Checkpointing Method Research Articles

Reliability assessment on prediction of pile bearing capacity

There are many prediction methods that can be used to determine the bearing capacity of pipe pile. However, most of these methods are highly sensitive to specific in situ conditions and hence usually result in significant error. Therefore, it is important to evaluate the reliability of different pile bearing capacity prediction methods. Based on reliability theory, a computer code is developed in this paper to calculate reliability. Random variable statistic properties and corresponding reliabilities for different prediction methods are investigated and analysed. Results show that the reliability index for logarithmic normal distribution is higher than normal distribution. Analysis results demonstrate that the checking point method (JC method) method has a slightly lower efficiency than the Monte-Carlo importance sampling method and the Monte-Carlo direct sampling method. The Monte-Carlo importance sampling method has a higher efficiency than the Monte-Carlo direct sampling method. The Monte-Carlo importance sampling method can be used in major engineering projects. It is concluded that the clustering centre method has higher reliability in predicting pile bearing capacity than the Eslami and Fellenius method, Almeida method and Powell method.

Reliability Analysis of Relevant Radom Variables in Pedestrian Evacuation Study in Underground Transportation Hub

In this study reliability theory was applied in evacuation time of pedestrians in the subway, especially taking the correlation of pedestrian speed and pedestrian flow coefficient into account. Firstly, the traditional evacuation time design formula was regarded as research model. Statistical distribution of pedestrian speed and pedestrian flow coefficient in the model was analyzed .Thus the reliability limit state equation was built. Then the evacuation time’s reliability probability was obtained according to the checking point method of generalized random space. At last the process of how different factors influence the reliability was analyzed. Results show that we should consider the correlation between pedestrian speed and export flow rate when correlation is big (absolute value is greater than 0.5, for example).Our conclusions will contribute to related research and the formulation of actual planning.

Reducing the computer memory requirement for 3D reverse-time migration with a boundary-wavefield extrapolation method

Reverse-time migration (RTM) using the crosscorrelation imaging condition requires that the forward-propagated source wavefield and the backward-propagated receiver wavefield be accessible within the imaging domain at the same time step. There are two categories of methods to balance the computer memory requirement and the computational complexity of RTM: checkpointing methods and source-wavefield reconstruction methods. We have developed a new source-wavefield reconstruction method to improve the balance between the computer memory requirement and the computational complexity of RTM. During the forward simulation of the source wavefield, we stored boundary wavefields only at one or two layers of spatial grid points and reconstructed the back-propagated source wavefield at the same time step as that of the back-propagated receiver wavefield, using a high-order wave-equation extrapolation scheme. One conventional RTM method uses boundary wavefields stored at multiple layers of spatial grid points and a high-order finite-difference (FD) scheme to reconstruct the back-propagated source wavefield. For an FD scheme with the eighth or sixteenth order of accuracy in space, our new method used only 37.5% of the computer memory required by this conventional method to store the boundary wavefields. This reduction of computer memory usage is significant because storing the boundary wavefields consumes most of the computer memory required for 3D migration using reconstructed source wavefields. Moreover, our method maintained the spatial order of accuracy of the FD scheme for the entire imaging domain, whereas some conventional methods reduce the spatial-order accuracy of the FD scheme near the boundaries to back-propagate the source wavefield to decrease the computer memory requirement. We validated our method using synthetic seismic data. Our method produced 2D and 3D migration images of complex subsurface structures as accurate as those yielded using an RTM method without reducing the spatial order of accuracy near the boundaries.

Reliability Analysis on the Foundation Bearing Capacity in Ningbo Rail Transit Engineering

According to the first-stage geologic investigation reports of the line 1 and line 2 in Ningbo rail transit, the natural density (ρ) and the vane strength (Cu) probability distribution of the typical layers in Ningbo area were studied in this paper. Besides, the reliabilities of the typical layers foundation bearing capacity in Ningbo area were evaluated by the checking point method. It is found that (1) the natural densities of the typical layers in Ningbo area show good normal distribution as their corresponding variation coefficients (δ) are small. Unfortunately, the vane strengths of the typical soils in Ningbo area show poor normal distribution as their corresponding variation coefficients (δ) are large. (2) The soil parameters variation has significant influence on the reliability index β. Moreover, β is more sensitive to the variation of ρ than to the variation of Cu. (3) As the safety coefficient methods can not consider the influence of the soil parameters variation on the foundation stability, it is suggested that the foundation stability in Ningbo area should be evaluated by the reliability analysis method.

