Methods to mitigate the risk posed by seismic and blast loads to structures are of high interest to researchers. Auxetic structures are a new class of metamaterials that exhibit counterintuitive negative Poisson's ratio (NPR) behavior based on their geometric configuration. Cellular auxetics are light-weight and cost-effective materials that have the potential to demonstrate high strength and resilience under axial forces. Existing research on metallic auxetics is scarce and based mostly on analytical studies. Apparent NPR behavior of auxetics has also been linked to enhanced energy absorbing potential. A pilot study was undertaken to investigate and understand auxetic behavior in tubes constructed using ductile metals commonly found in structural applications i.e. steel and aluminum. The main objective was to establish whether performance enhancements could be obtained through auxetic behavior in ductile metal tubes. In addition, any potential benefits to auxetic performance due to base material plasticity were studied. These objectives were fulfilled by conducting an experimental and analytical investigation, the results of which are presented in this thesis. The experimental program consisted of establishing a design methodology, manufacturing, and laboratory testing for tubular metallic specimens. A total of eight specimens were designed and manufactured comprising five steel and three aluminum. For each base metal, three different geometric configurations of cells were designed: one with a rectangular array of circular voids and two with void geometries based on the collapsed shape of circular cells in a design tube under uniaxial compressive stress. A parameter called the Deformation Ratio (DR) was introduced to quantify cell geometry. Designed tubes were manufactured via a six-axis laser cutting process. A custom-made test assembly was constructed and specimens were tested under reverse-cyclic uniaxial loading, with one exception. Digital Image Correlation (DIC) was used to acquire experimental strain data. The performance of the auxetic and non-auxetic tubular structures was evaluated based on the axial load-deformation characteristics, global deformations, and the specific energy absorption of the test specimens. The experimental test results confirmed that ductile metal tubes with special collapsed cell geometries were capable of demonstrating auxetic behavior under the applied elastic and inelastic uniaxial strains; both tensile and compressive. Base material plasticity was observed to have an insignificant effect on the auxetic response. Experimental results suggested that the unique deformation mechanism precipitated by the auxetic cell geometries resulted in more stable deformed shapes. Stability in global deformed shapes was observed to increase with an increase in DR value. In addition, the unique auxetic mechanism demonstrated an ability to distribute radial plastic strains uniformly over the height of the auxetic pattern. As a result, plastic strains were experienced by a greater fraction of auxetic tubes; this enhanced the energy-dissipating properties of auxetic specimens in comparison to the tested non-auxetic tubes. Tubes with cell geometries associated with higher DR values exhibited greater energy absorption relative to the non-auxetic specimen. For the same base metal, auxetic specimens exhibited greater axial strength and effective strain range, when compared to their non-auxetic counterparts. The increased strength was partially attributed to the increased cell wall thickness of the auxetic specimens. However, the increased strain range was attributed to the rotation in unit cells induced by the unique auxetic geometry. Experimental test data was used to validate the finite element (FE) and simplified macromechanical modeling approaches. These methods were adopted to develop design tools capable of replicating material performance and behavior as well as accurately predicting failure loads. Load-deformation response and effective Poisson's ratio behavior was established using FE models of as-built specimens, while simplified macromechanical equations were derived based on the equilibrium of forces to compute failure loads in tension. These equations relied on pattern geometry and measured experimental unit cell deformations. It was established that the manufacturing process had a detrimental effect on the properties of the aluminum specimens. Accordingly, empirical modifications were applied to the aluminum material model to capture this effect. FE models accurately replicated load-deformation behavior for both non-auxetic and auxetic specimens. Hence, the FE modeling approach was shown to be an effective tool for predicting material properties and response in ductile metal tubes without the need for experimental testing. The simplified strength equations also described material failure with reasonable accuracy, supporting their implementation as effective design tools to gauge tube strength. It is recommended that FE models be refined further through the addition of failure criteria and damage accumulation in material models. The result of this study established that auxetic behavior could be induced in ductile metal tubes through the introduction of unique cell geometry, thereby making them highly tunable and capable of exhibiting variable mechanical properties. Owing to their deformation mechanism and NPR behavior, auxetic tubes demonstrated geometric stability at greater deformations, which highlighted their potential for use as structural elements in systems designed to deform while bearing extreme loads e.g earthquakes and blast events. Additionally, the capability of auxetic geometries to distribute strains uniformly along their length was linked to the potential development of