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On Iwase's Construction of a Counterexample to Ganea's ConjectureToupin, Curtis January 2017 (has links)
In 1971, Ganea put forth a conjecture that the LS category of the Cartesian product of a topological space X with a sphere Sn is always exactly 1 higher than the LS category of X by itself. Several special cases of this conjecture were proven in the years following, however the question remained open until 1998 when Iwase produced not just one, but infinitely many counterexamples. In this thesis, we study the methods implemented by Iwase, culminating in the construction of his counterexample.
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Chroust maďalový (Melolontha hippocastani F.) – hospodářský význam a možnosti eliminace škod v gradačním území LS StrážniceOpavský, Tomáš January 2019 (has links)
The aim of this work was to evaluate the amount of damage caused by the grubs of forest cockchafer. The damage was assessed in relation to the habitat conditions of the mining and cultivation practices. The pilot plant treatment of Actara 25 WG and Force 1.5 G was evaluated for efficacy against 2nd and 3rd grub instars. A methodical design of aerial intervention to inhibit the forest cockchafer during the 2019 swarming was drawn up. When evaluating the amount of damage, 59,233 pieces of seedlings were checked in 2017. The pilot plant treatment was applied to 4 473 pieces of seedlings and the application was carried out in seven different variants on three districts of the Forestry Administration in Strážnice. The average amount of damage caused by the infestation of forest cockchafer grubs in the Forestry Administration in 2016–2018 is 36%. The Actara 25 WG applied by irrigation was evaluated as the most efficient variant during pilot plant treatment. Based on the vegetation inspection and the extent of the damaged area, an aerial intervention was proposed in two variants to inhibit the forest cockchafer swarming in 2019.
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Development and Verification of a Finite Element Model of a Fixed-Wing Unmanned Aerial System for Airborne Collision Severity EvaluationKota, Kalyan Raj 10 August 2018 (has links)
Unmanned aircraft systems (UASs) pose a potential threat to general aviation/commercial aircraft as UASs are increasingly incorporated into the National Airspace System. This overarching research is aimed at addressing the severity of a UAS mid-air collision with another aircraft. This study is primarily focused on the development of a finite element (FE) model of a ~4 lb fixed-wing UAS (FW-UAS) which will be used to evaluate the severity of small UAS mid-air collisions to manned aircraft. A series of impact tests were performed at the University of Dayton Research Institute - Impact Physics Lab, to study the impact behavior of the high-density components of the FW-UAS (i.e., motor, and battery). For each of the tests, a simulation was set up with the same initial conditions, and boundary conditions as the physical test and the same output parameters were correlated with the test results. A series of numerical stability checks were also performed using the validated FW-UAS FE model to ensure the stability of the explicit dynamic procedures. Simulated impacts between the FW-UAS FE model and targets (deformable flat plate, rigid flat plate, and rigid knife-edge) were performed as stability checks. The FW-UAS FE model developed in this work facilitated the evaluation of the severity of FW-UAS mid-air collision to commercial and business jet airframes performed at and in conjunction with National Institute for Aviation Research. A series of worst-case scenarios involving impacts between the FW-UAS and commercial narrow-body transport and business jet airframes were simulated. For each simulated impact, an impact severity index value was assigned to characterize the relative threat to a given aircraft. In addition, a UAS frangibility study was performed to assess key UAS design features that result in reduced damage to target air vehicles. A “pusher” engine configuration was modeled where the high-density motor is located aft of the UAS’s forward fuselage. Positioning the high-density motor in the aft fuselage played an important role in reducing the impact damage severity.
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Explicit Finite Element Comparison of the Lower Human Extremity under Blast LoadOyeka, Onyema 11 May 2013 (has links)
Most studies on blast explosion focus on a single technique or software. This Thesis directly compares several methods of simulating blast loads using LS-DYNA, ABAQUS and CTH software. The techniques appraised in this thesis include; Jones-Wilkins-Lee (JWL) equation of state (EOS), spherical incident wave formulation, and a direct planar blast load application. In the first section of this study, we analyzed a free air-blast generated by detonating 100 g of composition-4 (C-4). Next, we placed and examined the lower extremity model under the same blast parameters in different coupled and uncoupled scenarios. In the free air-blast study, all three codes gave similar results. The peak over pressure from ABAQUS was the closest in value to the experimentally measured data. In the second section, the JWL EOS method consistently produced higher-pressure response in the lower extremity elements compared to the other methods implemented.
