm is proposed to solve the inverse problem. The modal participation coefficients is obtained, basing on the evaluation index that ensures the frequency of the envelope wave and the vibration pattern quality. The localized vibration patterns including multiple points, points of proportional amplitude, bar and circle are achieved with a resolution of 3 cm and a perception frequency of about 200 Hz. This method is expected to be applied to virtual reality, blind assistance, and other potential applications to enhance tactile interaction experiences.
An approximate simplified analytic solution is proposed for the one DOF (degree of freedom) static and dynamic displacements alongside the stiffness (dynamic and static) and damping coefficients (minimum and maximum/critical values) of a parallel spring-damper suspension system connected to a solid mass-body gaining its energy by falling from height h. The analytic solution for the prescribed system is based on energy conservation equilibrium, considering the impact by a special G parameter. The formulation is based on the works performed by Timoshenko (1928), Mindlin (1945), and the U. S. army-engineering handbook (1975, 1982). A comparison between the prescribed studies formulations and current development has led to qualitative agreement. Moreover, quantitative agreement was found between the current prescribed suspension properties approximate value - results and the traditionally time dependent (transient, frequency) parameter properties. Also, coupling models that concerns the linkage between different work and energy terms, e.g., the damping energy, friction work, spring potential energy and gravitational energy model was performed. Moreover, approximate analytic solution was proposed for both cases (friction and coupling case), whereas the uncoupling and the coupling cases were found to agree qualitatively with the literature studies. Both coupling and uncoupling solutions were found to complete each other, explaining different literature attitudes and assumptions. In addition, some design points were clarified about the wire mounting isolators stiffness properties dependent on their physical behavior (compression, shear tension), based on Cavoflex catalog. Finally, the current study aims to continue and contribute the suspension, package cushioning and containers studies by using an initial simple pre – design analytic evaluation of falling mass- body (like cushion, containers, etc.).
This study evaluated the efficiency of an oil fence and spreading devices for one vessel in a towing tank. A series of model experiments and numerical calculations were conducted using an existing oil fence for two vessels and a new method for one vessel. Models of the oil fence and spreading devices were constructed on scale from waterproofed nylon fabric and canvas. The tensions acting on the model of the oil fences and the horizontal distance between the spreading devices were calculated numerically while the oil fences were being towed. The results were extremely close to the results of the model experiments. The ratio of the opening width to the total length of the oil fence, which shows the efficiency of the oil fence for one vessel, was 49.7% in 0.4 m/sec. Therefore, the proposed oil fence system should be very useful for oil containment at sea. As the opening width of the oil fence is not proportional to the length of the towing rope, it may be reasonable to maintain the towing rope at approximately 100 m. Furthermore, a reasonable towing speed, when operating the oil fence for one vessel equipped with spreading devices, was within 0.4 m/sec.
This paper describes a new implementation of a mixture of techniques not used before for fingerprint recognition. The implementation consists of three stages: the location of the core, which is done through Radon transformation; the extraction of features (out of which a square fingerprint is produced with the core, and the center of the mass is obtained from it); in stage three, the resulting image is used to train the neural network in order to obtain better LVQ classification. The improvement of effectiveness is tested using two databases of fingerprints. Correct recognition rates have exceeded 90 percent, which demonstrate its great stability with fingerprints that display a well-defined core.
Context:
Functional performance testing of athletes can determine physical limitations that may affect sporting activities. Optimal functional performance testing simulates the athlete’s activity.
Evidence Acquisition:
A Medline search from 1960 to 2012 was implemented with the keywords functional testing, functional impairment testing, and functional performance testing in the English language. Each author also undertook independent searches of article references.
Conclusion:
Functional performance tests can bridge the gap between general physical tests and full, unrestricted athletic activity.
In this paper we present the synthesis of novel reactionless spatial three-degrees-of-freedom (3-DoF) and 6-DoF mechanisms without any separate counter-rotation, using four-bar linkages. Based on the conditions of dynamic balancing of a single planar four-bar linkage developed elsewhere, the spatial problem is shown to be equivalent to ensuring that the inertia tensor of reactionless four-bar linkage(s), which is(are) attached on the moving link of a reactionless four-bar linkage, remains constant while moving. The reactionless conditions for planar four-bar linkages undergoing spatial motion are first given. Then, reactionless spatial 3-DoF mechanisms using four-bar linkages are synthesized. A numerical example of the reactionless spatial 3-DoF mechanism is given and, with the help of the dynamic simulation software ADAMS, it is shown that the mechanism is reactionless for arbitrary trajectories. Finally, this mechanism is used to synthesize reactionless 6-DoF parallel mechanisms.
