Impact response of preloaded structures with revolute joints

Many structural components designed to support static loads must also demonstrate the ability to withstand low probability events that can produce impact loading. For some constructs the structure is not only subjected to the initial impact, but is also subjected to rebound impacts as well. In some designs, support structures must be moved in and out of position as part of normal operations. These structures often employ revolute joints to allow the motions. In addition, functional requirements may require that a significant preload exist within the structure during normal operating conditions. This paper present the methodology needed for simulating the impact response of preloaded structures with revolute joints. A three-dimensional revolute joint is presented for use in explicit time integration analysis of problems with severe impacts. The computational engine used for the transient solution of preloaded structures is discussed. These developments are used in the analysis of a preloaded platen subjected to drop loads. The resulting transient response of the system is presented

Extrinsic Curvature and the Einstein Constraints

The Einstein initial-value equations in the extrinsic curvature (Hamiltonian) representation and conformal thin sandwich (Lagrangian) representation are brought into complete conformity by the use of a decomposition of symmetric tensors which involves a weight function. In stationary spacetimes, there is a natural choice of the weight function such that the transverse traceless part of the extrinsic curvature (or canonical momentum) vanishes.Comment: 8 pages, no figures; added new section; significant polishing of tex

Donor-acceptor dyads and triads employing core-substituted naphthalene diimides:a synthetic and spectro (electrochemical) study

Donor-acceptor dyads and triads comprising core-substituted naphthalene diimide (NDI) chromophores and either phenothiazine or phenoxazine donors are described. Synthesis combined with electrochemical and spectroelectrochemical investigations facilitates characterisation of the various redox states of these molecules, confirming the ability to combine arrays of electron donating and accepting moieties into single species that retain the redox properties of these individual moieties

Radiative Decay of a Long-Lived Particle and Big-Bang Nucleosynthesis

The effects of radiatively decaying, long-lived particles on big-bang nucleosynthesis (BBN) are discussed. If high-energy photons are emitted after BBN, they may change the abundances of the light elements through photodissociation processes, which may result in a significant discrepancy between the BBN theory and observation. We calculate the abundances of the light elements, including the effects of photodissociation induced by a radiatively decaying particle, but neglecting the hadronic branching ratio. Using these calculated abundances, we derive a constraint on such particles by comparing our theoretical results with observations. Taking into account the recent controversies regarding the observations of the light-element abundances, we derive constraints for various combinations of the measurements. We also discuss several models which predict such radiatively decaying particles, and we derive constraints on such models.Comment: Published version in Phys. Rev. D. Typos in figure captions correcte

Structural response of reactor-core hexcan subassemblies subjected to dynamic overpressurization under accident conditions

This paper presents a two-dimensional structural analysis for the evaluation of a single core subassembly due to internal overpressure associated with possible failure of fuel pins having high fission gas plenum pressure. Structural models are developed for the subassemblies and their surroundings with emphasis on the critical physical aspects of the problem. With these models the strains, deformations and the extent of permanent damage (plastic strain) to the subassemblies can be assessed. The nonlinear structural analyses was performed with a finite element program called STRAW (Structural Transient Response of Assembly Wrappers). This finite element program is applicable to nonlinear large displacement problems. The results of this study indicate that the permanent deformation (damage) is strongly influenced by the rise time (time to reach peak pressure) of the pressure pulse and the pressure in the fuel pin. The rise time is influenced by the opening time of the flow path for release of gas from the fuel pin plenum. Several examples are illustrated with various rise times and pressure magnitudes and the resulting permanent deformation of the hexcan wall

Structural response of rectilinear containment to overpressurization

Containment structures for nuclear reactors are the final barrier between released radionuclides and the public. Containment structures are constructed from steel, reinforced concrete, or prestressed concrete. US nuclear reactor containment geometries tend to be cylindrical with elliptical or hemispherical heads. The older Soviet designed reactors do not use a containment building to mitigate the effects of accidents. Instead, they employ a sealed set of rectilinear, interconnected compartments, collectively called the accident localization system (ALS), to reduce the release of radionuclides to the atmosphere during accidents. The purpose of this paper is to present a methodology that can be used to find the structural capacity of reinforced concrete structures. The method is applicable to both cylindrical and rectilinear geometries. As an illustrative example, the methodology is applied to a generic VVER-440/V213 design

Structural concerns in dynamic drop loads on transfer lock mechanisms

Drop loads are usually low probability events that can generate substantial loading to the impacted structures. When the impacted structure contains slender elements, the concern about dynamic buckling must be addressed. The problem of interest here is a structure is also under significant preload, which must be taken into account in the transient analysis. For complex structures, numerical simulations are the only viable option for assessing the transient response to short duration impactive loads. this paper addresses several analysis issues of preloaded structures with slender members subjected to drop loads. A three-dimensional beam element is validated for use in dynamic buckling analysis. the numerical algorithm used to solve the transient response of preloaded structures is discussed. The methodology is applied to an inter-compartment lock that is under significant preloads, and subjected to a drop load

Structural mechanics computations on parallel computing platforms

With recent advances in parallel supercomputers and network-connected workstations, the solution to large scale structural engineering problems has now become tractable. High-performance computer architectures, which are usually available at large universities and national laboratories, now can solve large nonlinear problems. At the other end of the spectrum, network connected workstations can be configured to become a distributed-parallel computer. This approach is attractive to small, medium and large engineering firms. This paper describes the development of a parallelized finite element computer program for the solution of static, nonlinear structural mechanics problems