Shock absorbers are crucial components of a vehicle’s chassis responsible for the trade-off between stability, handling, and passenger comfort. The aim of the thesis is to investigate the physical behavior of an advanced automotive racing shock absorber, known as TTR, developed by Öhlins Racing AB. This goal is achieved by developing a detailed lumped parameter numerical model of the entire TTR suspension in the advanced 1D simulation tool, AMESim. The shock absorber is mainly composed of the main cylinder with through-rod piston design and the gas reservoir located at the low pressure hydraulic line, which connects the compression and rebound sides. The mentioned sides are identical in terms of the components which are a High Speed Adjuster, a Low Speed Adjuster, and a check valve mounted in parallel. The adjusters are special hydraulic valves, which can be modified in terms of flow metering characteristics by means of external accessible screws. Adjustment is done in a series of discrete numbers called ‘clicks’. A fixed orifice and a spring-loaded poppet valve are responsible for controlling the piston low and high speed regions respectively. The developed AMESim numerical model is capable of capturing the physics behind the real shock absorber damping characteristics, under both static and dynamic conditions. The model is developed mainly using the standard AMESim mechanical, hydraulic and hydraulic component design libraries and allows discovering the impact of each single hydraulic component on the TTR overall behavior. In particular, the 1D model is presented in two levels of progressive physical complexity in order to improve the dynamic damping characteristics. Several physical phenomena are considered, such as the hydraulics volumes pressure dynamics, the contribution of external spring and pressure forces to the dynamic balance of the moving elements, the static and viscous frictions, and the elastic deformations induced by solid boundaries pressure. In this thesis, progressive model validation with different types of measurements is as well presented, covering the individual hydraulic components models as well as the entire shock absorber model. The measurements have been performed on the flow benches and dynamometers available at the Öhlins Racing measurements laboratory. These comparisons, deeply discussed in the thesis, allow discovering the impact of specific physical effects on the low and high speed hydraulic valves static performance and on the shock absorber dynamic behavior. Numerical results show good agreement, especially at low and medium frequencies and symmetric ‘click’ adjustments on compression and rebound sides. Further model development is necessary in the other areas, for example by considering more complex models of the valve dynamics and fluid flow patterns, i.e. flow forces, together with more advanced models of the sealing elements viscous friction, and thermal effects. Finally, the AMESim environments offered a good level of flexibility in designing the TTR hydro-mechanical system, by allowing the user to choose between different levels of model complexity.

A State-Switched Absorber (SSA) is a device capable of instantaneously changing its stiffness, thus it can switch between resonance frequencies, increasing its effective bandwidth as compared to classical tuned vibration absorbers for vibration control. This dissertation considers the performance of the SSA for vibration suppression of continuous systems, specifically a beam and a plate. The SSA tuning frequencies and attachment point on the continuous body were optimized using a simulated annealing algorithm. It was found that an optimized SSA outperforms and optimized TVA at controlling vibrations of both a beam and a plate. These performance gains were also observed experimentally employing magneto-rheological elastomers to achieve a stiffness change. This dissertation also considers zero strain switching criteria and the maximum work extraction switching rule used by the SSA. The zero strain switching criteria ensures the system remains stable as no energy is added or released across a switch event. The maximum work extraction switching rule is designed to maximize the power dissipated by the absorber, but also guarantees minimization of the motion of the base to which the absorber is attached.

