Structural cast-in-place SFRC: technology,control criteria and recent applications in spain

Steel fiber-reinforced concrete (SFRC) has been traditionally applied to pavements or tunnelling. However, classical structural applications have not been developed so fully. This paper examines different reasons which may justify the lack of this application. Several technologies on the fiber dosing system are presented and assessed. The SFRC reception control and acceptance criteria have been developed in accordance with the upcoming Spanish code. Adopting such criteria is justified on previous experiences and test viability under cast-in-place conditions. Some lines of action to promote the use of fibers with structural purposes are proposed. Two examples of recent applications are also set out, and a justification of the convenience of SFRC in terms of structural evaluation and durability under seawater conditions is provided.     

Numerical modeling of size effects with gradient elasticity - Formulation, meshless discretization and examples

A theory of gradient elasticity is used and numerically implemented by a meshless method to model size effects. Two different formulations of this model are considered, whereby the higher-order gradients are incorporated explicitly and implicitly, respectively. It turns out that the explicit gradient dependence leads to a straightforward spatial discretization, while use of the implicit gradient dependence can result in an awkward form of the stiffness matrix. For the numerical analyses the Element-Free Galerkin method has been used, due to its ability to incorporate higher-order gradients in a straightforward manner. Two boundary value problems have been considered, which show the capability of the gradient elasticity theory to capture size effects. In a follow-up paper, the formulation developed herein will be used to analyze additional configurations with attention to comparison with available experimental data on size effects and verification of available scaling laws for structural components.     

Structural modifications simulated by virtual distortions

A numerical strategy for the simulation of structural modifications by virtual distortions is proposed. Two cases of structural modification are considered: the first concerns modifications of material distribution, and the second modifications of local constitutive relations (e.g. unilateral constraints for stresses or deformations). A formaulation of the fundamental equations of the simulation method is presented. These equations are applicable to the general structural modification problem of a truss-like structure. Then numerical algorithms which refer to particular applications, such as progressive collapse analysis or the analysis of structures with gaps, are discussed. The versatility of the method is illustrated with a number of examples, and the computational advantages of structural modification by the virtual distortion method are discussed.     

Optimization of washing machine kinematics,dynamics, and stability during spinning using a multistep approach

The vibrations originating from badly distributed load inside the drum are in this paper channeled into cost functions which are used as objectives for optimization. The defined kinematic cost function deals with performance of tub motion and can ensure margins to collision of parts inside the washing machine or constitute a step in the process to increase the machine capacity. The dynamic cost function measures transmitted vertical force to the hosting structure. Forces which cause noise and vibration impact on the surroundings. Two different cost functions for stability of a washing machine in the sense of walking avoidance are also presented. The difference between these formulations is studied with an example, which shows that although it is costly to evaluate the second formulation it will give more freedom to find good washing machine designs. Three different applied problems which aim to optimize different suspension designs for new and existing washing machines are presented. For effective numerical computation of the complex multiobjective optimization problems a multistep approach for washing machine structural optimization is presented. With the help of parallel calculation of the response of dynamic models implemented in Adams?View, the approach has been used to solve the presented problems. Results derived from the solution to the optimization problems have been used in development of new washing machines which afterwards have been put on the market.     

Implicit modelling and mesh refinement for complex structures

When analysing complex structures it is rarely feasible to represent explicitly all the structural features which may contribute significantly to local or global structural performance. This paper presents a variety of methods for representing features which are below the economic analysis scale. Two approaches are described—referred to as implicit stiffness calculation and implicit mesh refinement. The former is essentially approximate and uses relatively simple formulae and computations. The latter involves quite extensive subsidiary calculation, but can lead to numerically exact simulation of fine mesh behaviour in so far as it affects neighbouring structure. Stiffness equivalence principles are stated and a number of computation schemes are presented and illustrated with simple two-dimensional examples.     

Fatigue strength CAE system for three-dimensional welded structures

ABSTRACT Fatigue strength assessment methods are applied to practical arc-welded structural features that have complex three-dimensional geometry. Two methods are investigated in the present research. The criterion of the first method is cyclic plastic zone size, which is calculated from stress singularity parameters. The criterion of the second method is hot spot stress. These fatigue strength criteria are proved to be applicable to the fatigue strength assessment of practical arc-welded structural features. These criteria enable a critical point at which fatigue cracks are most likely to initiate to be specified for each type of welded joint and load. Consequently, the critical point simplifies the classification of various welded joints. Furthermore, a fatigue strength computer-aided engineering system, which includes functional engines for the evaluation of the fatigue strength of a designed shape, is proposed.     

