Dissertations / Theses on the topic 'Closed tube'

Mestrado em Engenharia Mecânica
Estudos na área dos materiais têm desempenhado um importante papel na indústria automóvel. Com o tempo, a utilização de materiais pesados tem vindo a ser substítuido por materiais mais leves como ligas de aço avançados, ligas de alumínio e compósitos. Quanto mais leves forem as estruturas, melhor o seu desempenho em termos de consumo de combustível e emissão de gases. No entanto, as estruturas necessitam de manter a sua integridade, assegurando a segurança activa e passiva dos ocupantes. Sendo assim, este estudo concentra-se em estudar o comportamento mecânico à compressão de tubos de alumínio preenchidos com espumas de alumínio. As espumas fechadas são produzidas através do método de pulverotecnologia ao passo que as espumas abertas são fabricadas com recurso à técnica de fundição de precisão. Este estudo passa também pela análise de espumas abertas preenchidas com polímeros, neste caso silicone e epóxido, comummente chamadas espumas híbridas. Os testes de compressão foram realizados em condições quasi-estáticas e dinâmicas, sendo analisados com recurso a uma técnica não destrutiva (Termografia Infravermelha), na qual se obtêm imagens térmicas (termogramas), utilizados no estudo dos modos de deformação. A análise dos resultados passa não só pelo estudo dos modos de deformação mas também da sua influência na capacidade de absorção de energia, mas também na ocurrência de fendas e fracturas. Os resultados demonstram que os tubos preenchidos com espumas de alumínio de porosidade fechada durante a etapa de formação da própria espuma, designados in-situ, são aqueles que garantem melhor resposta mecânica, tendo um comportamento mais estável e prevísivel.
Research in materials has been playing and important role in automotive industry. With time, the use of heavier material is being replaced by lighter materials such as advanced steel alloys, aluminium alloys and composites. The lighter the structures the better in terms of fuel consumptions and gas emission’s reduction. However, these structures have to maintain their reliability, ensuring active and passive security to vehicles passengers. Therefore, this study concentrates on studying the mechanical behaviour of aluminium tubes filled with aluminium foams under compression. The closed foams are produced through a powder metallurgical method, while the open-cell foams are produced through investment casting. This study also focuses on the study of open-cell foams embedded with polymers, silicone and epoxy, commonly called ’Hybrid Foams’. Compression tests are made under quasi-static and dynamic conditions, and analysed with non-destructive technique (Infrared Thermography), which allows to obtain thermal images (thermogrames), used to study the deformation modes. The analyses of the results passes not only through the study of the deformation modes but also focuses on its influence in energy absorption capability, as well as in the occurrence of cracks and fractures. The results show that foam filled tubes with closed-cell, expanded inside the tube itself ( designated as in-situ), ensures a better mechanical response, due to its more stable and predictable behaviour.

