Optimization of excitation frequency and guided wave mode in acoustic wavenumber spectroscopy for shallow wall-thinning defect detection

In plate-like structures, wall-thinning defects resulting from corrosion may not be accompanied by any indication of damage on the surface. Thus, inspections are required to ensure that wall-thinning defects are within allowable limits. However, conventional ultrasonic techniques require physical contact to the structure. Alternatively, acoustic wavenumber spectroscopy (AWS) may be used for detecting, locating, and characterizing defects. This paper describes the performance of AWS in the estimation of a wall-thinning defect size in thinplate structures using finite element analysis (FEA). Through a series of FEAs, the structure’s steady-state response to a single-tone ultrasonic excitation is simulated, and the wall-thinning defect-size effect on the wavenumber-estimation accuracy is investigated. In general, the A0 guided wave mode is widely used to visualize defects because of the nature of the wave speed variation in relation to the plate thickness. However, it is not appropriate for the detection of relatively shallow wall-thinning defects, because the rate of change in wave speed with the thickness decreases with increasing plate thickness. To overcome this limitation, we propose a method to optimize excitation frequency and effective guided wave mode instead of utilizing the A0 mode. The results can be used to determine the size of shallow wall-thinning defects in plate-like structures.     

Reducing undesirable vibrations of planar linkage mechanism with joint clearance

An optimization design method is presented to reduce the undesirable vibrations caused by clearance for planar linkage mechanism. A clearance joint is defined and considered a contact/impact force constraint. Contact and impact force models for the clearance joint are established using a normal contact force model based on Hertz model with energy loss and a tangential friction model based on modified Coulomb model with dynamic friction coefficient, respectively. In view of the clearance joint, dynamic equations and optimization method for a planar four-bar mechanism are then presented as an application example. The optimization aims to minimize the maximum absolute acceleration peaks of the mechanism by determining the link lengths of the planar linkage mechanism. Finally, the optimization design is solved by a generalized reduced gradient algorithm. Results show evident decrease in vibration peaks of the mechanism and obvious reduction in the contact forces in the clearance joint, which contribute to a good performance of planar linkage mechanism systems.     

Measurement of residual stress using linearly integrated GMR sensor arrays

Tubular-type transmission towers have several advantages, but could be compromised if welding defects from the construction process are not found during deployment. This research derived an equation that illustrates how a change in stress accompanied with mechanical deformation triggered a change in distribution of magnetic flux density. Furthermore, it verified experimentally that a change in distribution of magnetic flux density occurred due to a change in stress at the welding zone. Using this principle, this research proposes a system to measure residual stress occurred in the welding zone of tubular-type transmission tower. The ultrasound examination results were compared and the result showed that ultrasound signals revealed defects in a place where sudden distribution of magnetic flux density was presented. However, when a number of welding defects occurred across the large area, the distribution of magnetic flux density may not change due to the alleviating effect of the stress concentration.     

Numerical investigation on residence time of cooling water and surface temperature distribution of water-cooled grates

Waste incineration is a treatment system that reduces waste volume while capturing or destroying potentially harmful substances and recovers energy and chemical contents from wastes. Grate incinerator is one of the thermal treatment methods in waste incinerations. The incineration grates are exposed to high heat flux due to the occurrence of combustion on their surface. Therefore, cooling the incineration grate is one of the main issues in these treatments. In this study, the conjugate heat transfer between the cooling water and incineration grate is investigated numerically. We consider different geometries of the internal guide vane in the cooling channel and analyze the effects of the shapes of the guide vane on the heat transfer performance in the incineration grate. We also calculate the fluid residence time in the cooling channel and investigate the relation between the heat transfer performance and residence time of the cooling fluid. Results confirm that the maximum residence time of the cooling fluid can be reduced, from which the heat transfer performance can be improved.     

A new equation of state to predict S-CO<Subscript>2</Subscript> flow with real gas effects

The accuracy of the thermodynamic properties prediction from the different Equation of state (EOS) varies upon the range of temperature and pressure. Despite the variety of EOS available, there is no de facto for selecting an EOS for particular computational modeling. The EOS model recently developed by Kumar and Kim (K-K EOS) determines more accurately the thermodynamic properties of CO₂ than earlier models. In this present study, K-K EOS is successfully implemented in the computational analysis of compressible supercritical CO₂ flow (S-CO₂) in the thermodynamic region near and away from the vapour-liquid critical point. Computational results of SCO₂ flow with the real gas properties predicted with the K-K EOS is compared with Span and Wagner (SW EOS) and ideal EOS.     