Fluid oscillations in an open,flexible container

In this paper we study normal oscillation modes of an incompressible fluid in an open container, part of the wall of which may be flexible. The flexible part of the container wall is modelled by a membrane. We first investigate the eigenfrequencies of an inviscid fluid in a flexible container. We are able to show, by analytical means, that the eigenfrequencies of an inviscid fluid decrease when part of the rigid container wall is replaced by a membrane. The problem of viscous fluid oscillations in a flexible container is then studied numerically using the finite-element technique. Two different types of eigenmodes are observed: free-surface oscillation modes and structural vibration modes. The dependence of the two modes on the Bond number (measure of the ratio of gravitational and tension forces) and the Reynolds number is investigated.     

Structural optimization by gradient‐based neural networks

In this paper a neurocomputing strategy is presented which combines data processing capabilities of neural networks and numerical structural optimization. In this strategy, an improved counterpropagation neural network is used. Two artificial neural networks are trained, one for the constraints and the other for the gradients of the constraints and structural optimization is accomplished by using these nets. All required parameters such as weight matrices in the neural networks or the gradient computations are automated in this neuro‐optimizer strategy. Numerical examples are included to demonstrate the accuracy of the results. Copyright © 1999 John Wiley & Sons, Ltd.     

Structural batteries: Advances,challenges and perspectives

The development of light-weight batteries has a great potential value for mobile applications, including electric vehicles and electric aircraft. Along with increasing energy density, another strategy for reducing battery weight is to endow energy storage devices with multifunctionality – e.g., creating an energy storage device that is able to bear structural loads and act as a replacement for structural components such that the weight of the overall system is reduced. This type of batteries is commonly referred to as “structural batteries”. Two general methods have been explored to develop structural batteries: (1) integrating batteries with light and strong external reinforcements, and (2) introducing multifunctional materials as battery components to make energy storage devices themselves structurally robust. In this review, we discuss the fundamental rules of design and basic requirements of structural batteries, summarize the progress made to date in this field, examine potential avenues and sources of inspiration for future research, and touch upon challenges remaining in this field such as safety, costs, and performance stability. Though more fundamental and technical research is needed to promote wide practical application, structural batteries show the potential to significantly improve the performance of electric vehicles and devices.     

Biomechanics of male erectile function.

Two major branches of engineering mechanics are fluid mechanics and structural mechanics, with many practical problems involving the effect of the first on the second. An example is the design of an aircraft's wings to bend within reasonable limits without breaking under the action of lift forces exerted by the air flowing over them; another is the maintenance of the structural integrity of a dam designed to hold back a water reservoir which would exert very large forces on it. Similarly, fluid and structural mechanics are involved in the engineering analysis of erectile function: it is the hydraulic action of increased blood flow into the corpora cavernosa that creates the structural rigidity necessary to prevent collapse of the penile column.     

兼具红外隐身的八毫米雷达波吸收材料的研究

对两类兼具红外隐身功能的八毫米雷达波吸收材料（ＲＡＭ）进行了研究，一类为贴片型材料，另一类是涂层型材料，对涂层型材料的进行合理的一体化多层结构设计，使其八毫米波段材料电性能和工艺性能得以提高，从而成为一中很有希望的多功能隐身材料。     

On-line identification, flutter testing and adaptive notching of structural mode parameters for V-22 tiltrotor aircraft

New algorithms and results are presented for flutter testing and adaptive notching of structural modes in V-22 tiltrotor aircraft based on simulated and flight-test data from Bell Helicopter Textron, Inc. (BHTI). For flutter testing and the identification of structural mode frequencies, dampings and mode shapes, time domain state space techniques based on Deterministic Stochastic Realization Algorithms (DSRA) are used to accurately identify multiple modes simultaneously from sine sweep and other multifrequency data, resulting in great savings over the conventional Prony method. Two different techniques for adaptive notching are explored in order to design an Integrated Flight Structural Control (IFSC) system. The first technique is based on on-line identification of structural mode parameters using DSRA algorithm and tuning of a notch filter. The second technique is based on decoupling rigid-body and structural modes of the aircraft by means of a Kalman filter and using rigid-body estimates in the feedback control loop. The difference between the two approaches is that on-line identification and adaptive notching in the first approach are entirely based on the knowledge of structural modes, whereas the Kalman filter design in the second approach is based on the rigid-body dynamic model only. In the first IFSC design, on-line identification is necessary for flight envelope expansion and to adjust the notch filter frequencies and suppress aero-servoelastic instabilities due to changing flight conditions such as gross weight, sling loads, and air speed. It is shown that by tuning the notch filter frequency to the identified frequency, the phase lag is reduced and the corresponding structural mode is effectively suppressed and stability is maintained. In the second IFSC design using Kalman filter design, the structural modes are again effectively suppressed. Furthermore, the rigid-body estimates are found to be fairly insensitive to both natural frequency and damping factor variations and therefore stability is maintained. The Kalman filter design might be a better choice when the rigid-body dynamics are well known because no adaptation is necessary in this case.     