L'interaction entre une onde de choc plane et un nuage de gouttes d'eau homogène, monodisperse est étudiée dans un tube à choc. Les influences de la fraction volumique d'eau, αd(1 %, 0.3 % et 0.1%), rapport du volume d'eau sur le volume du nuage, de la hauteur du nuage Hd (70 cm, 40 cm et 15 cm), du diamètre des gouttes φd (250 µm et 500 µm ) et du nombre de Mach M (1.3 et 1.5) sont étudiées pour des fractions volumiques inférieures au pour cent. Lors de cette interaction, la pression en paroi du tube à choc est mesurée et la visualisation du nuage est obtenue par une méthode ombroscopique directe. Une évolution temporelle caractéristique de la pression induite par la propagation d'une onde de choc dans un tel milieu, est mise en évidence. Cette allure, diffère significativement de celle obtenue avec un nuage constitué de particules solides: la fragmentation des gouttes en est responsable. Une zone où la pression diminue directement après le pic de pression est alors observée aux stations de mesure localisées dans le nuage. L'atténuation de la surpression est mise en évidence: elle peut atteindre 80% du pic de pression mesuré sans nuage. Dans la partie numérique de ce travail, deux modèles de fragmentation sont implémentés, comparés et validés dans un code de calcul monodimensionel, instationnaire, Eulérien appliqué aux écoulements dilués (αd<1 %). On montre que la formulation du taux de production des gouttes selon le taux d'accroissement soit de leur nombre, soit de leur diamètre doit être utilisée respectivement soit avec, soit sans la prise en compte l'étape de déformation de la fragmentation
The interaction between a planar shock wave and an both homogeneous and monodispersed droplet water cloud is studied in a shock tube. The effects of the water volume fraction αd (1% %, 0.3 % et 0.1%), ratio between the volume of water and the volume of the cloud, the height of the two-phase medium Hd (70 cm, 40 cm et 15 cm), the droplets diameters φd (250 µm et 500 µm ) and the Mach number M (1.3 et 1.5) are studied for a volume fraction smaller than one per cent. During this interaction, the pressure is measured and the visualization of the cloud is obtained by direct shadowgraphy. A characteristic temporal evolution of the pressure induced by the propagation of the shock wave in such a mixture is highlighted. This behavior differs significatively from the one obtained with a solid particles cloud : the droplet atomization is responsible of this change. A zone where the pressure decreases directly after the pressure peak is observed at different stations located into the water cloud. The mitiagtion of the overpressure is shown: it can reach 80%of the pressure peak measured without cloud. In the numerical part, two fragmentation models are added, compared and validated in a comptutational, one dimensional, instationnary, Eulerien code in the case of dilute flows (αd<1 %). We show that the formulation of the production rate of droplets defined by the number of droplets growth, or the diameter droplet growth, must be used, respectively, with and without taking into account the deformation stage of the droplet breakup. Thus, the numerical results are in good agrement with those obtained experimentally

Design of linear actuator for parallel kinematic structure is described in this master´s thesis. The parallel kinematic structure is described in the first part. Open kinematics structure and close kinematics structure are compared. Their benefits and disadvantages are also mentioned. Construction of some parallel robots is illustrated. Linear actuators of different company are described. Mechanical parameters and construction of linear actuator are compared. Design of linear actuator is described in practical part of master´s thesis. A few variation of linear actuator are introduced. Individual variants are evaluated by Multicriteria Decisional Analysis and a final conception is selected. Final conception of linear actuator is elaborated. Reasons for selection of every part of linear actuator are given and basic mechanical calculation design part is made. FEA analysis of the structural part of linear actuator is made. Design of linear actuator is evaluated in the final part.

碩士
國立臺灣大學
機械工程學系
85
In this study, we employ the numerical method to study the propagationbehavior of a premixed laminar flame in a closed circular tube. Anaxisymmetric flow is considered, and a one-step overall reaction with reactionrate governed by Arrhenius law is used to study the effects on the flamepropagation of the thickness of the initial hot spot, the gravity, and theboundary conditions. The numerical results show that a tulip-shaped flame, a mushroom-shapedflame or a flame with a shape between them will exist in the small closedcircular tube, depending on the given conditions. The results indicate that one of the factors controlling the flame shapeis the flow field of the mixture induced by the flame.

碩士
大葉大學
機械工程研究所
83
Here a hydrodynamic model was proposed for flame propagation in close tube effected by flow stretch. The flame is treated as a surface of discontinuity like in previous work. For the structure governing flame burning rate, large activation energy and large heat release assumptions are used in the model. It is well known that for laminar premixed flames with Lewis number smaller then one propagating in open space, the burning rate will increase when it is subjected to positive flow stretch and the reverse is true for negative flow stretch. And for flame with Lewis number bigger then one the trend is just the opposite. For flames propagating in open space the pressure is constant , while in present study the overall pressure is rising with the flame propagation . Present theoretical results suggest for flames propagating in closed tube the effect of flow stretch to the flame is the same as that in open space. That is for flame in closed tube positive flow stretch will increase the mass burning rate for flames with Lewis number smaller then one, and for flames with Lewis number bigger then one the mass burning rate will decrease. The trend will reverse for flames experiencing negative flow stretch.