A SURVEY OF CHECKPOINT/RESTART TECHNIQUES ON DISTRIBUTED MEMORY SYSTEMS

The road to exascale computing poses many challenges for the High Performance Computing (HPC) community. Each step on the exascale path is mainly the result of a higher level of parallelism of the basic building blocks (i.e., CPUs, memory units, networking components, etc.). The reliability of each of these basic components does not increase at the same rate as the rate of hardware parallelism. This results in a reduction of the mean time to failure (MTTF) of the whole system. A fault tolerance environment is thus indispensable to run large applications on such clusters. Checkpoint/Restart (C/R) is the classic and most popular method to minimize failure damage. Its ease of implementation makes it useful, but typically it introduces significant overhead to the application. Several efforts have been made to reduce the C/R overhead. In this paper we compare various C/R techniques for their overheads by implementing them on two different categories of applications. These approaches are based on parallel-file-system (PFS)-level checkpoints (synchronous/asynchronous) and node-level checkpoints. We utilize the Scalable Checkpoint/Restart (SCR) library for the comparison of node-level checkpoints. For asynchronous PFS-level checkpoints, we use the Damaris library, the SCR asynchronous feature, and application-based checkpointing via dedicated threads. Our baseline for overhead comparison is the naïve application-based synchronous PFS-level checkpointing method. A 3D lattice-Boltzmann (LBM) flow solver and a Lanczos eigenvalue solver are used as prototypical applications in which all the techniques considered here may be applied.

Circular Arc Gear Reliability Study Based on Modified FOSM Method

As different limit state functions are used to analyze reliability, there is a great distinctness among the calculated results. In this paper an improved LOSM method is proposed, namely, checking point method. The circular arc gear case is employed to demonstrate this method. In contrast to the results of Monte Carlo simulation, this method can greatly improve reliability calculations precision.

Study on Reliability of Bracing Structure for Foundation Pit by Excel Optimization Algorithm

On the basis of the theory of structure reliability, the optimization algorithm according to the geometric significance of the reliability index and the checking point method are studied to calculate the reliability of the bracing structure for foundation pit. Combined with a soil nailed wall engineering example, the primary data calculation table is established to solve the non-linear programming problem adopting the embedded planning solving method of Excel software and the results indicate that the reliability index and the coordinates of the checking point are same nearly using the checking point method and Excel planning solving method, but the latter is more efficient and convenient than the former, it means that it is feasible to calculate the reliability index of the bracing structure for foundation pit by Excel optimization algorithm.

Seismic Damage Assessment of Urban Water Supply Pipeline

Water supply pipeline system is a key issue in urban lifeline engineering, and the seismic assessment for the system damage is of significant importance. In this study, method of seismic damage assessment on underground water supply pipeline is introduced. With emphasis on the uncertainties of earthquake level, ground condition, soil-pipe interaction and capacity to resist pipe deformation in longitudinal direction, the check point method is applied to the reliability study of water pipeline, and a case study is presented to show the implementation of the proposed model.

IMCLA: Performance Evaluation of Integrated Multilevel Checkpointing Algorithms using Checkpointing Efficiency

Main objective of this research work is to improve the checkpoint efficiency for integrated multilevel checkpointing algorithms (IMLCA) and prevent checkpointing from becoming the bottleneck of cloud data centers. In order to find an efficient checkpoint interval, checkpointing overheads has also considered in this paper. Traditional checkpointing methods stores persistently snapshots of the present job state and use them for resuming the execution at a later time. The attention of this research is strategies for deciding when and whether a checkpoint should be taken and evaluating them in regard to minimizing the induced monetary costs. By varying rerun time of checkpoints performance comparisons are which will be used to evaluate optimal checkpoint interval. The purposed fail-over strategy will work on application layer and provide highly availability for Platform as a Service (PaaS) feature of cloud computing.

Deflection Reliability Analysis of PSC Box-Girder Bridge under High-Speed Railway Loads

A high-speed railway (HSR) construction boom has been observed in China during the past few years, in which prestressed concrete (PSC) box-girders are widely used for HSR bridges. Concerns have been raised regarding the long-term deflection of girders under the combined actions of concrete creep, shrinkage, and tendon relaxation, since the time-variant deflection significantly undermines the safety of high-speed trains. This paper presents the time-variant deflection reliability analysis of an existing HSR PSC box-girder bridge, in which a hybrid method, consisting of the response surface (RS) method, the finite element (FE) method and the checking point method (i.e., the JC method), is used. The pre-and post-cracking behaviors of the thin-walled box girder are described by using composite degenerated shell elements with the smeared cracking model and the Hordijk's tension softening relation. In particular, the CEB-FIP model for creep and shrinkage is applied in the finite-element (FE) analyses. By using the probabilistic sensitivity analyses, random variables that significantly affect the time-variant deflection are selected for the reliability calculation. It is found that the deflection reliabilities are high in the early stage of bridge service but decrease rapidly during the first 10 to 20 service years. Higher speed limits result in a significant decrease in deflection reliability indices, which may fall below the target value prior to the expected service life. The proposed methodologies can be used in the design optimization, speed control and making rational maintenance or repair strategies for HSR PSC bridges.

