Foundation and deflection monitoring device

A foundation shift detection device includes a foundation portion attached to a foundation to be monitored, a base portion attached to a base adjacent to the foundation and supporting the same, and a rotary indicator attached to the base portion and adapted for rotation responsive to displacement of the foundation relative to the base. The rotary indicator is visible to a casual or walking inspection from a moderate distance, as by a human inspector making a walking inspection of a number of such devices.

BACKGROUND

Foundations and load-bearing structures, although intended to remain fixed, can be subject to shifting and subtle movement from environmental, geological, and construction inefficiencies, degradation, and oversights. Of particular concern are wind turbine towers, for which dynamic forces and high fatigue loading may result in foundation failures and potentially reduce the expected design life.

SUMMARY

A foundation shift detection device includes a foundation portion attached to a foundation to be monitored, a tower base portion attached to a base adjacent to the foundation and supporting the same, and a rotary indicator attached to the tower base portion and adapted for rotation responsive to displacement of the foundation relative to the base. The rotary indicator is visible to a casual or walking inspection from a moderate distance, as by a human inspector making a walking inspection of a number of such devices.

Configurations herein are based, in part, on the observation that load-bearing concrete structures, despite their permanency and immobility, are subject to subtle shifting or settling or vibration, often from environmental forces. Of particular consideration are tower structures, such as for wind turbines, which tend to focus a concentrated force on a relatively small bearing area, and are subject to dynamic loads from the natural variance of the wind they are designed to respond to. Often, such as in fixed building structures, foundation settling is expected to some degree and the building load is sufficiently distributed to avoid damaging results. In other contexts, such as wind turbine towers, substantial temporary loads may be imposed on the foundation. Unfortunately, conventional approaches to tower foundation monitoring involve complex and expensive sensor monitoring techniques, such as strain gauges and finely tuned movement detection. This type of analysis is often undertaken only after visible foundation compromise has been observed, by which time remedial measures may be ineffective. Still worse, catastrophic failure such as collapse is possible if early detection of subtle foundation movement remains unnoticed.

In the context of a wind turbine tower, the structure tends to be subjected to substantial loads from the rotation of blades attached to a rotor for driving a power generator. Although wind turbines exhibit an increased potential for foundation shifting, any fixed foundation or load bearing structure may benefit from monitoring of incremental (on the order of 1-10 mm) shifts due to settling, loads or cracking. In a foundation prone to periodic shift or movement between the foundation and a fixed base, the passive foundation shift detection device as described herein includes a biased displacement member, such that the biased displacement member has a force bias tending to dispose the displacement member against an interference member. The interference member is adapted to permit incremental displacement of the biased displacement member based on movement of the foundation relative to the fixed base. The biased member includes a spring or tension loaded linear or rotary member that is prevented from travel only by the interference member attached to the foundation being monitored. Upon a small shift or even a temporary deflection (as in a tower swayed by wind), the interference member is drawn out of interference, and allows the biased member to travel a visually detectable degree. The visually detectable degree is such that it is observable by a casual sight inspection, while the movement resulting in the shift (1-10 mm) may not be visually detectable. Alternate configurations include applications to monitor the excessive motion of heavy machinery, such as monitoring excessive motion between mechanical components (e.g. motion between a frame or mount and a gearbox or bearing.

DETAILED DESCRIPTION

Depicted below is an example configuration of the foundation shift detection device in conjunction with a wind turbine tower. These towers are often built in close succession, lending themselves well to frequent but casual inspection from a “walk through” of a wind farm of multiple towers. Regarding terminology, a “foundation” may be defined as the lowest load-bearing part of a building, often below ground level. In the discussion herein, the foundation of the tower includes the bearing structure immediately under the tower (typically a concrete or reinforced concrete slab structure). The base refers to an adjacent, fixed mass to which movement relative to is measured. The base may be beside, or may extend beneath, the foundation. Generally, the foundation meets the base at a normal or substantially normal juncture, where a vertical foundation surface meets a horizontal base mass (typically both will be generally stationary concrete masses). The approach is applicability to other contexts where a vertical foundation surface to be evaluated for shifting/movement meets a stable, horizontal base surface against which relative movement is to be measured.

FIG. 1is a wind turbine environment100suitable for use with configurations herein. Referring toFIG. 1, a turbine110includes blades112attached to a rotor114that attaches to a generator and related mechanicals in a nacelle116that is rotatable to correspond to wind changes. The nacelle116pivots atop a tower120supported by a foundation122resting on a base124. In a foundation122prone to periodic shift or movement between the foundation122and a fixed base124, a passive foundation shift detection device150is placed in a perpendicular juncture between surfaces of the foundation122and the base124. The base124may be any substantial mass adjacent and/or beneath the foundation.

