Fakopp DynaTree User manual

Manual for the
DynaTree dynamic root evaluation system
2018.
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Table of Contents
Introduction......................................................................................................................................2
The pulling test................................................................................................................................3
The DynaTree dynamic root evaluation system..............................................................................4
How does DynaTree wor ?.............................................................................................................5
Some considerations concerning the measurement.........................................................................7
The distance between the measured tree and the anemometer...................................................7
Wind velocity..............................................................................................................................7
Statistical approach.....................................................................................................................7
Multiple measurements...............................................................................................................8
Advantages and disadvantages....................................................................................................8
System components.........................................................................................................................9
Anemometer................................................................................................................................9
Dual axis inclinometer................................................................................................................9
Extensiometer............................................................................................................................10
DynaTree software....................................................................................................................11
Operation guide..............................................................................................................................12
Inclinometer setup.....................................................................................................................12
Anemometer setup....................................................................................................................14
Extensiometer setup..................................................................................................................14
Transferring data from the SD card to a different device..........................................................15
Analysis using the DynaTree software......................................................................................39
Transferring data wirelessly on Windows.................................................................................43
Footnotes..............................................................................................................................44
Introduction
The stability of urban trees is a ey question that affects everyone. Diseased and unstable urban
trees pose much ris for everyone, and are a serious liability for municipalities in case of an
accident. Tree stability assessment is therefore of the utmost importance. In the meantime it tends to
be much neglected in many areas.
At present, there is only one accepted method for tree stability assessment. The pulling test, while
well established and accepted, has several drawbac s, both in terms of reliability and ease of use.
Dynamic root stability determination is based on real life wind loads, and is therefore more
appropriate for assessing real life ris s. It is also much simpler to carry out than the traditional
pulling test, with the only drawbac being that it requires windy weather to carry out.
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The pulling test
Figure 1: Schematic of the pulling test.
The pulling test is based on affixing a cable at approximately mid-height on the tree to be evaluated,
and applying a moderate load, while measuring the inclination at the base of the trun . The induced
inclination is very moderate (less than .25 degrees), to ma e sure that the test itself does not damage
or start uprooting the tree. Based on the measured load, it is possible to extrapolate to the
approximate torque required to uproot the tree. The maximum torque that may arise due to adverse
weather conditions can also be calculated based on the crown surface, aerodynamic drag factor and
the maximum wind velocity li ely to occur in the area. The ratio of the two values is the safety
factor (SF) of the given tree. If this value is above 1.5, the tree is declared safe, while a SF below 1
signals high ris . In-between these two values, the safety of the tree is considered uncertain.
The advantage of the pulling test is that it is a fairly straightforward, well-researched and
established method. On the other hand, the applied static load approximates the real life situation,
where trees are subjected to dynamic loading, rather poorly. It is also quite cumbersome; requires
heavy equipment (high capacity cable and ratchet) and a ladder to be carried to the test site, lengthy
preparation and physical exertion during testing. The pulling cable has to be fastened to some well-
secured object on the ground (li e another tree trun or stump) that may or may not be readily
available.
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The DynaTree dynamic root evaluation system
It would be much simpler to use the loads that arise from the actual wind rather than a loaded cable,
to assess the tree’s safety in a high wind situation. There are, however, two interrelated problems
that ma es this very complicated:
1. Trees consist of a complicated networ of trun , major, minor branches, twigs and (in the
summer) leafs. This situation is not unli e a multiple pendulum that reacts to loading in a
very unpredictable, erratic manner, when the load is not applied directly to the trun (as is
the case in the pulling test).
2. As a result, there is no direct relationship between the wind load (wind velocity) and the
immediate response of the tree, i.e. no correlation between the load and the inclination of the
trun (see Figure 2).
Figure 2: Two-dimensional time series plot of inclination and wind velocity.
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The behavior of a tree in the wind is highly sensitive to the initial conditions. Small differences in
initial conditions yield widely diverging outcomes for such dynamic systems (a situation popularly
referred to as “the butterfly effect”). It is impossible to predict the behavior of such systems on the
long run. A definite relationship exists between the wind velocity and the inclination of the tree, but
it is a complex relationship, not one of immediate cause and effect. One way to evaluate such
systems is using statistical parameters of the data ta en over longer intervals. There is no immediate
relationship between the wind velocity and the inclination at any given moment, but there is a
relationship between their averages and other statistical parameters observed over a longer interval.
The DynaRoot system ta es advantage of this statistical relationship.
How does DynaTree work
Figure 3: Components of the DynaTree system
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The DynaTree system consists of four components (see Figure 3):
1. Anemometer: an instrument for measuring wind velocity at or near the tree to be evaluated.
The closer to the better, but, depending on wind velocity DynaRoot may provide reliable
data even with measurements ta en several ilometres / miles away. The anemometer
provides wind velocity data of sufficient frequency, Ideally the anemometer should be clear
of buildings or other objects that may obstruct the wind, at a height of at least 10 m.
2. Inclinometer: an instrument affixed to the root collar that measures the inclination of the
trun in two different directions. The instrument provides very accurate inclination data with
sufficient frequency.
