Take-off Force Research Articles

Nonlinear Model Predictive Control of Heaving Wave Energy Converter with Nonlinear Froude–Krylov Forces

Wave energy holds significant promise as a renewable energy source due to the consistent and predictable nature of ocean waves. However, optimizing wave energy devices is essential for achieving competitive viability in the energy market. This paper presents the application of a nonlinear model predictive controller (MPC) to enhance the energy extraction of a heaving point absorber. The wave energy converter (WEC) model accounts for the nonlinear dynamics and static Froude–Krylov forces, which are essential in accurately representing the system’s behavior. The nonlinear MPC is tested under irregular wave conditions within the power production region, where constraints on displacement and the power take-off (PTO) force are enforced to ensure the WEC’s safety while maximizing energy absorption. A comparison is made with a linear MPC, which uses a linear approximation of the Froude–Krylov forces. The study comprehensively compares power performance and computational costs between the linear and nonlinear MPC approaches. Both MPC variants determine the optimal PTO force to maximize energy absorption, utilizing (1) a linear WEC model (LMPC) for state predictions and (2) a nonlinear model (NLMPC) incorporating exact Froude–Krylov forces. Additionally, the study analyzes four controller configurations, varying the MPC prediction horizon and re-optimization time. The results indicate that, in general, the NLMPC achieves higher energy absorption than the LMPC. The nonlinear model also better adheres to system constraints, with the linear model showing some displacement violations. This paper further discusses the computational load and power generation implications of adjusting the prediction horizon and re-optimization time parameters in the NLMPC.

NAJVEČJE SILE ZA DOSEGANJE NAJBOLJŠE VIŠINI IN DALJAVE LETA NA PRESKOKU V MOŠKI ORODNI TELOVADBI

Analysing the take-off forces on the vaulting table can help to inform the athlete about the vaulting technique. A measuring device was used to measure the forces during the Artistic World Championships 2019. The greatest forces were measured during Forward handspring. The mean maximum values were 5.4 times body weight (BW). The highest peak height was calculated for Forward handspring (tucked) at 2.9 m. The longest flight distance was 3.62 m for forward handspring and 3.59 m for tsukahara/kasamatsu. The statistical correlations between the forces and the peak height and flight distance could only be verified for Forward handspring. For the Tsukahara/Kasamatsu and the Yurchenko vaults, no correlation could be proven.

Influence of musculoskeletal injury history on countermovement jump performance in rugby players

ObjectiveTo examine whether musculoskeletal injury history is a factor that influences countermovement jump (CMJ) performance in rugby players and to compare CMJ performance between player's position (forwards or backs). MethodsThirty rugby players (15 with an injury history and 15 without an injury history) performed the CMJ using an inertial sensor (Baiobit®) to evaluate kinematic (Jump Height, Velocity and Phase duration) and kinetic data (rate of force development [RFD], impact peak [IP], take-off force and Stiffness]. The group comparison was performed with an independent t-test, and the association between CMJ performance, sociodemographic variables and injury history was investigated with Pearson's correlation test. ResultsRugby players with and without history of musculoskeletal injury differed in age and playing experience, but there was no difference in CMJ performance between groups. Jump height of uninjured players was positively correlated with take-off force and RFD and negatively correlated with concentric phase duration and RFD. Injured players demonstrated a negative correlation between take-off force and IP. Compared to backs, forwards were heavier and taller, showed greater IPs and were more likely to have an injury history. ConclusionsThere were no differences in CMJ performance between rugby players with and without an injury history. Forwards showed greater IPs and were more likelier to have an injury history than backs.

Research on the Influence of Humidity on the Manufacture of GFRP Vessels in the Equatorial

The objective of this research work is to analyze the behavior between fiberglass laminate under tensile tests, assembled under different humidity conditions. For which specimens were designed under the regime of the international standard ASTM D3039; which took an assembly process within a controlled environment; the design variables used were relative humidity and curing time. Subsequently, the traction-displacement behavior was checked under a uniaxial force, obtaining the maximum take-off force. In addition, Simpson numerical integration was applied to calculate elastic energy. Obtaining that the relative humidity and the days of curing influence the chemical and mechanical properties of the material. Se shows that the percentage of humidity recommended for assembling laminates in GRP is 66% since it has greater elastic energy and take-off force. Finally, it is concluded that to have a high resistance in the material at least 7 days of curing of the epoxy resin must be applied.

