The majority of offshore wind farms utilize monopile substructures. As these wind farms are typically located in water depths less than 30 meters, the effect of breaking waves on these structures is of great concern to design engineers. This research investigation examines many of the practical considerations and alternative ways of estimating breaking wave forces. A survey of existing European wind farms is used to establish a realistic range of basic design parameters. Based upon this information a parametric study was pursued and a series of realistic design scenarios were evaluated. Comparisons include the sensitivity to the wave force model as well as to analytical and numerical wave theories used to evaluate the wave kinematics. In addition, the effect of different kinematics stretching techniques for linear waves is addressed. Establishing whether the bathymetry will induce spilling or plunging wave breaking is critical. Spilling wave breaking can be addressed using existing wave and wave force theories; however for plunging wave breaking an additional impact force must be introduced. Dimensionless design curves are used to display pertinent trends across the full range of design cases considered. This research study provides insight into the evaluation of the maximum breaking wave forces and overturning moment for both spilling and plunging breaking waves as a function of bottom slope.

The pressures and impact forces acting on a hull while experiencing bow wave slamming is analyzed using Vorus' Impact Theory. The theory extends the hydrodynamic analysis of planing hulls from simple wedges to irregular shapes using a Boundary Element Method. A Fortran-based code developed by the Author is used to analyze hullforms. Linear strip theory is used to extend the analysis over a three dimensional hull. Post-processing of output data gives hull pressure distributions at different time steps and is visually presentable. Impact pressure, Impact force, Planing, Wave slamming, Bow impact, Vorus' theory, Boundary Element Method, Linear strip theory

To investigate the wheel/rail contact impact forces at insulated rail joints (IRJs), a three-dimensional finite element model and strain gauged experiments are employed and reported in this thesis. The 3D wheel/rail contact-impact FE model adopts a two-stage analysis strategy in which the wheel-IRJ railhead contact is first established in the static analysis and the results transferred to dynamic analysis for impact simulations. The explicit FE method was employed in the dynamic analysis. The Lagrange Multiplier method and the Penalty method for contact constraint enforcement were adopted for the static and dynamic analyses respectively. The wheel/rail contact-impact in the vicinity of the end post is exhibited via numerical examples from the FE modelling. The wheel/rail contact impact mechanism is investigated. The strain gauged experiments which consist of a lab test and a field test are reported. The signature of the strain time series from the field test demonstrates a plausible record of the dynamic responses due to the wheel/rail contact impact. By using the experimental data, both the static and the dynamic FE models are validated. It is found that the stiffness discontinuity of the IRJ structure causes a running surface geometry discontinuity during the wheel passages which then causes the impact in the vicinity of the end post. Through a series of sensitivity studies of several IRJ design parameters, it is shown that the IRJ performance can be effectively improved with optimised design parameters.

No description available.

Polypterus senegalus, an extant member of the ray-finned fishes, can both swim in water and walk overland. Both environments impose different locomotor requirements on Polypterus fins. In an aquatic environment, forward propulsion is largely generated through oscillations of the pectoral fins working in sync with each other. On land, the pectoral fins are engaged in a contralateral gait, and are involved in lifting the body off the ground while simultaneously balancing the body. Polypterus have been shown to undergo behavioural, anatomical, and physiological changes during both short- and long-term exposure to land. Differences in force environments and locomotor behaviour between aquatic and terrestrial environments are hypothesized to be the cause of these plastic changes observed in the musculoskeletal tissues of Polypterus. Despite these observable changes, it is unclear exactly how the pectoral fins are experiencing ground reaction forces (GRF) during terrestrial locomotion. By measuring and quantifying force production during walking in Polypterus, this thesis provides a first look at the relationship between GRFs produced and experienced during walking and the pectoral fins of the amphibious fish, Polypterus. The kinematics of the pectoral fins and fore body were analyzed during terrestrial locomotion, and strategic points across both pectoral fins and body were digitized. Kinematics were compared with GRFs in the thrust (X), stabilizing (Y) and lifting (Z) planes to understand how impact forces travel through the fin tissues. Further analysis, using inverse dynamics, is required to determine how these impact forces travel through the musculature of the pectoral fins, perhaps providing potential hypotheses as to the effects of GRFs and their role in not only how terrestrial locomotion affects the behavioural, anatomical, and physiological plasticity observed in Polypterus, but also the limbs of tetrapods during the evolutionary transition from aquatic to terrestrial environments.

