The improved line sampling （LS） technique, an effective numerical simulation method, is employed to analyze the probabilistic characteristics and reliability sensitivity of flutter with random structural parameter i...The improved line sampling （LS） technique, an effective numerical simulation method, is employed to analyze the probabilistic characteristics and reliability sensitivity of flutter with random structural parameter in transonic flow. The improved LS technique is a novel methodology for reliability and sensitivity analysis of high dimensionality and low probability problem with implicit limit state function, and it does not require any approximating surrogate of the implicit limit state equation. The improved LS is used to estimate the flutter reliability and the sensitivity of a two-dimensional wing, in which some structural properties, such as frequency, parameters of gravity center and mass ratio, are considered as random variables. Computational fluid dynamics （CFD） based unsteady aerodynamic reduced order model （ROM） method is used to construct the aerodynamic state equations. Coupling structural state equations with aerodynamic state equations, the safety margin of flutter is founded by using the critical velocity of flutter. The results show that the improved LS technique can effectively decrease the computational cost in the random uncertainty analysis of flutter. The reliability sensitivity, defined by the partial derivative of the failure probability with respect to the distribution parameter of random variable, can help to identify the important parameters and guide the structural optimization design.展开更多
Assessment of imprecise time-variant reliability in engineering is a critical task when accounting for both the variability of structural properties and loads over time and the presence of uncertainties involved in th...Assessment of imprecise time-variant reliability in engineering is a critical task when accounting for both the variability of structural properties and loads over time and the presence of uncertainties involved in the ambiguity of parameters simultaneously.To estimate the Imprecise Time-variant Failure Probability Function(ITFPF)and derive the imprecise reliability results as a byproduct,Adaptive Combination Augmented Line Sampling(ACALS)is proposed.It consists of three integrated features:Augmented Line Sampling(ALS),adaptive strategy,and the optimal combination.ALS is adopted as an efficient analysis tool to obtain the failure probability function w.r.t.imprecise parameters.Then,the adaptive strategy iteratively applies ALS while considering both imprecise parameters and time simultaneously.Finally,the optimal combination algorithm collects all result components in an optimal manner to minimize the Coefficient of Variance(C.o.V.)of the ITFPF estimate.Overall,the proposed ACALS method outperforms the original ALS method by efficiently estimating the ITFPF while guaranteeing a minimal C.o.V.Thus,the proposed approach can serve as an effective tool for imprecise time-variant reliability analysis in real engineering applications.Several examples are presented to demonstrate the superiority of the proposed approach in addressing the challenges of estimating the ITFPF.展开更多
For structural system with random basic variables as well as fuzzy basic variables,uncertain propagation from two kinds of basic variables to the response of the structure is investigated.A novel algorithm for obtaini...For structural system with random basic variables as well as fuzzy basic variables,uncertain propagation from two kinds of basic variables to the response of the structure is investigated.A novel algorithm for obtaining membership function of fuzzy reliability is presented with saddlepoint approximation(SA)based line sampling method.In the presented method,the value domain of the fuzzy basic variables under the given membership level is firstly obtained according to their membership functions.In the value domain of the fuzzy basic variables corresponding to the given membership level,bounds of reliability of the structure response satisfying safety requirement are obtained by employing the SA based line sampling method in the reduced space of the random variables.In this way the uncertainty of the basic variables is propagated to the safety measurement of the structure,and the fuzzy membership function of the reliability is obtained.Compared to the direct Monte Carlo method for propagating the uncertainties of the fuzzy and random basic variables,the presented method can considerably improve computational efficiency with acceptable precision.The presented method has wider applicability compared to the transformation method,because it doesn't limit the distribution of the variable and the explicit expression of performance function,and no approximation is made for the performance function during the computing process.Additionally,the presented method can easily treat the performance function with cross items of the fuzzy variable and the random variable,which isn't suitably approximated by the existing transformation methods.Several examples are provided to illustrate the advantages of the presented method.展开更多
