Applications in engineering science最新文献

While usually we don't know complete geometrical and physical information on the occurred inhomogeneity, but in order to study the related phenomena, continuum mechanics theory as well as exiting energy-based models need direct information from the desired system in order to A General Approach to the Mechanical Analysis of Continuous Local Inhomogeneity Using Continuum Mechanics Theory and A New General Energy-Based- Modelapply the field equations. Of course, theories and ideas based on the unification of mechanics and thermodynamics can offer other solutions. This paper establishes a general energy based model to study effects of local inhomogeneity on the mechanical behavior of materials using thermodynamic laws with a new deviation as well as new approach to the total energy. In fact, the main goal is that the established model can be used with a wide range of applications and appropriate accuracy, both theoretically and experimentally, while not getting involved with excessive computational complexity. It can be noted that the extracted formulations develop possibility to study inhomogeneity effects on the mechanical behavior without any more limiting conditions. In addition, due to that study of the stored and dissipated energy, usually, has the main role in the investigating of the inhomogeneity effects on the mechanical behavior, also the point of view in the presented model is in complete agreement to provide the conditions for this study directly. Therefore, the prediction possibility of the inhomogeneity effects on the mechanical behavior will be provided with the smallest volume of needed calculations. Also, due to that the structure and properties of the inhomogeneity are unknown usually, the formulations aren't dependent to these knowledge directly, and can be analyzed theoretically and experimentally to study the homogeneity part, as a known material. In the following, feasible processes are studied using extracted formulations. To validate the equations, a rectangular material shape with local inhomogeneity is considered, and extracted equations are developed for that. To consider our mean on the stored and dissipated energies, it is assumed that the homogeneity part of material has viscoelastic behavior, and the equations are developed to Maxwell and Kelvin viscoelastic models in different homogeneity parts of the body. In the following, classical continuum mechanic theory due to elasticity theory is used, and the field equations are developed to the considered body. Finally, results are discussed, compared as well as their differences, and corresponding capabilities for functional completion are discussed. Finally, the fundamental equivalence of the results is studied, and matching of the results between continuum mechanics theory and extracted formulations is shown.

We develop new rate-type constitutive relations on a set of orthonormal tensor basis and the corresponding set of Lode invariants, which require only 9 material parameters to predict the mechanical response of the human brain tissue. The mode-dependent response of the tissue is captured by invoking the Hill-stable elastic potential of Prasad and Kannan (2020) and constructing a new form for the rate of dissipation, thus introducing the mode-of-deformation dependent modulus terms and the mode-of-deformation-rate dependent viscosities into the rate-type thermodynamic framework of Rajagopal and Srinivasa (2000). Through the analysis-driven construction of the rate of dissipation, we incorporate maximum change in the viscosities with respect to the mode-of-deformation rates and limit the number of material parameters. Our model satisfactorily predicts the complicated load-unload cycles (pre-conditioned and conditioned) and the stress relaxation data under multiple modes of deformation and multiple rates for the Corona Radiata (CR) region of the brain tissue. It also captures the tension–compression asymmetry in the response and the higher relaxation time in compression loading than in shear loading.

Rotodynamic simulation of complex or/and large systems, for instance hydropower machines, may consist of models with many degrees of freedom and require multidisciplinary computations such as fluid-thermal-structure interactions or rotor-stator interactions due to electromagnetic forces. Simulating such systems is often computationally heavy and impractical, especially in the case of optimization or parametric study, where many iterations are required. This has, therefore, created a need for simplified dynamic models to improve computational efficiency without significantly affecting the accuracy of the simulation result. The purpose of this paper is to present simplified coordinate transformation matrices for journal bearings in vertical rotors, which require less computational effort. Matrix multiplications, which appear during coordinate transformation, were eliminated, and the bearing stiffness and damping matrices in the fixed reference frame were represented by local coefficients instead. The dynamic response of a vertical rotor with eight-shoe Tilting pad journal bearings was simulated using the proposed model for two operational conditions, i.e., when the rotor was spinning at constant and variable speeds. The results from the proposed model were compared to those from the original model and validated through experiments. The conclusion was that the presented simulation model is time efficient and can effectively be used in rotordynamic simulations and analyses.

This paper shows how tunable dampers can help control the instant centre of rotation of a 2D rigid body and its polode in planar motion, which in turn implies that the inertia tensor can also be controlled. For mechanisms equipped with some elasticity the results show that damping can also control their natural frequencies. The foundation of a general theory to control the polode is presented, exploring the chance of an optimal control formulation of the problem via a variational control principle, approached by the LQR (Linear Quadratic Regulator) method, after a suitable linearization. Application to automotive suspension linkages is presented that demonstrates the control of the instant roll centre and axis and consequently its instant roll vibration frequency to optimize the response, when excited by lateral inertia forces.

In this study, the exact analytical solutions of a two-dimensional linear homogeneous isotropic nano-beam in gradient elasticity are studied. Four different types of two-dimensional cantilever beams and related boundary conditions are considered. The cases are a cantilever beam under a concentrated force at the end, a cantilever beam under a uniform load, a propped cantilever beam under a uniform load, and a fixed-end beam under a uniform load. The two-dimensional stress gradient fields are investigated and obtained from the analytical solutions of a linear second-order partial differential equation written in terms of the classical and the gradient Airy stress functions. Additionally, the micro-size effects in the displacement components for different loads and support conditions for the two-dimensional cantilever beams by using strain gradient elasticity theory are investigated. Furthermore, for one-dimensional Euler–Bernoulli beam model, the associated stress and strain elasticity solutions are obtained from two-dimensional analytical solutions. The graphical presentations of the exact closed-form solutions are provided and discussed.