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: End stop impact forces are horizontal longitudinal forces imposed by the crane on the end stops. Both the previous South African loading code SABS 0160:1989 and the current South African loading code SANS 10160 , classify end stop impact force as an accidental load case , hence they are not expected to occur within the expected lifetime when the guide lines for crane operation are strictly adhered to. In the estimation of end stop impact force, the previous South African loading code SABS 0160:1989 gives two guidelines for estimating the end stop impact force. The first guideline is simplistic in its approach and it’s based on the assumption that the crane and its supporting structure act as rigid bodies; hence calculation is based on rigid body mechanics. Literature reviewed reveals that this is not correct. The second guideline is more explicit in its approach as it takes into account the crane speed, resilience of the buffers and resilience of the end stops. The current South African loading code, SANS 10160 gives a better representation of the dynamics of the crane movement. However, the dynamic factor recommended for the estimation of end stop impact force is empirical in nature and thus lacks adequate scientific backing. One of the purposes of this research was to investigate the influence of the stiffness of the crane bridge on the end stop impact force. This was achieved by conducting a series of FEA simulations on the double bridge EOHTC fitted with elastomeric buffers. For this set of simulations, the effect of each influencing parameter on the end stop impact force was investigated, and the maximum end stop impact force was obtained using a constraint optimization technique. From the results obtained, comparison was then made with the existing maximum end stop impact force for a single bridge EOHTC fitted with elastomeric buffers. Another purpose of this research was to investigate the end stop impact force for an electric overhead travelling cranes (EOHTC) fitted with hydraulic buffers taking into account the dynamics involved in the movement of the EOHTC. This was achieved by a series of experimental and numerical investigation. The numerical investigation was conducted using an existing numerical model of an EOHTC which captures the crane and its supporting structure as a coupled system. Finite element analysis (FEA) impact force histories obtained were calibrated to the base experimental impact force histories. Thereafter, a series of FEA simulations were conducted by changing the parameters which have a substantial effect on the end stop impact forces. This yielded various maximum impact peaks for various parameters. The maximum impact force was then mathematical obtained from the FEA impact force histories for a given level of reliability using a constraint optimization technique. Also, codified end stop impact forces were calculated for the SABS 0160:1989 and SANS 10160-6:2010. From the results obtained, comparison was made between the codified end stop impact force and the maximum impact force obtained from the constraint optimization technique. / AFRIKAANSE OPSOMMING: Ent buffer impak kragte is horisontale kragte wat deur die kraan op die entbuffers aangewend word. Beide die Suid Afrikaanse las kode SABS 0160:1989 en die voorgestelde Suid Afrikaanse las kode SANS 10160, klasifisseer die entbuffer impak kragte as ‘n ongeluks las geval, dus word die kragte nie verwag tydens die verwagte leeftyd van die kraan wanneer die riglyne van die kraan prosedures streng gevolg word nie. Volgens die Suid-Afrikaanse las kode SABS 0160:1989 word daar twee riglyne voorgestel om die entbuffer kragte te bepaal. Die eerste riglyn is ‘n eenvoudige riglyn en word gebaseer op die aaname dat die kraan en die ondersteunende struktuur as ‘n starre ligame reageer en dus word die kragte bereken deur star ligaam meganika, alhoewel, uit die literatuur word dit bewys as inkorrek. Die tweede riglyn is ‘n meer implisiete benadering aangesien dit die kraan snelheid, elastisiteit van die buffers sowel as die elastisiteit van die end stoppe in ag neem. SANS 10160-6:2019 gee ‘n beter benadering van die dinamiese beweging van die kraan. Die voorgestelde dinamiese faktor waarmee die ent_buffer_kragte bereken word, is empiries van natuur . Een van die doelstellings vir die navorsings projek was om te bepaal wat die invloed van die kraan brug se styfheid op die entbuffer kragte is. ‘n Aantal Eindige Element Analise (FEA) simulasies is uitgevoer op ‘n dubbel brug elektriese aangedrewe oorhoofse kraan met elastomeriese buffers. Van die stel FEA simulasies kan die invloed van elke parameter op die entbuffer impak_kragte bepaal word. Die maksimum entbuffer impak_kragte is bepaal met behulp van ‘n beperking optimiserings tegniek. Vanaf hierdie resultate is ‘n vergelyking gemaak met die bestaande maksimum ent_buffer impak_kragte vir ‘n enkel brug elektriese oorhoofse aangdrewe kraan met elastomeriese buffers. ‘n Tweede doel rede vir die navorsing was om te bepaal wat die ent buffer impak_kragte op ‘n elektriese aangedrewe oorhoofse kraan met hidrouliese buffers is. Dit is bepaal deur ‘n aantal eksperimentele en numeriese toetse uit te voer. Die numeriese toetse is uitgevoer deur gebruik te maak van ‘n huidige numeriese model van ‘n elektriese aangedrewe oorhoofse kraan wat die kraan en die ondersteunende struktuur as ‘n. Die Eindige Element Analise impak_kragte is gekalibreer teen die eksperimenteel bepaalde impak- kragte. Daarna is ‘n reeks Eindige Element Analise simulasies uitgevoer en sodoende die parameters te verander wat die mees beduidende invloed op die end stop impak_kragte het. Dit het verskeie impak_krag pieke vir verskillende parameters meegebring. Die maksimum impak kragte is bepaal van die impak kragte van die Eindige Element Analise vir ‘n gegewe vlak van betroubaarheid deur gebruik te maak van die beperking optimiserings tegniek. Daarmee saam is die gekodifiseerde ent buffer impak kragte bereken volgen SABS 0160:1989 en die SANS 10160- 6:2010. Vanaf hierdie resultate is ‘n vergelyking gemaak tussen die gekodifiseerde entbuffer impak_kragte en die maksimum impak_kragte wat bepaal is deur die (beperking optimiserings tegniek).

