Calculation of Maximum Allowable Free Span Length and Safety Assessment of the DF1-1 Submarine Pipeline

The DFI-1 submarine pipeline was investigated using a dual-frequency side-scan sonar and a swath sounder system. More than a hundred scour pits under the pipeline were found, most of which have caused the span of the pipeline to increase and threatened its safety. The maximum allowable free span length （MAFSL） of the pipeline was determined through the limitations re- garding maximum allowable stress under static or quasi-static loads and the onset of Vortex Induced Vibrations （VIV） under different hydrodynamic actions. The results show that the MAFSL under static conditions is 56m. However, the MAFSLs are 30m and 20m under ordinary weather conditions and hurricane-induced currents for the 100-year return period, respectively, to avoid VIV as cal- culated by using the highest safety class factor. It is suggested that spanning pipelines longer than 20 m should be supported. Addi- tionally, eight successive spans which may also threaten the pipeline were proposed. The most hazardous scour pits are along the pipeline section from KP42 to KP51.

Studies on the Hazardous Effects and the Maximum Allowable Concentration of Pyrophyllite Dust

Pyrophyllite (H2Al2,Si4 O22, ) dust (P-dust) is a mixture of silica (10-40% ), differentproportions of a luminium oxide (Al2O3 ), and various metal compounds. People with occupa-tions known to be associated with exposure to P-dust include miners, other industrial workersand persons engaged in artistic carving. Currently, little is known about pyrophyllite pneumo-coniosis from P-dust. This study was designed to investigate the hazardous effects of P-dustand to suggest a maximum allowable concentration (MAC) of the dust.This.study included four parts: (i) Occupational epidemiology surveys in 781 workersfrom 1 pyrophyllite mine (PM) and four pyrophyllite carving mills (PCM), with a registra-tion rate of 98 %. (ii) In vitro studies: Six groups of rats were expeed to different levels ofP-dust; the cytotoxicity of P-dust on rat alveolar macrophages (AM) was investigated by de-termining the potassium'content of AM and the activity levels of lactate dehydrogenase (LDH)in AM culture fluid. (iii) Mineralogical analysis of P-dust: The contents of silica (SiO2 ), alu-minium (Al), ferrum (Fe), niikel (Ni), zinc (Zn) and copper (Cu) in hath PM-dust andPCMdust were determined. (iv ) Determination of P-dust MAC: Using the life-talbemethod, an investigation of the hygiene standard of P-dust was carried out in 625 workers ex-POSed to either PM-dust or PCM-dust, uPon whom routine radiographs were Performed.The results suggest that the risk of developing pneumoconiosis from pyrophyllite dust issignificantly higher for PM workers than for PCM workers. The prevalence rate of PCM-dustpneumoconiosis is significantly higher in men than in women. The content of SiO2 and AlO3in the mixture of P-dust is the most important factor in the etiology of pyrophyllitosis. De-pending on the different P-dust MAC values, we suggest that 2 rng/m3 and 4 mg/m' shouldbe considered as the MAC for PM-dust and PCM-dust, respectively, and 3 mg/m' fOr P-dust. We believe that establishing different hygiene standards is more accurate even thoughworkers are exposured to the 'same' dust

Lower bound estimation of the maximum allowable initial error and its numerical calculation

In the numerical prediction of weather or climate events,the uncertainty of the initial values and/or prediction models can bring the forecast result’s uncertainty.Due to the absence of true states,studies on this problem mainly focus on the three subproblems of predictability,i.e.,the lower bound of the maximum predictable time,the upper bound of the prediction error,and the lower bound of the maximum allowable initial error.Aimed at the problem of the lower bound estimation of the maximum allowable initial error,this study first illustrates the shortcoming of the existing estimation,and then presents a new estimation based on the initial observation precision and proves it theoretically.Furthermore,the new lower bound estimations of both the two-dimensional ikeda model and lorenz96 model are obtained by using the cnop(conditional nonlinear optimal perturbation)method and a pso(particle swarm optimization)algorithm,and the estimated precisions are also analyzed.Besides,the estimations yielded by the existing and new formulas are compared;the results show that the estimations produced by the existing formula are often incorrect.