The examples herein depict the foundation122of the tower120on the base124. External forces, most notable wind, act on the tower120as shown by arrows102. Foundation cracking, excessive tower motion, settlement of a tower, or tilt, are some common failure patterns of deteriorating onshore wind turbines. The dynamic forces combined with high fatigue loading subjected on an aging wind turbine could result in foundation failures and may impact the designed service life. The cyclic loading subjected on the wind-turbine foundation system could also lead to modulus degradation of the foundation system.

A particular anomaly with tower foundations is transient conditions that may cause the tower to resiliently sway or flex, resulting in a temporary shift between the foundation122and base124, which retracts after the sway or flex movement subsides. Periodic measurements of the static structure will not reveal subtle periodic movements until much more substantial or catastrophic movement results. It would be beneficial to provide a device that passively measures any movement exceeding a threshold and retains the measured reading until subsequent inspection.

FIG. 2is a schematic diagram of the disclosed approach in the environment ofFIG. 1. Referring toFIGS. 1 and 2, a biased displacement member160(either rotary or linear), has a force bias shown by arrow162tending to dispose the displacement member160against an interference member152. The interference member152is adapted to permit incremental displacement of the biased displacement member based on movement of the foundation relative to the fixed base124. A distal portion of the interference member152defines an interference region154, while a proximate end155is fixed to the foundation122to displace with the foundation122. Upon foundation displacement, shown by arrow161, of a magnitude greater than the width of the interference region154, the displacement member160rotates in the biased direction162.

The displacement member160(rotary indicator) has a cam shape responsive to rotational increments based on linear movement of the foundation122reflected by the interference member152. The displacement member160has a plurality of radial sections165-1. . .165-N (165generally), and each radial section corresponds to an incrementally increasing radius portion of angular rotation of the displacement member160. Each radial section165has a progressively increasing radius166. The radii increase an increment from a previous radial extension based on a detection granularity of the foundation shift detection device. The displacement increment is typically between 1 mm and 2 mm, but may be any suitable increment.

The displacement member160continues rotation until an interference region154′ of the next radial increment corresponding to the successive radial section165. A visual marker170is attached to the displacement member160, such that the visual marker170is indicative of the movement based on an unmagnified visual inspection. The displacement of the displacement member160is greater than a movement of the interference member152that resulted in the displacement. Therefore, if the interference region154has a width of 2 mm, then advancement to the interference region154′ results from a foundation shift of 2 mm. At the same time, the visual indicator rotates by an angular degree equal to the radial section165. In this manner, a barely measurable or visible foundation shift of 2 mm translates to a radial difference of an angular section165, which is again translated to movement of visual indicator170magnified by the length of an indicator spoke172. The visual marker170attached to the displacement member160is indicative of the movement based on an unmagnified visual inspection. In a wind farm of many turbine towers120, a device150with visual indicators170adorned with bright colors and sufficient area, initialized to, say, extend horizontally, will result in a near upright positioning of the visual indicators170for towers experiencing a shift of 2 mm. An inspection involves merely walking along a row of towers120looking for visual indicators170pointing up instead of out.

FIG. 3is a perspective view of a foundation shift detection device as inFIG. 2. Referring toFIGS. 2 and 3, in implementation of the foundation shift detection device150, a fixed attachment to both the foundation and the base is employed. Further, the cam shape ofFIG. 2should avoid compression between the displacement member160and interference member, since if the interference member152just clears the displacement member on a transient shift, a return to a rest position may compress the interference member152in the advanced position of the displacement member160.

The foundation shift detection device150shown inFIG. 3includes a foundation portion300attached to the foundation122to be monitored, and a tower base portion310attached to the base124adjacent to the foundation122. The displacement member160takes the form of a rotary indicator360attached to the tower base portion310and adapted for rotation responsive to displacement of the foundation122relative to the base124.

Each radial section165defines a portion of angular rotation of the rotary indicator360, similar to the cam shaped displacement member160. However, each radial section165is defined by a hollow wedge365-1. . .365-N (365generally) having a rigid portion176for engaging the interference member and a void178defining a separation between a rigid portion of an adjacent hollow wedge365. Each hollow wedge365-N is therefore defined by the respective rigid portion176and void178. Once the interference member152displaces sufficiently to allow advance of the rotary indicator360to the next hollow wedge365, the interference member152passes through the void178and engages the next rigid portion176. This avoids binding and compression of the interference member122in a close tolerance with a recently advanced displacement member160.

