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Article · March 2015
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Magdy Bakry
Al-Azhar University
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Consultants
Civil Engineering
مهندســــون إستشــاريــــون
هندسة مدنية
: المشكلة القائمة
أثناء تشغيل وحدات أنتاج المياه (التشليرات) الموجودة بدور البدروم لوحظ وجود
أهتزازات بأرضية الدور األول
باألشارة ألي الموضوع عاليه فأننا نتشرف بتقديم العرضين الفني و المالي األتيين
VIBRATION ISOLATION OF CHILLERS (air
conditioning
compressor) 140-500 Tons (60 Hz), 140-400 Tons (50
Hz)
General:
Floor vibrations results from high static deflections
which can vary from 10 mm to 30+ mm leading to
vertical natural frequency ranging from 5 Hz to less
than 3 Hz.
Possible Solutions
The best solution to a vibration problem is to
avoid it in the first place. Intelligent design is far
more cost effective than building a bad design
and having to repair it later. The intelligent
Solution to any vibration problem involves the
following steps:
1) Characterize the system parameters (mass,
stiffness, damping) by experimental methods,
- مدينــه ركن حلوان الجديـــدة- ح تقسيــم جمعيـــة النصر4 قطعة
المعــــادى- كورنيش النيـــل
Mobile : 01014555350
Consultants
2
Consultants
Civil Engineering
مهندســــون إستشــاريــــون
هندسة مدنية
Manufacturer’s data, or a combination of both.
2) Model the system dynamics using a simple
lumped parameter model
a) Identify natural frequencies, look for
coincidence with excitation frequencies
b) if excitation forces and frequencies are known,
system response can be calculated
3) Use the model to assess the effect of changes in
system parameters
Vibration Solutions - Source
1) Relocate machine – place machine on as
rigid a foundation as possible (on grade is best)
and as far as possible from potential receivers
2) Replace machine with a higher quality or
different type of machine that is quieter (and
probably more expensive)
3) Change the operating speed of the unit to
avoid coinciding with structural resonances
4) Balance rotating elements,
5) Add a tuned vibration absorber
6) Use active vibration control
- مدينــه ركن حلوان الجديـــدة- ح تقسيــم جمعيـــة النصر4 قطعة
المعــــادى- كورنيش النيـــل
Mobile : 01014555350
Consultants
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Consultants
Civil Engineering
مهندســــون إستشــاريــــون
هندسة مدنية
Vibration Solutions - Path
Minimizing the vibration transmission generally
involves using isolator springs and/or inertia
blocks. The basic principle is to make the natural
frequency of the machine on its foundation as
far below the excitation frequency as possible.
The mathematics for this case, and isolator
selection procedures are discussed in the next
sections.
Vibration Solutions – Receiver
1) Change the natural frequencies of the
system to avoid coinciding with excitation
frequencies. This can be accomplished by
adding stiffeners (which raises the natural
frequency) or by adding mass (which lowers the
natural frequency)
2) Add structural damping
Vibration isolation problems can be divided into two
main groups:
Firstly, the need to reduce the transmission of
vibration from a machine to the structure supporting
- مدينــه ركن حلوان الجديـــدة- ح تقسيــم جمعيـــة النصر4 قطعة
المعــــادى- كورنيش النيـــل
Mobile : 01014555350
Consultants
4
Consultants
Civil Engineering
مهندســــون إستشــاريــــون
هندسة مدنية
it, these applications are usually solved fairly simply
and with readily available isolation products. The
fundamental rule of isolator selection can be stated as
follows: ‘The natural frequency of an isolation system
is in proportion to the linear deflection of that system
from the unloaded state.
Reducing Force Transmission from Machine to
Structure. The starting point is to determine the
lowest forcing frequency of the machine. Usually this
is determined by the lowest shaft speed in the
machine because of the potential residual unbalance
of that component.
The second group is the reverse of the above – the
need to reduce the transmission of vibration from a
vibrating structure to a machine or some equipment
supported by it, e.g. isolation of sensitive electrical
equipment from excessive building vibrations.
The solution of these problems generally requires a
lot more careful consideration if a good outcome is to
be achieved. Structural vibration generally arises
from machinery mounted on the structure that may
have forcing frequencies from (typically) 12 to 25 Hz.
Isolation may be required for operator comfort,
- مدينــه ركن حلوان الجديـــدة- ح تقسيــم جمعيـــة النصر4 قطعة
المعــــادى- كورنيش النيـــل
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Consultants
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مهندســــون إستشــاريــــون
هندسة مدنية
electrical or instrumentation protection or to
minimize false brandling of stationary machine
bearing.
General Remarks
A well compacted granular base course is strongly
recommended.
Base course thickness to be determined in
consultation with vibration, structural, and
geotechnical engineers
Steel framing works well.
Reinforced Concrete Framing is preferable especially
when Mechanical equipments are close to vibration
sensitive tools.
Concrete offers advantages over steel: much higher
stiffness, more damping, and larger mass,
redundancy, less sensitive to short duration
temperature fluctuations
Mitigating Vibrations from unavoidable sources.
- مدينــه ركن حلوان الجديـــدة- ح تقسيــم جمعيـــة النصر4 قطعة
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Consultants
Civil Engineering
مهندســــون إستشــاريــــون
هندسة مدنية
Selection of rotating equipment with stringent
balancing requirements (e.g. 0.025 in/sec RMS).
Spring support for rotating equipment.
Inertia bases are generally recommended for
supporting fans and pumps with sizable HP motors.
There are differing opinions on whether rotating
equipments should be rigidly mounted or spring
mounted.
Place heavy equipment on concrete housekeeping
pads, as close as possible to stiff elements (beams and
columns).
Flow carrying pipe and ducts near connected
equipments supported using spring hangers. Use
flexible connectors at equipments, to accommodate
relative motions and vibration Isolation.
Major pumps and fans could be instrumented with
accelerometers.
When Variable Frequency Drives (VFD) are used,
they may need to be programmed to avoid resonance.
- مدينــه ركن حلوان الجديـــدة- ح تقسيــم جمعيـــة النصر4 قطعة
المعــــادى- كورنيش النيـــل
Mobile : 01014555350
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مهندســــون إستشــاريــــون
هندسة مدنية
Consultants
Civil Engineering
العرض المالي:
-1يشمل العرض المالي أجراء قياسات األهتزازات أن لزم األمر و أجراء التحليل
الديناميكي لنتائج القياسات و كذلك أجراء تحليل ديناميكي أنشائئ كامل للتشليرات
و قواعدها المرتكزة عليها و أعطاء توصيات كاملة و فعالة لحل مشكلة
األهتزازات تماما و األشراف علي تنفيذ الحلول المقترحة في التقرير المفصل الذي
سوف يقدم فيما بعد
هذا و يجب التنويه ألي أنه من الوارد أجراء بعض األختبارات علي تربة التأسيس
أسفل التشليرات
نرجوا أن يحوز عرضنا هذا رضاكم الكريم و هللا سبحانه و تعالي ولي التوفيق
و تفضلوا بقبول فائق التقدير و األحترام
المهندس األستشاري مجدي عبد المحسن
5802\80\80
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قطعة 4ح تقسيــم جمعيـــة النصر -مدينــه ركن حلوان الجديـــدة -
كورنيش النيـــل -المعــــادى
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