For the stochastic structure with stochastic excitation, an advanced stratified line sampling (SLS) method is presented to obtain the cumulative distribution function (CDF) of the structural response and its sensitivi...For the stochastic structure with stochastic excitation, an advanced stratified line sampling (SLS) method is presented to obtain the cumulative distribution function (CDF) of the structural response and its sensitivity. The advanced stratified line sampling method introduces a set of middle failure subsets firstly. And for each subset, the conventional line sampling can be used to obtain the corresponding value of the response's CDF. At the same time, the sensitivity estimations of each failure subset can also be computed by modifying the important direction and corresponding reliability coefficients. The properties of CDF sensitivity are proved while the performance function is linear with normal random variables. After two simple examples are used to demonstrate the properties of CDF sensitivity and the feasibility of the presented method, the method employed to analyze the CDF and corresponding sensitivity of root bending moment (RBM) responses for the stochastic BAH is wing with gust excitation to a square-edged gust and to a Dryden gust. The results show that the parameters of the second and the fifth order modals exert more influence on the CDF of response than the other ones, and the presented SLS method can more significantly reduce the computational cost compared with Monte Carlo simulation (MCS).展开更多
The random variables are always truncated in aerospace engineering and the truncated distribution is more feasible and effective for the random variables due to the limited samples available.For high-reliability aeros...The random variables are always truncated in aerospace engineering and the truncated distribution is more feasible and effective for the random variables due to the limited samples available.For high-reliability aerospace mechanism with truncated random variables, a method based on artificial bee colony（ABC） algorithm and line sampling（LS） is proposed.The artificial bee colony-based line sampling（ABCLS） method presents a multi-constrained optimization model to solve the potential non-convergence problem when calculating design point（is also as most probable point, MPP） of performance function with truncated variables; by implementing ABC algorithm to search for MPP in the standard normal space, the optimization efficiency and global searching ability are increased with this method dramatically.When calculating the reliability of aerospace mechanism with too small failure probability, the Monte Carlo simulation method needs too large sample size.The ABCLS method could overcome this drawback.For reliability problems with implicit functions, this paper combines the ABCLS with Kriging response surface method,therefore could alleviate computational burden of calculating the reliability of complex aerospace mechanism.A numerical example and an engineering example are carried out to verify this method and prove the applicability.展开更多
In structural reliability analysis,simulation methods are widely used.The statistical characteristics of failure probability estimate of these methods have been well investigated.In this study,the sensitivities of the...In structural reliability analysis,simulation methods are widely used.The statistical characteristics of failure probability estimate of these methods have been well investigated.In this study,the sensitivities of the failure probability estimate and its statistical characteristics with regard to sample,called‘contribution indexes’,are proposed to measure the contribution of sample.The contribution indexes in four widely simulation methods,i.e.,Monte Carlo simulation(MCS),importance sampling(IS),line sampling(LS)and subset simulation(SS)are derived and analyzed.The proposed contribution indexes of sample can provide valuable information understanding the methods deeply,and enlighten potential improvement of methods.It is found that the main differences between these investigated methods lie in the contribution indexes of the safety samples,which are the main factors to the efficiency of the methods.Moreover,numerical examples are used to validate these findings.展开更多
Line transect sampling is a very useful method in survey of wildlife population. Confident interval estimation for density D of a biological population is proposed based on a sequential design. The survey area is occu...Line transect sampling is a very useful method in survey of wildlife population. Confident interval estimation for density D of a biological population is proposed based on a sequential design. The survey area is occupied by the population whose size is unknown. A stopping rule is proposed by a kernel-based estimator of density function of the perpendicular data at a distance. With this stopping rule, we construct several confidence intervals for D by difference procedures. Some bias reduction techniques are used to modify the confidence intervals. These intervals provide the desired coverage probability as the bandwidth in the stopping rule approaches zero. A simulation study is also given to illustrate the performance of this proposed sequential kernel procedure.展开更多