FIG. 4Ais a plan view of the foundation detector ofFIG. 3, andFIG. 4Bis a side elevation of the foundation detector ofFIG. 3. Referring toFIGS. 3, 4A and 4B, the interference member152attaches to the foundation portion300and is in communication with the rotary indicator360. A biasing spring314atop a shaft312provides rotational bias to the rotary indictor360so that constant pressure (bias) is exerted to advance the rigid portion176of each hollow wedge365past the interference member152. Each rigid portion176has an incrementally greater radial extension367-1. . .367-4(367generally), such that the length of the radial extension367causes engagement with the interference member152based on the displacement of the foundation122.

Since the rotary indicator360has a rotational bias in the direction of increasing radial extensions367, the rigid portion176is engaged in an interference with the interference member152for preventing biased rotation. Each rigid portion176, however, is responsive to release upon foundation displacement drawing the interference member152out of interference with the rigid portion176for permitting rotation of the rotary indicator360into interference engagement of the rigid portion176of a successive radial extension367-N+1.

FIGS. 5A-5Dshow operation of the foundation detector device150responding to incremental foundation shifts. Continuing to refer toFIGS. 4A and 4B, and toFIG. 5A-5D, a progression of rotation from hollow wedges365-1. . .365-4is shown. InFIG. 5A, the rigid portion176of wedge365-1is biased against the interference member152, secured to the foundation122by a fixation assembly153. The interference member152may be affixed to the foundation122by any suitable approach, such as adhesive, concrete anchors, magnetics, or other suitable attachment.

InFIG. 5B, the foundation shifts and retracts 2 mm to define foundation122′. Accordingly, the interference member152is drawn back 2 mm and out of interference with hollow wedge365-1. The bias advances the rotatory indicator until the rigid portion176of the next hollow wedge,365-2, engages the interference member152, since it has a radial extension367-22 mm greater than radial extension367-1. At the same time, visual indicator170is rotated to allow distant inspection (about 60 degrees). Since the rotary indicator360employs a radial “wedge” shape for each increment, rotation of the rotary indicator360advances an outermost point on the rigid portion176a greater distance than a movement of the interference member152that resulted in the rotation. In other words, a foundation122shift of 2 mm results in a 60° rotation of the rotary member360, magnified by the radius at the outermost point of the rigid portion176, and further enhanced by the length of the indicator spoke172and visual indicator170.

Any suitable radial increment may be employed, but in practice an increment of one or 2 mm is expected. Approximately 4 hollow wedges on a rotary member therefore provide a range and granularity of 1, 2, 3, and 4 mm or 2, 4, 6 and 8 mm.

FIG. 5Cdefines a further foundation deflection of 4 mm by the foundation122″. Hollow wedge365-3advances, and visual indicator170advances another 60° increment.FIG. 5Ddepicts the full displacement range of 6 mm as hollow wedge365-4is rotated into interference at foundation122′″ position. The visual indicator170has now advanced a full half rotation (approximately) from the starting position exhibited with an unshifted foundation.

Additional rotary increments may of course be employed to increase the granularity and/or range of shift detection.

FIG. 6is an alternate configuration adapted for a vertical component of movement. Referring toFIG. 6, the rotary indicator360mounts on a horizontal shaft312and the interference member152has a vertical orientation. Other suitable orientations may be provided, disposing the rotary indicator360at an axis of rotation substantially perpendicular to the interference member152for accurate shift detection. In a further configuration, a single rotary indicator360may be employed for both horizontal and vertical foundation shift detection.

In a further configuration, the interference member152can be resisted by a set of wedges (365-1,2,3, and4) having a rigid portion for engaging the interference member152that increase length as well as in width to provide an indication of motion in both the horizontal and vertical directions using a single cam indicator as the displacement member160.

Various alternatives may be envisioned to implement the method for measuring periodic and temporary foundation shifting by disposing a foundation portion having an interference member152on a foundation to be monitored, and disposing a tower base portion on a base124adjacent the foundation122to be monitored, such that the tower base portion124is in communication with the foundation portion122. The device150is configured for measuring a maximum relative movement of the foundation122relative to the base124by displacement of the displacement member160. In the examples shown, this results in the rotary indicator360, in interference with an interference member152attached to the foundation122, is such that foundation movement drawing the interference member out of interference with the displacement member160allows incremental advance of the displacement member160.

Visibility is enhanced to allow casual inspection because displacement of the displacement member is greater than a movement of the interference member that resulted in the displacement. Further, disposing a visual marker attached to the displacement member responsive to the movement of the tower base portion facilitates observation of the visual marker indicative of the movement based on an unmagnified visual inspection.