Predicting Acoustical Noise Generation in Complex Mechanical Systems

Fluid-Structure Coupling Effects on the Dynamic Response of Pump-Turbine Guide Vanes

Mechanical design have experienced a long process of development, the improvement of design method and optimization method have always been the pursuit of any designer. In recent years, introduction of CAD/CAE have increased greatly the speed of design and experiment, making mechanical design undergo a fundamental leap. However, the whole process: design-trial-improve- ment, still needs manual control to complete, designers still face the problem of complex repeating process. In views of this bottleneck, we will conduct parametric modeling on complex mechanical system in PRO/E, and let key parts import into ANSYS to be flexible .Then, we will build and analyze rigid-flexible mixture virtual prototyping in automatic dynamic analysis of mechanical systems. At last, we will integrate this process in ISIGHT3.5, exploring design-trial-improvement integrated optimization and simulation method through the optimization of the size of key parts of complex mechanical system.

A major goal in the control of complex mechanical systems such as advanced aircraft, spacecraft, and power plants is to achieve high performance with increased reliability, availability, component durability, and maintainability. The current state-of-the-art of control systems synthesis focuses on improving performance and diagnostic capabilities under constraints that often do not adequately represent the dynamic properties of the materials. The reason is that the traditional design is based upon the assumption of conventional materials with invariant characteristics. In view of high performance requirements and availability of improved materials, the lack of appropriate knowledge about the properties of these materials will lead to either less than achievable performance due to overly conservative design, or over-straining of the structure leading to unexpected failures and drastic reduction of the service life. The key idea of the research reported in this paper is that a significant improvement in service life can be achieved by a small reduction in the system dynamic performance. This requires augmentation of the current system-theoretic techniques for synthesis of decision and control laws with governing equations and inequality constraints that would model the properties of the materials for the purpose of damage representation and failure prognosis. The major challenge in this research is to characterize the damage generation process in a continuous-time setting, and then utilize this information for synthesizing algorithms of robust control, diagnostics, and risk assessment in complex mechanical systems. Damage mitigation for control of mechanical systems is reported in the two-part paper. The concept of damage mitigation is introduced and a continuous-time model of fatigue damage dynamics is formulated in this paper which is the first part. The second part which is a companion paper presents the synthesis of the open-loop control policy and the results of simulation experiments for transient operations of a reusable rocket engine.

Study on Immune Cloud Model Adapted to Complex Mechanical System Diagnosis

Pulsed detonation engines are slated to be the engines of the future promising better efficiencies and high Mach number applications. There are presently many centers of experimental PDE studies around the world. Most of the studies involve single shot and very short duration test runs. This paper looks at some of the issues faced by engineers studying PDEs, including issues that prevent longer duration testing, and offers some solutions that were developed during several years of PDE study. Some of the concerns investigated include the possibility of damage to the combustion chamber, auxiliary components, diagnostic devices, valves, ignition plugs and DDT enhancing devices, such as Shchelkin spirals, due to the innate extreme conditions of high heat and pressures found in PDEs. Viable solutions are offered that may help overcome these difficulties. Commercial solenoid valves and electronic fuel injectors are presented as the means to achieving higher operational frequencies. In addition, their modularity, low costs and their ability for precision digital control are clear advantages over heavier, more complex rotary or mechanical valving systems. Issues concerning data acquisition, such as proper implementing procedures for pressure transducers and choosing the appropriate sampling rates are discussed. A common concern during the data acquisition is the management of large amounts of data. Some simple and cost effective answers are proposed, such as implementing RAID for computing. EMI is a big concern for engineers in PDE studies because the instruments and devices used in the laboratories are sources of noise. Several solutions are pointed out to mitigate the effects of noise on the signals. Noise control should be looked at proactively during the design stage of the experimental set up because failing to do so can mean retroactive and sometimes costly modifications to experimental setup. Finally, some steps to improve safety during PDE studies are presented.