碩士
國立臺灣大學
機械工程學系
86
The propagation of a premixed laminar flame in an adiabatic closed circular tube is numerically investigated in this study. An axisymmetric flow is assumed and a global one-step chemical reaction with reaction rate governed by the Arrhenius law is adopted. A comparison between the numerical results and the experimental results shows that the numerical simulation can predict the flame transient behavior quite well. The numerical results indicate that the cause of the tulip-shaped flame formation is determined by the interaction between the hydrodynamics and the Darrieus-Landau instability. Although the flame behaviors differ in closed tubes with fixed tube aspect ratio, they are the same if the additional condition of fixed tube diameter to the flame thickness ratio is enforced. In this study, the effects on the flame development of the tube diameter, the shape of the ignition source, the gravity and the rotating speed of the tube are also investigated.

碩士
大葉大學
機械工程研究所
82
We propose a thermal theory for the propagation of premixed flame under pressure change with pertubation in energy equation. And the pertubation term can be assumed to simulate the effect of dilute spray on premixed flame.Coupled with equation relating flame burning rate and pressure build up in a closed tube we can model the effect of dilute spray on the propagation of premixed flame in a closed tube. It has long been know that premixed flame with Lewis number smaller than one is stable to one-dimensional disturbances while that with Lewis number bigger than one(Buckmaster and Ludford,1982).And this is reflected in the paper by McGreevy et al.(1992)for premixed flame in closed tube. They found that for flame with Le>1( Le represents Lewis number here after ) is sensitive to the initial condition and flame with Le<1 is not.And for Le>1 case two kinds of phenomena might happen,one is the flame propagates faster and faster,then induce homogenous explosion, the other is the flame propagates slower and slower, then extinction occur.From the present study we found that with a perturbation term in the energy equation, the propagation speed of premixed flame with Le>1 in a closed tube can be increased. Since the perturbation term in our study was assumed to simulate the effect of dilute spray. Which may indicate a way to improve the combustion in a lean-burn engine by dilute spray.

Purpose: The of this study was to explore the knowledge, level of practice, and the frequency of problems met during the use of CTSS amongst intensive care unit (ICU) nurses and suggest ways to improve the use of the system. Design: A non experimental exploratory design using a descriptive survey approach was employed. Sample: The sample of participants were taken from three governmental hospitals in Abu Dhabi chosen randomly. It included all nurses in the ICUs of three hospitals who happened to be working at the time of the study. The response was Eighty three staff nurses, three charge nurses, and one respiratory therapist. Instrument: A questionnaire consisting of twenty one questions was used to explore the ICU nurses' knowledge, experience, practice, and difficulties met by nurses. Averages, tables, figures, and correlation coefficient were used to analyze the data. Results: Results showed a positive correlation (+0.0433) between the level of knowledge and length of use of the system but the effect is minimal. Again the knowledge and the frequency of use on ventilated patients were minimally positive (+0.0898). On the other hand, the relation between the frequency of use and the years of experience was more positively related than the frequency of use and the knowledge. Conclusion: There is a need to set a plan aiming at making the system more frequently used. Not only that , but it should be used safely and appropriately and supported by policy and procedure guidelines.
Thesis (M.Cur.)-University of Natal, Durban, 2001.

