Damping Index Research Articles

Intracranial aneurysm stiffness assessment using 4D Flow MRI

BackgroundAlthough arterial stiffness is known as a biomarker for cardiovascular events and stroke, there is limited information in the literature regarding the stiffness of intracranial aneurysms. In this study, we aim to assess the stiffness of intracranial aneurysms using 4D Flow MRI. MethodsA total of 27 aneurysms in 25 patients with internal carotid artery aneurysms were included in this study. Using 4D Flow MRI, we measured the arterial pulse wave form during a cardiac cycle at planes proximal and distal to the target aneurysm. The damping of these waveforms through the aneurysm was defined as the aneurysm damping index (ADI) and compared to the contralateral side. We also investigated the clinical factors related to the ADI. ResultsADI assessment was successful in all cases. The average ADI was 1.18±0.28, which was significantly larger than 1.0 (P = 0.0027 [t-test]). The ADI on the aneurysm side was larger than on the contralateral side (1.19±0.30 vs 1.05±0.17, P = 0.029 [t-test]). On multivariate analysis, the use of beta-blockers (β=0.46, P = 0.015) and smoking history (β=-0.22, P = 0.024) showed a significant correlation with ADI. ConclusionWe have proposed a novel method to observe arterial pulse wave dumping through intracranial aneurysm using 4D Flow MRI. The damping can be quantitatively observed, and the ADI has correlations with clinical factors such as antihypertensive drugs and smoking. Further studies should focus more on evaluating aneurysm stiffness and its clinical applications.

In-plane testing and hysteretic modeling of steel-spline cross-laminated timber diaphragm connection with self-tapping screws

ABSTRACT This study examines experimentally and numerically the in-plane behavior of a steel-spline Cross-Laminated Timber (CLT) connection with self-tapping screws. Although this connection is a strong, rapid, and cost-effective alternative suitable for CLT diaphragms of tall timber-concrete buildings, no previous cyclic/monotonic testing has been documented. Two specimens were tested under axial and in-plane shear loads, where a ductile failure mode was observed due to bending and withdrawal of screws, and deformation and buckling of the strap. Mechanic properties, such as strength capacity, stiffness, ductility, energy dissipation, equivalent viscous damping, stiffness/strength degradation, and damage index characterize the joint. Furthermore, the yield point and ductility were calculated with the EEEP, CEN, and Yasumura–Kawai methods, the last approach most accurate, with a mean ductility of 7.25 and 5.50 for the axial and in-plane shear tests, respectively. Overstrength factors of about 2.6 and 1.9 were also estimated for respective tests by comparing analytical expressions from timber codes and literature. Finally, three numerical models (SAWS, DowelType, and ASPID) were assessed to measure their epistemic uncertainty, showing an adequate force and dissipated energy history simulation, with a normalized root mean square less than 8.8% and 4.5%, and R 2 over 87% and 97%, respectively.

Asymptotic stabilization for Bresse transmission systems with fractional damping

In this article, we study the asymptotic stability of Bresse transmission systems with two fractional dampings. The dissipation mechanism of control is given by the fractional damping term and acts on two equations. The relationship between the stability of the system, the fractional damping index \(\theta\in[0,1]\) and the different wave velocities is obtained. By using the semigroup method, we obtain the well-posedness of the system. We also prove that when the wave velocities are unequal or equal with \(\theta\neq 0\), the system is not exponential stable, and it is polynomial stable. In addition, the precise decay rate is obtained by the multiplier method and the frequency domain method. When the wave velocities are equal with \(\theta=0\), the system is exponential stable.
 For more information see https://ejde.math.txstate.edu/Volumes/2023/87/abstr.html

Piezoelectric Actuators Placement Using Genetic Algorithm and Active Vibration Control of Smart Plane Frame Structure

A Genetic Algorithm-based optimisation scheme is presented to find the optimum actuator elements infinite element analysis for active vibration control applications. The dynamic strain data is used to reduce the size of search domain for the actuators placement problem. A modal velocity, feedback control is employed to estimate the active damping of piezoelectric actuators. The structural damping index is taken as a fitness function; which directly reflects the status of active damping effect for a given piezoelectric actuator set. Modal preference is attempted by assigning a different weighting factor in the fitness function for desired modes to have better controllability. As an illustration, a 20-member smart plane frame is modeled with d3I based extension-bending piezoelectric actuators using 2-D piezoelectric Timoshenko beam element. It is shown that the vibration of first four elastic modes is actively controlled with optimally, selected four piezoelectric actuators.

