Case Study of Seismic Response for Shell Key Gasification Equipment Based on Transient Dynamic Analysis

Coal gasification is a key technology for clean coal conversion with high efficiency. During the past decade, more than twenty Shell Key Gasification Equipments (SKGE) used in the Shell Coal Gasification Process (SCGP) have been built in coal-to-chemicals industry in China. SKGE is composed of Gasifier and Syngas cooler which are connected by Transfer duct. The support skirt of the Gasifier base is fixed, while the Syngas cooler side is supported by a constant hanger (floating support). In this paper, a FE model of the largest 2000-ton SKGE system in China is established by using ANSYS. The global dynamic response under the seismic load is simulated. In order to verify the correction of the calculation, the results are also compared with that by using ABAQUS. Compared to the traditional static analysis, it can be found that the deformation and stress distribution, the force and moment on several specified cross sections of SKGE change over time under seismic load based on the transient dynamic analysis. As the result of the seismic analysis is the prerequisite and foundation for accurate calculation of each key part (e.g. connection between Transfer duct and Gas reversal chamber), the seismic analysis is one of the most important analyses in the Gasification design, which will ensure the essential safety of SKGE system.

Seismic Quantitative Risk Assessment of Process Plants Through Monte Carlo Simulations

This paper describes the application of Monte Carlo method for the quantitative seismic risk assessment (QSRA) of process plants. Starting from the seismic hazard curve of the site where the plant is located, the possible chains of accidents are modelled using a sequence of propagation levels in which Level 0 is represented by the components directly damaged by the earthquake whereas the subsequent Levels represent the resulting consequence propagation. In greater detail all units damaged by energy and materials releases from level 0 units are included in level 1 and so forth, so that referring to process units belonging to a generic i-th Level, they are damaged by level (i-1) units and damage units of level (i+1). The sequence of levels represents the damage propagation across the plant through any multiple interacting sequences of accidents. For each unit a damage (DM) - loss of containment (LOC) matrix is generated allowing to estimate the amount of energy and material releases as well as resulting physical effects based on which the scenario at i-th level is generated. The process stops when no further damage propagation is allowed.

Fundamental Study on Energy Necessary for Tensile Failure

Although, a part of damage of mechanical structures by actual seismic events is caused by cumulative damage, their seismic design is generally carried out by using momentary force or stress, because force and stress are calculated easily. Therefore, damage indicating parameters that can evaluate cumulative damage is necessary, and authors have focused on energy as the parameter. The energy can evaluate fatigue failure because the energy is derived from an integral of a product of force and deformation. In our previous paper, vibration and loading experiments were conducted, and the energy necessary for fatigue failure was reported. However the processes to clarify the energy necessary for failure by fatigue experiments take a long time. The processes will be shortened if the energy is clarified by tensile tests. This paper deals with the energy necessary for tensile failure. In this paper, tensile tests were carried out, and energy necessary for tensile failure was derived. The tensile tests were conducted with various tensile speeds. As a result, more energy is needed when tensile speed is slow. This relationship is same as the relationship confirmed by vibration and loading experiments in our previous papers.

An Investigation of Adaptive Rubber Bearings

Proposed in this study are several innovative seismic isolators composed of rubber materials that are called adaptive rubber bearings based on their adaptive characteristics. The materials used in the proposed isolators are free of lead commonly found in lead rubber bearings. The lead material results in a heavy environmental burden as well as lower yield strength and damping due to rising temperature during earthquakes, and thus causes larger displacements than we would expect. The designed mechanisms in the proposed isolators enable these devices to be manufactured relatively easily. They also provide extremely high damping to bearings, which is strongly desired by engineers in practice. The proposed rubber bearings are completely passive devices yet possess adaptive stiffness and adaptive high damping. The change in stiffness and damping is predictable and can be calculated at specifiable and controllable displacement amplitudes. The major benefit of the adaptive characteristics of seismic isolators is that a given system can be optimized separately for multiple performance objects at multiple levels of earthquakes. In this study, mathematical formulations are derived to explain the mechanisms of the proposed devices. Experimental results of high velocity cyclical loadings are also provided to verify the advanced concepts of the proposed devices.

Scheduling Strategy of Multiple Semi-Active Controllers With Information on the Disturbance and the Structural Response

A scheduling strategy of multiple semi-active control laws for various earthquake disturbances is proposed to maximize the control performance. Generally, the semi-active controller for a given structural system is designed as a single control law and the single control law is used for all the forthcoming earthquake disturbances. It means that the general semi-active control should be designed to achieve a certain degree of the control performance for all the assumed disturbances with various time and/or frequency characteristics. Such requirement on the performance robustness becomes a constraint to obtain the optimal control performance. We propose a scheduling strategy of multiple semi-active control laws. Each semi-active control law is designed to achieve the optimal performance for a single earthquake disturbance. Such optimal control laws are scheduled with the available data in the control system. As the scheduling mechanism of the multiple control laws, a command signal generator (CSG) is defined in the control system. An artificial neural network (ANN) is adopted as the CSG. The ANN-based CSG works as an interpolator of the multiple control laws. Design parameters in the CSG are optimized with the genetic algorithm (GA). Simulation study shows the effectiveness of the approach.