A Balanced Scheduling Algorithm with Fault Tolerant and Task Migration based on Primary Static Mapping (PSM) in Grid

In this paper we present a balanced scheduling algorithm with considering the fault tolerance and task migration of allocating independent tasks in grid systems. Resource scheduling and its management are great challenges in heterogeneous environment. Hence load balancing is one of the best solutions to achieve the above purposes. The scheduling algorithm which we will present in follow, with taking the fault tolerance, checkpointing method, task migration and priority for mapping independent tasks on heterogeneous computing environment, creates the specific situation to ensure high performance in grid systems. So by implementing these parameters we can achieve more efficient and dependable performance than similar previous algorithms. It will be done with better condition and achieve high performance in computational grids in compare with Min-min algorithm. Finally the experiment and simulated results show that proposed balanced scheduling algorithm performs significantly to ensure high throughput, reduced makespan, reliability and more efficiency in the grid environment.

UML Based Integrated Multilevel Checkpointing Algorithms for Cloud Computing Environment

Main objective of this research work is to improve the checkpoint efficiency for integrated multilevel checkpointing algorithms and prevent checkpointing from becoming the bottleneck of cloud data centers. In order to find an efficient checkpoint interval, checkpointing overheads has also considered in this paper. Traditional checkpointing methods stores persistently snapshots of the present job state and use them for resuming the execution at a later time. The attention of this research is strategies for deciding when and whether a checkpoint should be taken and evaluating them in regard to minimizing the induced monetary costs. By varying rerun time of checkpoints performance comparisons are which will be used to evaluate optimal checkpoint interval. The purposed fail-over strategy will work on application layer and provide highly availability for Platform as a Service (PaaS) feature of cloud computing.

Time-reversal checkpointing methods for RTM and FWI

Time-domain seismic simulation can form the basis of reverse time depth migration and full-waveform inversion. These applications need to temporally crosscorrelate a forward simulation state with an adjoint simulation state and therefore need to be able to access each time step of a forward simulation in time-reverse order. This requires saving all forward states for all times (which can require more memory than is typically available on a computer system for many problems of interest), or the ability to checkpoint information and rapidly recompute forward simulation states as needed. Prior work has suggested how to do the latter by optimally choosing which forward simulation time steps to checkpoint, thereby enabling the most efficient reuse of memory buffers and minimizing recomputation. The optimal trade-off between memory usage and recomputation can be further improved under the assumption that the information needed to do temporal crosscorrelation is smaller than the information required to restart a simulation from a given time step. This assumption is true for many geophysical problems of interest. The modification can yield a reduction in the memory requirement and recomputation time. The tested examples applied to isotropic elastic reverse time migration and anisotropic viscoelastic full-waveform inversion.

Reliability Analysis of Flexural Concrete Member Based on the Randomness of Pitting

In order to analyze the influence of stochastic pitting corrosion to the reliability of service structure, According to the theory of extreme values of random variables and the basic theory of reliability analysis, the reliability of flexural concrete member based on the randomness of pitting, the change of statistical parameters for both corroded steel bar and resistance is also analyzed based on the randomness of pitting. Based on the checking point method, the development law of reliability of concrete bending members with the number of random variables and the service life are studied. The results indicated that the influence of the randomness of pitting to the reliability of flexural concrete members is of the most significance, the reliability index was found to decline with the increase of number of random variables and the service life. The analysis show the research presented in the paper can provide theoretical basis of life prediction.