Numerical and experimental investigations on the seismic response of continuous girder bridge using winding rope fluid viscous dampers

Severe damage to the continuous girder bridges (CGB) has been observed in past earthquakes. To decrease the seismic response of CGB, a novel winding rope fluid viscous damper (WRFVD) is proposed. In this paper, theoretical mechanical equations for the WRFVD are derived. In addition, simplified numerical modeling approach on CGB with WRFVD is presented. To verify effectiveness of the WRFVD on CGB, a scaled three-span CGB equipped with WRFVD was tested using the shaking table test. The results showed that WRFVD can effectively reduce the internal force of the fixed pier and the deck displacement. In addition, the experimental results verified that the simplified numerical model can be used effectively to simulate the seismic response of multi-span CGB equipped with WRFVD. The verified numerical model was used in a parameter study to examine the influence of damping coefficient, damping index, number and rope pre-tension of WRFVD on the seismic response of a five-span CGB. The parameter study shows that the seismic response of multi-span CGB equipped with WRFVD decreases with the increasing damping coefficient, the increasing number of WRFVD and the decreasing damping index. The influence of the pre-tension of winding ropes is more efficient for the near-fault ground motions. The results demonstrate WRFVD can be used effectively to reduce the seismic response of CGB.

Seismic Performance and Parametric Study of a Winding Rope Fluid Viscous Damper (WRFVD) for Continuous Girder Bridges

ABSTRACT To decrease the seismic response of continuous girder bridges, the seismic performance of a novel winding rope fluid viscous damper (WRFVD) was investigated. This device was installed between the sliding piers and superstructure, and connected to the superstructure by winding ropes. WRFVD can accommodate the thermal deformation of superstructure under service condition, and make the fixed pier and sliding piers bear the seismic loads together by establishing the friction connection between the sliding piers and superstructure under earthquake action. In this study, the theoretical mechanism of WRFVD is derived, and verified by a dynamic performance test. A shaking table test was conducted on a scaled three-span continuous girder bridge employing WRFVD. The test results showed that WRFVD can effectively reduce the seismic response of continuous girder bridges. The parametric study of WRFVD on a five-span continuous girder bridge was investigated. The parametric study shows that the seismic response of multi-span continuous girder bridge equipped with WRFVD decrease with the increasing damping coefficient and friction coefficient, and the decreasing damping index.

Causal inference between indoor dampness and adverse health effects

Indoor dampness can promote the establishment of microbes in indoor environments, and as such, controlling dampness is important for maintaining a healthy indoor environment. Here, an index is proposed for evaluating indoor dampness based on checking for visible condensation, mold in living rooms and bedrooms, and moldy odors indoors. In this evaluation method, eight items related to visible condensation, presence of mold, and moldy odors are assigned a maximum score of 3 points; the total score (a maximum of 24 points) is then used as an index for the degree of dampness. We classified the total score into four rankings based on quartiles. Rank 4 represents the lowest rank and was assigned to houses that had the most severe levels of indoor dampness. We hypothesized that the lower the rank, the higher the incidence of sick housing syndrome (SHS) would be among young children. To clarify whether there was an association between child SHS and indoor dampness, we conducted an Internet-based cross-sectional survey on children aged 4–12 years. This study first identified potential confounding variables for exposure to indoor dampness using a directed acyclic graph. The results indicated that the higher the degree of dampness, the higher the health risk was for ocular, nasal, and throat symptoms. Dose-response relationships between indoor dampness and SHS were presented using the dampness index proposed in this study.

A new way to investigate the damping properties of NR/CIIR blends characterized by the rebound behaviors

AbstractIn this work, effects of natural rubber (NR) content on the vulcanization and damping properties of chlorinated butyl rubber (CIIR) were studied. A new method to characterize the damping performance of the NR/CIIR blends by the rebound behavior of rubber ball was proposed. And an optical laser‐based measurement was used to follow the movement of the rubber sample. The DMA results showed that better damping properties of the blends was obtained at higher proportion of CIIR in the blends at room temperature (20°C) and a frequency of 0.1–100 Hz. Furthermore, a propose was made that the damping properties of the blends can be characterized by the rebound behavior of the rubber ball, and two methods were developed to characterize the damping properties of the blends according to the rebound experimental results of the rubber ball. The functional relationship between the height of the nth bounce of the rubber ball and NR content was obtained by experimental fitting. The damping index (DI) was defined by combining the parameters such as bounce height, bounce times and bounce time of the rubber ball. It was expected that this study could provide a new idea for the characterization and testing of viscoelastic damping materials.