Due to the increase in demand on freight transportation it becomes necessary to avoid delays to ensure that the goods reach its destination on time. The main factors causing disturbances in the traffic on the mainline is the breakdown of vehicles mainly due to damaged wheels. The damaged wheels are identified through the wheel-rail impact force measurements provided by the wheel impact load detectors (WILD). This calls for the optimal schedule of maintenance of wheelsets and wagons in general. During the maintenance, the officials manually check for defective wheels and the exchange of wheelsets is performed based on the type of damage. The classification of wheel damages plays a vital role in providing ease of damage identification and insights to deduce a strategy for wheelset exchange. In this study, an attempt to classify the damaged wheelsets is done by analysing the wheel-rail impact force data from the wayside detectors. The data from the detectors are acquired from PredgeAB, a Luleå based startup pioneering in providing decision support on optimal maintenance schedules and predictive maintenance of rail wheels. Through their detection and prediction solutions it was observed that of all the wheels marked as damaged by the detectors 10% were undamaged. The source of the deviation in the impact force readings could help Predge make better estimations in damage detection and prediction. In this study, the sources contributing to the deviation is studied using multi-body simulations in GENSYS. A new method for modelling wheel damage is developed to overcome the shortcomings of the software. The findings of this study can then be used appropriately to make classifications of wheel damages. / På grund av den ökade efterfrågan på godstransporter är det nödvändigt attundvika förseningar för att säkerställa att varorna når sin destination i tid. Deviktigaste faktorerna som orsakar störningar i trafiken på huvudlinjen är stopp ispår av fordon, främst på grund av skadade hjul. De skadade hjulen identifierasmed hjälp av mätningar av slagkraft mellan hjul och spår som tillhandahållsav hjulbelastningsdetektorer (WILD). Detta kräver ett optimerat schema förunderhåll av hjulsatser och vagnar i allmänhet. Under underhållet kontrollerartjänstemännen manuellt för defekta hjul och utbytet av hjulsatser utförs baserat på typen av skada. Klassificeringen av hjulskador spelar en viktig roll närdet gäller att underlätta identifiering av skador och ge insikt för att bedöma enstrategi för hjulbyte. I den här studien görs ett försök att klassificera de skadade hjulsatserna genom att analysera data från slagkraften mellan spår ochhjul från detektorer. Uppgifterna från detektorerna hämtas från PredgeAB, enLuleå-baserad uppstartsbolag som är pionjärer för att ge beslutsstöd om optimala underhållsscheman och prediktivt underhåll av järnvägshjul. Genom sinadetekterings- och prediktiva lösningar observerades att 10% av alla hjul märktasom skadade av detektorerna var oskadade. Källan till avvikelsen i slagkraftavläsningarna kan hjälpa Predge att göra bättre uppskattningar när det gällerupptäckning och förutsägelse av skador. I den här studien studeras de källorsom bidrar till avvikelsen med simuleringar av flera kroppar i GENSYS. En nymetod för modellering av hjulskador har utvecklats för att övervinna programvarans brister. Resultaten av denna studie skulle kunna användas på lämpligtsätt för att göra klassificeringar av hjulskador.