The lubrication of the mechanical components reduces friction, and increases the efficiency and the reliability. However, the interaction of moving components with the lubricant leads to power losses due to viscous and inertial effects. Nowadays, the study of lubricant behavior can be carried out through computational fluid dynamics (CFD) simulations. Nevertheless, the modeling of the computational domain within complex mechanical systems (e.g., ordinary, planetary and cycloidal gearboxes, roller bearings, and pumps) requires the exploitation of specific CFD techniques. In the last decades, many mesh-based or meshless approaches have been developed to deal with the complex management of the topological changes of the computational domain or the modeling of complex kinematics. This paper aims to collect and to classify the scientific literature where these approaches have been exploited for the study of lubricated mechanical systems. The goal of this research is to shed a light on the current state of the art in performing CFD analysis of these systems. Moreover, the objective of this study is to stress the limits and the capabilities of the main CFD techniques applied in this field of research. Results show the main differences in terms of accuracy achievable and the level of complexity that can be managed with the different CFD approaches.

The characterization of friction is a multiscale problem involving a balance between asperity contact and fluid film forces. Periodic stick-slip phenomena are often associated with the friction force that causes mechanical vibration. This type of vibration can cause noise to radiate via structural modes of the system. Many mechanical systems have connections that involve friction, including bolted joints, bearings, and brakes. Avoiding stick slip conditions minimizes wear and vibration, while extending the life of the component. Understanding the exact conditions that stick slip occurs can be difficult, as it requires a characterization of the friction forces and the loss mechanisms in a complex mechanical system. Classic single degree of freedom models predict the stability criterion to be a function of the system damping, normal load, and the derivative of friction coefficient with respect to sliding speed. Many musical instruments utilize the stick slip phenomenon to produce sound. In this work, we study the stick slip phenomenon with a singing wineglass. The dynamic friction force and radiated pressure is measured under a variety of speed and load combinations. Friction models of increasing complexity are used to demonstrate the main features of the dynamic force and radiated pressure spectra.

The designs of modern electronic technology are complex mechanical systems with many rigid bonds, and their microminiature in many cases has reached the physical limit of the dimensional, charge and energy quantization of components. For such mechanical systems, with non-classical methods for mechanics of fastening of separate structural elements, it is difficult to build a design model, simple enough and at the same time one that well reflects physical and dynamic properties. To ensure mechanical strength of interconnects and ultra-thin electronic components, it is necessary to determine the stress-strain state of structural elements. These reasons necessitate the use of numerical methods to calculate the dynamic parameters of the design of electronic equipment interconnections, which will improve the reliability of the developed tools that meet the requirements of regulatory technical documentation on mechanical characteristics, shorten the time and cost of their creation. Subject matter of this work is the study of beam deformation of constant cross section under the action of axial forces, bending moments and torque relative to the longitudinal axis. Goal this work is to determine the deformation of the elements of the structure of the devices using the stiffness matrix with a known vector of external forces. To achieve this goal, it is necessary to solve the following tasks: to consider the existing methods of description and analysis, which take into account the specificity of the structures and technological processes used to manufacture specific structures MEMS; explore the nature of these methods; calculate displacements and deformations using the finite element method; using the stiffness matrix to determine the deformation of the structural elements of the devices; to calculate the deformation of the beam of constant cross-section under the action of axial forces, bending moments and torque relative to the longitudinal axis. Conclusions: stiffness matrix, constructed using functional analysis, allows for the calculation of deformation of MEMS elements and electronic interconnect flexible.