This paper presents a comprehensive design procedure of a brushless DC limited angle torque motor (LATM) based on magnetic equivalent circuit analysis which predicts its performance and magnetic characteristics. Design of toroidally wounded armature and rotor with two pole tip segments are developed using selected ferromagnetic material and rare earth permanent magnets. Derivation of airgap and other motor dimensions and design parameters with their expressions are given. A finite element analysis verification of designed LATM using a 2D modeling and simulating package is presented. Performance characteristic of analytical model and FEA model of designed LATM is compared which validates the design procedure.
An energy-saving oil drilling rig is researched. A large accumulator is adopted in this rig to store the energy of the motor during the auxiliary time of lifting the drill stem and the potential energy of the drill stem when lowered. The equipped power of this rig decreases remarkably compared with the conventional drilling rig, and this rig can also recover and reuse the potential energy of the drill stem. Therefore, this rig owns remarkable energy-saving effect compared with the conventional drilling rig, and the energy-saving effect of the energy-saving oil drilling rig is also verified by the field tests. The mathematical model of the energy-saving oil drilling rig lowering the drill stem was derived and simulation analysis was conducted. Through simulation the curves of the drill stem lowering velocity and lowering displacement with time were obtained, and some conclusions were reached: (1) the heavier the drill stem lowered, the higher the lowering velocity is, and the shorter the lowering time is; (2) the smaller the displacement of the variable pump-motor, the higher the lowering velocity is, and the shorter the lowering time is.
This paper aims at presenting a technique to replace each three-degree-of-freedom (3-dof) spring–mass system (or substructure) by a set of equivalent masses so that the dynamic characteristics of a rectangular plate (or main structure) carrying any number of elastically mounted lumped masses may be obtained from the same plate carrying the same sets of rigidly attached equivalent masses. Because the three degrees-of-freedom (dof’s) of the substructure are embedded in its equivalent masses, the total dof of the entire vibrating system (i.e., the main structure together with all the substructures) is independent on the total number of the substructures attached to the main structure in the presented equivalent mass method (EMM). However, in the conventional finite element method (FEM), the total dof of the entire vibrating system increases by three when one more substructure is attached to the main structure. Compared with FEM, the merits of EMM are double: Firstly, since the total dof of the entire vibrating system in EMM is smaller than that in FEM, some computer storage memory may be saved. Secondly, since the dof’s for all the substructures are eliminated, the associated natural frequencies and mode shapes are excluded from those of the main structure and some effort required for the analysis of computer-output data may also be saved. It is evident that the last merits of EMM will be more predominant if the total number of substructures attached to the main structure is large.
Abstract The following ,thesis presents a computer ,and ,mathematical ,model ,of the dynamics,of the tethered subsystem of the Arecibo Radio Telescope. The computer ,and mathematical ,model ,for this part of the ,Arecibo Radio Telescope involves the study of the ,dynamic ,equations governing ,the motion ,of the system. It is developed in its various components; the cables, towers, and platform are each modeled in succession. The cable, wind, and numerical integration models stem
In this work we studied Reconfigurable Flight Control Systems to achieve acceptable performance of a fighter aircraft, even in the event of wing damage to the aircraft at low speeds and high angle of attack, which is typical of many combat maneuvers. Equations of motion for the damaged aircraft were derived, which helped in building simulators. A new methodology combining experimental and numerical aerodynamic prediction was proposed and implemented. For this a wind-tunnel study of a similar configuration was carried out to study the aerodynamics at low speeds and high angle of attack. A baseline control system for undamaged aircraft was developed, and finally a reconfigurable flight control scheme was implemented to keep the aircraft flyable even after the damage.
This paper investigates the use of dierent soft contact and friction models, in Simulink, in the context of legged locomotion. The main crite- rion for assessing the models is the number of integration steps that are taken using variable step integration methods. The variables that are considered for the comparisons are the type of contact and friction models, the integration method, the desired integration accuracy, and mass of the colliding body.