3. Extensiometer: an instrument attached to the trun for measuring the micro elongation of the
trun
4. Evaluation software: a PC software for evaluating wind velocity, x and y inclination. The
data, recorded over a period of several hours, are transferred from the anemometer and
inclinometer on memory cards or wirelessly via Wi-Fi. The software brea s the data down
into shorter intervals, and calculates statistic parameters for each interval that are used for
the tree stability evaluation.
The Safety Factor calculation is not unli e the one used for the pulling test, except, in this case,
wind pressure is used instead of force, and statistical parameters used instead of the momentary
wind pressure and inclination values. There is a tangential relationship between the wind pressure
and the inclination of the tree, and the critical wind pressure can be calculated from the curves (see
Figure 4).
Figure 4: Relationship between the wind pressure and the inclination
This critical value is used for calculating the SF, which is interpreted much the same way as the one
calculated from the static pulltest.
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Figure 5: An important condition for DynaRoot to be applicable is a sufficiently large wind speed.
Some considerations concerning the measurement
The distance between the measured tree and the anemometer
The intensity of the wind gusts may be different from location to location, even within a relatively
small area. The relationship between wind intensity and inclination is obviously closer if wind
velocity is measured close to the tree. Nevertheless, fairly accurate correlations can be achieved if
the anemometer is located within 1.5 m (1 mile) of the tree, and meaningful data has been
collected when the distance was as high as 5 m (3 miles), unless wind gusts originate from
localized weather events (li e a tornado). It is, of course, best to set up the anemometer close to the
measured tree, but this may not always be possible due to the terrain constraints. It is also possible
that we want to assess multiple trees, or we want to use data from a nearby weather station (possible
if they can provide at least one wind velocity reading per second). As long as wind data is collected
reasonably close, the evaluation is possible.
Wind velocity
The most important condition for the application of this technique is windy weather. The higher the
wind, the better the accuracy of the measurement. The minimum requirement is a wind speed of at
least 25 m/h ~15 mph (see Figure 5).
Statistical approach
As mentioned before, instead of using momentary wind velocity and inclination data, values are
collected over a longer period, and several minutes’ worth of information is evaluated statistically.
The accuracy of the data (the tightness of the correlation) depends on the time interval (see
Figure6).
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Figure 6: Relationship between averaging time and the resulting correlation coefficient
The time interval may be specified in the software when evaluating. 10 minutes provides the best
results; however, this also means that long measurement periods are required to collect enough data
points. 5 min (default setting) or even 2 min measurement intervals offer more data points without
seriously compromising the accuracy of the measurements, if wind velocity is measured nearby. (If
wind velocity is measured more than 1.5 m or 1 mile away, we recommend long collection periods
and using 20-minute intervals for the statistics.)
Multiple measurements
The efficiency of the DynaRoot system multiples when measuring several trees simultaneously.
This is possible, because – unli e in the case of the pulling test – the operator doesn’t have to
supply the pulling load for each tree. The only thing required is a relatively inexpensive
inclinometer mounted on each tree to be evaluated, while the same anemometer can provide the
wind velocity data for each tree (within a radius of several ms or miles). There is no theoretical
limit to the number of trees to be assessed simultaneously.
Advantages and disadvantages
The DynaRoot system offers inclination measurements under real life wind load conditions, which
is a better approximation of the actual situation that eventually leads to the uprooting of a tree, and
therefore may be a more reliable measurement than the pulling test. It is also easier to set up and
carry out; no need for heavy equipment, ladders and physical exertion during the test. There are
only two disadvantages to this measurement. One is that sufficiently high wind velocities (at least
25 m/h or 15 mph) are required, which may be a problem when urgent results are expected. The
other issue is that the measurement is more time consuming than the traditional pulling test.
However, it does not require constant monitoring – after setup, the system can be left alone for the
several hours required to collect the data. It can also be more efficient then the traditional test when
measuring multiple trees simultaneously. Table 1 compares DynaRoot to the traditional pulling test.
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Issue Pulling test DynaTree
Required equipment Cable, ratchet, load cell, ladder,
inclinometer (approx. 50 g)
Anemometer, inclinometer,
extensiometers (approx. 10 g)
Load Static Realistic
Time required 1-3 hrs / tree 3 hrs / several trees
SF calculation Crown area, drag factor and
critical wind speed required
Only critical wind speed required
Weather conditions Wind speed < 25 m/h Wind speed > 25 m/h
Table 1: Comparison of DynaRoot and the traditional pulling test
System components
Anemometer
• Dual axis ultrasonic wind velocity meter
• Sampling rate: 1 Hz
• Measurement range: 0-150 m/h
• Accuracy: 0.2 m/h
• Integrated GPS
• Data storage capacity: 8 GB (SD card)
• Best location: open field, 10 m height,
undisturbed by buildings or other large
objects
• Completely weather proof
Dual axis inclinometer
• Measurement range ±2 degrees
• Resolution: 0.001 degree
• Temperature compensated
• Sampling rate: 10 Hz
• Integrated GPS
• Data storage capacity: 8 GB (SD card)
• Mounted by a single screw
• Operating voltage and current: 12V, 20 mA
• Completely weather proof, IP65
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Extensiometer
• LVDT extensiometers
• Dimensions: 30x30x270 mm (closed)
• Span: 250 mm
• Sampling rate: 1 Hz
• Resolution 0.3 μm
• Power source 2 pcs. of 9 V batteries
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