Damping of inter-area oscillations by combining control strategies in hydropower plants

This paper examines how the damping capability can be improved if inter-area oscillations occur by combining control strategies in hydropower plants. First, the control challenges of hydropower plants, such as the water hammer effect, are discussed. In a single-machine infinite bus system (SMIBS), the use of a Power System Stabilizer (PSS) in the generator excitation and in the governor control path as well as the combination of both strategies are examined for their effectiveness in terms of their damping capability. In addition, these results are compared with an optimal state space controller with an observer as a damping element. The Heffron-Phillips model is the design model for the PSS as well as for the model-based controller. The verification of the damping capability through the PSS variants is evaluated by using a three-machine model in the time domain and by using modal analysis.

Vibration Damping Behavior of Composite Laminates Interleaved with PZT- and SMA-Particle-Dispersed Resin Mixture Films

In this study, functional particles such as piezoelectric (PZT) ceramic and shape memory alloy (SMA) particles have been incorporated in composite laminates to accelerate the loss of vibration energy. PZT ceramic particles and SMA particles are mixed with epoxy resin and rolled into a film shape before they are interleaved between prepreg plies for better distribution of the particles. Loss factor (tan δ) was measured with various particle loadings to verify the effectiveness of interleaving in the vibration damping of laminate specimens. It was observed that there existed an optimal content for maximizing the damping ability avoiding an aggregation of the particles. In addition, when PZT and SMA particles are applied simultaneously, PZT could enhance the vibration damping capability of SMA because PZT particles could generate thermal energy, and it would accelerate the phase change of the SMA particles. In this research, the effective way for enhancing the particle dispersion was suggested, and the particle loading could be controlled by finding an optimal content. Flexural moduli of the specimens were also measured, and they exhibited no change as the content of the particles increases. Therefore, dispersed particles used in this study increased the vibration damping capacity without reducing the mechanical properties.

Vibration Fatigue Assessment of Additive Manufactured Nickel Alloy with Inherent Damping

The fatigue life behavior and internal surface conditions of inherently damped Additive Manufactured (AM) specimens subjected to vibration bending are under investigation. This study supports research that demonstrated 95% vibration suppression due to damping capability of AM components with 1-3% internal volume of unfused powder. The damping demonstrations have been carried out using laser powder bed fusion (LPBF) specimens of various thicknesses, lengths, and unfused internal powder configurations. In addition, damping is shown to be achievable with both nickel-based alloys and stainless steel specimens. Despite the promise of this method, the viability of fatigue performance is unknown. The following effort aims to address this structural integrity issue; specifically, this study explores whether internal pocket roughness or erosion caused by powder particle motion induces a fatigue life debit. These concerns are addressed by comparing the fatigue behaviors of unfused powder pocket and fully-fused nickel based alloy 718 specimens. Microscopy results confirmed a long suspected powder interaction phenomena as well as appearances of erosion. Furthermore, fractography supports that fatigue failures initiate near the surface of maximum strain/stress at porous features consistent with stock (non-optimized) LPBF process parameters.

Vibration Fatigue Assessment of Additive Manufactured Nickel Alloy With Inherent Damping

The fatigue life behavior and internal surface conditions of inherently damped Additive Manufactured (AM) specimens subjected to vibration bending are under investigation. This study supports research that demonstrated 95% vibration suppression due to damping capability of AM components with 1–3% internal volume of unfused powder. The damping demonstrations have been carried out using laser powder bed fusion (LPBF) specimens of various thicknesses, lengths, and unfused internal powder configurations. In addition, damping is shown to be achievable with both nickel-based alloys and stainless steel specimens. Despite the promise of this method, the viability of fatigue performance is unknown. The following effort aims to address this structural integrity issue; specifically, this study explores whether internal pocket roughness or erosion caused by powder particle motion induces a fatigue life debit. These concerns are addressed by comparing the fatigue behaviors of unfused powder pocket and fully-fused nickel based alloy 718 specimens. Microscopy results confirmed a long suspected powder interaction phenomena as well as appearances of erosion. Furthermore, fractography supports that fatigue failures initiate near the surface of maximum strain/stress at porous features consistent with stock (non-optimized) LPBF process parameters.

Effect of moisture absorption on the wear and dynamic mechanical behavior of polymer composites

The present study focuses on the effect of moisture uptake of jute/epoxy, hemp/epoxy, flax/epoxy and hybrid composites (jute/hemp/epoxy, hemp/flax/epoxy and jute/hemp/flax/epoxy) on the dynamic mechanical and tribological properties. Composite specimens were developed using hand lay-up compression technique. The developed composites were dipped in normal tap water at room temperature for the span of one year. Three parameters were used to analyze the results of dynamic mechanical analysis (damping capability, storage modulus and loss modulus), and three parameters (friction force, coefficient of friction and specific wear rate) were used to analyze the wear test results. Results of dynamic mechanical analysis and wear analysis after one year of moisture absorption were compared with already published results for specimens without moisture absorption. Substantial changes were observed in each parameter of dynamic mechanical analysis and tribology test performed after one year of water immersion. Water-saturated hybrid composite jute/hemp/epoxy achieved highest reduction of 16.03% in damping capability as compared to its dry specimens. Water-immersed jute/epoxy composite achieved highest increment of 763.2% and 589.8% in the value of storage modulus and loss modulus, respectively, as compared to its dry specimen. Hybrid composite jute/hemp/flax/epoxy achieved the highest increment of 13.5% and 19.9% in the value of coefficient of friction as compared to its dry specimen at 3 and 5 m/s sliding speed, respectively. Water-immersed hemp/flax/epoxy achieved the highest increment of 228.9% and 51.56% in the value of specific wear rate at 1 and 3 m/s sliding speed, respectively, as compared to its dry specimen.