Objective To understand the occupational injury situation of front-line workers in metallurgical and shipbuilding and repairing industry,and explore the risk factors of occupational injury.Methods From September 2023 ...Objective To understand the occupational injury situation of front-line workers in metallurgical and shipbuilding and repairing industry,and explore the risk factors of occupational injury.Methods From September 2023 to March 2024,using cluster sampling method,front-line workers from 2 metallurgical enterprises in Shaoguan and Jinan City and 2 shipbuildinggand repairing enterprises in Jiangmen and Shenzhen City were selected as the investigation objects.6248 questionnaires were distributed and collected,and 6178 were effective questionnaires,with a effective recovery rate of 98.88%.The basic information,living habits,working system,protection and occupational injury of workers were investigated,and the data of occupational injury in factories was collected.The types,jobs and main causes of occupational injuries in different industries were analyzed,and the influencing factors of occupational injuries were analyzed by univariate and multi-factor logistic regression.Results The incidence of occupational injury was 3.13%(128/4086)in metallurgical industry and 4.02%(84/2092)in shipbuilding and repairing industry.The top three occupational injuries in the metallurgical industry were furnace worker(17.19%,22/128),steel rolling worker(14.84%,19/128),maintenance worker(10.16%,13/128),and the top three injury types were mechanical injury(24.22%,31/128),height fall(20.31%,26/128)and object strikes(17.97%,23/128).The top three occupational injuries in shipbuilding and repairing industry were welder(20.24%,17/84),riveter(9.52%,8/84)and crane(8.33%,7/84).The top three injury types were hit by objects(34.52%,29/84),hit by falling objects(22.62%,19/84),and lifting injury(20.24%,17/84).The injuries of workers in metallurgical industry and shipbuilding and repairing industry weremainly fractures,accounting for 32.03%(41/128)and 60.71%(51/84),respectively.The incidence of occupational injury was higher in males,with sleep disorder,high temperature exposure and chemical toxicity exposure(P<0.05).There were significant differences in age,smoking degree,working age and emotional state between workers with occupational injury and those without occupational injury(P<0.05).Multivariate analysis showed that male,age above 50 years old,moderate smoking,working years of 5-9 years,mild anxiety,poor health status and high temperature exposure were risk factors for occupational injury(0R=25.57,3.72,14.27,2.09,1.50,4.36,0.66,P<0.05).Conclusion The incidence of occupational injury is higher in shipbuilding and repairing industry,and fracture is the main type of occupational injury.The occurrence of occupational injury is affected by gender,age,smoking,working age,emotional state,health status and high temperature exposure.展开更多
The saddlepoint approximation(SA)can directly estimate the probability distribution of linear performance function in non-normal variables space.Based on the property of SA,three SA based methods are developed for the...The saddlepoint approximation(SA)can directly estimate the probability distribution of linear performance function in non-normal variables space.Based on the property of SA,three SA based methods are developed for the structural system reliability analysis.The first method is SA based reliability bounds theory(RBT),in which SA is employed to estimate failure probability and equivalent normal reliability index for each failure mode firstly,and then RBT is employed to obtain the upper and the lower bounds of system failure probability.The second method is SA based Nataf approximation,in which SA is used to estimate the probability density function(PDF)and cumulative distribution function(CDF)for the approximately linearized performance function of each failure mode.After the PDF of each failure mode and the correlation coefficients among approximately linearized performance functions are estimated,Nataf distribution is employed to approximate the joint PDF of multiple structural system performance functions,and then the system failure probability can be estimated directly by numerical simulation using the joint PDF.The third method is SA based line sampling(LS).The standardization transformation is needed to eliminate the dimensions of variables firstly in this case.Then LS method can express the system failure probability as an arithmetic average of a set of failure probabilities of the linear performance functions,and the probabilities of the linear performance functions can be estimated by the SA in the non-normal variables space.By comparing basic concepts,implementations and results of illustrations,the following conclusions can be drawn:(1)The first method can only obtain the bounds of system failure probability and it is only acceptable for the linear limit state function;(2)the second method can give the estimation of system failure probability,and its error mostly results from the approximation of Nataf distribution for the joint PDF of the structural system performance functions and the linearization of the performance functions;(3)the SA based LS method can obtain the estimator of system failure probability,which converges to the actual value along with the increase of sample size.The SA based LS method considers the influence of nonlinearity of limit state function on the failure probability,and it is acceptable for the structural system both with a single failure mode and with multiple failure modes,therefore it has the widest applicability.展开更多
