Mean Wake Research Articles

The effect of local wake model on collision probability for risers subjected to current and random waves

The present paper provides a method to estimate the clearance between two flexible risers in tandem arrangement by taking into account the hydrodynamic wake interference when subjected to a current flow and a combined current plus waves flow. Modelling of the wake interference in the near wake field is based on the modification of the mean wake velocity deficit in the far wake field. Two modified wake models are introduced in the presented paper. The wake effects in steady current and in current plus waves are investigated by using both wake models. For the current-only flow, the deflection shapes of a pair of tandem risers in steep-wave configuration are presented, highlighting the importance of the wake effect on clearance estimation. For combined current plus waves, the wake interference is investigated by considering the position-dependent drag force, with different combinations of riser natural frequency and wave frequency. The collision failure probability is predicted when the risers are subjected to current plus random waves.

Hybrid spatially-evolving DNS model of flow past a sphere

Direct numerical simulation in the form of a hybrid spatially-evolving model is used to simulate the turbulent wake behind a towed sphere at a subcritical Reynolds number, Re=U∞D/ν=3700, where U∞ is the free stream velocity, D is the diameter of the sphere, and ν is the viscosity. The sphere is not present in the model domain but realistic inflow conditions are obtained from a body-inclusive simulation. As such, the model is a hybrid of both body-inclusive and body-exclusive simulations which greatly reduces computational cost and allows for downstream study of wake dynamics. Inlet conditions are extracted from three locations in the streamwise, x1, direction namely x1/D=3,6, and 10, to investigate the sensitivity of the results to extraction position. Simulations are performed considering both unstratified and stratified fluids with Froude numbers, Fr=U∞/ND=∞,3, and 1 where N is the buoyancy frequency of the background, to explore the model effectiveness for varying levels of stratification. It is found that a strategic choice in extraction location is required in order to accurately capture the flow physics. Simulation results show less agreement with the body-inclusive simulations at extraction location x1/D=3 than with x1/D=6 or x1/D=10. Mean wake decay of the hybrid model simulations is consistent with the body-inclusive simulations. The layered flow structure of the stratified wake is captured well while phase lines indicating internal wave propagation are clearly observed in vorticity contours and are consistent with the body-inclusive simulations. Accurate turbulent kinetic energy (t.k.e.) capture is noted for all cases. Additional simulations with higher resolution grids were performed and analyzed to demonstrate the impact of grid resolution on turbulence statistics. Examination of t.k.e. budget terms indicates that improved grid resolution results in better agreement with the body-inclusive simulation near the inlet where the resolution disparity between the hybrid and body-inclusive simulations is most significant. The hybrid model is shown to be a robust tool for the study of turbulent wake dynamics.

Large eddy simulation of flow over inclined wavy cylinders

The wavy cylinders have been proven effective in suppressing the Kármán vortex shedding and mitigating the aerodynamic forces. As yet their performance in the inclined incoming flow has not been well understood. In the current work, large eddy simulations are carried out to unveil the aerodynamics of the flow around inclined wavy cylinders at the Reynolds number of 5000. Three inclination angles, 0°, 30° and 45°, together with 2 × 2 combinations of shape parameters, namely λ∕Dm=2 and 6, a∕Dm=0.1 and 0.15, have been taken into consideration. Firstly, the aerodynamic force coefficients in terms of both the span-wise averaged and sectional values are discussed at length. It is revealed that the growing inclination angle invites not only a surge in their span-wise averaged values, but also an enlargement in the sectional difference of the force coefficients. The span-wise correlation of the lift force is found to be enhanced for the wavy cylinders with the increase of inclination angle, while the opposite is true for the normal cylinders. By examining the mean wake properties, it is disclosed that the increase in the span-wise averaged drag force coefficients is closely related to the shrinkage in the vortex formation length and the regression of the base pressure, whereas the sectional distribution of the drag coefficients is largely affected by the stagnation pressure. The mean wall shear stress fields are exploited to shed light on the flow topology of the cylinder surfaces. It is discovered that the wavy cylinders, especially the short-wavelength one, exhibit significant span-wise variation in the separation structure in the inclined flow. Besides, the chaotic surface flow in the rear side of the non-inclined cylinders could be regulated to maintain symmetry by the secondary axial flow in the near wake of the inclined cylinders. The instantaneous three-dimensional vortical structures are visualized by the Q isosurfaces at last to collaborate the previous discussions. A preliminary mechanism for the cessation of flow control efficacy for the wavy cylinders in inclined flow is also presented.