Many disciplines are wrought with high levels of uncertainty and many unknowns including trans-disciplinary design. Hence, to achieve some advancement within a discipline, we must provide aids in achieving mitigation of complexity and increasing understanding. We achieve this by investigating beyond the boundaries of the existing discipline's design concepts. This means stretching the boundaries of knowledge by traditional observation and analysis known as hard work using "elbow-grease" or reviewing those methods and processes of other disciplines, which might have applicability to our discipline's domain. Therefore, we addresses the challenge of minimizing ambiguity and fuzziness of understanding in large volumes of complex transdisciplinary information content and explore transdisciplinary synthesis via cognition based frameworks, for improving actionable decisions. Specifically, Recombinant Knowledge Assimilation (RNA) & Artificial Cognitive Neural Framework (ACNF) which recombine and assimilate knowledge based in human cognitive processes, formulated and embedded in a neural network of genetic algorithms and stochastic decision making, towards minimizing ambiguity and maximizing clarity. Thus, we introduce trans-disciplinary concepts, for application to specific problem sets, in order to achieve qualitative solutions for the large volumes of complex interconnected data and applications, which exist today.
This paper presents the machining potential field (MPF) and the explicit solutions of swept envelopes for 5-axis sculptured surface machining. The properties of the swept envelopes are analyzed. The results help us realize the geometric matching in tool-tip machining and understand the geometric machinability in tool-side machining. The complement of the swept envelope, which represents the in-process workpiece, is also addressed. It finally presents the swept envelope applications in tool orientation determination, machining interference avoidance, and run-time simulation.
Typically, mechanics education in engineering schools focuses on communicating explicit content to students, but deemphasizes the critical thought that underlies the discipline of mechanics. We give examples of the failure of students to apply basic principles of mechanics in solving problems. We develop assessment tools to measure critical thinking in student work, and how well mechanics textbooks engage students in critical analysis. Both tools focus on the treatment of three criteria that we judge to be fundamental, but which are commonly overlooked or undervalued – completeness of free body diagrams, consideration of physical dimension, and careful use of coordinates and sign conventions. Data collected from employing our assessment tools indicates that most of the time, students omit or misunderstand at least one critical idea when solving a problem, even when they obtain a correct answer. We also found that most of the textbooks surveyed had at least one major shortcoming pertaining to our criteria. Mechanics educators should vigorously emphasize fundamental aspects of mechanics, such as those that we suggest here, as a necessary (though insufficient) step to improve the ability of students to think critically and solve problems independently.
The paper concerns the usage of the method of multibody systems (MBS) in teaching students at the Warsaw University of Technology. Research results from the MBS discipline are being used in several ways. Large-scale computer software is being used to illustrate lecture material, some MBS research results are included in lecture topics and independent courses are taught, based directly on MBS research. During senior courses, advanced software is also used as a computational tool as well as an integral part of Virtual Prototyping. The paper presents also several examples of student projects created with MBS.
The mechanism of ground vibration in building demolition blasting was investigated, taking into account the prevailing influential
factors, including the building’s height of mass center, the quantity size, the structural feature, the component material
quantity, the demolition method, the geological structure of the region, earthquake resistance rank, as well as the earthquake
wave dissemination. The proposed method was applied efficiently to reduce the blasting effects on the environment, which enriches
the control theories of vibration caused by collapse in the blasting process and may provide a good reference for the related
engineering practices.
Keywordsdemolition blasting-collapse vibration-control technology-harmful effects
This study applies DE (discrete element) computational method to the dynamic problems of a vibrating string. The DE method
was originally initiated to analyze granular materials and now it has expanded to model fabric dynamics which is of interest
in a number of applications including those that manufacture or handle textiles, garments, and composite materials. Owing
to the complex interactions between each discrete element, simple circular geometric rigid model has been used in the conventional
DE method. However, in order to analyze the slender shape and flexibility of materials such as fabrics or strings, longer
and flexible geometric models, named as fiber models, was developed. The fiber model treats a series of connected circular
particles, and further can be classified as being either a RF (rigid fiber) or a CFF (completely flexible fiber) model. To
check the feasibility of those models, dynamic problems were solved and it is found that the fiber models accurately simulate
the dynamic and vibration behaviors of horizontally or vertically placed strings.