energy-dissipating structural components. It was suggested that new knowledge acquired in this study about auxetic behavior in ductile metals could support the development of new structural systems or methods of structural control based on NPR behavior. Finally, recommendations for future research were presented, based on the expansion of research to study the effects of multiple loading regimes and parametric changes on auxeticity as well as additional mechanical characteristics e.g shear resistance. / Master of Science / Special structures known as Auxetics have been studied that exhibit counterintuitive behavior based on their geometric configuration. The novel shapes and architecture of these structures allow them to deform such that they expand laterally in tension and contract laterally in compression; a property known as negative Poisson's ratio (NPR) which is rarely observed in naturally-occurring materials. Auxetic materials demonstrate mechanical properties such as high resilience, indentation resistance, and energy-absorption. An experimental and analytical study was undertaken to explore the beneficial properties of auxetic behavior, along with the effect of inelastic deformations in ductile metal auxetics. To this end, tubular test specimens, made with steel and aluminum, were designed and manufactured. To achieve auxetic behavior, a unique array of collapsed cells was cut out from metal tubes using a laser cutting process. Subsequently, specimens were tested in the laboratory under cyclic and monotonic loads. Experimental results indicate that tubes with auxetic geometries exhibited NPR behavior and a unique deformation mechanism based on the rotation of the unit cells. Owing to this mechanism, auxetic specimens possessed greater geometric stability under applied axial deformations, when compared to the tested non-auxetic specimens. The deformation mechanism was also responsible for a uniform distribution of strains along the length of the auxetic geometry which was linked to relatively better energy absorbing capacity than the non-auxetic tubes. Developed finite element (FE) models captured the response and behavior of all specimens with good accuracy. Derived simplified strength equations were also able to calculate the ultimate tensile failure loads for all specimens accurately. Both numerical methods demonstrated the potential to be utilized as design and evaluation tools for predicting material properties. Finally, recommendations to expand research, based on metal auxetic structures, were presented to further our understanding of auxetic behavior in ductile metals and to explore its benefits under varying loading regimes. Results from this research can be used to support the design of new structural systems or methods to control existing structures by exploiting NPR properties of ductile metal auxetics. Furthermore, energy-dissipating properties of metal auxetic materials may prove to be beneficial for structural applications under extreme loading conditions such as earthquakes and blasts.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / The work presented in this thesis forms part of the participation of the University of Stellenbosch in an electric vehicle project. The thesis deals with three aspects of the dynamics and energy management of the electric vehicle. The three aspects that are dealt with are the suspension system of an electric vehicle with in-wheel propulsion, the traction control of an electric vehicle and the energy system of such a vehicle. An investigation is presented in the thesis on the effect the mass of the hub motors has on the safety, stability and comfort of the electric vehicle. The investigation is done through a system frequency analysis and a comparative simulation. A comparison is made between a standard vehicle and a vehicle with in-wheel propulsion. A vehicle model is derived for the simulation of the vehicle. Finally, a few of the results of physical measurements performed are also presented. The traction control requirements of an EV are investigated. A discussion is given on the parts that make up an EV’s traction control system. A few examples of possible traction control systems are given through a step by step evolution of a traction control system. A vehicle model is derived for both static and kinetic friction conditions. The model is used in simulations to illustrate the need for traction control in EV’s. The thesis presents two methods for choosing a battery pack size, in terms of energy capacity etc. The difficulties associated with choosing a battery pack, using each of these methods are given. A battery pack choice for the specific electric vehicle, is presented. The measurements of one of the required charge-discharge cycles are presented to illustrate the charge and discharge curves of the battery cells used. The management of energy flow within the energy system of the EV is crucial, especially if regenerative braking is utilized. This is to protect the battery cells as well as to extend the range of the vehicle. The thesis presents the evaluation of an energy management system (EMS) using ultra capacitors as auxiliary storage device. An electronic load system is designed to simulate the operation of the vehicle motors. The transfer functions for the EMS and load system are derived and used to design the respective control algorithms. The control algorithms were implemented in both simulation as well as a laboratory setup to show the operation of the EMS. A new energy system configuration is presented. The aim of the new configuration is to solve certain problems encountered when implementing a conventional EMS. The operation of the new configuration is discussed. A comparative study is made between the conventional and the new configurations.