Jumping Motor Skills in Typically Developing Preschool Children Assessed Using a Battery of Tests.

The preschool period is characterised by the improvement in motor skills. One of the developmental tasks in children is the ability to jump. Jumping plays an important role in the development of leg strength and balance. It is the gateway to more complex movements. In the physiotherapy clinic, we see a lot of difficulties in jumping performance in 5-7-year-old children. The aim of this study is to present the jumping ability, assessed by the Motor Proficiency Test (MOT) and the G-sensor examination of the vertical countermovement jump (CMJ) and countermovement jump with arms thrust (CMJAT) parameters. A total of 47 children (14 boys and 33 girls) were randomly recruited. The mean age was 5.5 years. The mean height was 113 cm and the mean weight was 19.7 kg. The children were divided into two groups according to their results. Children with low basic motor skills have the greatest difficulty with jumping tasks. In the CMJ jump, the take-off force was lower than in the CMJAT (p = 0.04). Most CMJAT parameters correlate with age, weight, and height. Height correlates most with children's jumping performance. This study may be useful for sport educators and developmental researchers. The topic should be further explored and the CMJ and CMJAT parameters may be established as a basis.

Influence of colloidal silicon dioxide‑magnesium stearate interaction on flow and compaction behavior of an MCC-Lactose binary mixture

The amount of glidant and lubricant in a tablet formulation is driven by their primary functionalities of enhancing flowability and reducing particle-wall friction. However, their interaction can lead to undesirable outcomes. This study has examined the influence of this interaction on powder flow and compaction, using colloidal silicon dioxide as a glidant and magnesium stearate as a lubricant in a 50:50 w/w MCC:Lactose binary blend. The findings suggest that nano-sized CSD particles coat other particles in a blend. However, increasing CSD decreases exposed MgSt and reduces its lubricity, resulting in intriguing powder flow and compaction phenomena. CSD impacts powder flow more than MgSt. Increasing the CSD reduces exposed MgSt and increases particle-wall adhesion. Higher CSD concentrations decreased powder bed bulk density and permeability due to the formation of porous structures on primary host particles. A complex interplay between CSD and MgSt during tablet compaction affected tensile strength. CSD promoted tablet picking due to reduced exposed MgSt and increased tablet-punch adhesion. This is the first study correlating tablet picking with take-off force, and it was found that >5 N take-off force risked picking. Ejection force increased with CSD and decreased with MgSt, reaffirming CSD's impact on particle-wall adhesion.

Changes in Counter Movement Jump Height, Take-off Force and Maximum Concentric Power of Collegiate Athletes After Two Sessions Per Week Plyometric Training on Different Training Surfaces

Purpose: This study aimed to examine the effects of two sessions per week plyometric training on different surfaces on the counter movement jump height, take-off force, and maximum concentric power of collegiate athletes. Material and methods: Male collegiate athletes (n=24, age=18.46±1.14 years, weight=64.88±5.61 kg and height=1.72±0.07 metres)) from a physical training centre were randomly and equally assigned to three groups, each trained on different surfaces (synthetic, cinder and sand). The training intervention was implemented twice a week and lasted for 8 weeks. The athletes were tested before and after the intervention to assess changes in the performance of counter movement jump height (CMJHT), take-off force (CMJTOF) and maximum concentric power (CMJMCP). Results: Results showed that overall measurement of CMJHT, CMJTOF and CMJMCP improved significantly (p≤0.05, Δ %=10.50; p≤0.05, Δ%=11.11; p≤0.05, Δ%=11.41). However, training surfaces have no significant effect on the improvement of the selected variables (CMJHT:F(2,21)=2.37, p=0.118, ηp2=0.184; CMJTOF:F(2,21)=1.28, p=0.299, ηp2=0.109; CMJMCP:F(2,21)=0.061, p=0.941, ηp2=0.006). Further, for the synthetic track surface group CMJHT, CMJTOF and CMJMCP improved significantly (p≤0.05, Δ%=16.36; p≤0.05, Δ%=17.50; p≤0.05, Δ%=17.99); for the cinder track surface group CMJHT and CMJMCP improved significantly (p≤0.05, Δ%=9.15; p≤0.05, Δ%=10.33) and for the sand surface group only CMJHT improved significantly (p≤0.05, Δ%=5.68). Conclusions: The findings suggest that plyometric training on different surfaces can effectively improve athletic performance, but the specific surface type does not appear to impact the outcomes significantly. The study further suggested analysing the injury risk associated with plyometric training on various training surfaces and discovering the optimal training surface for minimising injury risk while maximising performance gains.

