Sami A. Kilic

Producing high-quality visualizations of large-scale simulation

This paper describes the work of a team of researchers in computer graphics, geometric computing, and civil engineering to produce a visualization of the September 2001 attack on the Pentagon. The immediate motivation for the project was to understand the behavior of the building under the impact. The longer term motivation was to establish a path for producing high-quality visualizations of large scale simulations. The first challenge was managing the enormous complexity of the scene to fit within the limits of state-of-the art simulation software systems and supercomputing resources. The second challenge was to integrate the simulation results into a high-quality visualization. To meet this challenge, we implemented a custom importer that simplifies and loads the massive simulation data in a commercial animation system. The surrounding scene is modeled using image-based techniques and is also imported in the animation system where the visualization is produced. A specific issue for us was to federate the simulation and the animation systems, both commercial systems not under our control and following internally different conceptualizations of geometry and animation. This had to be done such that scalability was achieved. The reusable link created between the two systems allows communicating the results to non-specialists and the public at large, as well as facilitating communication in teams with members having diverse technical backgrounds.

Modeling, simulation and visualization: the Pentagon on September 11th

Researchers used a custom importer to simplify and load simulation data from the September 11th Pentagon attack into a commercial animation system. The resulting high-quality impact visualization combines state-of-the-art graphics with a state-of-the-art engineering simulation.

Modeling the Slump Characteristics of the Hydrocarbon-Based Hybrid Rocket Fuels

Viscoelastic properties of the paraffin-based hybrid rocket fuel, SP-1a have been characterized based on the creep tests conducted at various temperatures and stress levels. Several material models have been developed to be used in the theoretical investigations of the slump behavior of paraffin-based fuel grains under storage and operational conditions. Analytical formulas have been derived for the time dependent deflection fields for simple configurations. Apart from the analytical solutions, a number of cases have been simulated using a commercially available finite element code, Ls-Dyna. The important conclusions that can be drawn from the results of this study are 1) at temperatures less than 35 C fuel slump is negligible, 2) under identical conditions a wall supported grain would suffer less viscoelastic deformation compared to a bottom supported grain, 3) for large motors the slump at elevated temperatures (> 40 C) sets a practical constraint on the storage periods, 4) for small motors viscoelastic deformations are less critical. * Senior Research Scientist, Computing Research Institute, Purdue University † Research Associate, Dept of Aeronautics and Astronautics, Stanford University ‡ Senior Engineer, Space Propulsion Group Inc. § Professor, Dept of Aeronautics and Astronautics, Stanford University 1) Nomenclature: A : Prony series coefficient a : Power law coefficient B : Modified time scale o D : Fuel grain outside diameter v E : Viscoelastic Young’s modulus G : Shear modulus o G : Fast response shear modulus g : Acceleration J : Shear compliance K : Bulk modulus L : Grain length n : Power law exponent r : Radial coordinate s : Laplace transform variable t : Time U , V : Radial and axial displacement w : Web thickness z : Axial coordinate β : Time constant γ : Shear strain v ν : Viscoelastic Poisson’s ratio

Assessment of Stone Arch Bridges under Static Loading Using Analytical Techniques

In this paper the maximum load carrying capacity of masonry arch bridges are assessed. Particularly, stone bridges under investigation have a perfect semicircular geometry and no binding material is used between voussoirs. Analytical methods adopted in this study are the method of virtual work and the mechanism method. In both cases the maximum concentrated load that the bridge can withstand is obtained. Drawing thrust lines for stone arches has a key role in the methods used. Additionally the concept of geometrical factor of safety is also addressed. As a case study, the first century A.D. Roman arch bridge; namely the Titus Tunnel Bridge, is investigated using the methods developed. CE Database subject headings: Stone arches, masonry bridges, mechanism method, thrust lines, geometrical factor of safety, Titus Tunnel Bridge, geometrical nonlinearity.

Capacity Assessment of the Titus Tunnel Bridge Using Analytical and Numerical Techniques

A great number of masonry arch bridges are still in service in Europe, the Middle East, and other parts of the world. Assessing the capacityofthesehistoricalstructuresisanimportantproblembothforsafetyandpreservationpurposes.Thispaperaddressestheassessment of theTitusTunnelBridge,asingle-span,Romanstonearchpedestrianbridge(CommonEra70)locatedinAntakya,Turkey,usinganalyticaland numerical techniques. The bridge is located in an active seismic zone and has survived several major earthquakes. Therefore, it is important to understand the Bridges subtle features that have helped the structure survive for the last two millennia. Furthermore, being a single-span semicircular stone arch, the bridge exemplifies the main construction blocks of several masonry bridges around the world. First, the analytical techniques, i.e., Heymans geometrical factor of safety and the mechanism method, are used to assess the capacity of the bridge under simple loadingconditionsandtovalidatethe finite-element(FE)models.Then,discreteFEmodelingwithexplicittimeintegrationisusedtoinvestigate the arch behavior under both gravity and earthquake loading conditions. It is observed that the Titus Tunnel Bridge has a significant margin of safety against collapse, which also explains the approximately 2,000-year lifetime of the structure. The results are also used to provide estimates on the maximum expected ground motions in the region using a precarious rocks analogy.DOI:10.1061/(ASCE)CF.1943-5509.0000408.

Effect of Ordering for Iterative Solvers in Structural Mechanics Problems

Direct solvers are commonly used in implicit finite element codes for structural mechanics problems. This study explores an alternative approach to solving the resulting linear systems by using the Conjugate Gradient algorithm. Pre-conditioning is applied by using the incomplete Cholesky factorization. The effect of ordering is investigated for the Reverse Cuthill–McKee scheme and the Approximate Minimum Degree Method. The solution time and the required storage space are reported for two test problems involving thin shell finite elements and hexahedral solid elements.

Numerical Study on the Uplift Response of RC Slabs Subjected to Blasts

AbstractThis study investigated the response of reinforced concrete (RC) slabs in building structures to internal explosions. The performances of two slabs designed in accordance with the protectiv...

Simulation of Sloshing Effects in Cylindrical Tanks and Evaluation of Seismic Performance

Past earthquakes have shown that metal cylindrical tanks containing liquid products at chemical processing plants undergo significant damage when subjected to strong ground motions. The most commonly used design code for cylindrical tanks is the American Petroleum Institutes API 650 Standard. The basis of the design calculations relies on modeling the sloshing phenomenon by two single degree of freedom oscillators that represent the impulsive and convective response of the liquid product inside. The use of more advanced analysis techniques is possible by taking into account the fluid-structure interaction directly. This study investigates the use of the Arbitrary Lagrangian Eulerian (ALE) method to simulate the sloshing effects by fluid-structure coupling. The seismic response of a typical cylindrical tank is analyzed. Comparisons are made with the API 650 approach. The overhead of using more advanced analysis techniques is discussed.