The graphene-polymer SA thin film using solution blending method and atomic layer graphene as saturable absorber (SA) used to generate femtosecond laser pulse were measured. Stable soliton-like pulses with the pulsewidth of 403 fs and 432 fs, the spectral linewidth of 6.32 nm and 6.16 nm, and the time-bandwidth product of 0.315 and 0.329 using graphene-PVA film and atomic layer graphene as SA were achieved, respectively, in mode-locked Er-doped fiber ring laser. The graphene-PVA SA suffered from larger loss caused by graphene flake aggregating, while the atomic layer graphene had smaller nonsaturable loss which exhibited lower mode locking threshold power. Atomic layer graphene also had stable fabricated process and controllable modulation depth depended on its layer numbers. To compare the mode locking performance of single wall carbon nanotubes (SWCNTs) and graphene SA, the same solution blending fabricated sample was used. Under similar nonsaturable loss and modulation depth, the SWCNTs SA with optimized concentration of 0.5wt% and thickness of 188£gm had shortest pulsewidth of 440 fs and 3-dB spectral linewidth of 6 nm. The shortest pulsewidth of 403 fs and broad spectral linewidth of 6.32 nm was obtained using graphene SA with concentration of 6.25wt% and thickness of 18£gm. Graphene has broad band absorbance and larger modulation depth, the experimental result indicates that graphene SA can generate shorter pulse and has chance to become the potential candidate of SA.

The objective of this research is to develop a new and efficient method of absorbing a vehicle??s kinetic energy for highway safety crash cushions. A vehicle that makes a direct impact with a rigid highway structure traveling at highway speeds can be fatal for its occupants. Crash cushions are implemented on roadways in front of these rigid structures with the intent to ??soften?? the impact. The cushion will bring a vehicle to a stop at safe rates before it impacts the rigid structure. The energy absorbing component of the crash cushion must meet four main requirements. The cushion must reduce the vehicles speed at a rate that does not allow the occupant to impact the vehicle interior at velocities greater than 12 m/s. The cushion must then bring the vehicle to a complete stop with deceleration rates below 20 g??s. A crash cushion must satisfy these requirements for an 820 kg vehicle and a 2000 kg vehicle traveling at 100 km/hr. Advanced design methodologies were applied to enable multiple, innovative design concepts. These concepts made use of the deformation of steel in structural pipe, structural angle, and structural plate to reduce the velocity of a vehicle at a safe rate. Critical design parameters were identified which allowed for efficient and effective numerical experiments to be conducted. The data collected from these experiments were then validated when compared to physical test data. After the data had been collected, each of the designs was compared to one another in order to decide upon the best design. The design selected was the deforming plate concept which makes use of steel plate mounted in a fashion that created two arms that acted similar to two cantilever beams. A wedge was forced beneath these arms deforming them upward. This design is effective because the deformation can be easily controlled by the thickness of the plate, the moment arm created by the wedge, and the geometry of the wedge. Steel plate is a readily available material that requires minimal manufacturing for installation preparation making it cost-effective, and easy to install. In the event of impact with the cushion, new parts will be inexpensive and readily available. Being reusable, easy to repair and low in cost, the energy absorbing concept presented herein is a cost effective alternative to existing energy absorbing technology. Due to replaceable parts being readily available, repair time and cost will be reduced compared to other designs that require new parts to be fabricated for replacement. This will make for a competitive design.

The dependence of single-wall carbon nanotubes-based saturable absorber (SWCNTs SA) on concentration and thickness for mode-locked laser pulse formation is comprehensively investigated. The peak absorption wavelength of SWCNTs SA is engineered within the gain band-width of erbium-doped fiber centered near 1550 nm. The optima full-width half-maximum (FWHM) of pulses was obtained as the concentrations of SWCNTs SA was 0.05 wt%. This indicates that the laser pulse become shorter as the concentration of SWCNTs SA increases. The result also showed that the FWHM of pulses from 3.43 to 1.85 ps were found as the thickness of SWCNTs SA increased from 8 to 100 um. This also indicates that the laser pulse become shorter as the thickness of SWCNTs SA increases. However, the pulse width significantly broadened as concentration increased to 0.1 wt% and became stable as thickness of SWCNTs SA increased from 100 to 264 um for passively mode-locked lasers. An in-depth study on the optimum fabrication of concentration and thickness of SWCNTs SA for laser pulse formation may allow developing a cost-effective mode-locked laser with high performance as well as broadly benefit to the utilization of many other low-cost nanodevices.

