Abstract

Since the introduction of mental disorders as networks of causally interacting symptoms, this novel framework has received considerable attention. The past years have resulted in over 40 scientific publications and numerous conference symposia and workshops. Now is an excellent moment to take stock of the network approach: What are its most fundamental challenges, and what are potential ways forward in addressing them? After a brief conceptual introduction, we first discuss challenges to network theory: (1) What is the validity of the network approach beyond some commonly investigated disorders such as major depression? (2) How do we best define psychopathological networks and their constituent elements? And (3) how can we gain a better understanding of the causal nature and real-life underpinnings of associations among symptoms? Next, after a short technical introduction to network modeling, we discuss challenges to network methodology: (4) heterogeneity of samples studied with network analytic models, and (5) a lurking replicability crisis in this strongly data-driven and exploratory field. Addressing these challenges may propel the network approach from its adolescence into adulthood and promises advances in understanding psychopathology both at the nomothetic and idiographic level. Keywords: clinical psychology; dynamic systems; mental disorders; networks; personalized medicine; psychiatry; reproducibility Document type: Part of book or chapter of book

Abstract

JODE purposes to deliver international readers with high quality peer-reviewed academic articles on a wide variety of issues related to open and distance learning, in areas such as technology-assisted learning, computer based training, computer-aided instruction or computer assisted instruction, internet-based training, web-based training, online training, virtual training, virtual learning environments, m-learning, digital education, education on social networking, massive online open courses, game-based learning, active learning, content design, e-assessment, mobile applications, e-video, the quality of open and distance education and accreditation etc. Document type: Part of book or chapter of book

Abstract

This paper provides an overview of the reliability-centered maintenance (RCM) engineering process. RCM is a unique tool used by reliability, safety, and/or maintenance engineers for developing optimum maintenance plans which define requirements and tasks to be performed in achieving, restoring, or maintaining the operational capability of a system or equipment. Implementing the RCM process requires the application of a decision logic that enables systematic analysis of failure mode, rate, and criticality data to determine the most effective maintenance requirements for maintenance-important items. It is through this process that the scheduled maintenance burden and support costs are reduced while sustaining the necessary readiness state. The RCM process is designed to focus engineering attention to the part level in a formal and disciplined manner leading logically to the formulation of a maintenance strategy and plan. RCM benefits include: *The development of high quality maintenance plans in less time and at lower cost. *The availability of a maintenace history for each system; one is able to correlate this experience with specific parts and their failure modes and criticalities. *The assurance that all maintenance-important parts and their failure modes and criticality are considered in the development of maintenance requirements. *The increased probability that the level and content of the maintenance requirement is optimally specified. *The basis for routine, on-line information exchange among the engineering staff and management even in a widely dispersed organization. Document type: Report

Abstract

Ultrasonic guided waves are often used in the detection of defects in oil and gas pipelines. It is common for these pipelines to be buried underground and this may restrict the length of the pipe that can be successfully tested. This is because acoustic energy travelling along the pipe walls may radiate out into the surrounding medium. Accordingly, it is important to develop a better understanding of the way in which elastic waves propagate along the walls of buried pipes, and so in this article a numerical model is developed that is suitable for computing the eigenmodes for uncoated and coated buried pipes. This is achieved by combining a one dimensional eigensolution based on the semi-analytic finite element (SAFE) method, with a perfectly matched layer (PML) for the infinite medium surrounding the pipe. This article also explores an alternative exponential complex coordinate stretching function for the PML in order to improve solution convergence. It is shown for buried pipelines that accurate solutions may be obtained over the entire frequency range typically used in long range ultrasonic testing (LRUT) using a PML layer with a thickness equal to the pipe wall thickness. This delivers a fast and computationally efficient method and it is shown for pipes buried in sand or soil that relevant eigenmodes can be computed and sorted in less than one second using relatively modest computer hardware. The method is also used to find eigenmodes for a buried pipe coated with the viscoelastic material bitumen. It was recently observed in the literature that a viscoelastic coating may effectively isolate particular eigenmodes so that energy does not radiate from these modes into the surrounding [elastic] medium. A similar effect is also observed in this article and it is shown that this occurs even for a relatively thin layer of bitumen, and when the shear impedance of the coating material is larger than that of the surrounding medium.

Abstract

Complex pipelines may have various structural supports and boundary conditions, as well as branches. To analyse the vibrational characteristics of piping systems, frequency modelling and solution methods considering complex constraints are developed here. A fourteen-equation model and Transfer Matrix Method (TMM) are employed to describe Fluid–Structure Interaction (FSI) in liquid-filled pipes. A general solution for the multi-branch pipe is proposed in this paper, offering a methodology to predict frequency responses of the complex piping system. Some branched pipe systems are built for the purpose of validation, indicating good agreement with calculated results.