The Comparison of Anaerobic Power using Two Tests in Patients with Cystic Fibrosis and Healthy Children

ABSTRACT
 
 
 Purpose: Cystic fibrosis (CF), a progressive and multi-systemic disease, causes reduced anaerobic performance. This study aimed to compare anaerobic power using two tests (Counter-movement Vertical Jump and Wingate Anaerobic Test) in CF patients and healthy children. 
 
 Material and Methods: Eighteen CF and 18 healthy children were included in this prospective study. Knee extensor muscle strength and body composition were assessed with a digital handheld dynamometer and Tanita-BC 418, respectively. Anaerobic power was evaluated with Wingate Anaerobic Test (WAnT) and Counter-movement Vertical Jump (CMJ) using a triaxial accelerometer (G-Walk). 
 
 Results: Maximum concentric power, peak speed, impact force, take-off force, and jump height were significantly worse in the CF group than in their healthy peers (p

New Formulation of Wave Energy Converter Control Using Extremum Seeking

Ocean wave energy converter (WEC) requires real-time control to maximise energy conversion. Effective control of wave energy converter is particularly challenging, since the ocean wave is highly uncertain and time-varying. Conventionally, instantaneous control methods are utilised, such as Bang-Bang control and model predictive control with wave prediction, which consequently requires fast controller and responses. In this paper, energy generated in a period of time is regarded as an entirety, and the main wave is considered to impose a periodic excitation force to WEC. Then, it is shown that the optimal power take-off force also follows a periodic function, by optimising which WEC is expected to generate maximum power output. The intriguing relationship among the harvested energy, wave properties and control force is derived in this paper. An extremum seeking control method is implemented to solve this reformulated problem. By extensive simulation results, the effectiveness of the proposed framework and control method is validated, which demonstrates high conversion efficiency comparing to Bang-Bang control and short-horizon optimal control.

Motion Analysis of A Wind-Wave Energy TLP Platform Considering Second-order Wave Forces

Offshore wind energy has become a major energy source, and various studies are underway to increase the economic feasibility of floating offshore wind turbines (FOWT). In this study, the characteristics of wave-induced motion of a combined wind-wave energy platform were analyzed to reduce the variability of energy extraction. A user subroutine was developed, and numerical analysis was performed in connection with the ANSYS-AQWA hydrodynamic program in the time domain. A platform combining the TLP-type FOWT and the Wavestar-type wave energy converter (WEC) was proposed. Each motion response of the platform on the second-order wave load, the effect of WEC attachment and Power take-off (PTO) force were analyzed. The mooring line tension according to the installation location was also analyzed. The vertical motion of a single FOWT was increased approximately three times due to the second-order sum-frequency wave load. The PTO force of the WEC played as a vertical motion damper for the combined platform. The tension of the mooring lines in front of the incident wave direction was dominantly affected by the pitch of the platform, and the mooring lines located at the side of the platform were mainly affected by the heave of the platform.