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Modeling and Evaluation of a Finite Element Cervical Spinal Cord for Injury Assessment / Modellering och utvärdering av en finita elementmodell av cervikal ryggmärg för bedömning av skador.Valle Olivera, Nicole January 2020 (has links)
Motor vehicles collisions and falls have gradually increase the risk for spinal cord injuries. An increased knowledge of the spinal behavior and its injury mechanisms can be used as preventive strategies. Total Human Model for Safety (THUMS) SAFER is used as a tool for injury prevention, however, there is a lack of studies that evaluate the spinal cord injuries. The aim of this thesis is to implement a cervical spinal cord into the THUMS model. The mesh element quality was modified and the spinal cord was further adjusted for a correct insertion into the THUMS. The strain of the posterior and anterior surface of the cervical spinal cord during a head flexion were analyzed against experiments. Subsequently, a comparison of the head kinematics in frontal collision of the THUMS with and without the cervical spinal cord was performed. A refinement of the mesh element quality for a suitable computational time was achieved. The strain evaluation of the the spinal cord showed the same behavior as in the experiment for the posterior surface but the results were contradictory for the anterior surface. The results of the head kinematics with and without spinal cord showed no good correlation with the experimental data. Moreover, the models exhibited a bigger difference between them during the extension of the head than flexion. A further improvement of the mesh element quality required smaller element size. Nonetheless, it is important to consider that computational time increases with a decrease of element size. Several factors were critical for the strain comparison, such as the lack of information for the calculation of the strain. The difference in head kinematics from the experiment may be due to the material properties of the neck skin and the lack of the active muscles. Moreover, the contact constraints in the model may result in the differences between the THUMS models. In general, the spinal cord has been refined to obtain a favorable computational time. The evaluations have indicated that further modifications in the neck skin and contact constraints are needed for a better resemblance with the human body. Likewise, further validations against experimental studies are suggested.
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LS-Dyna for Crashworthiness of Composite StructuresChatla, Priyanjali January 2012 (has links)
No description available.
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NONLINEAR STRAIN RATE DEPENDENT COMPOSITE MODEL FOR EXPLICIT FINITE ELEMENT ANALYSISZheng, Xiahua 17 May 2006 (has links)
No description available.
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MATERIAL MODELING OF STRAIN RATE DEPENDENT POLYMER AND 2D TRI-AXIALLY BRAIDED COMPOSITESCheng, Jingyun 17 May 2006 (has links)
No description available.
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UHPFRC Strengthening of Reinforced Concrete Flexural Members Subjected to Static and Blast LoadsLi, Chuanjing 01 May 2023 (has links)
Ultra-high performance fiber-reinforced concrete (UHPFRC) is an advanced cement-based composite with enhanced compressive strength, tensile resistance and toughness when compared to conventional concrete. Interest in the application of UHPFRC as a retrofit material has been rapidly increasing, and a few existing studies have examined the ability of UHPFRC to retrofit and strengthen existing reinforced concrete (RC) structures under static loading; however, very limited studies have examined the effectiveness of UHPFRC to improve the response of RC members under blast loading. This thesis aims at filing this research gap and investigates the behavior of UHPFRC retrofitted RC flexural members under both static and blast loads. A total of twenty-one (21) specimens, in two different series are tested. Series 1 includes nine (9) singly-reinforced beams built with high-strength concrete (HSC) and strengthened by UHPFRC to improve shear and flexural behaviour. Series 2 includes a further twelve (12) doubly-reinforced beams/columns built with normal-strength concrete (NSC), and strengthened by UHPFRC to improve response under blast, or combined blast-axial loading. Various test parameters are examined including the effects of varying retrofit types (full jacket, U-jacket or T-sided), surface roughening methods, longitudinal steel reinforcement ratio, single vs. repeated blasts, and the effects of axial loading.
