A Study on Mode Shape and Natural Frequency of Rotating Flexible Cracked Annular Thin Disk

As an important rotating component, the flexible annular thin disk is widely used in mechanical engineering. Cracks may occur in some weak disk parts, which will greatly shorten the equipment service life and even cause equipment failure. Due to the centrosymmetric structure of the flexible annular disk, two typical cracks are studied in this paper; one is radial crack parallel to diameter, including radial closed crack (RC-crack) and radial opening crack (RO-crack); the other one is vertical crack perpendicular to diameter, including circumferential crack (CF-crack) and tangential crack (TG-crack). The effect of crack parameters, such as crack length, direction, and position, on disk vibration characteristics are studied through theoretical simulation and experimental verification. The research shows that the effect of cracks on vibration characteristic gets more obvious with cracks extending in most cases, RO-crack decreases the natural frequency obviously, and vertical cracks would affect mode shapes. In addition, the bigger the nodal diameter is, the more obvious the effect gets. Meanwhile, the most obvious effect appears in the mode of a nodal diameter locating on the crack. The research possesses some guiding significance in industrial production; by comparing with the vibration characteristics of the flawless disk, the integrity of the rotating flexible disk can be judged to prevent possible equipment damage.

116 PROGNOSTIC IMPACT OF THE SHORT-AXIS DIAMETER FOR THE NODAL ASSESSMENT BEFORE PREOPERATIVE CHEMOTHERAPY IN ESOPHAGEAL CANCER

Clinical N category (cN) is generally assessed by measuring the nodal diameter by CT before the initiation of primary treatment in esophageal squamous cell carcinoma (ESCC). The short-axis diameter is recommended for evaluating treatment response in solid tumors by RECIST. This study aimed to elucidate the prognostic implication of the maximum short-axis diameter of lymph node (cN-size) before preoperative chemotherapy for ESCC. Methods We enrolled a total of 152 patients who underwent preoperative cisplatin/5-fluorouracil therapy (CF) followed by esophagectomy from 2005 to 2011. There were 127 men and 25 women with a median age of 65 years (range: 47–79 years). Clinically metastatic node was defined as follows; the node with cN-size ≥10 mm or that with 5 mm ≤ cN-size <10 mm and contrast enhancement, round shape and/or central necrosis in CT before starting CF. The association between the maximum cN-size and the overall survival (OS) after surgery was statistically investigated. The median follow-up period was 87 months (range: 36–145 months). Results The number of patients with cN0 and cN1–3 was 60 and 92, respectively. Twenty-seven and 65 patients with cN1–3 were classified into cN-size <10 mm and cN-size ≥10 mm group, respectively. The 5-year OS rates in cN0, cN-size <10 mm and cN-size ≥10 mm groups were 70%, 51% and 45%, respectively (P = 0.006). Among Ut-Mt tumors, the OS in the cN-size <10 mm group was significantly worse than that in the cN0 group (5-year OS rate: 45% vs. 74%, P = 0.048). However, there were no significant differences in the OS between these two groups in Lt tumors (67% vs. 64%, P = 0.789). Conclusion The maximum short-axis diameter of lymph node before preoperative chemotherapy is significantly associated with OS in patients with ESCC. Lymph node with 5 mm ≤ cN-size <10 mm in the short axis should be treated as a metastatic node especially in Ut or Mt tumors, considering the poor prognosis.

Development of a Multi-Shaker-Control to Investigate the Influence of the Interblade Phase Angle on Frictionally Damped Turbine Blades

Constructive damper concepts are developed and integrated in turbomachinery to reduce vibration amplitudes generated by dynamic loads. The potential damping effectiveness of friction-based damper concepts is strongly dependent on the relative motion between adjacent blades, besides other factors such as normal force. In cyclic symmetric structures the phase difference is determined by the excited nodal diameter, which leads to different damper movements and efficiencies for given mode shapes. Several studies on the investigation of the damper performance of different underplatform damper geometries have been carried out on non-rotating test stands consisting usually of two blades in order to reduce the experimental effort before setting up rotational tests. Based on the existing modes of the two blades and the application of commonly just one shaker, the investigations are limited to the in-phase and out-of-phase modes. In this paper an experimental approach is developed to reduce the gap of transferability between non-rotating and rotational tests to analyze the effects of a variable interblade phase angle on the damping effect of underplatform dampers. For this purpose, a cascaded control system using two shakers is being developed to control the force amplitudes and the phase difference between the response of the two blades. The control algorithm is designed in a model-based way by using a two degrees of freedom oscillator with friction contact and is subsequently integrated in the non-rotating test stand.

