The implementation was introduced.
Noise reduction can be achieved by: eliminating noise sources; blocking the AcMeialElectronicPul propagation path to attenuate noise during propagation; protecting the receiver iki.i 1 diesel generator set noise problem 1-1 generator set noise generator set noise Sources include: exhaust noise; mechanical running friction noise; combustion noise; cooling fan, exhaust channel noise; intake noise; generator rotating noise; unit vibration and noise.
The noise frequency of the diesel generator set is generally 30 Hz 8 kHz and the intensity is between 80 dB (A) and 120 dB (A). The noise propagates to the space in the form of radiation and vibration from the generator unit fuselage, the common base, the intake and exhaust manifold, etc. by means of air medium.
1-2 Noise Hazard The harm of noise is multi-faceted: under the stimulation of high noise, the attention of power supply personnel is not easy to concentrate, irritability, fatigue, slow response, slow working speed, and degraded work quality. Causes deafness and even causes an accident. The noise standard of industrial enterprises promulgated by the Ministry of Labor and Social Security stipulates that the noise standard of the workplace is not more than 85dB. (A) Table 1 noise and allowable working hours of workers are short-time - some high-precision equipment In addition to the basic quality assurance, the requirements for power supply also have special requirements for the power supply equipment, including the electromagnetic field interference limits of the power supply equipment to the load equipment. If the generator set does not make a certain magnetic shielding, it will have a strong interference effect on the automated production equipment and affect the normal operation of the high-precision equipment.
Seriously affected the communication quality within the communication hub (vehicle).
Larger environmental noise pollution also has an impact on the normal life of nearby residents. Noise above 50dB(A) will affect residents' sleep, and strong noise will also affect people's health.
2 Mechanism of noise reduction and ear and body. The following focuses on the introduction of barrier transmission routes. sound. Generally, the average door and window is separated by 1520dB(A), and the special door and window barrier propagation path includes resistive noise reduction and resistance noise reduction. Can drop 30dB (A). After the system noise reduction treatment can be reduced by 40dB (A), the seams should be strict. The best way to control the low- and medium-frequency noise is to eliminate the sound hole, and the micro-perforation is more empty. For low-frequency noise, the sound absorbing material is often not very effective, and the sound absorbing structure can be used. That is, a hole having a certain porosity is placed on the metal plate and the thin wood, and a cavity is provided thereafter. The air in the neck of the small hole moves back and forth like a piston under the action of sound waves. When the sound wave enters the neck of the hole, part of it is converted into heat energy due to the friction and damping of the neck wall. The general engine's resistant muffler works on this principle.
3 Noise reduction measures for generator sets The following sections analyze the working environment of the generator set and various aspects of the sound source and propose noise reduction measures.
The general unit has a certain isolation ring and pad. When checking the unit, pay attention to check whether the height is qualified. The vibration isolation of the unit and the machine room can be solved by digging a ring cable draining ditch around the unit, using cinder, asphalt and other damping materials at the bottom.
In the machine room, the sound insulation and noise reduction measures are required to fill the wall of the machine room. The gray seam is required to be filled, full, without holes, gaps, and the interior wall is painted. The surface should not be dense and smooth. The powder material is mixed with a certain amount of porous sound-absorbing effect. Sexual material. For example, a sound absorbing layer composed of cement, lime paste and wood chips. The sound absorbing material covering the surrounding area, the ceiling and the ground and covering the metal soundproofing plate have the functions of noise reduction and electromagnetic shielding.
The machine room and the operation room are separated by a partition wall, and the observation window of the two-layer glass is excavated on the partition wall. The glass is made of float glass of 6mm or more, and the interval between the two layers of glass is not less than 80mm, and the inner glass facing the machine room is slightly inclined to reflect the noise to the ground. The noise in the operating room between glass, window and wall can be controlled below 75dB(A).
In terms of equipment selection, low noise units are preferred. The concentricity of the single-support generator is easily ensured, which reduces the vibration and noise of the unit. For example, the D6114ZDA diesel unit is nearly 5dB (A) lower than the 6135 unit under the same conditions.
In terms of daily use, it is mainly to maintain and maintain the unit to avoid unnecessary noise.
The muffler has the largest exhaust noise and is mainly concentrated in the middle and high frequency bands of 250Hz4kHz, two of which have a peak frequency of 500Hz and an underground pipe type exhaust gas. The underground buried pipe uses a cement down pipe or introduces the exhaust pipe into the brick chimney. Unit exhaust noise can be basically eliminated. However, attention should be paid to exhaust resistance and ventilation, and smoke exhaustion does not affect other users. At the same time, pay attention to whether the drainage is smooth, and pay attention to the use of mesh to prevent small animals from entering along the tube.
The communication power station should add a muffler with good muffling effect on the main noise source exhaust pipe. The designed impedance composite muffler can be reduced by 2040dB(A). Generally, the noise is reduced by 10dB (A), which doubles the perceived noise.
There are three types of acoustic enclosures, namely partial, tunnel and sealed. The noise reduction effect is shown in Table 2 below.
Table 2 Noise reduction effect of different types of sound insulation cover Type of noise reduction / dB (A) effect Local type smaller tunnel type General sealing type Good noise reduction materials for sound insulation cover and wall are: Fiber type: Glass slag wool , seaweed, felt, etc.
Foam-like polyamine methyl ester acid foam, wood wool board, sugar cane board and the like.