Investigation of the effects of a fan-shaped Mewis duct before a propeller on propulsion performance

To define the guidelines for the design of a Mewis duct for a small bulk cargo ship, a numerical study was carried out to investigate the effects of a fan-shaped Mewis duct on propeller performance of a 38,000 t bulk cargo ship with a three-blade propeller. Calculations were performed using the STAR-CCM+ software based on the solution of the Reynolds averaged Navier–Stokes (RANS) equation. Computations were carried out for a wide range of locations from 0.11D to 0.21D upstream from the propeller disc, a radius of trailing edge from 0.65R to 1.05R, and angle of attack of the inner fins, where from 0° to 10° of the fan-shaped Mewis duct, where D is the diameter of the propeller and R is the radius of the propeller. With the installation of the duct, the axial mean wake fraction on the propeller disc decreased, while the tangential mean wake fraction increased significantly. As the installation position was far away from the propeller, the axial mean wake fraction varied in a wave pattern, while the tangential mean wake fraction increased. With the increase of the radius and the angle of attack of the inner fins of the duct, the axial mean wake fraction first decreased and then increased, while the tangential mean wake fraction increased gradually. Correspondingly, the propeller force coefficients and efficiencies with the duct were all more than those without the duct and changed with the variations of the duct parameters. When the propeller and duct were taken as a propulsion system, the efficiency of the system was less than that of only the propeller. At the same time, with variations of the location, radius, and angle of attack of the inner fins of the duct, the efficiency of the system first increased and then decreased gradually, which indicates that there was an optimum design value for all of the duct parameters. Moreover, only when the design of these duct parameters are reasonable can energy savings be achieved; otherwise, the opposite effect is produced. Eventually, with the installation of the fan-shaped Mewis duct, the wake harmonic degree on the propeller disc can be significantly improved.

Experimental study of the flow in the wake of a stationary sphere immersed in a turbulent boundary layer

In many applications, finite-sized particles are immersed in a turbulent boundary layer (TBL) and it is of interest to study wall effects on the instantaneous shedding of turbulence structures and associated mean velocity and Reynolds stress distributions. Here, 3D flow field dynamics in the wake of a prototypical, small sphere (D+=50, 692lReDl959) placed in the TBL's outer, logarithmic, and buffer layer, were measured using time-resolved tomo-PIV. Increasing wall proximity increasingly tilted the mean recirculating wake away from the wall implying a negative lift force. Mean velocity deficit recovery scaled with the mean wake length with minor effects of wall proximity. Farthest from the wall, streamwise Reynolds normal stresses encircled the mean wake as an axisymmetric tubular shell, while transverse and wall-normal stresses extended off its tip as axisymmetric tapered cones. Wall proximity removed axisymmetry and attenuated values near the wall. Reynolds shear stresses were distributed as antisymmetric lobes extending off the mean wake displaying increasing values with reducing sphere-wall gap. Instantaneous snapshots revealed a wake densely populated by archlike vortices with shedding frequencies lower than for a sphere in uniform flow except in the buffer layer. Tilting of the wake away from the wall resulted from self-induced motion of shed hairpinlike vortices whose symmetry plane was increasingly wall-normal oriented with reduced sphere-wall gap.