碩士
國立臺灣科技大學
機械工程系
99
Traditionally, the study of standing wave resonance inside a closed tube is focussed on the low frequency resonance system (generally below 200 Hz), which is limited by the mechanical transmission mechanisms used. In order to reduce the space taken by the mechanical transmission mechanisms, high frequency resonance system is favored. In addition, it is very difficult to measure the variations of physical quantities inside the resonance tube with current technologies available. However, this presents no difficulties in using numerical simulation to monitor the variations of physical quantities inside the tube. In this work, the resonance behaviors inside a closed tube (0.0435 m in length, 0.026 m inside diameter) driven by a reciprocating piston at a frequency of 4000 Hz are studied. The tube is assumed to be axis-symmetric and the walls are assumed to be adiabatic. The effects of detuning and frequency multiplication on the nonlinear resonance are investigated. Closed to the exact resonance, the pressure waveforms are significantly distorted and become asymmetric. Formation of shock waves can be clearly observed. Due to the steep velocity gradient inside the velocity boundary layer, significant shear stresses occurs near the velocity boundary layer and kinetic energy is dissipated and converted into heat. This heat will accumulate inside the velocity boundary layer due to the adiabatic boundary conditions. This, in turn, will lead to the growth of thermal boundary layer and result in a very thick thermal boundary layer. The results of the simulations can provide the necessary guidelines for the selection of the proper locations of the stack plates inside a thermoacoustic resonance tube.

碩士
輔仁大學
護理學系碩士班
93
This study aims at comparing of closed- and open-system endotracheal suctioning on the effects of artierial oxygenation and breathing effort during mechanical ventilation without pre-oxygenation. The independent variable is the endotracheal suctioning method and the dependent variables are the arterial blood oxygen pressure tested from the laboratory and the pressure-time product monitored by the pneumotachograph. The sample consisted 30 patients at the intensive care unit of a medical center in northern region of Taiwan. All the 30 cases were tested for the arterial blood oxygen pressure, only 22 of the 30 cases were tested for pressure-time product. A two groups cross-over experimental research design was applied, in which two patients were selected as a group and were randomly assigned one into Model 1, a closed-open sequencing of endotracheal suctioning system, and the other Model 2, an open-closed sequencing of endotracheal suctioning system. Thus, there were 15 patients in each model for test of arterial blood oxygen pressure and 11 patients for test of pressure-time product. Patients in model 1 were first applied a closed endotracheal suctioning system. Thereafter, these patients were received three measurement for arterial blood oxygen pressure at the time right before endotracheal suctioning, right after endotracheal suctioning and one minute after endotracheal suctioning, and were received six measurement for pressure-time product at the time right before endotracheal suctioning and once per minute for 5 minute after endotracheal suctioning. Thirty minutes after last data collected, patients' closed endotracheal suctioning system were transformed into open endotracheal suctioning system, and the same measures were repeated for tests of arterial blood oxygen pressure and pressure-time product. Patients in model 2, an open-closed sequencing of endotracheal suctioning system, the application of the endotracheal suctioning system was just reverse to model 1, but the measurement method for arterial blood oxygen pressure and pressure-time product was the same as of model 1. A better suctioning system should result in less decrease in the arterial blood oxygen pressure and less increase in the pressure-time product. There are two hypotheses in this study. Hypothesis 1 tests if the decrease on values of arterial blood oxygen pressure for pre-and post-endotracheal suctioning and to that of pre-endotracheal suctioning of the closed endotracheal suctioning system is less than that of the same comparison of the open endotracheal suction system. Result from the modified analysis of GEE model shows that the decrease of the arterial blood oxygen pressure between pre- and post-endotracheal suctioning on the closed endotracheal suctioning system is less than that of the open endotracheal suctioning system by 11.18 mmHg, but the difference does not reach the statistical significance level (p = .10). Hypothesis 2 tests if the increase on values of pressure-time product for pre- and post endotracheal suctioning of the closed endotracheal suctioning system is less than that of the same comparison of the open endotracheal suctioning system. Result from the modified analysis of GEE model shows that the increase of the pressure-time product between pre- and post-endotracheal suctioning on the closed endotracheal suctioning system is less than that of the open endotracheal suctioning system by 27.04 cmH2O．sec/breath, but the difference does not reach the statistical significance level (p = .39). It is suggested that a large sample size should be applied to retest these two hypotheses. Results of this study can be used as a reference to those who care for patients that are highly dependent on ventilators with high concentration of oxygen.

