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The multi-output response spectral replication correction algorithms for the multi-shaker random vibration test are investigated. In the existing matrix power correction algorithm, the control of auto and cross spectral densities is coupled which may bring some unexpected errors. The ideal spectral correction mode is that the control of auto and cross spectral densities should be independent of each other. For this purpose, a novel spectral decoupled correction algorithm is proposed with a spectral decoupling decomposition method in this work. Two lower triangular matrices are introduced to modify the auto and cross spectral densities separately during equalization procedure. Due to the positive definite constraint for the power spectral matrix, the coherence coefficient and phase difference in the cross spectral densities cannot be controlled independently when the number of the control channels is more than two. A simulation example is provided and the control results with the matrix power correction algorithm and proposed spectral decoupled correction algorithm are compared. Finally, a tri-axial shaker random vibration test is carried out and the results prove the effectiveness and feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

Vibro-acoustic systems in aviation engineering could operate in a thermal environment and suffer from high-frequency dynamic excitations. The high-frequency vibro-acoustic problems are commonly solved by the Statistical Energy Analysis method, in which the Coupling Loss Factor is the key parameter for modeling vibro-acoustic systems. This work investigates the CLFs of vibro-acoustic systems under thermal environment. First, based on the modal data considering different thermal effects, the modal CLFs between structural modes and acoustic modes are predicted by the Statistical modal Energy distribution Analysis. Then, the CLFs between the structural subsystem and the acoustic subsystem are calculated. The simulation models employed in this research include the coupled plate-cavity system and the cylindrical shell-cavity system. The influence of thermal effects on the CLFs is discussed. For the investigated cases, in which the boundaries of structural susbsystem are set to simply supported, the results demonstrate that the CLFs decrease with increasing temperature when only the temperature-dependent material properties are considered. However, when only the additional stress stiffness is considered, the CLFs experience a more dramatic decrease compared to when only the temperature-dependent material properties are taken into account. Moreover, when both effects are considered, the influence of the additional stress stiffness has a leading effect on the CLFs. The proposed method can be conveniently applied to various vibro-acoustic systems operating in the thermal environment. [ABSTRACT FROM AUTHOR]

Objective To establish an optimal limiting dose for dose limiting rings placed in the anterior and posterior regions of the neck for reducing head and neck lymphedema under intensity-modulated radiation therapy(IMRT) for early nasopharyngeal carcinoma(NPC) from a dosimetric perspective. Method Fifteen newly diagnosed early-stage nasopharyngeal carcinoma patients who underwent CT localization for radiotherapy at the Cancer Hospital of Guangzhou Medical University from January to September 2022 were included in the study. Each case was designed with five sets of radiotherapy plans. Plan A consisted of conventional unlimited-field plans, while Plans B-E consisted of limited-field plans with dose constraints set at 20, 18, 16, and 14 Gy, respectively, with the remaining parameters consistent with Plan A. The impact on target coverage and organ-at-risk constraints was evaluated through variance analysis and pairwise multiple comparisons using a randomized block design to determine the optimal dose limits. Results The gradient of 16Gy was determined as the optimal dose limiting cutoff point for achieving the balance between target coverage and organ limiting dose. Compared with the conventional plan, The plans with the placement of a cervical anterior and posterior dose limiting ring (16Gy) did not change the target dose coverage (P > 0.05), but only yielded a slight change in the homogeneity index (P < 0.05). It did not cause any changes of the dosage in the inner ear, mandible, and brainstem (all P > 0.05), but lead to statistically significant reductions in the oral cavity, throat, and thyroid (all P < 0.05). It caused a slight increase of the dose in the parotid gland and spinal cord (both P < 0.05), but the increased dose was anyhow within the tolerance range. Conclusion The dosimetric investigation determines an optimal dose limit cutoff point for the cervical anterior and posterior dose limiting rings. It is expected to provide a design method for IMRT plans to reduce head and neck lymphedema after radiotherapy for early NPC. [ABSTRACT FROM AUTHOR]

This article investigates Multi-Input Multi-Output (MIMO) mixed vibration control testing for Sinusoid on Random (SoR). The challenge of this vibration test is the mixed signal separation. The response signals at the control channels are composed of the broadband random component and the sinusoidal components. Firstly, the extracted accuracy of the Improved Correlation Integral Method (ICIM) is analyzed. The influences of the parameters used in ICIM are discussed in detail. Secondly, a new method, named Variance Minimum Method (VMM), is proposed for signal separation. Extraction accuracies of the ICIM and the proposed VMM are compared under different parameters. Finally, the control methods are proposed to iteratively update the driving signals of each component in the light of the deviations between the response signals and specified references. A cantilever beam example and biaxial vibration experiment manifest that the VMM and control method can be applied for the multi-shaker SoR vibration control tests. [ABSTRACT FROM AUTHOR]

This paper presents a novel mechanical environmental test method that multi-output random strain responses are replicated instead of acceleration responses. In this work, the positive-definite strain reference spectral matrix and reference kurtoses for multiple control channels are defined first, and then three types of strain random signals including stationary Gaussian, stationary non-Gaussian, and non-stationary are generated. The inverse Fourier transform is used to obtain the stationary Gaussian strain random signals and the stationary non-Gaussian strain signals are obtained by the zero-memory nonlinear transformation. To synthetize non-stationary strain random signals, an amplitude modulation function is introduced with time-varying root mean square values. The correction algorithms are employed to update the drive signals for matching the strain responses compared with corresponding reference values. The simulation and experimental results prove the effectiveness and feasibility of the proposed strain response control procedure. The presented work provides new perspectives to investigate the fatigue behavior and life estimation of structure under controlled strain response environments for vibration fatigue tests. [ABSTRACT FROM AUTHOR]