La aplicación de materiales compuestos de matriz polimérica reforzados mediante fibras largas (FRP, Fiber Reinforced Plastic), está en gradual crecimiento debido a las buenas propiedades específicas y a la flexibilidad en el diseño. Uno de los mayores consumidores es la industria aeroespacial, dado que la aplicación de estos materiales tiene claros beneficios económicos y medioambientales. Cuando los materiales compuestos se aplican en componentes estructurales, se inicia un programa de diseño donde se combinan ensayos reales y técnicas de análisis. El desarrollo de herramientas de análisis fiables que permiten comprender el comportamiento mecánico de la estructura, así como reemplazar muchos, pero no todos, los ensayos reales, es de claro interés. Susceptibilidad al daño debido a cargas de impacto fuera del plano es uno de los aspectos de más importancia que se tienen en cuenta durante el proceso de diseño de estructuras de material compuesto. La falta de conocimiento de los efectos del impacto en estas estructuras es un factor que limita el uso de estos materiales. Por lo tanto, el desarrollo de modelos de ensayo virtual mecánico para analizar la resistencia a impacto de una estructura es de gran interés, pero aún más, la predicción de la resistencia residual después del impacto. En este sentido, el presente trabajo abarca un amplio rango de análisis de eventos de impacto a baja velocidad en placas laminadas de material compuesto, monolíticas, planas, rectangulares, y con secuencias de apilamiento convencionales. Teniendo en cuenta que el principal objetivo del presente trabajo es la predicción de la resistencia residual a compresión, diferentes tareas se llevan a cabo para favorecer el adecuado análisis del problema. Los temas que se desarrollan son: la descripción analítica del impacto, el diseño y la realización de un plan de ensayos experimentales, la formulación e implementación de modelos constitutivos para la descripción del comportamiento del material, y el desarrollo de ensayos virtuales basados en modelos de elementos finitos en los que se usan los modelos constitutivos implementados. / The application of polymer-based composites reinforced by long fibers, called advanced Fiber Reinforced Plastic (FRP), is gradually increasing as a result of their good specific mechanical properties and increased flexibility of design. One of the largest consumers is the aerospace industry, since the application of these materials has clear economic and environmental benefits. When composites are to be used in structural components, a design development program is initiated, where a combination of testing and analysis techniques is typically performed. The development of reliable analysis tools that enable to understand the structure mechanical behavior, as well as to replace most, but not all, the real experimental tests, is of clear interest. Susceptibility to damage from concentrated out-of-plane impact forces is one of the major design concerns of structures made of advanced FRPs used in the aerospace industry. Lack of knowledge of the impact effects on these structures is a factor in limiting the use of composite materials. Therefore, the development of virtual mechanical testing models to analyze the impact damage resistance of a structure is of great interest, but even more, the prediction of the post-impact residual strength. In this sense, the present thesis covers a wide range of analysis of the low-velocity and large mass impact events on monolithic, flat, rectangular, polymer-based laminated composite plates with conventional stacking sequences. Keeping in mind that the main goal of this work is the prediction of the residual compressive strength of an impacted specimen coupon, a set of different tasks are performed in order to provide suitable tools to analyze the problem. Accordingly, the topics which are addressed in this thesis are: the analytical description of the impact, the design and the realization of an experimental test plan, the formulation and implementation of constitutive models for the description of the composite material behavior, and the assessment of the performance of virtual tests based on finite element models where the constitutive models are used.

La planche coréenne est une discipline de cirque exigeante d’un point de vue technique. Il s’agit d’une longue planche à bascule sur laquelle deux acrobates, placés à chaque extrémité, se catapultent continuellement pour effectuer des sauts acrobatiques. Les acrobates utilisent une technique spécifique pour le décollage et l’atterrissage. La planche coréenne, comme tout équipement de cirque, n’a pas de standard de fabrication et il existe une grande variété de planches. Les acrobates, les entraîneurs et les concepteurs d'équipements bénéficieraient d’avoir plus d'informations sur la biomécanique de la performance et sur la mécanique de la planche, afin d'améliorer le développement des techniques acrobatiques et la conception des planches. L’objectif de la thèse était de mieux comprendre l’interaction entre l’équipement de cirque et la performance acrobatique en planche coréenne. À cet égard, les quatre objectifs spécifiques étaient de : (1) Établir l’influence de la hauteur de saut, du participant, de la planche et de la technique de réception sur les forces d’impact et les taux de chargement; (2) Quantifier l’influence de plusieurs facteurs biomécaniques cinématiques sur la hauteur de saut; (3) Déterminer la différence de contribution musculaire et de durée des phases du mouvement entre acrobates débutants et acrobates élites; et (4) Caractériser mécaniquement différentes planches