Direct illumination rendering is an impor-tant technique in computer graphics.Precomputed radiance transfer algorithms can provide high quality rendering results in real time,but they can only support rigid models.On ...Direct illumination rendering is an impor-tant technique in computer graphics.Precomputed radiance transfer algorithms can provide high quality rendering results in real time,but they can only support rigid models.On the other hand,ray tracing algorithms are fexible and can gracefully handle animated models.With NVIDIA RTX and the AI denoiser,we can use ray tracing algorithms to render visually appealing results in real time.Visually appealing though,they can deviate from the actual one considerably.We propose a visibility-boundary edge oriented infinite triangle bounding volume hierarchy(BVH)traversal algorithm to dynamically generate visibility in vector form.Our algorithm utilizes the properties of visibility-boundary edges and infinite triangle BVH traversal to maximize the efficiency of the vector form visibility generation.A novel data structure,temporal vectorized visibility,is proposed,which allows visibility in vector form to be shared across time and further increases the generation efficiency.Our algorithm can efficiently render close-to-reference direct illumination results.With the similar processing time,it provides a visual quality improvement around 10 dB in terms of peak signal-to-noise ratio(PSNR)w.r.t.the ray tracing algorithm reservoir-based spatiotemporal importance resampling(ReSTIR).展开更多
基金Foundation items： National Natural Science Foundation of China （NSFC 10572117, 10802063, 50875213） National High-tech Research and Development Program （2007AA04Z401）+2 种基金 Aeronautical Science Foundation of China （2007ZA53012） New Century Program For Excellent Talents of Ministry of Education of China （NCET-05-0868） Ph.D. Program Foundation of Northwestern Polytechnical University （CX200801）.
文摘The improved line sampling （LS） technique, an effective numerical simulation method, is employed to analyze the probabilistic characteristics and reliability sensitivity of flutter with random structural parameter in transonic flow. The improved LS technique is a novel methodology for reliability and sensitivity analysis of high dimensionality and low probability problem with implicit limit state function, and it does not require any approximating surrogate of the implicit limit state equation. The improved LS is used to estimate the flutter reliability and the sensitivity of a two-dimensional wing, in which some structural properties, such as frequency, parameters of gravity center and mass ratio, are considered as random variables. Computational fluid dynamics （CFD） based unsteady aerodynamic reduced order model （ROM） method is used to construct the aerodynamic state equations. Coupling structural state equations with aerodynamic state equations, the safety margin of flutter is founded by using the critical velocity of flutter. The results show that the improved LS technique can effectively decrease the computational cost in the random uncertainty analysis of flutter. The reliability sensitivity, defined by the partial derivative of the failure probability with respect to the distribution parameter of random variable, can help to identify the important parameters and guide the structural optimization design.
基金The Aeronautical Science Foundation of China(Nos.20170968002,20230003068002)The National Major Science and Technology Projects of China(Nos.J2019-II-0022-0043,J2019-VII-0013-0153).
文摘Assessment of imprecise time-variant reliability in engineering is a critical task when accounting for both the variability of structural properties and loads over time and the presence of uncertainties involved in the ambiguity of parameters simultaneously.To estimate the Imprecise Time-variant Failure Probability Function(ITFPF)and derive the imprecise reliability results as a byproduct,Adaptive Combination Augmented Line Sampling(ACALS)is proposed.It consists of three integrated features:Augmented Line Sampling(ALS),adaptive strategy,and the optimal combination.ALS is adopted as an efficient analysis tool to obtain the failure probability function w.r.t.imprecise parameters.Then,the adaptive strategy iteratively applies ALS while considering both imprecise parameters and time simultaneously.Finally,the optimal combination algorithm collects all result components in an optimal manner to minimize the Coefficient of Variance(C.o.V.)of the ITFPF estimate.Overall,the proposed ACALS method outperforms the original ALS method by efficiently estimating the ITFPF while guaranteeing a minimal C.o.V.Thus,the proposed approach can serve as an effective tool for imprecise time-variant reliability analysis in real engineering applications.Several examples are presented to demonstrate the superiority of the proposed approach in addressing the challenges of estimating the ITFPF.