Vortex-induced vibration of a rotating sphere

Vortex-induced vibration (VIV) of a sphere represents one of the most generic fundamental fluid–structure interaction problems. Since vortex-induced vibration can lead to structural failure, numerous studies have focused on understanding the underlying principles of VIV and its suppression. This paper reports on an experimental investigation of the effect of imposed axial rotation on the dynamics of vortex-induced vibration of a sphere that is free to oscillate in the cross-flow direction, by employing simultaneous displacement and force measurements. The VIV response was investigated over a wide range of reduced velocities (i.e. velocity normalised by the natural frequency of the system): $3\leqslant U^{\ast }\leqslant 18$, corresponding to a Reynolds number range of $5000<Re<30\,000$, while the rotation ratio, defined as the ratio between the sphere surface and inflow speeds, $\unicode[STIX]{x1D6FC}=|\unicode[STIX]{x1D714}|D/(2U)$, was varied in increments over the range of $0\leqslant \unicode[STIX]{x1D6FC}\leqslant 7.5$. It is found that the vibration amplitude exhibits a typical inverted bell-shaped variation with reduced velocity, similar to the classic VIV response for a non-rotating sphere but without the higher reduced velocity response tail. The vibration amplitude decreases monotonically and gradually as the imposed transverse rotation rate is increased up to $\unicode[STIX]{x1D6FC}=6$, beyond which the body vibration is significantly reduced. The synchronisation regime, defined as the reduced velocity range where large vibrations close to the natural frequency are observed, also becomes narrower as $\unicode[STIX]{x1D6FC}$ is increased, with the peak saturation amplitude observed at progressively lower reduced velocities. In addition, for small rotation rates, the peak amplitude decreases almost linearly with $\unicode[STIX]{x1D6FC}$. The imposed rotation not only reduces vibration amplitudes, but also makes the body vibrations less periodic. The frequency spectra revealed the occurrence of a broadband spectrum with an increase in the imposed rotation rate. Recurrence analysis of the structural vibration response demonstrated a transition from periodic to chaotic in a modified recurrence map complementing the appearance of broadband spectra at the onset of bifurcation. Despite considerable changes in flow structure, the vortex phase ($\unicode[STIX]{x1D719}_{vortex}$), defined as the phase between the vortex force and the body displacement, follows the same pattern as for the non-rotating case, with the $\unicode[STIX]{x1D719}_{vortex}$ increasing gradually from low values in Mode I of the sphere vibration to almost $180^{\circ }$ as the system undergoes a continuous transition to Mode II of the sphere vibration at higher reduced velocity. The total phase ($\unicode[STIX]{x1D719}_{total}$), defined as the phase between the transverse lift force and the body displacement, only increases from low values after the peak amplitude response in Mode II has been reached. It reaches its maximum value (${\sim}165^{\circ }$) close to the transition from the Mode II upper plateau to the lower plateau, reminiscent of the behaviour seen for the upper to lower branch transition for cylinder VIV. Hydrogen-bubble visualisations and particle image velocimetry (PIV) performed in the equatorial plane provided further insights into the flow dynamics near the sphere surface. The mean wake is found to be deflected towards the advancing side of the sphere, associated with an increase in the Magnus force. For higher rotation ratios, the near-wake rear recirculation zone is absent and the flow is highly vectored from the retreating side to the advancing side, giving rise to large-scale shedding. For a very high rotation ratio of $\unicode[STIX]{x1D6FC}=6$, for which vibrations are found to be suppressed, a one-sided large-scale shedding pattern is observed, similar to the shear-layer instability one-sided shedding observed previously for a rigidly mounted rotating sphere.