Gym machines for simulating training of technical movements in curling

Curling is a team sports game played on ice. The athletes slide stones one by one toward a marked target area. This is a sport in which the exactness of a throw is the base of technique and one of the main components of a successful play. In sport, technique means the way of making a physical action. Technical preparation is a process of education and improvement of movement skills, serving a mean of sports fighting. For making a throw of a curling stone an athlete has to push himself off a hack and slide in a deep lunge position holding a stone in his hand. In front of the hog line an athlete releases the stone. This paper describes the machines for training the technique of throwing a curling stone. Using empirical research methods we have created and used the machines which were used during the training process at the special preparation stage of the preparation period. A special training roller ground for throwing curling stones was developed. The useful model RU 192760 patent was published on September 30, 2019. The developed equipment allows to do imitative training of movements and technique of curling stones throwing. A training roller ground for a curling player’s boot was designed. The useful model RU 193702 patent was published on November 11, 2019. The conditions for simulating training of exactness of take-off force in curling were created

Effect of plyometric training on repeated countermovement jump performance of collegiate athletes

The goal of the present study was to find out the effect of plyometric training on repeated countermovement jump performance of collegiate athletes. A total of six variables of repeated countermovement jump, i.e., height (HT), take-off force (TOF), impact force (IF), maximum concentric power (MCP), peak speed (PS), and take-off speed (TOS), were selected to fulfil the objective of the study. A total of twenty (N=20) participants were randomly selected from a physical training centre of the Gwalior area of India as the subjects for the study. The average age of the participants was 18.40±1.19 years. The subjects were randomly divided into two groups. Each group consists of ten participants. One group was treated as the experimental group, and another was treated as the control group. To find out the effect of plyometric training a randomized control group pre-test post-test design was adopted in which the experimental group received eight weeks of plyometric training whereas the control group received dummy training. The training was given twice a week to both groups. Pre and post-data were collected before and after the eight weeks of plyometric training. The statistical technique independent t-test was used to compare the performance of the experimental and control groups, whereas paired t-tests were used to compare pre-and post-test data at 0.05 level of significance. The findings showed that eight weeks of plyometric training significantly improved the variable height, take-off force and maximum concentric power.

The Acute Influence of Whole-Body Cryotherapy on Electromyographic Signals and Jumping Tasks

Whole-body cryotherapy (WBC) is a popular treatment in prevention as well as post-injury therapy. The parameter used to assess the risk of injury is the ability of the human body to absorb and recover energy (elasticity). Therefore, this study aimed to assess the impact of whole-body cryotherapy (WBC) at 1 and 3 min intervals on the bioelectric activity of lower-limb muscles and countermovement jumps (CMJs) using trained subjects. A total of 24 individuals participated in the study. The mean age of the study group was 27.9 ± 7.9 years, mean body weight was 77.9 ± 8.8 kg, and mean body height was equal to 181 ± 6 cm. The training routine included 2–4 training sessions per week that lasted for at least 2 h at a time (mainly football). Along with the surface electromyography (sEMG) test of the rectus femoris, the BTS G-Sensor inertia measurement device was applied. After three minutes of WBC, a 6% difference in take-off force was noted, with a 7% (p < 0.04) decrease in elasticity. In the bioelectrical activity of the rectus femoris after MVC normalization, differences (p < 0.05) were noted 3 min after WBC. In this conducted study, a reduction in flexibility of the lower-limb muscle groups in the CMJ task was noted after 3 min of WBC.

Strength and Biomechanical Risk Factors for Noncontact ACL Injury in Elite Female Footballers: A Prospective Study.

This study aimed to determine if a preseason field-based test battery was prospectively associated with noncontact anterior cruciate ligament (ACL) injury in elite female footballers. In total, 322 elite senior and junior female Australian Rules Football and soccer players had their isometric hip adductor and abductor strength, eccentric knee flexor strength, countermovement jump (CMJ) kinetics, and single-leg hop kinematics assessed during the 2019 preseason. Demographic and injury history details were also collected. Footballers were subsequently followed for 18 months for ACL injury. Fifteen noncontact ACL injuries occurred during the follow-up period. Prior ACL injury (odds ratio [OR], 9.68; 95% confidence interval (95% CI), 2.67-31.46), a lower isometric hip adductor to abductor strength ratio (OR, 1.98; 95% CI, 1.09-3.61), greater CMJ peak take-off force (OR, 1.74; 95% CI, 1.09-3.61), and greater single-leg triple vertical hop average dynamic knee valgus (OR, 1.97; 95% CI, 1.06-3.63) and ipsilateral trunk flexion (OR, 1.60; 95% CI, 1.01-2.55) were independently associated with an increased risk of subsequent ACL injury. A multivariable prediction model consisting of CMJ peak take-off force, dynamic knee valgus, and ACL injury history that was internally validated classified ACL injured from uninjured footballers with 78% total accuracy. Between-leg asymmetry in lower limb strength and CMJ kinetics were not associated with subsequent ACL injury risk. Preseason field-based measures of lower limb muscle strength and biomechanics were associated with future noncontact ACL injury in elite female footballers. These risk factors can be used to guide ACL injury screening practices and inform the design of targeted injury prevention training in elite female footballers.