Neste trabalho apresenta-se uma avaliação do estado da arte de aspectos hidráulicos relacionados aos vertedores em degraus submetidos aos diferentes regimes de escoamento. Em uma segunda parte, é sugerida uma metodologia adimensional e simplificada para o pré-dimensionamento do comprimento de bacias de dissipação por ressalto hidráulico, além de uma abordagem conceitual voltada ao escoamento sobre um degrau. Entre os tópicos tratados na avaliação do estado da arte, pode-se citar, por exemplo, a dissipação de energia promovida pelos degraus, o risco de cavitação, a aeração do escoamento, o uso de aeradores de fundo e geometrias não convencionais. Quanto à metodologia desenvolvida, fundamentada na segunda lei do movimento de Newton associada à equação de Darcy-Weisbach, apresenta-se algumas comparações com dados experimentais de diferentes pesquisadores, além de exemplos de aplicação. Foi possível concluir, com a avaliação do estado da arte, que há um interesse crescente pelo conhecimento das características hidráulicas de vertedores em degraus. Através da metodologia desenvolvida, graças às comparações com dados experimentais de diferentes pesquisadores, foi possível concluir que não há um consenso absoluto sobre a magnitude do fator de resistência de Darcy-Weisbach. Com os exemplos de aplicação apresentados, notou-se que para um mesmo problema, o uso de diferentes métodos pode conduzir a projetos significativamente diferentes. / This work presents a state-of-the-art evaluation of aspects related hydraulic to stepped spillways submitted to the different flow regimes. In a second part, it is suggested a dimensionless and simplified methodology for preliminary design of the stilling basin length, besides a conceptual approach related to the free fall hydraulics. Among topics treaties in the state-of-the-art evaluation, it can cite, for example, the energy dissipation promoted by the steps, incipient cavitation, the air entrainment, the use of bottom aerator and unconventional geometries. Regarding the developed methodology, based in the Newton\'s law of motion associate to Darcy-Weisbach equation, it presents some comparisons with experimental data of different researchers, besides application examples. It was possible to conclude, with the state-of-the-art evaluation, that there is an increasing interest for hydraulics characteristic of stepped spillways knowledge. Through the developed methodology, after comparisons with experimental data of different researchers, was possible to conclude that there is not an absolute consensus about the Darcy-Weisbach friction factor magnitude. With the application examples, it noticed that for a same problem, the different methods use can lead for significantly different designs.

Objetiva-se discutir e explorar as consequências da conservação do momento angular em situações físicas que apresentem dissipação de energia. Frequentemente, sistemas mecânicos dissipativos são omitidos nas formulações matemáticas da mecânica clássica. No entanto, a conservação da energia mecânica é uma idealização drasticamente incompatível, a longos períodos de tempo, com a maioria das situações reais. Apesar de parecer controversa, esta abordagem é compreensível desde que é incluída na dissipação toda a complexidade dos sistemas mecânicos, os quais não podemos modelar completamente. Espera-se assim que os resultados obtidos sejam parcialmente comprovados em experimentos, sendo que a discrepância é atribuída à parte desconhecida do fenômeno, que muitas vezes é considerada irrelevante para fins práticos. Devido à mencionada complexidade de fenômenos dissipativos, a postura adotada nesta dissertação foi analisar específicos exemplos, de natureza distinta, simplificados, que apresentem as duas propriedades em questão. Concentrou-se especialmente no problema de dissipação de energia em corpos deformáveis na ausência de estímulos externos. / The goal of this work is to study physical systems where angular momentum is a conserved quantity while energy is dissipated. It is a common practice among people working on classical mechanics to neglect energy dissipation. While this hypothesis leads to beautiful mathematical theories, it is strongly violated by the majority of real world systems. The physical complexity of the many ways in which energy is dissipated turns the mathematical modelling of dissipative forces troublesome. There is essentially no general mathematical model for dissipative forces in good agreement with a wide range of experiments. This is in contrast to the very few accepted conservative force models: gravity, elasticity and magneto-electricity. The dissipative force model usually varies among the various physical situations. So, in this work several systems where energy is dissipated while angular momentum is conserved will be considered. The main example will be the motion of a deformable body free from external forces and torques.