碩士
國立成功大學
電機工程研究所
81
Exciting ZnS:Cu,halogen phosphor to emit light by the AC high electric field, is called AC powder or thick electro- luminescence. AC powder EL is an important back light sourceof LCD, because it is light, thin and low cost, and has un- iformlight em ission. At present,the methods that are used to prepare AC pow-der EL phosphor include the open tube und er S gas methodand the close tube method. In this paper, the close tube method is used to pr oduce ZnS:Cu,Br phosphor first. The closetube meth od is to mix ZnS powder with Cu and Br sources: Cu (CHCOOH),Br(NH) and put the mixture into a vacuum, closequartz tube and then firing the mixture to s ynthesize phos-phor at high temperature. The advan tages of the close tubemethod include that the los ing of sulfur from ZnS crystal isslight,the impuri ties can be easy and effective doped into ZnS and the phsophor particle can grow more fast. In this paper,we also try to produce AC powder EL phosphor by a no-vel method. In this method, ZnS:Br phosph or is synthesizedfirst, then coating a copper-rich er layer on the surface of phosphor particle,and t hen Cu ions are diffused into ZnS toform phosphor. The phosphor is found appear blue light emission u nder high AC electric field. The experimental results show the main factors that dete-rmine the phosphor EL brightness are the doping Cu concentration and the cooling speed. The reason may be the concentration of CuS deposition in the phosphor particle by the above factors. In our experiment, AC powder EL phosphor be doped Cu by after-diffusion method show better EL brightn essthan that be doped Cu at the particle growth st age, and the former always have blue light emissio n.

碩士
國立清華大學
動力機械工程學系
104
This study aims to investigate the thermocapillary migration of long bubbles in closed cylinder tubes. Different experimental conditions like bubble length, temperature gradient, tube radius and surface property were changed to find the influence on the migration velocity. Linear temperature field was established by using current experimental setup. The temperature gradient in current experiment can be adjusted ranging from 0 to 4℃/cm. The molecule based temperature sensor technique has also been applied to the experiments for fluid temperature measurements inside cylinder tubes. The temperature data acquired by molecule based temperature sensor show good agreement with the one measured by thermocouples and the deviation between them is within 5 %. The glass cylinder tubes with hydrophilic surface have also been prepared by evaporating silane inside the cylinder surface. Deionized water and Ethanol which can form wetted surface inside cylinder tubes regardless the surface properties were chosen as the working fluid. It is found that the migration velocity linearly increases with the temperature gradient and the tube radius which differ from previous studies. They are due to the effect of evaporation/condensation and the vertical thermocapillary force observed in current experiments. These effects make the film thicker at the top of cylinder which causes fluid passing similar to parallel plate flow. Previous studies reported that the migration velocity has a linear dependence on modified capillary number if parallel plate flow dominates the flow field around the bubble. The results also show that bubble moving speed in hydrophobic cylinder tubes at low temperature gradients has 46 percent faster compared to the hydrophilic cylinder tubes.

This work analytically solves the governing equations of the laminar film condensation from pure vapors in vertical tubes to find the condensate film thickness. The solution is then extended to turbulent flow conditions for steam. All other relevant quantities are derived from the film thickness solution. For laminar film condensation of quiescent vapors, an exact explicit solution and an approximate closed-form solution were found by using a new definition of the dimensionless film thickness, the Lambert W-function, and a logarithmic function approximation. For laminar mixed-convection film condensation with interfacial shear stress, an approximate closed-form solution was found by using a new definition of the pressure gradient. For turbulent film condensation of steam, correlations of the turbulent vapor and liquid viscosities were formed by asymptotically comparing this approximate laminar closed-form solution to a turbulent flow numerical solution. The present solutions compared very well to published numerical and experimental data.

