Thesis (Ed.D.)--Boston University.

Tool chatter in longitudinal turning is addressed with a new perspective using a complex machining model describing the coupled tool-workpiece dynamics subject to nonlinear regenerative cutting forces, instantaneous depth-of-cut (DOC) and workpiece whirling due to material imbalance. The workpiece is modeled as a system of three rotors: unmachined, being machined and machined, connected by a flexible shaft. The model enables workpiece motions relative to the tool and tool motions relative to the machining surface to be three-dimensionally established as functions of spindle speed, instantaneous DOC, rate of material removal and whirling. Excluding workpiece vibrations from the cutting model is found improper. A rich set of nonlinear behaviors of both the tool and the workpiece including period-doubling bifurcation and chaos signifying the extent of machining instability at various DOCs is observed. Presented numerical results agree favorably with physical experiments reported in the literature. It is found that whirling is non-negligible if the fundamental characteristics of machining dynamics are to be fully understood. The 3D model is explored along with its 1D counterpart, which considers only tool motions and disregards workpiece vibrations. Numerical simulations reveal diverse behaviors for the 3D coupled and 1D uncoupled equations of motion for the tool. Most notably, observations made with regard to the inconsistency in describing stability limits raise the concern for using 1D models to obtain stability charts. The nonlinear 3D model is linearized to investigate the implications of applying linear models to the understanding of machining dynamics. Taylor series expansion about the operating point where optimal machining conditions are desired is applied to linearize the model equations of motion. Modifications are also made to the nonlinear tool stiffness term to minimize linearization errors. Numerical experiments demonstrate inadmissible results for the linear model and good agreement with available physical data in describing machining stability and chatter for the nonlinear model. Effects of tool geometry, feed rate, and spindle speed on cutting dynamics are also explored. It is observed that critical DOC increases with increasing spindle speed and small DOCs can induce cutting instability -- two of the results that agree qualitatively well with published experimental data.

Tool chatter in longitudinal turning is addressed with a new perspective using a complex machining model describing the coupled tool-workpiece dynamics subject to nonlinear regenerative cutting forces, instantaneous depth-of-cut (DOC) and workpiece whirling due to material imbalance. The workpiece is modeled as a system of three rotors: unmachined, being machined and machined, connected by a flexible shaft. The model enables workpiece motions relative to the tool and tool motions relative to the machining surface to be three-dimensionally established as functions of spindle speed, instantaneous DOC, rate of material removal and whirling. Excluding workpiece vibrations from the cutting model is found improper. A rich set of nonlinear behaviors of both the tool and the workpiece including period-doubling bifurcation and chaos signifying the extent of machining instability at various DOCs is observed. Presented numerical results agree favorably with physical experiments reported in the literature. It is found that whirling is non-negligible if the fundamental characteristics of machining dynamics are to be fully understood. The 3D model is explored along with its 1D counterpart, which considers only tool motions and disregards workpiece vibrations. Numerical simulations reveal diverse behaviors for the 3D coupled and 1D uncoupled equations of motion for the tool. Most notably, observations made with regard to the inconsistency in describing stability limits raise the concern for using 1D models to obtain stability charts. The nonlinear 3D model is linearized to investigate the implications of applying linear models to the understanding of machining dynamics. Taylor series expansion about the operating point where optimal machining conditions are desired is applied to linearize the model equations of motion. Modifications are also made to the nonlinear tool stiffness term to minimize linearization errors. Numerical experiments demonstrate inadmissible results for the linear model and good agreement with available physical data in describing machining stability and chatter for the nonlinear model. Effects of tool geometry, feed rate, and spindle speed on cutting dynamics are also explored. It is observed that critical DOC increases with increasing spindle speed and small DOCs can induce cutting instability -- two of the results that agree qualitatively well with published experimental data.