Associations between indoor environment and lifestyles and sick building syndrome symptoms among adults in Taiyuan and Urumqi of China.

The complex and uncertain causes of sick building syndrome (SBS) have become one of the most challenging and hot issues worldwide. Studies on the correlation between indoor environment and SBS based on local characteristics are relatively limited in China. We studied typical SBS risk factors related to the indoor environment and lifestyle in two northern Chinese cities. The study population was drawn from parents of pre-school children in randomized daycare centers in Taiyuan, Shanxi, and Urumqi, Xinjiang, China (N=6838). Data on SBS and indoor environment were obtained from cross-sectional questionnaires. Odds ratios (OR) were estimated by multilevel logistic regression and adjusted using gender, atopy, own smoking, home size, and dampness index. Results showed that location, homeownership, year of construction completion, changes in the indoor environment (new furniture and decorations), and changes in indoor air (smoking, burning mosquito repellent and incense, cooking fuels including electricity, natural gas, coal, and wood) might contribute to different levels of SBS in Chinese adults, including eye, nasal, throat, dermal symptoms, and headache and tiredness. The results of the subgroup analysis suggest city and gender differences in susceptibility. Daily cleaning, window opening, and improved ventilation effectively improved SBS. People should improve their indoor environment and lifestyles based on sensitivity factors, gender, and geographic characteristics to reduce SBS risks.

Spleen Transient Elastography and Damping Index Identify a Subgroup of Patients Without an Acute or Chronic Response to Beta-Blockers.

Background and AimsMonitoring of acute or chronic response to beta-blockers in patients with liver cirrhosis is based on the measurement of the HVPG. Our aim was to evaluate the response to beta-blockers with non-invasive techniques.Patients and MethodsThis is a prospective observational study. Consecutive patients with an indication of primary or secondary prophylaxis of variceal bleeding who did not meet exclusion criteria were included. Acute response and chronic response were evaluated. Baseline and after acute and chronic response hepatosplenic measurements of TE and ARFI were obtained. Contrast-enhanced Doppler ultrasound was performed before and after acute and chronic responses.ResultsFrom June 2015 to May 2018, 55 patients (14 with exclusion criteria) were included. We analyzed 41 patients, mean age 57 (SD: 8), 82.9% men, alcohol 43.9%, children A/B/C 78%/17.1%/4.9%, and 87.8% on primary prophylaxis. In all, the acute response was performed and was positive in 68.3% (CI 95: 55–85%). The chronic response was performed in 30 (73.2%) and was positive in 36.7% (CI 95: 18–55%). Basal measurements significantly related to acute response were spleen TE [responders 58.4 (SD: 23.0) KPa vs. non-responders 75 (SD: 0) KPa; p = 0.02] and damping index [non-responders 0.96 (0.8) vs. responders 0.44 (0.4), p = 0.01], and with chronic response, the spleen TE [responders 58.1 (SD: 21.4) KPa vs. non-responders 73.2 (SD: 5.5) KPa; p = 0.02], and damping index [non-chronic responders 0.8 (0.7) vs. chronic responders 0.4 (0.4), p = 0.04]. A spleen TE ≥ 74 KPa had a high sensitivity of 100% and specificity of 60% and a high NPV100% for predicting poor acute response to beta-blockers. The damping index > 0.6 showed moderate sensitivity of 67% and specificity of 69% with a high NPV of 82% for predicting poor acute response to beta-blockers. The combination of both measurements for predicting poor acute response to beta-blockers had an AUC of 0.8 (CI 95: 0.5–0.9). A spleen TE ≥ 74 KPa had a high sensitivity of 87% and specificity of 71% with a high NPV of 71% for predicting poor chronic response to beta-blockers. A damping index > 0.6 had moderate sensitivity of 60%, specificity of 82%, and NPV of 56% for predicting poor chronic response to beta-blockers. The combination of both measurements for predicting poor chronic response to beta-blockers had an AUC of 0.8 (CI 95: 0.7–0.9).ConclusionSpleen TE and damping index can identify a subgroup of patients with poor acute or chronic response to beta-blockers.