The results from this thesis are presented in six journal articles. Papers 1 and 2 study the effects of UHPFRC jacketing on the static and blast behaviour of the singly-reinforced HSC beams in Series 1, while Paper 3 discusses the effects of additional parameters such as: the effect of retrofit type, roughening method and steel detailing on blast behaviour. Under static loading (Paper 1), the UHPFRC jacketing was found to be effective in increasing shear resistance (by preventing shear failure), and improving flexural behaviour (by increasing strength, stiffness, ductility and overall toughness) when compared to control beams built without UHPFRC. Similarly, under blast loads (Paper 2) the use of UHPFRC jacketing prevented shear failure, and improved flexural behaviour by reducing displacements at equivalent blasts, increasing overall blast capacity, and improving damage tolerance. On the other hand, the results show that UHPFRC-retrofitted beams with low longitudinal steel ratios may be vulnerable to brittle bar fracture failures. As part of the numerical research, finite element (FE) modelling is used to predict the static and blast behaviour of the test beams using software LS-DYNA (Papers 1 and 2). The results from Paper 3, provide further insights into the effects of retrofit type (FJ, UJ and T) and roughening method on blast performance; both the UJ and FJ retrofits were found to be effective in increasing shear resistance, reducing blast-displacements and increasing blast capacity, while the benefit of the T-sided retrofit was limited by the crushing capacity of HSC concrete. The effect of roughening method was found to be negligible, except at the very late stages of blast loading.
Papers 4, 5 and 6 present the experimental results from the doubly-reinforced NSC beams tested in Series 2, with a focus on the effect of UHPFRC jacketing, UHPFRC retrofitting type and Axial loading, respectively. Paper 4 shows that the UHPFRC jacketing increased the stiffness and strength of the beams under both static and blast loading, however the high bond capacity of the UHPFRC and relatively low tension steel ratio increased the vulnerability of bar rupture failure. The numerical parametric study investigates the effects of steel ratio and blast load scenario, jacket thickness and interface location on blast performance and failure model. Paper 5 confirms that the blast performance of the beams is influenced by the retrofit type, with optimal performance obtained when using full- or U-jacketing. The efficient use of localized "hinge" retrofits was also found to be effective, and reduced the vulnerability to bar rupture. The numerical parametric study investigates the effects of steel ratio and blast load scenario (single vs. repeated) on the blast performance of the beams. Paper 6, studies the effect of UHPFRC jacketing in columns tested under combined axial and blast loading. The retrofit is shown to increase blast capacity and reduce blast-induced displacements and damage, though the final failure of the columns was governed by bar rupture. As part of the numerical parametric study the effects of axial load ratio, boundary conditions, steel ratio, jacket thickness and jacket design are studied numerically and found to have significant effects on blast behaviour and failure mode.
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Structural Analysis of Underwater DetonationsSjöstrand, Edvin January 2021 (has links)
The knowledge how an object withstand an underwater detonation is critical within the defense industry. This is mostly done today with physicals test which are both time consuming and connected with high costs. The aim of this thesis is to provide recommendations and guidelines on how to model and analyze a structural response of underwater detonations. This investigation are focused on firstly investigate several theoretical simulation methods and thereafter develop a model of the chosen method. The simulation method was decided to be the Multi-Material Arbitrary Lagrangian Euler(MMALE) using the software LS-Dyna. To receive a model with functionality to simulate an explosion a method of six steps is developed to increase the complexity. The final step is to be able to analyze a structural response of an object. The validation phase contained several convergence studies of the two Equations of states and a varying element size compared to analytical equations. The plan was to perform a validation test but because of travel restrictions due to the Covid-19 situation an alternative validation method was used. This method involved two external reports with specified measurement data. The aim to develop a model is reached as the model performs well against the cylinder in the validation phase, however the element size is the most important parameter in an accurate model. The developed model shows good agreement regarding the structural response of an object when compared to well defined and reported experiments.
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