Vulnerability-Based Design of Sliding Concave Bearings for the Seismic Isolation of Steel Storage Tanks

Liquid steel storage tanks are strategic structures for industrial facilities and have been widely used both in nuclear and non-nuclear power plants. Typical damage to tanks occurred during past earthquakes such as cracking at the bottom plate, elastic or elastoplastic buckling of the tank wall, failure of the ground anchorage system, and sloshing damage around the roof, etc. Due to their potential and substantial economic losses as well as environmental hazards, implementations of seismic isolation and energy dissipation systems have been recently extended to liquid storage tanks. Although the benefits of seismic isolation systems have been well known in reducing seismic demands of tanks; however, these benefits have been rarely investigated in literature in terms of reduction in the probability of failure. In this paper, A vulnerability-based design approach of a sliding concave bearing system for an existing elevated liquid steel storage tank is presented by evaluating the probability of exceeding specific limit states. Firstly, nonlinear time history analyses of a three-dimensional stick model for the examined case study are performed using a set of ground motion records. Fragility curves of different failure modes of the tank are then obtained by the well-known cloud method. In the following, a seismic isolation system based on concave sliding bearings is proposed. The effectiveness of the isolation system in mitigating the seismic response of the tank is investigated by means of fragility curves. Finally, an optimization of design parameters for sliding concave bearings is determined based on the reduction of the tank vulnerability or the probability of failure.

The OECD-NEA Programme on Metallic Component Margins Under High Seismic Loads (MECOS)

MECOS is Post-Fukushima OECD/NEA initiative, with the following main objectives: - To quantify the existing margins in seismic analysis of safety class components and assess the existing design practices within a benchmark activity. - To make proposals for new design/evaluation criteria of pressurized piping systems, accounting for their actual failure mode under strong input motions. The first part of MECOS consisted of gathering information on i) current design practices and ii) piping system experimentation carried out around the world that could be suitable for benchmarking. Part 2 is the benchmark itself and Part 3 proposals for new criteria. The purpose of the proposed paper is to present the experimental background and the benchmark exercise.

Pipeline Design Method Against Large Displacement of Strike-Slip Fault

This study proposes a method for designing a water pipeline system against fault displacement by incorporating earthquake resistant ductile iron pipes (ERDIPs). An ERDIP pipeline is capable of absorb the large ground displacements that occur during severe earthquakes by movement of its joint (expansion, contraction and deflection) and the use of the joint locking system. Existing ERDIP pipelines have been exposed to several severe earthquakes such as the 1995 Kobe Earthquake and the 2011 Great East Japan Earthquake, and there has been no documentation of their failure in the last 40 years. In the case of a pipeline that crosses a fault, there is the possibility of the occurrence of a local relative displacement between the pipeline and the ground. It is known that an ERDIP pipeline withstands a fault of axial compression direction by past our study. Hence, this present study was targeted at developing a method for designing an ERDIP pipeline that is capable of withstanding a strike-slip fault of axial tensile direction for a pipeline. This was done by FEM analysis wherein the ERDIPs and spring elements were used to model the soil and ERDIP joints. An ERDIP pipeline can accommodate a fault displacement of about 2 m by joint expansion/contraction and deflection, while maintaining the stress in the pipeline within the elastic limit. However, additional countermeasure is required when the fault displacement exceeds 2 m because such could stress the pipeline beyond the elastic limit. The use of large displacement absorption unit is an effective countermeasure for displacements exceeding 2 m. The expansion/contraction capacity of a unit is 10 times that of an ERDIP joint and it is able to absorb a locally-concentrated axial displacement of the pipeline. It was confirmed in the present study that an ERDIP pipeline with large displacement absorption unit, referred to as a large displacement absorption system, could accommodate fault displacement in excess of 2 m within the elastic stress range of the pipeline.

Fragility Analysis Methods for Steel Storage Tanks in Seismic Prone Areas

Catastrophic failure of above ground storage tanks was observed due to past earthquakes causing serious economic and environmental consequences. Therefore, the evaluation of the seismic vulnerability of existing liquid storage tanks located in seismic prone areas is an important task. Seismic fragility functions are useful tools in order to quantify the seismic vulnerability of structures. These functions give a probability that a seismic demand on a structural component meets or exceeds its capacity, and are generally derived by a variety of approaches, e.g., field observations of damage, static structural analyses, judgment, or analytical fragility functions. Unlike the other methods, the analytical fragility functions are developed from a coupling of the structural response analysis and a probabilistic seismic demand model. The objective of this study is to investigate the seismic vulnerability of above ground steel storage tanks using different analytical methods of the fragility function. A comparison of the well-known cloud method and the incremental dynamic analysis is performed at different limit states for two existing cylindrical steel storage tanks. The first tank represents a slender geometry with a fixed-roof and the second one is a broad tank, unanchored, and provided with a floating roof.

Yield Strength Reduction Factor of Nonlinear SDOF Systems on the Supporting Structures

Equipment installed on the supporting structure responds to the earthquake floor motion, which is strongly amplified by the structural response of the supporting structure. The required yield strength of equipment can be reduced by allowing inelastic deformation of the supporting structure and its equipment. Inelastic behavior of the supporting structure can significantly reduce elastic floor response spectra, especially their peak values. Furthermore, the allowance of inelastic deformation of equipment in strongly amplified spectral region produces a significant reduction in the required yield strength of equipment. In this study, we discussed inelastic behavior of single-degree-of-freedom(SDOF) systems installed on the supporting structures by using constant-ductility floor response spectra. Constant-ductility floor response spectra readily provide the yield strength of a SDOF system necessary to limit the ductility demand imposed by an earthquake floor motion to a specified value. Based on these discussions, we propose simple and conservative equations of the yield strength reduction factor of nonlinear inelastic SDOF systems with the natural period, the ductility factor and the stiffness ratio for earthquake floor motions.