Esta tese objetiva caracterizar o escoamento provocado pela incidência de um jato vertical em um fundo plano, descrevendo assim as características médias e flutuantes das pressões a partir da investigação experimental. O modelo utilizado é composto por um jato retangular posicionado, perpendicularmente, a uma distância de 0,92 m do fundo plano de um canal. Utilizando transdutores de pressão instalados na posição de incidência do jato, adquiriu-se os valores de pressão “instantânea” a uma frequência de 128 Hz durante 10 minutos. Foram ensaiadas cinco (5) vazões: 25 l/s (Fr1 = 7,12), 30 l/s (Fr1 = 8,51), 36,6 l/s (Fr1 = 10,35), 42,7 l/s (Fr1 = 12,12) e 50l/s (Fr1 = 14,23), além de vinte (20) diferentes espessuras de colchão d'água. Com os dados de pressão, efetuou-se análises no domínio do tempo, da frequência e da posição. No domínio do tempo, analisou-se a variação dos parâmetros estatísticos essenciais (média, desvio padrão, assimetria e curtose) bem como a identificação de valores máximo e mínimos das pressões. No domínio da frequência, procurou-se avaliar por meio da análise espectral a identificação de frequências significativas associadas à energia macroturbulenta. No que tange à análise no domínio da posição buscou-se analisar a faixa de influência do jato junto ao fundo, a região de subpressões e o alcance das pressões dinâmicas. Outro aspecto importante abordado é a apresentação dos resultados em gráficos adimensionalizados, o que confere ao estudo um caráter geral dentro da faixa de valores ensaiados. Os resultados definem um colchão mínimo de água da ordem de 3 vezes a altura crítica do escoamento, para o amortecimento das pressões dinâmicas. A análise dos momentos estatísticos demonstra que a distribuição das pressões não segue a distribuição normal. Dentro disso, estão disponibilizados coeficientes estatísticos de probabilidade para a determinação das pressões extremas. Ainda, estão definidas quatro zonas a jusante do impacto do jato: Zona I - região do impacto, Zona II - reflexão do jato, Zona III - Acomodação do escoamento e por fim, a Zona IV - caracterizada pelo fim da influência do jato. Além disso, uma análise deste escoamento sob a perspectiva da formação de um ressalto hidráulico é realizada, indicando que apenas os parâmetros utilizados, não descrevem o escoamento como tal. Esta tese é produto da parceria entre Laboratório de Obras Hidráulicas do Instituto de Pesquisas Hidráulicas da Universidade Federal do Rio Grande do Sul (LOH/IPH/UFRGS) e o Laboratório de Hidráulica Experimental e Recursos Hídricos de Furnas Centrais Elétricas S. A. (LAHE/FURNAS). / This thesis aims to characterize the flow prompted by the incidence of a vertical jet on a flat bottom, thus describing the mean and floating characteristics of the pressures from the experimental investigation. The model used is comprised of a rectangular jet positioned perpendicularly at a distance of 0.92 m from the flat bottom of a channel. Using pressure transducers installed in the jet incidence position, the "instantaneous" pressure values were acquired at a frequency of 128 Hz for 10 minutes. Five (5) discharges were tested: 25 l/s (Fr1 = 7.12), 30 l/s (Fr1 = 8.51), 36.6 l/s (Fr1 = 10.35), 42.7 l/s (Fr1 = 12.12) and 50 1/s (Fr1 = 14.23), as well as twenty (20) different waterbed thicknesses. The pressure data were analyzed in terms of time, frequency and position domains. In the time domain, the variation of the essential statistical parameters (mean, standard deviation, asymmetry and kurtosis) was analyzed, as well as the identification of maximum and minimum pressure values. In the frequency domain, it was sought to assess, by means of the spectral analysis, the identification of significant frequencies associated with macroturbulent energy. Regarding the analysis in the position domain, this study aimed to analyze the range of influence of the jet near the bottom, the region of subpressions and the reach of the dynamic pressures. Another important aspect is the presentation of the results in dimensionless graphs, which grants the study a general character within the range of values tested. The results define a minimum waterbed of the order of 3 times the critical height of the flow for the damping of the dynamic pressures. Statistical moments analysis shows that the