KeywordsCompletely flexible fiber model-DEM (Discrete Element Method)-Rigid fiber model-String vibration
This work proposes design, optimization and validation of a new two degree-of-freedom (DOF) rotational optical image stabilizer
(OIS) that is suitable for installing into a mobile-phone-camera. This OIS differs from the previous designs since it stabilizes
the lens holder directly by two-DOF translational mechanisms that are actuated by voice coil motors. The work can be divided
into three main parts: (1) designs of mechanism and genetic algorithm (GA) optimization of magnetic field, (2) establishments
of the dynamic model and equation of motions (EOM) of a dual-axis rotational structure, and (3) realizations of a sliding
mode control (SMC) controller with fine performance. The dynamic of the dual-axis rotational OIS system has been analyzed
and the EOM has been derived. Based on the Lagrange’s method, the motions of the OIS have been modeled through considering
kinetic energy and electromagnetic torques. In the last part, the theory of SMC is applied, and the associated simulations
are conducted. Based on the simulation results, the SMC controller is forged with the assistances from MATLAB pre-simulation
and tested by a microprocessor module. After a series of experiments and verifications, the prototype of the novel OIS is
finally accomplished with satisfactory performance of vibration reduction.
To optimize a swell compensator when a trailing suction hopper dredger (TSHD) is dredging at sea, the mathematical models were built about the effects of piston force, the distance of the piston movement, the speed of the piston movement, vessel motions and the cable-pulley system; the mathematical models proved that reducing the variation of cable tension force can lead to a smaller normal force on the draghead from seabed, and the optimizing factors were found as a result; then the factors were applied in modeling and simulation by the software of ADAMS to make known the multibody dynamic behavior of a TSHD; It is obvious that the simulation results tallied closely with the mathematical model.
Whenever we dealing with the kinematics problems, the “equations of motion” including displacement, velocity and acceleration equations are needed. We must do some mathematical operations such as calculus, inner or cross product, etc., to get these equations. It will be a troublesome work for us to do the operation of algebra. This paper presents an interesting mathematical method, graphical operation, to overcome this imperfection. By means of graphical operation, we could exactly simplify necessary algebraic operations to get the simplified equations and obtain the equations of motion in compact forms.
To return to their feet, inverted click-beetles (Elateridae) jump without using their legs. When a beetle is resting on its dorsal side, a hinge mechanism is locked to store elastic energy in the body and releases it abruptly to launch the beetle into the air. While the functional morphology of the jumping mechanism is well known, the level of control that the beetle has over this jumping technique and the mechanical constraints governing the jumps are not entirely clear. Here we show that while body rotations in air are highly variable, the jumps are morphologically constrained to a constant "takeoff" angle (79.9°±1.56°, n = 9 beetles) that directs 98% of the jumping force vertically against gravity. A physical-mathematical model of the jumping action, combined with measurements from live beetle, imply that the beetle may control the speed at takeoff but not the jumping angle. In addition, the model shows that very subtle changes in the exact point of contact with the ground can explain the vigorous rotations of the body seen while the beetle is airborne. These findings suggest that the evolution of this unique non-legged jumping mechanism resulted in a jumping technique that is capable of launching the body high into the air but it is too constrained and unstable to allow control of body orientation at landing.
Although zebra mussels (Dreissena polymorpha) initially colonized shallow habitats within the North American Great Lakes, quagga mussels (Dreissena bugensis) are becoming dominant in both shallow- and deep-water habitats. Shell morphology differs among zebra, shallow quagga and deep quagga mussels but functional consequences of such differences are unknown. We examined effects of shell morphology on locomotion for the three morphotypes on hard (typical of shallow habitats) and soft (characteristic of deep habitats) sedimentary substrates. We quantified morphology using the polar moment of inertia, a parameter used in calculating kinetic energy that describes shell area distribution and resistance to rotation. We quantified mussel locomotion by determining the ratio of rotational (K(rot)) to translational kinetic energy (K(trans)). On hard substrate, K(rot):K(trans) of deep quagga mussels was fourfold greater than for the other morphotypes, indicating greater energy expenditure in rotation relative to translation. On soft substrate, K(rot):K(trans) of deep quagga mussels was approximately one-third of that on hard substrate, indicating lower energy expenditure in rotation on soft substrate. Overall, our study demonstrates that shell morphology correlates with differences in locomotion (i.e. K(rot):K(trans)) among morphotypes. Although deep quagga mussels were similar to zebra and shallow quagga mussels in terms of energy expenditure on sedimentary substrate, their morphology was energetically maladaptive for linear movement on hard substrate. As quagga mussels can possess two distinct morphotypes (i.e. shallow and deep morphs), they might more effectively utilize a broader range of substrates than zebra mussels, potentially enhancing their ability to colonize a wider range of habitats.