Experimental research on seismic performance of steel fiber-reinforced recycled concrete-filled circular steel tube columns

To study the seismic performance of steel fiber-reinforced recycled concrete-filled steel tube (SRACFST) columns, 14 circular specimens with different replacement rates (Rp) of recycled coarse aggregate (RCA), volume fractions (Vf) of steel fiber, axial compression ratios (n), steel tube thickness (t), and concrete strengths were tested to failure under constant axial and lateral cyclic loads. All the specimens exhibited a similar typical compression bending failure mode. Subsequently, the effect of different parameters on the various seismic characteristics in terms of the lateral load-displacement (P−Δ) hysteresis curve, skeleton curve, ductility, stiffness degradation, strength degradation and energy dissipation were obtained and studied comprehensively. The results indicated that the addition of steel fiber to core concrete can effectively compensate for the marginal negative influence of the defects of recycled aggregate concrete (RAC). Furthermore, the lateral bearing capacity, ductility, and energy dissipation capacity were improved as the steel fiber fraction increased. An increase in the thickness of the steel tube resulted in a remarkable improvement in the overall seismic behaviour. However, a higher axial compression ratio resulted in inferior seismic performance, particularly in terms of the deformation capacity and ductility. The bearing capacity and energy dissipation improved as the concrete strength increased. However, the ductility, stiffness stability, and strength stability weakened. The equivalent viscous damping index corresponding near failure attained 0.281–0.414, and the ductility was higher than 3.0. This demonstrated that the SRACFST columns could be used in load-bearing structures in seismic regions. The Code AIJ-2001 was recommended to calculate the compression bending bearing capacity of SRACFST columns under cyclic seismic loading, with an expansion index of 1.15 for calculation accuracy. Further, the fiber modelling (FM) method was established to predict the skeleton curves. The calculated results matched the experimental results well, and this indicated the relevance of this method for further elastoplastic analysis of SRACFST columns during earthquakes.

Thermoelastic Damping Limited Quality Factor Enhancement and Energy Dissipation Analysis of Rectangular Plate Resonators Using Nonclassical Elasticity Theory

Among the different energy dissipation mechanisms, thermoelastic damping plays a vital role and needs to be alleviated in vibrating resonators to mitigate parameters by improving the thermoelastic damping limited quality factor, QTED. The maximum energy dissipation is also interrelated with the critical dimension h c of the plates, and by optimizing the dimensions, the peaking of energy dissipation can be diminished. As the size of the devices is scaled down, classical continuum theories become incompetent to explain the size-effect related mechanical nature at the micron and submicron levels, and, as a result, nonclassical continuum theories have been pioneered with the inception of internal length scale parameters. In this work, an analysis of isotropic rectangular microplates based on the Kirchhoff model and a higher order theory like Modified Couple Stress Theory is utilized to study size-dependent thermoelastic damping and its impact on the quality factor and critical dimensions. The Hamilton principle is adapted to derive the governing equations of motion, and the coupled heat conduction equation is employed to formulate the thermoelastic damping limited quality factor of the plates. Five different structural materials (PolySi, diamond, Si, GaAs, and SiC) are used for optimizing QTED and hc, which depends on two material performance index parameters: the thermoelastic damping index (TDI) and the material thermal diffusion length, l T . According to this work, the maximum QTED is attained for PolySi with the lowest TDI, and hcmax is obtained for Si with the maximum l T . The impacts of the dimensionless length-scale parameters (l/h), vibration modes, and boundary conditions (clamped-clamped and simply supported) on QTED and hc are also investigated. From the current analysis, QTED can be further enhanced by selecting higher vibration modes and clamped-clamped boundary conditions. QTED can be maximized by fixing the internal length scale parameter (l) and making the thickness of the beam equal to l. The analytical study is numerically simulated by using MATLAB 2015 software. Prior knowledge of QTED and hc will help designers to produce high-performance and low-loss resonators for the futuristic technological applications.