基金supported by the National Natural Science Foundation of China(Grant Nos.10572117,50875213)the Program for New Century Excellent Talents in University(Grant No.NCET-05-0868)+1 种基金the Aviation Science Foundation(Grant No.2007ZA53012)the National Hi-Tech Research and Development Program of China("863"Project)(Grant No.2007AA04Z401)
文摘For structural system with random basic variables as well as fuzzy basic variables,uncertain propagation from two kinds of basic variables to the response of the structure is investigated.A novel algorithm for obtaining membership function of fuzzy reliability is presented with saddlepoint approximation(SA)based line sampling method.In the presented method,the value domain of the fuzzy basic variables under the given membership level is firstly obtained according to their membership functions.In the value domain of the fuzzy basic variables corresponding to the given membership level,bounds of reliability of the structure response satisfying safety requirement are obtained by employing the SA based line sampling method in the reduced space of the random variables.In this way the uncertainty of the basic variables is propagated to the safety measurement of the structure,and the fuzzy membership function of the reliability is obtained.Compared to the direct Monte Carlo method for propagating the uncertainties of the fuzzy and random basic variables,the presented method can considerably improve computational efficiency with acceptable precision.The presented method has wider applicability compared to the transformation method,because it doesn't limit the distribution of the variable and the explicit expression of performance function,and no approximation is made for the performance function during the computing process.Additionally,the presented method can easily treat the performance function with cross items of the fuzzy variable and the random variable,which isn't suitably approximated by the existing transformation methods.Several examples are provided to illustrate the advantages of the presented method.
基金the National Nature Science Foundation of China (Grant No. 51175425)the Aviation Science Foundation (Grant No. 2011ZA53015)+1 种基金the Aerospace Science and Technology Innovative Foundation (Grant No. 2011200093)the Nature Science Basic Research Fund of Shaanxi Province (Grant No. 2012JQ1015)
文摘For the stochastic structure with stochastic excitation, an advanced stratified line sampling (SLS) method is presented to obtain the cumulative distribution function (CDF) of the structural response and its sensitivity. The advanced stratified line sampling method introduces a set of middle failure subsets firstly. And for each subset, the conventional line sampling can be used to obtain the corresponding value of the response's CDF. At the same time, the sensitivity estimations of each failure subset can also be computed by modifying the important direction and corresponding reliability coefficients. The properties of CDF sensitivity are proved while the performance function is linear with normal random variables. After two simple examples are used to demonstrate the properties of CDF sensitivity and the feasibility of the presented method, the method employed to analyze the CDF and corresponding sensitivity of root bending moment (RBM) responses for the stochastic BAH is wing with gust excitation to a square-edged gust and to a Dryden gust. The results show that the parameters of the second and the fifth order modals exert more influence on the CDF of response than the other ones, and the presented SLS method can more significantly reduce the computational cost compared with Monte Carlo simulation (MCS).
基金supported by the National Basic Research Program of China (No.2013CB733002)
文摘The random variables are always truncated in aerospace engineering and the truncated distribution is more feasible and effective for the random variables due to the limited samples available.For high-reliability aerospace mechanism with truncated random variables, a method based on artificial bee colony（ABC） algorithm and line sampling（LS） is proposed.The artificial bee colony-based line sampling（ABCLS） method presents a multi-constrained optimization model to solve the potential non-convergence problem when calculating design point（is also as most probable point, MPP） of performance function with truncated variables; by implementing ABC algorithm to search for MPP in the standard normal space, the optimization efficiency and global searching ability are increased with this method dramatically.When calculating the reliability of aerospace mechanism with too small failure probability, the Monte Carlo simulation method needs too large sample size.The ABCLS method could overcome this drawback.For reliability problems with implicit functions, this paper combines the ABCLS with Kriging response surface method,therefore could alleviate computational burden of calculating the reliability of complex aerospace mechanism.A numerical example and an engineering example are carried out to verify this method and prove the applicability.