distribution of pressures does not follow the normal distribution. Therein, probability statistical coefficients are available for the determination of extreme pressures. Also, four zones are defined downstream of the impact of the jet: Zone I - region of impact, Zone II - reflection of the jet, Zone III - accommodation of the flow and, finally, Zone IV - characterized by the end of the influence of the jet. Furthermore, an analysis of this flow from the perspective of the formation of a hydraulic jump is conducted, indicating that the parameters used alone do not describe the flow as such. This thesis is a product of the partnership between the Hydraulic Works Laboratory of the Hydraulic Research Institute of the Federal University of Rio Grande do Sul (LOH/IPH/UFRGS) and the Laboratory of Experimental Hydraulics and Hydraulic Resources of Furnas Centrais Elétricas SA (LAHE/FURNAS).

A comparison of concrete containing recycled concrete coarse aggregates and natural coarse aggregates subjected to high strain, low cycle compressive fatigue is presented. Using a strain based feedback control loop, concrete cylinders are compressed at 15µε/s to a specified strain then unloaded to zero stress for 10 cycles. After cycling, all samples are loaded to a strain of 0.008. Direct concrete material variables are the water to cement (w/c) ratio, taken as 0.60, 0.45, and 0.39, and percent coarse recycled concrete aggregate content, varied from zero to 100 percent. The primary testing variable is the specified unloading strain. Unloading strains include 60, 75, 90, 100, and 120 percent of the strain at peak stress. Ten batches of concrete were made, generating a total of 224 samples for testing. Findings confirm previous research showing a reduction in strength with increasing recycled concrete coarse aggregate content, an equivalent concrete with only 25 percent replacement of natural coarse aggregates and an equivalent strength concrete with a decrease in the w/c ratio and 100 percent recycled concrete coarse aggregates. Fatigue testing indicates that each cycle’s maximum stress remains unchanged, but the stiffness degrades more rapidly with increasing recycled aggregate content and a constant w/c ratio.

Internal waves occur in the interface between two layers of fluids with density stratification. In order to better understand the characteristics of continuous internal waves, a series of experiments were conducted in a laboratory tank. The upper and lower layers are fresh water of 15 cm thick and salt water of 30 cm thick, respectively. The periods of internal waves are 2.5, 5.5 and 6.6 sec. A micro-ADV is used to measure velocity profiles. Wave profiles at the density interface and the free surface are monitored respectively by an ultrasonic and capacitance wave gauges. Our results indicate that particle velocities (u and w) above and below the density interface have opposite directions. The speed is peaked near the density interface and it becomes weaker further away from the interface. Empirical Mode Decomposition is used to remove noise from the observed particle velocities, and the period is consistent with those derived from the interface elevations. The observed particle velocities also compare favorably with the theoretical results. When internal waves propagate without the interference of a sloping bottom, the turbulence induced is rather insignificant. The turbulence is more significant only near the density interface. With the existence of a sloping bottom, the internal waves gradually shoal and deform, the crest becomes sharp and steep, finally the waves become unstable, break and overturn. In this study the effect of bottom slope and the steepness of internal waves on the reflectivity of incoming waves are investigated. The reflectivity is smaller with gentler slope, and it increases and reaches a constant value with steeper slopes. The observed energy dissipation rate£`is higher near the slope. Three methods were used to estimate the energy dissipation rate and shear stress; namely, the inertial dissipation, the TKE and auto-correlation method. The£` estimated from the auto-correlation method is larger than that from the other two methods, but their trend is similar. The energy dissipation rate is found to increase with a gentler sloping bottom.

