On the Suitability of Vibration Acceptance Criteria of Process Pipework

The risk of vibration-induced fatigue in process pipework is usually assessed through vibration measurements. For small-bore pipework, integrity personnel would measure the vibration of the pipework and refer to widely used charts to quantify the risk of vibration-induced fatigue. If the vibration levels are classified as OK, no action is required on behalf of the operators. However, if it is a CONCERN or PROBLEM vibration level, strain measurements are required to adequately quantify the risk through a fatigue life assessment. In this paper, we examine the suitability of a widely used vibration acceptance criteria through finite element models. A total of 4,800 models are used to study the suitability of this vibration acceptance criteria by monitoring both the vibration and dynamic stress. The model comprises a small-bore pipe (2″ SCH 40) that is fitted on a mainline size 5″ SCH 40 using a weldolet; the length of the mainline takes three values resulting in three models. The mainline supporting conditions will be varied using translational and rotational springs. The finite element models will be excited using a point load resembling flow-induced forces (with varying flow velocity and fluid composition). These excitations are obtained from the literature and are based on experimental studies as power spectral density functions. The results show that the studied vibration acceptance criterion is suitable in 99.73% of all the studied models with 68.27% confidence level. For the models with a shorter mainline pipe, the criterial is suitable in 76.5% of the time with 68.27% confidence level.

Monte Carlo-discrete dislocation dynamics: A technique for studying the formation and evolution of dislocation structures

A novel Monte Carlo (MC) based solver for discrete dislocation dynamics (DDD) has been developed, by which dislocation lines are inserted to the system in succession subject to a user-defined acceptance criterion. Utilizing this solver, dislocation structure evolution can be examined in a controlled fashion that is not possible using conventional DDD methods. The outcomes of the MC-DDD simulations establish for the first time that dislocation wall structures can adopt a characteristic width that naturally arises from elastic interactions within the network. This characteristic width does not alter as additional dislocation lines are inserted and the density in the wall increases, meaning it is independent of the mean dislocation spacing. However, the wall width is influenced by the acceptance criterion used during MC steps; the wall gets thinner as the interactions within the wall become more attractive. Finally, we demonstrate that algorithmic aspects of MC-DDD simulations can provide insights into structure evolution. Overall, this new MC-DDD technique will allow systematic studies of dislocation structures, providing unprecedented insight into the underlying mechanics.

Experimental and Numerical Study on the Compressive Failure of Composite Laminates with Fiber Waviness Defects

Fiber waviness defects are found in the inner surface of the hat-shaped stringers manufactured by a process system. In order to establish the acceptance criterion for the stringers with the fiber waviness defects, experimental testing and numerical simulation were carried out in this study. Specially induced fiber waviness defects of four pre-defined severity levels were manufactured and tested. A maximum of a 58.1% drop in compressive failure load is observed for the most severe level in the experimental results. A finite element model with progressive damage method and cohesive zone technique was developed to simulate the failure process and the impact of fiber waviness defects. The numerical simulation results of compressive failure load have a good agreement with experimental results qualitatively and quantitatively. In addition, two simple parameters, i.e., aspect ratio A/H and the number of plies with fiber waviness, are proposed to characterize the influence of the fiber waviness on the compressive failure load for the purpose of fast engineering quality checks.

Development and validation of a novel HILIC method for the quantification of low-levels of cuprizone in cuprizone-containing chow

Cuprizone is an amide compound that has been wildly used in various animal studies, such as in the investigation of remyelination in mouse model. It is important to control the amount of cuprizone dosed in animals to be consistent as different amounts may lead to different clinical observations. Cuprizone is usually administrated as a minor component (i.e., 0.3%) of a mixture with powdered or pelleted rodent chow. Its low content, combined with the complex nature of chow, represents a significant challenge for the quantification of cuprizone in the mixture. To the best of our knowledge, no method has been reported in the literature so far. In this study, a simple, selective, and sensitive hydrophilic interaction liquid chromatographic method was developed for the quantification of cuprizone in cuprizone pre-clinical formulations. The analytical method comprises a fast ultrasound assisted extraction with acetonitrile/water as a solvent followed by gradient separation using a Waters Xbridge HILIC column with 0.1% TFA in water and acetonitrile as mobile phases and UV detection at 220 nm. The specificity, linearity, accuracy, repeatability, and limit of quantitation (LOQ) of the method were established. The method was determined to be linear in the range of 10–200 μg/mL. Accuracy was assessed by spiking a chow placebo with various amounts of a cuprizone reference standard to achieve target concentration levels and the recoveries were within the acceptance criterion of 90–110% of the target concentrations. Repeatability was demonstrated at the nominal concentration of 100 µg/mL and LOQ level of 2.5 μg/mL. This method has been demonstrated to be suitable for its intended use and has been successfully applied to the quantification of low levels of cuprizone in chow formulations. It was found that the cuprizone content in chow could varied significantly between batches and the potential causes of the variability were investigated.