ROLE OF COLOR DOPPLER ULTRASONOGRAPHY IN THE EVALUATION OF PORTAL VENOUS HYPERTENSION

Chronic alcoholism, obesity and viral hepatitis (B & C virus) are main causes for chronic liver disease. In cirrhotic patients, portal hypertension and its complications lead to signicant morbidity and mortality. Ultrasound technique, such as duplex ultrasonography ,spectral and color Doppler imaging are the modalities of choice. Study was undertaken to evaluate spectrum of color Doppler sonographic ndings in portal hypertension, to study ow metric changes in portal hypertension and to look for presence of various Porto-systemic collaterals. Result of study shows alcoholic liver disease as the main cause for liver cirrhosis. Maximum number of patients with splenorenal collaterals. Color Doppler sonography is a valuable non-invasive alternative which provides precise information in localizing and characterizing portal vein in patients with portal hypertension and identify the presence of various Porto-systemic collaterals. The hepatic vein damping index (DI) correlates well with the severity of liver dysfunction in terms of Child Pugh score.

Non‐Invasive Assessment of Damping of Blood Flow Velocity Pulsatility in Cerebral Arteries With MRI

BackgroundDamping of heartbeat‐induced pressure pulsations occurs in large arteries such as the aorta and extends to the small arteries and microcirculation. Since recently, 7 T MRI enables investigation of damping in the small cerebral arteries.PurposeTo investigate flow pulsatility damping between the first segment of the middle cerebral artery (M1) and the small perforating arteries using magnetic resonance imaging.Study TypeRetrospective.SubjectsThirty‐eight participants (45% female) aged above 50 without history of heart failure, carotid occlusive disease, or cognitive impairment.Field Strength/Sequence3 T gradient echo (GE) T1‐weighted images, spin‐echo fluid‐attenuated inversion recovery images, GE two‐dimensional (2D) phase‐contrast, and GE cine steady‐state free precession images were acquired. At 7 T, T1‐weighted images, GE quantitative‐flow, and GE 2D phase‐contrast images were acquired.AssessmentVelocity pulsatilities of the M1 and perforating arteries in the basal ganglia (BG) and semi‐oval center (CSO) were measured. We used the damping index between the M1 and perforating arteries as a damping indicator (velocity pulsatilityM1/velocity pulsatilityCSO/BG). Left ventricular stroke volume (LVSV), mean arterial pressure (MAP), pulse pressure (PP), and aortic pulse wave velocity (PWV) were correlated with velocity pulsatility in the M1 and in perforating arteries, and with the damping index of the CSO and BG.Statistical TestsCorrelations of LVSV, MAP, PP, and PWV with velocity pulsatility in the M1 and small perforating arteries, and correlations with the damping indices were evaluated with linear regression analyses.ResultsPP and PWV were significantly positively correlated to M1 velocity pulsatility. PWV was significantly negatively correlated to CSO velocity pulsatility, and PP was unrelated to CSO velocity pulsatility (P = 0.28). PP and PWV were uncorrelated to BG velocity pulsatility (P = 0.25; P = 0.68). PWV and PP were significantly positively correlated with the CSO damping index.Data ConclusionOur study demonstrated a dynamic damping of velocity pulsatility between the M1 and small cerebral perforating arteries in relation to proximal stress.Level of Evidence4Technical EfficacyStage 1

Influence of Al particle layer on damping behavior of Alp/7075Al composites fabricated by hot rolling

The Al particle reinforced 7075 Al matrix composites with the layered structure are prepared by hot rolling to improve the damping property of the alloy. Numerous interparticle interfaces are observed in the Al particle layer (reinforcement), and the traces of no interfacial reaction or elemental diffusion are found between the matrix and reinforcement layer. The tensile strength of the composite is 29% higher than that of the matrix. The internal friction values of the Alp/7075Al lamellar composite and the 7075 Al matrix are found to increase with the increase in temperature and strain, respectively. At 570 K, the internal friction values of the composites are found to be as high as 0.105, which is 337% higher than that of the matrix, and an internal friction peak (P2) appears in the composites due to the recrystallization of Al particles at high temperature. The comprehensive damping index of the composite is found to be about 2.9-fold of the 7075 Al matrix. The damping mechanism of the composite is mainly attributed to dislocation damping, grain boundary damping, and interface damping.