Towards realistic power performance and techno-economic performance of wave power farms: The impact of control strategies and wave climates

This paper performs an investigation of power performance and techno-economic performance of wave power farms in realistic wave climates, where hydrodynamic interaction and influence of control strategies employed by power take-off systems are fully considered in mathematical modeling and numerical analysis. This is of great significance for a commercial wave power farm operated in a specific sea site over a long time of years, as wave energy converters will encounter a wide range of sea states, which requires that associated power take-off systems of individual units must be controlled accordingly to maximize the converted energy and to reduce the levelized cost of energy (LCOE). To that end, a fully-coupled numerical model, where the power take-off systems of wave energy converters are coordinately controlled/tuned for each sea state by employing an optimal linear passive control strategy and an optimal active control strategy, respectively. Numerical results show that power performance and LCOE of wave power farms vary over wave climates, and machinery constraints of power take-off force must be considered. Globally coordinated control of wave power farms by employing a constrained optimal linear active control strategy yields a LCOE of 0.17−0.54 $/kWh and increases the annual energy generation at least three times in specific wave climates of China, United States, Australia and Ireland.

Ground Reaction Forces Comparison of Sauté Jump Landing between Dancers with Different Levels of Proficiency

ABSTRACT Ballet dancers are exposed to the high likelihood of lower extremity injury due to repeated high-impact jumps under stringent ballet rules. The injury incidences occurring in dancers during jump landings are highly associated with excessive vertical ground reaction forces (vGRF) and the sharp loading rate (LR). The aim of this study was to compare vGRF and LR during ballet sauté jump landings in dancers with two different skill levels. Impact peak force (F1) and active peak force (F2) were both significantly varied between novice and experienced dancers. The LR was also significantly different between the two groups but no significant differences were found in peak take-off force and jump height. The difference of vGRF during jump landings in different skill levels can be considered as an influential factor for dance instructors, educators, physicians, and dancers themselves in order to support a better jump performance and reduce the likelihood of potential injury.

Comparative Study of Oscillating Surge Wave Energy Converter Performance: A Case Study for Southern Coasts of the Caspian Sea

The search for renewable energy supplies for today’s global energy demand, particularly ocean wave energy for coastal areas, has become undeniably widespread in the last two decades. The Caspian Sea represents an immense opportunity for using ocean renewable energy, especially considering its long shoreline. In this study, the locations with maximum potential wave energy were chosen in the central, eastern, and western zones of the Caspian Sea’s southern coasts. Accordingly, the wave and bathymetric data were used as the input to calculate the oscillating surge wave energy converter’s flap geometric dimensions based on previous studies. Then, the geometric model was designed, and then the wave energy converters were modeled in the Wave Energy Converter Simulator (WEC-Sim) module in the MATLAB software. Furthermore, eight models in each sea state were simulated to find the best value of the PTO damping coefficient, which led to the highest capture factor. Finally, all the external forces on the WEC’s flap and the converter’s power output results were compared, taking into account the effects of the flap height on the total power output. It was found that Nowshahr port has more potential than the Anzali and Amirabad ports, as the converter’s absorbed power proved to be 16.7 kW/m (Capture factor = 63%) at this site. Consequently, by conducting a comparative analysis between the selected sites, the excitation, radiation damping, and power take-off forces were scrutinized. The results show that the highest applied forces to the converter’s flap occurred at Nowshahr port, followed by the Anzali and Amirabad ports, due to the directional characteristics of the waves at the central coasts of the Caspian Sea.

Maturity alters drop vertical jump landing force-time profiles but not performance outcomes in adolescent females.