Particle-type sound-absorbing bricks, micro-hole sound-absorbing bricks, expanded perlite and the like.
These materials have a good noise reduction effect on high frequency noise. Sound-absorbing materials and sound-insulating materials for sound-insulating enclosures (machine room) should be reasonably selected and adopt appropriate structural forms, taking into account the reasonable arrangement and heat dissipation of the air inlet and exhaust ducts in the enclosure. Mainly used for sound absorption, commonly used glass wool, polyamine methyl ester acid foam (should add flame retardant), expanded perlite, slag cotton and so on.
Since different sound absorbing materials have different sound absorbing coefficients, and the same sound absorbing material has different sound absorbing coefficients for noise in different frequency ranges, when using sound absorbing materials, considering working conditions, structure, and price, More should consider the sound absorption coefficient at a specific frequency. For example, the use of polyaminomethyl ester acid foam as a sound absorbing material sometimes has a poor effect because polyaminomethyl methacrylate foam has better sound absorption performance in a high frequency region, and noise of a diesel generator set is mainly distributed in Near 500Hz. For this frequency range, the 10mm thick polyester foam has a sound absorption coefficient of only 0.36, and the 10mm thick glass wool has a sound absorption coefficient of 0.88. Therefore, from the viewpoint of sound absorption, it is suitable to use glass wool. However, the general diesel generator sets usually require manual operation, and the glass wool is harmful to human health. To reduce the damage of the glass wool to the human body, the glass wool should be exposed in the structure. In this case, other sound absorbing materials can be used to cover the On the glass wool, it can absorb sound together with the glass wool, and prevent the glass fiber from spreading into the air. Moreover, since the sound absorbing materials of different thicknesses have different sound absorption coefficients in different frequency ranges, when materials of different thicknesses and materials are used in combination, in addition to environmental protection, the sound absorbing effect is better than that of a single material of the same thickness. In addition, the interface between the two materials can also reflect a part of the noise back into the warehouse, so that the sound insulation cover can not only absorb sound, but also have sound insulation effect.
On the basis of selecting the sound absorbing material, the perforated sheet material can be combined for denoising. This structure mainly uses the perforation resonance on the board to consume noise energy. Since the perforated plate has a high sound absorption coefficient in the middle and low frequency regions, and its shape is relatively easy to install in the acoustic enclosure, this form is widely used in the noise reduction of the unit.
Sound absorption has a good effect on high-frequency noise, and can be reduced by up to 15dB (A) when the suction drop is good.
In the design of low noise power station, the author used the combination of polyaminomethyl ester acid foam and glass wool as the structure of the sound insulation cover, which reduced the power station noise from 105dB(A) to 89dB(A). If the inner wall iron mesh is changed to a perforated plate, the noise can be reduced to 85 dB (A). It can be seen that the sound-reducing sound cover of the perforated plate has the functions of rainproof, moisture-proof, sun-proof and anti-freezing.
When making the soundproof cover and setting the inner wall soundproofing, consider electromagnetic shielding at the same time, it can prevent the enemy radar wave reconnaissance communication power station and the surrounding command organization. In the production process, special attention is paid to doors, windows, holes, holes, etc. It is not easy to shield with metal orifices. Metal mesh plates with a certain aperture and porosity can be used. The actual effect is also good.
Active noise reduction and other noise reduction equipment The above measures are passive control of the noise control of the internal combustion engine power station, that is, the method of sound insulation, sound absorption and impedance composite principle is used for control. These measures have obvious effects on medium and high frequency noise, but have a poor effect on low frequency noise, especially the low frequency airflow noise of the cooling air duct. Such low frequency noise is actively controlled, ie adaptive active noise control (adaptive active noise control). The specific method is to generate a secondary sound field by using a controllable secondary sound source, and the sound field noise phase is opposite to the source noise phase, thereby canceling the noise sound field.
Staff wearing headphones, earmuffs, helmets, etc. can drop 10 40dB (A). For example, rocket launcher staff and pilots have certain noise reduction effects.
4 ventilation and heat dissipation problems and measures sound insulation and ventilation heat dissipation is a contradiction. The ventilation vents of the generator set can transmit noise and affect noise reduction.
Ventilation and cooling commonly used fans and blinds, but the reliability of the fan affects the reliability of the power station; also the use of upper wind, space duct, underground air duct, air intake hood, Z-type pipeline, labyrinth type barrier, or dedicated for intake and exhaust Device, etc. The wind outside enters the air duct, and the noise in the warehouse (room) is blocked by the straight line and is blocked at the air duct. In addition, the inner wall of the air duct is also affixed with sound absorbing materials. Through these forms, the vents meet the ventilation requirements, and the noise reduction needs are also met, and the sound insulation effect is good.
The use of the lower exhaust mode to reduce the noise ratio is better than the upper exhaust mode, and the radiant heat of the exhaust pipe to the machine room is significantly reduced. If the combustion exhaust gas is introduced into the lower water pipe, the discharge effect is best.
The exhaust pipe should be wrapped with asbestos weave instead of asbestos twisted rope and wrapped with fiberglass cloth. Finally, the galvanized iron wire is tightly wound in a spiral shape. To reduce the heat storage in the machine room.
When the ventilation and heat dissipation, the temperature of the generator room should not exceed 45C, otherwise the electronic components of the unit control will be overheated due to high temperature.
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