NONLINEAR STABILITY ANALYSIS OF A GENERIC FAN WITH DISTORTED INFLOW USING PASSAGE-SPECTRAL METHOD

The dependence of the aerodynamic stability of fan blades with the nodal diameter and amplitude of the inlet perturbations is studied. The analysis is conducted using a block-wise spatial Fourier decomposition of reduced-passages to reconstruct the full-annulus solution. The explicit spatial Fourier approximation is exploited to characterize the relevance of each nodal diameter of the inlet perturbation in the fan stall process and study the nonlinear stability in a harmonic by harmonic basis. This approximation allows studying the contribution to stall of each circumferential mode separately. The methodology has been assessed for the NASA rotor 67. The maximum amplitude of total pressure distortion at which the compressor becomes unstable and triggers a stall process has been mapped. It has been proven that despite the complexity of a screen-induced total pressure distortion the only relevant parameter for the nonlinear stability of the fan is the most unstable nodal diameter. Full-annulus simulations have been conducted to assess the accuracy of the simplified nonlinear stability limit. It is concluded that performing a nonlinear simulation with the proper single harmonic perturbation is enough to assess fan stability. It is shown that for the NASA rotor 67 running at the nominal speed the most unstable nodal diameter is the first. This study not only shows a reduction in computational time to assess nonlinear fan stability by a factor of seven but also creates an efficient methodology for understanding the nonlinear instability of fans due to inlet distortion profiles.

Investigation of the Starting-Up Axial Hydraulic Force and Structure Characteristics of Pump Turbine in Pump Mode

During the starting up of the pump mode in pump turbines, the axial hydraulic force acting on the runner would develop with the guide vane opening. It causes deformation and stress on the support bracket, main shaft and runner, which influence the operation security. In this case, the axial hydraulic force of the pump turbine is studied during the starting up of pump mode. Its influences on the support bracket and main shaft are investigated in detail. Based on the prediction results of axial hydraulic force, the starting-up process can be divided into “unsteady region” and “Q flat region” with obviously different features. The mechanism is also discussed by analyzing pressure distributions and streamlines. The deformation of the support bracket and main shaft are found to have a relationship with the resultant force on the crown and band. A deflection is found on the deformation of the runner with the nodal diameter as the midline in the later stages of the starting-up process. The reason is discussed according to pressure distributions. The stress concentration of the support bracket is found on the connection between thrust seating and support plates. The stress of the runner is mainly on the connection between the crown and the blade’s leading-edge. This work will provide more useful information and strong references for similar cases. It will also help in the design of pump turbine units with more stabilized systems for reducing over-loaded hydraulic force, and in the solving of problems related to structural characteristics.

Nonlinear Modal Analysis of Frictional Ring Damper for Compressor Blisk

The use of integrally blisk is becoming popular because of the advantages in aerodynamic efficiency and mass reduction. However, in an integrally blisk, the lack of the contact interface leads to a low structural damping compared to an assembled bladed-disk. One emerging damping technique for the integrally blisk is based on the use of friction ring damper which exploits the contact interfaces at the underneath of the disk. In this paper, three different geometries of the ring dampers are investigated for damping enhancement of a blisk. A full-scale compressor blisk is considered as a case study where a node to node con- tact model is used to compute the contact forces. The dynamic behaviour of the blisk with the ring damper is investigated by using nonlinear modal analysis which allows a direct estimation of the damping generated by the friction interface. The damping performance for the different ring dampers are evaluated and compared. It appears that the damping efficiency as well as the shift in the resonant frequency for the different geometries are highly related to the nodal diameter and contact pressure/gap distributed within contact interface. The geometry of the ring damper has significant impact on the damping performance.

IMPACT OF DOWNSTREAM POTENTIAL PERTURBATIONS ON THE NONLINEAR STABILITY OF A GENERIC FAN

The dependence of the aerodynamic stability of fan blades with amplitude and nodal diameter of potential perturbations associated with the presence of pylons is studied. The analysis is conducted using a novel block-wise spatial Fourier decomposition of the reduced-passages to reconstruct the full-annulus solution. The method represents very efficiently unsteady flows generated by outlet static pressure non-uniformities. The explicit spatial Fourier approximation is exploited to characterize the relevance of each nodal diameter of outlet perturbations in the fan stall process, and its nonlinear stability is studied in a harmonic by harmonic basis filtering the nonlinear contribution of the rest. The methodology has been assessed for the NASA rotor 67. The maximum amplitude of the downstream perturbation at which the compressor becomes unstable and triggers a stall process has been mapped. It is concluded that the fan stability dependence with the amplitude of the perturbation is weaker than in the case of intake distortion. For perturbations with an odd number of nodal diameters, the nonlinear stability analysis leads to the same conclusions as to the small amplitude linear stability analysis. However, if the perturbations have an even number nodal diameters, the flow exhibits a supercritical bifurcation and have a stabilizing effect.