The precise detection of polyester filament yarn (PFY) tension in the spinning process is critical to ensure product quality. The laser Doppler vibrometer (LDV) method is proposed to achieve non-contact detection of PFY tension in this paper. By employing the Hamilton principle, the transverse dynamics differential equations of PFY are derived, which are discretized and solved by the Galerkin method and Runge–Kutta method, respectively. In the equations, the PFY between two adjacent rollers is simplified as an axially moving string to verify the generality of calculating natural frequencies. The calculated natural frequencies from the axially moving string model are compared with solved results from the transverse dynamics differential equations. It is shown that the approximation of natural frequencies can be obtained from the axially moving string model. This study attempts to establish an approximate generic model among the PFY tension, the spinning speed and the first natural frequency based on axially moving string model, from which the PFY tension can be calculated efficiently by employing the measured natural frequencies. The LDV method is used to measure the natural frequencies. A major advantage of the proposed method is to realize non-contact detection of PFY tension. The method is more useful under high-speed spinning conditions where contact tension detectors are not available. An experimental analysis is carried out to verify the effectiveness and accuracy of the proposed method. Therefore, it is believed that the non-contact detection of PFY tension in the spinning process by the LDV method is feasible.

The precise measuring and control of fiber tension are critically important for enhancing structural and mechanical properties in spinning processes, as tension directly influences orientation, crystallinity, and mechanical properties. However, current tension measurement methods primarily operate offline and lack real-time measuring capabilities. A non-contact fiber tension detection system is introduced to investigate the effects of draw tension and its uniformity on the structure and mechanical properties of polyester fibers. During experiments conducted at a spinning speed of 1200 m/min across different draw ratios, the non-contact system demonstrated strong agreement with the contact tension detector. The results showed that increasing the tension from 34 cN to 164 cN reduced the monofilament diameter from 39.61 µm to 20.35 µm. Simultaneously, the orientation factor nearly tripled, while crystallinity increased from 55.72% to 77.39%. Mechanical testing revealed a 50.96% improvement in breaking strength, rising from 1.57 to 2.37 cN/dtex, accompanied by a significant decrease in elongation at break from 275.55% to 34.95%. However, tension fluctuations, characterized by an average fluctuation coefficient increase from 4.51% to 18.18%, caused diameter inconsistency. These fluctuations also reduced the orientation factor by 10.78%, lowered crystallinity, and substantially deteriorated mechanical properties. These findings underscore the critical importance of real-time, online tension monitoring for ensuring polyester fiber quality and performance during production.

It is difficult to simulate both the flow field and the chemical reaction using, respectively, the flow state and kinetics calculations and actually reflect the influence of the gas flow state on the chemical change in a selective catalytic reduction (SCR) system. In this study, the flow field and the chemical reaction were therefore coupled to simulate a full Cu-Zeolite SCR system and the boundary conditions of the simulation were set by a relevant diesel engine bench test which included the exhaust temperature, the mass flow, and the exhaust pressure. Then, the influence of the gas flow state on the NO_x conversion efficiency was investigated. Specifically, an orthogonal experimental design was used to study the influence of the injection parameters (position, angle, and speed) on the NH₃ distribution by establishing the NH₃ uniformity coefficient γ at the SCR catalyst capture surface in the flow field simulation. Then, the velocity capture surface of the SCR catalyst front section was sliced into coupled data transfer interfaces to study the effects of exhaust temperature, ammonia to NO_x ratio (ANR), and the NO₂/NO_x on the NO_x conversion efficiency. This was used as guidelines to optimize the SCR system control strategy. The results showed that a 1150 mm injection position, a 45°injection angle, and a 23 m/s injection velocity provided the most uniform NH₃ distribution on the SCR catalyst capture surface. For constant injection parameters, the NO_x conversion efficiency was the highest when the exhaust temperature was 200°C—400°C, the ANR was 1.1, and NO₂/NO_x was 0.5.

The negative impact of nonuniform tension on the product quality in the production process of carbon fiber prepreg tape cannot be overlooked. It is essential to consider the influence of nonuniform tension on the transverse vibration characteristics of the moving carbon fiber prepreg tape. This paper investigates the transverse vibration characteristics and plane stress distribution of the moving carbon fiber prepreg tape under a nonuniform coefficient of tension. The governing equation for the transverse vibration of the tape is derived using Kirchhoff’s thin plate theory and Hamilton’s principle, and the Galerkin method is applied to solve for the natural frequencies. The study focuses on the transverse vibration characteristics and stability of the tape, exploring the influence of geometric, material, and process parameters on its natural frequencies and critical velocities. In addition, the negative impact of nonuniform tension on the plane stress distribution of the carbon fiber prepreg tape is quantitatively expressed through coefficient of variation. The research findings underscore the importance of incorporating the nonuniform coefficient of tension into theoretical analysis and simulation modeling, enabling a precise investigation of the vibration characteristics and plane stress distribution exhibited by carbon fiber prepreg tape during the production process.

Tension detection during the spinning process of carbon fiber precursor filaments plays a crucial role in enhancing the quality of carbon fibers. The noncontact tension detection method is proposed for carbon fiber precursor filaments in this paper. Based on Hamilton’s principle, the dynamic differential equations of the ribbonlike filament bundle are established, and a general formula relating filament bundle tension to vibration frequency is derived. In terms of signal processing methods, the Improved Aquila Optimization algorithm is first used to optimize the variational mode decomposition parameters, including the number of modes K and the penalty factor α, to decompose the signal into components of different frequencies. Subsequently, a combined screening method using the Pearson correlation coefficient, amplitude-sensitive arrangement entropy, and DBSCAN is employed to identify and remove noise signals, thereby achieving signal denoising. Experimental results indicate that this method for screening signal components achieves better results compared with the single correlation coefficient screening method. The measurement errors of laser-Doppler-vibrometer-based tension detection are within ±11.5%. This method enables noncontact and nondestructive tension detection, providing a new solution for situations where traditional contact-based detection is not feasible. Therefore, this method has significant research potential.