This study analyses dynamic influence of stochastic vibro-impact ship behaviour on the ship's launch and recovery capability. To deliver cargo and people to the Arctic regions, ships must withstand harsh environmental conditions and interact with large floating ice pieces. This interaction may result in impact-type loading of a ship hull by ice, preventing planned navigation and even causing to abort of some routine launch and recovery operations of delivering cargo or other equipment. The major safety concern is the risk of collision between the payload and the mother ship hull. The ship-based crane, which served for conducting launch and recovery operations, was assumed to be rigid, mimicking the ship dynamics, whereas the payload is modelled as a single-degree-of-freedom pendulum. This study advocates practical engineering approach, applicable to various scenarios with vessels operating in relevant in situ environmental sea and ice conditions. The proposed study intends to contribute to improving launch and recovery operational reliability, as well as motion control, especially in Arctic aquatic regions. When mentioning Arctic and defence technologies, launch and recovery systems have significant relevance for unmanned vehicles onboard ships.

A new class of unilaterally constrained problems for fully coupled poroelastic models stemming from hydraulic fracturing is introduced and studied with respect to its well-posedness. The poroelastic medium contains a fluid-driven crack, which is subjected to non-penetration conditions and cohesion forces between the crack faces. Existence of solution for the governing elliptic–parabolic variational inequality under the unilateral constraint with a small cohesion is established using the incremental approximation based on Rothe’s semi-discretization in time.

Rotary pleating is a widely used process for making filters out of nonwoven fabric sheets. This involves indirect elastic–plastic bending of pre-weakened creases by continuously injecting material into an accordion-shaped pack. This step can fail through a localization instability that creates a kink in a pleat facet instead of in the desired crease location. In the present work, we consider the effects of geometric and material parameters on the rotary pleating process. We formulate the process as a multi-point variable-arc-length boundary value problem for planar inextensible rods, with hinge connections. Both the facets (rods) and creases (hinges) obey nonlinear moment–curvature or moment–angle constitutive laws. Some unexpected aspects of the sleeve boundary condition at the point of material injection, common to many continuous sheet processes, are noted. The process, modeled as quasistatic, features multiple equilibria which we explore by numerical continuation. The presence of, presumably stable, kinked equilibria is taken as a conservative sign of potential pleating failure. Failure may also occur due to localization at the injection point. We may thus obtain “pleatability surfaces” that separate the parameter space into regions where mechanical pleating will succeed or fail. Successful pleating depends primarily on the distance between the injection point and the pleated pack. Other factors, such as the crease stiffness and strength relative to that of the facets, also have an influence. Our approach can be adapted to study other pleating and forming processes, the deployment and collapse of folded structures, or multi-stability in compliant structures.

Numerous research has investigated the effects of blast furnace slag as a cementitious or substitute cementing material on the characteristics of concrete. Blast furnace slag cement (BFSC) shows promise in the concrete permeability domain, where this extra cementing ingredient enhances the chloride attack resistance of concrete. Four mixtures of BFSC concrete made with 0.5, and 0.6 water-to-cement ratios (w/c) were studied. The effect of using an air-entraining agent (AEA) and a change in the surface of tested samples (top, bottom, and side) on the chloride penetration and its diffusion coefficient has been investigated. The properties of fresh and hardened concrete were determined. This research has its novelty for the first time, where the chloride contents were determined through specimens' top, bottom, and side surfaces using potentiometric titration. The results indicated that the air-entraining agent and w/c ratio had inversely affected the invested concrete properties. The measured total and soluble chloride content at a depth of 20∼30 mm is less than the limits of the corrosion threshold for the three studied surfaces. Also, changes in the w/c ratio, cement content, and AEA affect the diffusion coefficient.

Over the last 50 years several sediment transport models in coastal environments based on Shallow Water(SW) type models have been developed in the literature. The water flow over an abrupt moving topography quickly spatially variable becomes accelerated and strongly varied arising the turbulence (distortion). The acceleration and strong variation of the flow facilitate the transport of a large quantity of sediments present at the bottom while modifying it. The mathematical models based on SW type models widely used to describe the sediment transport phenomena do not account the distortion effects. Indeed, it is well-known that the SW models are derived from first order approximation of long wave theory. The acceleration and strong variation of the water flow near the bottom is due to the distortion of the horizontal velocity profile along the vertical direction. One can regard distortion as a combination of strain and rotation. The effect of the rotational component is to weaken the effect of the strain somewhat. In this work, we put in place a king theory of sediment transport derived from the second order approximation of long wave theory that can describe sediment transport processes in distortion-free-boundary nonhomogeneous fluid flows. The derived model accounts the distortion (fluctuation with great correlation lengths) that creates the turbulence. Moreover, the model differentiates the fluid velocity from sediment velocity (phase-lag) near the sediment bed. The proposed theory significantly reduces the modeling errors observed in several sediment transport models based on nonhomogeneous shallow water equations and has a great potential to increase the predictive power of sediment transport models in rivers, lakes, coastal flows, ocean basins and so on. The proposed theory improves several existing sediment transport theories recently developed in the literature and can be apply with some degree confidence.