WBC-ALC: A Weak Blocking Coordinated Application-Level Checkpointing for MPI Programs

As supercomputers increase in size, the mean time between failures (MTBF) of a system becomes shorter, and the reliability problem of supercomputers becomes more and more serious. MPI is currently the de facto standard used to build high-performance applications, and researches on the fault tolerance methods of MPI are always hot topics. However, due to the characteristics of MPI programs, most current checkpointing methods for MPI programs need to modify the MPI library (even operating system), or implement a complicated protocol by logging lots of messages. In this paper, we carry forward the idea of Application-Level Checkpointing (ALC). Based on the general fact that programmers are familiar with the communication characteristics of applications, we have developed BC-ALC, a new portable blocking coordinated ALC for MPI programs. BC-ALC neither modifies the MPI library (even operating system) nor logs any message. It implements coordination only by the Barrier operations instead of any complicated protocol. Furthermore, in order to reduce the cost of fault-tolerance, we reduce the synchronization range of the barrier, and design WBC-ALC, a weak blocking coordinated ALC utilizing group synchronization instead of global synchronization based on the communication relationship between processes. We also propose a fault-tolerance framework developed on top of WBC-ALC and discuss an implementation of it. Experimental results on NPB3.3-MPI benchmarks validate BC-ALC and WBC-ALC, and show that compared with BC-ALC, the average coordination time and the average backup time of a single checkpoint in WBC-ALC are reduced by 44.5% and 5.7% respectively.

Parametric Statistics of Building Lifting-Up Engineering and Reliability Evaluation of Lifting Support

During constructing of lifting-up engineering of Humanity Hall of Nanjing Museum, the sizes of steel lifting supports, loads distribution and lifting force changes were surveyed, which controls the safety of Lifting-up engineering. By establishing limit state function of H-shaped steel lifting support, based on those data, the reliability of lifting supports at three states of design, weighing after columns cut and lifting process was calculated respectively using checking point method. Results shows: the reliability in constructing process of building reconstruct engineering is lower than that of general engineering because more difficulty in construction, and in lifting process the time-dependent reliability of KZ1 is lower 63.1% than design reliability.

Reliability-Based Stability Analysis of Foundation Pit Supported by Micro-Pile Composite Soil Nailing

Considering the co-action of micro-pile and soil nailing, the state equation of limit equilibrium and the performance function of inner global stability of foundation pit supported by the micro-pile composite soil nailing is set up with the slope limit equilibrium theory and the circular sliding slice method. The calculating model of sliding surface for inner global stability of foundation pit is established with the geometry controlling method and the optimization searching of the most dangerous sliding surface is achieved. Then with the shear strength indexes of soil as random variables, the partial derivatives of the performance function to all random variables is deduced and the reliability index of inner global stability of foundation pit supported by micro-pile composite soil nailing is calculated with the design checking point method. Finally, the effects of coefficients of variability of the random variables on reliability index are analyzed.

A Secure Mobile Agent System against Tailgating Attacks

Problem statement: A lot of real time applications have extended their hands towards Mobile Agents to accomplish various tasks, due to its flexibility in its functionalities. Since Mobile Agent Systems are used in a distributed environment, it is obvious that they may be vulnerable to various security threats. Most of the security threats faced by the mobile agent systems are overcome by existing security algorithms and architectures. One of the major threats which are not of much focus in a mobile agent system is the Tailgating attack. Approach: In this study, mobile agent system architecture has been proposed to overcome Tailgating. The proposed architecture uses the mechanism of Dual Check-point to preclude Tailgating attacks. Also, to support the mechanism, we use fragmentation and defragmentation techniques. This assures a free flow of data within the system. Results: The results obtained prove that the system is much efficient in its operations as well is immune to Tailgating attacks. Conclusion: The security of the system is improved with the implementation of the Dual Check-point method.

Reliability Analysis of Stability of Foundation Pit Supported by Composite Soil Nailing

Based on the limit equilibrium theory and the circular slip surface method, the state equation of limit equilibrium and the calculation model of the most dangerous sliding surface for inner global stability of foundation pit supported by the prestressed anchor composite soil nailing is established with the disturbing force method. And the searching and solving method of the most dangerous sliding surface is optimized with the SLP optimization method and the simplex optimization method. Then with the mechanical parameters of soil as random variables, the reliability index of inner global stability of foundation pit is calculated with the design checking point method. Finally, a practical project is used to analyze the sensitivity of the reliability index to the coefficients of variability of all random variables.

The cost of false alarms in Hellman and rainbow tradeoffs

Cryptanalytic time memory tradeoff algorithms are generic one-way function inversion techniques that utilize pre-computation. Even though the online time complexity is known up to a small multiplicative factor for any tradeoff algorithm, false alarms pose a major obstacle in its accurate assessment. In this work, we study the expected pre-image size for an iteration of functions and use the result to analyze the cost incurred by false alarms. We are able to present the expected online time complexities for the Hellman tradeoff and the rainbow table method in a manner that takes false alarms into account. We also analyze the effects of the checkpoint method in reducing false alarm costs. The ability to accurately compute the online time complexities will allow one to choose their tradeoff parameters more optimally, before starting the expensive pre-computation process.