Experimental and numerical verification of transient spatial temperature distribution in thick-walled pressure components

The aim of this work is to present a method to determine the transient-state spatial temperature distribution in a cylindrical component. The presented method involves solving the inverse heat conduction problem based on the Finite volume method (FVM). This approach enables determination of transient-state temperature fields with boundary conditions known on one surface of the component only. The proposed method is verified using the laboratory installation located at the Cracow University of Technology. The main components of the laboratory stand are, among others, a steam outlet header and a steam boiler. During the experiment, the steam header is heated up abruptly from the inside by contact with dry saturated steam. The spatial transient-state temperature distribution within the steam outlet header is determined using the proposed method, which is based on temperature measurements made by 19 thermocouples located on the outer surface of the component. The temperature histories in three selected nodes are compared with the measurement results obtained from thermocouples located inside the component wall. The exact location of the thermocouples corresponds to the nodal position at selected control volumes. Moreover, the Ansys Mechanical APDL software is used to verify calculations and experimental data. A transient- state simulation is performed. The temperature histories at the inner and outer surfaces are set as the model boundary conditions. In order to enable verification of the temperature measurements, the component discrete model includes nodes at appropriate locations. An error analysis is performed between calculated and measured temperature values. The results obtained from the numerical and experimental validation demonstrate fully satisfactory agreement. Additionally, a stress analysis of the outlet header is performed in the Ansys software based on the transient-state temperature distribution within the steam outlet header. The method proposed in this paper is a convenient and accurate tool for monitoring working conditions of the power boiler thick-walled components.     

Effect of the blade loading distribution on hydrodynamic performance of a centrifugal pump with cylindrical blades

The effect of the blade loading distribution on head, radial force and pressure pulsation of a low specific-speed centrifugal pump with cylindrical impeller blades were investigated in the present study. Blade shapes were obtained by adopting the 1D inverse design method, impellers with different blade loading curves were obtained while the distribution of the blade loading was carefully tailored. Threedimensional URANS simulation method based on the Shear stress transport (SST) k-ω turbulence model was employed for the analyzation of flow patterns. Numerical results including the pressure distribution and velocity profile were validated by comparing with the available experimental data, and an acceptable agreement was obtained. Three typical parameters of the blade loading curve, including the location of the fore-loading point (m_pre), location of the aft-loading point (m_post) and slope of the rectilinear segment (K), were analyzed. Results showed that the well-designed blade loading curve, such as the fore-loading impeller, can effectively reduce the pressure pulsation amplitude and the radial force. The significant effect of the variation of the aft-loading point on pump hydrodynamic performance was also investigated. Meanwhile, pressure and velocity distributions at different slopes of the blade loading curves show that the fore-loading impeller produces more uniform flow issuing from the impeller than that of the pump with aft-loading impeller, thus reduces the radial force and pressure pulsation of the pump.     

Eigensolution of a BTA deep-hole drilling shaft system

A numerical investigation is conducted to obtain the eigensolution of a deep-hole drilling shaft system. The rotating drilling shaft is modeled as a Rayleigh beam that conveys cutting fluid and is subjected to torque, compressive axial force, and support constraints. The governing equation of the drilling shaft system for lateral vibration is obtained by considering fluid-structure interaction, rotational inertia, gyroscopic effect, effect of motion constraints, and frictional damping generated by the surrounding fluid. The influence of cutting fluid flow velocity, rotational angular velocity, torque, compressive axial force, and support constraints on the natural frequency and stability of the drilling shaft system is examined. Cutting fluid flow velocity, compressive axial force, and torque decrease the natural frequency of the system, whereas rotational angular velocity and support constraints improve system stability.     

A tunable dynamic vibration absorber for unbalanced rotor system

A tunable dynamic vibration absorber for unbalanced rotor system which is made up of coil springs and magnetic spring is presented. The structure of the absorber is introduced and the stiffness tuning mechanism of the magnetic spring is explained. A finite element model of the rotor-absorber system was built and the influencing factors to the appearance of the absorber were studied numerically. Finally, experiments were carried out to verify the numerical results, and PID control strategy was tested. The numerical and experimental results show that the present absorber is effective for vibration suppression of an unbalanced rotor system, and the control strategy is effective.     

Analysis for forced response of a non-contact piezoelectric driving system modulated by electromagnetic field under coupling excitation

For a non-contact piezoelectric driving system modulated by electromagnetic field, the dynamic equations of the driving system under coupling excitation are deduced. Using the Duhamel’s integral, forced response of displacement in the time-domain and frequency-domain were investigated, and the influence of some system parameters on the displacement response is analyzed. The results show that in the same excitation frequency, the displacement responses of the driving beams is the most significant, and the vibration response of the central shaft is relatively less obvious. The larger displacement responses of the driving beam end is beneficial to increasing the step angle of the driving system, and the smaller vibration of the central is beneficial to stable torque output of drive system. Therefore, the design of this structure is more reasonable. The results are useful for design of the operating performance of the driving system.