Passive pitching of splitters in the trailing edge of elliptic cylinders

The distinctive pitching of hinged splitters in the trailing edge of elliptic cylinders was experimentally studied at various angles of attack ($AoA$) of the cylinder, Reynolds numbers, splitter lengths, aspect ratios ($AR$) of the cylinder and freestream turbulence levels. High-resolution telemetry and hotwire anemometry were used to characterize and gain insight on the dynamics of splitters and wake flow. Results show that the motions of the splitters contain various dominating modes, e.g. $f_{p}$ and $f_{v}$, which are induced by the mean flow and wake dynamics. High background turbulence dampens the coherence of the regular vortex shedding leading to negligible $f_{v}$. For a sufficiently long splitter, namely twice the semimajor axis of the cylinder, dual vortex shedding mode exists close to the leading and trailing edges of the splitter. In general, the splitters oscillate around an equilibrium position nearly parallel to the mean direction of the flow; however, a skewed equilibrium is also possible with a strong recirculation region. This is the case with cylinders of low $AR$ and high $AoA$, where higher lift and drag occurs. Flow measurements at various transverse locations within the wake of the cylinder–splitter system indicate that the signature of the low-frequency splitter pitching is shifted in the wake in the cases with non-zero $AoA$ of the cylinder. Although the splitter pitching exhibits two dominant vortex shedding modes in various configurations, only the higher frequency is transmitted to the wake.

Direct numerical simulation of stratified flow past a sphere at a subcritical Reynolds number of 3700 and moderate Froude number

Direct numerical simulation of flow past a sphere in a stratified fluid is carried out at a subcritical Reynolds number of 3700 and $Fr=U_{\infty }/ND=1,2$ and 3 to understand the dynamics of moderately stratified flows with $Fr=O(1)$. Here, $U_{\infty }$ is the free stream velocity, $N$ is the background buoyancy frequency and $D$ is the sphere diameter. The unstratified flow past the sphere consists of a separated shear layer that transitions to turbulence, a recirculation zone and a wake with a mean centreline deficit velocity, $U_{0}$, that decreases with downstream distance as a power law. With increasing stratification, the separated shear layer plunges inward vertically and its roll up is inhibited, the recirculation zone is shortened and the mean wake decays at a slower rate of $U_{0}\propto (x_{1}/D)^{-0.25}$ in the non-equilibrium (NEQ) region. The transition from the near wake where $U_{0}$ has a decay rate similar to the unstratified case to the NEQ regime occurs as an oscillatory modulation by a steady lee wave pattern with a period of $t=2\unicode[STIX]{x03C0}/N$ that leads to accelerated $U_{0}$ between $Nt=\unicode[STIX]{x03C0}$ and approximately $Nt=2\unicode[STIX]{x03C0}$. Far downstream, the wake is dominated by coherent horizontal motions. The acceleration of $U_{0}$ by the lee wave and the lower turbulence production in the NEQ regime, thereby less loss to turbulence, prolongs the lifetime of the wake relative to its unstratified counterpart. The intensity, temporal spectra and structure of turbulent fluctuations in the wake are assessed. Buoyancy induces significant anisotropy among the velocity components and between their vertical and horizontal profiles. Consequently, the near wake ($x_{1}/D<10$) exhibits significant differences in turbulence profiles relative to its unstratified counterpart. Spectra of vertical velocity show a discrete peak in the near wake that is maintained further downstream. The turbulent kinetic energy (TKE) balance is computed and contributions from pressure transport and buoyancy are found to become increasingly important as stratification increases. The findings of this investigation will be helpful in designing accurate initial conditions for the temporally evolving model of stratified wakes.

Flow control with rotating cylinders

We study the use of small counter-rotating cylinders to control the streaming flow past a larger main cylinder for drag reduction. In a water tunnel experiment at a Reynolds number of 47 000 with a three-dimensional and turbulent wake, particle image velocimetry (PIV) measurements show that rotating cylinders narrow the mean wake and shorten the recirculation length. The drag of the main cylinder was measured to reduce by up to 45 %. To examine the physical mechanism of the flow control in detail, a series of two-dimensional numerical simulations at a Reynolds number equal to 500 were conducted. These simulations investigated a range of control cylinder diameters in addition to rotation rates and gaps to the main cylinder. Effectively controlled simulated flows present a streamline that separates from the main cylinder, passes around the control cylinder, and reattaches to the main cylinder at a higher pressure. The computed pressure recovery from the separation to reattachment points collapses with respect to a new scaling, which indicates that the control mechanism is viscous.