Many oceanographers have postulated that internal wave form inversion would take place at the turning point where the thickness of the upper and bottom layer are equal in a stratified two-layer fluid system. This implies that an internal wave of depression may convert into elevation as the wave propagates over a continental margin comprising continental slope and shelf. Laboratory experiments were conducted on the propagation of a depression ISW over a trapezoidal obstacle in a stratified two-layer fresh/brine water system in a steel framed wave tank of 12m long with cross section of 0.7m high by 0.5m wide. The relative difference in water depth between the upper and lower layer and the initial ISW amplitude were the main controlling parameters, among others. The water depth in the stratified two-layer system on the horizontal plateau of the trapezoid obstacle fell into one of the following case: (1) the upper layer larger than lower (H1>¢Ö2'); or (2) equal depth in the upper and lower layer (H1=¢Ö2'); or (3) the upper layer less than lower layer (H1<¢Ö2'). In addition of the depth ratio, the difference in the length of the horizontal plateau and the thickness of the phycnocline above if were also parameters affecting the outcome of the experiments. In these experiments, three different type of the height and length of the trapezoidal obstacle were used, including long (4.8x0.37m), medium (1x0.35m) and short (0.5x0.35m) types. A full account on the characteristics of the ISW evolution observed during this experimental study is presented in this thesis. As an ISW propagated on the fronting slope, were run-down, vortex motion, internal hydraulic jump (IHJ) and run-up were occurred. Once the wave passed the turning point (where the depth of upper and lower layer equal), the wave form became elevation on the plateau above the obstacle. Based on the laboratory data available, the effect on internal wave evolution can be evaluated by the relative fluid thickness (H1/¢Ö2') on the plateau. The outcome can be classified into three categories: (1) H1>¢Ö2', the relative layer thickness on the plateau unfits for depression ISW propagation and waveform behaves like elevation type; (2) H1=¢Ö2', wave boluses containing mixed fluid propagating on the plateau after breaking on the slope; (3) H1<¢Ö2', ISW propagated over trapezoidal obstacle subjected to shoaling and viscosity effect, without change in waveform. As a depression ISW propagated over the variable length of the plateau, another important factor affecting the intensity of the internal hydraulic jump was the water volume drawn from the plateau. In the case of long horizontal plateau, the interaction range was large, and the IHJ was strong. Consequently, the thickness of the increased which caused the IHJ to move upward along the fronting slope. However, the amplitude and phase speed of the resulting internal wave decreased as if propagated further.

The locomotion robots have wheeled, biped, quadruped and so on. Walking robot may not move faster or more popular than wheeled robot. But walking robot is a good assistant to pass through the rough roadway and to explore unknown landforms. The advantages of walking robot have: mobility, walking in danger environment, across obstacles, up stairs and down stairs and nimbleness. These difficulties environment are the obstacles for the wheeled robot. Today, many robots are designed to make up for human body and ability. Application in explore the outer space, to relieve the victims of a disaster, to move work, to offer greater convenience to the people, housekeeper, to substitute for handicapped limbs and so on. In the thesis, we analyze the gait of biped robot. Biped robot arrive a destination rapidly in the limit environment. Biped can use turning motion gait to bypass obstacles. We purpose to maintain motion velocity of biped robot and come out the speed and stride distance of the biped robot. The studies have: biped robot turning design, planning humanoid motion gait and experiment motion gait.

Thesis (M.S. in M.E.)--School of Mechanical Engineering, Georgia Institute of Technology, 2004. Directed by Thomas Kurfess. / Includes bibliographical references (leaves 108-111).

Thesis (Ph. D.)--Worcester Polytechnic Institute. / Keywords: Chip breaking; prediction; turning; grooved inserts. Includes bibliographical references (p. 113-121).

Denna uppsats är skriven på avancerad nivå inom socialt arbete. Dess syfte är att belysa turning points från kriminalitet och utgår från intervjuer med personer som tidigare haft en kriminell karriär. Intervjuerna har varit semistrukturerade och berört orsaken till turning points och motivationskällor till upprätthållandet av beslutet. Analysen har genomförts med hjälp av symbolisk interaktionism och teorier om stämpling, stigma och strain. Resultatet visar nätverkets betydelse för processen kring en turning point samt vikten av individens egna vilja till förändring. I resultatet går det även att utläsa hur personligt engagemang från omgivningen påverkar individen positivt vid en turning point. I diskussionen lyfter författaren resultatet och diskuterar även samhällets insatser utifrån uppsatsens resultat. Efter analys och diskussion framkommer författaren med slutsatsen att en turning point sker först när individen själv vill genomgå en förändring. När individen har tagit det beslutet fungerar nätverket både motiverande samt som en resurskälla. Med personligt engagemang från omgivningen så kan individen stå fast vid sitt beslut om en turning point och motiveras till ett liv utan kriminalitet.

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Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 108-112). Available also in a digital version from Dissertation Abstracts.