An innovative test method for mechanical properties of sandstone under instantaneous unloading confining pressure

With the increase of underground engineering construction depth,the phenomenon of surrounding rock sudden failure caused by supporting structure failure occurs frequently.The conventional unloading con-fining pressure(CUCP)test cannot simulate the plastic yielding and instantaneous unloading process of supporting structure to rock.Thus,a high stress loading-instantaneous unloading confining pressure(HSL-IUCP)test method was proposed and applied by considering bolt’s fracture under stress.The wall thickness of confining pressure plates and the material of bolts were changed to realize different confin-ing pressure loading stiffness(CPLS)and lateral maximum allowable deformation(LMAD).The superio-rity of HSL-ICPU method is verified compared with CUCP.The rock failure mechanism caused by sudden failure of supporting structure is obtained.The results show that when CPLS increases from 1.35 to 2.33 GN/m,rock’s peak strength and elastic modulus increase by 25.18%and 23.70%,respectively.The fracture characteristics change from tensile failure to tensile-shear mixed failure.When LMAD decreases from 0.40 to 0.16 mm,rock’s residual strength,peak strain,and residual strain decrease by 91.80%,16.94%,and 21.92%,respectively,and post-peak drop modulus increases by 140.47%.The test results obtained by this method are closer to rock’s real mechanical response characteristics compared with CUCP.

Stability of singular networked control systems with control constraint

Based on bounded network-induced time-delay, the networked control system is modeled as a linear time-variant singular system. Using the Lyapunov theory and the linear matrix inequality approach, the criteria for delay-independent stability and delay-dependent stability of singular networked control systems are derived and transformed to a feasibility problem of linear matrix inequality formulation, which can be solved by the Matlab LMI toolbox, and the feasible solutions provide the maximum allowable delay bound that makes the system stable. A numerical example is provided, which shows that the analysis method is valid and the stability criteria are feasible.

Delay-dependent stability and stabilization criteria of networked control systems with multiple time-delays

This paper deals with the problem of delay-dependent stability and stabilization for networked control systems（NCSs）with multiple time-delays. In view of multi-input and multi-output（MIMO） NCSs with many independent sensors and actuators, a continuous time model with distributed time-delays is proposed. Utilizing the Lyapunov stability theory combined with linear matrix inequalities（LMIs） techniques, some new delay-dependent stability criteria for NCSs in terms of generalized Lyapunov matrix equation and LMIs are derived. Stabilizing controller via state feedback is formulated by solving a set of LMIs. Compared with the reported methods, the proposed methods give a less conservative delay bound and more general results. Numerical example and simulation show that the methods are less conservative and more effective.

Delay-dependent robust stability of uncertain networked control systems with multiple state time-delays

In this paper, delay-dependent robust stability for a class of uncertain networked control systems （NCSs） with multiple state time-delays is investigated. Modeling of multi-input and multi-output （MIMO） NCSs with networkinduced delays and uncertainties through new methods are proposed. Some new stability criteria in terms of LMIs are derived by using Lyapunov stability theory combined with linear matrix inequalities （LMIs） techniques. We analyze the delay-dependent asymptotic stability and obtain maximum allowable delay bound （MADB） for the NCSs with the proposed methods. Compared with the reported results, the proposed results obtain a much less conservative MADB which are more general. Numerical example and simulation is used to illustrate the effectiveness of the proposed methods.

Specific Enthalpy Based Heat Stress Index for Indoor Environments without Radiation Effect

Over 100 human thermal indices have been developed to predict the combined thermal impact on the body.In principle,these indices based on energy thermal budget equations should not only be the most complex but also be the most accurate.However,the simple indices based on algebraic or statistical models[e.g.,the wet-bulb globe temperature(WBGT)]continue to be the most popular.A new heat stress index,the enthalpy dry-bulb temperature(EnD)for indoor environments is developed and validated in this study.The EnD index is unique in that it uses the air specific enthalpy,not the wet-bulb temperature,to measure the latent heat transfer from the skin to the surrounding environment.Theoretically,the EnD index can be treated as the equivalent temperature based on the convective heat transfer coefficient h_(c).Comparison is made between the EnD index and the widely used WBGT index based on the experimental data taken from three independent studies available in the scientific literature.The results show that the EnD index can reduce the overestimation of the dry-bulb air temperature and thus reduce heat stress in most cases,especially for hot and humid environments.It can be concluded that the EnD index has the potential to replace the WBGT index as the standard heat stress index in the future.