A New Miniature Wind Turbine for Wind Tunnel Experiments. Part II: Wake Structure and Flow Dynamics

An optimized three-bladed horizontal-axis miniature wind turbine, called WiRE-01, with the rotor diameter of 15 cm is designed and fully characterized in Part I of this study. In the current part of the study, we investigate the interaction of the turbine with a turbulent boundary layer. The comparison of the spectral density of the thrust force and the one of the incoming velocity revealed new insights on the use of turbine characteristics to estimate incoming flow conditions. High-resolution stereoscopic particle image-velocimetry (S-PIV) measurements were also performed in the wake of the turbine operating at optimal conditions. Detailed information on the velocity and turbulence structure of the turbine wake is presented and discussed, which can serve as a complete dataset for the validation of numerical models. The PIV data are also used to better understand the underlying mechanisms leading to unsteady loads on a downstream turbine at different streamwise and spanwise positions. To achieve this goal, a new method is developed to quantify and compare the effect of both turbulence and mean shear on the moment of the incoming momentum flux for a hypothetical turbine placed downstream. The results show that moment fluctuations caused by turbulence are bigger under full-wake conditions, whereas those caused by mean shear are clearly dominant under partial-wake conditions. Especial emphasis is also placed on how the mean wake flow distribution is affected by wake meandering. Conditional averaging based on the instantaneous position of the wake center revealed that when the wake meanders laterally to one side, a high-speed region exists on the opposite side. The results show that, due to this high-speed region, large lateral meandering motions do not lead to the expansion of the mean wake cross-section in the lateral direction.

The effect of incidence angle on the mean wake of surface-mounted finite-height square prisms

The mean wake of a surface-mounted finite-height square prism was studied experimentally in a low-speed wind tunnel to explore the combined effects of incidence angle (α) and aspect ratio (AR). Measurements of the mean wake velocity field were made with a seven-hole pressure probe for finite square prisms of AR=9, 7, 5 and 3, at a Reynolds number of Re=3.7×104, for incidence angles from α=0° to 45°. The relative thickness of the boundary layer on the ground plane, compared to the prism width, was δ/D=1.5. As the incidence angle increases from α=0° to 15°, the mean recirculation zone shortens and the mean wake shifts in the direction opposite to that of the mean lift force. The downwash is also deflected to this side of the wake and the mean streamwise vortex structures in the upper part of the wake become strongly asymmetric. The shortest mean recirculation zone, and the greatest asymmetry in the mean wake, is found at the critical incidence angle of αcritical≈15°. As the incidence angle increases from α=15° to 45°, the mean recirculation zone lengthens and the mean streamwise vortex structures regain their symmetry. These vortices also elongate in the wall-normal direction and become contiguous with the horseshoe vortex trailing arms. The mean wake of the prism of AR=3 has some differences, such as an absence of induced streamwise vorticity near the ground plane, which support its classification as lying below the critical aspect ratio for the present flow conditions.

Wake losses from averaged and time-resolved power measurements at full scale wind turbines

This work deals with the experimental analysis of wake losses fluctuations at full-scale wind turbines. The test case is a wind farm sited on a moderately complex terrain: 4 turbines are installed, having 2 MW of rated power each. The sources of information are the time-resolved data, as collected from the OPC server, and the 10-minutes averaged SCADA data. The objective is to compare the statistical distributions of wake losses for far and middle wakes, as can be observed through the “fast” lens of time-resolved data, for certain selected test-case time series, and through the “slow” lens of SCADA data, on a much longer time basis that allow to set the standards of the mean wake losses along the wind farm. Further, time-resolved data are used for an insight into the spectral properties of wake fluctuations, highlighting the role of the wind turbine as low-pass filter. Summarizing, the wind rose, the layout of the site and the structure of the data sets at disposal allow to study middle and far wake behavior, with a “slow” and “fast” perspective.

