Statistical Properties Of Response Research Articles

Probabilistic Analysis of Extreme Riser Responses for a Weather-Vaning FPSO in Tropical Cyclones

The probability distributions of extreme responses of a flexible riser connected to a weather-vaning floating production storage and offloading (FPSO) are developed and investigated numerically for two tropical cyclones. Statistical properties of riser responses provide the foundation for response based analysis (RBA), a comprehensive approach for the prediction of extreme responses and design metocean conditions of offshore systems. The storm-based probabilistic analysis is applied to responses of flexible risers with the objective to develop their distributions in a storm and to determine their most probable maximum (MPM) values. An asymptotic form of the response distribution in a storm is formulated, which can be used in the random event, method of Tromans and Vandersohuren (1995, “Response Based Design Conditions in the North Sea: Application of a New Method,” Offshore Technology Conference, Houston, TX, May 1–4). The methodology is illustrated by two case studies for an FPSO in cyclonic storms at a location offshore Australia. Time domain simulations are employed to predict the FPSO motions, critical riser responses, and their probability distributions. It is shown that the maximum storm responses can be reproduced by governing “equivalent” metocean intervals with increased percentiles or inflated durations. Effects of different environmental excitation upon the risers and their impact on the statistical properties of responses are discussed, providing important insights for extension toward a multistorm RBA approach. The study also discusses issues with practices such as the analysis for a 3 h design event and presents observations on the variability of several types of responses, which reveal their environmental sensitivities.

Statistical properties of response for nonlinear structural systems with random parameters

A probabilistic algorithm for calculating the statistical properties of response due to uncertainties in geometry and material properties for geometrically nonlinear structural dynamics is presented. It is shown here that this technique is readily applicable to geometrically nonlinear small strain dynamic problems in which the equations of motion of structures are derived using the finite element method. A general formulation for problems of this type is presented. The efficiency of the method is illustrated by application to nonlinear vibration of a cantilever beam with random parameters.

A Non-Gaussian Gust Model for Aircraft Response Analysis

N UMEROUS investigations have been performed on the dynamic response of aircraft to continuous atmospheric turbulence (gust) by assuming that the turbulence field can be modeled as one, or a number of individually Gaussian and stationary patches. However, the observed statistical properties of atmospheric turbulence encountered by aircraft, especially those with the highest severity and potentially most destructive, are in many cases non-Gaussian. For instance, Ref. 1 deals with the aeronautical effects of surface winds and gusts. Tke investigation revealed that turbulence can rarely be realistically represented by a Gaussian process. This paper describes a non-Gaussian model for continuous atmospheric turbulence based on zero-memory transformation of a Gaussian model. Single or multiple transformation parameters are used to control the severity and other statistical characteristics of the non-Gaussian process. The composite nature of gust patches of various intensity is accounted for through the accumulative statistics. Methods to predict the aircraft response statistics to the non-Gaussian gust model are developed by approximating the response integral as its Riemann sum. Application of the probabilistic theory indicates that the statistical properties of response can be expressed in multifold integral forms and its moments can be expressed in explicit forms.

Statistical Properties of Surface-Recorded Electrocochleographic Responses

If surface-recorded electrocochleographic responses are to be used as the basis of a diagnostic procedure, then the statistical properties of the responses obtained from normally-hearing subjects need to be known so that accurate comparisons with the responses obtained from patients can be made. The data were obtained from 6 normally-hearing subjects who were tested at four stimulus levels, each measurement being replicated twice in each of two test sessions. The distributions of the latency and amplitude values were tested for normality, and the restrictions required by the use of parametric statistical methods are defined. Analyses of variance were carried out to investigate subject, session and subject-session interaction effects. The relationships between response peak parameters, and the overall mean values of latency and amplitude were computed at each stimulus level. From these the joint distributions of latency and amplitude and their relationships were derived. The relationship between response a...