ENGLISH ABSTRACT: This thesis forms part of the Control Surfaces in Confined Spaces (CoSICS) project conducted at Stellenbosch University. The aim of this project is reduction of control surface actuator footprints on the existing wing structures of commercial airliners such as the Airbus A320 and A330. This is achieved by reducing control surface hinge moments through the application of trailing edge tabs. This results in smaller actuator requirements. The first tier of the project focussed on the geometric optimisation of the tab applied to an aileron. This thesis focusses on the development of dynamic control of the aileron through either tab-only or concurrent tab and aileron actuation. In the effort to develop dynamic control, a fully coupled generalised dynamic model of the tab and aileron is derived and presented. Through linearisation of this model, linear controllers are developed. Two distinctly different controllers are presented; the first controller makes use of classical methods for control of the tab-only actuated aileron and the second controller makes use of modern control techniques such as full state feedback to facilitate controlled concurrent tab and aileron actuation. Each proposed controller is evaluated in terms of dynamic performance, robustness, disturbance rejection and noise immunity. Based on the controller development, a summary of dynamic actuator requirements is given. Practical verification of the model and the controller performance is then undertaken. The development of the necessary hardware and software is also presented. The concept of aileron control through tab-only actuation and concurrent tab and aileron actuation is then validated. Conclusion are then drawn about the accuracy of the theoretical model and the practical performance of the controllers. The thesis is concluded with recommendations for future work to increase the fidelity of the model. Important aspects about the practical implementation of the concept on commercial jetliners are also summarised. AFRIKAANSE OPSOMMING: Hierdie tesis is deel van die Control Surfaces in Confined Spaces1 projek by Stellenbosch Universiteit. Die doel van hierdie projek behels die verkleining van die aktueerder spasie en ondersteunings struktuur vereistes, op die bestaande vlerk struktuur van kommersiële vliegtuie soos die Airbus A320 en Airbus A330. Dit is bereik deur die vermindering van die beheeroppervlak skarnier se draaimoment met behulp van aerodinamiese hulpvlakke. Kleiner aktueerders word dus benodig. Die eerste stadium van die projek fokus op die geometriese optimisering van die hulpvlak op ’n aileron. Hierdie tesis fokus op die ontwikkeling van dinamiese beheer van die aileron deur middel van hulpvlak aktueering alleenlik of met die gelyktydige aktueering van die hulpvlak en aileron. In die proses van onwikkeling is ’n volgekoppelde veralgemeende dinamiese model van die hulpvlak en aileron afgelei en voorgelê. Deur middel van linearisasie van die model is linieêre beheerders ontwikkel. Tans is twee verskillende beheerders ontwikkel. Die eerste beheerder is gebaseer op die klassieke metodes en maak staat op die aktueering van die hulpvlak alleenlik. Die tweede beheerder maak gebruik van moderne beheer tegnieke soos vol toestand terugvoer om gelyktydige hulpvlak en aileron aktueering te realiseer. Die beheerders is elk geëvalueer in terme van dinamiese gedrag, robuustheid, versteurings verwerping en ruis verwerping. Die beheerstelsel ontwikkeling lei tot ’n opsomming van die dinamiese aktueerder vereistes. Dit word gevolg deur praktiese verifikasie van die model en die beheerstelsel gedrag. ’n Opsomming van die ontwikkeling van nodige hardeware en sagteware word voorgelê. In hierdie proses is die konsep van beide hulpvlak alleenlike aktueering en gelyktydige hulpvlak en aileron aktueering bewys. Gevolgtrekkings word gemaak oor die akkuraatheid van die model en die praktiese gedrag van die beheerders. Die tesis word afgerond met voorstelle vir toekomstige werk wat die model se betroubaarheid kan verbeter. Verder word belangrike punte oor die praktiese aspekte van konsep implementering op kommersiële vliegtuie ook uitgelig. Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011.
A virtual reality (VR) haptic dental training system could be a promising tool for future dental education. One major challenge is to develop a virtual tooth model which similarly reflected a real tooth having multiple layers with different mechanical hardness in each layer. The multi-layered virtual tooth model was successfully constructed in our virtual system. The constructed model allows us to feel tooth cutting which is similar to that with a real tooth. Through a cutting experiment by using the real tooth, a spring coefficient and a damping coefficient of a dental hard tissue were determined 0.8 N/mm and 1.79 Nsec/mm respectively. The feedback force smoothly altered when crossing the border of regions having different mechanical hardnesses. The constructed model introduced in this study could be a promising tool for acquiring dental hand skills in a virtual learning system.
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