Wake meandering and its relationship with the incoming wind characteristics: a statistical approach applied to long-term on-field observations

In several papers, the importance of the atmospheric flow in the wake development of wind turbines (WT) has been pointed out, making it clear that it is necessary to have long-term on-field observations for an appropriate description of the wake development, its structure and dynamics. This work presents a statistical approach to wake meandering, yw, and the relationship that this behavior has with the incoming wind conditions and neighboring wakes. The work was developed in the framework of the French project SMARTEOLE. The study is based on a 7-month measurement campaign in which a pulsed scanning LiDAR system was used. The ground based LiDAR, measures the flow field in a segment such that the wake of two wind turbines can be captured quasi-horizontally. The analysis filters the incoming wind conditions according to the thermal stability, wind direction and wind velocity at hub height; therefore, the wakes that are developed in periods with similar wind conditions are expected to be analogous, hence meandering can be tracked and statistically analyzed. A well-defined wake evolution was found and the uncertainty analysis made on the wake meandering uncovered some interesting characteristics, including the number of samples required to reach a statistical uncertainty on the mean wake position between 2 × 10-2 D and 8 × 10-2 D for a confidence interval of 95%.

Turbulent wake behind a T-shaped plate: Comparison with a cross-shaped plate

The wake behind T-shaped intersecting flat plates has been studied by direct numerical simulations and compared with the wake behind intersecting plates forming a cross. The Reynolds number based on the uniform inflow velocity and the plate width d was 1000. Similar to the cross-plate the vortex shedding was suppressed in a 4d wide intersection region with a substantial base suction pressure reduction. Shear-layer (K-H) instabilities have been observed and its characteristic frequency obtained. In contrast to the cross-plate, a main feature of the mean wake structure behind the T-plate is the formation of two symmetrically positioned swirling vortices close to the internal corners of the T. This was examined by considering pressure contours and the turbulent production terms of mean streamwise vorticity. In spite of some similarities, major features of the wake behind the T-plate turned out to be distinctly different from the wake behind a cross-plate configuration.

Blind test comparison of the performance and wake flow between two in-line wind turbines exposed to different turbulent inflow conditions

Abstract. This is a summary of the results of the fourth blind test workshop that was held in Trondheim in October 2015. Herein, computational predictions on the performance of two in-line model wind turbines as well as the mean and turbulent wake flow are compared to experimental data measured at the wind tunnel of the Norwegian University of Science and Technology (NTNU). A detailed description of the model geometry, the wind tunnel boundary conditions and the test case specifications was published before the workshop. Expert groups within computational fluid dynamics (CFD) were invited to submit predictions on wind turbine performance and wake flow without knowing the experimental results at the outset. The focus of this blind test comparison is to examine the model turbines' performance and wake development with nine rotor diameters downstream at three different turbulent inflow conditions. Aside from a spatially uniform inflow field of very low-turbulence intensity (TI = 0.23 %) and high-turbulence intensity (TI = 10.0 %), the turbines are exposed to a grid-generated highly turbulent shear flow (TI = 10.1 %).Five different research groups contributed their predictions using a variety of simulation models, ranging from fully resolved Reynolds-averaged Navier–Stokes (RANS) models to large eddy simulations (LESs). For the three inlet conditions, the power and the thrust force of the upstream turbine is predicted fairly well by most models, while the predictions of the downstream turbine's performance show a significantly higher scatter. Comparing the mean velocity profiles in the wake, most models approximate the mean velocity deficit level sufficiently well. However, larger variations between the models for higher downstream positions are observed. Prediction of the turbulence kinetic energy in the wake is observed to be very challenging. Both the LES model and the IDDES (improved delayed detached eddy simulation) model, however, consistently manage to provide fairly accurate predictions of the wake turbulence.