A Fast and Scalable Heuristic for the Solution of Large-Scale Capacitated Vehicle Routing Problems

In this paper, we propose a fast and scalable, yet effective, metaheuristic called FILO to solve large-scale instances of the Capacitated Vehicle Routing Problem. Our approach consists of a main iterative part, based on the Iterated Local Search paradigm, which employs a carefully designed combination of existing acceleration techniques, as well as novel strategies to keep the optimization localized, controlled, and tailored to the current instance and solution. A Simulated Annealing-based neighbor acceptance criterion is used to obtain a continuous diversification, to ensure the exploration of different regions of the search space. Results on extensively studied benchmark instances from the literature, supported by a thorough analysis of the algorithm’s main components, show the effectiveness of the proposed design choices, making FILO highly competitive with existing state-of-the-art algorithms, both in terms of computing time and solution quality. Finally, guidelines for possible efficient implementations, algorithm source code, and a library of reusable components are open-sourced to allow reproduction of our results and promote further investigations.

Non-Proportionality Indices and Error Constraint in Modal Analysis of Viscously Damped Linear Structures

Use of modal procedures in systems with non-proportional damping (such as structures with added viscous damping systems) results in response errors, shown in this study to depend on dissimilar and often conflicting conditions for different variables and stories; thus, it is not possible to propose simple rules based on structural or damping properties to limit the error in a global way. However, four existing indices (originally proposed to measure damping non-proportionality) present a positive correlation with the extreme errors in modal procedures for all variables and stories. Thus, limiting the index value is a sufficient condition to keep the error in all variables within a given threshold. For practical application, limit values for these indices are tabulated as a function of error and can be used as an acceptance criterion for the validity of modal procedures.

Rail Roughness Acceptance Criterion Based on Interior Noise

Severe rail roughness leads to a series of problems in metro systems, particularly the vehicle noise problem. To ensure a better acoustic environment, rail roughness control is therefore one of the main concerns for the metro operators. But the existing roughness acceptance criteria are not suitable for metro interior noise control. It is an appropriate method to determine the rail roughness limit based on interior noise. A rail roughness acceptance criterion based on metro interior noise is accordingly proposed in this paper. The relationship between rail roughness and interior noise can be derived with wheel–rail noise as link. With this objective, a combined test and simulation method is adopted. A validated wheel–rail noise prediction model is thus established to determine the relationship between rail roughness and wheel–rail noise. Moreover, the transfer function of wheel–rail noise to interior noise is developed based on extensive field test. Using this method, the noise sensitivity to roughness wavelength and acceptance criteria at different speeds and track structures are investigated. Finally, an eclectic rail corrugation acceptance criterion on curved track is suggested in consideration of practical application.

An Augmented Variable Neighborhood Search to Solve the Capacitated Location-Routing Problem

In this paper we proposed a new variable neighborhood search (VNS) for solving the location- routing problem with considering capacitated depots and vehicles. A set of capacitated vehicles, a set of depots with restricted capacities, and associated opening costs, and a set of customers with deterministic demands are given. The problem aims to determine the depots to be opened, fleet assignment to each depot, and the routes to be performed to satisfy the demand of the customers. The objective is to minimize the total costs of the open depots, the setup cost associated with the used vehicles, and transportation cost. We proposed a new VNS which is augmented with a probabilistic acceptance criterion as well as a set of efficient local searches. The computational results implemented on four well-known data sets demonstrate that the proposed algorithm is competitive with other well- known algorithms while reaching many best-known solutions and updating six best new results with reasonable computational time. Conclusions and future research avenues close the paper.

A Note on the Structural Assessment of Perforated Panels used in Façade

Different materials such as glass and composite cladding panels are common in the façade industry due to their architectural appearance. The direct sun rays enter the building and might produce discomfort to the occupants, especially in office and institutional buildings. Nowadays, perforated panels are widely used in facades and becoming more popular in the middle east. These panels are a formal exploration inspired by the Islamic patterns used in traditional Mashrabiya. This paper provides an overview of the application of Mashrabiya "perforated panels" and present structural assessment using software codes such as Robot and SAP2000 for vertical and horizontal installed cases. These panels are fabricated in different sizes with different thicknesses depends on their applications and uses. In this paper, rectangular, square fixed at the roof and vertically fixed panels are assessed. These are usually supported by steel or aluminium tubes designed for a wind load specified by project specifications. The cases presented here for the perforated panels arechecked for the induced stresses and deflections obtained from the numerical model using shell elements. The adopted framing systems and fixing detailing has been found satisfactory according to different acceptance criterion. The paper gives helpful design tools for the façade engineers.