Abstract

The 2D heat transfer from offshore, completely buried pipelines is studied with reference to transient working conditions. In particular, the start-up case is considered (i.e., the case of a pipeline initially at equilibrium with the surrounding soil). Two different start-up cases are investigated: the step-rising case and the smooth-rising case. (In the latter, the steady-state wall temperature is reached in a finite time.) The energy balance equation is written in a dimensionless form and solved numerically by means of a finite element method. The dimensionless temperature field in the soil and the thermal power exchanged per unit length by the pipeline with the soil are determined. A comparison with a simpler one-dimensional model of the phenomenon (“extra-soil layer” approximation) is performed.

Abstract

The market for driver-assistance systems for modern automobiles is rapidly growing. Formerly only provided for the luxury automotive market, these systems are nowadays more and more available for mid- and compact-class vehicles as well. This development is not only limited to the passenger car segment but is also more and more important for commercial vehicles and trucks. Some driving assistance systems have already become mandatory, e.g., the antilock breaking system (ABS). Some governments are currently thinking about requiring automatic distance control by law for heavy trucks. Automatic distance control in combination with an automatic emergency breaking system is one of the rising stars for enhancing traffic safety. Radar- based distance control mostly interacts with cruise control systems and it adapts the speed of the driver's car to the distance to the car or obstacle in front of the vehicle. Furthermore, unavoidable accidents are detected and actions for reducing the effects of the crash are automatically initiated for some systems. © 2012 IEEE.

Abstract

The two-dimensional problem of an elastic-plate impact onto an undisturbed surface of water of infinite depth is analysed. The plate is forced to move with a constant horizontal velocity component which is much larger than the vertical velocity component of penetration. The small angle of attack of the plate and its vertical velocity vary in time, and are determined as part of the solution, together with the elastic deflection of the plate and the hydrodynamic loads within the potential flow theory. The boundary conditions on the free surface and on the wetted part of the plate are linearized and imposed on the initial equilibrium position of the liquid surface. The wetted part of the plate depends on the plate motion and its elastic deflection. To determine the length of the wetted part we assume that the spray jet in front of the advancing plate is negligible. A smooth separation of the free-surface flow from the trailing edge is imposed. The wake behind the moving body is included in the model. The plate deflection is governed by Euler’s beam equation, subject to free–free boundary conditions. Four different regimes of plate motion are distinguished depending on the impact conditions: ("jats:italic"a"/jats:italic") the plate becomes fully wetted; ("jats:italic"b"/jats:italic") the leading edge of the plate touches the water surface and traps an air cavity; ("jats:italic"c"/jats:italic") the free surface at the forward contact point starts to separate from the plate; ("jats:italic"d"/jats:italic") the plate exits the water. We could not detect any impact conditions which lead to steady planing of the free plate after the impact. It is shown that a large part of the total energy in the fluid–plate interaction leaves the main bulk of the liquid with the spray jet. It is demonstrated that the flexibility of the plate may increase the hydrodynamic loads acting on it. The impact loads can cause large bending stresses, which may exceed the yield stress of the plate material. The elastic vibrations of the plate are shown to have a significant effect on the fluid flow in the wake.

Abstract

In this work we report an experimental modal analysis of a cantilever beam, carried out by use of a Brillouin optical time-domain analysis (BOTDA) setup operated at a fixed pump–probe frequency shift. The employed technique permitted us to carry out distributed strain measurements along the vibrating beam at a maximum acquisition rate of 108 Hz. The mode shapes of the first three bending modes (1.7, 10.8, 21.6 Hz) were measured for the structure under test. The good agreement between the experimental and numerical results based on a finite-element method (FEM) analysis demonstrates that Brillouin based distributed sensors are well suited to perform the modal analysis of a vibrating structure. This type of analysis may be useful for applications in structural health monitoring where changes in mode shapes are used as indicators of the damage to the structure.

Abstract

A model of hydrodynamic loads acting on a rigid floating body during the lifting of the body from the liquid surface is presented. The liquid is of infinite depth, inviscid and incompressible. Initially the liquid is at rest. The body suddenly starts to move upwards from the liquid at a constant acceleration. Boundary conditions on the liquid surface are linearized and imposed on the equilibrium position of the liquid surface. The resulting boundary problem is solved by the methods of analytical functions. Negative pressures are allowed and the pressure is assumed continuous at the periphery of the wetted area. The unknown size of the wetted area is determined by the condition that the speed of the contact points is proportional to the local velocity of the flow. This condition provides a nonlinear Abel-type integral equation which is solved explicitly. Both two-dimensional and axisymmetric configurations are considered. Predicted hydrodynamic forces are compared with the computational fluid dynamics results by Piro & Maki ("jats:italic"11th International Conference on Fast Sea Transport. Honolulu, Hawaii, USA"/jats:italic", 2011) for both a rigid wedge and circular cylinder, which initially enter the water and then exit from it.