Yes
Springtails (Collembola) are unique in Hexapoda for bearing a ventral tube (collophore) on the first abdominal segment. Although numerous studies have been conducted on the functions of the ventral tube, its fine structure has not been thoroughly elucidated to date. In this paper, we observed the jumping behavior of the clover springtail Sminthurus viridis (Linnaeus, 1758) and dissected the ventral tube using light microscopy to elucidate the fine structure and the possible function of the ventral tube. The results show that a pair of eversible vesicles can be extended from the apical opening of the ventral tube. The eversible vesicles are furnished with numerous small papillae, and can be divided into a basal part and a distal part. The eversible vesicles have a central lumen connected to the tiny papillae and leading to the body cavity. The eversible vesicles can reach any part of the body, and may serve as following functions: (a) absorbing moisture; (b) uptaking water; (c) cleaning the body surface; and (d) fastening the body on a smooth surface.

A crystal structure of OFP has been solved at 2.0 A resolution. It reveals that OFP is tetrameric and exists as a dimer of homo-dimer. It adopts the characteristic 11-stranded beta-can structure of GFP-like proteins. Based on the crystal structure, four special mutants were created primarily by site-directed random mutagenesis and error-prone PCR techniques. The first mutant is named Y37F in which a substitution of tyrosine (Y37) for phenylalanine creates a green emitter with an excitation maximum of 480 nm. The emission spectrum of Y37F is similar to that of EGFP and peaked at 498 nm. The second mutant is named K79R in which a substitution of lysine (K79) for arginine creates a red emitter with an excitation maximum of 548 nm. While the excitation maximum of K79R was literally unchanged with respected to OFP, the two emission maxima of K79R are both red-shifted to 512.5 nm and 583 nm. The third mutant is a dimeric mutant named OFP2 with W118K and V120E mutations. The absorption spectrum of OFP2 is identical to that of OFP. The emission spectrum of OFP2 has two emission maxima at 498 nm and 568 nm, respectively. Only bright orange fluorescence maximum at 568 nm is observed when OFP2 is excited at 515 nm or above. When OFP is excited between 430 nm and 470 nm, however, roughly equal amount of green emission maximum at 498 nm is also observed. The fluorescence quantum yield of OFP2 is about the same as OFP. The last mutant is named OFPm. It is a monomeric mutant of OFP2. A total of seven extra mutations (T141A/T144H/F155V/Y188P/K192S/R194S1N199A) were introduced on OFP2. The absorption maximum of OFPm is slightly red-shifted to 560 nm as compared to OFP2. The emission spectrum of OFPm has two emission maxima at 504 nm and 576.5 nm, respectively. Only red fluorescence maximum at 576.5 nm is observed when OFPm is excited at 525 nm or above. When OFPm is excited between 430 nm and 470 nm, however, the emission is mainly green fluorescence peaked at 504 nm with small amount red light peaked at 576.5 nm. The fluorescence quantum yield of OFPm is about 0.32.
A novel Orange Fluorescent Protein (OFP) was cloned from the tentacles of Cnidarian tube anemone Cerianthus sp. This protein consists of 222 amino acid residues with the calculated molecular mass of 25.1-kDa. A BLAST protein sequence homology search revealed that native OFP has 81% sequence identity to Cerianthus membranaceus green fluorescent protein (cmFP512), 38% identity to Entacmaea quadricolor red fluorescent protein (egFP611), 37% identity to Discosoma red fluorescent protein (DsRed), 36% identity to Fungia concinna Kusabira-Orange fluorescent protein (KO), and a mere 21% identity to Aequorea victoria green fluorescent protein (GFP). Spectroscopic analysis indicated that it has a wide absorption spectrum peak at 548 nm with two shoulders at 483 and 515 nm. Bright orange fluorescence maximum at 568 nm was observed when OFP was excited at 515 nm or above. When OFP was excited well below 500 nm, a considerable amount of green emission maximum at 498 nm was also observed. It has a fluorescence quantum yield (phiF) of 0.64 at 25°C. The molar absorption coefficients (epsilon) of folded OFP at 278 and 548 nm are 47,000 and 60,000 M-1 · cm -1, respectively. Its fluorescent brightness (epsilon · phi F) at 25°C is 38,400 M-1 · cm -1. Fluorescent intensity of OFP is detectable over a pH range of 3 to 12. OFP was readily expressed as soluble protein in Escherichia coli at 37°C.
Ip, Tsz Ming.
"November 2007."
Source: Dissertation Abstracts International, Volume: 69-08, Section: B, page: 4733.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2007.
Includes bibliographical references (p. 139-149).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstracts in English and Chinese.
School code: 1307.