基金NSAF(Grant No.U1530122)the Aeronautical Science Foundation of China(Grant No.ASFC-20170968002)the Fundamental Research Funds for the Central Universities of China(XMU,20720180072).
文摘In structural reliability analysis,simulation methods are widely used.The statistical characteristics of failure probability estimate of these methods have been well investigated.In this study,the sensitivities of the failure probability estimate and its statistical characteristics with regard to sample,called‘contribution indexes’,are proposed to measure the contribution of sample.The contribution indexes in four widely simulation methods,i.e.,Monte Carlo simulation(MCS),importance sampling(IS),line sampling(LS)and subset simulation(SS)are derived and analyzed.The proposed contribution indexes of sample can provide valuable information understanding the methods deeply,and enlighten potential improvement of methods.It is found that the main differences between these investigated methods lie in the contribution indexes of the safety samples,which are the main factors to the efficiency of the methods.Moreover,numerical examples are used to validate these findings.
基金Supported by the National Natural Science Funds for Distinguished Young Scholar(No.70825004)the National Natural Science Foundation of China(No.10731010,10628104 and 10721101)Leading Academic Discipline Program,the 10th five year plan of 211 Project for Shanghai University of Finance and Economics and 211 Project for Shanghai University of Finance and Economics(the 3rd phase)
文摘Line transect sampling is a very useful method in survey of wildlife population. Confident interval estimation for density D of a biological population is proposed based on a sequential design. The survey area is occupied by the population whose size is unknown. A stopping rule is proposed by a kernel-based estimator of density function of the perpendicular data at a distance. With this stopping rule, we construct several confidence intervals for D by difference procedures. Some bias reduction techniques are used to modify the confidence intervals. These intervals provide the desired coverage probability as the bandwidth in the stopping rule approaches zero. A simulation study is also given to illustrate the performance of this proposed sequential kernel procedure.
文摘Objective To understand the occupational injury situation of front-line workers in metallurgical and shipbuilding and repairing industry,and explore the risk factors of occupational injury.Methods From September 2023 to March 2024,using cluster sampling method,front-line workers from 2 metallurgical enterprises in Shaoguan and Jinan City and 2 shipbuildinggand repairing enterprises in Jiangmen and Shenzhen City were selected as the investigation objects.6248 questionnaires were distributed and collected,and 6178 were effective questionnaires,with a effective recovery rate of 98.88%.The basic information,living habits,working system,protection and occupational injury of workers were investigated,and the data of occupational injury in factories was collected.The types,jobs and main causes of occupational injuries in different industries were analyzed,and the influencing factors of occupational injuries were analyzed by univariate and multi-factor logistic regression.Results The incidence of occupational injury was 3.13%(128/4086)in metallurgical industry and 4.02%(84/2092)in shipbuilding and repairing industry.The top three occupational injuries in the metallurgical industry were furnace worker(17.19%,22/128),steel rolling worker(14.84%,19/128),maintenance worker(10.16%,13/128),and the top three injury types were mechanical injury(24.22%,31/128),height fall(20.31%,26/128)and object strikes(17.97%,23/128).The top three occupational injuries in shipbuilding and repairing industry were welder(20.24%,17/84),riveter(9.52%,8/84)and crane(8.33%,7/84).The top three injury types were hit by objects(34.52%,29/84),hit by falling objects(22.62%,19/84),and lifting injury(20.24%,17/84).The injuries of workers in metallurgical industry and shipbuilding and repairing industry weremainly fractures,accounting for 32.03%(41/128)and 60.71%(51/84),respectively.The incidence of occupational injury was higher in males,with sleep disorder,high temperature exposure and chemical toxicity exposure(P<0.05).There were significant differences in age,smoking degree,working age and emotional state between workers with occupational injury and those without occupational injury(P<0.05).Multivariate analysis showed that male,age above 50 years old,moderate smoking,working years of 5-9 years,mild anxiety,poor health status and high temperature exposure were risk factors for occupational injury(0R=25.57,3.72,14.27,2.09,1.50,4.36,0.66,P<0.05).Conclusion The incidence of occupational injury is higher in shipbuilding and repairing industry,and fracture is the main type of occupational injury.The occurrence of occupational injury is affected by gender,age,smoking,working age,emotional state,health status and high temperature exposure.