The stretch-shortening cycle (SSC) assists in effective force attenuation upon landing and augments force generation at take-off during a drop vertical jump (DVJ). General performance outcomes such as jump height or peak measures have been used to assess SSC function in youth populations; however, these discrete metrics fail to provide insight into temporal jump-landing characteristics. This study assessed DVJ force-time profiles in 1013middle and high-school female athletes (n=279 prepubertal, n=401 pubertal, and n=333 postpubertal). Maturity status was determined using the Pubertal Maturation Observation Scale. Ground reaction force data were analyzed to extract a range of variables to characterize force-time profiles. SSC function was categorized as poor, moderate, or good dependent on the presence of an impact peak and spring-like behavior. No differences in jump height or ground contact time were observed between maturity groups (p>0.05). Significant differences in absolute peak landing and take-off force were evident between all maturational statuses (p<0.05). Relative to bodyweight normalized forces, only peak take-off force was significantly different between prepubertal and postpubertal groups (p<0.05; d=0.22). Spring-like behavior showed small improvements from pubertal to postpubertal (p<0.05; d=0.25). Most females displayed poor SSC function at prepubertal (79.6%), pubertal (77.3%), and postpubertal (65.5%) stages of maturity. Large increases in absolute forces occur throughout maturation in female athletes; however, only small maturational differences were found in relative force or spring-like behavior. Consequently, most girls display poor SSC function irrespective of maturity.

Effects of power take-off parameters and harvester shape on wave energy extraction and output of a hydraulic conversion system

Considering nonlinear hydrodynamic forces of a harvester in irregular waves and a nonlinear hydraulic power take-off system, a time-domain nonlinear motion model and nonlinear hydraulic power take-off models are established to investigate the harvester motion response, the hydraulic system dynamic performance, the power extraction, the motor output power and efficiency. Matlab/Simulink is used to establish and simulate the system models. The convolution identification of nonlinear radiation force is based on a state-space model. The parameters of the state-space model and the infinity frequency added mass are fitted based on the least square method. The nonlinear hydrostatic storing force is considered for cone and hemisphere. The Pierson–Moskowitz 2-parameter spectrum is adopted for the irregular waves. The Coulomb friction force and viscous friction force based on the pressure difference and hydraulic cylinder parameters are modeled in the power take-off force. Under a given sea state, for cone, cylinder and hemisphere, the optimal hydraulic power take-off parameters are predicted based on a genetic algorithm for the maximum motor output power. The effects of the hydraulic cylinder piston working area, the motor displacement, the high pressure accumulator pre-charge pressure and initial volume, the significant wave height and energy period, the harvester diameter, draft and shape on the extracted power, the extraction efficiency, the motor output power and the hydraulic conversion efficiency are investigated. The extraction ability of the cone harvester is the highest among three shapes under the same diameter and draft. The conversion efficiency increases as the motor displacement decreases.

Passive Model Predictive Control on a Two-Body Self-Referenced Point Absorber Wave Energy Converter

Wave energy is nowadays one of the most promising renewable energy sources; however, wave energy technology has not reached the fully-commercial stage, yet. One key aspect to achieve this goal is to identify an effective control strategy for each selected Wave Energy Converter (WEC), in order to extract the maximum energy from the waves, while respecting the physical constraints of the device. Model Predictive Control (MPC) can inherently satisfy these requirements. Generally, MPC is formulated as a quadratic programming problem with linear constraints (e.g., on position, speed and Power Take-Off (PTO) force). Since, in the most general case, this control technique requires bidirectional power flow between the PTO system and the grid, it has similar characteristics as reactive control. This means that, under some operating conditions, the energy losses may be equivalent, or even larger, than the energy yielded. As many WECs are designed to only allow unidirectional power flow, it is necessary to set nonlinear constraints. This makes the optimization problem significantly more expensive in terms of computational time. This work proposes two MPC control strategies applied to a two-body point absorber that address this issue from two different perspectives: (a) adapting the MPC formulation to passive loading strategy; and (b) adapting linear constraints in the MPC in order to only allow an unidirectional power flow. The results show that the two alternative proposals have similar performance in terms of computational time compared to the regular MPC and obtain considerably more power than the linear passive control, thus proving to be a good option for unidirectional PTO systems.