Coordinated control among PSS, WTG and BESS for improving Small-Signal Stability

Abstract The goal towards attaining a sustainable future has led to the rapid increase in the integration of converter control based generators (CCBGs). The low inertia response characteristics of CCBGs and the weak tie lines in interconnected systems pose a huge threat to Small-Signal Stability (SSS). Adequate damping of low-frequency oscillations (LFO) is pivotal in ensuring the maximum power transfer through the critical transmission corridors. These operational issues become more serious with the significant reduction in system inertia as a result of the high penetration of CCBGs. Therefore, appropriate control techniques are an absolute requirement for preventing LFOs from limiting the penetration of CCBGs in interconnected networks. This may also eventually lead to revisions in grid codes mandating CCBGs to provide auxiliary damping control. But, the progressive addition of multiple damping controllers for specific target modes can lead to the drifting of eigenvalues (EVs) associated with other electromechanical modes (EMs) in the system. This is due to the adverse interactions between multiple damping controllers in the uncoordinated control approach and may result in deteriorating SSS. Therefore, this paper proposes a simultaneous coordinated control among Battery Energy Storage System (BESS), Wind Turbine Generators (WTG) and Power System Stabilizer (PSS) for enhancing SSS in networks with high wind penetration by considering both inter-area (IA) and local modes. The performance of the proposed coordinated control is corroborated using IEEE 68 bus system for multiple operating scenarios for which the critical modes in the system have the lowest damping index (DI). The effectiveness of modulating the active power, reactive power and simultaneous modulation of both active and reactive power injected by BESS along with a dual-channel Optimized WTG Damping Controller (DOWDC) and PSS is evaluated. The impact of the different coordinated control strategies on voltage dynamics is also investigated. The simulation results validate the better performance of the proposed coordinated control over uncoordinated control approaches.

Effect of porous particle layer on damping capacity and storage modulus of AlSi30p/5052Al composites

The AlSi30p/5052Al composite with porous particle layer was successfully produced by hot rolling. Numerous interparticle interfaces and pores were seen in the particle layer. The dynamic mechanical analysis shows that the internal friction and the storage modulus of the composites are higher than that of the matrix. Due to the presence of an intermediate particle layer, dislocation and residual internal stress increase in the composites, and thereby improve the storage modulus of the composites. The comprehensive damping index of the composites is better than that of the matrix. The synergistic damping effect caused by the porous structure and a large number of interfaces between particles in the particle layer improve the damping capacity of the composites.

Sliding-mode secure control for jump cyber– physical systems with malicious attacks

This paper develops the secure control strategy design issue for jump cyber–physical systems (CPSs) with malicious attacks. In the jump CPSs, the jump signals are assumed to obey the semi-Markov distribution with the transition probability depends on the stochastic sojourn-time, the physical plant and actuator simultaneous subject to the adversarial attack. A secure control strategy on robust sliding-mode control (SMC) is designed to deal with the malicious attacks. Firstly, an integral sliding-mode hyperplane is constructed, and the sliding-mode dynamics is discussed. Then, the slide-mode parameters are solved by the linear matrix inequality method with prescribed H∞ damping index. Furthermore, a robust sliding-mode controller is presented, and the reachability of the sliding-mode motion is analyzed. Finally, two examples are implemented to prove the potential of the secure control approach.

INVESTIGATION INTO INDOOR ENVIRONMENTS AND HOME DAMPNESS

A recent meta-analysis of dampness in homes has shown that dampness and mold in indoor environments are factors in approximately 30-50% of all respiratory and asthma-related health ailments. Although the specific indoor dampness factors related to such issues have yet to be fully explored, there are clear and urgent needs for improved architectural techniques and optimized occupant behavior patterns that can prevent or eliminate excessive dampness inside buildings. Furthermore, if the underlying structures linking dampness to adverse health effects could be more closely estimated through epidemiological surveys, prevention methodologies for serious problems related to indoor dampness might be discovered. With these points in mind, we previously proposed a home dampness estimation method based on occupants’ self-reported answers to questions regarding indoor dampness during winter. This resulted in an indoor dampness index covering a range from 0 to 24 that classifies houses into four ranks, with those in Rank 4 presenting the most serious dampness-related problems.

Research on Damping Control Index of Ultra-Low-Frequency Oscillation in Hydro-Dominant Power Systems

In recent years, ultra-low-frequency oscillation (ULFO) is a prominent problem in power systems of dominant hydropower. In order to suppress ULFO, the most effective strategy is the governor parameters optimization to improve the system damping within the ultra-low-frequency band. However, no explicit standard has been established to stipulate the level of system damping for ULFO suppression. In this paper, the key factors that affect the amplitude and damping of ULFO are firstly analyzed. Then, the design principle of the damping control index of ULFO is put forward. According to it, a damping control index is proposed. After that, a case of ULFO in an actual power system proves the rationality of the proposed index. Finally, the application of the index in the Southwest China Power Grid illustrates its effectiveness and feasibility.