基金supported by the National Natural Science Foundation of China(Grant Nos.10572117,50875213)the Program for New Century Excellent Talents in University(Grant No.NCET-05-0868)+2 种基金Aviation Science Foundation(Grant No.2007ZA53012)the National Hi-Tech Research and Development Program of China("863"Project)(Grant No.2007AA04Z401)the Doctorate Foundation of Northwestern Poly-technical University(Grant No.CX200801)
文摘The saddlepoint approximation(SA)can directly estimate the probability distribution of linear performance function in non-normal variables space.Based on the property of SA,three SA based methods are developed for the structural system reliability analysis.The first method is SA based reliability bounds theory(RBT),in which SA is employed to estimate failure probability and equivalent normal reliability index for each failure mode firstly,and then RBT is employed to obtain the upper and the lower bounds of system failure probability.The second method is SA based Nataf approximation,in which SA is used to estimate the probability density function(PDF)and cumulative distribution function(CDF)for the approximately linearized performance function of each failure mode.After the PDF of each failure mode and the correlation coefficients among approximately linearized performance functions are estimated,Nataf distribution is employed to approximate the joint PDF of multiple structural system performance functions,and then the system failure probability can be estimated directly by numerical simulation using the joint PDF.The third method is SA based line sampling(LS).The standardization transformation is needed to eliminate the dimensions of variables firstly in this case.Then LS method can express the system failure probability as an arithmetic average of a set of failure probabilities of the linear performance functions,and the probabilities of the linear performance functions can be estimated by the SA in the non-normal variables space.By comparing basic concepts,implementations and results of illustrations,the following conclusions can be drawn:(1)The first method can only obtain the bounds of system failure probability and it is only acceptable for the linear limit state function;(2)the second method can give the estimation of system failure probability,and its error mostly results from the approximation of Nataf distribution for the joint PDF of the structural system performance functions and the linearization of the performance functions;(3)the SA based LS method can obtain the estimator of system failure probability,which converges to the actual value along with the increase of sample size.The SA based LS method considers the influence of nonlinearity of limit state function on the failure probability,and it is acceptable for the structural system both with a single failure mode and with multiple failure modes,therefore it has the widest applicability.
基金supported by the Innovation and Technology Fund from the Innovation and Technology Commission of the Hong Kong Special Administrative Region(Fund Number ITS/065/21).
文摘Direct illumination rendering is an impor-tant technique in computer graphics.Precomputed radiance transfer algorithms can provide high quality rendering results in real time,but they can only support rigid models.On the other hand,ray tracing algorithms are fexible and can gracefully handle animated models.With NVIDIA RTX and the AI denoiser,we can use ray tracing algorithms to render visually appealing results in real time.Visually appealing though,they can deviate from the actual one considerably.We propose a visibility-boundary edge oriented infinite triangle bounding volume hierarchy(BVH)traversal algorithm to dynamically generate visibility in vector form.Our algorithm utilizes the properties of visibility-boundary edges and infinite triangle BVH traversal to maximize the efficiency of the vector form visibility generation.A novel data structure,temporal vectorized visibility,is proposed,which allows visibility in vector form to be shared across time and further increases the generation efficiency.Our algorithm can efficiently render close-to-reference direct illumination results.With the similar processing time,it provides a visual quality improvement around 10 dB in terms of peak signal-to-noise ratio(PSNR)w.r.t.the ray tracing algorithm reservoir-based spatiotemporal importance resampling(ReSTIR).