碩士
逢甲大學
機械工程學所
94
Traditionally, the analytical solutions of the transmission loss (TL) of mufflers can be found if the acoustic mode of (0,1,0) is not excited. The acoustic waves in the expansion chamber before the cut-on frequency thus can be regarded as 1-D plane waves, and the results from theoretical, numerical and experimental solutions of the transmission loss agree well. For mufflers with extended tubes that in close propinquity, traditional research assumes a 1-D plane acoustic wave to occur, but this is an irrational hypothesis due to the fact that acoustic waves propagate in 3-D form even at low frequencies. In this case, the peak of the transmission loss can occur at low frequencies around 700 Hz and the quantity of the TL is about 60 dB ~ 80 dB. When the extended tubes in mufflers are in close proximity and are the same distance apart, the effects of the resonators are identical regardless of any geometrical condition shifts. These effects also make a peak TL occur at low frequencies. The alteration of geometrical values only affects the peak frequency. Therefore, engineers can use this phenomenon to attenuate sound energy at certain frequencies.

Thesis (M.S.)--University of Wisconsin--Madison, 1986.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 58-64).

Die vorliegende Arbeit beschäftigt sich mit der Konzeptionierung und Entwicklung eines neuartigen Fahrerassistenzsystems für Nutzfahrzeuge, welches die lichte Höhe von vor dem Fahrzeug befindlichen Hindernissen berechnet und über einen Abgleich mit der einstellbaren Fahrzeughöhe die Passierbarkeit bestimmt. Dabei werden die von einer Monokamera aufgenommenen Bildsequenzen genutzt, um durch indirekte und direkte Rekonstruktionsverfahren ein 3D-Abbild der Fahrumgebung zu erschaffen. Unter Hinzunahme einer Radodometrie-basierten Eigenbewegungsschätzung wird die erstellte 3D-Repräsentation skaliert und eine Prädiktion der longitudinalen und lateralen Fahrzeugbewegung ermittelt. Basierend auf dem vertikalen Höhenplan der Straßenoberfläche, welcher über die Aneinanderreihung mehrerer Ebenen modelliert wird, erfolgt die Klassifizierung des 3D-Raums in Fahruntergrund, Struktur und potentielle Hindernisse. Die innerhalb des Fahrschlauchs liegenden Hindernisse werden hinsichtlich ihrer Entfernung und Höhe bewertet. Ein daraus abgeleitetes Warnkonzept dient der optisch-akustischen Signalisierung des Hindernisses im Kombiinstrument des Fahrzeugs. Erfolgt keine entsprechende Reaktion durch den Fahrer, so wird bei kritischen Hindernishöhen eine Notbremsung durchgeführt. Die geschätzte Eigenbewegung und berechneten Hindernisparameter werden mithilfe von Referenzsensorik bewertet. Dabei kommt eine dGPS-gestützte Inertialplattform sowie ein terrestrischer und mobiler Laserscanner zum Einsatz. Im Rahmen der Arbeit werden verschiedene Umgebungssituationen und Hindernistypen im urbanen und ländlichen Raum untersucht und Aussagen zur Genauigkeit und Zuverlässigkeit des Verfahrens getroffen. Ein wesentlicher Einflussfaktor auf die Dichte und Genauigkeit der 3D-Rekonstruktion ist eine gleichmäßige Umgebungsbeleuchtung innerhalb der Bildsequenzaufnahme. Es wird in diesem Zusammenhang zwingend auf den Einsatz einer Automotive-tauglichen Kamera verwiesen. Die durch die Radodometrie bestimmte Eigenbewegung eignet sich im langsamen Geschwindigkeitsbereich zur Skalierung des 3D-Punktraums. Dieser wiederum sollte durch eine Kombination aus indirektem und direktem Punktrekonstruktionsverfahren erstellt werden. Der indirekte Anteil stützt dabei die Initialisierung des Verfahrens zum Start der Funktion und ermöglicht eine robuste Kameraschätzung. Das direkte Verfahren ermöglicht die Rekonstruktion einer hohen Anzahl an 3D-Punkten auf den Hindernisumrissen, welche