et mettre en évidence la contribution du renvoi de flexion de la planche sur la hauteur de sauts. Cette thèse présente l’ensemble des travaux effectués pour lier les caractéristiques de la planche au mouvement de l’acrobate. En effet, le mouvement de l’acrobate, sauter à grande hauteur, génère des forces élevées sur la planche lors de la réception, ce qui met en mouvement la planche. L’équipement ensuite permet un transfert de force vers l’acrobate qui s’élance. Finalement, ce dernier doit utiliser une technique optimale avec une synchronisation et une contribution musculaire précis, afin de gagner une hauteur suffisante pour la performance. Nos différentes études ont permis de montrer que le facteur qui influence le plus les forces d’impact et le taux de chargement lors de la réception est la hauteur de saut (40% d’influence relative). La force maximale mesurée est de 13.5 fois le poids corporel de l’acrobate, ce qui peut représenter un risque de blessure. La hauteur de saut est en majorité influencée par la vitesse verticale du centre de masse de l’acrobate-partenaire qui se réceptionne, de la vitesse verticale de la planche et de l’amplitude des hanches lors du décollage. Ces deux derniers paramètres peuvent être contrôlés par les acrobates ou les concepteurs de planche coréenne. Nous démontrons, de plus, que les acrobates débutants sont plus longs dans la préparation au décollage, le décollage et l’atterrissage comparativement aux acrobates experts. Cependant, il n’y avait pas de différence claire entre les débutants et les professionnels quant à l’activité musculaire lors du décollage et atterrissage, ce qui indique que la temporalité est sûrement plus importante que l’activité musculaire. Nous trouvons aussi que le renvoi de flexion (énergie élastique de la planche) est non négligeable (46 % d’influence relative) et contribue donc à la hauteur de saut. Finalement, le paramètre mécanique le plus important pour quantifier et comparer les planches est la raideur. Les quatre planches de l’étude ont une raideur qui varie entre 12.2 kN/m et 19.6 kN/m. Ce paramètre peut probablement guider les futures conceptions de planche. Collectivement, ces quatre études mettent en évidence que la synchronisation temporelle du mouvement des acrobates et du mouvement de la planche est l’élément crucial dans cette discipline. / Korean teeterboard is a technically demanding circus discipline. The apparatus resembles a seesaw, and two acrobats take turns jumping vertically, performing complex acrobatic figures and landing back on the apparatus. Acrobats use a specific technique during take-off and landing. Furthermore, like most circus equipment, there are no standards regarding the design of the teeterboard and there is a wide variety of teeterboards. Acrobats, trainers and equipment’s designers would benefit to know more about the relationship between the biomechanics of the performance and the mechanics of the board. This understanding would help improving acrobatic techniques and optimize the design of teeterboards. The purpose of the thesis was to better understand the interaction between the circus equipment and the acrobats’ performance in Korean teeterboard. To this end, this thesis was divided into four specific goals: (1) Define the influence of the jump height, the teeterboard and the landing technique on impact forces and loading rates; (2) Quantify the influence of various kinematic factors to the jump height; (3) Determine the differences between expert and novice acrobats with respect to muscular contribution and duration of the phases of the movement ; and, (4) mechanically characterize different types of teeterboards and highlight the contribution of the recoil effect to the jump height. This thesis covers the work carried out to link the characteristics of the teeterboard to the movement of the acrobat. The movement of the acrobat, i.e., jumping at high height, generates high forces during landing, which set in motion the board. The equipment then enables the transfer of this force to the other acrobat taking-off. This acrobat should use an optimal technique with a precise timing and muscular contribution, to gain sufficient height for their performance. This body of work demonstrated that the most important factor influencing the impact forces and loading rates was jump height (40% of relative influence). Maximal recorded force was 13.5 times the acrobat’s bodyweight, raising concerns about risk of injury. Jump height was mainly influenced by the vertical velocity of the center of mass of the acrobat landing, the vertical velocity of the teeterboard and the hip range of motion at take-off. The last two parameters can be controlled by acrobats, trainers, or designers of Korean teeterboard. We also found that novice acrobats are longer in the following phases: preparation for take-off, take-off, and landing. However, there was no clear difference in muscular amplitude during take-off and landing between novice and professional acrobats. This indicates that timing may be more important than muscular amplitude. We showed that recoil effect (elastic strain energy of the board) strongly contributed to the jump height (46% of relative influence). Finally, the most important mechanical parameter to quantify and compare teeterboards was the stiffness. The stiffness of the four teeterboards analyzed in this study ranged from 12.2 kN/m to19.6 kN/m. This result can guide future designs of teeterboard. The results from this thesis highlight the fact that temporal synchronization of the movement from both acrobats and the movement of the board is crucial in this discipline.