Characterization of the mean flow field in the far wake region behind ocean current turbines

This paper forms, optimizes, and evaluates three numerical approaches for characterizing mean velocities in far wake region behind ocean current turbines. These approaches are derived from wake models originally developed for wind turbines and are referred here as the Larsen/Larsen, Larsen/Ainslie, and Jensen/Ainslie approaches based on the researchers originally credited with developing the expressions for dependence of the mean wake velocity on centerline and/or radial locations. The numerical coefficients utilized by these approaches are optimized to best match Computational fluid dynamics (CFD) generated wake velocity data. After optimizing the coefficients, this study finds that the Larsen/Ainslie and Jensen/Ainslie approaches best match the CFD generated flow data, with Larsen/Ainslie being the best match for an ambient turbulence intensity (TI) of 3% and Jensen/Ainslie being the best match for TIs of 6 and 9%.

Effects of Yoga and Aerobic Exercise on Actigraphic Sleep Parameters in Menopausal Women with Hot Flashes

To determine effects of yoga and aerobic exercise compared with usual activity on objective assessments of sleep in midlife women. Secondary analyses of a randomized controlled trial in the Menopause Strategies: Finding Lasting Answers for Symptoms and Health (MsFLASH) network conducted among 186 late transition and postmenopausal women aged 40-62 y with hot flashes. Women were randomized to 12 w of yoga, supervised aerobic exercise, or usual activity. The mean and coefficient of variation (CV) of change in actigraph sleep measures from each intervention group were compared to the usual activity group using linear regression models. Baseline values of the primary sleep measures for the entire sample were mean total sleep time (TST) = 407.5 ± 56.7 min; mean wake after sleep onset (WASO) = 54.6 ± 21.8 min; mean CV for WASO = 37.7 ± 18.7 and mean CV for number of long awakenings > 5 min = 81.5 ± 46.9. Changes in the actigraphic sleep outcomes from baseline to weeks 11-12 were small, and none differed between groups. In an exploratory analysis, women with baseline Pittsburgh Sleep Quality Index higher than 8 had significantly reduced TST-CV following yoga compared with usual activity. This study adds to the currently scant literature on objective sleep outcomes from yoga and aerobic exercise interventions for this population. Although small effects on self-reported sleep quality were previously reported, the interventions had no statistically significant effects on actigraph measures, except for potentially improved sleep stability with yoga in women with poor self-reported sleep quality.

Dual Orexin Receptor Antagonist, Almorexant, in Elderly Patients With Primary Insomnia: A Randomized, Controlled Study.

Sleep laboratory study to determine the dose-related efficacy and safety of almorexant in elderly patients with primary chronic insomnia. Patients aged ≥65 years with primary insomnia were enrolled into a prospective, randomized, double-blind, placebo-controlled, multicenter dose-finding study with a five-period, five-way Latin square cross-over design. Patients were randomized to one of 10 unique sequences of two-night treatment with oral almorexant 25, 50, 100, or 200 mg capsules, or matching placebo. The primary efficacy endpoint was polysomnography (PSG)-determined mean wake time after sleep onset (WASO). Secondary and exploratory efficacy endpoints were also assessed. 112 patients were randomized (mean [SD] age 72.1 [5.0] years; 69.9% female). Significant, dose-related improvements (reductions) in mean WASO were observed with almorexant. Least-squares mean (95% CI) treatment effects in the almorexant 200, 100, 50, and 25 mg dose groups versus placebo were -46.5 minutes (-53.0, -39.9; p < .0001), -31.4 minutes (-38.0, -24.9; p < .0001), -19.2 minutes (-25.7, -12.6; p < .0001), and -10.4 minutes (-17.0, -3.9; p = .0018), respectively. Mean total sleep time was significantly increased with each almorexant dose (mean increases versus placebo ranged 55.1-14.3 minutes; p < .0001 for each dose). Latency to persistent sleep was statistically significantly reduced only with almorexant 200 mg versus placebo (mean [95% CI] treatment effect -10.2 minutes, [-15.4, -5.0]; p = .0001). No unexpected safety concerns were identified. Adverse events were similar between all almorexant dose groups and placebo. Two-night oral administration of almorexant was effective and well tolerated in treating primary insomnia in elderly patients.