A detailed investigation of novel air-coupled absorbers for use in a diesel engine exhaust-driven ammonia-water absorption system operating in extreme ambient conditions was conducted. Electrically driven vapor-compression systems are under scrutiny due to the environmental impact of synthetic refrigerants and the exacerbation of electric utility loads during peak demand periods. One alternative to vapor-compression systems is the absorption heat pump that uses environmentally benign working fluids and can be driven by a variety of heat sources, including waste heat and solar thermal processes. Direct air coupling of the absorber and condenser instead of indirect hydronic coupling can reduce absorption system size, complexity, and inefficiency, but materials compatibility issues with ammonia-water and the poor heat transfer properties of air present challenges. Heat and mass transfer modeling was used to predict the performance of round-tube corrugated-fin and compact tube-array absorbers designed for a 2.64-kW absorption chiller operated in high ambient temperature (51.7°C) conditions. A single-pressure ammonia-water test facility was constructed and used in conjunction with a temperature- and humidity-controlled air-handling unit to evaluate the absorbers at design and off-design operating conditions. Absorber performance was recorded over a range of air temperatures (35-54.4°C), air flow rates (0.38-0.74 m3 s-1), inlet solution temperatures (92-102°C), concentrated solution flow rates (0.006-0.010 kg s-1), and concentrated solution concentrations (38-46%). At design conditions, round-tube corrugated-fin absorbers of 394 and 551 Fins Per Meter (FPM) demonstrated comparable performance (Q394-FPM,exp = 4.521±0.271 kW; Q551-FPM,exp = 4.680±0.260 kW), and measured heat transfer rates were 0.7-1.9% AAD higher than those predicted through modeling. The measured heat transfer rate in the prototype tube-array absorber was significantly lower than the values predicted at design conditions (Qprot,exp = 2.22±0.24 kW; Qprot,mod = 4.33 kW). Maldistribution of the two-phase flow in the tube array is the probable cause of the disparity between the prototype absorber data and model predictions. Results from this investigation can be used to guide the development of air-coupled heat and mass exchangers for compact absorption heat pumps.

Within a wave energy converter's operational bandwidth, device operation tends to be optimal in converting mechanical energy into a more useful form at an incident wave period that is proximal to that of a power-producing mode of motion. Point absorbers, a particular classification of wave energy converters, tend to have a relative narrow optimal bandwidth. When not operating within the narrow optimal bandwidth, a point absorber's response and efficiency is attenuated. Given the wide range of sea-states that can be expected during a point absorber's operational life, these devices require a means to adjust, or control, their natural response to maximize the amount of energy absorbed in the large population of non-optimal conditions. In the field of wave energy research, there is considerable interest in the use of non-linear control techniques to this end. Non-linear control techniques introduce time-varying and state dependent control parameters into the point absorber motion equations, which usually motivates a computationally expensive numerical integration to determine the response of the device - important metrics such as gross converted power and relative travels of the device's pieces are extracted through post processing of the time series data. As an alternative, the work presented in this thesis was based on a closed form perturbation based approach for analysis of the response of a device with periodically-varying control parameters, subject to regular wave forcing, in the frequency domain. The proposed perturbation based method provides significant savings in computational time and enables the device's response to be represented in a closed form manner with a relatively small number of solution components - each component is comprised of a complex amplitude and oscillation frequency. This representation of the solution was found to be very concise and descriptive, and to lend itself to the calculation of gross absorbed power and travel constraint violations, making it extremely useful in the automated design optimization process; the methodology allows large number of design iterations, including both physical design and control variables, to be evaluated and conclusively compared. In the development of the perturbation method, it was discovered that the device's motion response can be calculated from an in nite series of second order ordinary differential equations that can be truncated without destroying the solution accuracy. It was found that the response amplitude operator for the generic form of a solution component provides a means to gauge the device's response to a given wave input and control parameter variation, including a gauge of the solution process stability. It is unclear as of yet if this is physical, a result of the solution process, or both. However, for a given control parameter set resulting in an unstable solution, the instability was shown to be, at least in part, a result of the device's dynamics. If the stability concerns can be addressed through additional constraints and updates to the wave energy converter hydrodynamic parameters, the methodology will expand on the commonly accepted boundaries for wave energy converter frequency domain analysis methods and be of much practical importance in the evaluation of control techniques in the field of wave energy converter technology. / Graduate