zumeist die Unterkante beinhalten. Die Unterkante kann in einer Entfernung bis zu 20 m detektiert und verfolgt werden. Der größte Einflussfaktor auf die Genauigkeit der Berechnung der lichten Höhe von Hindernissen ist die Modellierung des Fahruntergrunds. Zur Reduktion von Ausreißern in der Höhenberechnung eignet sich die Stabilisierung des Verfahrens durch die Nutzung von zeitlich vorher zur Verfügung stehenden Berechnungen. Als weitere Maßnahme zur Stabilisierung wird zudem empfohlen die Hindernisausgabe an den Fahrer und den automatischen Notbremsassistenten mittels einer Hysterese zu stützen. Das hier vorgestellte System eignet sich für Park- und Rangiervorgänge und ist als kostengünstiges Fahrerassistenzsystem interessant für Pkw mit Aufbauten und leichte Nutzfahrzeuge.
The present work deals with the conception and development of a novel advanced driver assistance system for commercial vehicles, which estimates the clearance height of obstacles in front of the vehicle and determines the passability by comparison with the adjustable vehicle height. The image sequences captured by a mono camera are used to create a 3D representation of the driving environment using indirect and direct reconstruction methods. The 3D representation is scaled and a prediction of the longitudinal and lateral movement of the vehicle is determined with the aid of a wheel odometry-based estimation of the vehicle's own movement. Based on the vertical elevation plan of the road surface, which is modelled by attaching several surfaces together, the 3D space is classified into driving surface, structure and potential obstacles. The obstacles within the predicted driving tube are evaluated with regard to their distance and height. A warning concept derived from this serves to visually and acoustically signal the obstacle in the vehicle's instrument cluster. If the driver does not respond accordingly, emergency braking will be applied at critical obstacle heights. The estimated vehicle movement and calculated obstacle parameters are evaluated with the aid of reference sensors. A dGPS-supported inertial measurement unit and a terrestrial as well as a mobile laser scanner are used. Within the scope of the work, different environmental situations and obstacle types in urban and rural areas are investigated and statements on the accuracy and reliability of the implemented function are made. A major factor influencing the density and accuracy of 3D reconstruction is uniform ambient lighting within the image sequence. In this context, the use of an automotive camera is mandatory. The inherent motion determined by wheel odometry is suitable for scaling the 3D point space in the slow speed range. The 3D representation however, should be created by a combination of indirect and direct point reconstruction methods. The indirect part supports the initialization phase of the function and enables a robust camera estimation. The direct method enables the reconstruction of a large number of 3D points on the obstacle outlines, which usually contain the lower edge. The lower edge can be detected and tracked up to 20 m away. The biggest factor influencing the accuracy of the calculation of the clearance height of obstacles is the modelling of the driving surface. To reduce outliers in the height calculation, the method can be stabilized by using calculations from older time steps. As a further stabilization measure, it is also recommended to support the obstacle output to the driver and the automatic emergency brake assistant by means of hysteresis. The system presented here is suitable for parking and maneuvering operations and is interesting as a cost-effective driver assistance system for cars with superstructures and light commercial vehicles.