Analytical assessment of the load-carrying capacity of axially loaded wooden reinforced tubes

As a natural resource, an efficient use of wood should be also a requirement for structural timber design, but the usual structural solid sections do not achieve the required optimal behaviour. The performance of the structural elements (serviceability and strength) depends not only on the material properties, but mainly on the moment of inertia of the cross section. The Timber Construction Institute of Technische Universität Dresden has developed a process for the manufacture of structural wood profiles. The resulting profiles combine economy, an efficient use of the material and optimal structural performance. They are externally reinforced with composite fibres, which improve the mechanical characteristics of the wood and protect it from weathering. The available experimental tests to axial loading show the outstanding properties of this new technology. Herein, the preliminary model developed to obtain the axial strength of longitudinally compressed tubes is presented. Two different analytical algorithms are discussed and applied. The model adequately predicts the axial strength of fibre reinforced wood profiles. The analytical results are within an error less than 10% to the available experimental results, with a mean error ratio less than 3%.     

An experimental investigation of the serviceability of modules of the paste-cooled insulating wall of a pulsed MHD generator under conditions of repeated heat loading

The results are given of the test development of different structural options of full-scale pastecooled modules of the insulating wall of the channel of a pulsed MHD generator of the Pamir type [1,2] under conditions of repeated heat loading in the jet of a plasma generator. Two cooling agents are employed for this development, which are characterized by different fillers, namely, ammonium oxalate and carbamide. A module in the form of a perforated cup exhibits the best results.     

一类用于结构振动控制的输出反馈控制器的设计

本文探讨一类设计简捷的直接输出反馈控制器应用于结构振动控制的设计问题，在导得的计及作动机构动特性的结构振动控制特性的基础上，提出了两种设计准则及其设计方法以及必须解决的设计前提。文末以两算例（提高结构模态阻尼与稳定性控制）说明本设计准则与方法的应用，以及其控制效果。     

Optimal design of a composite structure

This paper presents a design methodology for a laminated composite stiffened panel, subjected to multiple in-plane loads and bending moments. Design variables include the skin and stiffener ply orientation angles and stiffener geometry variables. Optimum designs are sought which minimize structural weight and satisfy mechanical performance requirements. Two types of mechanical performance requirements are placed on the panel, maximum strain and minimum strength. Minimum weight designs are presented which document that the choice of mechanical performance requirements cause changes in the optimum design. The effects of lay-up constraints which limit the ply angles to user specified values, such as symmetric or quasi-isotropic laminates, are also investigated.     

FAST望远镜外环曲梁的结构方案优化分析

FAST望远镜的AB转轴机构相当于具有两个水平正交轴的万向节,用于调整馈源舱内设备的指向角。其外环(A环)曲梁跨度大,承载重,且要求轻质和高刚度。基于弯扭耦合的曲梁理论建立了A环结构的基本微分方程,给出了结构变形挠度与结构参数之间的关系。以结构总重量作为结构优化总目标,以不同倾角下曲梁跨中最大扰度及最大扰度差作为主要约束条件,应用信赖域法对实腹式箱梁和桁架式梁两种结构方案进行了优化计算,并对两种结构方案进行了比较。初步的优化结果表明桁架式梁结构方案具有更轻的结构重量。     

Blast response simulation of an elastic structure: Evaluation of the fluid–structure interaction effect

Blast pressure wave interaction with an elastic structure is investigated using a numerical analysis approach, which considers fluid–structure interaction (FSI) within an Arbitrary Lagrange Euler (ALE) framework. Approximate numerical procedures for solving the Riemann problem associated with the shock are implemented within the Godunov finite volume scheme for the fluid domain. The structural displacement predicted by ignoring FSI is larger than the corresponding displacement considering FSI. The influence of the structural and blast pressure wave parameters on the importance of FSI is studied using an analysis of variables. Two non-dimensional parameters corresponding to the ratios of blast duration to the time period of the structure and the velocity of the structure to the particle velocity of the incident blast pressure wave are identified. It is shown that for a given blast pressure wave, the error in the maximum displacement predicted by ignoring FSI effect during structural motion is directly proportional to the ratio of the structure velocity to the particle velocity of the incident blast pressure wave. There is a continuous exchange of energy between the structure and air during the structural motion, which is significant when the structural velocity is significant compared to the particle velocity of incident blast pressure wave. FSI effect become insignificant when the ratio of velocities starts approaching zero.     

Semi-implicit numerical simulations of geometrically nonlinear beam,plate, and shell dynamical systems

The following article serves three purposes: (i) it presents a simple semi-implicit numerical formulation for nonlinear structural dynamics problems, which is computationally inexpensive and simple to use in nonlinear dynamics and chaos simulations; (ii) it serves as an introduction to numerical studies of nonlinear structural dynamics for engineering students; and (iii) it formulates a nonlinear structural dynamical system for studies of nonlinear dynamics and chaos. Numerical formulations along with results are presented for nonlinear oscillators, beams, Föppl–von Kármán plates, and thin shallow shells.