No description available.

L'énergie solaire représente un énorme potentiel pour la production d'électricité. Les recherches dans ce domaine se sont donc accélérées au cours des dernières années; en particulier le développement de matériaux semiconducteurs non-toxiques pouvant être élaborés par une technique bas côut et facile de mise en oeuvre telle que les croissances en chimie liquide. C'est dans ce contexte que l'oxyde de zinc (ZnO) prend une place de plus en plus importante au sein des laboratoires de recherche.Cette thèse a été effectuée dans plusieurs buts. Le premier était d'améliorer notre compréhension des mécanismes mis jeu lors de la croissance de nanofils de ZnO par dépôt en bain chimique, et notamment le rôle des précurseurs chimiques introduits dans le bain. Par la suite, des études morphologiques et du recuit de cristallisation de couches minces de TiO2 et de Sb2S3 déposées sous forme de coquilles sur les nanofils de ZnO par ALD, SILAR et pyrolyse d'aérosol se sont révélées primordiales pour l'élaboration de cellules solaires composées d'hétérostructures à base de nanofils de ZnO/TiO2/SB2S3. Dans ce type de cellule le ZnO joue le rôle de conducteur d'électrons alors que le TiO2 passive les états de surface des nanofils de ZnO et les protège. Le Sb2S3, quant à lui,absorbe les photons du spectre solaire et produit des excitons pour la création de courant.Ces hétérostructures sont élaborées pour la toute première fois et n'ont jamais été rapportées dans la littérature. Un rendement de photoconversion de 2,3% a été déterminé. Cette valeur est encourageante pour la suite des études et représente le premier rendement efficace pour ce type d'hétérostructures très prometteuses. / Solar energy has a huge potential for the futur electricity generation. The research in this area is therefore accelerating these last years; Especially, the development of non-toxic semiconductor materials, which can be elaborated by a low-cost and easy-to-use techniques such as growths in liquid chemistry. In this context, zinc oxide (ZnO) has become increasingly important in research laboratories.This thesis has been carried out for several purposes. The first was to improve our understanding of the mechanisms involved in the growth of ZnO nanowires by chemical bath deposition, and, in particular, the role of chemical precursors introduced into the bath. Subsequently, morphological studies and crystallization annealing studies of TiO2 and Sb2S3 shells deposited on ZnO nanowires by ALD, SILAR and spray pyrolysis are found to be essential for the preparation of heterostructures based on ZnO nanowires/TiO2/SB2S3 for solar cells. In this kind of cell, the ZnO is the electron conductor, whereas the TiO2 passivates the surface of the ZnO nanowires and protects them. The Sb2S3 absorbs the photons of the solar spectrum and produces excitons for the creation of current.These heterostructures are elaborated for the first time and have never been reported in the literature. A photoconversion efficiency of 2.3% was determined in this manuscript. This value is encouraging for the next studies on these materials and represents the first effective efficiency for this kind of promising heterostructures.

An aim of the given thesis is creating of a computational model of strain-stress behaviour of shock absorbers made of plastic and hyperelastic material. First step is get ecquaint with theory of large strains, theory of hyperelasticity and plasticity. Next step is get ecquaint with options of commercial programs based on MKP. Based on this knowledge, models of simple shock absorber are made. With created models, crash tests are simulated and property of shock absorbers are compared.