In the scope of the study, prismatic roughness elements with different longitudinal spacing and arrangements have been tested in a rectangular flume in order to reveal their effects on fundamental characteristics of a hydraulic jump. Two basic roughness types with altering arrangements have been tested. Roughness elements of the first type extends through the channel width against the flow with varying length and pitch ratios for different arrangements. The second type is of staggered essence and produced by piecing the roughness elements defined in the initial type into three parts which are equal in length. The doublet formed from the pieces on the sides is shifted to the consequent row to make two successive roughness rows encapsulate the channel span completely. Staggered roughness type is formed with the repetition of this arrangement along the flume. Independent of their type and arrangement, the entirety of roughness elements are embedded in the channel bed in order to avoid their protuberance into the flow, based on the presumption that the crests of the roughness elements levelled with the channel inlet would be less exposed to caving effects of flow than the protruding elements. In the study, influence of the proposed roughness elements on the fundamental engineering concerns as the length, height (tail water depth) and energy dissipation capacity of hydraulic jumps has been questioned in the light of empirical work and related literature on forced and smooth hydraulic jumps. At the final stage of the study, it was concluded that both strip and staggered roughness have positive effects on the characteristics of hydraulic jump given above. 3-7% more energy dissipation was observed in jumps on rough beds compared to classical hydraulic jumps. For tailwater dept reduction, whereas strip roughness provided 5-13%, staggered roughness led to 7-15% tailwater depth reduction compared to classical hydraulic jump. While strip roughness reduced jump length around 40%, 35-55% reduction was observed with staggered roughness when compared to classical hydraulic jump.

Previous studies have shown that screens may be utilized efficiently for dissipating the energy of water. For the present study, a series of experimental works are executed to investigate the tailwater and multiple screen effects on the energy dissipation through screens. Water flowing beneath a sliding gate is used to simulate the flow downstream of a hydraulic structure. In the present study, one double screen and two double screen arrangements with porosity of 40% and inclination angle of 90 degree is used. A tailwater gate structure is used to adjust the tailwater depth. The major parameters for the present study are upstream flow depth, tailwater gate height, location of the screen together with the supercritical upstream flow Froude number for a range covering from 5.0 to 22.5. The gate opening simulating a hydraulic structure is adjusted at heights of 2 cm and 3 cm during the study. The results of the experiments show that the tailwater depth has no significant additional contribution on the energy dissipation, whereas multiple screen arrangement dissipates more energy as compared to one double screen arrangement.

Seismic provisions for steel buildings present limiting width-thickness and slenderness ratios for bracing members. Most of these limits were established based on experimental observations. The number of experimental studies is limited due to the costs associated with them. With the rapid increase in computing power / however, it is now possible to conduct finite element simulation of brace components using personal computers. A finite element study has been undertaken to evaluate the aforementioned limits for pin-ended pipe section steel braces. Fifty four tubular pipe brace models possessing different diameter-to-thickness ratios varying from 5 to 30 and slenderness ratios varying from 40 to 200 were analyzed. The effect of cyclic hardening modulus on the response of braces was explored. In all analysis, the models were subjected to reversed cyclic displacements up to ten times the yield displacement. Local buckling was traced during the loading history using a criterion based on local strains. Results are presented in terms of the ductility level attained by the member at the onset of local buckling. It is shown that local buckling of the section is influenced by the diameter-to-thickness and the slenderness ratios of the member. Moreover, the amount of hardening modulus was found to affect the local buckling response significantly. The need to include this material property into seismic provisions is demonstrated. Finally, the hysteretic energy dissipated by the member was quantified for each displacement excursion.