Sleep-Wake Concordance in Couples Is Inversely Associated With Cardiovascular Disease Risk Markers.

To determine whether interdependence in couples' sleep (sleep-wake concordance i.e., whether couples are awake or asleep at the same time throughout the night) is associated with two markers of cardiovascular disease (CVD) risk, ambulatory blood pressure (BP) and systemic inflammation. This community-based study is a cross-sectional analysis of 46 adult couples, aged 18-45 years, without known sleep disorders. Percent sleep-wake concordance, the independent variable, was calculated for each individual using actigraphy. Ambulatory BP monitors measured BP across 48 h. Dependent variables included mean sleep systolic BP (SBP) and diastolic BP (DBP), mean wake SBP and DBP, sleep-wake SBP and DBP ratios, and C-reactive protein (CRP). Mixed models were used and were adjusted for age, sex, education, race, and body mass index. Higher sleep-wake concordance was associated with lower sleep SBP (b = -.35, SE = .01) and DBP (b = -.22, SE = .10) and lower wake SBP (b = -.26, SE = .12; all p values < .05). Results were moderated by sex; for women, high concordance was associated with lower BP. Men and women with higher sleep-wake concordance also had lower CRP values (b = -.15, SE = .03, p < .05). Sleep-wake concordance was not associated with wake DBP or sleep/wake BP ratios. Significant findings remained after controlling for individual sleep quality, duration, and wake after sleep onset. Sleep-wake concordance was associated with sleep BP, and this association was stronger for women. Higher sleep-wake concordance was associated with lower systemic inflammation for men and women. Sleep-wake concordance may be a novel mechanism by which marital relationships are associated with long-term CVD outcomes.

A Sleep Hygiene and Relaxation Intervention for Children With Acute Lymphoblastic Leukemia: A Pilot Randomized Controlled Trial.

Background:Sleep disturbance and fatigue are common and distressing pediatric cancer-related outcomes. Sleep hygiene education and relaxation techniques are recommended to improve sleep in healthy children and adult cancer survivors. No studies have tested these interventions to improve sleep and fatigue for children with acute lymphoblastic leukemia (ALL) in the home setting.Objectives:The aim of this study is to establish the feasibility and acceptability of a sleep hygiene and relaxation intervention to improve sleep and fatigue for children receiving maintenance chemotherapy for ALL. The child's fatigue and sleep data were collected to inform sample size calculations for a future trial.Methods:In this pilot randomized controlled trial, 20 children were allocated randomly to the sleep intervention or control group. The sleep intervention group received a 60-minute educational session to discuss sleep and fatigue in children with cancer and strategies to improve sleep, including use of 2 storybooks to teach deep breathing and progressive muscle relaxation. Objective sleep data were collected using actigraphy and fatigue was measured using the Childhood Cancer Fatigue Scale.Results:The intervention was acceptable to families, and feasibility of the intervention and data collection was clearly established. Although not statistically significant, increases in mean nighttime sleep and decreases in mean wake time after sleep onset in the sleep intervention group represented clinically important improvements.Conclusions:This pilot study demonstrated the feasibility and acceptability of a sleep hygiene and relaxation intervention for children undergoing maintenance chemotherapy for ALL.Implications for practice:Given the clinically important improvements in sleep observed, replication in a larger, adequately powered randomized controlled trial is merited.