High performance computing promotes the solution of large mathematical models of complex mechanical systems and lays a foundation for the theoretical analysis of complicated and difficult problems in the mechanical field. At the same time, the high reliability transmission of wireless data makes it possible for a variety of motion state mechanical systems to measure and control. In this paper, we present the energy loss model of the wet axle transmission system based on bond graph theory, and obtain the heat source boundary condition of the thermal analysis of the wet axle by calculating the mathematical model of the energy loss. Moreover, thermal network method is proposed to analysis heat accumulation and disequilibrium of multistage closed wet axle, by analyzing heat source distribution and heat transfer characteristics among machine elements, oil and air, finally the mathematic model of thermal analysis is established. The thermal numerical calculation of the thermal network for the complex mechanical system and the verification of the whole vehicle test for the results of the thermal calculation have been realized, then thermal optimization is done for wet axle heat equilibrium. Theory and experiment results indicate that heat accumulation in wet hub and heat disequilibrium of different parts are severe especially under efficient operating condition; thermal network calculation and optimization results verified by real vehicle experiment are true and valid. The research proves that high performance computer and high reliable wireless data transmission technology have promoted the optimization design of complex mechanical system.

In the paper, in keeping with the fact that the robots are complex mechanical systems, on the basis of matrix exponentials, some notions applicable in advanced dynamics of mechanical systems, as well as variational principle from analytical mechanics will be analyzed. There will be presented the D’Alembert-Lagrange principle, written in the generalized form, and a few formulations on the Hamilton’s variational principle. On the basis of these aspects, by using of important mass distribution parameters, there will be expressed the kinetic energy and first and second order of the acceleration energy, the last one into a new formulation.

Classical mechanics is mainly based on two mechanical principles, the principle of linear momentum (Isaac Newton) and the principle of angular momentum (Leonhard Euler). The principle of angular momentum implies that the time derivative of the angular momentum equals the sum of all torques, acting on the body. Concerning all types of education it is particularly important that theoretical basic principles are profoundly understood. This often enables to understand difficult mechanical systems by drawing parallels between complex mechanical systems and simple basic principles. One way to generate profound understanding of theoretical correlations is to use interesting experimental examples. In this paper, a teaching model is presented, which has the ability both to demonstrate the effects of the principle of angular momentum and to catch the attention of students. For this purpose, a remote-controlled model car was built carrying a high-speed gyroscope on its top. The gyroscope can cause that the car turns over to the inside of a turn against the centrifugal force. Even more, it is possible to drive in a circle on the inner tires of the RC vehicle.

Modal Complexity Factors as indexes for modal parameter identification in Operational Modal Analysis of coupled dynamic systems

Optimization of noisiness of mechanical system by using a pneumatic tuner during a failure of piston machine

The shoulder is a complex mechanical system. Alterations in the position and/or orientation of its joints may interfere with optimal shoulder coordination. Scapular dyskinesis (SDK) is defined as mal-positioning or mal-movement of the scapula along the thoracic wall. It is not well established the role of scapular dyskinesis as the cause or the effect of shoulder pathologies. The Upper-Quarter Y-Balance test (UQYBT) has been suggested as a return-to-play tool for athletes with upper extremity injuries. The objective of this study was to quantify the relation between the UQYBT and SDK. Six males and five females participated in the study, age 18-30 years old. All participants’ shoulders were evaluated by a certified athletic trainer using Kibler Scapular Dyskinesis Test (SDT) as having dyskinesis or not. Each participant performed three of the SDT and three of the UQYBT. The outcomes of the UQYBT were the highest score for each direction SuperiorLateral Reach (SLR), Inferior-Lateral Reach (ILR), and Medial Reach (MR) and the Composite score. An independent t-test with unequal variances was performed to determine statistical differences between normal and SDK shoulders during the UQYBT. Results indicate significant differences between the normal and SDK shoulders in the Composite score (p=.048). No significance was found during the ILR, SLR, and MR. In conclusions, when the SDK shoulder was stabilizing during the UQYBT higher scores were seen in every direction compared to the normal shoulder. These suggest that SDK may affect the scores of UQYBT.

EXPERIMENTAL STUDY OF A MECHANICAL SYSTEM CONTAINING A LOCAL CONTINUOUS STIFFNESS NON-LINEARITY UNDER PERIODIC EXCITATION AND A STATIC LOAD